Quantifying Airborne Induced Polarization effects in helicopter time domain electromagnetics
NASA Astrophysics Data System (ADS)
Macnae, James
2016-12-01
This paper derives the Airborne Induced Polarization (AIP) response of an airborne electromagnetic (AEM) system to a horizontal, thin sheet conductor. A vertical component double-dipole approximates helicopter systems with towed concentric horizontal transmitter and receiver loops in frequency- or time-domain. In time domain, the AIP effect typically shows up as late-time negative data with amplitude 4 to 5 orders of magnitude smaller than the early-time peak of the positive AEM responses. Because of limited bandwidth from the short sample time after the decay of inductive responses, accurate extraction of intrinsic AIP parameters other than a minimum chargeability is almost impossible. Modelling further suggests that AIP effects in double-dipole AEM systems can only be reliably detected from polarizable material in the top few tens of metres. A titanium mineral exploration case history from the Lac Brûlé area, Quebec, Canada illustrates strong spatial coherence of AIP minimum chargeability estimates and their independence from other effects such as conductivity and magnetic susceptibility.
Singular value decomposition as a denoising tool for airborne time domain electromagnetic data
NASA Astrophysics Data System (ADS)
Reninger, P.-A.; Martelet, G.; Deparis, J.; Perrin, J.; Chen, Y.
2011-10-01
Airborne time domain electromagnetic (TDEM) surveys are increasingly carried out in anthropized areas as part of environmental studies. In such areas, noise arises mainly from either natural sources, such as spherics, or cultural sources, such as couplings with man-made installations. This results in various distortions on the measured decays, which make the EM noise spectrum complex and may lead to erroneous inversion and subsequent misinterpretations. Thresholding and stacking standard techniques, commonly used to filter TDEM data, are less efficient in such environment, requiring a time-consuming and subjective manual editing. The aim of this study was therefore to propose an alternative fast and efficient user-assisted filtering approach. This was achieved using the singular value decomposition (SVD). The SVD method uses the principal component analysis to extract into components the dominant shapes from a series of raw input curves. EM decays can then be reconstructed with particular components only. To do so, we had to adapt and implement the SVD, firstly, to separate clearly and so identify easily the components containing the geological signal, and then to denoise properly TDEM data. The reconstructed decays were used to detect noisy gates on their corresponding measured decays. This denoising step allowed rejecting efficiently mainly spikes and oscillations. Then, we focused on couplings with man-made installations, which may result in artifacts on the inverted models. An analysis of the map of weights of the selected "noisy components" highlighted high correlations with man-made installations localized by the flight video. We had therefore a tool to cull most likely decays biased by capacitive coupling noises. Finally, rejection of decays affected by galvanic coupling noises was also possible locating them through the analysis of specific SVD components. This SVD procedure was applied on airborne TDEM data surveyed by SkyTEM Aps. over an anthropized area
Accurate 2D/3D electromagnetic modeling for time-domain airborne EM systems
NASA Astrophysics Data System (ADS)
Yin, C.; Hodges, G.
2012-12-01
The existing industry software cannot deliver correct results for 3D time-domain airborne EM responses. In this paper, starting from the Fourier transform and convolution, we compare the stability of different modeling techniques and analyze the reason for instable calculations of the time-domain airborne EM responses. We find that the singularity of the impulse responses of EM systems at very early time that are used in the convolution is responsible for the instability of the modeling (Fig.1). Based on this finding, we put forward an algorithm that uses step response rather than impulse response of the airborne EM system for the convolution and create a stable algorithm that delivers precise results and maintains well the integral/derivative relationship between the magnetic field B and the magnetic induction dB/dt. A three-step transformation procedure for the modeling is proposed: 1) output the frequency-domain EM response data from the existing software; 2) transform into step-response by digital Fourier/Hankel transform; 3) convolve the step response with the transmitting current or its derivatives. The method has proved to be working very well (Fig. 2). The algorithm can be extended to the modeling of other time-domain ground and airborne EM system responses.Fig. 1: Comparison of impulse and step responses for an airborne EM system Fig. 2: Bz and dBz/dt calculated from step (middle panel) and impulse responses (lower panel) for the same 3D model as in Fig.1.
3D parallel inversion of time-domain airborne EM data
NASA Astrophysics Data System (ADS)
Liu, Yun-He; Yin, Chang-Chun; Ren, Xiu-Yan; Qiu, Chang-Kai
2016-12-01
To improve the inversion accuracy of time-domain airborne electromagnetic data, we propose a parallel 3D inversion algorithm for airborne EM data based on the direct Gauss-Newton optimization. Forward modeling is performed in the frequency domain based on the scattered secondary electrical field. Then, the inverse Fourier transform and convolution of the transmitting waveform are used to calculate the EM responses and the sensitivity matrix in the time domain for arbitrary transmitting waves. To optimize the computational time and memory requirements, we use the EM "footprint" concept to reduce the model size and obtain the sparse sensitivity matrix. To improve the 3D inversion, we use the OpenMP library and parallel computing. We test the proposed 3D parallel inversion code using two synthetic datasets and a field dataset. The time-domain airborne EM inversion results suggest that the proposed algorithm is effective, efficient, and practical.
3D time-domain airborne EM forward modeling with topography
NASA Astrophysics Data System (ADS)
Yin, Changchun; Qi, Yanfu; Liu, Yunhe; Cai, Jing
2016-11-01
The time-domain finite-difference method has been widely used in simulation of the electromagnetic field diffusion. However, this method is severely restricted by the mesh size and time step. To overcome the defect, we adopted edge finite-element method for unstructured grid with Backward Euler method to conduct 3D airborne electromagnetic forward modeling directly in time-domain. The tetrahedral meshes provide the flexibility required for representing the rugged topography and complex-shape anomalous bodies. We simulated the practical shape, size and attitude of transmitting source by directly setting the loop into the well-generated grids. The characteristic properties of vector basic functions guarantee automatic satisfaction of divergence-free property of electric fields. The Galerkin's method is used to discretize the governing equations and a direct solver is adopted to solve the large sparse linear system. We adopted an algorithm with constant step in each time segment to speed up the forward modeling. Further we introduced the local mesh strategy to reduce the calculations, in which an optimized grid is designed for each sounding station. We check the accuracy of our 3D modeling results against the solution for a homogenous half-space and those for a buried vertical plate model using integral equation. The numerical experiments for a hill, a valley or undulating topography model with buried anomalous bodies were further studied that show that the topography has a serious effect on airborne EM data.
Interpretation of time domain electromagnetic soundings near geological contacts
Wilt, M.J.
1991-12-01
Lateral changes in geology pose a serious problem in data interpretation for any surface geophysical method. Although many geophysical techniques are designed to probe vertically, the source signal invariably spreads laterally, so any lateral variations in geology will affect the measurements and interpretation. This problem is particularly acute for controlled source electromagnetic soundings because only a few techniques are available to interpret the data if lateral effects are present. In this thesis we examine the effects of geological contacts for the time domain electromagnetic sounding method (TDEM). Using two simple two-dimensional models, the truncated thin-sheet and the quarter-space, we examine the system response for several commonly used TDEM sounding configurations. For each system we determine the sensitivity to the contact, establish how to the contact anomaly may be distinguished from other anomalies and, when feasible, develop methods for interpreting the contact geometry and for stripping the contact anomaly from the observed data. Since no numerical models were available when this work was started, data were collected using scale models with a system designed at the University of California at Berkeley. The models were assembled within a table-top modeling tank from sheets or blocks of metal using air or mercury as a host medium. Data were collected with a computer-controlled acquisition system.
Some recent developments of the discontinous Galerkin method for time-domain electromagnetics
NASA Astrophysics Data System (ADS)
Durochat, C.; Lanteri, S.; Moya, L.; Viquerat, J.; Descombes, S.; Scheid, C.
2012-09-01
We discuss about recent developments aiming at improving the accuracy, the flexibility and the computational performances of a high order discontinuous Galerkin time domain (DGTD) method for the simulation of time-domain electromagnetic wave propagation problems involving irregularly shaped objects and complex propagation media.
Modeling ferrite electromagnetic response in the time domain
Johnson, J.; DeFord, J.F.; Craig, G.D.
1989-04-06
The behavior of ferrite loads commonly found in induction accelertors has important consequences for the performance of these accelerators. Previous work by the authors on modeling the electromagnetic fields in induction cavities has focussed upon use of a simple, phenomenological model for the process of magnetization reversal in these ferrite loads. In this paper we consider a model for magnetization reversal which is more deeply rooted in theory, and present a simulation of the reversal process based upon this model for an idealized set of boundary conditions. 7 refs., 3 figs.
Even Shallower Exploration with Airborne Electromagnetics
NASA Astrophysics Data System (ADS)
Auken, E.; Christiansen, A. V.; Kirkegaard, C.; Nyboe, N. S.; Sørensen, K.
2015-12-01
Airborne electromagnetics (EM) is in many ways undergoing the same type rapid technological development as seen in the telecommunication industry. These developments are driven by a steadily increasing demand for exploration of minerals, groundwater and geotechnical targets. The latter two areas demand shallow and accurate resolution of the near surface geology in terms of both resistivity and spatial delineation of the sedimentary layers. Airborne EM systems measure the grounds electromagnetic response when subject to either a continuous discrete sinusoidal transmitter signal (frequency domain) or by measuring the decay of currents induced in the ground by rapid transmission of transient pulses (time domain). In the last decade almost all new developments of both instrument hardware and data processing techniques has focused around time domain systems. Here we present a concept for measuring the time domain response even before the transient transmitter current has been turned off. Our approach relies on a combination of new instrument hardware and novel modeling algorithms. The newly developed hardware allows for measuring the instruments complete transfer function which is convolved with the synthetic earth response in the inversion algorithm. The effect is that earth response data measured while the transmitter current is turned off can be included in the inversion, significantly increasing the amount of available information. We demonstrate the technique using both synthetic and field data. The synthetic examples provide insight on the physics during the turn off process and the field examples document the robustness of the method. Geological near surface structures can now be resolved to a degree that is unprecedented to the best of our knowledge, making airborne EM even more attractive and cost-effective for exploration of water and minerals that are crucial for the function of our societies.
Recent advances on a DGTD method for time-domain electromagnetics
NASA Astrophysics Data System (ADS)
Descombes, Stéphane; Durochat, Clément; Lanteri, Stéphane; Moya, Ludovic; Scheid, Claire; Viquerat, Jonathan
2013-11-01
During the last ten years, the discontinuous Galerkin time-domain (DGTD) method has progressively emerged as a viable alternative to well established finite-difference time-domain (FDTD) and finite-element time-domain (FETD) methods for the numerical simulation of electromagnetic wave propagation problems in the time-domain. In this paper, we review the historical development of the DGTD method and emphasize its recent adoption by the nanophotonic research community. In addition, we discuss about some of our recent efforts aiming at improving the accuracy, flexibility and efficiency of a non-dissipative order DGTD method, and also report on some preliminary works towards its extension to the numerical treatment of physical models and problems that are relevant to nanophotonics.
Parallel electromagnetic simulator based on the Finite-Difference Time Domain method
NASA Astrophysics Data System (ADS)
Walendziuk, Wojciech
2006-03-01
In the following paper the parallel tool for electromagnetic field distribution analysis is presented. The main simulation programme is based on the parallel algorithm of the Finite-Difference Time-Domain method and use Message Passing Interface as a communication library. In the paper also ways of communications among computation nodes in a parallel environment and efficiency of the parallel algorithm are presented.
Calibrating a salt water intrusion model with time-domain electromagnetic data.
Herckenrath, Daan; Odlum, Nick; Nenna, Vanessa; Knight, Rosemary; Auken, Esben; Bauer-Gottwein, Peter
2013-01-01
Salt water intrusion models are commonly used to support groundwater resource management in coastal aquifers. Concentration data used for model calibration are often sparse and limited in spatial extent. With airborne and ground-based electromagnetic surveys, electrical resistivity models can be obtained to provide high-resolution three-dimensional models of subsurface resistivity variations that can be related to geology and salt concentrations on a regional scale. Several previous studies have calibrated salt water intrusion models with geophysical data, but are typically limited to the use of the inverted electrical resistivity models without considering the measured geophysical data directly. This induces a number of errors related to inconsistent scales between the geophysical and hydrologic models and the applied regularization constraints in the geophysical inversion. To overcome these errors, we perform a coupled hydrogeophysical inversion (CHI) in which we use a salt water intrusion model to interpret the geophysical data and guide the geophysical inversion. We refer to this methodology as a Coupled Hydrogeophysical Inversion-State (CHI-S), in which simulated salt concentrations are transformed to an electrical resistivity model, after which a geophysical forward response is calculated and compared with the measured geophysical data. This approach was applied for a field site in Santa Cruz County, California, where a time-domain electromagnetic (TDEM) dataset was collected. For this location, a simple two-dimensional cross-sectional salt water intrusion model was developed, for which we estimated five uniform aquifer properties, incorporating the porosity that was also part of the employed petrophysical relationship. In addition, one geophysical parameter was estimated. The six parameters could be resolved well by fitting more than 300 apparent resistivities that were comprised by the TDEM dataset. Except for three sounding locations, all the TDEM data
Xyz Airborne Time Domain Em: P-Them Test in Reid Mahaffy
NASA Astrophysics Data System (ADS)
Vetrov, A.
2012-12-01
The vertical axis transmitter loop and receiver coil combination is widely used in Airborne Time-Domain EM systems. In such configurations the largest portion of the transmitter magnetic moment, which is distributed in a vertical direction, is transmitted to the subsurface, and the strongest vertical response from underground conductors is acquired with a vertical axis (Z) receiver coil. However, the horizontal axis (X and Y) components carry valuable information about target body geometry and their borders/edges. Most Airborne Time Domain systems currently in use are configured such that the X component is aligned with the flight direction. At typical survey speeds (60 to 80 kph) towed bird systems may expect to be subject to vibration that results in movement of horizontal and vertical receiver's axis from its desired nominal position. The mechanical design of the P-THEM transmitter and receiver is based on Bernard Kremer's (THEM Geophysics) developments finished and improved by Pico Envirotec Inc. The P-THEM system consists of a loop-transmitter assembly, powered by a motor generator and a 3-axis (XYZ) coil receiver attached at the midpoint of a tow cable between transmitter and a helicopter. The suspension system of the receiver coils assembly allows the Z-coil to remain horizontal at all the time during the flight. Pico Envirotec has developed methodology to recalculate the data from three axis of the receiver that allows mechanical vibration influence to be eliminated from the acquired data. The recalculated X-component gives very useful information for interpretation of the observation results. The P-THEM system has been test flown over the Reid Mahaffy geological test site located in Northern Ontario in Canada. The test site, created by the Ontario Geological Survey, contains the main conductor formed with three sub-vertical sliced conductive bodies. Three lines (L30, L40 and L50) over the test site have been flown in North and South direction with the P
Results of time-domain electromagnetic soundings in Everglades National Park, Florida
Fitterman, D.V.; Deszcz-Pan, Maria; Stoddard, C.E.
1999-01-01
This report describes the collection, processing, and interpretation of time-domain electromagnetic soundings from Everglades National Park. The results are used to locate the extent of seawater intrusion in the Biscayne aquifer and to map the base of the Biscayne aquifer in regions where well coverage is sparse. The data show no evidence of fresh, ground-water flows at depth into Florida Bay.
Inclusion of lumped elements in finite difference time domain electromagnetic calculations
Thomas, V.A.; Jones, M.E.; Mason, R.J.
1994-12-31
A general approach for including lumped circuit elements in a finite difference, time domain (FD-TD) solution of Maxwell`s equations is presented. The methodology allows the direct access to SPICE to model the lumped circuits, while the full 3-Dimensional solution to Maxwell`s equations provides the electromagnetic field evolution. This type of approach could be used to mode a pulsed power machine by using a SPICE model for the driver and using an electromagnetic PIC code for the plasma/electromagnetics calculation. The evolution of the driver can be made self consistent with the behavior of the plasma load. Other applications are also possible, including modeling of nonlinear microwave circuits (as long as the non-linearities may be expressed in terms of a lumped element) and self-consistent calculation of very high speed computer interconnections and digital circuits.
A time domain energy theorem for scattering of plane electromagnetic waves
NASA Astrophysics Data System (ADS)
de Hoop, A. T.
1984-10-01
A time domain analysis of the scattering problem reveals the more general conditions under which the relevant theorems in the theory of the scattering of electromagnetic waves by an obstacle of bounded extent may also hold in the time domain. The present investigation is concerned with the energy theorem for plane wave scattering. Three different kinds of time behavior are considered, taking into account transient fields, time-periodic fields, and perpetuating fields. The derived energy theorem relates the energy which is both absorbed and scattered by the object to the spherical-wave amplitude of the scattered field in the far-field region, when observed in the direction of propagation of the incident plane wave.
The electromagnetic modeling of thin apertures using the finite-difference time-domain technique
NASA Technical Reports Server (NTRS)
Demarest, Kenneth R.
1987-01-01
A technique which computes transient electromagnetic responses of narrow apertures in complex conducting scatterers was implemented as an extension of previously developed Finite-Difference Time-Domain (FDTD) computer codes. Although these apertures are narrow with respect to the wavelengths contained within the power spectrum of excitation, this technique does not require significantly more computer resources to attain the increased resolution at the apertures. In the report, an analytical technique which utilizes Babinet's principle to model the apertures is developed, and an FDTD computer code which utilizes this technique is described.
On-Board Compact System for the Full-Time-Domain Electromagnetic Interference Measurements
NASA Astrophysics Data System (ADS)
Azpurua, M. A.; Pous, M.; Silva, F.
2016-05-01
This paper presents a compact system for the measurement of electromagnetic interferences in the time domain. The measurement system is based on a USB oscilloscope, used as digitizer, and specific software for signal processing and spectral estimation. The measurement system is suitable for both conducted and radiated electromagnetic emissions up to 200 MHz. Its accuracy, precision and dynamic range are sufficient for the intended application. It is particularly suitable for measuring transient disturbances due to its triggering capabilities. Its relative low weight and cost makes it a valuable tool for investigating on-board the indirect effects of lightning strikes as disturbances coupled to cables and antennas inside launch vehicles, aircrafts, and unmanned aerial vehicles.
Fitterman, David V.; Prinos, Scott T.
2011-01-01
Time-domain electromagnetic (TEM) soundings were made in Miami-Dade and southern Broward Counties to aid in mapping the landward extent of saltwater in the Biscayne aquifer. A total of 79 soundings were collected in settings ranging from urban to undeveloped land, with some of the former posing problems of land access and interference from anthropogenic features. TEM soundings combined with monitoring-well data were used to determine if the saltwater front had moved since the last time it was mapped, to provide additional spatial coverage where existing monitoring wells were insufficient, and to help interpret a previously collected helicopter electromagnetic (HEM) survey flown in the southernmost portion of the study area. TEM soundings were interpreted as layered resistivity-depth models. Using information from well logs and water-quality data, the resistivity of the freshwater saturated Biscayne aquifer is expected to be above 30 ohm-meters, and the saltwater-saturated aquifer will have resistivities of less than 10 ohm-meters allowing determination of water quality from the TEM interpretations. TEM models from 29 soundings were compared to electromagnetic induction logs collected in nearby monitoring wells. In general, the agreement of these results was very good, giving confidence in the use of the TEM data for mapping saltwater encroachment.
Application of the symplectic finite-difference time-domain scheme to electromagnetic simulation
Sha, Wei . E-mail: ws108@ahu.edu.cn; Huang, Zhixiang; Wu, Xianliang; Chen, Mingsheng
2007-07-01
An explicit fourth-order finite-difference time-domain (FDTD) scheme using the symplectic integrator is applied to electromagnetic simulation. A feasible numerical implementation of the symplectic FDTD (SFDTD) scheme is specified. In particular, new strategies for the air-dielectric interface treatment and the near-to-far-field (NFF) transformation are presented. By using the SFDTD scheme, both the radiation and the scattering of three-dimensional objects are computed. Furthermore, the energy-conserving characteristic hold for the SFDTD scheme is verified under long-term simulation. Numerical results suggest that the SFDTD scheme is more efficient than the traditional FDTD method and other high-order methods, and can save computational resources.
A Moving Window Technique in Parallel Finite Element Time Domain Electromagnetic Simulation
Lee, Lie-Quan; Candel, Arno; Ng, Cho; Ko, Kwok; /SLAC
2010-06-07
A moving window technique for the finite element time domain (FETD) method is developed to simulate the propagation of electromagnetic waves induced by the transit of a charged particle beam inside large and long structures. The window moving along with the beam in the computational domain adopts high-order finite-element basis functions through p refinement and/or a high-resolution mesh through h refinement so that a sufficient accuracy is attained with substantially reduced computational costs. Algorithms to transfer discretized fields from one mesh to another, which are the key to implementing a moving window in a finite-element unstructured mesh, are presented. Numerical experiments are carried out using the moving window technique to compute short-range wakefields in long accelerator structures. The results are compared with those obtained from the normal FETD method and the advantages of using the moving window technique are discussed.
IP effects on electromagnetic data of deep-sea hydrothermal deposits in time domain
NASA Astrophysics Data System (ADS)
KIM, H. J.; Jang, H.; Ha, W.
2015-12-01
A transient electromagnetic (TEM) system using a small loop source is advantageous to the development of compact, autonomous instruments which are well suited to submersible-based surveys. Since electrical conductivity of subseafloor materials can be frequency dependent, these induced polarization (IP) effects may affect the reliability of TEM data interpretation. In this study, we investigate IP effects on TEM responses of deep-sea hydrothermal mineral deposits with a thin sediment cover. Time-domain target signals are larger and appear earlier in horizontal magnetic fields than in vertical ones. IP effects cause transient magnetic fields to enhance initially, to decay rapidly and then to reverse the polarity. The DC conductivity and IP chargeability in Cole-Cole parameters influence the time of sign reversal and the enhancement of the target response, simultaneously. The reversal time is almost invariant with the time constant while the target signal is almost invariant with the frequency exponent.
NASA Astrophysics Data System (ADS)
Salazar Rodriguez, J. M.; Vargas Jiménez, C. A.
2015-12-01
In this research, various configurations of reservoirs were simulated using finite elements in 3D, in order to analyze the subsoil electromagnetic responses in the time domain. Apparent resistivity curves both early and late time and their respective sensitivities in detecting hydrocarbon reservoirs are found. The maximum sensitivity obtained in the early and late times was 55.72% and 49.32% respectively. The separation of 1km between the transmitter and receiver was used in the simulations, because at shorter distances problems were encountered in in determining the resistivity curves. In addition, it was determined that the current dipole transmitter must be over 800A • m to overcome the level of noise instrumental of the receptor coil.
NASA Astrophysics Data System (ADS)
1993-10-01
Due to advances in different areas of microwave and millimeter-wave techniques, demand for efficient CAD tools has grown. This statement is today as true as it was at our last workshop held two years ago in Munich on this topic. The numerical analysis in time domain is attractive since it describes the evolution of physical quantities in a natural way. The two basic concepts, the modelling of fields and networks, are more closely related than it seems at first glance. In the TLM method, for example, the network model is the basis for modelling electromagnetic fields. Another example is the application of generalized S-matrix methods and diacoptics in field theory. The purpose of this conference is to stimulate synoptic considerations of field theory and to promote a lively exchange between researchers engaged in these fields
NASA Astrophysics Data System (ADS)
Imamura, N.; Schultz, A.
2015-12-01
Recently, a full waveform time domain solution has been developed for the magnetotelluric (MT) and controlled-source electromagnetic (CSEM) methods. The ultimate goal of this approach is to obtain a computationally tractable direct waveform joint inversion for source fields and earth conductivity structure in three and four dimensions. This is desirable on several grounds, including the improved spatial resolving power expected from use of a multitude of source illuminations of non-zero wavenumber, the ability to operate in areas of high levels of source signal spatial complexity and non-stationarity, etc. This goal would not be obtainable if one were to adopt the finite difference time-domain (FDTD) approach for the forward problem. This is particularly true for the case of MT surveys, since an enormous number of degrees of freedom are required to represent the observed MT waveforms across the large frequency bandwidth. It means that for FDTD simulation, the smallest time steps should be finer than that required to represent the highest frequency, while the number of time steps should also cover the lowest frequency. This leads to a linear system that is computationally burdensome to solve. We have implemented our code that addresses this situation through the use of a fictitious wave domain method and GPUs to speed up the computation time. We also substantially reduce the size of the linear systems by applying concepts from successive cascade decimation, through quasi-equivalent time domain decomposition. By combining these refinements, we have made good progress toward implementing the core of a full waveform joint source field/earth conductivity inverse modeling method. From results, we found the use of previous generation of CPU/GPU speeds computations by an order of magnitude over a parallel CPU only approach. In part, this arises from the use of the quasi-equivalent time domain decomposition, which shrinks the size of the linear system dramatically.
Rieben, Robert N.
2004-01-01
The goal of this dissertation is two-fold. The first part concerns the development of a numerical method for solving Maxwell's equations on unstructured hexahedral grids that employs both high order spatial and high order temporal discretizations. The second part involves the use of this method as a computational tool to perform high fidelity simulations of various electromagnetic devices such as optical transmission lines and photonic crystal structures to yield a level of accuracy that has previously been computationally cost prohibitive. This work is based on the initial research of Daniel White who developed a provably stable, charge and energy conserving method for solving Maxwell's equations in the time domain that is second order accurate in both space and time. The research presented here has involved the generalization of this procedure to higher order methods. High order methods are capable of yielding far more accurate numerical results for certain problems when compared to corresponding h-refined first order methods , and often times at a significant reduction in total computational cost. The first half of this dissertation presents the method as well as the necessary mathematics required for its derivation. The second half addresses the implementation of the method in a parallel computational environment, its validation using benchmark problems, and finally its use in large scale numerical simulations of electromagnetic transmission devices.
NASA Astrophysics Data System (ADS)
Rieben, Robert N.
The goal of this dissertation is twofold. The first part concerns the development of a numerical method for solving Maxwell's equations on unstructured hexahedral grids that employs both high order spatial and high order temporal discretizations. The second part involves the use of this method as a computational tool to perform high fidelity simulations of various electromagnetic devices such as optical transmission lines and photonic crystal structures to yield a level of accuracy that has previously been computationally cost prohibitive. This work is based on the initial research of Daniel White who developed a provably stable, charge and energy conserving method for solving Maxwell's equations in the time domain that is second order accurate in both space and time. The research presented here has involved the generalization of this procedure to higher order methods. High order methods are capable of yielding far more accurate numerical results for certain problems when compared to corresponding h-refined first order methods, and often times at a significant reduction in total computational cost. The first half of this dissertation presents the method as well as the necessary mathematics required for its derivation. The second half addresses the implementation of the method in a parallel computational environment, its validation using benchmark problems, and finally its use in large scale numerical simulations of electromagnetic transmission devices.
On recovering distributed IP information from inductive source time domain electromagnetic data
NASA Astrophysics Data System (ADS)
Kang, Seogi; Oldenburg, Douglas W.
2016-10-01
We develop a procedure to invert time domain induced polarization (IP) data for inductive sources. Our approach is based upon the inversion methodology in conventional electrical IP (EIP), which uses a sensitivity function that is independent of time. However, significant modifications are required for inductive source IP (ISIP) because electric fields in the ground do not achieve a steady state. The time-history for these fields needs to be evaluated and then used to define approximate IP currents. The resultant data, either a magnetic field or its derivative, are evaluated through the Biot-Savart law. This forms the desired linear relationship between data and pseudo-chargeability. Our inversion procedure has three steps: (1) Obtain a 3-D background conductivity model. We advocate, where possible, that this be obtained by inverting early-time data that do not suffer significantly from IP effects. (2) Decouple IP responses embedded in the observations by forward modelling the TEM data due to a background conductivity and subtracting these from the observations. (3) Use the linearized sensitivity function to invert data at each time channel and recover pseudo-chargeability. Post-interpretation of the recovered pseudo-chargeabilities at multiple times allows recovery of intrinsic Cole-Cole parameters such as time constant and chargeability. The procedure is applicable to all inductive source survey geometries but we focus upon airborne time domain EM (ATEM) data with a coincident-loop configuration because of the distinctive negative IP signal that is observed over a chargeable body. Several assumptions are adopted to generate our linearized modelling but we systematically test the capability and accuracy of the linearization for ISIP responses arising from different conductivity structures. On test examples we show: (1) our decoupling procedure enhances the ability to extract information about existence and location of chargeable targets directly from the data maps
Feasibility of a time-domain electromagnetic survey for mapping deep-sea hydrothermal deposits
NASA Astrophysics Data System (ADS)
Jang, H.; KIM, H. J.
2014-12-01
Marine controlled-source electromagnetic (CSEM) surveying has already become a popular tool for hydrocarbon exploration. Possible targets of the marine CSEM survey, other than hydrocarbon, may be marine hydrothermal mineral deposits. In transient EM (TEM) measurements, secondary fields which contain information on hydrothermal deposits in the seafloor can be measured in the absence of strong primary fields. The TEM system is useful to the development of compact, autonomous instruments which are well suited to submersible-based surveys. In this paper, we investigate the possibility of applying an in-loop TEM system to the detection of marine hydrothermal deposits through a one-dimensional modeling and inversion study. The feasibility study showed that TEM responses are very sensitive to a highly conductive layer. Time-domain target responses are larger and appear earlier in horizontal magnetic fields than in vertical ones. An inverse problem is formulated with the Gauss-Newton method and solved with the damped and smoothness-constrained least-squares approach. The test example for a marine hydrothermal TEM survey demonstrated that the depth extent, conductivity and thickness of the highly conductive layer are well resolved.
Evaluation of a thin-slot formalism for finite-difference time-domain electromagnetics codes
Turner, C.D.; Bacon, L.D.
1987-03-01
A thin-slot formalism for use with finite-difference time-domain (FDTD) electromagnetics codes has been evaluated in both two and three dimensions. This formalism allows narrow slots to be modeled in the wall of a scatterer without reducing the space grid size to the gap width. In two dimensions, the evaluation involves the calculation of the total fields near two infinitesimally thin coplanar strips separated by a gap. A method-of-moments (MoM) solution of the same problem is used as a benchmark for comparison. Results in two dimensions show that up to 10% error can be expected in total electric and magnetic fields both near (lambda/40) and far (1 lambda) from the slot. In three dimensions, the evaluation is similar. The finite-length slot is placed in a finite plate and an MoM surface patch solution is used for the benchmark. These results, although less extensive than those in two dimensions, show that slightly larger errors can be expected. Considering the approximations made near the slot in incorporating the formalism, the results are very promising. Possibilities also exist for applying this formalism to walls of arbitrary thickness and to other types of slots, such as overlapping joints. 11 refs., 25 figs., 6 tabs.
Time-domain electromagnetic tests in the Wadi Bidah District, Kingdom of Saudi Arabia
Flanigan, Vincent J.; Sadek, Hamdy; Smith, Bruce; Tippens, C.L.
1983-01-01
A time-domain electromagnetic (TDEM) method was tested in two areas of mineralization in Precambrian rocks in the Wadi Bidah district, Kingdom of Saudi Arabia. Transient-decay voltages in profile mode were measured across the Sha'ab at Tare and Rabathan prospects by use of three transmitterreceiver loop configurations. At the Sha'ab at Tare prospect all of the loop configurations indicated the mineralized zone. Analysis of the coincident loop data at Sha'ab at Tare reveals that gossanous and altered rock of i0 ohm-m resistivity extends to a depth of 35 m, where there is an unweathered, dry mineralized zone of about 1 ohm-m resistivity. The model further suggests that the rocks at a depth of 55 m and below the water table are even less resistive (0. 1 ohm-m). The TDEM method successfully discriminated conductors within from those below the weathered zone at the Rabathan prospect. Conductors below the weathered zone are identified by a lack of transient response in the early part of the transient decay curve, followed by an increasing response in the middle to late parts of the transient decay curve. Results of these limited tests suggest the potential value of integrating TDEM with other geophysical tools in the Kingdom. Recommendations are made to expand these tests into a more comprehensive program that will evaluate the TDEM potential in various geologic environments that are host to mineral deposits of diverse origin.
NASA Astrophysics Data System (ADS)
Ji, Yanju; Li, Dongsheng; Yuan, Guiyang; Lin, Jun; Du, Shangyu; Xie, Lijun; Wang, Yuan
2016-06-01
A denoising method based on wavelet analysis is presented for the removal of noise (background noise and random spike) from time domain electromagnetic (TEM) data. This method includes two signal processing technologies: wavelet threshold method and stationary wavelet transform. First, wavelet threshold method is used for the removal of background noise from TEM data. Then, the data are divided into a series of details and approximations by using stationary wavelet transform. The random spike in details is identified by zero reference data and adaptive energy detector. Next, the corresponding details are processed to suppress the random spike. The denoised TEM data are reconstructed via inverse stationary wavelet transform using the processed details at each level and the approximations at the highest level. The proposed method has been verified using a synthetic TEM data, the signal-to-noise ratio of synthetic TEM data is increased from 10.97 dB to 24.37 dB at last. This method is also applied to the noise suppression of the field data which were collected at Hengsha island, China. The section image results shown that the noise is suppressed effectively and the resolution of the deep anomaly is obviously improved.
NASA Astrophysics Data System (ADS)
Laukaitis, A.; Sinica, M.; Balevičius, S.; Levitas, B.
2008-03-01
The electromagnetic wave absorbers prepared from autoclaved aerated concrete containing carbon fibers as additions in the shape of slabs with pyramids cut on one plane of these slabs were tested using dc microwave source and the time-domain method. It was demonstrated that autoclaved aerated concrete allows one to fabricate electromagnetic wave absorbers which have a reflection coefficient up to -30 dB in the frequency range from 2 GHz to 18 GHz.
Mapping permafrost with airborne electromagnetics
NASA Astrophysics Data System (ADS)
Minsley, B. J.; Ball, L. B.; Bloss, B. R.; Kass, A.; Pastick, N.; Smith, B. D.; Voss, C. I.; Walsh, D. O.; Walvoord, M. A.; Wylie, B. K.
2014-12-01
Permafrost is a key characteristic of cold region landscapes, yet detailed assessments of how the subsurface distribution of permafrost impacts the environment, hydrologic systems, and infrastructure are lacking. Data acquired from several airborne electromagnetic (AEM) surveys in Alaska provide significant new insight into the spatial extent of permafrost over larger areas (hundreds to thousands of square kilometers) than can be mapped using ground-based geophysical methods or through drilling. We compare several AEM datasets from different areas of interior Alaska, and explore the capacity of these data to infer geologic structure, permafrost extent, and related hydrologic processes. We also assess the impact of fires on permafrost by comparing data from different burn years within similar geological environments. Ultimately, interpretations rely on understanding the relationship between electrical resistivity measured by AEM surveys and the physical properties of interest such as geology, permafrost, and unfrozen water content in the subsurface. These relationships are often ambiguous and non-unique, so additional information is useful for reducing uncertainty. Shallow (upper ~1m) permafrost and soil characteristics identified from remotely sensed imagery and field observations help to constrain and aerially extend near-surface AEM interpretations, where correlations between the AEM and remote sensing data are identified using empirical multivariate analyses. Surface nuclear magnetic resonance (sNMR) measurements quantify the contribution of unfrozen water at depth to the AEM-derived electrical resistivity models at several locations within one survey area. AEM surveys fill a critical data gap in the subsurface characterization of permafrost environments and will be valuable in future mapping and monitoring programs in cold regions.
Model based approach to UXO imaging using the time domain electromagnetic method
Lavely, E.M.
1999-04-01
Time domain electromagnetic (TDEM) sensors have emerged as a field-worthy technology for UXO detection in a variety of geological and environmental settings. This success has been achieved with commercial equipment that was not optimized for UXO detection and discrimination. The TDEM response displays a rich spatial and temporal behavior which is not currently utilized. Therefore, in this paper the author describes a research program for enhancing the effectiveness of the TDEM method for UXO detection and imaging. Fundamental research is required in at least three major areas: (a) model based imaging capability i.e. the forward and inverse problem, (b) detector modeling and instrument design, and (c) target recognition and discrimination algorithms. These research problems are coupled and demand a unified treatment. For example: (1) the inverse solution depends on solution of the forward problem and knowledge of the instrument response; (2) instrument design with improved diagnostic power requires forward and inverse modeling capability; and (3) improved target recognition algorithms (such as neural nets) must be trained with data collected from the new instrument and with synthetic data computed using the forward model. Further, the design of the appropriate input and output layers of the net will be informed by the results of the forward and inverse modeling. A more fully developed model of the TDEM response would enable the joint inversion of data collected from multiple sensors (e.g., TDEM sensors and magnetometers). Finally, the author suggests that a complementary approach to joint inversions is the statistical recombination of data using principal component analysis. The decomposition into principal components is useful since the first principal component contains those features that are most strongly correlated from image to image.
Bedrosian, Paul A.; Burgess, Matthew K.; Nishikawa, Tracy
2013-01-01
Within the south-western Mojave Desert, the Joshua Basin Water District is considering applying imported water into infiltration ponds in the Joshua Tree groundwater sub-basin in an attempt to artificially recharge the underlying aquifer. Scarce subsurface hydrogeological data are available near the proposed recharge site; therefore, time-domain electromagnetic (TDEM) data were collected and analysed to characterize the subsurface. TDEM soundings were acquired to estimate the depth to water on either side of the Pinto Mountain Fault, a major east-west trending strike-slip fault that transects the proposed recharge site. While TDEM is a standard technique for groundwater investigations, special care must be taken when acquiring and interpreting TDEM data in a twodimensional (2D) faulted environment. A subset of the TDEM data consistent with a layered-earth interpretation was identified through a combination of three-dimensional (3D) forward modelling and diffusion time-distance estimates. Inverse modelling indicates an offset in water table elevation of nearly 40 m across the fault. These findings imply that the fault acts as a low-permeability barrier to groundwater flow in the vicinity of the proposed recharge site. Existing production wells on the south side of the fault, together with a thick unsaturated zone and permeable near-surface deposits, suggest the southern half of the study area is suitable for artificial recharge. These results illustrate the effectiveness of targeted TDEM in support of hydrological studies in a heavily faulted desert environment where data are scarce and the cost of obtaining these data by conventional drilling techniques is prohibitive.
Use of the finite-difference time-domain method in electromagnetic dosimetry
Sullivan, D.M.
1987-01-01
Although there are acceptable methods for calculating whole body electromagnetic absorption, no completely acceptable method for calculating the local specific absorption rate (SAR) at points within the body has been developed. Frequency domain methods, such as the method of moments (MoM) have achieved some success; however, the MoM requires computer storage on the order of (3N)/sup 2/, and computation time on the order of (3N)/sup 3/ where N is the number of cells. The finite-difference time-domain (FDTD) method has been employed extensively in calculating the scattering from metallic objects, and recently is seeing some use in calculating the interaction of EM fields with complex, lossy dielectric bodies. Since the FDTD method has storage and time requirements proportional to N, it presents an attractive alternative to calculating SAR distribution in large bodies. This dissertation describes the FDTD method and evaluates it by comparing its results with analytic solutions in 2 and 3 dimensions. The results obtained demonstrate that the FDTD method is capable of calculating internal SAR distribution with acceptable accuracy. The construction of a data base to provide detailed, inhomogeneous man models for use with the FDTD method is described. Using this construction method, a model of 40,000 1.31 cm. cells is developed for use at 350 MHz, and another model consisting of 5000 2.62 cm. cells is developed for use at 100 MHz. To add more realism to the problem, a ground plane is added to the FDTD software. The needed changes to the software are described, along with a test which confirms its accuracy. Using the CRAY II supercomputer, SAR distributions in human models are calculated using incident frequencies of 100 MHz and 350 MHz for three different cases: (1) A homogeneous man model in free space, (2) an inhomogeneous man model in free space, and (3) an inhomogeneous man model standing on a ground plane.
A time-domain electromagnetic sounder for detection and characterization of groundwater on Mars
NASA Astrophysics Data System (ADS)
Grimm, Robert E.; Berdanier, Barry; Warden, Robert; Harrer, James; Demara, Raymond; Pfeiffer, James; Blohm, Richard
2009-09-01
A prototype time-domain electromagnetic (TDEM) sounder was developed to technical readiness level (TRL) 5 to detect and characterize deep groundwater on Mars. The TDEM method induces eddy currents in the subsurface by abrupt extinction of a steady current in a large, flat-lying loop antenna, and the subsurface response is measured using the same loop or a separate receiver. TDEM has been widely used in terrestrial groundwater exploration and is ideally suited to sense the high electrical conductivity associated with saline groundwater expected on Mars. The inductive regime of TDEM is distinct from ground-penetrating radar: the latter has higher resolution but smaller depth of investigation. Our Mars-prototype TDEM was tested in the laboratory and at a local field site before the principal test was performed on Maui, Hawaii. This location was chosen because of its analogy to Mars in electrical properties: dry, resistive basalt over saline pore water. Results compared favorably to soundings made with a commercial TDEM, clearly detecting the seawater interface at depths of 250 m. We subsequently developed a ballistic deployment system for the loop antenna suitable for robotic missions. Compressed gas launches two projectiles; each consists of two spools on a guide stick. Payout on one spool is back towards the launcher and on the other toward its twin on the other projectile. In this way a triangular loop antenna is formed. The full system was tested twice, successfully achieving a distance of ˜70 m in both. A system capable of deploying a 200 m loop antenna on Mars would have mass <6 kg (including 0.3 kg electronics) and within one sol could detect groundwater at depths up to 5 km. TDEM can probe to depths not possible for radar and answer the question: does groundwater - and a likely subsurface habitable zone - exist on Mars?
NASA Astrophysics Data System (ADS)
Vetrov, A.; Mejzr, I.
2010-12-01
While developing a new Helicopter Time Domain Electromagnetic system (P-THEM), Pico Envirotec Inc (PEI) has studied the effect of the transmitter assembly on the acquired data. The P-THEM system consists of a loop-transmitter assembly, powered by a motor generator, 3-axis coil receiver attached at the midpoint of a tow cable and an additional Z-axis (dB/dt) receiver installed on the rear section of the transmitter loop. The system is towed by a helicopter on a 230 foot long tow cable. The transmitter loop is designed to produce a peak magnetic moment of approximately 250,000 NIA with a base frequency of 30 Hz (adjustable to 25Hz) and a quarter length duty cycle (4 ms on-time). The secondary field acquired with a dB/dt receiver coil consists of a ground response and a system response: SF=Rg+Rsys, where SF - the secondary field, Rg - ground response, Rsys - system response. The system itself, especially the transmitter assembly, being a conductor in an induced magnetic field, creates a magnetic anomaly. The influence of the transmitter assembly anomaly on the received signal depends on the position of the receiver coil against the transmitter, the intensity of on-time pulse and transmitter electro-magnetic properties. At the same time, the ground response acquired with a receiver coil depends on the length and the moment of transmitter pulse, as well as the position and distance of the receiver coil from the ground. This can be for vertical field (Z) receiver coil described as RXz(t)=e(t)pz(t)Rgz(t)+d(t)k(t)j(t)TXz(t), where RXz(t) - receiver response, e(t) - elevation of the receiver over the ground, pz(t) - horizontal projection of the receiver coil, Rgz(t) - vertical component of ground response, d(t) - distance (elevation) between the receiver coil and the transmitter loop, k(t) - the position of the receiver in the transmitter field, j(t) - the transmitter assembly electromagnetic properties, TXz(t) -transmitter field (Primary field on-time, and transmitter
Time-domain electromagnetic soundings collected in Dawson County, Nebraska, 2007-09
Payne, Jason; Teeple, Andrew
2011-01-01
Between April 2007 and November 2009, the U.S. Geological Survey, in cooperation with the Central Platte Natural Resources District, collected time-domain electro-magnetic (TDEM) soundings at 14 locations in Dawson County, Nebraska. The TDEM soundings provide information pertaining to the hydrogeology at each of 23 sites at the 14 locations; 30 TDEM surface geophysical soundings were collected at the 14 locations to develop smooth and layered-earth resistivity models of the subsurface at each site. The soundings yield estimates of subsurface electrical resistivity; variations in subsurface electrical resistivity can be correlated with hydrogeologic and stratigraphic units. Results from each sounding were used to calculate resistivity to depths of approximately 90-130 meters (depending on loop size) below the land surface. Geonics Protem 47 and 57 systems, as well as the Alpha Geoscience TerraTEM, were used to collect the TDEM soundings (voltage data from which resistivity is calculated). For each sounding, voltage data were averaged and evaluated statistically before inversion (inverse modeling). Inverse modeling is the process of creating an estimate of the true distribution of subsurface resistivity from the mea-sured apparent resistivity obtained from TDEM soundings. Smooth and layered-earth models were generated for each sounding. A smooth model is a vertical delineation of calculated apparent resistivity that represents a non-unique estimate of the true resistivity. Ridge regression (Interpex Limited, 1996) was used by the inversion software in a series of iterations to create a smooth model consisting of 24-30 layers for each sounding site. Layered-earth models were then generated based on results of smooth modeling. The layered-earth models are simplified (generally 1 to 6 layers) to represent geologic units with depth. Throughout the area, the layered-earth models range from 2 to 4 layers, depending on observed inflections in the raw data and smooth model
Data Analysis of Airborne Electromagnetic Bathymetry.
1985-04-01
ploration Method. CIMM Bulletin, May, pp. 1-12. terpretation of Airborne Electromagnetic Data. Turnross, J., H. F. Morrison, and A. Becker (1984...System. CIMM Bulletin, v. 66, pp. 104-109. Fraser. D. C. (1978). Resistivity Mapping with an Air- report, Office of Naval Research, Washington, DC
Tian, Yuan; Han, Yiping; Ai, Xia; Liu, Xiuxiang
2014-12-15
In this paper, we investigate the propagation of terahertz (THz) electromagnetic wave in an anisotropic magnetized plasma by JE convolution-finite difference time domain method. The anisotropic characteristic of the plasma, which leads to right-hand circularly polarized (RCP) and right-hand circularly polarized (LCP) waves, has been taken into account. The interaction between electromagnetic waves and magnetized plasma is illustrated by reflection and transmission coefficients for both RCP and LCP THz waves. The effects of both the magnetized plasma thickness and the external magnetized field are analyzed and numerical results demonstrate that the two factors could influence the THz wave greatly. It is worthy to note that besides the reflection and transmission coefficients in the frequency domain, the waveform of the electric field in the time domain varying with thicknesses and external magnetic fields for different polarized direction has been studied.
NASA Astrophysics Data System (ADS)
Saeed, Ali; Ajeel, Ali; dragonetti, giovanna; Comegna, Alessandro; Lamaddalena, Nicola; Coppola, Antonio
2016-04-01
The ability to determine and monitor the effects of salts on soils and plants, are of great importance to agriculture. To control its harmful effects, soil salinity needs to be monitored in space and time. This requires knowledge of its magnitude, temporal dynamics, and spatial variability. Conventional ground survey procedures by direct soil sampling are time consuming, costly and destructive. Alternatively, soil salinity can be evaluated by measuring the bulk electrical conductivity (σb) directly in the field. Time domain reflectometry (TDR) sensors allow simultaneous measurements of water content, θ, and σb. They may be calibrated for estimating the electrical conductivity of the soil solution (σw). However, they have a relatively small observation window and thus they are thought to only provide local-scale measurements. The spatial range of the sensors is limited to tens of centimeters and extension of the information to a large area can be problematic. Also, information on the vertical distribution of the σb soil profile may only be obtained by installing sensors at different depths. In this sense, the TDR may be considered as an invasive technique. Compared to the TDR, other geophysical methods based for example on Electromagnetic Induction (EMI) techniques are non-invasive methods and represent a viable alternative to traditional techniques for soil characterization. The problem is that all these techniques give depth-weighted apparent electrical conductivity (σa) measurements, depending on the specific depth distribution of the σb, as well as on the depth response function of the sensor used. In order to deduce the actual distribution of the bulk electrical conductivity, σb, in the soil profile, one needs to invert the signal coming from EMI. Because of their relatively lower observation window, TDR sensors provide quasi-point values and do not adequately integrate the spatial variability of the chemical concentration distribution in the soil
Bultman, Mark W.
2002-01-01
This report tests the usefulness of airborne time-domain electromagnetic (TEM) data on three mineral-resource-related issues: (1) to test whether known mineral deposits at or near the surface display any signal in the TEM data; 2) determine whether TEM data can be used to locate bedrock concealed by basin fill; and (3) if the exposed mineral deposits display a signal in the TEM data, to determine if whether deposits are recognizable at depth in outcropping bedrock or in bedrock concealed beneath basin fill. Because Earth's total-intensity magnetic field data are also acquired with the TEM data, these data are included in the analysis. The Cottonwood Canyon area in Santa Cruz County, Arizona, contains several polymetallic vein deposits, including those of the Tyndall, Salero, and Wrightson mining districts, all of which have had significant mineral production. Polymetallic vein deposits, which generally consist of veins of disseminated metallic minerals, commonly exhibit a response to electrical geophysical methods. Also, on the basis of other studies, the conditions that produced the polymetallic vein mineralization in the region are believed to extend offshore into the bedrock concealed by basin fill. The polymetallic vein deposits of the Cottonwood Canyon area all display a geophysical signature in the TEM data. These deposits occur in bedrock that has, in general, a very low resistivity. The polymetallic vein deposits are associated with high-conductivity regions that extend from deep in the bedrock to the surface. These high-conductivity regions can be quite narrow (100 m) or quite wide (1 km); most are relatively narrow. Every known mineral deposit or prospect is associated with a high-conductivity feature. High-conductivity regions can also occur without an association with known mineral deposits. Airborne TEM data appear to be able to locate the basin fill/bedrock contact beneath basin fill. The basin fill (both dry and saturated) is generally more
Use of airborne electromagnetic methods for resource mapping
NASA Astrophysics Data System (ADS)
Palacky, G. J.
1993-11-01
Airborne electromagnetic (AEM) methods complement spaceborne remote sensing techniques. AEM surveys carried out from low flying aircraft are capable of detecting geological structures not visible on the surface. The flight height of AEM systems above the ground ranges from 30 to 120 m. Most systems generate primary EM fields by using a loop transmitter; conducting coils are used as antenna to measure the secondary magnetic field caused by conductive inhomogeneities in the ground. The frequency used in AEM surveys (100 Hz to 50 kHz) allows ground penetration in excess of 100 m. At present, two types of AEM systems are widely used: helicopter, frequency-domain, and fixed-wing, towed-bird, time-domain. The most common survey products are apparent conductivity maps. AEM methods are extensively used in prospecting for base and precious metal deposits, kimberlites, uranium, and also in geological mapping, groundwater exploration and environmental investigations.
Finite Difference Time Domain Electromagnetic Scattering from Frequency-Dependent Lossy Materials
NASA Technical Reports Server (NTRS)
Luebbers, Raymond J.; Beggs, John H.
1991-01-01
During this effort the tasks specified in the Statement of Work have been successfully completed. The extension of Finite Difference Time Domain (FDTD) to more complicated materials has been made. A three-dimensional FDTD code capable of modeling interactions with both dispersive dielectric and magnetic materials has been written, validated, and documented. This code is efficient and is capable of modeling interesting targets using a modest computer work station platform. However, in addition to the tasks in the Statement of Work, a significant number of other FDTD extensions and calculations have been made. RCS results for two different plate geometries have been reported. The FDTD method has been extended to computing far zone time domain results in two dimensions. Finally, the capability to model nonlinear materials has been incorporated into FDTD and validated. The FDTD computer codes developed have been supplied, along with documentation, and preprints describing the other FDTD advances have been included with this report as attachments.
Turner, C. David; Kotulski, Joseph Daniel; Pasik, Michael Francis
2005-12-01
This report investigates the feasibility of applying Adaptive Mesh Refinement (AMR) techniques to a vector finite element formulation for the wave equation in three dimensions. Possible error estimators are considered first. Next, approaches for refining tetrahedral elements are reviewed. AMR capabilities within the Nevada framework are then evaluated. We summarize our conclusions on the feasibility of AMR for time-domain vector finite elements and identify a path forward.
Chen, Hao; Tang, Juming; Liu, Fang
2007-01-01
Due to the complexity of interactions between microwaves and food products, a reliable and efficient simulation model can be a very useful tool to guide the design of microwave heating systems and processes. This research developed a model to simulate coupled phenomena of electromagnetic heating and conventional heat transfer by combining commercial electromagnetic software with a customer built heat transfer model. Simulation results were presented and compared with experimental results for hot water and microwave heating in a single mode microwave system at 915 MHz. Good agreement was achieved, showing that this model was able to provide insight into industrial electromagnetic heating processes.
Exploration of an alluvial aquifer in Oman by time-domain electromagnetic sounding
NASA Astrophysics Data System (ADS)
Young, M. E.; de Bruijn, R. G. M.; Al-Ismaily, A. Salim
One-third of the population of Oman depends upon groundwater extracted from the alluvium of the Batinah Plain, on the coast of the Gulf of Oman. Deep geophysical exploration techniques were used to determine the depth and nature of the alluvium and the boundaries of the aquifer. The base and structural controls of the alluvial basin at its contact with Tertiary marine sediments and Cretaceous ophiolite were mapped with seismic reflection data, recorded originally for oil exploration. The base of the alluvium dips northward from the foothills of the Northern Oman Mountains, reaching a maximum depth of 2000m at the coast. The varying facies of the alluvium are grossly characterised by different, overlapping ranges of electrical resistivity, depending largely on the clay content and degree of cementation. Resistivities near the coast are reduced by saline intrusion. These variations of resistivity were mapped with time-domain electromagnetic sounding along 400km of profile, to distinguish among the three zones of the alluvial aquifer. The wedge of saline intrusion was also delineated, up to 10km from the coast. The thickness of the saturated gravel aquifer ranges from 20-160m in an area greater than 600km2. Résumé Un tiers de la population d'Oman est alimenté par de l'eau souterraine pompée dans les alluvions de la plaine de Batinah, sur la côte du golfe d'Oman. Des techniques d'exploration géophysique profonde ont été mises en oeuvre pour déterminer la profondeur et la nature des alluvions et les limites de l'aquifère. La base et les contrôles structuraux du bassin alluvial au contact des sédiments marins tertiaires et des ophiolites crétacées ont été cartographiés à partir des données de sismique réflexion obtenues à l'origine pour la recherche pétrolière. La base des alluvions plonge vers le nord à partir du piémont du massif septentrional d'Oman, pour atteindre une profondeur maximale de 2000m sur la côte. Les divers faciès alluviaux
Finite difference time domain electromagnetic scattering from frequency-dependent lossy materials
NASA Technical Reports Server (NTRS)
Luebbers, Raymond J.; Beggs, John H.
1991-01-01
Four different FDTD computer codes and companion Radar Cross Section (RCS) conversion codes on magnetic media are submitted. A single three dimensional dispersive FDTD code for both dispersive dielectric and magnetic materials was developed, along with a user's manual. The extension of FDTD to more complicated materials was made. The code is efficient and is capable of modeling interesting radar targets using a modest computer workstation platform. RCS results for two different plate geometries are reported. The FDTD method was also extended to computing far zone time domain results in two dimensions. Also the capability to model nonlinear materials was incorporated into FDTD and validated.
Time-domain electromagnetic energy in a frequency-dispersive left-handed medium
NASA Astrophysics Data System (ADS)
Cui, Tie Jun; Kong, Jin Au
2004-11-01
From Maxwell’s equations and the Poynting theorem, the time-domain electric and magnetic energy densities are generally defined in the frequency-dispersive media based on the conservation of energy. As a consequence, a general definition of electric and magnetic energy is proposed. Comparing with existing formulations of electric and magnetic energy in frequency-dispersive media, the new definition is more reasonable and is valid in any case. Using the new definition and staring from the equation of motion, we have shown rigorously that the total energy density and the individual electric and magnetic energy densities are always positive in a realistic artificial left-handed medium (LHM) [
2008-02-01
frequency electromagnetic exposure: tutorial review on experimental dosimetry.” Bioelectromagnetics . 1996;17(3):195-208. [8] Chou, C. K., G. W...Chen, A. W. Guy, and K. H. Luk, “Formulas for Preparing Phantom Muscle Tissue at Various Radiofrequencies,” Bioelectromagnetics , 1984, 5, 435-441
Hussein, Y.A.; Spencer, J.E.; El-Ghazaly, S.M.; Goodnick, S.M.; /Arizona State U.
2005-09-20
This paper presents an efficient full-wave time-domain simulator for accurate modeling of PIN diode switches. An equivalent circuit of the PIN diode is extracted under different bias conditions using a drift-diffusion physical model. Net recombination is modeled using a Shockley-Read-Hall process, while generation is assumed to be dominated by impact ionization. The device physics is coupled to Maxwell's equations using extended-FDTD formulism. A complete set of results is presented for the on and off states of the PIN switch. The results are validated through comparison with independent measurements, where good agreement is observed. Using this modeling approach, it is demonstrated that one can efficiently optimize PIN switches for better performance.
NASA Astrophysics Data System (ADS)
Shaaban, H.; El-Qady, G.; Al-Sayed, E.; Ghazala, H.; Taha, A. I.
2016-12-01
The Nile Delta is one of the oldest known ancient delta, largest and most important depositional complex in the Mediterranean sedimentary basin. Furthermore, it is a unique site in Egypt that is suitable for accumulation and preservation of the Quaternary sediments. In this work we applied time-domain electromagnetic (TEM) method to investigate the Quaternary sediments sequence as well as detecting the groundwater aquifer in the area of study. A suite of 232 TEM sounding at 43 stations were carried out using a "SIROTEM MK-3" time-domain electromagnetic system. A simple coincident loop configuration, in which the same loop transmits and receives signals, was employed with loop side length of 25 m. The 1-D modeling technique was applied to estimate the depth and the apparent resistivity of the interpreted geoelectrical data. Based on the interpretation of the acquired geophysical data, four geoelectric cross-sections were constructed. These sections show that the Upper Quaternary sequence consists of three geoelectric layers. The Holocene Nile mud is separated into two layers: the agricultural root zone (Layer 1) and thick water saturated mud (Layer 2). The Upper Pleistocene sandy aquifer (Layer 3) is very complicated non-linear boundary. This aquifer is the most important unit since it is considered as the main water bearing unit in the study area.
High-Performance Computational Electromagnetics in Frequency-Domain and Time-Domain
2015-03-04
for sound-hard acoustic scattering problems were put forth in [15]; use of these equations gives rise to very significant improvements in iterations...Bruno, O., Elling, T. and Turc, C., Regularized integral equations and fast high-order solvers for sound-hard acoustic scattering problems...solutions for some of the most challenging scattering problems in science and engineering. Electromagnetic scattering . Frequency domain solvers. Integral
NASA Astrophysics Data System (ADS)
Koshurnikov, A.; Gunar, A.; Tumskoy, V. E.; Shakhova, N. E.; Semiletov, I. P.; Valuyskiy, S.
2015-12-01
Different geophysical methods are used to study and map submarine permafrost on the Arctic Shelf. Due to specific features of submarine permafrost, none of geophysical methods can provide conclusive data when gas-charged sediments and taliks occur within permafrost. Experimental data show that electrical properties of frozen grounds change significantly. For example, depending on ground lithology and wetness, electrical resistivity can increase up to 103 times upon freezing. Thus, electromagnetic methods could be considered more informative and valuable tool for characterizing subsea permafrost. Investigation of submarine permafrost on the shallow Arctic Shelf requires modifications of electromagnetic methods to cover specific needs of working from the fast ice. Winter expeditions devoted to subsea permafrost investigations were performed in March-April of 2012-2015 in the near-shore area of the Laptev Sea. TEM was applied to predict permafrost down to 1 km depth. TEM systems are advantageous when many stations are required, because many short deployments can be performed in a single survey. Working from the fast ice allowed collection of few tens of stations to cover the entire polygon. Interpretation of data collected in 2012 allowed to predict position of the permafrost table near-shore near Muostakh Island, which was validated by followed up permafrost drilling. Surveys performed in 2013-2015 also confirmed good agreement between electromagnetic data and observational data obtained by drilling. Accuracy of the methods reached 3.5%. Note, that in March-April of 2014 and 2015, we used the modified TEM which allows obtaining continuous subsea permafrost table profiles.
NASA Astrophysics Data System (ADS)
Marklein, R.; Langenberg, K.-J.; Hübschen, G.; Willems, H.
2000-05-01
In principle, apart from laser generated ultrasound, two types of transducers, electromagnetic acoustic transducers (EMAT) and piezoelectric transducers, are applied in ultrasonic NDT. Piezoelectric transducers are primarily used to generate pressure, shear vertical, and Rayleigh waves; whereas electromagnetic acoustic transducers are primarily used to generate shear horizontal as well as Rayleigh waves. This paper presents numerical results for both transducer types in 2-D applying the EFIT code (EFIT: Elastodynamic Finite Integration Technique), which has been developed to simulate in 2-D the SH case and P-SV case separately. Three different cases will be studied in detail: (1.) detection of a backwall breaking notch in an isotropic test block, (2.) crack detection in an isotropic pipeline, and (3.) detection of a cracking an austenitic weld. In case (1.) and (3.) different wave modes (P-, SV-, and R-wave) as well as different inclination angles are used, whereas in case (2.), different wave modes are generated (guided SH-waves and R-waves). The numerical results will be validated against measurements if available.
NASA Astrophysics Data System (ADS)
Kabakian, Adour Vahe
1998-12-01
Most time-domain solvers of Maxwell's equations that are applied to electromagnetic wave scattering problems are based on second- or third-order finite-difference and finite-volume schemes. Since linear wave propagation phenomena tend to be very susceptible to numerical dissipation and dispersion errors, they place high accuracy demands on the numerical methods employed. Starting with the premise that the required accuracy can be achieved more efficiently with high-order methods, a new numerical scheme based on spectral collocation is developed for solving Maxwell's equations in the time domain. The three-dimensional method is formulated over generalized curvilinear coordinates. It employs Fourier and Chebyshev spectral collocation for the spatial derivatives, while time advancement is achieved by the explicit third-order Adams-Moulton-Bashforth scheme. A domain decomposition method supplementing the spectral solver is also developed, extending its range of applications to geometries more complex than those traditionally associated with spectral methods. Reflective and absorbing boundary conditions are developed specifically for the spectral scheme. Finally, a grid stretching function is incorporated into the solver, which can be used, when needed, to relieve the stability restriction associated with the Chebyshev spacing of the collocation points, at the expense of only moderate loss in accuracy. The numerical method is applied to solve electromagnetic wave scattering problems from perfectly conducting solid targets, using both single and multi-domain grids. The geometries considered are the circular cylinder, the square cylinder, and the sphere. Solutions are evaluated and validated by the accuracy of the radar cross-section and, in some instances, the surface currents. Compared to commonly used finite-difference and finite-volume solvers, the spectral scheme produces results that are one to two orders of magnitude more accurate, using grids that are an order of
NASA Astrophysics Data System (ADS)
Blake, Douglas Clifton
A new methodology is presented for conducting numerical simulations of electromagnetic scattering and wave-propagation phenomena on massively parallel computing platforms. A process is constructed which is rooted in the Finite-Volume Time-Domain (FVTD) technique to create a simulation capability that is both versatile and practical. In terms of versatility, the method is platform independent, is easily modifiable, and is capable of solving a large number of problems with no alterations. In terms of practicality, the method is sophisticated enough to solve problems of engineering significance and is not limited to mere academic exercises. In order to achieve this capability, techniques are integrated from several scientific disciplines including computational fluid dynamics, computational electromagnetics, and parallel computing. The end result is the first FVTD solver capable of utilizing the highly flexible overset-gridding process in a distributed-memory computing environment. In the process of creating this capability, work is accomplished to conduct the first study designed to quantify the effects of domain-decomposition dimensionality on the parallel performance of hyperbolic partial differential equations solvers; to develop a new method of partitioning a computational domain comprised of overset grids; and to provide the first detailed assessment of the applicability of overset grids to the field of computational electromagnetics. Using these new methods and capabilities, results from a large number of wave propagation and scattering simulations are presented. The overset-grid FVTD algorithm is demonstrated to produce results of comparable accuracy to single-grid simulations while simultaneously shortening the grid-generation process and increasing the flexibility and utility of the FVTD technique. Furthermore, the new domain-decomposition approaches developed for overset grids are shown to be capable of producing partitions that are better load balanced and
NASA Astrophysics Data System (ADS)
Sridhar, M.; Markandeyulu, A.; Chaturvedi, A. K.
2017-01-01
Mapping of subtrappean sediments is a complex geological problem attempted by many interpreters applying different geophysical techniques. Variations in thickness and resistivity of traps and underlying sediments, respectively, results in considerable uncertainty in the interpretation of geophysical data. It is proposed that the transient electromagnetic technique is an effective geophysical tool for delineation of the sub-trappean sediments, due to marked resistivity contrast between the Deccan trap, and underlying sediments and/or basement. The northern margin of the Kaladgi basin is covered under trap. A heliborne time domain electromagnetic survey was conducted to demarcate the basin extent and map the sub-trappean sediments. Conductivity depth transformations were used to map the interface between conductive trap and resistive 'basement'. Two resistivity contrast boundaries are picked: the first corresponds to the bottom of the shallow conductive unit interpreted as the base of the Deccan Volcanics and the second - picked at the base of a deeper subsurface conductive zone - is interpreted as the weathered paleo-surface of the crystalline basement. This second boundary can only be seen in areas where the volcanics are thin or absent, suggesting that the volcanics are masking the EM signal preventing deeper penetration. An interesting feature, which shows prominently in the EM data but less clearly imaged in the magnetic data, is observed in the vicinity of Mudhol. The surface geology interpreted from satellite imagery show Deccan trap cover around Mudhol. Modelling of TDEM data suggest the presence of synclinal basin structure. The depth of penetration of the heliborne TDEM data is estimated to be approximately 350 m for the study area. This suggests that heliborne TDEM could penetrate significant thicknesses of conductive Deccan trap cover to delineate structure below in the Bagalkot Group.
NASA Astrophysics Data System (ADS)
Hamano, Yozo
2002-09-01
We present a new time-domain approach to the forward modelling of 3-D electromagnetic induction in a heterogeneous conducting sphere excited by external and internal sources. This method utilizes the standard decomposition of the magnetic field into toroidal and poloidal parts, and spherical harmonic expansions of both the magnetic fields and the conductivity heterogeneity. Resulting induction equations for the spherical harmonics are solved simultaneously in the time domain. Coupling terms between the electromagnetic fields and the conductivity structure are re-expanded in spherical harmonics, so that the terms can be calculated by matrix multiplications at each time step of the computation. A finite difference approximation was used to solve the set of diffusion equations for the spherical harmonics up to degree 20. This method can be efficiently used to analyse transient geomagnetic variations to estimate the 3-D conductivity structure of the Earth. In order to validate the present approach, we solved an induction problem in simple four-layer mantle models, which consist of the surface layer (r= 6371 - 6351 km, σ=1 S m-1), the upper mantle (r= 6351 - 5971 km, σ= 0.01 S m-1), the transition layer (r= 5971 - 5671 km, σ= 0.01-1 S m-1), and the lower mantle (r= 5671 - 3481 km, σ= 1 S m-1). Conductivity heterogeneities are considered in the surface layer or the transition layer. For these models, temporal variations of the Gauss coefficients in response to a sudden application of P10-type external field were calculated, and the impulse response function of each harmonic component was obtained by differentiating the calculated variations with time. The response functions of the primary induced components, g10, have large initial values and monotonously decay with time. Changes of the decay rate reflect the radial distribution of the electrical conductivity. For the surface heterogeneous models, temporal variations of other secondary induced components have two
Silva, F. da; Hacquin, S.
2005-03-01
We present a novel numerical signal injection technique allowing unidirectional injection of a wave in a wave-guiding structure, applicable to 2D finite-difference time-domain electromagnetic codes, both Maxwell and wave-equation. It is particularly suited to continuous wave radar-like simulations. The scheme gives an unidirectional injection of a signal while being transparent to waves propagating in the opposite direction (directional coupling). The reflected or backscattered waves (returned) are separated from the probing waves allowing direct access to the information on amplitude and phase of the returned wave. It also facilitates the signal processing used to extract the phase derivative (or group delay) when simulating radar systems. Although general, the technique is particularly suited to swept frequency sources (frequency modulated) in the context of reflectometry, a fusion plasma diagnostic. The UTS applications presented here are restricted to fusion plasma reflectometry simulations for different physical situations. This method can, nevertheless, also be used in other dispersive media such as dielectrics, being useful, for example, in the simulation of plasma filled waveguides or directional couplers.
Kauahikaua, J.
1981-01-01
A controlled-source time-domain electromagnetic (TDEM) sounding survey was completed on the lower portion of the East Rift of Kilauea Volcano, Hawaii (locally known as the Puna area) during the summer of 1974 as part of the geophysical task of the Hawaii Geothermal Project. Interpretations as obtained by a layered-earth TDEM inversion computer program are presented. Interpretations in terms of layered half-space models can be used to localize low-resistivity zones vertically as well as horizontally. The results show that much of the area is underlain by an anomalously conductive zone at depths of 250 to 1300 below sea level. Twenty-four TDEM soundings were attempted in the area using four different grounded wire current sources and a 42-conductor, horizontal loop sensor. The TDEM sounding data were in the form of voltages (proportional to the time derivative of the induced magnetic field) measured at discrete times after a break in the source current. Seventeen of the soundings are interpreted here.
Airborne Electromagnetic Mapping of Subsurface Permafrost
NASA Astrophysics Data System (ADS)
Abraham, J. D.; Minsley, B. J.; Cannia, J. C.; Smith, B. D.; Walvoord, M. A.; Voss, C. I.; Jorgenson, T. T.; Wylie, B. K.; Anderson, L.
2011-12-01
Concerns over the impacts of climate change have recently energized research on the potential impacts thawing permafrost may have on groundwater flow, infrastructure, forest health, ecosystems, energy production, CO2 release, and contaminant transport. There is typically little knowledge about subsurface permafrost distributions, such as thickness and where groundwater-surface-water connections may occur through taliks. In June of 2010, the U.S. Geological Survey undertook an airborne electromagnetic (AEM) survey in the area of Fort Yukon, Alaska in order to map the 3-D distribution of permafrost and provide information for the development of groundwater models within the Yukon River Basin. Prior to the development of these models, information on areas of groundwater-surface water interaction was extremely limited. Lithology determined from a borehole drilled in Fort Yukon in 1994 agrees well with the resistivity depth sections inferred from the airborne survey. In addition to lithology, there a thermal imprint appears on the subsurface resistivity values. In the upper 20-50 m, the sections show continuous areas of high electrical resistivity, consistent with alluvial gravel deposits that are likely frozen. At depth, unfrozen gravel deposits have intermediate-to-high resistivity; frozen silts have intermediate resistivity; and unfrozen silts have low resistivity. Under the Yukon River and lakes where the subsurface is not frozen, zones of moderate resistivity intermix with areas of low resistivity. The areas of loess hills on the margins of the Yukon Flats have very-high electrical resistivity, indicating higher ice content, and are associated with the some of the greatest thickness of permafrost in the survey area. This work provides the first look into the 3-D distribution of permafrost in the areas around Fort Yukon and is a demonstration of the application of AEM to permafrost mapping. The AEM survey provides unprecedented 3-D images of subsurface electrical
Airborne electromagnetic imaging of discontinuous permafrost
NASA Astrophysics Data System (ADS)
Minsley, Burke J.; Abraham, Jared D.; Smith, Bruce D.; Cannia, James C.; Voss, Clifford I.; Jorgenson, M. Torre; Walvoord, Michelle A.; Wylie, Bruce K.; Anderson, Lesleigh; Ball, Lyndsay B.; Deszcz-Pan, Maryla; Wellman, Tristan P.; Ager, Thomas A.
2012-01-01
The evolution of permafrost in cold regions is inextricably connected to hydrogeologic processes, climate, and ecosystems. Permafrost thawing has been linked to changes in wetland and lake areas, alteration of the groundwater contribution to streamflow, carbon release, and increased fire frequency. But detailed knowledge about the dynamic state of permafrost in relation to surface and groundwater systems remains an enigma. Here, we present the results of a pioneering ˜1,800 line-kilometer airborne electromagnetic survey that shows sediments deposited over the past ˜4 million years and the configuration of permafrost to depths of ˜100 meters in the Yukon Flats area near Fort Yukon, Alaska. The Yukon Flats is near the boundary between continuous permafrost to the north and discontinuous permafrost to the south, making it an important location for examining permafrost dynamics. Our results not only provide a detailed snapshot of the present-day configuration of permafrost, but they also expose previously unseen details about potential surface - groundwater connections and the thermal legacy of surface water features that has been recorded in the permafrost over the past ˜1,000 years. This work will be a critical baseline for future permafrost studies aimed at exploring the connections between hydrogeologic, climatic, and ecological processes, and has significant implications for the stewardship of Arctic environments.
Airborne electromagnetic imaging of discontinuous permafrost
Minsley, B.J.; Abraham, J.D.; Smith, B.D.; Cannia, J.C.; Voss, C.I.; Jorgenson, M.T.; Walvoord, M.A.; Wylie, B.K.; Anderson, L.; Ball, L.B.; Deszcz-Pan, M.; Wellman, T.P.; Ager, T.A.
2012-01-01
The evolution of permafrost in cold regions is inextricably connected to hydrogeologic processes, climate, and ecosystems. Permafrost thawing has been linked to changes in wetland and lake areas, alteration of the groundwater contribution to streamflow, carbon release, and increased fire frequency. But detailed knowledge about the dynamic state of permafrost in relation to surface and groundwater systems remains an enigma. Here, we present the results of a pioneering ∼1,800 line-kilometer airborne electromagnetic survey that shows sediments deposited over the past ∼4 million years and the configuration of permafrost to depths of ∼100 meters in the Yukon Flats area near Fort Yukon, Alaska. The Yukon Flats is near the boundary between continuous permafrost to the north and discontinuous permafrost to the south, making it an important location for examining permafrost dynamics. Our results not only provide a detailed snapshot of the present-day configuration of permafrost, but they also expose previously unseen details about potential surface – groundwater connections and the thermal legacy of surface water features that has been recorded in the permafrost over the past ∼1,000 years. This work will be a critical baseline for future permafrost studies aimed at exploring the connections between hydrogeologic, climatic, and ecological processes, and has significant implications for the stewardship of Arctic environments.
NASA Astrophysics Data System (ADS)
Panayappan, Kadappan
With the advent of sub-micron technologies and increasing awareness of Electromagnetic Interference and Compatibility (EMI/EMC) issues, designers are often interested in full- wave solutions of complete systems, taking to account a variety of environments in which the system operates. However, attempts to do this substantially increase the complexities involved in computing full-wave solutions, especially when the problems involve multi- scale geometries with very fine features. For such problems, even the well-established numerical methods, such as the time domain technique FDTD and the frequency domain methods FEM and MoM, are often challenged to the limits of their capabilities. In an attempt to address such challenges, three novel techniques have been introduced in this work, namely Dipole Moment (DM) Approach, Recursive Update in Frequency Domain (RUFD) and New Finite Difference Time Domain ( vFDTD). Furthermore, the efficacy of the above techniques has been illustrated, via several examples, and the results obtained by proposed techniques have been compared with other existing numerical methods for the purpose of validation. The DM method is a new physics-based approach for formulating MoM problems, which is based on the use of dipole moments (DMs), as opposed to the conventional Green's functions. The absence of the Green's functions, as well as those of the vector and scalar potentials, helps to eliminate two of the key sources of difficulties in the conventional MoM formulation, namely the singularity and low-frequency problems. Specifically, we show that there are no singularities that we need to be concerned with in the DM formulation; hence, this obviates the need for special techniques for integrating these singularities. Yet another salutary feature of the DM approach is its ability to handle thin and lossy structures, or whether they are metallic, dielectric-type, or even combinations thereof. We have found that the DM formulation can handle these
Goldman, M.; Gvirtzman, H.; Hurwitz, S.
2004-01-01
An extensive time domain electromagnetic (TDEM) survey covering the Sea of Galilee with a dense grid of points has been recently carried out. A total of 269 offshore and 33 supplementary onshore TDEM soundings were performed along six N-S and ten W-E profiles and at selected points both offshore and onshore along the whole coastal line. The interpreted resistivities were calibrated with the direct salinity measurements in the Haon-2 borehole and relatively deep (5 m) cores taken from the lake bottom. It was found that resistivities below 1 ohm-m are solely indicative of groundwater salinity exceeding 10,000 mg Cl/l. Such low resistivities (high salinities) were detected at depths greater than 15 m below almost the entire bottom of the lake. At some parts of the lake, particularly in the south, the saline water was detected at shallower depths, sometimes at a few meters below the bottom. Relatively high resistivity (fresh groundwater) was found along the margins of the lake down to roughly 100 m, the maximum exploration depth of the system. The detected sharp lateral contrasts at the lake margin between high and low resistivities coincide with the faults separating the carbonate and clastic units, respectively. The geometry of the fresh/saline groundwater interface below the central part of the lake is very similar to the shape of the lake bottom, probably due to the diffusive salt transport from the bottom sediments to the lake water. The above geophysical observations suggest differentsalt transport mechanisms from the sediments to the central part of the lake (diffusion) and from regional aquifers to the margins of the lake (advection). ?? 2004 Science From Israel/LPPLtd.
NASA Astrophysics Data System (ADS)
Grimm, Robert E.
2003-04-01
The time domain electromagnetic (TDEM) method has enjoyed wide success in terrestrial groundwater exploration, and the contrast in electrical conductivity between dry overburden and groundwater containing even a small amount of dissolved solids on Mars will yield a robust response. However, moist clays or even ores (e.g., massive hematite) will also be electrically conductive and could be mistaken for aquifers on Mars if proper geologic context is lacking. Surface nuclear magnetic resonance (SNMR) is the only noninvasive geophysical method that responds nearly uniquely to water. As the measured EMF is proportional to the proton-precession frequency, which in turn is proportional to the planet's static magnetic field, SNMR signals are comparatively weak. Using small systems of several kilograms and several watts, the exploration depth of SNMR is one to two orders of magnitude smaller than TDEM: the latter can detect water to depths up to a few kilometers, whereas the former is limited to depths of a few tens of meters. There is no improvement in SNMR signal-to-noise with increasing static field where penetration is controlled by aquifer salinity (skin depth). As reasonable integration times cannot substantially increase the exploration depth, much larger transmitter current or loop mass (either requiring system masses of tens to hundreds of kilograms) are the only way to implement SNMR for exploration to depths of at least hundreds of meters. In spite of some ambiguity in target identification, TDEM is recommended for the first generation of in situ active-source EM measurements for groundwater on Mars.
Shah, Sachin D.; Kress, Wade H.; Land, Lewis A.
2007-01-01
During July 2005, the U.S. Geological Survey, in cooperation with the New Mexico Bureau of Geology and Mineral Resources, conducted a reconnaissance study in the Estancia Valley in central New Mexico to characterize water quality using time-domain electromagnetic (TDEM) surface-geophysical soundings. TDEM sounding is one of a number of surface geophysical methods that provide a relatively quick and inexpensive means to characterize subsurface geologic and hydrogeologic properties. TDEM surface geophysical methods can be used to detect variations in the electrical resistivity of the subsurface, which in turn can be related to variations in the physical and chemical properties of soil, rock, and pore fluids.
NASA Astrophysics Data System (ADS)
Tobón, Luis E.; Ren, Qiang; Liu, Qing Huo
2015-02-01
A new Discontinuous Galerkin Time Domain (DGTD) method for solving the 3D time dependent Maxwell's equations via the electric field intensity E and magnetic flux density B fields is proposed for the first time. It uses curl-conforming and divergence-conforming basis functions for E and B, respectively, with the same order of interpolation. In this way, higher accuracy is achieved at lower memory consumption than the conventional approach based on the field variables E and H. The centered flux and Riemann solver are both used to treat interfaces with non-conforming meshes, and both explicit Runge-Kutta method and implicit Crank-Nicholson method are implemented for time integration. Numerical examples for realistic cases will be presented to verify that the proposed method is a non-spurious and efficient DGTD scheme.
Bedrosian, Paul A.; Ball, Lyndsay B.; Bloss, Benjamin R.
2014-01-01
From December 2010 to January 2011, the U.S. Geological Survey conducted airborne electromagnetic and magnetic surveys of Leach Lake Basin within the National Training Center, Fort Irwin, California. These data were collected to characterize the subsurface and provide information needed to understand and manage groundwater resources within Fort Irwin. A resistivity stratigraphy was developed using ground-based time-domain electromagnetic soundings together with laboratory resistivity measurements on hand samples and borehole geophysical logs from nearby basins. This report releases data associated with the airborne surveys, as well as resistivity cross-sections and depth slices derived from inversion of the airborne electromagnetic data. The resulting resistivity models confirm and add to the geologic framework, constrain the hydrostratigraphy and the depth to basement, and reveal the distribution of faults and folds within the basin.
NASA Astrophysics Data System (ADS)
Carlson, B. E.; Bitzer, P. M.; Burchfield, J.
2015-12-01
Major unknowns in lightning research include the mechanism and dynamics of lightning channel extension. Such processes are most simple during the initial growth of the channel, when the channel is relatively short and has not yet branched extensively throughout the cloud. During this initial growth phase, impulsive electromagnetic emissions (preliminary breakdown pulses) can be well-described as produced by current pulses generated as the channel extends, but the overall growth rate, channel geometry, and degree of branching are not known. We approach such issues by examining electric field change measurements made with the Huntsville Alabama Marx Meter Array (HAMMA) during the first few milliseconds of growth of a lightning discharge. We compare HAMMA observations of electromagnetic emissions and overall field change to models of lightning channel growth and development and attempt to constrain channel growth rate, degree of branching, channel physical properties, and uniformity of thunderstorm electric field. Preliminary comparisons suggest that the lightning channel branches relatively early in the discharge, though more complete and detailed analysis will be presented.
Lin, Bang-Yan; Hsu, Hui-Chen; Teng, Chun-Hao; Chang, Hung-Chun; Wang, Juen-Kai; Wang, Yuh-Lin
2009-08-03
In this study, we report the investigation of both near- and far-field electromagnetic characteristics of two-dimensional silver nanorod arrays embedded in anodic aluminum oxide with the use of a high-accuracy three-dimensional Legendre pseudospectral time-domain scheme. The simulated far-field scattering spectra agree with the experimental observations. We show that enhanced electric field is created between adjacent nanorods and, most importantly, far-field scattered light wave is mainly contributed from surface magnetic field, instead of the surface enhanced electric field. The identified near-field to far-field connection produces an important implication in the development of efficient surface-enhanced Raman scattering substrates.
Bedrock mapping of buried valley networks using seismic reflection and airborne electromagnetic data
NASA Astrophysics Data System (ADS)
Oldenborger, G. A.; Logan, C. E.; Hinton, M. J.; Pugin, A. J.-M.; Sapia, V.; Sharpe, D. R.; Russell, H. A. J.
2016-05-01
In glaciated terrain, buried valleys often host aquifers that are significant groundwater resources. However, given the range of scales, spatial complexity and depth of burial, buried valleys often remain undetected or insufficiently mapped. Accurate and thorough mapping of bedrock topography is a crucial step in detecting and delineating buried valleys and understanding formative valley processes. We develop a bedrock mapping procedure supported by the combination of seismic reflection data and helicopter time-domain electromagnetic data with water well records for the Spiritwood buried valley aquifer system in Manitoba, Canada. The limited spatial density of water well bedrock observations precludes complete depiction of the buried valley bedrock topography and renders the water well records alone inadequate for accurate hydrogeological model building. Instead, we leverage the complementary strengths of seismic reflection and airborne electromagnetic data for accurate local detection of the sediment-bedrock interface and for spatially extensive coverage, respectively. Seismic reflection data are used to define buried valley morphology in cross-section beneath survey lines distributed over a regional area. A 3D model of electrical conductivity is derived from inversion of the airborne electromagnetic data and used to extrapolate buried valley morphology over the entire survey area. A spatially variable assignment of the electrical conductivity at the bedrock surface is applied to different features of the buried valley morphology identified in the seismic cross-sections. Electrical conductivity is then used to guide construction of buried valley shapes between seismic sections. The 3D locus of points defining each morphological valley feature is constructed using a path optimization routine that utilizes deviation from the assigned electrical conductivities as the cost function. Our resulting map represents a bedrock surface of unprecedented detail with more
INTERPRETATION OF AIRBORNE ELECTROMAGNETIC AND MAGNETIC DATA IN THE 600 AREA
CUMMINS GD
2010-11-11
As part of the 200-PO-1 Phase I geophysical surveys, Fugro Airborne Surveys was contracted to collect airborne electromagnetic (EM) and magnetic surveys of the Hanford Site 600 Area. Two helicopter survey systems were used with the HeliGEOTEM{reg_sign} time domain portion flown between June 19th and June 20th, 2008, and the RESOLVE{reg_sign} frequency domain portion was flown from June 29th to July 1st, 2008. Magnetic data were acquired contemporaneously with the electromagnetic surveys using a total-field cesium vapor magnetometer. Approximately 925 line kilometers (km) were flown using the HeliGEOTEM{reg_sign} II system and 412 line kilometers were flown using the RESOLVE{reg_sign} system. The HeliGEOTEM system has an effective penetration of roughly 250 meters into the ground and the RESOLVE system has an effective penetration of roughly 60 meters. Acquisition parameters and preliminary results are provided in SGW-39674, Airborne Electromagnetic Survey Report, 200-PO-1 Groundwater Operable Unit, 600 Area, Hanford Site. Airborne data are interpreted in this report in an attempt to identify areas of likely preferential groundwater flow within the aquifer system based on the presence of paleochannels or fault zones. The premise for the interpretation is that coarser-grained intervals have filled in scour channels created by episodic catastrophic flood events during the late Pleistocene. The interpretation strategy used the magnetic field anomaly data and existing bedrock maps to identify likely fault or lineament zones. Combined analysis of the magnetic, 60-Hz noise monitor, and flight-altitude (radar) data were used to identify zones where EM response is more likely due to cultural interference and or bedrock structures. Cross-sectional and map view presentations of the EM data were used to identify more electrically resistive zones that likely correlate with coarser-grained intervals. The resulting interpretation identifies one major northwest-southeast trending
NASA Astrophysics Data System (ADS)
Hurtado Cardador, Manuel; Cuevas, Antonio L.; Watanabe, Hidehiko; Saito, Akira; Wada, Kazushige; Ishikawa, Hidehiro; Okuzumi, Koichi
2003-02-01
In Mexico, an experimental study with a Long-Offset Time-Domain Electromagnetic Method (LOTDEM) was carried out in the Tampico-Misantla basin of northeastern Mexico. The main objective was to evaluate this method for hydrocarbon exploration. The selected area is suitable for LOTDEM experiments because high quality seismic data, geological information and well logging data are available. The results obtained are excellent, and allow us to determine the types of fluids present in the rock pores and fractures of the studied geological structures. Resistivity anomalies correlate in position and depth with the geological structures observed in the seismic sections where the LOTDEM survey was carried out, and with well logging data from the nearby Franco Española oil field. In the studied area, these structures are 800-1200 m deep, in carbonate rocks with high clay content and are invaded by salt water. Consequently, the resistivity and primary porosities are very low. The main reservoirs of oil and gas in this region are a naturally fractured basinal facies, consisting of fine-grained limestones and shaly limestones, that corresponds to the Cretaceous units San Felipe, Agua Nueva, Tamaulipas Superior and Tamaulipas Inferior. The fractured rocks reservoirs are very difficult to detect, even with well logs. However, the results of this survey show the higher resolution, the greater depth of investigation, and the advantages that the LOTDEM method present compared to the traditional frequency domain electric and electromagnetic (FEM) methods.
White, Eric A.; Day-Lewis, Frederick D.; Johnson, Carole D.; Lane, John
2016-01-01
In 2014 and 2015, the U.S. Geological Survey (USGS), conducted frequency-domain electromagnetic (FDEM) surveys at the USGS Amargosa Desert Research Site (ADRS), approximately 17 kilometers (km) south of Beatty, Nevada. The FDEM surveys were conducted within and adjacent to a closed low-level radioactive waste disposal site located at the ADRS. FDEM surveys were conducted on a grid of north-south and east-west profiles to assess the locations and boundaries of historically recorded waste-disposal trenches. In 2015, the USGS conducted time-domain (TDEM) soundings along a profile adjacent to the disposal site (landfill) in cooperation with the U.S. Environmental Protection Agency (USEPA), to assess the thickness and characteristics of the underlying deep unsaturated zone, and the hydrostratigraphy of the underlying saturated zone.FDEM survey results indicate the general location and extent of the waste-disposal trenches and reveal potential differences in material properties and the type and concentration of waste in several areas of the landfill. The TDEM surveys provide information on the underlying hydrostratigraphy and characteristics of the unsaturated zone that inform the site conceptual model and support an improved understanding of the hydrostratigraphic framework. Additional work is needed to interpret the TDEM results in the context of the local and regional structural geology.
NASA Astrophysics Data System (ADS)
Soule, D.; Everett, M.
2007-05-01
Comet and asteroid bombardment along with impact crater formation has occurred continuously throughout Earth's history. The greatest impact-related geohazard is due to moderate sized impactors which represent the worst-case trade-off between frequency of occurrence, difficulty of mitigation, and severity of environmental destruction. Impacts in this size range pose a significant regional threat to densely populated areas. The primary objective of this research is to evaluate the ground-impact geohazard via high resolution seismic imaging of the remnants of a moderate-sized impact event, namely that associated with the 50 ka Odessa (TX) Group IAB iron meteorite. We provide high-resolution subsurface images of the 150-m diameter crater, the outcropping crater rim, the ejecta blanket, and the surrounding plain. The subsurface images are analyzed in terms of the deformation and thrusting of the underlying Cretaceous limestone and shale strata and the likely environmental effects caused by the impact. The analysis will build upon and extend our previous geophysical investigations based on magnetic gradiometry and time-domain electromagnetic data.
Development of 3D electromagnetic modeling tools for airborne vehicles
NASA Technical Reports Server (NTRS)
Volakis, John L.
1992-01-01
The main goal of this report is to advance the development of methodologies for scattering by airborne composite vehicles. Although the primary focus continues to be the development of a general purpose computer code for analyzing the entire structure as a single unit, a number of other tasks are also being pursued in parallel with this effort. One of these tasks discussed within is on new finite element formulations and mesh termination schemes. The goal here is to decrease computation time while retaining accuracy and geometric adaptability.The second task focuses on the application of wavelets to electromagnetics. Wavelet transformations are shown to be able to reduce a full matrix to a band matrix, thereby reducing the solutions memory requirements. Included within this document are two separate papers on finite element formulations and wavelets.
Deszcz-Pan, Maria; Rodriguez, B.D.; Doucette, J.P.; Godbout, Michel; Williams, J.M.; Sawyer, D.A.; Stone, B.D.; Grauch, V.J.
2000-01-01
The Albuquerque-Santa Fe region is rapidly growing. The Santa Fe Group aquifer in the Middle Rio Grande Basin (MRGB) is the main source of municipal water for the greater Albuquerque metropolitan area and is more limited than previously thought (Thorn et al., 1993). The MRGB, as defined hydrologically and used here, is the area within the Rio Grande Valley extending from Cochiti Dam downstream to the community of San Acacia (Figure 1). Because approximately 600,000 people (40 percent of the population of New Mexico) live in the study area (Bartolino, 1999), water shortfalls could have serious consequences for the state. Future growth and land management in the region depends on accurate assessment and protection of the region’s groundwater resources. An important issue in understanding the ground water resources is a better understanding of the hydrogeology of the Santa Fe Group, the sedimentary deposits that fill the Rio Grande rift and contain the principal groundwater aquifers.
NASA Astrophysics Data System (ADS)
Martínez-Moreno, F. J.; Monteiro-Santos, F. A.; Madeira, J.; Bernardo, I.; Soares, A.; Esteves, M.; Adão, F.
2016-11-01
Water demand in islands, focused in agriculture, domestic use and tourism, is usually supplied by groundwater. Thus the information about groundwater distribution is an important issue in islands water resources management. Time Domain Electromagnetic (TDEM) provides underground resistivity distribution at greater depths and is of easier application than other methods. In this study TDEM technique was used for groundwater prospection in two volcanic islands with water supply problems, the islands of Fogo and Santo Antão in the Republic of Cape Verde. The 10 islands of Cape Verde Archipelago, located off the coast of Senegal (W Africa), present a semi-arid climate and thus suffer from irregular and scarce precipitation. In the Island of Fogo 26 TDEM soundings, presenting an area distribution, were performed on the SW flank of the volcanic edifice. These allowed obtaining a 3D model composed of 5 layers parallel to the topographic surface separated by 50 m depth down to - 250 m. The results indicate the presence of the water-table at a depth of 150 m in the lower ranges of the W flank of the island, and at > 200 m depth in the area above 250 m above sea level (a.s.l.). In the Island of Santo Antão 32 TDEM soundings, distributed along 5 linear profiles, were obtained on the north-eastern half of the island. The profiles are located in two regions exposed to different humidity conditions to the N and S of the main water divide. The northern flank receives the dominant trade winds first and most of the precipitation and, therefore, the water-table is shallower ( 50 m depth) than in the S ( 100 m depth). Our study demonstrates the applicability and usefulness of the TDEM method for groundwater prospection in high resistivity contexts such as in volcanic islands.
NASA Astrophysics Data System (ADS)
Wu, Xianghong
Two electromagnetic methods were used to analyse the geoelectric structure of the subsurface of regions of the Precambrian Shield in Canada: the magnetotelluric (MT) and time-domain electromagnetic (TEM) methods. Magnetotelluric soundings were made at 60 sites in the southwestern Northwest Territories, Canada, along the LITHOPROBE SNORCLE Transect Corridor 1 and 1A, in the summer of 1996. The sites are located in southwestern Northwest Territories, Canada, between latitudes 60°--65°N and longitudes 110°--125°W, and cross the Archean Slave Province, the Proterozoic Buffalo Head, Great Bear Magmatic Arc, Hottah, Fort Simpson and Nahanni terranes, and the Great Slave Lake Shear Zone. Phanerozoic sedimentary rocks overlie the Proterozoic terranes. The main object of this project is to map the fracture zones and fresh/saline water interface in Precambrian granitic rocks using the surface TEM method. The TEM surveys were completed at Sites B, D, URL and A. A GEONICS PROTEM47 system with a 100 m transmitter loop was used. The data were collected for receiver offsets ranging from 0--280 m on four sides of transmitter loop. Analysis of the TEM and borehole log data indicates a basic three-layer structure: a thin conductive surface layer, a thick resistive second layer with an embedded conductive layer at some stations, and a conductive bottom layer. The results of this study show the TEM method can be used to investigate the fracture zones and groundwater salinity distribution in the Precambrian granitic rocks and contribute to site investigations for nuclear waste deposit. The TEM study in the Lac du Bonnet Batholith was successful in demonstrating the potential of the TEM methods in mapping groundwater salinity in granitic batholith. The PROTEM47 instrument, in combination with a 100 m transmitter loop, provides a suitable TEM system for mapping the resistivity structure of the Lac du Bonnet batholith down to a depth of 300--400 m. For deeper penetration and more
NASA Astrophysics Data System (ADS)
Doll, William E.; Bell, David T.; Gamey, T. Jeffrey; Beard, Les P.; Sheehan, Jacob R.; Norton, Jeannemarie
2010-04-01
Over the past decade, notable progress has been made in the performance of airborne geophysical systems for mapping and detection of unexploded ordnance in terrestrial and shallow marine environments. For magnetometer systems, the most significant improvements include development of denser magnetometer arrays and vertical gradiometer configurations. In prototype analyses and recent Environmental Security Technology Certification Program (ESTCP) assessments using new production systems the greatest sensitivity has been achieved with a vertical gradiometer configuration, despite model-based survey design results which suggest that dense total-field arrays would be superior. As effective as magnetometer systems have proven to be at many sites, they are inadequate at sites where basalts and other ferrous geologic formations or soils produce anomalies that approach or exceed those of target ordnance items. Additionally, magnetometer systems are ineffective where detection of non-ferrous ordnance items is of primary concern. Recent completion of the Battelle TEM-8 airborne time-domain electromagnetic system represents the culmination of nearly nine years of assessment and development of airborne electromagnetic systems for UXO mapping and detection. A recent ESTCP demonstration of this system in New Mexico showed that it was able to detect 99% of blind-seeded ordnance items, 81mm and larger, and that it could be used to map in detail a bombing target on a basalt flow where previous airborne magnetometer surveys had failed. The probability of detection for the TEM-8 in the blind-seeded study area was better than that reported for a dense-array total-field magnetometer demonstration of the same blind-seeded site, and the TEM-8 system successfully detected these items with less than half as many anomaly picks as the dense-array total-field magnetometer system.
Evaluation of airborne thermal, magnetic, and electromagnetic characterization technologies
Josten, N.E.
1992-03-01
The identification of Buried Structures (IBS) or Aerial Surveillance Project was initiated by the US Department of Energy (DOE) Office of Technology Development to demonstrate airborne methods for locating and identifying buried waste and ordnance at the Idaho National Engineering Laboratory (INEL). Two technologies were demonstrated: (a) a thermal infrared imaging system built by Martin Marietta Missile Systems and (b) a magnetic and electromagnetic (EM) geophysical surveying system operated by EBASCO Environmental. The thermal system detects small differences in ground temperature caused by uneven heating and cooling of the ground by the sun. Waste materials on the ground can be detected when the temperature of the waste is different than the background temperature. The geophysical system uses conventional magnetic and EM sensors. These sensors detect disturbances caused by magnetic or conductive waste and naturally occurring magnetic or conductive features of subsurface soils and rock. Both systems are deployed by helicopter. Data were collected at four INEL sites. Tests at the Naval Ordnance Disposal Area (NODA) were made to evaluate capabilities for detecting ordnance on the ground surface. Tests at the Cold Simulated Waste Demonstration Pit were made to evaluate capabilities for detecting buried waste at a controlled site, where the location and depth of buried materials are known. Tests at the Subsurface Disposal Area and Stationary Low-Power Reactor-1 burial area were made to evaluate capabilities for characterizing hazardous waste at sites that are typical of DOE buried waste sites nationwide.
NASA Astrophysics Data System (ADS)
Minsley, B. J.; Kass, M. A.; Bloss, B.; Pastick, N.; Panda, S. K.; Smith, B. D.; Abraham, J. D.; Burns, L. E.
2012-12-01
More than 8000 square kilometers of airborne electromagnetic (AEM) data were acquired along the Alaska Highway Corridor in 2005-2006 by the Alaska Department of Natural Resources Division of Geological and Geophysical Surveys. Because this large AEM dataset covers diverse geologic and permafrost settings, it is an excellent testbed for studying the electrical geophysical response from a wide range of subsurface conditions. These data have been used in several recent investigations of geology, permafrost, and infrastructure along the highway corridor. In this study, we build on existing interpretations of permafrost features by re-inverting the AEM data using traditional least squares inversion techniques as well as recently developed stochastic methods aimed at quantifying uncertainty in geophysical data. Ground-based geophysical measurements, including time-domain electromagnetic soundings, surface nuclear magnetic resonance soundings, and shallow frequency-domain electromagnetic profiles, have also been acquired to help validate and extend the AEM interpretations. Here, we focus on the integration of different types of data to yield an improved characterization of permafrost, including: methods to discriminate between geologic and thermal controls on resistivity; identifying relationships between shallow resistivity and active layer thickness by incorporating auxiliary remote sensing data and ground-based measurements; quantifying apparent slope-aspect-resistivity relationships, where south-facing slopes appear less resistive than north-facing slopes within similar geologic settings; and investigating an observed decrease in resistivity beneath several areas associated with recent fires.
Voxel inversion of airborne electromagnetic data for improved model integration
NASA Astrophysics Data System (ADS)
Fiandaca, Gianluca; Auken, Esben; Kirkegaard, Casper; Vest Christiansen, Anders
2014-05-01
Inversion of electromagnetic data has migrated from single site interpretations to inversions including entire surveys using spatial constraints to obtain geologically reasonable results. Though, the model space is usually linked to the actual observation points. For airborne electromagnetic (AEM) surveys the spatial discretization of the model space reflects the flight lines. On the contrary, geological and groundwater models most often refer to a regular voxel grid, not correlated to the geophysical model space, and the geophysical information has to be relocated for integration in (hydro)geological models. We have developed a new geophysical inversion algorithm working directly in a voxel grid disconnected from the actual measuring points, which then allows for informing directly geological/hydrogeological models. The new voxel model space defines the soil properties (like resistivity) on a set of nodes, and the distribution of the soil properties is computed everywhere by means of an interpolation function (e.g. inverse distance or kriging). Given this definition of the voxel model space, the 1D forward responses of the AEM data are computed as follows: 1) a 1D model subdivision, in terms of model thicknesses, is defined for each 1D data set, creating "virtual" layers. 2) the "virtual" 1D models at the sounding positions are finalized by interpolating the soil properties (the resistivity) in the center of the "virtual" layers. 3) the forward response is computed in 1D for each "virtual" model. We tested the new inversion scheme on an AEM survey carried out with the SkyTEM system close to Odder, in Denmark. The survey comprises 106054 dual mode AEM soundings, and covers an area of approximately 13 km X 16 km. The voxel inversion was carried out on a structured grid of 260 X 325 X 29 xyz nodes (50 m xy spacing), for a total of 2450500 inversion parameters. A classical spatially constrained inversion (SCI) was carried out on the same data set, using 106054
Bultman, Mark W.; Gettings, Mark E.; Wynn, Jeff
1999-01-01
In March of 1997, an airborne electromagnetic (AEM) survey of the Fort Huachuca Military Reservation and immediate surrounds was conducted. This survey was sponsored by the U.S. Army and contracted through the Geologic Division of the U.S. Geological Survey (USGS). Data were gathered by Geoterrex-Dighem Ltd. of Ottawa, Canada. The survey aircraft is surrounded by a coil through which a large current pulse is passed. This pulse induces currents in the Earth which are recorded by a set of three mutually perpendicular coils towed in a "bird" about 100 m behind and below the aircraft. The bird also records the Earth's magnetic field. The system samples the Earth response to the electromagnetic pulse about every 16 m along the aircraft flight path. For this survey, the bulk of the flightpaths were spaced about 400 m apart and oriented in a northeast-southwest direction extending from bedrock over the Huachuca Mountains to bedrock over the Tombstone Hills. A preliminary report on the unprocessed data collected in the field was delivered to the U.S. Army by USGS in July 1997 (USGS Open-File Report 97–457). The final data were delivered in March, 1998 by the contractor to USGS and thence to the U.S. Army. The present report represents the final interpretive report from USGS. The objectives of the survey were to: 1) define the structure of the San Pedro basin in the Sierra Vista-Fort Huachuca-Huachuca City area, including the depth and shape of the basin, and to delineate large faults that may be active within the basin fill and therefore important in the hydrologic regime; 2) define near surface and subsurface areas that contain a large volume fraction of silt and clay in the basin fill and which both reduce the volume of available storage for water and reduce the permeability of the aquifer; and 3) to evaluate the use of the time domain electromagnetic method in the southwest desert setting as a means of mapping depth to water.
Airborne electromagnetic surveys in support of groundwater models in western Nebraska
NASA Astrophysics Data System (ADS)
Abraham, J. D.; Viezzoli, A.; Cannia, J. C.; Smith, B. D.; Brown, W.; Peterson, S. M.
2010-12-01
The USGS, SkyTEM, Aarhus Geophysics, North Platte, South Platte and Twin Platte Natural Resource Districts have collaborated to collect airborne time domain geophysical surveys over selected of areas of western Nebraska. The objective of the surveys was to map the aquifers and bedrock topography of the area to help improve the understanding of groundwater-surface water relations to be used in water management decisions. The base of aquifer in many of these areas is in excess of 100 meters deep and little detailed information of the configuration of the bedrock exits. Many of the aquifers exist as alluvial fills in paleochannels upon complex bedrock topography. Controlling factors for groundwater flow are the variations of the hydraulic properties of the fill and the boundary geometry of the paleochannels. Results from groundwater modeling efforts prior to the addition of the airborne data revealed the hydrogeologic framework was sufficient for the regional scale models, but when these models were reduced to 40 acres cell size, the lack of detail adversely affected model results. The SkyTEM system is a helicopter-borne time-domain electromagnetic system capable of detecting small changes in resistivity from the near-surface down to depths of up to 300 m and is well-suited for aquifer mapping. An innovative design of the receiver coils and transmitter pattern eliminates the self response that is characteristic of airborne systems and spatial measurement sensors mounted on a rigid frame enable rigorous quantitative interpretation of the EM data. The ability to quickly collect and deliver high quality, high resolution geophysical data contributes significantly to modeling efforts and further understanding of subsurface hydrological systems. The raw AEM data have to be edited to exclude data that have been affected by coupling with man made infrastructures. For resistivity data to be related to lithologic information to refine groundwater model inputs, and to make the
1993-05-01
AD-A268 703 Comparison of Airborne * Electromagnetic Induction and Subsurface Radar Sounding of Freshwater Bathymetry Austin Kovacs and J , Scott Holladay...Laboratory Comparison of Airborne Electromagnefic Induction and Subsurface Radar Sounding of Freshwater Bcdhymetry Austin Kovacs and J . Scott Holladay May 1993...Engineer, of the Applied Research Branch, Experimental Engineering Division, U.S. Army Cold Regions Research and Engineering Laboratory, and J . Scott Holladay
Airborne Electromagnetic Sounding of Sea Ice Thickness and Sub-Ice Bathymetry,
1987-12-01
the ground using techniques which are standard for mineral exploration surveys. Phasing en- sures that the signal used as a time reference in...been developed, because standard airborne electromagnetic calibration techniques used for mineral exploration proved inadequate for sea ice thickness
NASA Astrophysics Data System (ADS)
Liu, Yun; Wang, Xu-Ben; Wang, Yun
2013-06-01
To effectively minimize the electromagnetic field response in the total field solution, we propose a numerical modeling method for the two-dimensional (2D) timedomain transient electromagnetic secondary field of the line source based on the DuFort-Frankel finite-difference method. In the proposed method, we included the treatment of the earth-air boundary conductivity, calculated the normalized partial derivative of the induced electromotive force (Emf), and determined the forward time step. By extending upward the earth-air interface to the air grid nodes and the zero-value boundary conditions, not only we have a method that is more efficient but also simpler than the total field solution. We computed and analyzed the homogeneous half-space model and the flat layered model with high precision—the maximum relative error is less than 0.01% between our method and the analytical method—and the solution speed is roughly three times faster than the total-field solution. Lastly, we used the model of a thin body embedded in a homogeneous half-space at different delay times to depict the downward and upward spreading characteristics of the induced eddy current, and the physical interaction processes between the electromagnetic field and the underground low-resistivity body.
Yang, Li; Ge, Manling; Guo, Jia; Wang, Qingmeng; Jiang, Xiaochi; Yan, Weili
2007-01-01
Finite-difference time-domain (FDTD) method and specific absorption rate (SAR) are employed here to study the relationship between the radiation of a mobile handset and the human being health. Nowadays, much more attention has been paid to the simulations for the effects of RF radiation on the particular organs, such as the eyes or the ears because they are more sensitive and more near to the working mobile. In the paper, the simulation of the RF fields is focused on the eyes model and the eyes with glasses of metal frame respectively. A planar inverted F antenna is used as an exposure source at 900 MHz. Under this case, the intensity of the electrical field is calculated and analyzed. Also, SAR is utilized to evaluate the absorption of the organs to the radiation. Through the simulation, the peak values of SAR per 1G tissue at the radiating power being 600mW are obtained. It is concluded that when people are wearing glasses of metal framework, the peak value of SAR is shown to be a little higher than the safety limits. It is suggested that the radiation from the mobile handset do more harmful effect on the eyes with the glasses of metal frameworks.
NASA Astrophysics Data System (ADS)
Cresswell, Richard G.; Mullen, Ian C.; Kingham, Rob; Kellett, Jim; Dent, David L.; Jones, Grant L.
2007-05-01
Airborne geophysics has been used at the catchment scale to map salt stores, conduits and soil variability, but few studies have evaluated its usefulness as a land management tool at the field scale. We respond to questions posed by land managers with: (1) comparison of airborne and ground-based electromagnetic surveys in the Lower Balonne catchment, Queensland, and (2) comparison with historical and anecdotal knowledge of landscape response in the country around Jamestown in mid-South Australia. In the Lower Balonne, direct comparison between ground electromagnetic survey (EM) and airborne electromagnetics (AEM) showed a strong relationship for both the absolute values and spatial patterns of conductivity. The penetration of AEM to greater than 100 m is valuable in defining hydrological barriers. In the Jamestown area, AEM conductivity corresponded well with specific outbreaks of salinity and observed variability in crop response; local inconsistencies at the ground surface could be resolved when sub-surface data were considered. AEM can provide valuable information at the field scale that is relevant to salinity management. Farmers can have confidence in any of these techniques (historical information, EM and AEM) and they may directly compare or integrate the results.
Time-Domain Filtering of Metasurfaces
Wakatsuchi, Hiroki
2015-01-01
In general electromagnetic response of each material to a continuous wave does not vary in time domain if the frequency component remains the same. Recently, it turned out that integrating several circuit elements including schottky diodes with periodically metallised surfaces, or the so-called metasurfaces, leads to selectively absorbing specific types of waveforms or pulse widths even at the same frequency. These waveform-selective metasurfaces effectively showed different absorbing performances for different widths of pulsed sine waves by gradually varying their electromagnetic responses in time domain. Here we study time-filtering effects of such circuit-based metasurfaces illuminated by continuous sine waves. Moreover, we introduce extra circuit elements to these structures to enhance the time-domain control capability. These time-varying properties are expected to give us another degree of freedom to control electromagnetic waves and thus contribute to developing new kinds of electromagnetic applications and technologies, e.g. time-windowing wireless communications and waveform conversion. PMID:26564027
Bultman, M.W.; Gettings, M.E.; Wynn, Jeff
1999-01-01
Executive Summary -- In March of 1997, an airborne electromagnetic (AEM) survey of the Fort Huachuca Military Reservation and immediate surrounds (location map, http://geopubs.wr.usgs.gov/open-file/of99-007-b/index.jpg) was conducted. This survey was sponsored by the U.S. Army and contracted through the Geologic Division of the U.S. Geological Survey (USGS). Data were gathered by Geoterrex-Dighem Ltd. of Ottawa, Canada. The survey aircraft is surrounded by a coil through which a large current pulse is passed. This pulse induces currents in the Earth which are recorded by a set of three mutually perpendicular coils towed in a 'bird' about 100 m behind and below the aircraft. The bird also records the Earth's magnetic field. The system samples the Earth response to the electromagnetic pulse about every 16 m along the aircraft flight path. For this survey, the bulk of the flightpaths were spaced about 400 m apart and oriented in a northeast-southwest direction extending from bedrock over the Huachuca Mountains to bedrock over the Tombstone Hills. A preliminary report on the unprocessed data collected in the field was delivered to the U.S. Army by USGS in July 1997 (USGS Open-File Report 97?457). The final data were delivered in March, 1998 by the contractor to USGS and thence to the U.S. Army. The present report represents the final interpretive report from USGS. The objectives of the survey were to: 1) define the structure of the San Pedro basin in the Sierra Vista-Fort Huachuca-Huachuca City area, including the depth and shape of the basin, and to delineate large faults that may be active within the basin fill and therefore important in the hydrologic regime; 2) define near surface and subsurface areas that contain a large volume fraction of silt and clay in the basin fill and which both reduce the volume of available storage for water and reduce the permeability of the aquifer; and 3) to evaluate the use of the time domain electromagnetic method in the southwest
Airborne electromagnetic modelling options and their consequences in target definition
NASA Astrophysics Data System (ADS)
Ley-Cooper, Alan Yusen; Viezzoli, Andrea; Guillemoteau, Julien; Vignoli, Giulio; Macnae, James; Cox, Leif; Munday, Tim
2015-10-01
Given the range of geological conditions under which airborne EM surveys are conducted, there is an expectation that the 2D and 3D methods used to extract models that are geologically meaningful would be favoured over 1D inversion and transforms. We do after all deal with an Earth that constantly undergoes, faulting, intrusions, and erosive processes that yield a subsurface morphology, which is, for most parts, dissimilar to a horizontal layered earth. We analyse data from a survey collected in the Musgrave province, South Australia. It is of particular interest since it has been used for mineral prospecting and for a regional hydro-geological assessment. The survey comprises abrupt lateral variations, more-subtle lateral continuous sedimentary sequences and filled palaeovalleys. As consequence, we deal with several geophysical targets of contrasting conductivities, varying geometries and at different depths. We invert the observations by using several algorithms characterised by the different dimensionality of the forward operator. Inversion of airborne EM data is known to be an ill-posed problem. We can generate a variety of models that numerically adequately fit the measured data, which makes the solution non-unique. The application of different deterministic inversion codes or transforms to the same dataset can give dissimilar results, as shown in this paper. This ambiguity suggests the choice of processes and algorithms used to interpret AEM data cannot be resolved as a matter of personal choice and preference. The degree to which models generated by a 1D algorithm replicate/or not measured data, can be an indicator of the data's dimensionality, which perse does not imply that data that can be fitted with a 1D model cannot be multidimensional. On the other hand, it is crucial that codes that can generate 2D and 3D models do reproduce the measured data in order for them to be considered as a plausible solution. In the absence of ancillary information, it could
Electromagnetic Model Reliably Predicts Radar Scattering Characteristics of Airborne Organisms
NASA Astrophysics Data System (ADS)
Mirkovic, Djordje; Stepanian, Phillip M.; Kelly, Jeffrey F.; Chilson, Phillip B.
2016-10-01
The radar scattering characteristics of aerial animals are typically obtained from controlled laboratory measurements of a freshly harvested specimen. These measurements are tedious to perform, difficult to replicate, and typically yield only a small subset of the full azimuthal, elevational, and polarimetric radio scattering data. As an alternative, biological applications of radar often assume that the radar cross sections of flying animals are isotropic, since sophisticated computer models are required to estimate the 3D scattering properties of objects having complex shapes. Using the method of moments implemented in the WIPL-D software package, we show for the first time that such electromagnetic modeling techniques (typically applied to man-made objects) can accurately predict organismal radio scattering characteristics from an anatomical model: here the Brazilian free-tailed bat (Tadarida brasiliensis). The simulated scattering properties of the bat agree with controlled measurements and radar observations made during a field study of bats in flight. This numerical technique can produce the full angular set of quantitative polarimetric scattering characteristics, while eliminating many practical difficulties associated with physical measurements. Such a modeling framework can be applied for bird, bat, and insect species, and will help drive a shift in radar biology from a largely qualitative and phenomenological science toward quantitative estimation of animal densities and taxonomic identification.
Electromagnetic Model Reliably Predicts Radar Scattering Characteristics of Airborne Organisms
Mirkovic, Djordje; Stepanian, Phillip M.; Kelly, Jeffrey F.; Chilson, Phillip B.
2016-01-01
The radar scattering characteristics of aerial animals are typically obtained from controlled laboratory measurements of a freshly harvested specimen. These measurements are tedious to perform, difficult to replicate, and typically yield only a small subset of the full azimuthal, elevational, and polarimetric radio scattering data. As an alternative, biological applications of radar often assume that the radar cross sections of flying animals are isotropic, since sophisticated computer models are required to estimate the 3D scattering properties of objects having complex shapes. Using the method of moments implemented in the WIPL-D software package, we show for the first time that such electromagnetic modeling techniques (typically applied to man-made objects) can accurately predict organismal radio scattering characteristics from an anatomical model: here the Brazilian free-tailed bat (Tadarida brasiliensis). The simulated scattering properties of the bat agree with controlled measurements and radar observations made during a field study of bats in flight. This numerical technique can produce the full angular set of quantitative polarimetric scattering characteristics, while eliminating many practical difficulties associated with physical measurements. Such a modeling framework can be applied for bird, bat, and insect species, and will help drive a shift in radar biology from a largely qualitative and phenomenological science toward quantitative estimation of animal densities and taxonomic identification. PMID:27762292
Electromagnetic Model Reliably Predicts Radar Scattering Characteristics of Airborne Organisms.
Mirkovic, Djordje; Stepanian, Phillip M; Kelly, Jeffrey F; Chilson, Phillip B
2016-10-20
The radar scattering characteristics of aerial animals are typically obtained from controlled laboratory measurements of a freshly harvested specimen. These measurements are tedious to perform, difficult to replicate, and typically yield only a small subset of the full azimuthal, elevational, and polarimetric radio scattering data. As an alternative, biological applications of radar often assume that the radar cross sections of flying animals are isotropic, since sophisticated computer models are required to estimate the 3D scattering properties of objects having complex shapes. Using the method of moments implemented in the WIPL-D software package, we show for the first time that such electromagnetic modeling techniques (typically applied to man-made objects) can accurately predict organismal radio scattering characteristics from an anatomical model: here the Brazilian free-tailed bat (Tadarida brasiliensis). The simulated scattering properties of the bat agree with controlled measurements and radar observations made during a field study of bats in flight. This numerical technique can produce the full angular set of quantitative polarimetric scattering characteristics, while eliminating many practical difficulties associated with physical measurements. Such a modeling framework can be applied for bird, bat, and insect species, and will help drive a shift in radar biology from a largely qualitative and phenomenological science toward quantitative estimation of animal densities and taxonomic identification.
Development of 3D electromagnetic modeling tools for airborne vehicles
NASA Technical Reports Server (NTRS)
Volakis, John L.
1992-01-01
The main goal of this project is to develop methodologies for scattering by airborne composite vehicles. Although our primary focus continues to be the development of a general purpose code for analyzing the entire structure as a single unit, a number of other tasks are also pursued in parallel with this effort. These tasks are important in testing the overall approach and in developing suitable models for materials coatings, junctions and, more generally, in assessing the effectiveness of the various parts comprising the final code. Here, we briefly discuss our progress on the five different tasks which were pursued during this period. Our progress on each of these tasks is described in the detailed reports (listed at the end of this report) and the memoranda included. The first task described below is, of course, the core of this project and deals with the development of the overall code. Undoubtedly, it is the outcome of the research which was funded by NASA-Ames and the Navy over the past three years. During this year we developed the first finite element code for scattering by structures of arbitrary shape and composition. The code employs a new absorbing boundary condition which allows termination of the finite element mesh only 0.3 lambda from the outer surface of the target. This leads to a remarkable reduction of the mesh size and is a unique feature of the code. Other unique features of this code include capabilities to model resistive sheets, impedance sheets and anisotropic materials. This last capability is the latest feature of the code and is still under development. The code has been extensively validated for a number of composite geometries and some examples are given. The validation of the code is still in progress for anisotropic and larger non-metallic geometries and cavities. The developed finite element code is based on a Galerkin's formulation and employs edge-based tetrahedral elements for discretizing the dielectric sections and the region
Dickinson, Jesse E.; Pool, D.R.; Groom, R.W.; Davis, L.J.
2010-01-01
An airborne transient electromagnetic (TEM) survey was completed in the Upper San Pedro Basin in southeastern Arizona to map resistivity distributions within the alluvial aquifer. This investigation evaluated the utility of 1D vertical resistivity models of the TEM data to infer lithologic distributions in an alluvial aquifer. Comparisons of the resistivity values and layers in the 1D resistivity models of airborne TEM data to 1D resistivity models of ground TEM data, borehole resistivity logs, and lithologic descriptions in drill logs indicated that the airborne TEM identified thick conductive fine-grained sediments that result in semiconfined groundwater conditions. One-dimensional models of ground-based TEM surveys and subsurface lithology at three sites were used to determine starting models and constraints to invert airborne TEM data using a constrained Marquardt-styleunderparameterized method. A maximum structural resolution of six layers underlain by a half-space was determined from the resistivity structure of the 1D models of the ground TEM data. The 1D resistivity models of the airborne TEM data compared well with the control data to depths of approximately 100 m in areas of thick conductive silt and clay and to depths of 200 m in areas of resistive sand and gravel. Comparison of a 3D interpolation of the 1D resistivity models to drill logs indicated resistive (mean of 65 ohm-m ) coarse-grained sediments along basin margins and conductive (mean of 8 ohm-m ) fine-grained sediments at the basin center. Extents of hydrologically significant thick silt and clay were well mapped by the 1D resistivity models of airborne TEM data. Areas of uncertain lithology remain below conductive fine-grained sediments where the 1D resistivity structure is not resolved: in areas where multiple lithologies have similar resistivity values and in areas of high salinity.
Time Domain Electromagnetic Waves in Multilayered Media
1991-07-15
the form = ,j(n(Om) /j) - k2 (16a) UM 0 1. imaJ .(p 0F m ka J’ (maJP) 0 The expressions for T(k,, z) P(k,) I T ,aj) (16b)3 ,z) Tm(k, z, 0,) and k,2...bottom walls. These current modes are I.#., ) - mJT(k..) I8b given by for m 0. The integrals, with y, = koaJ. are defined by imaj I forp<aj . a 4 r m- n...2 O, for p > aj "JA ++2)/2(yj /2) J(,.-.-2)2( Yj /2) - imaJ (m +n -2 ) im M_)2(Yj/2) ,j, for p < aj (15b) .m_. )n(yj/2) 0, for P > aj +mJm, )/2(Yi/2
Airborne electromagnetic and magnetic survey data of the Paradox and San Luis Valleys, Colorado
Ball, Lyndsay B.; Bloss, Benjamin R.; Bedrosian, Paul A.; Grauch, V.J.S.; Smith, Bruce D.
2015-01-01
In October 2011, the U.S. Geological Survey (USGS) contracted airborne magnetic and electromagnetic surveys of the Paradox and San Luis Valleys in southern Colorado, United States. These airborne geophysical surveys provide high-resolution and spatially comprehensive datasets characterizing the resistivity structure of the shallow subsurface of each survey region, accompanied by magnetic-field information over matching areas. These data were collected to provide insight into the distribution of groundwater brine in the Paradox Valley, the extent of clay aquitards in the San Luis Valley, and to improve our understanding of the geologic framework for both regions. This report describes these contracted surveys and releases digital data supplied under contract to the USGS.
Burgess, Matthew K.; Bedrosian, Paul A.; Buesch, David C.
2014-01-01
Between 2010 and 2012, a total of 79 time-domain electromagnetic (TEM) soundings were collected in 12 groundwater basins in the U.S. Army Fort Irwin National Training Center (NTC) study area to help improve the understanding of the hydrogeology of the NTC. The TEM data are discussed in this chapter in the context of geologic observations of the study area, the details of which are provided in the other chapters of this volume. Selection of locations for TEM soundings in unexplored basins was guided by gravity data that estimated depth to pre-Tertiary basement complex of crystalline rock and alluvial thickness. Some TEM data were collected near boreholes with geophysical logs. The TEM response at locations near boreholes was used to evaluate sounding data for areas without boreholes. TEM models also were used to guide site selection of subsequent boreholes drilled as part of this study. Following borehole completion, geophysical logs were used to ground-truth and reinterpret previously collected TEM data. This iterative process was used to site subsequent TEM soundings and borehole locations as the study progressed. Although each groundwater subbasin within the NTC boundaries was explored using the TEM method, collection of TEM data was focused in those basins identified as best suited for development of water resources. At the NTC, TEM estimates of some lithologic thicknesses and electrical properties in the unsaturated zone are in good accordance with borehole data; however, water-table elevations were not easily identifiable from TEM data.
NASA Astrophysics Data System (ADS)
Høyer, Anne-Sophie; Møller, Ingelise; Jørgensen, Flemming
2013-04-01
Glaciotectonic structures have traditionally been recognized through observations in the landscape or exposures like cliffs. However, mapping of these structures can highly benefit from geophysical data, which can give information on buried glaciotectonic complexes. In the current study, we focus on the appearance of glaciotectonic structures in data from four commonly used geophysical methods: Ground penetrating radar (GPR), geoelectrical, high-resolution seismic and airborne transient electromagnetic (SkyTEM). The data are collected within a study area that covers 100 km2 and is located in the western part of Denmark. The study area is characterized by a highly heterogeneous geological setting, which has been influenced by multiple glacial deformation phases resulting in a buried glaciotectonic complex. The glaciotectonic structures appear as folds and faults and are recognizable at all scales. As a consequence of the different resolution capabilities of the methods, different degrees of detail are observed: Large-scale structures are recognized based on the seismic and airborne transient electromagnetic data, whereas small-scale structures are interpreted based on the GPR and geoelectrical data. At the same time, the nature of the methods results in different types of information from the data: The GPR and the seismic data generally provide detailed structural information, whereas the electric and electromagnetic data provide a more 'blurred' resistivity image of the subsurface. In order to recognize geological structures on the electric and electromagnetic data, the structures therefore need to influence sediments with contrasting resistivities to the surroundings. The structures are recognizable on all the different data sets, but the understanding and thus, the interpretation, of the geological environment strongly benefits from the combined observations from the different types of data.
Gravitational Waves and Time Domain Astronomy
NASA Technical Reports Server (NTRS)
Centrella, Joan; Nissanke, Samaya; Williams, Roy
2012-01-01
The gravitational wave window onto the universe will open in roughly five years, when Advanced LIGO and Virgo achieve the first detections of high frequency gravitational waves, most likely coming from compact binary mergers. Electromagnetic follow-up of these triggers, using radio, optical, and high energy telescopes, promises exciting opportunities in multi-messenger time domain astronomy. In the decade, space-based observations of low frequency gravitational waves from massive black hole mergers, and their electromagnetic counterparts, will open up further vistas for discovery. This two-part workshop featured brief presentations and stimulating discussions on the challenges and opportunities presented by gravitational wave astronomy. Highlights from the workshop, with the emphasis on strategies for electromagnetic follow-up, are presented in this report.
An Improved High-Sensitivity Airborne Transient Electromagnetic Sensor for Deep Penetration
Chen, Shudong; Guo, Shuxu; Wang, Haofeng; He, Miao; Liu, Xiaoyan; Qiu, Yu; Zhang, Shuang; Yuan, Zhiwen; Zhang, Haiyang; Fang, Dong; Zhu, Jun
2017-01-01
The investigation depth of transient electromagnetic sensors can be effectively increased by reducing the system noise, which is mainly composed of sensor internal noise, electromagnetic interference (EMI), and environmental noise, etc. A high-sensitivity airborne transient electromagnetic (AEM) sensor with low sensor internal noise and good shielding effectiveness is of great importance for deep penetration. In this article, the design and optimization of such an AEM sensor is described in detail. To reduce sensor internal noise, a noise model with both a damping resistor and a preamplifier is established and analyzed. The results indicate that a sensor with a large diameter, low resonant frequency, and low sampling rate will have lower sensor internal noise. To improve the electromagnetic compatibility of the sensor, an electromagnetic shielding model for a central-tapped coil is established and discussed in detail. Previous studies have shown that unclosed shields with multiple layers and center grounding can effectively suppress EMI and eddy currents. According to these studies, an improved differential AEM sensor is constructed with a diameter, resultant effective area, resonant frequency, and normalized equivalent input noise of 1.1 m, 114 m2, 35.6 kHz, and 13.3 nV/m2, respectively. The accuracy of the noise model and the shielding effectiveness of the sensor have been verified experimentally. The results show a good agreement between calculated and measured results for the sensor internal noise. Additionally, over 20 dB shielding effectiveness is achieved in a complex electromagnetic environment. All of these results show a great improvement in sensor internal noise and shielding effectiveness. PMID:28106718
An Improved High-Sensitivity Airborne Transient Electromagnetic Sensor for Deep Penetration.
Chen, Shudong; Guo, Shuxu; Wang, Haofeng; He, Miao; Liu, Xiaoyan; Qiu, Yu; Zhang, Shuang; Yuan, Zhiwen; Zhang, Haiyang; Fang, Dong; Zhu, Jun
2017-01-17
The investigation depth of transient electromagnetic sensors can be effectively increased by reducing the system noise, which is mainly composed of sensor internal noise, electromagnetic interference (EMI), and environmental noise, etc. A high-sensitivity airborne transient electromagnetic (AEM) sensor with low sensor internal noise and good shielding effectiveness is of great importance for deep penetration. In this article, the design and optimization of such an AEM sensor is described in detail. To reduce sensor internal noise, a noise model with both a damping resistor and a preamplifier is established and analyzed. The results indicate that a sensor with a large diameter, low resonant frequency, and low sampling rate will have lower sensor internal noise. To improve the electromagnetic compatibility of the sensor, an electromagnetic shielding model for a central-tapped coil is established and discussed in detail. Previous studies have shown that unclosed shields with multiple layers and center grounding can effectively suppress EMI and eddy currents. According to these studies, an improved differential AEM sensor is constructed with a diameter, resultant effective area, resonant frequency, and normalized equivalent input noise of 1.1 m, 114 m², 35.6 kHz, and 13.3 nV/m², respectively. The accuracy of the noise model and the shielding effectiveness of the sensor have been verified experimentally. The results show a good agreement between calculated and measured results for the sensor internal noise. Additionally, over 20 dB shielding effectiveness is achieved in a complex electromagnetic environment. All of these results show a great improvement in sensor internal noise and shielding effectiveness.
Time-domain robotic vision application
NASA Technical Reports Server (NTRS)
Tolliver, C. L.
1987-01-01
The quest for the highest resolution microwaves imaging and the principle of time-domain imaging is the primary motivation for recent developments in time-domain techniques. With the present technology fast time varying signals can now be measured and recorded both in magnitude and in phase. It has also enhanced the ability to extract relevant details concerning the scattering object. In the past, the inference of object geometry or shape from scattered signals has received substantial attention in radar technology. Various inverse scattering theories were proposed to develop analytical solutions to this problem. Furthermore, the random inversion, frequenty swept holography, and the synthetic radar imaging, all of which have two things in common: the physical optic far-field approximation and the utilization of the channels as an extra physical dimension, were also advanced significantly. Despite the inherent vectorial nature of electromagnetic waves, these scalar treatments have brought forth some promising results in practice with notable examples in subsurface and structure sounding. The use of time-domain imaging for space robotic vision applications was proposed. A multisensor approach to vision was shown to have several advantages over the video-only approach.
NASA Astrophysics Data System (ADS)
Viezzoli, A.; Tosi, L.; Teatini, P.; Silvestri, S.
2010-01-01
A comprehensive investigation of the mixing between salt/fresh surficial water and groundwater in transitional environments is an issue of paramount importance considering the ecological, cultural, and socio-economic relevance of coastal zones. Acquiring information, which can improve the process understanding, is often logistically challenging, and generally expensive and slow in these areas. Here we investigate the capability of airborne electromagnetics (AEM) at the margin of the Venice Lagoon, Italy. The quasi-3D interpretation of the AEM outcome by the spatially constrained inversion (SCI) methodology allows us to accurately distinguish several hydrogeological features down to a depth of about 200 m. For example, the extent of the saltwater intrusion in coastal aquifers and the transition between the upper salt saturated and the underlying fresher sediments below the lagoon bottom are detected. The research highlights the AEM capability to improve the hydrogeological characterization of subsurface processes in worldwide lagoons, wetlands, deltas.
A 0.4 to 10 GHz airborne electromagnetic environment survey of USA urban areas
NASA Technical Reports Server (NTRS)
Taylor, R. E.; Hill, J. S.
1976-01-01
An airborne electromagnetic-environment survey of some U.S. metropolitan areas measured terrestrial emissions within the broad frequency spectrum from 0.4 to 10 GHz. A Cessna 402 commercial aircraft was fitted with both nadir-viewing and horizon-viewing antennas and instrumentation, including a spectrum analyzer, a 35 mm continuous film camera, and a magnetic tape recorder. Most of the flights were made at a nominal altitude of 10,000 feet, and Washington, D. C., Baltimore, Philadelphia, New York, and Chicago were surveyed. The 450 to 470 MHz land-mobile UHF band is especially crowded, and the 400 to 406 MHz space bands are less active. This paper discusses test measurements obtained up to 10 GHz. Sample spectrum analyzer photograhs were selected from a total of 5,750 frames representing 38 hours of data.
0.4- to 10-GHz airborne electromagnetic-environment survey of United States urban areas
NASA Technical Reports Server (NTRS)
Taylor, R. E.; Hill, J. S.
1976-01-01
An airborne electromagnetic-environment survey of some U.S. metropolitan areas measured terrestrial emissions within the broad-frequency spectrum from 0.4 to 10 GHz. A Cessna 402 commercial aircraft was fitted with both nadir-viewing and horizon-viewing antennas and instrumentation, including a spectrum analyzer, a 35-mm continuous-film camera, and a magnetic-tape recorder. Most of the flights were made at a nominal altitude of 10,000 ft, and Washington, Baltimore, Philadelphia, New York, and Chicago were surveyed. The 450- to 470-MHz land-mobile UHF band is especially crowded, and the 400- to 406-MHz space bands are less active. Test measurements obtained up to 10 GHz are discussed. Sample spectrum-analyzer photographs were selected from a total of 5750 frames representing 38 hours of data.
NASA Astrophysics Data System (ADS)
Li, Jing; Dou, Mei; Lu, Yiming; Peng, Cong; Yu, Zining; Zhu, Kaiguang
2017-01-01
The airborne electromagnetic (AEM) systems have been used traditionally in mineral exploration. Typically the system transmits a single pulse waveform to detect conductive anomaly. Conductivity-depth imaging (CDI) of data is generally applied in identifying conductive targets. A CDI algorithm with double-pulse transmitting current based on model fusion is developed. The double-pulse is made up of a half-sine pulse of high power and a trapezoid pulse of low power. This CDI algorithm presents more shallow information than traditional CDI with a single pulse. The electromagnetic response with double-pulse transmitting current is calculated by linear convolution based on forward modeling. The CDI results with half-sine and trapezoid pulse are obtained by look-up table method, and the two results are fused to form a double-pulse conductivity-depth imaging result. This makes it possible to obtain accurate conductivity and depth. Tests on synthetic data demonstrate that CDI algorithm with double-pulse transmitting current based on model fusion maps a wider range of conductivities and does a better job compared with CDI with a single pulse transmitting current in reflecting the whole geological conductivity changes.
Application of Time Domain Reflectometers in Urban Settings
Time domain reflectometers (TDRs) are sensors that measure the volumetric water content of soils and porous media. The sensors consist of stainless steel rods connected to a circuit board in an epoxy housing. An electromagnetic pulse is propagated along the rods. The time, or per...
Directly coupled vs conventional time domain reflectometry in soils
Technology Transfer Automated Retrieval System (TEKTRAN)
Time domain reflectometry (TDR), a technique for estimation of soil water, measures the travel time of an electromagnetic pulse on electrodes embedded in the soil, but has limited application in commercial agriculture due to costs, labor, and sensing depth. Conventional TDR systems have employed ana...
Flexible time domain averaging technique
NASA Astrophysics Data System (ADS)
Zhao, Ming; Lin, Jing; Lei, Yaguo; Wang, Xiufeng
2013-09-01
Time domain averaging(TDA) is essentially a comb filter, it cannot extract the specified harmonics which may be caused by some faults, such as gear eccentric. Meanwhile, TDA always suffers from period cutting error(PCE) to different extent. Several improved TDA methods have been proposed, however they cannot completely eliminate the waveform reconstruction error caused by PCE. In order to overcome the shortcomings of conventional methods, a flexible time domain averaging(FTDA) technique is established, which adapts to the analyzed signal through adjusting each harmonic of the comb filter. In this technique, the explicit form of FTDA is first constructed by frequency domain sampling. Subsequently, chirp Z-transform(CZT) is employed in the algorithm of FTDA, which can improve the calculating efficiency significantly. Since the signal is reconstructed in the continuous time domain, there is no PCE in the FTDA. To validate the effectiveness of FTDA in the signal de-noising, interpolation and harmonic reconstruction, a simulated multi-components periodic signal that corrupted by noise is processed by FTDA. The simulation results show that the FTDA is capable of recovering the periodic components from the background noise effectively. Moreover, it can improve the signal-to-noise ratio by 7.9 dB compared with conventional ones. Experiments are also carried out on gearbox test rigs with chipped tooth and eccentricity gear, respectively. It is shown that the FTDA can identify the direction and severity of the eccentricity gear, and further enhances the amplitudes of impulses by 35%. The proposed technique not only solves the problem of PCE, but also provides a useful tool for the fault symptom extraction of rotating machinery.
Airborne electromagnetic mapping of the base of aquifer in areas of western Nebraska
Abraham, Jared D.; Cannia, James C.; Bedrosian, Paul A.; Johnson, Michaela R.; Ball, Lyndsay B.; Sibray, Steven S.
2012-01-01
Airborne geophysical surveys of selected areas of the North and South Platte River valleys of Nebraska, including Lodgepole Creek valley, collected data to map aquifers and bedrock topography and thus improve the understanding of groundwater - surface-water relationships to be used in water-management decisions. Frequency-domain helicopter electromagnetic surveys, using a unique survey flight-line design, collected resistivity data that can be related to lithologic information for refinement of groundwater model inputs. To make the geophysical data useful to multidimensional groundwater models, numerical inversion converted measured data into a depth-dependent subsurface resistivity model. The inverted resistivity model, along with sensitivity analyses and test-hole information, is used to identify hydrogeologic features such as bedrock highs and paleochannels, to improve estimates of groundwater storage. The two- and three-dimensional interpretations provide the groundwater modeler with a high-resolution hydrogeologic framework and a quantitative estimate of framework uncertainty. The new hydrogeologic frameworks improve understanding of the flow-path orientation by refining the location of paleochannels and associated base of aquifer highs. These interpretations provide resource managers high-resolution hydrogeologic frameworks and quantitative estimates of framework uncertainty. The improved base of aquifer configuration represents the hydrogeology at a level of detail not achievable with previously available data.
NASA Astrophysics Data System (ADS)
Marker, P. A.; Foged, N.; He, X.; Christiansen, A. V.; Refsgaard, J. C.; Auken, E.; Bauer-Gottwein, P.
2015-09-01
Large-scale hydrological models are important decision support tools in water resources management. The largest source of uncertainty in such models is the hydrostratigraphic model. Geometry and configuration of hydrogeological units are often poorly determined from hydrogeological data alone. Due to sparse sampling in space, lithological borehole logs may overlook structures that are important for groundwater flow at larger scales. Good spatial coverage along with high spatial resolution makes airborne electromagnetic (AEM) data valuable for the structural input to large-scale groundwater models. We present a novel method to automatically integrate large AEM data sets and lithological information into large-scale hydrological models. Clay-fraction maps are produced by translating geophysical resistivity into clay-fraction values using lithological borehole information. Voxel models of electrical resistivity and clay fraction are classified into hydrostratigraphic zones using k-means clustering. Hydraulic conductivity values of the zones are estimated by hydrological calibration using hydraulic head and stream discharge observations. The method is applied to a Danish case study. Benchmarking hydrological performance by comparison of performance statistics from comparable hydrological models, the cluster model performed competitively. Calibrations of 11 hydrostratigraphic cluster models with 1-11 hydraulic conductivity zones showed improved hydrological performance with an increasing number of clusters. Beyond the 5-cluster model hydrological performance did not improve. Due to reproducibility and possibility of method standardization and automation, we believe that hydrostratigraphic model generation with the proposed method has important prospects for groundwater models used in water resources management.
NASA Astrophysics Data System (ADS)
Gondwe, Bibi R. N.; Ottowitz, David; Supper, Robert; Motschka, Klaus; Merediz-Alonso, Gonzalo; Bauer-Gottwein, Peter
2012-11-01
Geometry and connectivity of high-permeability zones determine groundwater flow in karst aquifers. Efficient management of karst aquifers requires regional mapping of preferential flow paths. Remote-sensing technology provides tools to efficiently map the subsurface at such scales. Multi-spectral remote sensing imagery, shuttle radar topography data and frequency-domain airborne electromagnetic (AEM) survey data were used to map karst-aquifer structure on the Yucatan Peninsula, Mexico. Anomalous AEM responses correlated with topographic features and anomalous spectral reflectance of the terrain. One known preferential flow path, the Holbox fracture zone, showed lower bulk electrical resistivity than its surroundings in the AEM surveys. Anomalous structures delineated inland were sealed above by a low-resistivity layer (resistivity: 1-5 Ωm, thickness: 5-6 m). This layer was interpreted as ejecta from the Chicxulub impact (Cretaceous/Paleogene boundary), based on similar resistivity signatures found in borehole logs. Due to limited sensitivity of the AEM survey, the subsurface configuration beneath the low-resistivity layer could not be unambiguously determined. AEM measurements combined with remote-sensing data analysis provide a potentially powerful multi-scale methodology for structural mapping in karst aquifers on the Yucatan Peninsula and beyond.
A Feasibility Study of RF Time-Domain Reflectometry as a Railgun Armature Tracking Technique
2007-08-08
SUBJECT TERMS armature, radio frequency (RF), time-domain reflectometry ( TDR ), HEMCL, electromagnetic noise (EMI) 15. NUMBER OF PAGES 14 16. PRICE CODE...are very sensitive to electromagnetic noise (EMI). A frequent cause of electromagnetic noise within the railgun is that caused by arcing at the...the moving armature), radio frequency (RF), time-domain reflectometry ( TDR ) may potentially be used to obtain the position history of armature
Airborne Electromagnetic Surveys for Baseline Permafrost Mapping and Potential Long-Term Monitoring
NASA Astrophysics Data System (ADS)
Smith, B. D.; Walvoord, M. A.; Cannia, J. C.; Voss, C. I.
2010-12-01
Concerns over the impacts of climate change have recently energized research on permafrost and the potential impacts that thawing permafrost may have on groundwater flow, infrastructure, ecosystems, and contaminant transport. There is typically little known at watershed or regional scales about the three-dimensional distribution of permafrost, including its thickness and the distribution of taliks (unfrozen zones), and other permafrost features thereby impeding the assessment of consequences of permafrost degradation. Airborne remote sensing methods for mapping permafrost are attractive, particularly in arctic and subarctic studies where ground access is difficult and ecosystems are fragile. As part of its Climate Effect Network (CEN) research and observation effort in the Yukon River Basin, the U.S. Geological Survey (USGS) has initiated an effort to map permafrost using airborne geophysics to complement hydrologic and biogeochemical studies in the study area. Interpretation of airborne geophysical data will be integrated with other remotely sensed data to supply critical hydrogeologic information needed for refining groundwater flow models in the Yukon Flats Basin. Airborne surveys also provide baseline data for estimating 3D permafrost distribution that can be compared to future permafrost surveys to estimate a volumetric change over time. In June 2010, the USGS conducted a helicopter frequency domain electromagnetic (HFEM) survey in the area of Fort Yukon, Alaska to map permafrost distribution. Flight line data processing has been completed that includes data leveling and a simple transformation to resistivity-depth along the flight lines. Preliminary resistivity-depth images from the survey can be qualitatively compared with known permafrost features and used to establish new permafrost features. Electrical properties of earth materials are impacted by temperature and the presence of ice causing them to become substantially more resistive when frozen. The area
Imaging Hidden Water in Three Dimensions Using an Active Airborne Electromagnetic System
NASA Astrophysics Data System (ADS)
Wynn, J.
2001-05-01
The San Pedro Basin aquifer in southeastern Arizona and northern Mexico is important not only for local agriculture and residential communities, but also because it is the source of the San Pedro River. Declared a Riparian Conservation Area by Congress in 1988, the San Pedro is a critical element of one of four major migratory bird fly-ways over North America. The basin crosses the international frontier, extending into northern Mexico, where about 12,000 acre-ft of water is withdrawn yearly by the Cananea Mine. An additional 11,000 acre-ft is withdrawn by the US Army base at Fort Huachuca and surrounding towns including Sierra Vista. About 6,000 to 8,000 acre-ft of water is also estimated as lost to evapotranspiration, while recharge (mainly from the Huachuca Mountains) ranges from 12,500 to 15,000 acre-ft per year. This apparent net deficit is considered a serious threat by environmental groups to the integrity of the Riparian Conservation Area. Efforts have been underway to develop catchments and to implement water-conservation measures, but these have been hampered by a lack of detailed knowledge of the three-dimensional geometry and extent of the aquifer beneath the entire basin - at least until recently. In an effort to identify subcomponents and interconnectivities within the San Pedro Basin aquifer, the US Army funded several airborne EM surveys, conducted in 1997 and 1999 under the supervision of the US Geological Survey east of Fort Huachuca. These surveys used the Geoterrex GEOTEM system with 20 gated time-domain windows in three perpendicular orientations. The 60+ channel information was inverted using two different methods into conductivity-depth transforms, i.e., conductivity vs. depth along each flight-line. The resulting inversions have been assembled into a three-dimensional map of the aquifer, which in this arid region is quite conductive (the average is 338 micro-S/cm, around 30 ohm-meters). The coverage is about 1,000 square kilometers down to a
1991-10-25
Fields of Wire Antenas with Diodes N. Sclieffer 13-40 Calculating Frequency Domain Data by Time Domain Methods M. Delder 11-55 - Break- 14-15 Time...vector in z direction . The voltage V between the plates is given by V = -dE, (10) where d is the distance between the plates. V V(x,y,t)= -jL, OJ(X-,Yt...the directions tj and t2, respectively, are given by i and i2, and v is the voltage between the metal plates. The inhomogeneous terms ul, U2 and U3
NASA Astrophysics Data System (ADS)
Delhaye, Robert; Rath, Volker; Jones, Alan G.; Reay, Derek; The Iretherm Team
2015-04-01
In this study we present results from geophysical investigation of the sedimentary Rathlin Basin in Northern Ireland in order to assess the potential for low-to-medium enthalpy geothermal aquifers within the porous Permian and Triassic sandstone groups. The area and groups were identified as a potential geothermal resource due to the presence of both an elevated geothermal gradient (observed in two deep boreholes onshore) and favourable hydraulic properties (measured on core samples in the offshore part of the basin). Previous seismic experiments were not able to fully characterise the sediments beneath the overlying flood basalt. Complementing these earlier results, magnetotelluric data were acquired on a grid of 56 sites across the north-eastern portion of the onshore Rathlin Basin, and an additional 12 sites on the nearby Rathlin Island, in order to image the thickness, depth, and lateral continuity of the target sediments. Analysis and 3D modelling, including the effects of the highly conducting ocean, has been successful in deriving a resistivity model that maps the variation in the top of the sediments (base of the basalts) and the truncation of the basin sediments against the Tow Valley Fault, and gives a reasonable estimate of the thickness of the sediment fill. However, the resulting models show significant effects from distortion caused by near-surface inhomogeneities in the responses that cannot be resolved using the given frequency range and site density. Fortunately, for the area of Rathlin Basin, airborne electromagnetic data from the TELLUS project (http://www.bgs.ac.uk/gsni/tellus/contact/index.html) are available. These data were measured at four frequencies between 0.9 kHz and 25 kHz in a verical-coplanar loop configuration, with the dipole axis in flight direction. The spatial sampling distance was less than 25 m, with about 200 m distance between flight lines. Survey altitudes vary between 56 m and 244 m. Thus, for the top ˜100 m penetrated by
NASA Astrophysics Data System (ADS)
Hein, A.; Armstrong, R. S.; Holbrook, W. S.; Parsekian, A.
2015-12-01
The rivers that supply water to most of the West rise in the Rocky Mountains. As drought increases across the country, understanding the hydrology of these alpine regions becomes important to assuring water supplies in the future. Near surface geophysics can help in this effort. In this study, resistivity data from an airborne electromagnetic survey in the Snowy Range was analyzed to map groundwater distribution. The EM survey covered an area of approximately 60 km2 to a depth of around 150 m. Nuclear magnetic resonance (NMR) point soundings provided ground truthing by testing whether water was present, at what depth, and how much. The survey area contained vertically dipping metasedimentary rocks, covered in places by unconsolidated glacial and fluvial deposits. The resistivity data showed horizontal variation in water content much more clearly than vertical changes, which were best detected by NMR. To allow for comparisons across different lithologies and depths, resistivity measurements were first log transformed to produce a more normal distribution, then classed by depth and formation and assigned standardized scores using the mean and standard deviation for those classes. To determine the typical appearance of wet areas, points in the near surface were classed as wet or dry based on proximity to surface water. Logistic regression was used to determine the probability that points with a given standardized score were wet. Where a relationship existed between proximity to surface water and conductivity, this information was translated into a map of groundwater distribution at greater depths. NMR soundings provided quantitative measurements of water content, which were used as known points within these horizontal maps to determine the actual water levels being detected.
Estimation of Resolution of Shallow Layers by Frequency Domain Airborne Electromagnetic Measurements
NASA Astrophysics Data System (ADS)
Smith, B. D.; Minsley, B. J.; Kass, M. A.; Abraham, J. D.; Sams, J. I.; Veloski, G. A.; Esfahani, A.; Hodges, G.
2012-12-01
Helicopter frequency domain electromagnetic (HFDEM) that were conducted in two very different geoelectrical settings, permafrost and conductive alluvium, have been used to examine and quantify some aspects of the resolution of shallow layers (less than 5 meters). The surveys have used the Resolve system with six frequencies ranging from 400 Hz to 140 kHz. Though most discussion of the resolution of earth resistivity for airborne EM systems has concentrated on estimating the maximum depth of mapping or the resolution of deep layers, there are important applications for mapping shallow layers and it is useful to understand the capabilities and limitations of the HFDEM system in different environments. In permafrost terrains, mapping of the shallow active layer is important in understanding its distribution relative to surface processes such as thermal history, fires and carbon storage as well as in monitoring applications. Here the shallow active layer is a conductor relative to the very resistive permafrost. Mapping shallow layers in alluvial environments has been the focus of a study of subsurface drip irrigation in the Powder River of Wyoming. Here the focus of the HFDEM study has been in mapping the distribution of conductive clays and naturally occurring saline waters. Mapping of shallow layers in alluvial environments is important in agricultural applications to map recharge, soil salinity, and thickness of alluvium. Parameters for layered models (layer resistivity and thickness) have been estimated by inversion methods and the resolution of parameters has been evaluated using stochastic methods and an evaluation of linear estimates of resolution and uncertainty. Statistical estimates of resolution of parameters are compared with estimates from ground surveys.
NASA Astrophysics Data System (ADS)
Wang, Yuan
2013-09-01
A grounded electrical source airborne transient electromagnetic (GREATEM) system on an airship enjoys high depth of prospecting and spatial resolution, as well as outstanding detection efficiency and easy flight control. However, the movement and swing of the front-fixed receiving coil can cause severe baseline drift, leading to inferior resistivity image formation. Consequently, the reduction of baseline drift of GREATEM is of vital importance to inversion explanation. To correct the baseline drift, a traditional interpolation method estimates the baseline `envelope' using the linear interpolation between the calculated start and end points of all cycles, and obtains the corrected signal by subtracting the envelope from the original signal. However, the effectiveness and efficiency of the removal is found to be low. Considering the characteristics of the baseline drift in GREATEM data, this study proposes a wavelet-based method based on multi-resolution analysis. The optimal wavelet basis and decomposition levels are determined through the iterative comparison of trial and error. This application uses the sym8 wavelet with 10 decomposition levels, and obtains the approximation at level-10 as the baseline drift, then gets the corrected signal by removing the estimated baseline drift from the original signal. To examine the performance of our proposed method, we establish a dipping sheet model and calculate the theoretical response. Through simulations, we compare the signal-to-noise ratio, signal distortion, and processing speed of the wavelet-based method and those of the interpolation method. Simulation results show that the wavelet-based method outperforms the interpolation method. We also use field data to evaluate the methods, compare the depth section images of apparent resistivity using the original signal, the interpolation-corrected signal and the wavelet-corrected signal, respectively. The results confirm that our proposed wavelet-based method is an
2010-05-01
basalt flows or other iron-bearing soils and rocks impede the performance of magnetometer systems. Although this is not a universal problem, it occurs...sensors at less than 0.5 m above ground level (AGL). Airborne and ground magnetometer systems are susceptible to interference from magnetic rocks and...where magnetite bearing basaltic rocks are problematic. The airborne TEM-8 system demonstrates a similar advantage over airborne magnetometer systems
Ball, Lyndsay B.; Smith, Bruce D.; Minsley, Burke J.; Abraham, Jared D.; Voss, Clifford I.; Astley, Beth N.; Deszcz-Pan, Maria; Cannia, James C.
2011-01-01
In June 2010, the U.S. Geological Survey conducted airborne electromagnetic and magnetic surveys of the Yukon Flats and Fort Wainwright study areas in central Alaska. These data were collected to estimate the three-dimensional distribution of permafrost at the time of the survey. These data were also collected to evaluate the effectiveness of these geophysical methods at mapping permafrost geometry and to better define the physical properties of the subsurface in discontinuous permafrost areas. This report releases digital data associated with these surveys. Inverted resistivity depth sections are also provided in this data release, and data processing and inversion methods are discussed.
Finite difference time domain calculations of antenna mutual coupling
NASA Technical Reports Server (NTRS)
Luebbers, Raymond J.; Kunz, Karl S.
1991-01-01
The Finite Difference Time Domain (FDTD) technique was applied to a wide variety of electromagnetic analysis problems, including shielding and scattering. However, the method has not been exclusively applied to antennas. Here, calculations of self and mutual admittances between wire antennas are made using FDTD and compared with results obtained during the method of moments. The agreement is quite good, indicating the possibilities for FDTD application to antenna impedance and coupling.
Finite difference time domain calculations of antenna mutual coupling
NASA Technical Reports Server (NTRS)
Luebbers, Raymond J.; Kunz, Karl S.
1991-01-01
The Finite Difference Time Domain (FDTD) technique has been applied to a wide variety of electromagnetic analysis problems, including shielding and scattering. However, the method has not been extensively applied to antennas. In this short paper calculations of self and mutual admittances between wire antennas are made using FDTD and compared with results obtained using the Method of Moments. The agreement is quite good, indicating the possibilities for FDTD application to antenna impedance and coupling.
Analysis of time-domain scattering by periodic structures
NASA Astrophysics Data System (ADS)
Gao, Yixian; Li, Peijun
2016-11-01
This paper is devoted to the mathematical analysis of a time-domain electromagnetic scattering by periodic structures which are known as diffraction gratings. The scattering problem is reduced equivalently into an initial-boundary value problem in a bounded domain by using an exact transparent boundary condition. The well-posedness and stability of the solution are established for the reduced problem. Moreover, a priori energy estimates are obtained with minimum regularity requirement for the data and explicit dependence on the time.
NASA Astrophysics Data System (ADS)
Kruse Christensen, Nikolaj; Ferre, Ty Paul A.; Fiandaca, Gianluca; Christensen, Steen
2017-03-01
We present a workflow for efficient construction and calibration of large-scale groundwater models that includes the integration of airborne electromagnetic (AEM) data and hydrological data. In the first step, the AEM data are inverted to form a 3-D geophysical model. In the second step, the 3-D geophysical model is translated, using a spatially dependent petrophysical relationship, to form a 3-D hydraulic conductivity distribution. The geophysical models and the hydrological data are used to estimate spatially distributed petrophysical shape factors. The shape factors primarily work as translators between resistivity and hydraulic conductivity, but they can also compensate for structural defects in the geophysical model. The method is demonstrated for a synthetic case study with sharp transitions among various types of deposits. Besides demonstrating the methodology, we demonstrate the importance of using geophysical regularization constraints that conform well to the depositional environment. This is done by inverting the AEM data using either smoothness (smooth) constraints or minimum gradient support (sharp) constraints, where the use of sharp constraints conforms best to the environment. The dependency on AEM data quality is also tested by inverting the geophysical model using data corrupted with four different levels of background noise. Subsequently, the geophysical models are used to construct competing groundwater models for which the shape factors are calibrated. The performance of each groundwater model is tested with respect to four types of prediction that are beyond the calibration base: a pumping well's recharge area and groundwater age, respectively, are predicted by applying the same stress as for the hydrologic model calibration; and head and stream discharge are predicted for a different stress situation. As expected, in this case the predictive capability of a groundwater model is better when it is based on a sharp geophysical model instead of a
NASA Astrophysics Data System (ADS)
Yang, Dikun; Oldenburg, Douglas W.; Haber, Eldad
2014-03-01
Airborne electromagnetic (AEM) methods are highly efficient tools for assessing the Earth's conductivity structures in a large area at low cost. However, the configuration of AEM measurements, which typically have widely distributed transmitter-receiver pairs, makes the rigorous modelling and interpretation extremely time-consuming in 3-D. Excessive overcomputing can occur when working on a large mesh covering the entire survey area and inverting all soundings in the data set. We propose two improvements. The first is to use a locally optimized mesh for each AEM sounding for the forward modelling and calculation of sensitivity. This dedicated local mesh is small with fine cells near the sounding location and coarse cells far away in accordance with EM diffusion and the geometric decay of the signals. Once the forward problem is solved on the local meshes, the sensitivity for the inversion on the global mesh is available through quick interpolation. Using local meshes for AEM forward modelling avoids unnecessary computing on fine cells on a global mesh that are far away from the sounding location. Since local meshes are highly independent, the forward modelling can be efficiently parallelized over an array of processors. The second improvement is random and dynamic down-sampling of the soundings. Each inversion iteration only uses a random subset of the soundings, and the subset is reselected for every iteration. The number of soundings in the random subset, determined by an adaptive algorithm, is tied to the degree of model regularization. This minimizes the overcomputing caused by working with redundant soundings. Our methods are compared against conventional methods and tested with a synthetic example. We also invert a field data set that was previously considered to be too large to be practically inverted in 3-D. These examples show that our methodology can dramatically reduce the processing time of 3-D inversion to a practical level without losing resolution
NASA Astrophysics Data System (ADS)
Hauser, Juerg; Gunning, James; Annetts, David
2016-04-01
Airborne electromagnetic (AEM) data are often inverted with the aim of delineating near-surface geological interfaces, such as the boundaries of an aquifer or the base of regolith. Not all approaches to the inversion of AEM data are equally amenable to the recovery of such spatially coherent interfaces. If the AEM data are inverted for a 1D model on a station-by-station basis, or if a smooth resistivity distribution has been derived, qualitative interpretation of these inversion results is often required to obtain a spatially coherent interface. Regularised deterministic inversions can take spatial correlation between 1D models into account, and be used to directly invert for a spatially coherent interface if a blocky model is sought from the data. However, inversion of AEM data is non-unique, and therefore estimating the uncertainty of an inversion result is as important as finding a single best-fitting model. Markov chain Monte Carlo (McMC) algorithms have been successful in exploring the 1D uncertainty space that arises in station-independent models. In a set of laterally independent 1D models, abrupt transverse changes in model parameters can occur, making it difficult to derive a spatially coherent interface. Full McMC sampling for laterally correlated models is computationally expensive, and independent 1D samplers are often the only feasible alternative if one wishes to explore the joint model space. Here we introduce a Bayesian parametric bootstrap approach to invert for spatially coherent layer properties, interfaces and related uncertainties. The Bayesian parametric bootstrap treats prior information on the model and its spatial correlation as implied observations, and then applies the classical parametric bootstrap. Numerical examples demonstrate that our Bayesian parametric bootstrap will explore model space adequately for non-pathological situations, while requiring many fewer forward problem solves than a comparable McMC algorithm. Recovered
NASA Astrophysics Data System (ADS)
Barfod, Adrian A. S.; Møller, Ingelise; Christiansen, Anders V.
2016-11-01
We present a large-scale study of the petrophysical relationship of resistivities obtained from densely sampled ground-based and airborne transient electromagnetic surveys and lithological information from boreholes. The overriding aim of this study is to develop a framework for examining the resistivity-lithology relationship in a statistical manner and apply this framework to gain a better description of the large-scale resistivity structures of the subsurface. In Denmark very large and extensive datasets are available through the national geophysical and borehole databases, GERDA and JUPITER respectively. In a 10 by 10 km grid, these data are compiled into histograms of resistivity versus lithology. To do this, the geophysical data are interpolated to the position of the boreholes, which allows for a lithological categorization of the interpolated resistivity values, yielding different histograms for a set of desired lithological categories. By applying the proposed algorithm to all available boreholes and airborne and ground-based transient electromagnetic data we build nation-wide maps of the resistivity-lithology relationships in Denmark. The presented Resistivity Atlas reveals varying patterns in the large-scale resistivity-lithology relations, reflecting geological details such as available source material for tills. The resistivity maps also reveal a clear ambiguity in the resistivity values for different lithologies. The Resistivity Atlas is highly useful when geophysical data are to be used for geological or hydrological modeling.
Time Domain Switched Accelerometer Design and Fabrication
2014-09-01
TECHNICAL REPORT 2052 September 2014 Time -Domain Switched Accelerometer Design and Fabrication Paul Swanson Andrew Wang...Approved for public release. SSC Pacific San Diego, CA 92152-5001 TECHNICAL REPORT 2052 September 2014 Time ...objective of this report is to record the decision-making process for developing the device design and fabrication workflow for the time -domain switched
A time domain, weighted residual formulation of Maxwell's equations
NASA Technical Reports Server (NTRS)
Young, Jeffrey L.; Brueckner, Frank P.
1993-01-01
A finite element model is developed and used to simulate two-dimensional electromagnetic wave propagation and scattering. The spatial discretization of the time-domain electrodynamic equations is accomplished by a Galerkin approach. The semi-discrete equations are solved explicitly using a second-order Runge-Kutta scheme. Both the electric and magnetic fields are discretized using a single grid, with the divergence-free conditions satisfied through a correction approach. Examples depicting the scattering of plane waves in 2D geometries are given to demonstrate the validity of the methodology.
Radar target imaging by time-domain inverse scattering
NASA Astrophysics Data System (ADS)
Morag, M.
1981-03-01
This thesis describes the study and development of a workable inverse scattering method for imaging and identification of radar targets. The space-time integral approach is used for iterative target shape reconstruction. Following an overview of transient electromagnetics, the integral equation is applied for thin-wire transient response computation. The analytical time domain integral equation is derived and solved numerically, for general conducting bodies of revolution. Finally the algorithm for an inverse scattering computer solution is derived and tested under simulation of physical environments.
2009-12-01
Jefferson (Ohio) site, six acres in size, is located in an area where a glacial till layer, typically 50–200 feet (ft) thick, overlies Silurian age...lower cost per acre than ground-based systems. Furthermore, the data may be acquired in a shorter period of time. Airborne systems are particularly...Figure 6. 22 Alternating positive and negative "on-time" current pulses with linear on- and off-ramps are separated by "off-time" periods during
Airborne electromagnetics (EM) as a three-dimensional aquifer-mapping tool
Wynn, Jeff; Pool, Don; Bultman, Mark; Gettings, Mark; Lemieux, Jean
2000-01-01
The San Pedro River in southeastern Arizona hosts a major migratory bird flyway, and was declared a Riparian Conservation Area by Congress in 1988. Recharge of the adjacent Upper San Pedro Valley aquifer was thought to come primarily from the Huachuca Mountains, but the U. S. Army Garrison of Fort Huachuca and neighboring city of Sierra Vista have been tapping this aquifer for many decades, giving rise to claims that they jointly threatened the integrity of the Riparian Conservation Area. For this reason, the U. S. Army funded two airborne geophysical surveys over the Upper San Pedro Valley (see figure 1), and these have provided us valuable information on the aquifer and the complex basement structure underlying the modern San Pedro Valley. Euler deconvolution performed on the airborne magnetic data has provided a depth-to-basement map that is substantially more complex than a map obtained earlier from gravity data, as would be expected from the higher-resolution magnetic data. However, we found the output of the Euler deconvolution to have "geologic noise" in certain areas, interpreted to be post-Basin-and-Range Tertiary volcanic flows in the sedimentary column above the basement but below the ground surface.
Time domain reflectometry in time variant plasmas
NASA Technical Reports Server (NTRS)
Scherner, Michael J.
1992-01-01
The effects of time-dependent electron density fluctuations on a synthesized time domain reflectometry response of a one-dimensional cold plasma sheath are considered. Numerical solutions of the Helmholtz wave equation, which describes the electric field of a normally incident plane wave in a specified static electron density profile, are used. A study of the effects of Doppler shifts resulting from moving density fluctuations in the electron density profile of the sheath is included. Varying electron density levels corrupt time domain and distance measurements. Reducing or modulating the electron density levels of a given electron density profile affects the time domain response of a plasma and results in motion of the turning point, and the effective motion has a significant effect on measuring electron density locations.
Calculation of nonzero-temperature Casimir forces in the time domain
Pan, Kai; Reid, M. T. Homer; McCauley, Alexander P.; Rodriguez, Alejandro W.; White, Jacob K.; Johnson, Steven G.
2011-04-15
We show how to compute Casimir forces at nonzero temperatures with time-domain electromagnetic simulations, for example, using a finite-difference time-domain (FDTD) method. Compared to our previous zero-temperature time-domain method, only a small modification is required, but we explain that some care is required to properly capture the zero-frequency contribution. We validate the method against analytical and numerical frequency-domain calculations, and show a surprising high-temperature disappearance of a nonmonotonic behavior previously demonstrated in a pistonlike geometry.
Casimir forces in the time domain: Theory
Rodriguez, Alejandro W.; McCauley, Alexander P.; Joannopoulos, John D.; Johnson, Steven G.
2009-07-15
We present a method to compute Casimir forces in arbitrary geometries and for arbitrary materials based on the finite-difference time-domain (FDTD) scheme. The method involves the time evolution of electric and magnetic fields in response to a set of current sources, in a modified medium with frequency-independent conductivity. The advantage of this approach is that it allows one to exploit existing FDTD software, without modification, to compute Casimir forces. In this paper, we focus on the derivation, implementation choices, and essential properties of the time-domain algorithm, both considered analytically and illustrated in the simplest parallel-plate geometry.
Anderson localization in the time domain
NASA Astrophysics Data System (ADS)
Sacha, Krzysztof; Delande, Dominique
2016-08-01
In analogy with the usual Anderson localization taking place in time-independent disordered quantum systems where the disorder acts in configuration space, systems exposed to temporally disordered potentials can display Anderson localization in the time domain. We demonstrate this phenomenon with one-dimensional examples where a temporally disordered potential induces localization during the quantum evolution of wave packets, in contrast with a fully delocalized classical dynamics. This is an example of a time crystal phenomenon, i.e., a crystalline behavior in the time domain.
NASA Astrophysics Data System (ADS)
Ji, Yanju; Li, Dongsheng; Yu, Mingmei; Wang, Yuan; Wu, Qiong; Lin, Jun
2016-05-01
The ground electrical source airborne transient electromagnetic system (GREATEM) on an unmanned aircraft enjoys considerable prospecting depth, lateral resolution and detection efficiency, etc. In recent years it has become an important technical means of rapid resources exploration. However, GREATEM data are extremely vulnerable to stationary white noise and non-stationary electromagnetic noise (sferics noise, aircraft engine noise and other human electromagnetic noises). These noises will cause degradation of the imaging quality for data interpretation. Based on the characteristics of the GREATEM data and major noises, we propose a de-noising algorithm utilizing wavelet threshold method and exponential adaptive window width-fitting. Firstly, the white noise is filtered in the measured data using the wavelet threshold method. Then, the data are segmented using data window whose step length is even logarithmic intervals. The data polluted by electromagnetic noise are identified within each window based on the discriminating principle of energy detection, and the attenuation characteristics of the data slope are extracted. Eventually, an exponential fitting algorithm is adopted to fit the attenuation curve of each window, and the data polluted by non-stationary electromagnetic noise are replaced with their fitting results. Thus the non-stationary electromagnetic noise can be effectively removed. The proposed algorithm is verified by the synthetic and real GREATEM signals. The results show that in GREATEM signal, stationary white noise and non-stationary electromagnetic noise can be effectively filtered using the wavelet threshold-exponential adaptive window width-fitting algorithm, which enhances the imaging quality.
NASA Astrophysics Data System (ADS)
Kowalski, Adam; Hawley, Suzanne; Davenport, James; Berlicki, Arkadiusz; Cauzzi, Gianna; Fletcher, Lyndsay; Heinzel, Petr; Notsu, Yuta; Loyd, Parke; Martinez Oliveros, Juan Carlos; Pugh, Chloe; Schmidt, Sarah Jane; Karmakar, Subhajeet; Pye, John; Flaccomio, Ettore
2016-07-01
Proceedings for the splinter session "Flares in Time-Domain Surveys" convened at Cool Stars 19 on June 07, 2016 in Uppsala, Sweden. Contains a two page summary of the splinter session, links to YouTube talks, and a PDF copy of the slides from the presenters.
Time-Domain Simulation of RF Couplers
Smithe, David; Carlsson, Johan; Austin, Travis
2009-11-26
We have developed a finite-difference time-domain (FDTD) fluid-like approach to integrated plasma-and-coupler simulation [1], and show how it can be used to model LH and ICRF couplers in the MST and larger tokamaks.[2] This approach permits very accurate 3-D representation of coupler geometry, and easily includes non-axi-symmetry in vessel wall, magnetic equilibrium, and plasma density. The plasma is integrated with the FDTD Maxwell solver in an implicit solve that steps over electron time-scales, and permits tenuous plasma in the coupler itself, without any need to distinguish or interface between different regions of vacuum and/or plasma. The FDTD algorithm is also generalized to incorporate a time-domain sheath potential [3] on metal structures within the simulation, to look for situations where the sheath potential might generate local sputtering opportunities. Benchmarking of the time-domain sheath algorithm has been reported in the references. Finally, the time-domain software [4] permits the use of particles, either as field diagnostic (test particles) or to self-consistently compute plasma current from the applied RF power.
Valder, Joshua F.; Delzer, Gregory C.; Carter, Janet M.; Smith, Bruce D.; Smith, David V.
2016-09-28
The city of Sioux Falls is the fastest growing community in South Dakota. In response to this continued growth and planning for future development, Sioux Falls requires a sustainable supply of municipal water. Planning and managing sustainable groundwater supplies requires a thorough understanding of local groundwater resources. The Big Sioux aquifer consists of glacial outwash sands and gravels and is hydraulically connected to the Big Sioux River, which provided about 90 percent of the city’s source-water production in 2015. Managing sustainable groundwater supplies also requires an understanding of groundwater availability. An effective mechanism to inform water management decisions is the development and utilization of a groundwater-flow model. A groundwater-flow model provides a quantitative framework for synthesizing field information and conceptualizing hydrogeologic processes. These groundwater-flow models can support decision making processes by mapping and characterizing the aquifer. Accordingly, the city of Sioux Falls partnered with the U.S. Geological Survey to construct a groundwater-flow model. Model inputs will include data from advanced geophysical techniques, specifically airborne electromagnetic methods.
Time-domain flicker measurement technique
NASA Astrophysics Data System (ADS)
Miseli, Joseph
1999-04-01
The visibility of flicker on a display depends upon many factors, including the observer's sensitivity to flicker. Whenever flicker is observed, it is probably undesirable and often unacceptable. Much has been written about flicker, its perception, and its variability. Methods have been presented to the industry that use frequency domain analysis of measured flicker response. Here we prose an alternate method to quantify flicker in the time domain, just as people see it, and we will try to understand how the measurements relate to what people see. Both the frequency domain and time domain flicker measurements can be found in the Video Electronics Standards Association Flat Panel Display Measurements Standard. An attempt is made to compare the two methods and show how the simpler measurement can be employed for many display technologies.
LHC RF System Time-Domain Simulation
Mastorides, T.; Rivetta, C.; /SLAC
2010-09-14
Non-linear time-domain simulations have been developed for the Positron-Electron Project (PEP-II) and the Large Hadron Collider (LHC). These simulations capture the dynamic behavior of the RF station-beam interaction and are structured to reproduce the technical characteristics of the system (noise contributions, non-linear elements, and more). As such, they provide useful results and insight for the development and design of future LLRF feedback systems. They are also a valuable tool for the study of diverse longitudinal beam dynamics effects such as coupled-bunch impedance driven instabilities and single bunch longitudinal emittance growth. Results from these studies and related measurements from PEP-II and LHC have been presented in multiple places. This report presents an example of the time-domain simulation implementation for the LHC.
Time-Domain Stability Margin Assessment
NASA Technical Reports Server (NTRS)
Clements, Keith
2016-01-01
The baseline stability margins for NASA's Space Launch System (SLS) launch vehicle were generated via the classical approach of linearizing the system equations of motion and determining the gain and phase margins from the resulting frequency domain model. To improve the fidelity of the classical methods, the linear frequency domain approach can be extended by replacing static, memoryless nonlinearities with describing functions. This technique, however, does not address the time varying nature of the dynamics of a launch vehicle in flight. An alternative technique for the evaluation of the stability of the nonlinear launch vehicle dynamics along its trajectory is to incrementally adjust the gain and/or time delay in the time domain simulation until the system exhibits unstable behavior. This technique has the added benefit of providing a direct comparison between the time domain and frequency domain tools in support of simulation validation.
Time Domain Stability Margin Assessment Method
NASA Technical Reports Server (NTRS)
Clements, Keith
2017-01-01
The baseline stability margins for NASA's Space Launch System (SLS) launch vehicle were generated via the classical approach of linearizing the system equations of motion and determining the gain and phase margins from the resulting frequency domain model. To improve the fidelity of the classical methods, the linear frequency domain approach can be extended by replacing static, memoryless nonlinearities with describing functions. This technique, however, does not address the time varying nature of the dynamics of a launch vehicle in flight. An alternative technique for the evaluation of the stability of the nonlinear launch vehicle dynamics along its trajectory is to incrementally adjust the gain and/or time delay in the time domain simulation until the system exhibits unstable behavior. This technique has the added benefit of providing a direct comparison between the time domain and frequency domain tools in support of simulation validation.
Magnified time-domain ghost imaging
NASA Astrophysics Data System (ADS)
Ryczkowski, Piotr; Barbier, Margaux; Friberg, Ari T.; Dudley, John M.; Genty, Goëry
2017-04-01
Ghost imaging allows the imaging of an object without directly seeing this object. Originally demonstrated in the spatial domain, it was recently shown that ghost imaging can be transposed into the time domain to detect ultrafast signals, even in the presence of distortion. We propose and experimentally demonstrate a temporal ghost imaging scheme which generates a 5× magnified ghost image of an ultrafast waveform. Inspired by shadow imaging in the spatial domain and building on the dispersive Fourier transform of an incoherent supercontinuum in an optical fiber, the approach overcomes the resolution limit of standard time-domain ghost imaging generally imposed by the detectors speed. The method can be scaled up to higher magnification factors using longer fiber lengths and light source with shorter duration.
Inversion of SPECTREM airborne electromagnetic data for groundwater assessment in outback Australia
NASA Astrophysics Data System (ADS)
Ley-Cooper, A. Y.; Munday, T. J.
2012-12-01
Inversion methods based on 1D forward model responses accurately honour flat laying layered environments and they have a valuable role in extracting hydrogeological information from a range of AEM systems. The conversion of a non-linear EM response to accurate estimates of ground conductivity is essential for groundwater assessment and aquifer characterisation. It is critical to ensure the forward response accurately models the system transfer function used in the inversion. The weathered conductive nature of the Australian overburden, presents a challenge for all EM induction techniques. Target geometry can be modelled for each system, but field conditions add complexity. We examine effects arising from applying a 1D inversion on SPECTREM2000 AEM data in areas with 3D anisotropy, and consider its suitability for regional surveys in outback Australia. The accurate recovery of conductivity models from AEM systems normally considered as targeting tools, has become particularly important where their conjunctive use for mineral exploration and groundwater assessment is now being canvassed. SPECTREM is a fixed wing, time domain EM system that employs a bipolar full cycle square current waveform operating with a variable base frequency from 25Hz upwards. Its rms transmitter dipole moment is 400 000 A.m2 , and flies at a nominal height of 90m above the ground with the 'bird' towed approximately 131m behind and 40m below the aircraft. Both X and Z component data are recorded and then processed to produce a step response at each fiducial. Through a consideration of approaches to primary field removal, data normalisation, and an understanding of transmitter(TX) - receiver(RX) geometry we have a procedure to model and invert data from this system. Relative separations of TX and RX are not monitored in flight, requiring they be estimated afterwards. The challenge, with this system having a transmitter always active, is to separate the measured total field into the transmitted
Holographic imaging based on time-domain data of natural-fiber-containing materials
Bunch, Kyle J.; McMakin, Douglas L.
2012-09-04
Methods and apparatuses for imaging material properties in natural-fiber-containing materials can utilize time-domain data. In particular, images can be constructed that provide quantified measures of localized moisture content. For example, one or more antennas and at least one transceiver can be configured to collect time-domain data from radiation interacting with the natural-fiber-containing materials. The antennas and the transceivers are configured to transmit and receive electromagnetic radiation at one or more frequencies, which are between 50 MHz and 1 THz, according to a time-domain impulse function. A computing device is configured to transform the time-domain data to frequency-domain data, to apply a synthetic imaging algorithm for constructing a three-dimensional image of the natural-fiber-containing materials, and to provide a quantified measure of localized moisture content based on a pre-determined correlation of moisture content to frequency-domain data.
Finite difference time domain analysis of chirped dielectric gratings
NASA Technical Reports Server (NTRS)
Hochmuth, Diane H.; Johnson, Eric G.
1993-01-01
The finite difference time domain (FDTD) method for solving Maxwell's time-dependent curl equations is accurate, computationally efficient, and straight-forward to implement. Since both time and space derivatives are employed, the propagation of an electromagnetic wave can be treated as an initial-value problem. Second-order central-difference approximations are applied to the space and time derivatives of the electric and magnetic fields providing a discretization of the fields in a volume of space, for a period of time. The solution to this system of equations is stepped through time, thus, simulating the propagation of the incident wave. If the simulation is continued until a steady-state is reached, an appropriate far-field transformation can be applied to the time-domain scattered fields to obtain reflected and transmitted powers. From this information diffraction efficiencies can also be determined. In analyzing the chirped structure, a mesh is applied only to the area immediately around the grating. The size of the mesh is then proportional to the electric size of the grating. Doing this, however, imposes an artificial boundary around the area of interest. An absorbing boundary condition must be applied along the artificial boundary so that the outgoing waves are absorbed as if the boundary were absent. Many such boundary conditions have been developed that give near-perfect absorption. In this analysis, the Mur absorbing boundary conditions are employed. Several grating structures were analyzed using the FDTD method.
Time-domain spectroscopy in the mid-infrared.
Lanin, A A; Voronin, A A; Fedotov, A B; Zheltikov, A M
2014-10-20
When coupled to characteristic, fingerprint vibrational and rotational motions of molecules, an electromagnetic field with an appropriate frequency and waveform offers a highly sensitive, highly informative probe, enabling chemically specific studies on a broad class of systems in physics, chemistry, biology, geosciences, and medicine. The frequencies of these signature molecular modes, however, lie in a region where accurate spectroscopic measurements are extremely difficult because of the lack of efficient detectors and spectrometers. Here, we show that, with a combination of advanced ultrafast technologies and nonlinear-optical waveform characterization, time-domain techniques can be advantageously extended to the metrology of fundamental molecular motions in the mid-infrared. In our scheme, the spectral modulation of ultrashort mid-infrared pulses, induced by rovibrational motions of molecules, gives rise to interfering coherent dark waveforms in the time domain. These high-visibility interference patterns can be read out by cross-correlation frequency-resolved gating of the field in the visible generated through ultrabroadband four-wave mixing in a gas phase.
Metrology for terahertz time-domain spectrometers
NASA Astrophysics Data System (ADS)
Molloy, John F.; Naftaly, Mira
2015-12-01
In recent years the terahertz time-domain spectrometer (THz TDS) [1] has emerged as a key measurement device for spectroscopic investigations in the frequency range of 0.1-5 THz. To date, almost every type of material has been studied using THz TDS, including semiconductors, ceramics, polymers, metal films, liquid crystals, glasses, pharmaceuticals, DNA molecules, proteins, gases, composites, foams, oils, and many others. Measurements with a TDS are made in the time domain; conversion from the time domain data to a frequency spectrum is achieved by applying the Fourier Transform, calculated numerically using the Fast Fourier Transform (FFT) algorithm. As in many other types of spectrometer, THz TDS requires that the sample data be referenced to similarly acquired data with no sample present. Unlike frequency-domain spectrometers which detect light intensity and measure absorption spectra, a TDS records both amplitude and phase information, and therefore yields both the absorption coefficient and the refractive index of the sample material. The analysis of the data from THz TDS relies on the assumptions that: a) the frequency scale is accurate; b) the measurement of THz field amplitude is linear; and c) that the presence of the sample does not affect the performance characteristics of the instrument. The frequency scale of a THz TDS is derived from the displacement of the delay line; via FFT, positioning errors may give rise to frequency errors that are difficult to quantify. The measurement of the field amplitude in a THz TDS is required to be linear with a dynamic range of the order of 10 000. And attention must be given to the sample positioning and handling in order to avoid sample-related errors.
Time-domain multiple-quantum NMR
Weitekamp, D.P.
1982-11-01
The development of time-domain multiple-quantum nuclear magnetic resonance is reviewed through mid 1982 and some prospects for future development are indicated. Particular attention is given to the problem of obtaining resolved, interpretable, many-quantum spectra for anisotropic magnetically isolated systems of coupled spins. New results are presented on a number of topics including the optimization of multiple-quantum-line intensities, analysis of noise in two-dimensional spectroscopy, and the use of order-selective excitation for cross polarization between nuclear-spin species.
Butler, K.L.
1985-09-01
Airborne measurements of the absolute vertical electric field (E-field) of the radiated electromagnetic pulse were attempted for Shots Little Feller II and Small Boy. Instrumentation included calibrated vertical whip antennas, wideband magnetic tape recorders, and photographs of oscilloscope traces. One instrumented aircraft participated in Little Feller II (C-131F); two aircraft participated in Small Boy (a C-131F and an A-3A). No detectable signals were recorded for either event. It is concluded that the vertical E-field intensities encountered were below the calibrated levels of the instrumentation or the method of instrumentation and calibration was inadequate for nonrepetitive pulse signals.
Numerical methods for time-domain and frequency-domain analysis: applications in engineering
NASA Astrophysics Data System (ADS)
Tamas, R. D.
2015-11-01
Numerical methods are widely used for modeling different physical phenomena in engineering, especially when an analytic approach is not possible. Time-domain or frequency- domain type variations are generally investigated, depending on the nature of the process under consideration. Some methods originate from mechanics, although most of their applications belong to other fields, such as electromagnetism. Conversely, other methods were firstly developed for electromagnetism, but their field of application was extended to other fields. This paper presents some results that we have obtained by using a general purpose method for solving linear equations, i.e., the method of moments (MoM), and a time-domain method derived for electromagnetism, i.e., the Transmission Line Matrix method (TLM).
Time domain para hydrogen induced polarization.
Ratajczyk, Tomasz; Gutmann, Torsten; Dillenberger, Sonja; Abdulhussaein, Safaa; Frydel, Jaroslaw; Breitzke, Hergen; Bommerich, Ute; Trantzschel, Thomas; Bernarding, Johannes; Magusin, Pieter C M M; Buntkowsky, Gerd
2012-01-01
Para hydrogen induced polarization (PHIP) is a powerful hyperpolarization technique, which increases the NMR sensitivity by several orders of magnitude. However the hyperpolarized signal is created as an anti-phase signal, which necessitates high magnetic field homogeneity and spectral resolution in the conventional PHIP schemes. This hampers the application of PHIP enhancement in many fields, as for example in food science, materials science or MRI, where low B(0)-fields or low B(0)-homogeneity do decrease spectral resolution, leading to potential extinction if in-phase and anti-phase hyperpolarization signals cannot be resolved. Herein, we demonstrate that the echo sequence (45°-τ-180°-τ) enables the acquisition of low resolution PHIP enhanced liquid state NMR signals of phenylpropiolic acid derivatives and phenylacetylene at a low cost low-resolution 0.54 T spectrometer. As low field TD-spectrometers are commonly used in industry or biomedicine for the relaxometry of oil-water mixtures, food, nano-particles, or other systems, we compare two variants of para-hydrogen induced polarization with data-evaluation in the time domain (TD-PHIP). In both TD-ALTADENA and the TD-PASADENA strong spin echoes could be detected under conditions when usually no anti-phase signals can be measured due to the lack of resolution. The results suggest that the time-domain detection of PHIP-enhanced signals opens up new application areas for low-field PHIP-hyperpolarization, such as non-invasive compound detection or new contrast agents and biomarkers in low-field Magnetic Resonance Imaging (MRI). Finally, solid-state NMR calculations are presented, which show that the solid echo (90y-τ-90x-τ) version of the TD-ALTADENA experiment is able to convert up to 10% of the PHIP signal into visible magnetization.
A Fourier collocation time domain method for numerically solving Maxwell's equations
NASA Technical Reports Server (NTRS)
Shebalin, John V.
1991-01-01
A new method for solving Maxwell's equations in the time domain for arbitrary values of permittivity, conductivity, and permeability is presented. Spatial derivatives are found by a Fourier transform method and time integration is performed using a second order, semi-implicit procedure. Electric and magnetic fields are collocated on the same grid points, rather than on interleaved points, as in the Finite Difference Time Domain (FDTD) method. Numerical results are presented for the propagation of a 2-D Transverse Electromagnetic (TEM) mode out of a parallel plate waveguide and into a dielectric and conducting medium.
NASA Technical Reports Server (NTRS)
Luebbers, Raymond J.; Beggs, John H.
1991-01-01
Radar cross section (RCS) calculations for flat, perfectly conducting plates are readily available through the use of conventional frequency domain techniques such as the Method of Moments (MOM). However, if the plate is covered with a dielectric material that is relatively thick in comparison with the wavelength in the material, these frequency domain techniques become increasingly difficult to apply. We present the application of the Finite Difference Time Domain (FDTD) Technique to the problem of electromagnetic scattering and RCS calculations from a thin, perfectly conducting plate that is coated with a thick layer of lossless dielectric material. Both time domain and RCS calculations are presented and disclosed.
NASA Technical Reports Server (NTRS)
Luebbers, Raymond J.; Beggs, John H.
1991-01-01
Radar cross section (RCS) calculations for flat, perfectly conducting plates are readily available through the use of conventional frequency domain techniques such as the Method of Moments (MOM). However, if the plate is covered with a dielectric material that is relatively thick in comparison with the wavelength in the material, these frequency domain techniques become increasingly difficult to apply. The application is presented of the Finite Difference Time Domain (FDTD) technique to the problem of electromagnetic scattering and RCS calculations from a thin, perfectly conducting plate that is coated with a thick layer of lossless dielectric material. Both time domain and RCS calculations are presented and discussed.
Applications of pattern classification to time-domain signals
NASA Astrophysics Data System (ADS)
Bertoncini, Crystal Ann
Many different kinds of physics are used in sensors that produce time-domain signals, such as ultrasonics, acoustics, seismology, and electromagnetics. The waveforms generated by these sensors are used to measure events or detect flaws in applications ranging from industrial to medical and defense-related domains. Interpreting the signals is challenging because of the complicated physics of the interaction of the fields with the materials and structures under study. Often the method of interpreting the signal varies by the application, but automatic detection of events in signals is always useful in order to attain results quickly with less human error. One method of automatic interpretation of data is pattern classification, which is a statistical method that assigns predicted labels to raw data associated with known categories. In this work, we use pattern classification techniques to aid automatic detection of events in signals using features extracted by a particular application of the wavelet transform, the Dynamic Wavelet Fingerprint (DWFP), as well as features selected through physical interpretation of the individual applications. The wavelet feature extraction method is general for any time-domain signal, and the classification results can be improved by features drawn for the particular domain. The success of this technique is demonstrated through four applications: the development of an ultrasonographic periodontal probe, the identification of flaw type in Lamb wave tomographic scans of an aluminum pipe, prediction of roof falls in a limestone mine, and automatic identification of individual Radio Frequency Identification (RFID) tags regardless of its programmed code. The method has been shown to achieve high accuracy, sometimes as high as 98%.
Casimir forces in the time domain: Applications
McCauley, Alexander P.; Rodriguez, Alejandro W.; Joannopoulos, John D.; Johnson, Steven G.
2010-01-15
Our previous article [Phys. Rev. A 80, 012115 (2009)] introduced a method to compute Casimir forces in arbitrary geometries and for arbitrary materials that was based on a finite-difference time-domain (FDTD) scheme. In this article, we focus on the efficient implementation of our method for geometries of practical interest and extend our previous proof-of-concept algorithm in one dimension to problems in two and three dimensions, introducing a number of new optimizations. We consider Casimir pistonlike problems with nonmonotonic and monotonic force dependence on sidewall separation, both for previously solved geometries to validate our method and also for new geometries involving magnetic sidewalls and/or cylindrical pistons. We include realistic dielectric materials to calculate the force between suspended silicon waveguides or on a suspended membrane with periodic grooves, also demonstrating the application of perfectly matched layer (PML) absorbing boundaries and/or periodic boundaries. In addition, we apply this method to a realizable three-dimensional system in which a silica sphere is stably suspended in a fluid above an indented metallic substrate. More generally, the method allows off-the-shelf FDTD software, already supporting a wide variety of materials (including dielectric, magnetic, and even anisotropic materials) and boundary conditions, to be exploited for the Casimir problem.
Time-domain diffuse correlation spectroscopy
Sutin, Jason; Zimmerman, Bernhard; Tyulmankov, Danil; Tamborini, Davide; Wu, Kuan Cheng; Selb, Juliette; Gulinatti, Angelo; Rech, Ivan; Tosi, Alberto; Boas, David A.; Franceschini, Maria Angela
2016-01-01
Physiological monitoring of oxygen delivery to the brain has great significance for improving the management of patients at risk for brain injury. Diffuse correlation spectroscopy (DCS) is a rapidly growing optical technology able to non-invasively assess the blood flow index (BFi) at the bedside. The current limitations of DCS are the contamination introduced by extracerebral tissue and the need to know the tissue’s optical properties to correctly quantify the BFi. To overcome these limitations, we have developed a new technology for time-resolved diffuse correlation spectroscopy. By operating DCS in the time domain (TD-DCS), we are able to simultaneously acquire the temporal point-spread function to quantify tissue optical properties and the autocorrelation function to quantify the BFi. More importantly, by applying time-gated strategies to the DCS autocorrelation functions, we are able to differentiate between short and long photon paths through the tissue and determine the BFi for different depths. Here, we present the novel device and we report the first experiments in tissue-like phantoms and in rodents. The TD-DCS method opens many possibilities for improved non-invasive monitoring of oxygen delivery in humans. PMID:28008417
Reengineering observatory operations for the time domain
NASA Astrophysics Data System (ADS)
Seaman, Robert L.; Vestrand, W. T.; Hessman, Frederic V.
2014-07-01
Observatories are complex scientific and technical institutions serving diverse users and purposes. Their telescopes, instruments, software, and human resources engage in interwoven workflows over a broad range of timescales. These workflows have been tuned to be responsive to concepts of observatory operations that were applicable when various assets were commissioned, years or decades in the past. The astronomical community is entering an era of rapid change increasingly characterized by large time domain surveys, robotic telescopes and automated infrastructures, and - most significantly - of operating modes and scientific consortia that span our individual facilities, joining them into complex network entities. Observatories must adapt and numerous initiatives are in progress that focus on redesigning individual components out of the astronomical toolkit. New instrumentation is both more capable and more complex than ever, and even simple instruments may have powerful observation scripting capabilities. Remote and queue observing modes are now widespread. Data archives are becoming ubiquitous. Virtual observatory standards and protocols and astroinformatics data-mining techniques layered on these are areas of active development. Indeed, new large-aperture ground-based telescopes may be as expensive as space missions and have similarly formal project management processes and large data management requirements. This piecewise approach is not enough. Whatever challenges of funding or politics facing the national and international astronomical communities it will be more efficient - scientifically as well as in the usual figures of merit of cost, schedule, performance, and risks - to explicitly address the systems engineering of the astronomical community as a whole.
How Swift is redefining time domain astronomy
NASA Astrophysics Data System (ADS)
Gehrels, N.; Cannizzo, J. K.
2015-09-01
NASA's Swift satellite has completed ten years of amazing discoveries in time domain astronomy. Its primary mission is to chase gamma-ray bursts (GRBs), but due to its scheduling flexibility it has subsequently become a prime discovery machine for new types of behavior. The list of major discoveries in GRBs and other transients includes the long-lived X-ray afterglows and flares from GRBs, the first accurate localization of short GRBs, the discovery of GRBs at high redshift (z > 8), supernova shock break-out from SN Ib, a jetted tidal disruption event, an ultra-long class of GRBs, high energy emission from flare stars, novae and supernovae with unusual characteristics, magnetars with glitches in their spin periods, and a short GRB with evidence of an accompanying kilonova. Swift has developed a dynamic synergism with ground based observatories. In a few years gravitational wave observatories will come on-line and provide exciting new transient sources for Swift to study.
Nondestructive Evaluation of Aircraft Composites Using Terahertz Time Domain Spectroscopy
2008-12-10
Taday, P. F., Pepper , M. (2008). Elimination of scattering effects in spectral measurement of granulated materials using terahertz time domain...W., Ferguson , B., Rainsford, T., Mickan, S. P., & Abbott, D. (2005). Material parameter extraction for terahertz time-domain spectroscopy using... Ferguson , B., Rainsford, T., Mickan, S. P., & Abbott, D. (2005). Simple material parameter estimation via terahertz time-domain spectroscopy
A Persistent Feature of Multiple Scattering of Waves in the Time-Domain: A Tutorial
NASA Technical Reports Server (NTRS)
Lock, James A.; Mishchenko, Michael I.
2015-01-01
The equations for frequency-domain multiple scattering are derived for a scalar or electromagnetic plane wave incident on a collection of particles at known positions, and in the time-domain for a plane wave pulse incident on the same collection of particles. The calculation is carried out for five different combinations of wave types and particle types of increasing geometrical complexity. The results are used to illustrate and discuss a number of physical and mathematical characteristics of multiple scattering in the frequency- and time-domains. We argue that frequency-domain multiple scattering is a purely mathematical construct since there is no temporal sequencing information in the frequency-domain equations and since the multi-particle path information can be dispelled by writing the equations in another mathematical form. However, multiple scattering becomes a definite physical phenomenon in the time-domain when the collection of particles is illuminated by an appropriately short localized pulse.
Time Domain Viscoelastic Full Waveform Inversion
NASA Astrophysics Data System (ADS)
Fabien-Ouellet, Gabriel; Gloaguen, Erwan; Giroux, Bernard
2017-03-01
Viscous attenuation can have a strong impact on seismic wave propagation, but it is rarely taken into account in full waveform inversion (FWI). When viscoelasticity is considered in time domain FWI, the displacement formulation of the wave equation is usually used instead of the popular velocity-stress formulation. However, inversion schemes rely on the adjoint equations, which are quite different for the velocity-stress formulation than for the displacement formulation. In this paper, we apply the adjoint state method to the isotropic viscoelastic wave equation in the velocity-stress formulation based on the generalized standard linear solid rheology. By applying linear transformations to the wave equation before deriving the adjoint state equations, we obtain two symmetric sets of partial differential equations for the forward and adjoint variables. The resulting sets of equations only differ by a sign change and can be solved by the same numerical implementation. We also investigate the crosstalk between parameter classes (velocity and attenuation) of the viscoelastic equation. More specifically, we show that the attenuation levels can be used to recover the quality factors of P- and S- waves, but that they are very sensitive to velocity errors. Finally, we present a synthetic example of viscoelastic FWI in the context of monitoring CO2 geological sequestration. We show that FWI based on our formulation can indeed recover P- and S- wave velocities and their attenuation levels when attenuation is high enough. Both changes in velocity and attenuation levels recovered with FWI can be used to track the CO2 plume during and after injection. Further studies are required to evaluate the performance of viscoelastic FWI on real data.
Time-domain reconstruction using sensitivity coefficients for limited view ultrawide band tomography
NASA Astrophysics Data System (ADS)
Abdullah, M. Z.; Yin, W.; Bilal, M.; Armitage, D. W.; Mackin, R.; Peyton, A. J.
2007-08-01
This article addresses time-domain ultrawide band (UWB) electromagnetic tomography for reconstructing the unknown spatial characteristic of an object from observations of the arrivals of short electromagnetic (EM) pulses. Here, the determination of the first peak arrival of the EM traces constitutes the forward problem, and the inverse problem aims to reconstruct the EM property distribution of the media. In this article, the finite-difference time-domain method implementing a perfectly matched layer is used to solve the forward problem from which the system sensitivity maps are determined. Image reconstruction is based on the combination of a linearized update and regularized Landweber minimization algorithm. Experimental data from a laboratory UWB system using targets of different contrasts, sizes, and shapes in an aqueous media are presented. The results show that this technique can accurately detect and locate unknown targets in spite of the presence of significant levels of noise in the data.
Time-Domain vs. Frequency-Domain CSEM: Implications for Marine Exploration
NASA Astrophysics Data System (ADS)
Connell, D. M.; Key, K. W.
2010-12-01
The frequency-domain marine controlled source electromagnetic (CSEM) method is now routinely applied to map resistive hydrocarbons buried beneath the seabed in deepwater. Alternatively, it has been suggested that time-domain CSEM methods may offer improved resolution of difficult targets such as deeply buried reservoirs. Furthermore, time-domain methods may overcome a sensitivity limitation imposed by the airwave saturation that is experienced for shallow-water frequency-domain CSEM. In order to examine and test these claims, we have developed a modeling code for computing time-domain responses for layered 1D models with arbitrarily located and oriented transmitters and receivers. Our code extends the open-source frequency domain code Dipole1D by efficiently computing the time-domain step-on and impulse responses by Fourier transformation of the frequency-domain kernels. By applying a realistic noise model to synthetic data generated from this code, we systematically examine the sensitivity and resolution of time-domain and frequency-domain CSEM to representative targets of interest for offshore hydrocarbon exploration and exploration surveys of seafloor volcanic and hydrothermal systems. These studies have practical implications for marine EM survey systems that use either towed or stationary transmitters and receivers.
Application of Time Domain Reflectometers in Urban Settings ...
Time domain reflectometers (TDRs) are sensors that measure the volumetric water content of soils and porous media. The sensors consist of stainless steel rods connected to a circuit board in an epoxy housing. An electromagnetic pulse is propagated along the rods. The time, or period, required for the signal to travel down the rods and back varies with the volumetric water content of the surrounding media and temperature. A calibration curve is needed for the specific media. TDRs were developed mostly for agricultural applications; however, the technology has also been applied to forestry and ecological research. This study demonstrates the use of TDRs for quantifying drainage properties in low impact development (LID) stormwater controls, specifically permeable pavement and rain garden systems. TDRs were successfully used to monitor the responses of urban fill, engineered bioretention media, and the aggregate storage layer under permeable pavement to multiple rain events of varying depth, intensity, and duration. The hydrologic performance of permeable pavement and rain garden systems has previously been quantified for underdrain systems, but there have been few studies of systems that drain to the underlying soils. We know of no published studies outlining the use of TDR technology to document drainage properties in media other than soil. In this study TDRs were installed at multiple locations and depths in underlying urban fill soils, engineered bior
Implicit time-domain simulation of metamaterials on GPUs
NASA Astrophysics Data System (ADS)
Cooke, Simon; Levush, Baruch
2010-11-01
Metamaterials present a challenge to 3D electromagnetic simulation due to their sub-wavelength structural features, demanding spatial grid cell sizes typically λ/50. This is similar to the situation found modeling conventional slow-wave structures, such as TWTs. For explicit, finite-difference time-domain (FDTD) techniques, numerical stability further dictates the use of very small time steps, leading to long simulation times for wave propagation in metamaterials. We present simulations using a new alternating direction implicit (ADI) FDTD algorithm [1,2] implemented efficiently for high performance graphics processing units (GPUs). Our method uses a complex-envelope representation for the field amplitudes to factor out the rf timescale, and is absolutely stable. Consequently, we are able to use time steps comparable to the rf period for narrow-bandwidth simulations, and reduce simulation times by orders of magnitude compared to conventional FDTD on CPUs. Simulation results will be presented for a number of metamaterial structures. [1] S. J. Cooke et al., Int. J. Numer. Model., 22, 187 (2009) [2] M. Botton et al., IEEE Trans. Plasma Sci., 38 (6), 1439 (2010)
Time-domain measurement of broadband coherent Cherenkov radiation
Miocinovic, P.; Gorham, P. W.; Guillian, E.; Milincic, R.; Field, R. C.; Walz, D.; Saltzberg, D.; Williams, D.
2006-08-15
We report on further analysis of coherent microwave Cherenkov impulses emitted via the Askaryan mechanism from high-energy electromagnetic showers produced at the Stanford Linear Accelerator Center (SLAC). In this report, the time-domain based analysis of the measurements made with a broadband (nominally 1-18 GHz) log periodic dipole array antenna is described. The theory of a transmit-receive antenna system based on time-dependent effective height operator is summarized and applied to fully characterize the measurement antenna system and to reconstruct the electric field induced via the Askaryan process. The observed radiation intensity and phase as functions of frequency were found to agree with expectations from 0.75-11.5 GHz within experimental errors on the normalized electric field magnitude and the relative phase; {sigma}{sub RvertcalbarEverticalbar}=0.039 {mu}V/MHz/TeV and {sigma}{sub {phi}}=17 deg. This is the first time this agreement has been observed over such a broad bandwidth, and the first measurement of the relative phase variation of an Askaryan pulse. The importance of validation of the Askaryan mechanism is significant since it is viewed as the most promising way to detect cosmogenic neutrino fluxes at E{sub {nu}}(greater-or-similar sign)10{sup 15} eV.
Time-Domain Measurement of Broadband Coherent Cherenkov Radiation
Miocinovic, P.; Field, R.C.; Gorham, P.W.; Guillian, E.; Milincic, R.; Saltzberg, D.; Walz, D.; Williams, D.; /UCLA
2006-03-13
We report on further analysis of coherent microwave Cherenkov impulses emitted via the Askaryan mechanism from high-energy electromagnetic showers produced at the Stanford Linear Accelerator Center (SLAC). In this report, the time-domain based analysis of the measurements made with a broadband (nominally 1-18 GHz) log periodic dipole antenna (LPDA) is described. The theory of a transmit-receive antenna system based on time-dependent effective height operator is summarized and applied to fully characterize the measurement antenna system and to reconstruct the electric field induced via the Askaryan process. The observed radiation intensity and phase as functions of frequency were found to agree with expectations from 0.75-11.5 GHz within experimental errors on the normalized electric field magnitude and the relative phase; {sigma}{sub R|E|} = 0.039 {micro}V/MHz/TeV and {sigma}{sub {phi}} = 17{sup o}. This is the first time this agreement has been observed over such a broad bandwidth, and the first measurement of the relative phase variation of an Askaryan pulse. The importance of validation of the Askaryan mechanism is significant since it is viewed as the most promising way to detect cosmogenic neutrino fluxes at E{sub v} {ge} 10{sup 15} eV.
Gabran, S R I; Saad, J H; Salama, M M A; Mansour, R R
2009-01-01
This paper demonstrates the electromagnetic modeling and simulation of an implanted Medtronic deep brain stimulation (DBS) electrode using finite difference time domain (FDTD). The model is developed using Empire XCcel and represents the electrode surrounded with brain tissue assuming homogenous and isotropic medium. The model is created to study the parameters influencing the electric field distribution within the tissue in order to provide reference and benchmarking data for DBS and intra-cortical electrode development.
NASA Technical Reports Server (NTRS)
Kowalski, Marc Edward
2009-01-01
A method for the prediction of time-domain signatures of chafed coaxial cables is presented. The method is quasi-static in nature, and is thus efficient enough to be included in inference and inversion routines. Unlike previous models proposed, no restriction on the geometry or size of the chafe is required in the present approach. The model is validated and its speed is illustrated via comparison to simulations from a commercial, three-dimensional electromagnetic simulator.
NASA Astrophysics Data System (ADS)
Minsley, B. J.; Brodie, R. C.; Bedrosian, P.; Esfahani, A.
2013-12-01
Geophysical data are typically used to infer a single ';best' model consistent with observations and prior information. However, because of non-uniqueness, limited resolution, and data errors, many models satisfy both the data and reasonable prior assumptions. Instead of seeking to describe the properties of any single model, we developed a trans-dimensional Bayesian Markov chain Monte Carlo (McMC) algorithm for the analysis of airborne electromagnetic (AEM) surveys that assesses the characteristics of models that are consistent with observations and prior assumptions. This is a powerful tool for model assessment and uncertainty analysis, and provides a wealth of information that can be used to make inferences about plausible subsurface properties. For example, we can estimate the likelihood of geological interfaces as a function of depth, quantify the probability that resistivity is above or below a certain threshold within a given depth range, assess model resolution and depth of investigation, or query subsets of models that are consistent with auxiliary datasets. Model assessment and uncertainty analysis is compounded by the large volume of data that are typically acquired for AEM surveys. Here, we discuss the mechanics of a McMC algorithm developed for the analysis of time- or frequency-domain airborne electromagnetic data, along with examples where this algorithm has been used to add new insight into model uncertainty and geological interpretations. Specific aspects of the algorithm that will be discussed include: the trans-dimensional nature of the program, which allows the number of layers to be a free parameter; the capability to assess random and/or systematic data errors as unknown parameters; the use of parallel computing tools to run multiple chains for a single dataset in order to assess convergence, and to analyze many datasets simultaneously; the use of stochastic Newton sampling to optimize sampling efficiency; and the ability to integrate multiple
NASA Astrophysics Data System (ADS)
Pryet, A.; d'Ozouville, N.; Violette, S.; Deffontaines, B.; Auken, E.
2012-08-01
Many volcanic islands face freshwater stress and the situation may worsen with climate change and sea level rise. In this context, an optimum management of freshwater resources becomes crucial, but is often impeded by the lack of data. With the aim of investigating the hydrogeological settings of Southern San Cristóbal Island (Galapagos), we conducted an helicopter-borne, transient electromagnetic survey with the SkyTEM system. It provided unprecedented insights in the 3-D resistivity structure of this extinct basaltic shield. Combined with remote sensing and fieldwork, it allowed the definition of the first hydrogeological conceptual model of the island. Springs are fed by a series of perched aquifers overlying a regional basal aquifer subject to seawater intrusion. Dykes, evidenced by alignments of eruptive cones at the surface, correspond to sharp sub-vertical contrasts in resistivity in the subsurface, and impound groundwater in a summit channel. Combined with geomorphological observations, airborne electromagnetics is shown to be a useful tool for hydrogeological exploratory studies in complex, poorly known environments. It allows optimal development of land-based geophysical surveys and drilling campaigns.
NASA Astrophysics Data System (ADS)
Pryet, A.; d'Ozouville, N.; Violette, S.; Deffontaines, B.; Auken, E.
2012-12-01
Many volcanic islands face freshwater stress and the situation may worsen with climate change and sea level rise. In this context, an optimum management of freshwater resources becomes crucial, but is often impeded by the lack of data. With the aim of investigating the hydrogeological settings of southern San Cristóbal Island (Galapagos), we conducted a helicopter-borne, transient electromagnetic survey with the SkyTEM system. It provided unprecedented insights into the 3-D resistivity structure of this extinct basaltic shield. Combined with remote sensing and fieldwork, it allowed the definition of the first hydrogeological conceptual model of the island. Springs are fed by a series of perched aquifers overlying a regional basal aquifer subject to seawater intrusion. Dykes, evidenced by alignments of eruptive cones at the surface, correspond to sharp sub-vertical contrasts in resistivity in the subsurface, and impound groundwater in a summit channel. Combined with geomorphological observations, airborne electromagnetics are shown to be a useful for hydrogeological exploratory studies in complex, poorly known environments. They allow optimal development of land-based geophysical surveys and drilling campaigns.
NASA Astrophysics Data System (ADS)
Viquerat, Jonathan; Lanteri, Stéphane
2016-01-01
During the last ten years, the discontinuous Galerkin time-domain (DGTD) method has progressively emerged as a viable alternative to well established finite-difference time-domain (FDTD) and finite-element time-domain (FETD) methods for the numerical simulation of electromagnetic wave propagation problems in the time-domain. The method is now actively studied in various application contexts including those requiring to model light/matter interactions on the nanoscale. Several recent works have demonstrated the viability of the DGDT method for nanophotonics. In this paper we further demonstrate the capabilities of the method for the simulation of near-field plasmonic interactions by considering more particularly the possibility of combining the use of a locally refined conforming tetrahedral mesh with a local adaptation of the approximation order.
2016-07-06
The work reported in this paper is a part of on-going studies to clarify how and to what extent soil electromagnetic properties affect the...performance of induction metal detectors widely used in humanitarian demining. This paper studies the specific case of the time-domain response of a small
Femtosecond time-domain observation of atmospheric absorption in the near-infrared spectrum
NASA Astrophysics Data System (ADS)
Hammond, T. J.; Monchocé, Sylvain; Zhang, Chunmei; Brown, Graham G.; Corkum, P. B.; Villeneuve, D. M.
2016-12-01
As light propagates through a medium, absorption caused by electronic or rovibrational transitions is evident in the transmitted spectrum. The incident electromagnetic field polarizes the medium and the absorption is due to the imaginary part of the linear susceptibility. In the time domain, the field establishes a coherence in the medium that radiates out of phase with the initial field. This coherence can persist for tens of picoseconds in atmospheric molecules such as H2O . We propagate a few-cycle laser pulse centered at 1.8 μ m through the atmosphere and measure the long-lasting molecular coherence in the time domain by high-order harmonic cross correlation. The measured optical free-induction decay of the pulse is compared with a calculation based on the calculated rovibrational spectrum of H2O absorption.
Sarshar, A.; Iravani, M.R.; Li, J.
1996-01-01
In this paper, noncharacteristic harmonics of an HVdc converter station are calculated based on the use of digital time-domain simulation methods. An enhanced version of the Electromagnetic Transients Program (EMTP) is used for the studies. The noncharacteristic harmonics of interest are (1) the dc side triplen harmonics, and (2) the ac side second harmonic. Impacts of loading conditions, neutral filter, and converter firing angle on the dc side triplen harmonics are discussed. Effects of ac side network parameters, static VAR compensator (SVC), transformer half-cycle saturation, and Geomagnetically Induced Current (GIC) on the ac side second harmonic instability are also presented. This paper concludes that the digital time-domain simulation method provides significant flexibility for accurate prediction of (1) generation mechanism, and (2) adverse impacts of HVdc noncharacteristic harmonics.
In-Vivo Time Domain Measurement of Dielectric Properties of Human Body Tissue
NASA Astrophysics Data System (ADS)
Koyama, Kazunori; Hirata, Akimasa; Wang, Jianquing; Fujiwara, Osamu
It is essential to measure dielectric properties of human tissues for the safety evaluation of electromagnetic field exposures. In this paper, towards developing an in-vivo measurement method for living human tissues, we employed an open-ended coaxial probe together with a time domain reflectometry (TDR) technique, which probably enables us to extract a reflected waveform from some specified tissues in the time domain. We compared the TDR-measured dielectric properties for human surface tissues with those derived from a conventional frequency-domain technique. As a result, we found a fair agreement between them in the frequency range from 300 MHz to 6 GHz. This result suggests the possibility of in-vivo dielectric property measurement for superficial human tissues by using the proposed TDR technique.
SanFilipo, Bill
2000-04-01
The objective of this program is to perform research to advance the science in the application of both passive and active electromagnetic measurement techniques for the detection and spatial delineation of underground facilities. Passive techniques exploit the electromagnetic fields generated by electrical apparatus within the structure, including generators, motors, power distribution circuitry, as well as communications hardware and similar electronics equipment. Frequencies monitored are generally in the audio range (60-20,000 Hz), anticipating strong sources associated with normal AC power (i.e., 50 or 60 Hz and associated harmonics), and low frequency power from broad-band sources such as switching circuits. Measurements are made using receiver induction coils wired to electronics that digitize and record the voltage induced by the time varying magnetic fields. Active techniques employ electromagnetic field transmitters in the form of AC current carrying loops also in the audio frequency range, and receiving coils that measure the resultant time varying magnetic fields. These fields are perturbed from those expected in free space by any conductive material in the vicinity of the coils, including the ground, so that the total measured field is comprised of the primary free-space component and the secondary scattered component. The latter can be further delineated into an average background field (uniform conductive half-space earth) and anomalous field associated with heterogeneous zones in the earth, including both highly conductive objects such as metallic structures as well as highly resistive structures such as empty voids corresponding to rooms or tunnels. Work performed during Phase I included the development of the prototype GEM-2H instrumentation, collection of data at several test sites in the passive mode and a single site in the active mode, development of processing and interpretation software. The technical objectives of Phase II were to: (1
Time domain solutions for a coasting beam with impedance feedback
Blaskiewicz, M.
1993-06-01
Time domain solutions for a coasting beam interacting with a longitudinal or transverse impedance are presented. The treatment is limited to first order perturbation theory, but it includes Landau damping.
Time domain solutions for a coasting beam with impedance feedback
Blaskiewicz, M.
1993-01-01
Time domain solutions for a coasting beam interacting with a longitudinal or transverse impedance are presented. The treatment is limited to first order perturbation theory, but it includes Landau damping.
Time domain referencing in intensity modulation fiber optic sensing systems
NASA Technical Reports Server (NTRS)
Adamovsky, Grigory
1986-01-01
Intensity modulation sensors are classified by the way in which the reference and signal channels are separated: in space, wavelength, or time domains. To implement the time-domain referencing, different types of fiber-optic loops have been used. A pulse of short duration sent into the loop results in a series of pulses of different amplitudes. The information about the measured parameter is retrieved from the relative amplitudes of pulses in the same train.
Time domain referencing in intensity modulation fiber optic sensing systems
NASA Technical Reports Server (NTRS)
Adamovsky, G.
1986-01-01
Intensity modulation sensors are classified depending on the way in which the reference and signal channels are separated: in space, wavelength (frequency), or time domains. To implement the time domain referencing different types of fiber optic (FO) loops have been used. A pulse of short duration sent into the loop results in a series of pulses of different amplitudes. The information about the measured parameter is retrieved from the relative amplitudes of pulses in the same train.
3D Vectorial Time Domain Computational Integrated Photonics
Kallman, J S; Bond, T C; Koning, J M; Stowell, M L
2007-02-16
The design of integrated photonic structures poses considerable challenges. 3D-Time-Domain design tools are fundamental in enabling technologies such as all-optical logic, photonic bandgap sensors, THz imaging, and fast radiation diagnostics. Such technologies are essential to LLNL and WFO sponsors for a broad range of applications: encryption for communications and surveillance sensors (NSA, NAI and IDIV/PAT); high density optical interconnects for high-performance computing (ASCI); high-bandwidth instrumentation for NIF diagnostics; micro-sensor development for weapon miniaturization within the Stockpile Stewardship and DNT programs; and applications within HSO for CBNP detection devices. While there exist a number of photonics simulation tools on the market, they primarily model devices of interest to the communications industry. We saw the need to extend our previous software to match the Laboratory's unique emerging needs. These include modeling novel material effects (such as those of radiation induced carrier concentrations on refractive index) and device configurations (RadTracker bulk optics with radiation induced details, Optical Logic edge emitting lasers with lateral optical inputs). In addition we foresaw significant advantages to expanding our own internal simulation codes: parallel supercomputing could be incorporated from the start, and the simulation source code would be accessible for modification and extension. This work addressed Engineering's Simulation Technology Focus Area, specifically photonics. Problems addressed from the Engineering roadmap of the time included modeling the Auston switch (an important THz source/receiver), modeling Vertical Cavity Surface Emitting Lasers (VCSELs, which had been envisioned as part of fast radiation sensors), and multi-scale modeling of optical systems (for a variety of applications). We proposed to develop novel techniques to numerically solve the 3D multi-scale propagation problem for both the microchip
ASIC-enabled High Resolution Optical Time Domain Reflectometer
NASA Astrophysics Data System (ADS)
Skendzic, Sandra
Fiber optics has become the preferred technology in communication systems because of what it has to offer: high data transmission rates, immunity to electromagnetic interference, and lightweight, flexible cables. An optical time domain reflectometer (OTDR) provides a convenient method of locating and diagnosing faults (e.g. break in a fiber) along a fiber that can obstruct crucial optical pathways. Both the ability to resolve the precise location of the fault and distinguish between two discrete, closely spaced faults are figures of merit. This thesis presents an implementation of a high resolution OTDR through the use of a compact and programmable ASIC (application specific integrated circuit). The integration of many essential OTDR functions on a single chip is advantageous over existing commercial instruments because it enables small, lightweight packaging, and offers low power and cost efficiency. Furthermore, its compactness presents the option of placing multiple ASICs in parallel, which can conceivably ease the characterization of densely populated fiber optic networks. The OTDR ASIC consists of a tunable clock, pattern generator, precise timer, electrical receiver, and signal sampling circuit. During OTDR operation, the chip generates narrow electrical pulse, which can then be converted to optical format when coupled with an external laser diode driver. The ASIC also works with an external photodetector to measure the timing and amplitude of optical reflections in a fiber. It has a 1 cm sampling resolution, which allows for a 2 cm spatial resolution. While this OTDR ASIC has been previously demonstrated for multimode fiber fault diagnostics, this thesis focuses on extending its functionality to single mode fiber. To validate this novel approach to OTDR, this thesis is divided into five chapters: (1) introduction, (2) implementation, (3), performance of ASIC-based OTDR, (4) exploration in optical pre-amplification with a semiconductor optical amplifier, and
Time-domain boundary conditions for outdoor ground surfaces
NASA Astrophysics Data System (ADS)
Collier, Sandra L.; Ostashev, Vladimir E.; Wilson, D. Keith; Marlin, David H.
2003-10-01
Finite-difference time-domain techniques are promising for detailed dynamic simulations of sound propagation in complex atmospheric environments. Success of such simulations requires the development of new techniques to accurately handle the reflective and absorptive properties of a porous ground. One method of treating the ground boundary condition in the time domain [Salomons et al., Acta Acust. 88, 483-492 (2002)] is to use modified fluid dynamic equations, where the ground is considered as a porous medium described by its physical properties. However, this approach significantly increases computation time, as the domain must be extended into the ground and a large number of grid points are needed. Standard impedance models for the ground boundary condition are frequency-domain models, which generally are non-causal [Y. H. Berthelot, J. Acoust. Soc. Am. 109, 1736-1739 (2001)]. The development of a time-domain boundary condition from these models requires removing the singularity from the impedance equation when transforming from the frequency domain to the time domain. Alternatively, as the impedance boundary condition is a flux equation, a time-domain boundary condition can be derived from first principles, using the physical properties of the ground. We report on our development of a time-domain ground boundary condition.
Aberration correction for time-domain ultrasound diffraction tomography.
Mast, T Douglas
2002-07-01
Extensions of a time-domain diffraction tomography method, which reconstructs spatially dependent sound speed variations from far-field time-domain acoustic scattering measurements, are presented and analyzed. The resulting reconstructions are quantitative images with applications including ultrasonic mammography, and can also be considered candidate solutions to the time-domain inverse scattering problem. Here, the linearized time-domain inverse scattering problem is shown to have no general solution for finite signal bandwidth. However, an approximate solution to the linearized problem is constructed using a simple delay-and-sum method analogous to "gold standard" ultrasonic beamforming. The form of this solution suggests that the full nonlinear inverse scattering problem can be approximated by applying appropriate angle- and space-dependent time shifts to the time-domain scattering data; this analogy leads to a general approach to aberration correction. Two related methods for aberration correction are presented: one in which delays are computed from estimates of the medium using an efficient straight-ray approximation, and one in which delays are applied directly to a time-dependent linearized reconstruction. Numerical results indicate that these correction methods achieve substantial quality improvements for imaging of large scatterers. The parametric range of applicability for the time-domain diffraction tomography method is increased by about a factor of 2 by aberration correction.
NASA Astrophysics Data System (ADS)
Hanson, Jordan
2014-03-01
The Antarctica Ross Ice Shelf Antenna Neutrino Array (ARIANNA) is a high energy astrophysical neutrino detector, currently under construction near McMurdo Station, Antarctica. The ARIANNA detector design is optimized for detection of Askaryan radio frequency pulses, created in the ice shelf above the Antarctic ocean, that originate from cosmogenic GZK neutrino interactions. A formal analysis of the electromagnetic properties of the ARIANNA detection chain in the time domain is presented, and combined with a theoretical understanding of the Askaryan signal. This combination produces signal templates, used to distinguish thermal backgrounds from true signal in the current ARIANNA data. The results of this data analysis are also presented.
Stretched-coordinate PMLs for Maxwell's equations in the discontinuous Galerkin time-domain method.
König, Michael; Prohm, Christopher; Busch, Kurt; Niegemann, Jens
2011-02-28
The discontinuous Galerkin time-domain method (DGTD) is an emerging technique for the numerical simulation of time-dependent electromagnetic phenomena. For many applications it is necessary to model the infinite space which surrounds scatterers and sources. As a result, absorbing boundaries which mimic its properties play a key role in making DGTD a versatile tool for various kinds of systems. Popular techniques include the Silver-Mϋller boundary condition and uniaxial perfectly matched layers (UPMLs). We provide novel instructions for the implementation of stretched-coordinate perfectly matched layers in a discontinuous Galerkin framework and compare the performance of the three absorbers for a three-dimensional test system.
Distributed fiber optical sensing of oxygen with optical time domain reflectometry.
Eich, Susanne; Schmälzlin, Elmar; Löhmannsröben, Hans-Gerd
2013-05-31
In many biological and environmental applications spatially resolved sensing of molecular oxygen is desirable. A powerful tool for distributed measurements is optical time domain reflectometry (OTDR) which is often used in the field of telecommunications. We combine this technique with a novel optical oxygen sensor dye, triangular-[4] phenylene (TP), immobilized in a polymer matrix. The TP luminescence decay time is 86 ns. The short decay time of the sensor dye is suitable to achieve a spatial resolution of some meters. In this paper we present the development and characterization of a reflectometer in the UV range of the electromagnetic spectrum as well as optical oxygen sensing with different fiber arrangements.
ANTARES: progress towards building a 'broker' of time-domain alerts
NASA Astrophysics Data System (ADS)
Saha, Abhijit; Wang, Zhe; Matheson, Thomas; Narayan, Gautham; Snodgrass, Richard; Kececioglu, John; Scheidegger, Carlos; Axelrod, Tim; Jenness, Tim; Ridgway, Stephen; Seaman, Robert; Taylor, Clark; Toeniskoetter, Jackson; Welch, Eric; Yang, Shuo; Zaidi, Tayeb
2016-07-01
The Arizona-NOAO Temporal Analysis and Response to Events System (ANTARES) is a joint effort of NOAO and the Department of Computer Science at the University of Arizona to build prototype software to process alerts from time-domain surveys, especially LSST, to identify those alerts that must be followed up immediately. Value is added by annotating incoming alerts with existing information from previous surveys and compilations across the electromagnetic spectrum and from the history of past alerts. Comparison against a knowledge repository of properties and features of known or predicted kinds of variable phenomena is used for categorization. The architecture and algorithms being employed are described.
Pastick, Neal J.; Jorgenson, M. Torre; Wylie, Bruce K.; Minsley, Burke J.; Ji, Lei; Walvoord, Michelle A.; Smith, Bruce D.; Abraham, Jared D.; Rose, Joshua R.
2013-01-01
Machine-learning regression tree models were used to extrapolate airborne electromagnetic resistivity data collected along flight lines in the Yukon Flats Ecoregion, central Alaska, for regional mapping of permafrost. This method of extrapolation (r = 0.86) used subsurface resistivity, Landsat Thematic Mapper (TM) at-sensor reflectance, thermal, TM-derived spectral indices, digital elevation models and other relevant spatial data to estimate near-surface (0–2.6-m depth) resistivity at 30-m resolution. A piecewise regression model (r = 0.82) and a presence/absence decision tree classification (accuracy of 87%) were used to estimate active-layer thickness (ALT) (< 101 cm) and the probability of near-surface (up to 123-cm depth) permafrost occurrence from field data, modelled near-surface (0–2.6 m) resistivity, and other relevant remote sensing and map data. At site scale, the predicted ALTs were similar to those previously observed for different vegetation types. At the landscape scale, the predicted ALTs tended to be thinner on higher-elevation loess deposits than on low-lying alluvial and sand sheet deposits of the Yukon Flats. The ALT and permafrost maps provide a baseline for future permafrost monitoring, serve as inputs for modelling hydrological and carbon cycles at local to regional scales, and offer insight into the ALT response to fire and thaw processes.
International Symposium on Airborne Geophysics
NASA Astrophysics Data System (ADS)
Mogi, Toru; Ito, Hisatoshi; Kaieda, Hideshi; Kusunoki, Kenichiro; Saltus, Richard W.; Fitterman, David V.; Okuma, Shigeo; Nakatsuka, Tadashi
2006-05-01
Airborne geophysics can be defined as the measurement of Earth properties from sensors in the sky. The airborne measurement platform is usually a traditional fixed-wing airplane or helicopter, but could also include lighter-than-air craft, unmanned drones, or other specialty craft. The earliest history of airborne geophysics includes kite and hot-air balloon experiments. However, modern airborne geophysics dates from the mid-1940s when military submarine-hunting magnetometers were first used to map variations in the Earth's magnetic field. The current gamut of airborne geophysical techniques spans a broad range, including potential fields (both gravity and magnetics), electromagnetics (EM), radiometrics, spectral imaging, and thermal imaging.
NASA Technical Reports Server (NTRS)
Ryan, Deirdre A.; Langdon, H. Scott; Beggs, John H.; Steich, David J.; Luebbers, Raymond J.; Kunz, Karl S.
1992-01-01
The approach chosen to model steady state scattering from jet engines with moving turbine blades is based upon the Finite Difference Time Domain (FDTD) method. The FDTD method is a numerical electromagnetic program based upon the direct solution in the time domain of Maxwell's time dependent curl equations throughout a volume. One of the strengths of this method is the ability to model objects with complicated shape and/or material composition. General time domain functions may be used as source excitations. For example, a plane wave excitation may be specified as a pulse containing many frequencies and at any incidence angle to the scatterer. A best fit to the scatterer is accomplished using cubical cells in the standard cartesian implementation of the FDTD method. The material composition of the scatterer is determined by specifying its electrical properties at each cell on the scatterer. Thus, the FDTD method is a suitable choice for problems with complex geometries evaluated at multiple frequencies. It is assumed that the reader is familiar with the FDTD method.
NASA Astrophysics Data System (ADS)
Viezzoli, Andrea; Kaminski, Vlad
2016-07-01
There have been multiple occurrences in the literature in the past several years of what has been referred to as the induced polarisation (IP) effect in airborne time domain electromagnetic (TDEM) data. This phenomenon is known to be responsible for incorrect inversion modelling of electrical resistivity, lower interpreted depth of investigation (DOI) and lost information about chargeability of the subsurface and other valuable parameters. Historically, there have been many suggestions to account for the IP effect using the Cole-Cole model. It has been previously demonstrated that the Cole-Cole model can be effective in modelling synthetic TDEM transients. In the current paper we show the possibility of extracting IP information from airborne TDEM data using this same concept, including inverse modelling of chargeability from TDEM data collected by VTEM, with field examples from Canada (Mt Milligan deposit) and Russia (Amakinskaya kimberlite pipe).
Hammack, R. W.
2006-12-28
subtle mine pool anomalies. However, post-survey modeling suggested that thicker, more conductive mine pools might be detected at a more suitable location. The current study sought to identify the best time domain electromagnetic sensor for detecting mine pools and to test it in an area where the mine pools are thicker and more conductive that those in southwestern Virginia. After a careful comparison of all airborne time domain electromagnetic sensors (including both helicopter and fixed-wing systems), the SkyTEM system from Denmark was determined to be the best technology for this application. Whereas most airborne time domain electromagnetic systems were developed to find large, deep, highly conductive mineral deposits, the SkyTEM system is designed for groundwater exploration studies, an application similar to mine pool detection.
Time-Domain Filtering for Spatial Large-Eddy Simulation
NASA Technical Reports Server (NTRS)
Pruett, C. David
1997-01-01
An approach to large-eddy simulation (LES) is developed whose subgrid-scale model incorporates filtering in the time domain, in contrast to conventional approaches, which exploit spatial filtering. The method is demonstrated in the simulation of a heated, compressible, axisymmetric jet, and results are compared with those obtained from fully resolved direct numerical simulation. The present approach was, in fact, motivated by the jet-flow problem and the desire to manipulate the flow by localized (point) sources for the purposes of noise suppression. Time-domain filtering appears to be more consistent with the modeling of point sources; moreover, time-domain filtering may resolve some fundamental inconsistencies associated with conventional space-filtered LES approaches.
Time domain averaging based on fractional delay filter
NASA Astrophysics Data System (ADS)
Wu, Wentao; Lin, Jing; Han, Shaobo; Ding, Xianghui
2009-07-01
For rotary machinery, periodic components in signals are always extracted to investigate the condition of each rotating part. Time domain averaging technique is a traditional method used to extract those periodic components. Originally, a phase reference signal is required to ensure all the averaged segments are with the same initial phase. In some cases, however, there is no phase reference; we have to establish some efficient algorithms to synchronize the segments before averaging. There are some algorithms available explaining how to perform time domain averaging without using phase reference signal. However, those algorithms cannot eliminate the phase error completely. Under this background, a new time domain averaging algorithm that has no phase error theoretically is proposed. The performance is improved by incorporating the fractional delay filter. The efficiency of the proposed algorithm is validated by some simulations.
Wind-instrument reflection function measurements in the time domain.
Keefe, D H
1996-04-01
Theoretical and computational analyses of wind-instrument sound production in the time domain have emerged as useful tools for understanding musical instrument acoustics, yet there exist few experimental measurements of the air-column response directly in the time domain. A new experimental, time-domain technique is proposed to measure the reflection function response of woodwind and brass-instrument air columns. This response is defined at the location of sound regeneration in the mouthpiece or double reed. A probe assembly comprised of an acoustic source and microphone is inserted directly into the air column entryway using a foam plug to ensure a leak-free fit. An initial calibration phase involves measurements on a single cylindrical tube of known dimensions. Measurements are presented on an alto saxophone and euphonium. The technique has promise for testing any musical instrument air columns using a single probe assembly and foam plugs over a range of diameters typical of air-column entryways.
New frontiers in time-domain diffuse optics, a review
NASA Astrophysics Data System (ADS)
Pifferi, Antonio; Contini, Davide; Mora, Alberto Dalla; Farina, Andrea; Spinelli, Lorenzo; Torricelli, Alessandro
2016-09-01
The recent developments in time-domain diffuse optics that rely on physical concepts (e.g., time-gating and null distance) and advanced photonic components (e.g., vertical cavity source-emitting laser as light sources, single photon avalanche diode, and silicon photomultipliers as detectors, fast-gating circuits, and time-to-digital converters for acquisition) are focused. This study shows how these tools could lead on one hand to compact and wearable time-domain devices for point-of-care diagnostics down to the consumer level and on the other hand to powerful systems with exceptional depth penetration and sensitivity.
Time-Domain Impedance Boundary Conditions for Computational Aeroacoustics
NASA Technical Reports Server (NTRS)
Tam, Christopher K. W.; Auriault, Laurent
1996-01-01
It is an accepted practice in aeroacoustics to characterize the properties of an acoustically treated surface by a quantity known as impedance. Impedance is a complex quantity. As such, it is designed primarily for frequency-domain analysis. Time-domain boundary conditions that are the equivalent of the frequency-domain impedance boundary condition are proposed. Both single frequency and model broadband time-domain impedance boundary conditions are provided. It is shown that the proposed boundary conditions, together with the linearized Euler equations, form well-posed initial boundary value problems. Unlike ill-posed problems, they are free from spurious instabilities that would render time-marching computational solutions impossible.
Time domain finite element analysis of multimode microwave applicators
Dibben, D.C.; Metaxas, R.
1996-05-01
Analysis of multimode applicators in the frequency domain via the finite element technique produces a set of very ill-conditioned equations. This paper outlines a time domain finite element method (TDFE) for analyzing three dimensional microwave applicators where this ill-conditioning is avoided. Edge elements are used in order to handle sharp metal edges and to avoid spurious solutions. Analysis in the time domain allows field distributions at a range of different frequencies to be obtained with a single calculation. Lumping is investigated as a means of reducing the time taken for the calculation. The reflection coefficient is also obtained.
NASA Astrophysics Data System (ADS)
Armstrong, R. S.; Holbrook, W. S.; Flinchum, B. A.; Provart, M.; Carr, B. J.; Auken, E.; Pedersen, J. B.
2014-12-01
Surface/groundwater interactions are an important, but poorly understood, facet of mountain hydrology. We utilize ground electrical resistivity data as a key tool for mapping groundwater pathways and aquifers. However, surface resistivity profiling is limited in both spatial extent and depth, especially in mountainous headwater environments because of inaccessibility and terrain. Because this important groundwater recharge environment is poorly understood, WyCEHG has focused efforts to increase knowledge about the dynamics and location of groundwater recharge. Currently, traditional hydrologic measurements estimate that only 10% of annual snowmelt enters the groundwater system while the rest is immediately available to surface flow. The Wyoming Center for Environmental Hydrology and Geophysics (WyCEHG) collected a 40 sq. km survey of helicopter transient electromagnetic (HTEM) and aeromagnetic data during the fall of 2013 as the first step in a "top down" geophysical characterization of a mountainous headwater catchment in the Snowy Range, Wyoming. Furthermore, mountain springs in the Snowy Range suggests that the "groundwatershed" acts as both a sink and source to surface watersheds. HTEM data show horizontal electrical conductors at depth, which are currently interpreted as fluid-filled subsurface fractures. Because these fractures eventually connect to the surface, they could be geophysical evidence of connectivity between the watershed and "groundwatershed." However, current HTEM inversion techniques assume a layered homogenous subsurface model, which directly contradicts two characteristics of the Snowy Range: the subvertical bedding of the Cheyenne Belt and heterogeneous distribution of surface water. Ground electrical resistivity surveys and surface nuclear magnetic resonance (NMR) measurements collected during the summer of 2014 target these anomalies to determine their validity and further understand the complicated dynamic of surface and groundwater flow.
Wakefield Simulation of CLIC PETS Structure Using Parallel 3D Finite Element Time-Domain Solver T3P
Candel, A.; Kabel, A.; Lee, L.; Li, Z.; Ng, C.; Schussman, G.; Ko, K.; Syratchev, I.; /CERN
2009-06-19
In recent years, SLAC's Advanced Computations Department (ACD) has developed the parallel 3D Finite Element electromagnetic time-domain code T3P. Higher-order Finite Element methods on conformal unstructured meshes and massively parallel processing allow unprecedented simulation accuracy for wakefield computations and simulations of transient effects in realistic accelerator structures. Applications include simulation of wakefield damping in the Compact Linear Collider (CLIC) power extraction and transfer structure (PETS).
Investigation of coastal areas in Northern Germany using airborne geophysical surveys
NASA Astrophysics Data System (ADS)
Miensopust, Marion; Siemon, Bernhard; Wiederhold, Helga; Steuer, Annika; Ibs-von Seht, Malte; Voß, Wolfgang; Meyer, Uwe
2014-05-01
Since 2000, the German Federal Institute for Geosciences and Natural Resources (BGR) carried out several airborne geophysical surveys in Northern Germany to investigate the coastal areas of the North Sea and some of the North and East Frisian Islands. Several of those surveys were conducted in cooperation with the Leibniz Institute for Applied Geophysics (LIAG). Two helicopter-borne geophysical systems were used, namely the BGR system, which collects simultaneously frequency-domain electromagnetic, magnetic and radiometric data, and the SkyTEM system, a time-domain electromagnetic system developed by the University of Aarhus. Airborne geophysical surveys enable to investigate huge areas almost completely with high lateral resolution in a relatively short time at economic cost. In general, the results can support geological and hydrogeological mapping. Of particular importance are the airborne electromagnetic results, as the surveyed parameter - the electrical conductivity - depends on both lithology and groundwater status. Therefore, they can reveal buried valleys and the distribution of sandy and clayey sediments as well as salinization zones and fresh-water occurrences. The often simultaneously recorded magnetic and radiometric data support the electromagnetic results. Lateral changes of Quaternary and Tertiary sediments (shallow source - several tens of metres) as well as evidences of the North German Basin (deep source - several kilometres) are revealed by the magnetic results. The radiometric data indicate the various mineral compositions of the soil sediments. This BGR/LIAG project aims to build up a geophysics data base (http://geophysics-database.de/) which contains all airborne geophysical data sets. However, the more significant effort is to create a reference data set as basis for monitoring climate or man-made induced changes of the salt-water/fresh-water interface at the German North Sea coast. The significance of problems for groundwater extraction
Time domain measurement of frequency stability: A tutorial introduction
NASA Technical Reports Server (NTRS)
Vanier, J.; Tetu, M.
1978-01-01
The theoretical basis behind the definition of frequency stability in the time domain is outlined. Various types of variances were examined. Their differences and interrelation are pointed out. Systems that are generally used in the measurement of these variances are described.
Frequency calibration of terahertz time-domain spectrometers
Naftaly, M.; Dudley, R. A.; Bernard, F.; Thomson, C.; Tian, Z.; Fletcher, J. R.
2009-07-15
We present three techniques of calibrating frequency and spectral profile measurements of terahertz time-domain spectrometers. The first utilizes the etalon effect generated by multiple reflections in thin nonabsorbing samples. The second employs a CO gas cell to provide multiple narrow absorption lines at known frequencies. The third aims to use a grating monochromator to produce an independently measured comparable spectrum.
Application of Time Domain Reflectometers to Urban Settings
Time domain reflectometers (TDRs) are in-situ monitoring probes that produce a temperature-compensated signal proportional to soil moisture content of the surrounding material when calibrated to a particular media. Typically used in agricultural settings, TDRs may also be applied...
Advanced propeller noise prediction in the time domain
NASA Technical Reports Server (NTRS)
Farassat, F.; Dunn, M. H.; Spence, P. L.
1992-01-01
The time domain code ASSPIN gives acousticians a powerful technique of advanced propeller noise prediction. Except for nonlinear effects, the code uses exact solutions of the Ffowcs Williams-Hawkings equation with exact blade geometry and kinematics. By including nonaxial inflow, periodic loading noise, and adaptive time steps to accelerate computer execution, the development of this code becomes complete.
Data Management, Infrastructure and Archiving for Time-Domain Astronomy
NASA Astrophysics Data System (ADS)
Schade, David
2012-04-01
The workshop on Data Management issues for Time-Domain Astronomy was conceived as a forward-looking discussion of the primary issues that need to be addressed for science in the time domain. The very broad diversity of the science areas presented in the main Symposium made it clear that most of the general issues for astronomy data management-for example, large data volumes, the need for timely processing and network performance-would be pertinent in the time domain. In addition, there might be other tight time constraints on data processing when the output was required to trigger rapid follow-up observations, while science based on very long time-baselines might require careful consideration of long-term data preservation and availability issues. But broadly speaking, data management challenges in the time domain are not at variance to any significant degree with those for astronomy or data-intensive research in general. The workshop framed and debated a number of questions: What is the biggest challenge faced by future projects? How do grid and cloud computing figure in data management plans? Is the Virtual Observatory important to future projects? How are the issues of data life cycle being addressed?
The coating curing properties study using terahertz time domain spectroscopy
NASA Astrophysics Data System (ADS)
Ren, Jiaojiao; Zhao, Duo; Li, Lijuan
2015-10-01
Coating curing curve is one of the most important methods to reflect the coating curing properties. It is of great significance for the coating curing properties. In this paper, by using the reflective Terahertz (THz) time-domain spectroscope technique, the curing properties of coating with different thicknesses are studied. Three different parameters used for studying the properties of coating curing curve are proposed in this paper. They are respectively the differential time of flight, power spectrum and amplitude for reflective THz time-domain waveform. In this paper, two kinds of coating (with different thicknesses) curing properties curves are established and the relative errors from three parameter analysis methods are compared respectively. This study shows that the study on coating curing properties curves by using the power spectrum of reflective THz time-domain waveform is superior to the amplitude parameter method. But for the thick coating, the differential time of flight for the reflective THz time-domain waveform can also better reflect the coating curing properties.
Application of Time Domain Reflectometers in Urban Settings
This is a poster for the Million Trees NYC research symposium in New York City, NY, March 5-6, 2010. The poster gives a summary of how time domain reflectometers can be installed in urban fill soil, engineered bioretention media, and recycled concrete aggregate to document the ...
Broadband Trailing Edge Noise Predictions in the Time Domain. Revised
NASA Technical Reports Server (NTRS)
Casper, Jay; Farassat, Fereidoun
2003-01-01
A recently developed analytic result in acoustics, "Formulation 1B," is used to compute broadband trailing edge noise from an unsteady surface pressure distribution on a thin airfoil in the time domain. This formulation is a new solution of the Ffowcs Willliams-Hawkings equation with the loading source term, and has been shown in previous research to provide time domain predictions of broadband noise that are in excellent agreement with experimental results. Furthermore, this formulation lends itself readily to rotating reference frames and statistical analysis of broadband trailing edge noise. Formulation 1B is used to calculate the far field noise radiated from the trailing edge of a NACA 0012 airfoil in low Mach number flows, by using both analytical and experimental data on the airfoil surface. The acoustic predictions are compared with analytical results and experimental measurements that are available in the literature. Good agreement between predictions and measurements is obtained.
Time Domain Partitioning of Electricity Production Cost Simulations
Barrows, C.; Hummon, M.; Jones, W.; Hale, E.
2014-01-01
Production cost models are often used for planning by simulating power system operations over long time horizons. The simulation of a day-ahead energy market can take several weeks to compute. Tractability improvements are often made through model simplifications, such as: reductions in transmission modeling detail, relaxation of commitment variable integrality, reductions in cost modeling detail, etc. One common simplification is to partition the simulation horizon so that weekly or monthly horizons can be simulated in parallel. However, horizon partitions are often executed with overlap periods of arbitrary and sometimes zero length. We calculate the time domain persistence of historical unit commitment decisions to inform time domain partitioning of production cost models. The results are implemented using PLEXOS production cost modeling software in an HPC environment to improve the computation time of simulations while maintaining solution integrity.
Technical and Observational Challenges for Future Time-Domain Surveys
NASA Astrophysics Data System (ADS)
Bloom, Joshua S.
2012-04-01
By the end of the last decade, robotic telescopes were established as effective alternatives to the traditional role of astronomer in planning, conducting and reducing time-domain observations. By the end of this decade, machines will play a much more central role in the discovery and classification of time-domain events observed by such robots. While this abstraction of humans away from the real-time loop (and the nightly slog of the nominal scientific process) is inevitable, just how we will get there as a community is uncertain. I discuss the importance of machine learning in astronomy today, and project where we might consider heading in the future. I will also touch on the role of people and organisations in shaping and maximising the scientific returns of the coming data deluge.
Time domain responses of a prestressed beam and prestress identification
NASA Astrophysics Data System (ADS)
Law, S. S.; Lu, Z. R.
2005-12-01
The time-domain response of a prestressed Euler-Bernoulli beam under external excitation is studied based on modal superposition. The prestress force is then identified in the time domain by a system identification approach and Tikhonov regularization technique is used to provide bounds to the ill-conditioned results in the identified problem. Both measured displacements and strains are used. The noise effect is improved using the orthogonal polynomial function, and cases with either sinusoidal or impulsive excitations are illustrated to give very good results from the lower three measured modes and data obtained from three measurement points. Work in this paper demonstrates the feasibility of indirectly identifying the prestress force in a beam.
Raman-assisted vector Brillouin optical time domain analysis
NASA Astrophysics Data System (ADS)
Angulo-Vinuesa, X.; Bacquet, D.; Martin-Lopez, S.; Corredera, P.; Szriftgiser, P.; Gonzalez-Herraez, M.
2013-05-01
Raman-assistance (RA) has become a promising technique to enhance the sensing range of standard Brillouin Optical Time Domain Analysis (BOTDA) fiber sensors due to its ability to amplify in a distributed way all the interacting signals within the fiber. Unfortunately, Raman amplification introduces a great amount of Relative Intensity Noise (RIN) to the detected low-frequency probe wave. This RIN transfer problem has been widely identified as a major limitation in RABOTDA. In Vector Brillouin Optical Time Domain Analysis (VBOTDA) the detected signal is transferred to a highfrequency carrier where the Raman RIN transfer turns out to be much less harmful. In this work we demonstrate, for the first time to our knowledge, Raman-assistance in a VBOTDA. Our results show significant reduction of the RIN transfer effect in RA-VBOTDA compared to standard RA-BOTDA, making this type of scheme particularly interesting for long range distributed sensing.
THz time-domain spectroscopy imaging for mail inspection
NASA Astrophysics Data System (ADS)
Zhang, Liquan; Wang, Zhongdong; Ma, Yanmei; Hao, Erjuan
2011-08-01
Acquiring messages from the mail but not destroying the envelope is a big challenge in the war of intelligence. If one can read the message of the mail when the envelope is closed, he will benefit from the message asymmetry and be on a good wicket in the competition. In this paper, we presented a transmitted imaging system using THz time-domain spectroscopy technology. We applied the system to image the mail inside an envelope by step-scanning imaging technology. The experimental results show that the THz spectroscopy can image the mail in an envelope. The words in the paper can be identified easily from the background. We also present the THz image of a metal blade in the envelope, in which we can see the metal blade clearly. The results show that it is feasible of THz Time-Domain Spectroscopy Imaging for mail inspection applications.
Finite difference time domain grid generation from AMC helicopter models
NASA Technical Reports Server (NTRS)
Cravey, Robin L.
1992-01-01
A simple technique is presented which forms a cubic grid model of a helicopter from an Aircraft Modeling Code (AMC) input file. The AMC input file defines the helicopter fuselage as a series of polygonal cross sections. The cubic grid model is used as an input to a Finite Difference Time Domain (FDTD) code to obtain predictions of antenna performance on a generic helicopter model. The predictions compare reasonably well with measured data.
Time domains of the hypoxic ventilatory response in ectothermic vertebrates.
Porteus, Cosima; Hedrick, Michael S; Hicks, James W; Wang, Tobias; Milsom, William K
2011-04-01
Over a decade has passed since Powell et al. (Respir Physiol 112:123-134, 1998) described and defined the time domains of the hypoxic ventilatory response (HVR) in adult mammals. These time domains, however, have yet to receive much attention in other vertebrate groups. The initial, acute HVR of fish, amphibians and reptiles serves to minimize the imbalance between oxygen supply and demand. If the hypoxia is sustained, a suite of secondary adjustments occur giving rise to a more long-term balance (acclimatization) that allows the behaviors of normal life. These secondary responses can change over time as a function of the nature of the stimulus (the pattern and intensity of the hypoxic exposure). To add to the complexity of this process, hypoxia can also lead to metabolic suppression (the hypoxic metabolic response) and the magnitude of this is also time dependent. Unlike the original review of Powell et al. (Respir Physiol 112:123-134, 1998) that only considered the HVR in adult animals, we also consider relevant developmental time points where information is available. Finally, in amphibians and reptiles with incompletely divided hearts the magnitude of the ventilatory response will be modulated by hypoxia-induced changes in intra-cardiac shunting that also improve the match between O(2) supply and demand, and these too change in a time-dependent fashion. While the current literature on this topic is reviewed here, it is noted that this area has received little attention. We attempt to redefine time domains in a more 'holistic' fashion that better accommodates research on ectotherms. If we are to distinguish between the genetic, developmental and environmental influences underlying the various ventilatory responses to hypoxia, however, we must design future experiments with time domains in mind.
Historical Time-Domain: Data Archives, Processing, and Distribution
NASA Astrophysics Data System (ADS)
Grindlay, Jonathan E.; Griffin, R. Elizabeth
2012-04-01
The workshop on Historical Time-Domain Astronomy (TDA) was attended by a near-capacity gathering of ~30 people. From information provided in turn by those present, an up-to-date overview was created of available plate archives, progress in their digitization, the extent of actual processing of those data, and plans for data distribution. Several recommendations were made for prioritising the processing and distribution of historical TDA data.
Characteristic Based Methods for the Time-Domain Maxwell Equations
1993-08-09
2-D results on Cartesian frame demonstrated a potential for numerical efficiency improvement. 14. SUBJECT TERMS 15. NUMBER OF PAGES Time-domain...11 4 Discussion of Numerical Results ........................ 19 5 C onclusion...l ill tiit, pruIcIt a1lyis lder this’ Iranirwurk. Ilulilerical results it’lect tfi heIcst puss,’ibk 1)1(2pefon~lI liace of t he iiew aiiuiirical j
Time Domain Reflectometry for Damage Detection of Laminated CFRP plate
2011-08-18
Final Report PROJECT ID: AOARD-10-4112 Title: Time Domain Reflectometry for damage detection of laminated CFRP plate Researcher: Professor Akira...From July/2010 To July/2011 Abstract Recently, high toughness Carbon Fiber Reinforced Polymer ( CFRP ) laminates are used to primary structures. The...tough CFRP yields small fiber breakages when delamination crack is made in many cases. This requires a detection system of fiber breakages at low cost for
Time-domain Ramsey interferometry with interacting Rydberg atoms
NASA Astrophysics Data System (ADS)
Sommer, Christian; Pupillo, Guido; Takei, Nobuyuki; Takeda, Shuntaro; Tanaka, Akira; Ohmori, Kenji; Genes, Claudiu
2016-11-01
We theoretically investigate the dynamics of a gas of strongly interacting Rydberg atoms subject to a time-domain Ramsey interferometry protocol. The many-body dynamics is governed by an Ising-type Hamiltonian with long-range interactions of tunable strength. We analyze and model the contrast degradation and phase accumulation of the Ramsey signal and identify scaling laws for varying interrogation times, ensemble densities, and ensemble dimensionalities.
Anderson localization and Mott insulator phase in the time domain
Sacha, Krzysztof
2015-01-01
Particles in space periodic potentials constitute standard models for investigation of crystalline phenomena in solid state physics. Time periodicity of periodically driven systems is a close analogue of space periodicity of solid state crystals. There is an intriguing question if solid state phenomena can be observed in the time domain. Here we show that wave-packets localized on resonant classical trajectories of periodically driven systems are ideal elements to realize Anderson localization or Mott insulator phase in the time domain. Uniform superpositions of the wave-packets form stationary states of a periodically driven particle. However, an additional perturbation that fluctuates in time results in disorder in time and Anderson localization effects emerge. Switching to many-particle systems we observe that depending on how strong particle interactions are, stationary states can be Bose-Einstein condensates or single Fock states where definite numbers of particles occupy the periodically evolving wave-packets. Our study shows that non-trivial crystal-like phenomena can be observed in the time domain. PMID:26074169
High frequency resolution terahertz time-domain spectroscopy
NASA Astrophysics Data System (ADS)
Sangala, Bagvanth Reddy
2013-12-01
A new method for the high frequency resolution terahertz time-domain spectroscopy is developed based on the characteristic matrix method. This method is useful for studying planar samples or stack of planar samples. The terahertz radiation was generated by optical rectification in a ZnTe crystal and detected by another ZnTe crystal via electro-optic sampling method. In this new characteristic matrix based method, the spectra of the sample and reference waveforms will be modeled by using characteristic matrices. We applied this new method to measure the optical constants of air. The terahertz transmission through the layered systems air-Teflon-air-Quartz-air and Nitrogen gas-Teflon-Nitrogen gas-Quartz-Nitrogen gas was modeled by the characteristic matrix method. A transmission coefficient is derived from these models which was optimized to fit the experimental transmission coefficient to extract the optical constants of air. The optimization of an error function involving the experimental complex transmission coefficient and the theoretical transmission coefficient was performed using patternsearch algorithm of MATLAB. Since this method takes account of the echo waveforms due to reflections in the layered samples, this method allows analysis of longer time-domain waveforms giving rise to very high frequency resolution in the frequency-domain. We have presented the high frequency resolution terahertz time-domain spectroscopy of air and compared the results with the literature values. We have also fitted the complex susceptibility of air to the Lorentzian and Gaussian functions to extract the linewidths.
Udagedara, Indika; Premaratne, Malin; Rukhlenko, Ivan D; Hattori, Haroldo T; Agrawal, Govind P
2009-11-09
Finite-difference time-domain (FDTD) simulations of any electromagnetic problem require truncation of an often-unbounded physical region by an electromagnetically bounded region by deploying an artificial construct known as the perfectly matched layer (PML). As it is not possible to construct a universal PML that is non-reflective for different materials, PMLs that are tailored to a specific problem are required. For example, depending on the number of dispersive materials being truncated at the boundaries of a simulation region, an FDTD code may contain multiple sets of update equations for PML implementations. However, such an approach is prone to introducing coding errors. It also makes it extremely difficult to maintain and upgrade an existing FDTD code. In this paper, we solve this problem by developing a new, unified PML algorithm that can effectively truncate all types of linearly dispersive materials. The unification of the algorithm is achieved by employing a general form of the medium permittivity that includes three types of dielectric response functions, known as the Debye, Lorentz, and Drude response functions, as particular cases. We demonstrate the versatility and flexibility of the new formulation by implementing a single FDTD code to simulate absorption of electromagnetic pulse inside a medium that is adjacent to dispersive materials described by different dispersion models. The proposed algorithm can also be used for simulations of optical phenomena in metamaterials and materials exhibiting negative refractive indices.
Conductivity of solvated electrons in hexane investigated with terahertz time-domain spectroscopy.
Knoesel, Ernst; Bonn, Mischa; Shan, Jie; Wang, Feng; Heinz, Tony F
2004-07-01
We present investigations of the transient photoconductivity and recombination dynamics of quasifree electrons in liquid n-hexane and cyclohexane performed using terahertz time-domain spectroscopy (THz-TDS). Quasifree electrons are generated by two-photon photoionization of the liquid using a femtosecond ultraviolet pulse, and the resulting changes in the complex conductivity are probed by a THz electromagnetic pulse at a variable delay. The detection of time-domain wave forms of the THz electric field permits the direct determination of both the real and the imaginary part of the conductivity of the electrons over a wide frequency range. The change in conductivity can be described by the Drude model, thus yielding the quasifree electron density and scattering time. The electron density is found to decay on a time scale of a few hundred picoseconds, which becomes shorter with increasing excitation density. The dynamics can be described by a model that assumes nongeminate recombination between electrons and positive ions. In addition, a strong dependence of the quasifree electron density on temperature is observed, in agreement with a two-state model in which the electron may exist in either a quasifree or a bound state.
Interpretation of field change array data with time domain fractal lightning modeling
NASA Astrophysics Data System (ADS)
Carlson, B. E.; Liang, C.; Bitzer, P. M.; Christian, H. J.; Lehtinen, N. G.; Inan, U. S.
2011-12-01
Despite much study, the physical processes involved in lightning and the associated electromagnetic emissions remain a mystery, with much effort thus far devoted to categorizing and describing the emissions. Time domain fractal lightning (TDFL) modeling provides an opportunity to improve on such reporting by connecting the observations to theories of the physics of lightning. Such connection allows meaningful interpretation of the observations in the context of the physics and provides better understanding of the behavior of the lightning channel. We present comparison of time domain fractal lightning modeling with lightning mapping array data and electric field records from the Huntsville Alabama Marx Meter Array (HAMMA), a network of field change meters with high time resolution capable of reconstructing the geometry and time development of the charge motions in a lightning discharge. These data are used to constrain the TDFL simulations, while the TDFL results are used to interpret the field change data. The role of the evolution of the lightning channel electrical properties, the channel corona sheath, and the geometric development of the channel are examined, and the physical implications of the HAMMA data are studied.
Finite difference time domain calculation of transients in antennas with nonlinear loads
NASA Technical Reports Server (NTRS)
Luebbers, Raymond J.; Beggs, John H.; Kunz, Karl S.; Chamberlin, Kent
1991-01-01
Determining transient electromagnetic fields in antennas with nonlinear loads is a challenging problem. Typical methods used involve calculating frequency domain parameters at a large number of different frequencies, then applying Fourier transform methods plus nonlinear equation solution techniques. If the antenna is simple enough so that the open circuit time domain voltage can be determined independently of the effects of the nonlinear load on the antennas current, time stepping methods can be applied in a straightforward way. Here, transient fields for antennas with more general geometries are calculated directly using Finite Difference Time Domain (FDTD) methods. In each FDTD cell which contains a nonlinear load, a nonlinear equation is solved at each time step. As a test case, the transient current in a long dipole antenna with a nonlinear load excited by a pulsed plane wave is computed using this approach. The results agree well with both calculated and measured results previously published. The approach given here extends the applicability of the FDTD method to problems involving scattering from targets, including nonlinear loads and materials, and to coupling between antennas containing nonlinear loads. It may also be extended to propagation through nonlinear materials.
Finite-difference time-domain analysis for the dynamics and diffraction of exciton-polaritons.
Chen, Minfeng; Chang, Yia-Chung; Hsieh, Wen-Feng
2015-10-01
We adopted a finite-difference time-domain (FDTD) scheme to simulate the dynamics and diffraction of exciton-polaritons, governed by the coupling of polarization waves with electromagnetic waves. The polarization wave, an approximate solution to the Schrödinger's equation at low frequencies, essentially captures the exciton behavior. Numerical stability of the scheme is analyzed and simple examples are provided to prove its validity. The system considered is both temporally and spatially dispersive, for which the FDTD analysis has attracted less attention in the literature. Here, we demonstrate that the FDTD scheme could be useful for studying the optical response of the exciton-polariton and its dynamics. The diffraction of a polariton wave from a polaritonic grating is also considered, and many sharp resonances are found, which manifest the interference effect of polariton waves. This illustrates that the measurement of transmittance or reflectance near polariton resonance can reveal subwavelength features in semiconductors, which are sensitive to polariton scattering.
Transient analysis of printed lines using finite-difference time-domain method
Ahmed, Shahid
2012-03-29
Comprehensive studies of ultra-wideband pulses and electromagnetic coupling on printed coupled lines have been performed using full-wave 3D finite-difference time-domain analysis. Effects of unequal phase velocities of coupled modes, coupling between line traces, and the frequency dispersion on the waveform fidelity and crosstalk have been investigated in detail. To discriminate the contributions of different mechanisms into pulse evolution, single and coupled microstrip lines without (ϵ_{r} = 1) and with (ϵ_{r} > 1) dielectric substrates have been examined. To consistently compare the performance of the coupled lines with substrates of different permittivities and transients of different characteristic times, a generic metric similar to the electrical wavelength has been introduced. The features of pulse propagation on coupled lines with layered and pedestal substrates and on the irregular traces have been explored. Finally, physical interpretations of the simulation results are discussed in the paper.
Evaluation of Waveform Structure Features on Time Domain Target Recognition under Cross Polarization
NASA Astrophysics Data System (ADS)
Selver, M. A.; Seçmen, M.; Zoral, E. Y.
2016-08-01
Classification of aircraft targets from scattered electromagnetic waves is a challenging application, which suffers from aspect angle dependency. In order to eliminate the adverse effects of aspect angle, various strategies were developed including the techniques that rely on extraction of several features and design of suitable classification systems to process them. Recently, a hierarchical method, which uses features that take advantage of waveform structure of the scattered signals, is introduced and shown to have effective results. However, this approach has been applied to the special cases that consider only a single planar component of electric field that cause no-cross polarization at the observation point. In this study, two small scale aircraft models, Boeing-747 and DC-10, are selected as the targets and various polarizations are used to analyse the cross-polarization effects on system performance of the aforementioned method. The results reveal the advantages and the shortcomings of using waveform structures in time-domain target identification.
[Application of terahertz time domain spectroscopy to explosive and illegal drug].
Liu, Gui-Feng; Zhao, Hong-Wei; Ge, Min; Wang, Wen-Feng
2008-05-01
Terahertz waves (THz, T-ray) lie between far-infrared and microwave in electromagnetic spectrum with frequency from 0.1 to 10 THz. Many explosives and illicit drugs show characteristic spectral features in the terahertz. Compared with conventional methods of detecting a variety of threats, such as weapons, explosives and illegal drugs, THz radiation is low frequency and non-ionizing, and does not give rise to safety concerns. Moreover, THz can penetrate many barrier materials, such as clothing and common packaging materials. THz technique has a great potential and advantage in antiterrorism and security inspection of explosives and illegal drugs due to the ability of high-sensitivity, nondestructive and stand-off inspection of many substances. The present paper summarizes the latest progress in the application of terahertz time domain spectroscopy (THz-TDS) to explosives and illegal drugs. Studies on RDX are discussed in details and many factors affecting experiments are also introduced.
Non-linear Conjugate Gradient Time-Domain Controlled Inversion Source
Newman, Gregory A.; Commer, Michael
2006-11-16
Software that simulates and inverts time-domain electromagnetic field data for subsurface electrical properties (electrical conductivity) of geological media. The software treats data produced by a step-wise source signal from either galvanic (grounded wires) or inductive (magnetic loops) sources. The inversion process is carried inductive (magnetic loops) sources. The inversion process is carried out using a non-linear conjugate gradient optimization scheme, which minimizes the misfit between field data and model data using a least squares criteria. The software is an upgrade from the code TEM3D ver. 2.0. The upgrade includes the following components: (1) Improved (faster)memory access during gradient computation. (2) Data parellelization scheme: Multiple transmitters (sources) can be distributed accross several banks of processors (daa-planes). Similarly, the receivers of each source are also distributed accross the corresponding data-plane. (3) Improved data-IO.
NASA Astrophysics Data System (ADS)
Kameni Ntichi, Abelin; Modave, Axel; Boubekeur, Mohamed; Preault, Valentin; Pichon, Lionel; Geuzaine, Christophe
2013-11-01
This article presents a time domain discontinuous Galerkin method applied for solving the con-servative form of Maxwells' equations and computing the radiated fields in electromagnetic compatibility problems. The results obtained in homogeneous media for the transverse magnetic waves are validated in two cases. We compare our solution to an analytical solution of Maxwells' equations based on characteristic method. Our results on shielding effectiveness of a conducting wall are same as those obtained from analytical expression in frequency domain. The propagation in heterogeneous medium is explored. The shielding effectiveness of a composite wall partially filled by circular conductives inclusions is computed. The proposed results are in conformity with the classical predictive homogenization rules. Contribution to the Topical Issue "Numelec 2012", Edited by Adel Razek.
Current sheets in the Discontinuous Galerkin Time-Domain method: an application to graphene
NASA Astrophysics Data System (ADS)
Werra, Julia F. M.; Wolff, Christian; Matyssek, Christian; Busch, Kurt
2015-05-01
We describe the treatment of thin conductive sheets within the Discontinuous Galerkin Time-Domain (DGTD) method for solving the Maxwell equations and apply this approach to the efficient computation of the optical properties of graphene-based systems. In particular, we show that a thin conductive sheet can be handled by incorporating the associated jump conditions of the electromagnetic field into the numerical flux of the DGTD approach. This results in a flexible and efficient numerical scheme that can be applied to a number of systems. Specifically, we show how to treat individual graphene sheets on substrates as well as finite stacks of alternating graphene and dielectric layers by modeling the dispersive and dissipative properties of graphene via a two-term critical-point model for its electrostatically doped conductivity.
Using time domain characteristics to discriminate physiologic and parkinsonian tremors.
Edwards, R; Beuter, A
2000-01-01
Tremor amplitude and frequency do not always clearly differentiate subjects with particular pathologies from control subjects or from subjects with other pathologies, especially in early stages of a disease. For patients with early stages of Parkinson's disease (PD) the discriminative power of amplitude was compared with that of other time domain characteristics of tremor recordings that are probably not evident clinically. Postural tremor with and without visual feedback and rest tremor were recorded in both hands of a group of patients with Parkinson's disease (n = 21) and a group of healthy control subjects (n = 30) using displacement lasers. Velocity and acceleration data were derived from displacement data. Twelve time domain characteristics were calculated on each recording and the discriminating power of each was evaluated using the worse hand in each case. Postural tremor with no visual feedback separates the two groups of subjects most efficiently, especially in velocity and acceleration. Tremor in Parkinson's disease (in comparison to normal physiologic tremor) has a specific morphology, has a distinctive histogram, is more periodic, and contains indications of nonlinearity in the underlying dynamics. There may also be greater difference in amplitude between the two hands and time asymmetry in tremor of patients with PD. A series of finger flexions seems to enhance normal tremor but not tremor in PD and may thus aid in discrimination. Discrimination of tremor attributable to PD from normal physiologic tremor can be enhanced by measuring time domain characteristics subtler than amplitude, particularly when amplitude itself is not large. Tremor measurement should not be limited to acceleration data because some information is more visible in other variables.
Finite difference time domain modeling of spiral antennas
NASA Technical Reports Server (NTRS)
Penney, Christopher W.; Beggs, John H.; Luebbers, Raymond J.
1992-01-01
The objectives outlined in the original proposal for this project were to create a well-documented computer analysis model based on the finite-difference, time-domain (FDTD) method that would be capable of computing antenna impedance, far-zone radiation patterns, and radar cross-section (RCS). The ability to model a variety of penetrable materials in addition to conductors is also desired. The spiral antennas under study by this project meet these requirements since they are constructed of slots cut into conducting surfaces which are backed by dielectric materials.
Finite-difference time-domain simulation of spacetime cloak.
Cornelius, Jason; Liu, Jinjie; Brio, Moysey
2014-05-19
In this work, we present a numerical method that remedies the instabilities of the conventional FDTD approach for solving Maxwell's equations in a space-time dependent magneto-electric medium with direct application to the simulation of the recently proposed spacetime cloak. We utilize a dual grid FDTD method overlapped in the time domain to provide a stable approach for the simulation of a magneto-electric medium with time and space varying permittivity, permeability and coupling coefficient. The developed method can be applied to explore other new physical possibilities offered by spacetime cloaking, metamaterials, and transformation optics.
Selecting Variables for the Time Domain Spectroscopic Survey
NASA Astrophysics Data System (ADS)
Morganson, Eric; TDSS; SDSS; Pan-STARRS1
2014-01-01
The Time Domain Spectroscopic Survey is an eBOSS subprogram that will obtain spectroscopy for 400,000 objects that vary more than 0.1 magnitudes. 100,000 of these objects will be unique to TDSS and 300,000 will be shared with other subprograms. We use a combination of Pan-STARRS1 and SDSS photometry to select a sample of variables that is 95% pure and 60% complete. This sample is obtained with three dimension Kernel Density Analysis. Our data and method are particularly effective at selecting long term variables, and more than 300,000 of our variables will be quasars.
New Flutter Analysis Technique for Time-Domain Computational Aeroelasticity
NASA Technical Reports Server (NTRS)
Pak, Chan-Gi; Lung, Shun-Fat
2017-01-01
A new time-domain approach for computing flutter speed is presented. Based on the time-history result of aeroelastic simulation, the unknown unsteady aerodynamics model is estimated using a system identification technique. The full aeroelastic model is generated via coupling the estimated unsteady aerodynamic model with the known linear structure model. The critical dynamic pressure is computed and used in the subsequent simulation until the convergence of the critical dynamic pressure is achieved. The proposed method is applied to a benchmark cantilevered rectangular wing.
Astrophysics in the Era of Massive Time-Domain Surveys
NASA Astrophysics Data System (ADS)
Djorgovski, G.
Synoptic sky surveys are now the largest data producers in astronomy, entering the Petascale regime, opening the time domain for a systematic exploration. A great variety of interesting phenomena, spanning essentially all subfields of astronomy, can only be studied in the time domain, and these new surveys are producing large statistical samples of the known types of objects and events for further studies (e.g., SNe, AGN, variable stars of many kinds), and have already uncovered previously unknown subtypes of these (e.g., rare or peculiar types of SNe). These surveys are generating a new science, and paving the way for even larger surveys to come, e.g., the LSST; our ability to fully exploit such forthcoming facilities depends critically on the science, methodology, and experience that are being accumulated now. Among the outstanding challenges, the foremost is our ability to conduct an effective follow-up of the interesting events discovered by the surveys in any wavelength regime. The follow-up resources, especially spectroscopy, are already and, for the predictable future, will be severely limited, thus requiring an intelligent down-selection of the most astrophysically interesting events to follow. The first step in that process is an automated, real-time, iterative classification of events, that incorporates heterogeneous data from the surveys themselves, archival and contextual information (spatial, temporal, and multiwavelength), and the incoming follow-up observations. The second step is an optimal automated event prioritization and allocation of the available follow-up resources that also change in time. Both of these challenges are highly non-trivial, and require a strong cyber-infrastructure based on the Virtual Observatory data grid, and the various astroinformatics efforts. Time domain astronomy is inherently an astronomy of telescope-computational systems, and will increasingly depend on novel machine learning and artificial intelligence tools
Fast Brillouin Optical Time Domain Analysis for dynamic sensing.
Peled, Yair; Motil, Avi; Tur, Moshe
2012-04-09
A new technique for the fast implementation of Brillouin Optical Time Domain Analysis (BOTDA) is proposed and demonstrated, carrying the classical BOTDA method to the dynamic sensing domain. By using a digital signal generator which enables fast switching among 100 scanning frequencies, we demonstrate a truly distributed and dynamic measurement of a 100 m long fiber with a sampling rate of ~10 kHz, limited only by the fiber length and the frequency granularity. With 10 averages the standard deviation of the measured strain was ~5 µε.
Balanced detection in Brillouin optical time domain analysis
NASA Astrophysics Data System (ADS)
Dominguez-Lopez, Alejandro; Lopez-Gil, Alexia; Martin-Lopez, Sonia; Gonzalez-Herraez, Miguel
2014-05-01
We propose the use of balanced detection in Brillouin Optical Time Domain Analysis (BOTDA) sensors. Balanced detection can be effectively accomplished among the Stokes and anti-Stokes bands in the probe signal. This type of detection leads to a doubling of the trace amplitude and at least a √2 increase in signal to noise ratio over the conventional configuration. Moreover, it leads to a complete cancellation of the common-mode noise in the probe signal, including relative intensity noise in Raman-assisted configurations. We show all these benefits both theoretically and experimentally.
Sources of noise in Brillouin optical time-domain analyzers
NASA Astrophysics Data System (ADS)
Urricelqui, Javier; Soto, Marcelo A.; Thévenaz, Luc
2015-09-01
This paper presents a thorough study of the different sources of noise affecting Brillouin optical time-domain analyzers (BOTDA), providing a deep insight into the understanding of the fundamental limitations of this kind of sensors. Analytical and experimental results indicate that the noise source ultimately fixing the sensor performance depends basically on the fiber length and the input pump-probe powers. Thus, while the phase-to-intensity noise conversion induced by stimulated Brillouin scattering can have a dominating effect at short distances, a combination of sources determines the noise in longrange sensing, basically dominated by probe double Rayleigh scattering.
Time-domain simulation of nonlinear radiofrequency phenomena
Jenkins, Thomas G.; Austin, Travis M.; Smithe, David N.; Loverich, John; Hakim, Ammar H.
2013-01-15
Nonlinear effects associated with the physics of radiofrequency wave propagation through a plasma are investigated numerically in the time domain, using both fluid and particle-in-cell (PIC) methods. We find favorable comparisons between parametric decay instability scenarios observed on the Alcator C-MOD experiment [J. C. Rost, M. Porkolab, and R. L. Boivin, Phys. Plasmas 9, 1262 (2002)] and PIC models. The capability of fluid models to capture important nonlinear effects characteristic of wave-plasma interaction (frequency doubling, cyclotron resonant absorption) is also demonstrated.
NASA Astrophysics Data System (ADS)
Schrader, T.; Münter, K.; Battermann, S.; Garbe, H.
2005-05-01
This work describes a method to detect and to quantify any local or mid-range discontinuity on extended flat metal planes. Often these planes are used for antenna calibration (open area test site - OATS) or the plane could be the ground of a semi-anechoic chamber used in Electromagnetic Compatibility (EMC) testing. The measurement uncertainty of antenna calibration or EMC testing depends on the groundplane's quality, which can be accessed using this method. A vector network analyzer with time-domain option is used to determine the complex-valued input scattering parameter S11,F of an aperture antenna in a monostatic setup. S;11,F contains the information desired about the discontinuities and is measured in the frequency domain with high dynamic range. But only after a linear filtering utilizing the Chirp-Z-Transform the obtained time-domain signal S11,T evidence of local and mid-range discontinuities.
Fiber laser hydrogen sensor codified in the time domain
NASA Astrophysics Data System (ADS)
Barmenkov, Yuri O.; Ortigosa-Blanch, Arturo; Diez, Antonio; Cruz Munoz, Jose Luis; Andres, Miguel V.
2004-10-01
A novel scheme for a fiber optic hydrogen sensor is presented. The sensor is based on an erbium-doped fiber laser with a Pd-coated tapered fiber within the laser cavity acting as the hydrogen-sensing element. When the sensing element is exposed to a hydrogen atmosphere, its attenuation decreases changing the cavity losses, which leads to a modification of the switching-on laser transient. The hydrogen concentration can be obtained by a simple measurement of the build-up time of the laser. This technique translates the measurement of hydrogen concentration into the time domain. Sensing techniques translating the measurement to the time domain offer the possibility to acquire and process the information very easily and accurately using reliable and low-cost electronics. We have also studied the influence of the pumping conditions. We have found that changing from a 100% modulation depth of the pump to biasing the laser with a certain pump power (being this value always below the laser threshold) the sensitivity of the sensor is substantially enhanced. Hence the sensitivity of the fiber laser sensor can be adjusted to certain requirements by simply controlling the pump. Relative build-up times variations of up to 55% for 10% hydrogen concentration are demonstrated.
[Aging explosive detection using terahertz time-domain spectroscopy].
Meng, Kun; Li, Ze-ren; Liu, Qiao
2011-05-01
Detecting the aging situation of stock explosive is essentially meaningful to the research on the capability, security and stability of explosive. Existing aging explosive detection techniques, such as scan microscope technique, Fourier transfer infrared spectrum technique, gas chromatogram mass spectrum technique and so on, are either not able to differentiate whether the explosive is aging or not, or not able to image the structure change of the molecule. In the present paper, using the density functional theory (DFT), the absorb spectrum changes after the explosive aging were calculated, from which we can clearly find the difference of spectrum between explosive molecule and aging ones in the terahertz band. The terahertz time-domain spectrum (THz-TDS) system as well as its frequency spectrum resolution and measured range are analyzed. Combined with the existing experimental results and the essential characters of the terahertz wave, the application of THz-TDS technique to the detection of aging explosive was demonstrated from the aspects of feasibility, veracity and practicability. On the base of that, the authors advance the new method of aging explosive detection using the terahertz time-domain spectrum technique.
Terahertz time-domain spectroscopy and application on peanut oils
NASA Astrophysics Data System (ADS)
Li, Jiusheng; Yao, Jianquan; Li, Jianrui
2008-12-01
Many materials were previously studied using far-infrared Fourier transform spectroscopy (FTS) in transmission and reflection modes. Recently, there has been a remarkable effort in employing terahertz time-domain spectroscopy (THz-TDS) for investigating material properties, including environment pollutants, semiconductors, polymers, explosive materials, and gases, etc. Since the absorption coefficient and the refractive index of the material studied are directly related to the amplitude and phase respectively of the transmitted field, both parts of the complex permittivity can be obtained by THz-TDS. In this letter, the optical properties of peanut oils in the frequency range from 0.2 to 2.5 THz were studied by employing terahertz time-domain spectroscopy. Several peanut oils, such as clean unused peanut oil, peanut oil after five minutes of boiling, and peanut oil after ten minutes of boiling were tested. The time delays of clean unused peanut oil, peanut oil after five minutes of boiling, and peanut oil after ten minutes of boiling are 8.33ps, 8.46ps and 8.46ps, respectively. The refractive indices of the three oil samples show slow a decrease as the terahertz wave frequency increases. The power absorption coefficients increase as the frequency increases within the investigated terahertz wave frequency range.
Early Results and Plans for the Time Domain Spectroscopic Survey
NASA Astrophysics Data System (ADS)
Green, Paul J.; Anderson, S. F.; Morganson, E.; Ruan, J. J.; PS1; SDSS-III; SDSS-IV
2014-01-01
With PanSTARRS-1 just finishing and LSST over the horizon, time-domain astronomy is a celestial tsunami just now hitting our shores. We outline the Time Domain Spectroscopic Survey (TDSS) - the first large-scale, all-sky spectroscopic survey of celestial variables. As part of SDSS-IV eBOSS program, the TDSS has begun obtaining BOSS-quality spectroscopy of variable objects selected primarily from the PS1 3pi survey. During the duration of SDSS-IV (2014-2020), TDSS should garner of order 1E+05 first-ever spectra of variables to i-band mag about 21. While AGN will dominate the sample, all kinds of variable stars will also be revealed, including RR Lyr, flare stars, eclipsing binaries, pulsating white dwarfs and more. We will outline target selection, and discuss early results. We also describe a TDSS subprogram testing for spectroscopic variability by obtaining 2d or 3d epoch spectra of several carefully chosen source classes.
Time domain Rankine-Green panel method for offshore structures
NASA Astrophysics Data System (ADS)
Li, Zhifu; Ren, Huilong; Liu, Riming; Li, Hui
2017-02-01
To solve the numerical divergence problem of the direct time domain Green function method for the motion simulation of floating bodies with large flare, a time domain hybrid Rankine-Green boundary element method is proposed. In this numerical method, the fluid domain is decomposed by an imaginary control surface, at which the continuous condition should be satisfied. Then the Rankine Green function is adopted in the inner domain. The transient free surface Green function is applied in the outer domain, which is used to find the relationship between the velocity potential and its normal derivative for the inner domain. Besides, the velocity potential at the mean free surface between body surface and control surface is directly solved by the integration scheme. The wave exciting force is computed through the convolution integration with wave elevation, by introducing the impulse response function. Additionally, the nonlinear Froude-Krylov force and hydrostatic force, which is computed under the instantaneous incident wave free surface, are taken into account by the direct pressure integration scheme. The corresponding numerical computer code is developed and first used to compute the hydrodynamic coefficients of the hemisphere, as well as the time history of a ship with large flare; good agreement is obtained with the analytical solutions as well as the available numerical results. Then the hydrodynamic properties of a FPSO are studied. The hydrodynamic coefficients agree well with the results computed by the frequency method; the influence of the time interval and the truncated time is investigated in detail.
Time-domain analysis of scrotal thermoregulatory impairment in varicocele.
Ismail, Enas; Orlando, Giuseppe; Pompa, Paolo; Gabrielli, Daniela; Di Donato, Luigino; Cardone, Daniela; Merla, Arcangelo
2014-01-01
Varicocele is a common male disease defined as the pathological dilatation of the pampiniform plexus and scrotal veins with venous blood reflux. Varicocele usually impairs the scrotal thermoregulation via a hemodynamic alteration, thus inducing an increase in cutaneous temperature. The investigation of altered scrotal thermoregulation by means of thermal infrared imaging has been proved to be useful in the study of the functional thermal impairment. In this study, we use the Control System Theory to analyze the time-domain dynamics of the scrotal thermoregulation in response to a mild cold challenge. Four standard time-domain dynamic parameters of a prototype second order control system (Delay Time, Rise Time, closed poles locations, steady state error) and the static basal temperatures were directly estimated from thermal recovery curves. Thermal infrared imaging data from 31 healthy controls (HCS) and 95 varicocele patients were processed. True-positive predictions, by comparison with standard echo color Doppler findings, higher than 87% were achieved into the proper classification of the disease stage. The proposed approach could help to understand at which specific level the presence of the disease impacts the scrotal thermoregulation, which is also involved into normal spermatogenesis process.
Time-domain fitting of battery electrochemical impedance models
NASA Astrophysics Data System (ADS)
Alavi, S. M. M.; Birkl, C. R.; Howey, D. A.
2015-08-01
Electrochemical impedance spectroscopy (EIS) is an effective technique for diagnosing the behaviour of electrochemical devices such as batteries and fuel cells, usually by fitting data to an equivalent circuit model (ECM). The common approach in the laboratory is to measure the impedance spectrum of a cell in the frequency domain using a single sine sweep signal, then fit the ECM parameters in the frequency domain. This paper focuses instead on estimation of the ECM parameters directly from time-domain data. This may be advantageous for parameter estimation in practical applications such as automotive systems including battery-powered vehicles, where the data may be heavily corrupted by noise. The proposed methodology is based on the simplified refined instrumental variable for continuous-time fractional systems method ('srivcf'), provided by the Crone toolbox [1,2], combined with gradient-based optimisation to estimate the order of the fractional term in the ECM. The approach was tested first on synthetic data and then on real data measured from a 26650 lithium-ion iron phosphate cell with low-cost equipment. The resulting Nyquist plots from the time-domain fitted models match the impedance spectrum closely (much more accurately than when a Randles model is assumed), and the fitted parameters as separately determined through a laboratory potentiostat with frequency domain fitting match to within 13%.
Time-domain diffuse optics: towards next generation devices
NASA Astrophysics Data System (ADS)
Contini, Davide; Dalla Mora, Alberto; Arridge, Simon; Martelli, Fabrizio; Tosi, Alberto; Boso, Gianluca; Farina, Andrea; Durduran, Turgut; Martinenghi, Edoardo; Torricelli, Alessandro; Pifferi, Antonio
2015-07-01
Diffuse optics is a powerful tool for clinical applications ranging from oncology to neurology, but also for molecular imaging, and quality assessment of food, wood and pharmaceuticals. We show that ideally time-domain diffuse optics can give higher contrast and a higher penetration depth with respect to standard technology. In order to completely exploit the advantages of a time-domain system a distribution of sources and detectors with fast gating capabilities covering all the sample surface is needed. Here, we present the building block to build up such system. This basic component is made of a miniaturised source-detector pair embedded into the probe based on pulsed Vertical-Cavity Surface-Emitting Lasers (VCSEL) as sources and Single-Photon Avalanche Diodes (SPAD) or Silicon Photomultipliers (SiPM) as detectors. The possibility to miniaturized and dramatically increase the number of source detectors pairs open the way to an advancement of diffuse optics in terms of improvement of performances and exploration of new applications. Furthermore, availability of compact devices with reduction in size and cost can boost the application of this technique.
A Time Domain Fluorescence Tomography System for Small Animal Imaging
Raymond, Scott B.; Dunn, Andrew K.; Bacskai, Brian J.; Boas, David A.
2010-01-01
We describe the application of a time domain diffuse fluorescence tomography system for whole body small animal imaging. The key features of the system are the use of point excitation in free space using ultrashort laser pulses and noncontact detection using a gated, intensified charge-coupled device (CCD) camera. Mouse shaped epoxy phantoms, with embedded fluorescent inclusions, were used to verify the performance of a recently developed asymptotic lifetime-based tomography algorithm. The asymptotic algorithm is based on a multiexponential analysis of the decay portion of the data. The multiexponential model is shown to enable the use of a global analysis approach for a robust recovery of the lifetime components present within the imaging medium. The surface boundaries of the imaging volume were acquired using a photogrammetric camera integrated with the imaging system, and implemented in a Monte-Carlo model of photon propagation in tissue. The tomography results show that the asymptotic approach is able to separate axially located fluorescent inclusions centered at depths of 4 and 10 mm from the surface of the mouse phantom. The fluorescent inclusions had distinct lifetimes of 0.5 and 0.95 ns. The inclusions were nearly overlapping along the measurement axis and shown to be not resolvable using continuous wave (CW) methods. These results suggest the practical feasibility and advantages of a time domain approach for whole body small animal fluorescence molecular imaging, particularly with the use of lifetime as a contrast mechanism. PMID:18672432
NASA Astrophysics Data System (ADS)
Ibey, Bennett L.; Payne, Jason A.; Mixon, Dustin G.; Thomas, Robert J.; Roach, William P.
2008-02-01
Assessing the biological reaction to electromagnetic (EM) radiation of all frequencies and intensities is essential to the understanding of both the potential damage caused by the radiation and the inherent mechanisms within biology that respond, protect, or propagate damage to surrounding tissues. To understand this reaction, one may model the electromagnetic irradiation of tissue phantoms according to empirically measured or intelligently estimated dielectric properties. Of interest in this study is the terahertz region (0.2-2.0 THz), ranging from millimeter to infrared waves, which has been studied only recently due to lack of efficient sources. The specific interaction between this radiation and human tissue is greatly influenced by the significant EM absorption of water across this range, which induces a pronounced heating of the tissue surface. This study compares the Monte Carlo Multi-Layer (MCML) and Finite Difference Time Domain (FDTD) approaches for modeling the terahertz irradiation of human dermal tissue. Two congruent simulations were performed on a one-dimensional tissue model with unit power intensity profile. This works aims to verify the use of either technique for modeling terahertz-tissue interaction for minimally scattering tissues.
Padhi, Shantanu K.; Howard, John
2013-01-01
Nonlinear microwave imaging heavily relies on an accurate numerical electromagnetic model of the antenna system. The model is used to simulate scattering data that is compared to its measured counterpart in order to reconstruct the image. In this paper an antenna system immersed in water is used to image different canonical objects in order to investigate the implication of modeling errors on the final reconstruction using a time domain-based iterative inverse reconstruction algorithm and three-dimensional FDTD modeling. With the test objects immersed in a background of air and tap water, respectively, we have studied the impact of antenna modeling errors, errors in the modeling of the background media, and made a comparison with a two-dimensional version of the algorithm. In conclusion even small modeling errors in the antennas can significantly alter the reconstructed image. Since the image reconstruction procedure is highly nonlinear general conclusions are very difficult to make. In our case it means that with the antenna system immersed in water and using our present FDTD-based electromagnetic model the imaging results are improved if refraining from modeling the water-wall-air interface and instead just use a homogeneous background of water in the model. PMID:23606825
Two methods for transmission line simulation model creation based on time domain measurements
NASA Astrophysics Data System (ADS)
Rinas, D.; Frei, S.
2011-07-01
The emission from transmission lines plays an important role in the electromagnetic compatibility of automotive electronic systems. In a frequency range below 200 MHz radiation from cables is often the dominant emission factor. In higher frequency ranges radiation from PCBs and their housing becomes more relevant. Main sources for this emission are the conducting traces. The established field measurement methods according CISPR 25 for evaluation of emissions suffer from the need to use large anechoic chambers. Furthermore measurement data can not be used for simulation model creation in order to compute the overall fields radiated from a car. In this paper a method to determine the far-fields and a simulation model of radiating transmission lines, esp. cable bundles and conducting traces on planar structures, is proposed. The method measures the electromagnetic near-field above the test object. Measurements are done in time domain in order to get phase information and to reduce measurement time. On the basis of near-field data equivalent source identification can be done. Considering correlations between sources along each conductive structure in model creation process, the model accuracy increases and computational costs can be reduced.
Theory of mirrored time domain sampling for NMR spectroscopy.
Ghosh, Arindam; Wu, Yibing; He, Yunfen; Szyperski, Thomas
2011-12-01
A generalized theory is presented for novel mirrored hypercomplex time domain sampling (MHS) of NMR spectra. It is the salient new feature of MHS that two interferograms are acquired with different directionality of time evolution, that is, one is sampled forward from time t=0 to the maximal evolution time tmax, while the second is sampled backward from t=0 to -tmax. The sampling can be accomplished in a (semi) constant time or non constant-time manner. Subsequently, the two interferograms are linearly combined to yield a complex time domain signal. The manifold of MHS schemes considered here is defined by arbitrary settings of sampling phases ('primary phase shifts') and amplitudes of the two interferograms. It is shown that, for any two given primary phase shifts, the addition theorems of trigonometric functions yield the unique linear combination required to form the complex signal. In the framework of clean absorption mode (CAM) acquisition of NMR spectra being devoid of residual dispersive signal components, 'secondary phase shifts' represent time domain phase errors which are to be eliminated. In contrast, such secondary phase shifts may be introduced by experimental design in order to encode additional NMR parameters, a new class of NMR experiments proposed here. For generalization, it is further considered that secondary phase shifts may depend on primary phase shifts and/or sampling directionality. In order to compare with MHS theory, a correspondingly generalized theory is derived for widely used hypercomplex ('States') sampling (HS). With generalized theory it is shown, first, that previously introduced 'canonical' schemes, characterized by primary phases being multiples of π/4, afford maximal intensity of the desired absorptive signals in the absence of secondary phase shifts, and second, how primary phases can be adjusted to maximize the signal intensity provided that the secondary phase shifts are known. Third, it is demonstrated that theory enables
Finite Difference Time Domain Modeling at USA Instruments, Inc.
NASA Astrophysics Data System (ADS)
Curtis, Richard
2003-10-01
Due to the competitive nature of the commercial MRI industry, it is essential for the financial health of a participating company to innovate new coil designs and bring product to market rapidly in response to ever-changing market conditions. However, the technology of MRI coil design is still early in its stage of development and its principles are yet evolving. As a result, it is not always possible to know the relevant electromagnetic effects of a given design since the interaction of coil elements is complex and often counter-intuitive. Even if the effects are known qualitatively, the quantitative results are difficult to obtain. At USA Instruments, Inc., the acquisition of the XFDTDâ electromagnetic simulation tool from REMCOM, Inc., has been helpful in determining the electromagnetic performance characteristics of existing coil designs in the prototype stage before the coils are released for production. In the ideal case, a coil design would be modeled earlier at the conceptual stage, so that only good designs will make it to the prototyping stage and the electromagnetic characteristics better understood very early in the design process and before the testing stage has begun. This paper is a brief overview of using FDTD modeling for MRI coil design at USA Instruments, Inc., and shows some of the highlights of recent FDTD modeling efforts on Birdcage coils, a staple of the MRI coil design portfolio.
Time domain analysis of the weighted distributed order rheological model
NASA Astrophysics Data System (ADS)
Cao, Lili; Pu, Hai; Li, Yan; Li, Ming
2016-11-01
This paper presents the fundamental solution and relevant properties of the weighted distributed order rheological model in the time domain. Based on the construction of distributed order damper and the idea of distributed order element networks, this paper studies the weighted distributed order operator of the rheological model, a generalization of distributed order linear rheological model. The inverse Laplace transform on weighted distributed order operators of rheological model has been obtained by cutting the complex plane and computing the complex path integral along the Hankel path, which leads to the asymptotic property and boundary discussions. The relaxation response to weighted distributed order rheological model is analyzed, and it is closely related to many physical phenomena. A number of novel characteristics of weighted distributed order rheological model, such as power-law decay and intermediate phenomenon, have been discovered as well. And meanwhile several illustrated examples play important role in validating these results.
Time domain simulations of preliminary breakdown pulses in natural lightning.
Carlson, B E; Liang, C; Bitzer, P; Christian, H
2015-06-16
Lightning discharge is a complicated process with relevant physical scales spanning many orders of magnitude. In an effort to understand the electrodynamics of lightning and connect physical properties of the channel to observed behavior, we construct a simulation of charge and current flow on a narrow conducting channel embedded in three-dimensional space with the time domain electric field integral equation, the method of moments, and the thin-wire approximation. The method includes approximate treatment of resistance evolution due to lightning channel heating and the corona sheath of charge surrounding the lightning channel. Focusing our attention on preliminary breakdown in natural lightning by simulating stepwise channel extension with a simplified geometry, our simulation reproduces the broad features observed in data collected with the Huntsville Alabama Marx Meter Array. Some deviations in pulse shape details are evident, suggesting future work focusing on the detailed properties of the stepping mechanism.
Opening the 100-Year Window for Time-Domain Astronomy
NASA Astrophysics Data System (ADS)
Grindlay, Jonathan; Tang, Sumin; Los, Edward; Servillat, Mathieu
2012-04-01
The large-scale surveys such as PTF, CRTS and Pan-STARRS-1 that have emerged within the past 5 years or so employ digital databases and modern analysis tools to accentuate research into Time Domain Astronomy (TDA). Preparations are underway for LSST which, in another 6 years, will usher in the second decade of modern TDA. By that time the Digital Access to a Sky Century @ Harvard (DASCH) project will have made available to the community the full sky Historical TDA database and digitized images for a century (1890-1990) of coverage. We describe the current DASCH development and some initial results, and outline plans for the ``production scanning'' phase and data distribution which is to begin in 2012. That will open a 100-year window into temporal astrophysics, revealing rare transients and (especially) astrophysical phenomena that vary on time-scales of a decade. It will also provide context and archival comparisons for the deeper modern surveys.
Time domain BEM for sound radiation of tires
NASA Astrophysics Data System (ADS)
Banz, Lothar; Gimperlein, Heiko; Nezhi, Zouhair; Stephan, Ernst P.
2016-07-01
This work investigates a time domain boundary element method for the acoustic wave equation in an exterior domain in the half-space mathbb {R}^3_+. The Neumann problem is formulated as a boundary integral equation of the second kind, and the convergence and stability of conforming Galerkin approximations is studied in the complex geometry of a car or truck tire above a street. After a validation experiment, numerical results are presented in time or frequency domain for realistic benchmarks in traffic noise: the sound emission of vibrating tires, noise amplification in the horn-like geometry between the tire and the road, as well as the Doppler effect of a moving tire. The results are compared with calculations in frequency domain.
Time Domain Reflectometric and spectroscopic studies on toluene + butyronitrile solution
NASA Astrophysics Data System (ADS)
Karthick, N. K.; Arivazhagan, G.; Kumbharkhane, A. C.; Joshi, Y. S.; Kannan, P. P.
2016-03-01
The dielectric parameters of toluene + butyronitrile solution have been obtained by time domain reflectometry (TDR) technique in the frequency range from 10 MHz to 30 GHz at 298 K. Spectroscopic (FTIR and 13C NMR) studies have also been carried out on the solution and the results of the studies show that neat butyronitrile is self-associative through C-H⋯N contacts and weak intermolecular forces of C-H⋯N and C-H⋯π type are operative in the solution. The obtained dielectric parameters such as Kirkwood correlation factor g, relaxation time τ etc. have been analyzed in view of these weak intermolecular forces. The weak non-covalent interactions between heteromolecules appear to have no influence on the ideality of ɛm vs X2 curve of the solution. Heteromolecular entities with weak intermolecular forces experience larger hindrance leading to longer relaxation time τ.
Time domain simulations of preliminary breakdown pulses in natural lightning
NASA Astrophysics Data System (ADS)
Carlson, B. E.; Liang, C.; Bitzer, P.; Christian, H.
2015-06-01
Lightning discharge is a complicated process with relevant physical scales spanning many orders of magnitude. In an effort to understand the electrodynamics of lightning and connect physical properties of the channel to observed behavior, we construct a simulation of charge and current flow on a narrow conducting channel embedded in three-dimensional space with the time domain electric field integral equation, the method of moments, and the thin-wire approximation. The method includes approximate treatment of resistance evolution due to lightning channel heating and the corona sheath of charge surrounding the lightning channel. Focusing our attention on preliminary breakdown in natural lightning by simulating stepwise channel extension with a simplified geometry, our simulation reproduces the broad features observed in data collected with the Huntsville Alabama Marx Meter Array. Some deviations in pulse shape details are evident, suggesting future work focusing on the detailed properties of the stepping mechanism.
Time domain analysis of coherent terahertz synchrotron radiation
NASA Astrophysics Data System (ADS)
Hübers, H.-W.; Semenov, A.; Holldack, K.; Schade, U.; Wüstefeld, G.; Gol'tsman, G.
2005-10-01
The time structure of coherent terahertz synchrotron radiation at the electron storage ring of the Berliner Elektronensynchrotron und Speicherring Gesellschaft has been analyzed with a fast superconducting hot-electron bolometer. The emission from a single bunch of electrons was found to last ˜1500ps at frequencies around 0.4THz, which is much longer than the length of an electron bunch in the time domain (˜5ps). It is suggested that this is caused by multiple reflections at the walls of the beam line. The quadratic increase of the power with the number of electrons in the bunch as predicted for coherent synchrotron radiation and the transition from stable to bursting radiation were determined from a single storage ring fill pattern of bunches with different populations.
Characterization of Wheat Varieties Using Terahertz Time-Domain Spectroscopy
Ge, Hongyi; Jiang, Yuying; Lian, Feiyu; Zhang, Yuan; Xia, Shanhong
2015-01-01
Terahertz (THz) spectroscopy and multivariate data analysis were explored to discriminate eight wheat varieties. The absorption spectra were measured using THz time-domain spectroscopy from 0.2 to 2.0 THz. Using partial least squares (PLS), a regression model for discriminating wheat varieties was developed. The coefficient of correlation in cross validation (R) and root-mean-square error of cross validation (RMSECV) were 0.985 and 1.162, respectively. In addition, interval PLS was applied to optimize the models by selecting the most appropriate regions in the spectra, improving the prediction accuracy (R = 0.992 and RMSECV = 0.967). Results demonstrate that THz spectroscopy combined with multivariate analysis can provide rapid, nondestructive discrimination of wheat varieties. PMID:26024421
SVD compression for magnetic resonance fingerprinting in the time domain.
McGivney, Debra F; Pierre, Eric; Ma, Dan; Jiang, Yun; Saybasili, Haris; Gulani, Vikas; Griswold, Mark A
2014-12-01
Magnetic resonance (MR) fingerprinting is a technique for acquiring and processing MR data that simultaneously provides quantitative maps of different tissue parameters through a pattern recognition algorithm. A predefined dictionary models the possible signal evolutions simulated using the Bloch equations with different combinations of various MR parameters and pattern recognition is completed by computing the inner product between the observed signal and each of the predicted signals within the dictionary. Though this matching algorithm has been shown to accurately predict the MR parameters of interest, one desires a more efficient method to obtain the quantitative images. We propose to compress the dictionary using the singular value decomposition, which will provide a low-rank approximation. By compressing the size of the dictionary in the time domain, we are able to speed up the pattern recognition algorithm, by a factor of between 3.4-4.8, without sacrificing the high signal-to-noise ratio of the original scheme presented previously.
Nonlinear ultrasonic resonators: a numerical analysis in the time domain.
Vanhille, Christian; Campos-Pozuelo, Cleofé
2006-12-22
In the framework of the study of nonlinear acoustic phenomena arising in high-power ultrasonic resonators, this paper deals with the numerical prediction of the behaviour of strongly nonlinear waves in resonators. In particular three-dimensional cavities in complex modal configurations are analyzed. The main motivation of this work is the understanding and optimisation of high-power ultrasonic applications in fluids. Based on conservation laws written in Lagrangian coordinates and the isentropic state equation, several evolution equations (one-dimensional, two-dimensional, three-dimensional and axisymmetric) are proposed and numerically solved in the time domain. No restriction on nonlinearity level is imposed. These developments allow the simulation of the time evolution of the pressure distribution inside the cavity, as well as the harmonics distribution. Distortion, nonlinear attenuation and rms pressure can be studied. Periodic (continue) and pulsed signal excitation are possible. Some results referred to complicated nonlinear waves are presented.
Uncertainty in Terahertz Time-Domain Spectroscopy Measurement of Liquids
NASA Astrophysics Data System (ADS)
Yang, Fei; Liu, Liping; Song, Maojiang; Han, Feng; Shen, Li; Hu, Pengfei; Zhang, Fang
2017-02-01
Terahertz time-domain spectroscopy (THz-TDS) is a significant technique for characterizing materials as it allows fast and broadband measurement of optical constants in the THz regime. The measurement precision of the constants is highly influenced by the complicated measurement procedure and data processing. Taking THz transmission measurement of liquids into account, the sources of error existing in THz-TDS process are identified. The contributions of each source to the uncertainty of optical constants in THz-TDS process are formulated, with particular emphasis on the effect of multilayer reflections and plane wave assumption. As a consequence, an analytical model is proposed for uncertainty evaluation in a THz-TDS measurement of liquids. An actual experiment with a Di 2-Ethyl Hexyl Phthalate (DEHP) sample is carried out to show that the proposed model could be a basis to evaluate the measurement precision of optical constants of liquids.
Time-domain response of the ARIANNA detector
NASA Astrophysics Data System (ADS)
Barwick, S. W.; Berg, E. C.; Besson, D. Z.; Duffin, T.; Hanson, J. C.; Klein, S. R.; Kleinfelder, S. A.; Piasecki, M.; Ratzlaff, K.; Reed, C.; Roumi, M.; Stezelberger, T.; Tatar, J.; Walker, J.; Young, R.; Zou, L.
2015-03-01
The Antarctic Ross Ice Shelf Antenna Neutrino Array (ARIANNA) is a high-energy neutrino detector designed to record the Askaryan electric field signature of cosmogenic neutrino interactions in ice. To understand the inherent radio-frequency (RF) neutrino signature, the time-domain response of the ARIANNA RF receiver must be measured. ARIANNA uses Create CLP5130-2N log-periodic dipole arrays (LPDAs). The associated effective height operator converts incident electric fields to voltage waveforms at the LDPA terminals. The effective height versus time and incident angle was measured, along with the associated response of the ARIANNA RF amplifier. The results are verified by correlating to field measurements in air and ice, using oscilloscopes. Finally, theoretical models for the Askaryan electric field are combined with the detector response to predict the neutrino signature.
Time domain simulation and sound synthesis for the snare drum.
Bilbao, Stefan
2012-01-01
The snare drum is a complex system, relying on the interaction of multiple components: the drumheads, or membranes, a set of snares, the surrounding acoustic field and an internal cavity. Because these components are multidimensional, and due to a strong distributed non-linearity (the snare interaction), many techniques used frequently in physical modeling synthesis applications, such as digital waveguides and modal methods are difficult to apply. In this article, finite difference time domain techniques are applied to a full 3D system, and various features of interest, such as the coupling between membranes, and the interaction between the membranes and the snares, are examined in detail. Also discussed are various numerical features, such as spurious splitting of degenerate modes and bandwidth limitation, and estimates of computational complexity are provided. Sound examples are presented.
Detecting Rare Events in the Time-Domain
Rest, A; Garg, A
2008-10-31
One of the biggest challenges in current and future time-domain surveys is to extract the objects of interest from the immense data stream. There are two aspects to achieving this goal: detecting variable sources and classifying them. Difference imaging provides an elegant technique for identifying new transients or changes in source brightness. Much progress has been made in recent years toward refining the process. We discuss a selection of pitfalls that can afflict an automated difference imagine pipeline and describe some solutions. After identifying true astrophysical variables, we are faced with the challenge of classifying them. For rare events, such as supernovae and microlensing, this challenge is magnified because we must balance having selection criteria that select for the largest number of objects of interest against a high contamination rate. We discuss considerations and techniques for developing classification schemes.
Discontinuous Galerkin time-domain computations of metallic nanostructures.
Stannigel, Kai; König, Michael; Niegemann, Jens; Busch, Kurt
2009-08-17
We apply the three-dimensional Discontinuous-Galerkin Time-Domain method to the investigation of the optical properties of bar- and V-shaped metallic nanostructures on dielectric substrates. A flexible finite element-like mesh together with an expansion into high-order basis functions allows for an accurate resolution of complex geometries and strong field gradients. In turn, this provides accurate results on the optical response of realistic structures. We study in detail the influence of particle size and shape on resonance frequencies as well as on scattering and absorption efficiencies. Beyond a critical size which determines the onset of the quasi-static limit we find significant deviations from the quasi-static theory. Furthermore, we investigate the influence of the excitation by comparing normal illumination and attenuated total internal reflection setups. Finally, we examine the possibility of coherently controlling the local field enhancement of V-structures via chirped pulses.
Synthetic Spectrum Approach for Brillouin Optical Time-Domain Reflectometry
Nishiguchi, Ken'ichi; Li, Che-Hsien; Guzik, Artur; Kishida, Kinzo
2014-01-01
We propose a novel method to improve the spatial resolution of Brillouin optical time-domain reflectometry (BOTDR), referred to as synthetic BOTDR (S-BOTDR), and experimentally verify the resolution improvements. Due to the uncertainty relation between position and frequency, the spatial resolution of a conventional BOTDR system has been limited to about one meter. In S-BOTDR, a synthetic spectrum is obtained by combining four Brillouin spectrums measured with different composite pump lights and different composite low-pass filters. We mathematically show that the resolution limit, in principle, for conventional BOTDR can be surpassed by S-BOTDR and experimentally prove that S-BOTDR attained a 10-cm spatial resolution. To the best of our knowledge, this has never been achieved or reported. PMID:24608011
Time Domain Simulations of Arm Locking in LISA
NASA Technical Reports Server (NTRS)
Thorpe, J. I.; Maghami, P.; Livas, Jeff
2011-01-01
Arm locking is a technique that has been proposed for reducing laser frequency fluctuations in the Laser Interferometer Space Antenna (LISA). a gravitational-wave observatory sensitive' in the milliHertz frequency band. Arm locking takes advantage of the geometric stability of the triangular constellation of three spacecraft that comprise LISA to provide a frequency reference with a stability in the LISA measurement band that exceeds that available from a standard reference such as an optical cavity or molecular absorption line. We have implemented a time-domain simulation of arm locking including the expected limiting noise sources (shot noise, clock noise. spacecraft jitter noise. and residual laser frequency noise). The effect of imperfect a priori knowledge of the LISA heterodyne frequencies and associated "pulling" of an arm locked laser is included. We find that our implementation meets requirements both on the noise and dynamic range of the laser frequency.
The time domain response of some systems for sound reproduction
NASA Astrophysics Data System (ADS)
Nelson, P. A.; Rose, J. F. W.
2006-09-01
The perception in a listener of the existence of a "virtual" source of sound at a prescribed spatial position can be produced by ensuring that the acoustic signals at the listener's ears faithfully replicate those that would be produced by a "real" source at the same position. When loudspeakers are used to transmit the signals, it is necessary to pass the signals intended for presentation at the listener's ears through a matrix of filters that provide the inverse of the matrix of transfer functions that relates the loudspeaker input signals to the listener's ear signals. The characteristics of such filter matrices are profoundly influenced by the conditioning of the matrix to be inverted. This filter design problem is reviewed here by representing the loudspeakers as simple point monopole sources the head of the listener as a rigid sphere. The case of a virtual acoustic imaging system that uses two loudspeakers in order to reproduce the signals at the two ears is first described in some detail and previous work is reviewed. It is confirmed that the time domain response of the reproduced field is of long duration at frequencies where the inversion problem is ill-conditioned. The influence of the presence of the listener's head on this time domain behaviour is also evaluated. The principle is then extended to four input-four output reproduction systems and the computational model is used to explain some previous experimental observations. Finally, the conditioning of five input-four output systems is also examined and shown to have some potentially desirable characteristics.
A Time Domain Along-Track SAR Interferometry Method
NASA Astrophysics Data System (ADS)
Cao, N.; Lee, H.; Jung, H. C.
2015-12-01
Differential interferometric synthetic aperture radar (DInSAR) has already been proven to be a useful technique for measuring ground displacement at millimeter level. One major drawback of traditional DInSAR technique is that only 1-D deformation in slant range direction can be detected. In order to obtain along-track displacement using a single InSAR pair, two major attempts have been made. The first one is based on cross-correlation between two SAR amplitude images. The second attempt is based on split-beam processing to generate two SAR images from forward- and backward-looking beams. Comparing with the former method, this multiple-aperture SAR interferometry (MAI) can achieve much better measurement accuracy. The major drawback of the MAI method is degraded signal to noise ratio (SNR) and along-track resolution since total along-track integration time decreases in the split-beam procedure. In order to improve the SNR and along-track resolution as well as to extract the terrain displacement in the along-track direction, a time domain along-track SAR interferometry method is proposed in this study. Using traditional time domain backprojection method, the phase component corresponding to slant range direction offset can be estimated and removed from the range compressed SAR signal. Then a phase estimation procedure is implemented to obtain the phase component in the along-track direction. Using ALOS PALSAR data over Kilauea Volcano area in Hawai'i, our experimental results demonstrate the improved performance of the proposed method in extracting 2-D terrain deformation map from one pair of SAR images.
Time-domain electromagnetic scattering by a sphere in uniform translational motion.
Garner, Timothy J; Lakhtakia, Akhlesh; Breakall, James K; Bohren, Craig F
2017-02-01
Scattering by a uniformly translating sphere of a pulse that modulates the amplitude of a linearly polarized plane wave was formulated using the frame-hopping method involving a laboratory inertial reference frame and the sphere's comoving inertial reference frame. The incident signal was defined in the laboratory frame and transformed to the comoving frame with the Lorentz transformation, thereby altering the incident signal's spectrum, direction of propagation of the carrier plane wave, and the direction of the incident electric field, depending on the sphere's velocity. In the comoving frame, the incident signal was Fourier-transformed to the frequency domain, and the scattered field phasors were computed in all directions using the constitutive parameters of the material of the sphere at rest. The scattered signal in the comoving frame was obtained using the inverse Fourier transform. Finally, the scattered signal in the laboratory frame was obtained by inverting the original Lorentz transformation. The backscattered signal was found to depend strongly on the sphere's velocity, when the sphere's speed is an appreciable fraction of the speed of light in free space. The change in the backscattered signal compared with the backscattered signal from a stationary sphere is the greatest when the sphere's velocity is either parallel or antiparallel to the direction of propagation of the incident signal. The backscattered signal is also affected by motion transverse to the incident signal's direction of propagation; then, the backscattered signal depends on whether or not the motion is aligned with the direction of the incident electric field.
NASA Astrophysics Data System (ADS)
Gaunaurd, G. C.; Strifors, H. C.; Sullivan, A.
2008-06-01
Using a Method-of-Moments (MoM) code, we earlier simulated ultra-wideband (UWB) returned echoes from two targets, one penetrable and one impenetrable, buried in a soil with known electric properties. The simple shape of mines, coupled with their predictable deployment in the ground, has also provided a fundamental understanding of the underlying backscatter phenomenology. In particular, the backscattered waveform from a mine can be decomposed into a collection of closely spaced copies of an elemental wave object with different amplitudes and time delays. This wave object is here defined as the derivative of the waveform incident on the target. The spacing of the copies or replicas of the wave object could be determined by the round trip time delay between scattering centers. This methodology was previously applied to impenetrable targets and is now applied also to a penetrable target. The previously computed returns from each target for a given incident pulse are modeled by a few copies of the elemental wave object with the time delay and amplitude of each copy taken as unknown parameters. These parameters are then determined by minimizing in the least square sense the difference between the MoM computed signal and the model signal using the differential evolution method (DEM). The methodology is extended by way of our previously developed target translated method (TTM) to approximate the computation of the backscattered model signal when the target is buried at a different depth in the soil with a different moisture content.
Double absorbing boundaries for finite-difference time-domain electromagnetics
NASA Astrophysics Data System (ADS)
LaGrone, John; Hagstrom, Thomas
2016-12-01
We describe the implementation of optimal local radiation boundary condition sequences for second order finite difference approximations to Maxwell's equations and the scalar wave equation using the double absorbing boundary formulation. Numerical experiments are presented which demonstrate that the design accuracy of the boundary conditions is achieved and, for comparable effort, exceeds that of a convolution perfectly matched layer with reasonably chosen parameters. An advantage of the proposed approach is that parameters can be chosen using an accurate a priori error bound.
Fast Time Domain Integral Equation Solvers for Large-Scale Electromagnetic Analysis
2004-10-01
separable and non-separable source expansions. The separable representations will rely on divergence-conforming Nedelec elements defined on geometrically...the work of Ha-Duong/Aboud/ Nedelec , such solvers, when carefully implemented, are stable. Their implementation however is very difficult; moreover
Higher-Order Mixed Finite Element Methods for Time Domain Electromagnetics
White, D; Stowell, M; Koning, J; Rieben, R; Fisher, A; Champagne, N; Madsen, N
2004-02-06
This is the final report for LDRD 01-ERD-005. The Principal Investigator was Niel Madsen of the Defense Sciences Engineering Division (DSED). Collaborators included Daniel White, Joe Koning and Nathan Champagne of DSED, Mark Stowell of Center for Applications Development and Software Engineering (CADSE), and Ph.D. students Rob Rieben and Aaron Fisher at the UC Davis Department of Applied Science. It should be noted that the students were partially supported by the LLNL Student-Employee Graduate Research Fellow program. We begin with an Introduction which provides background and motivation for this research effort. Section II contains high-level description of our Approach, and Section III summarizes our key research Accomplishments. A description of the Software deliverables is provided in Section IV, and Section V includes simulation Validation and Results. It should be noted we do not get into the mathematical details in this report, rather these can be found in our publications which are listed in Section III.
Wakefield Computations for the CLIC PETS using the Parallel Finite Element Time-Domain Code T3P
Candel, A; Kabel, A.; Lee, L.; Li, Z.; Ng, C.; Schussman, G.; Ko, K.; Syratchev, I.; /CERN
2009-06-19
In recent years, SLAC's Advanced Computations Department (ACD) has developed the high-performance parallel 3D electromagnetic time-domain code, T3P, for simulations of wakefields and transients in complex accelerator structures. T3P is based on advanced higher-order Finite Element methods on unstructured grids with quadratic surface approximation. Optimized for large-scale parallel processing on leadership supercomputing facilities, T3P allows simulations of realistic 3D structures with unprecedented accuracy, aiding the design of the next generation of accelerator facilities. Applications to the Compact Linear Collider (CLIC) Power Extraction and Transfer Structure (PETS) are presented.
NASA Astrophysics Data System (ADS)
Chun, Kyungwon; Kim, Huioon; Hong, Hyunpyo; Chung, Youngjoo
GMES which stands for GIST Maxwell's Equations Solver is a Python package for a Finite-Difference Time-Domain (FDTD) simulation. The FDTD method widely used for electromagnetic simulations is an algorithm to solve the Maxwell's equations. GMES follows Object-Oriented Programming (OOP) paradigm for the good maintainability and usability. With the several optimization techniques along with parallel computing environment, we could make the fast and interactive implementation. Execution speed has been tested in a single host and Beowulf class cluster. GMES is open source and available on the web (http://www.sf.net/projects/gmes).
NASA Astrophysics Data System (ADS)
Beker, B.
1992-12-01
Numerical modeling of electromagnetic (EM) interaction is normally performed by using either differential or integral equation methods. Both techniques can be implemented to solve problems in frequency or time domain. The method of moments (MOM) approach to solving integral equations has matured to the point where it can be used to solve complex problems. In the past, MOM has only been applied to scattering and radiation problems involving perfectly conducting or isotropic penetrable, lossy or lossless objects. However, many materials, (e.g., composites that are used on the Navy's surface ships in practical applications) exhibit anisotropic properties. To account for these new effects, several integral equation formulations for scattering and radiation by anisotropic objects have been developed recently. The differential equation approach to EM interaction studies has seen the emergence of the finite-difference time-domain (FD-TD) method as the method of choice in many of today's scattering and radiation applications. This approach has been applied to study transient as well as steady-state scattering from many complex structures, radiation from wire antennas, and coupling into wires through narrow apertures in conducting cavities. It is important to determine whether or not, and how effectively, the FD-TD can be used to solve EM interaction problems of interest to the Navy, such as investigating potential EM interference in shipboard communication systems. Consequently, this report partly addresses this issue by dealing exclusively with FD-TD modeling of time-domain EM scattering and radiation.
TIME-DOMAIN METHODS FOR DIFFUSIVE TRANSPORT IN SOFT MATTER
Fricks, John; Yao, Lingxing; Elston, Timothy C.; Gregory Forest, And M.
2015-01-01
Passive microrheology [12] utilizes measurements of noisy, entropic fluctuations (i.e., diffusive properties) of micron-scale spheres in soft matter to infer bulk frequency-dependent loss and storage moduli. Here, we are concerned exclusively with diffusion of Brownian particles in viscoelastic media, for which the Mason-Weitz theoretical-experimental protocol is ideal, and the more challenging inference of bulk viscoelastic moduli is decoupled. The diffusive theory begins with a generalized Langevin equation (GLE) with a memory drag law specified by a kernel [7, 16, 22, 23]. We start with a discrete formulation of the GLE as an autoregressive stochastic process governing microbead paths measured by particle tracking. For the inverse problem (recovery of the memory kernel from experimental data) we apply time series analysis (maximum likelihood estimators via the Kalman filter) directly to bead position data, an alternative to formulas based on mean-squared displacement statistics in frequency space. For direct modeling, we present statistically exact GLE algorithms for individual particle paths as well as statistical correlations for displacement and velocity. Our time-domain methods rest upon a generalization of well-known results for a single-mode exponential kernel [1, 7, 22, 23] to an arbitrary M-mode exponential series, for which the GLE is transformed to a vector Ornstein-Uhlenbeck process. PMID:26412904
Closed-loop quantum control utilizing time domain maps
NASA Astrophysics Data System (ADS)
Biteen, Julie S.; Geremia, J. M.; Rabitz, Herschel
2003-05-01
Closed-loop laser control of quantum dynamics phenomena may be accomplished through frequency domain manipulations in the laboratory guided by a learning algorithm. This paper presents an alternative method based on the use of nonlinear input→output maps generated in the time domain, although the actual experiments and control optimization are carried out in the frequency domain. The procedure first involves the construction of input→output maps relating the field structure to the observed control performance. These maps are utilized as a substitute for actual experiments in the subsequent optimization stage in order to find the field that drives the system to a specified target. This closed-loop learning process is repeated with a sufficient number of maps until a control field is found that yields the target observable as best as possible. The overall algorithm is simulated with two model quantum systems. It is shown that excellent quality control can be achieved through this sequential learning procedure, even with individual maps that have only modest global accuracy.
A New Time Domain Formulation for Broadband Noise Predictions
NASA Technical Reports Server (NTRS)
Casper, J.; Farassat, F.
2002-01-01
A new analytic result in acoustics called "Formulation 1B," proposed by Farassat, is used to compute the loading noise from an unsteady surface pressure distribution on a thin airfoil in the time domain. This formulation is a new solution of the Ffowcs Williams-Hawkings equation with the loading source term. The formulation contains a far field surface integral that depends on the time derivative and the surface gradient of the pressure on the airfoil, as well as a contour integral on the boundary of the airfoil surface. As a first test case, the new formulation is used to compute the noise radiated from a flat plate, moving through a sinusoidal gust of constant frequency. The unsteady surface pressure for this test case is analytically specified from a result based on linear airfoil theory. This test case is used to examine the velocity scaling properties of Formulation 1B and to demonstrate its equivalence to Formulation 1A of Farassat. The new acoustic formulation, again with an analytic surface pressure, is then used to predict broadband noise radiated from an airfoil immersed in homogeneous, isotropic turbulence. The results are compared with experimental data previously reported by Paterson and Amiet. Good agreement between predictions and measurements is obtained. Finally, an alternative form of Formulation 1B is described for statistical analysis of broadband noise.
A New Time Domain Formulation for Broadband Noise Predictions
NASA Technical Reports Server (NTRS)
Casper, Jay H.; Farassat, Fereidoun
2002-01-01
A new analytic result in acoustics called "Formulation 1B," proposed by Farassat, is used to compute the loading noise from an unsteady surface pressure distribution on a thin airfoil in the time domain. This formulation is a new solution of the Ffowcs Williams-Hawkings equation with the loading source term. The formulation contains a far field surface integral that depends on the time derivative and the surface gradient of the pressure on the airfoil, as well as a contour integral on the boundary of the airfoil surface. As a first test case, the new formulation is used to compute the noise radiated from a flat plate, moving through a sinusoidal gust of constant frequency. The unsteady surface pressure for this test case is analytically specied from a result based on linear airfoil theory. This test case is used to examine the velocity scaling properties of Formulation 1B and to demonstrate its equivalence to Formulation 1A of Farassat. The new acoustic formulation, again with an analytic surface pressure, is then used to predict broadband noise radiated from an airfoil immersed in homogeneous, isotropic turbulence. The results are compared with experimental data previously reported by Paterson and Amiet. Good agreement between predictions and measurements is obtained. Finally, an alternative form of Formulation 1B is described for statistical analysis of broadband noise.
Statistical and Mathematical Methods for Synoptic Time Domain Surveys
NASA Astrophysics Data System (ADS)
Mahabal, Ashish A.; SAMSI Synoptic Surveys Time Domain Working Group
2017-01-01
Recent advances in detector technology, electronics, data storage, and computation have enabled astronomers to collect larger and larger datasets, and moreover, pose interesting questions to answer with those data. The complexity of the data allows data science techniques to be used. These have to be grounded in sound techniques. Identify interesting mathematical and statistical challenges and working on their solutions is one of the aims of the year-long ‘Statistical, Mathematical and Computational Methods for Astronomy (ASTRO)’ program of SAMSI. Of the many working groups that have been formed, one is on Synoptic Time Domain Surveys. Within this we have various subgroups discussing topics such as Designing Statistical Features for Optimal Classification, Scheduling Observations, Incorporating Unstructured Information, Detecting Outliers, Lightcurve Decomposition and Interpolation, Domain Adaptation, and also Designing a Data Challenge. We will briefly highlight some of the work going on in these subgroups along with their interconnections, and the plans for the near future. We will also highlight the overlaps with the other SAMSI working groups and also indicate how the wider astronomy community can both participate and benefit from the activities.
Demonstration of Time Domain Multiplexed Readout for Magnetically Coupled Calorimeters
NASA Technical Reports Server (NTRS)
Porst, J.-P.; Adams, J. S.; Balvin, M.; Bandler, S.; Beyer, J.; Busch, S. E.; Drung, D.; Seidel, G. M.; Smith, S. J.; Stevenson, T. R.
2012-01-01
Magnetically coupled calorimeters (MCC) have extremely high potential for x-ray applications due to the inherent high energy resolution capability and being non-dissipative. Although very high energy-resolution has been demonstrated, until now there has been no demonstration of multiplexed read-out. We report on the first realization of a time domain multiplexed (TDM) read-out. While this has many similarities with TDM of transition-edge-sensors (TES), for MGGs the energy resolution is limited by the SQUID read-out noise and requires the well established scheme to be altered in order to minimize degradation due to noise aliasing effects. In cur approach, each pixel is read out by a single first stage SQUID (SQ1) that is operated in open loop. The outputs of the SQ1 s are low-pass filtered with an array of low cross-talk inductors, then fed into a single-stage SQUID TD multiplexer. The multiplexer is addressed from room temperature and read out through a single amplifier channel. We present results achieved with a new detector platform. Noise performance is presented and compared to expectations. We have demonstrated multiplexed X-ray spectroscopy at 5.9keV with delta_FWHM=10eV. In an optimized setup, we show it is possible to multiplex 32 detectors without significantly degrading the Intrinsic detector resolution.
Nitrocellulose membrane sample holder using for terahertz time domain spectroscopy
NASA Astrophysics Data System (ADS)
Zhao, Xiaojing; Liu, Shangjian; Wang, Cuicui; Zuo, Jian; Zhang, Cunlin
2016-11-01
Terahertz (THz) technology has promising applications for the detection and identification of materials because it has a great advantage in measuring material fingerprint spectrum. Terahertz time-domain spectroscopy (THz-TDS) is a key technique that is applied to spectroscopic measurement of materials. However, it is difficult to press a pellet with small mass of sample and a bulking medium such as polyethylene (PE) powder usually need to be added. Characteristic absorption peaks of the solution in liquid cell is hard to be observed due to the interaction between materials and water molecules. Therefore, one method using the hydrophilic nitrocellulose (NC) membrane as a sample holder was applied to detect samples in an aqueous medium by THz-TDS. In this study, the α-lactose samples were mixed with 20 μl of deionized water and then applied directly onto the double-layered NC membrane sample holder. This mixture is located on the gap of two piece of NC membranes. Firstly the NC membranes with different pore sizes were tested in the experiment. And then the α-lactose solutions with different concentrations were measured on the NC with different pore sizes. Consequently, the small mass of samples can be detected and the characteristic absorption peaks become stronger with the increase of NC pore size. Moreover, compared to the traditional pellet-making and liquid cell detection, this membrane method is more convenient and easy to operate.
Determining Phthalic Acid Esters Using Terahertz Time Domain Spectroscopy
NASA Astrophysics Data System (ADS)
Liu, L.; Shen, L.; Yang, F.; Han, F.; Hu, P.; Song, M.
2016-09-01
In this report terahertz time domain spectroscopy (THz-TDS) is applied for determining phthalic acid esters (PAEs) in standard materials. We reported the THz transmission spectrum in the frequency range of 0.2 to 2.0 THz for three PAEs: di-n-butyl phthalate (DBP), di-isononyl phthalate (DINP), and di-2-ethylhexyl phthalate ester (DEHP). The study provided the refractive indices and absorption features of these materials. The absorption spectra of three PAEs were simulated by using Gaussian software with Density Functional Theory (DFT) methods. For pure standard PAEs, the values of the refractive indices changed between 1.50 and 1.60. At 1.0 THz, the refractive indices were 1.524, 1.535, and 1.563 for DINP, DEHP, and DBP, respectively. In this experiment different concentrations of DBP were investigated using THz-TDS. Changes were measured in the low THz frequency range for refractive indices and characteristic absorption. The results indicated that THz-TDS is promising as a new method in determining PAEs in many materials. The results of this study could be used to support the practical application of THz-TDS in quality detection and food monitoring. In particular, this new technique could be used in detecting hazardous materials and other substances present in wine or foods.
Optical identification based on time domain optical coherence tomography.
Gandhi, Vishal; Semenov, Dmitry; Honkanen, Seppo; Hauta-Kasari, Markku
2015-09-01
We present a novel method for optical identification, i.e., authenticating valuable documents such as a passport, credit cards, and bank notes, using optical coherence tomography (OCT). An OCT system can capture three-dimensional (3D) images and visualize the internal structure of an object. In our work, as an object, we consider a multilayered optical identification tag composed of a limited number of thin layers (10-100 μm thick). The thickness, width, and location of the layers in the tag encode a unique identification information. Reading of the tag is done using a time domain OCT (TD-OCT) system. Typically, a TD-OCT system requires continuous mechanical scanning in one or more directions to get a 3D volume image of an object. The continuous scanning implies a complicated optical setup, which makes an OCT system fragile and expensive. We propose to avoid the conventional scanning by (1) not requiring 3D imaging, and (2) utilizing the motion of the optical tag itself. The motion is introduced to the tag reader, for example, by a user, which replaces the need for conventional scanning. The absence of a conventional scanning mechanism makes the proposed OCT method very simple and suited for identification purposes; however, it also puts some constraints to the construction of the optical tag, which we discuss in this paper in detail.
Time domain simulations of arm locking in LISA
Thorpe, J. I.; Livas, J.; Maghami, P.
2011-06-15
Arm locking is a proposed laser frequency stabilization technique for the Laser Interferometer Space Antenna (LISA), a gravitational-wave observatory sensitive in the milliHertz frequency band. Arm locking takes advantage of the geometric stability of the triangular constellation of three spacecraft that compose LISA to provide a frequency reference with a stability in the LISA measurement band that exceeds that available from a standard reference such as an optical cavity or molecular absorption line. We have implemented a time-domain simulation of a Kalman-filter-based arm-locking system that includes the expected limiting noise sources as well as the effects of imperfect a priori knowledge of the constellation geometry on which the design is based. We use the simulation to study aspects of the system performance that are difficult to capture in a steady-state frequency-domain analysis such as frequency pulling of the master laser due to errors in estimates of heterodyne frequency. We find that our implementation meets requirements on both the noise and dynamic range of the laser frequency with acceptable tolerances and that the design is sufficiently insensitive to errors in the estimated constellation geometry that the required performance can be maintained for the longest continuous measurement intervals expected for the LISA mission.
A 128 Multiplexing Factor Time-Domain SQUID Multiplexer
NASA Astrophysics Data System (ADS)
Prêle, D.; Voisin, F.; Piat, M.; Decourcelle, T.; Perbost, C.; Chapron, C.; Rambaud, D.; Maestre, S.; Marty, W.; Montier, L.
2016-07-01
A cryogenic 128:1 Time-Domain Multiplexer (TDM) has been developed for the readout of kilo-pixel Transition Edge Sensor (TES) arrays dedicated to the Q&U Bolometric Interferometer for Cosmology (QUBIC) instrument which aims to measure the B-mode polarization of the Cosmic Microwave Background. Superconducting QUantum Interference Devices (SQUIDs) are usually used to read out TESs. Moreover, SQUIDs are used to build TDM by biasing sequentially the SQUIDs connected together—one for each TES. In addition to this common technique which allows a typical 32 multiplexing factor, a cryogenic integrated circuit provides a 4:1 second multiplexing stage. This cryogenic integrated circuit is one of the original part of our TDM achieving an unprecedented 128 multiplexing factor. We present these two dimension TDM stages: topology of the SQUID multiplexer, operation of the cryogenic integrated circuit, and integration of the full system to read out a TES array dedicated to the QUBIC instrument. Flux-locked loop operation in multiplexed mode is also discussed.
Time domain simulations of preliminary breakdown pulses in natural lightning
Carlson, B E; Liang, C; Bitzer, P; Christian, H
2015-01-01
Lightning discharge is a complicated process with relevant physical scales spanning many orders of magnitude. In an effort to understand the electrodynamics of lightning and connect physical properties of the channel to observed behavior, we construct a simulation of charge and current flow on a narrow conducting channel embedded in three-dimensional space with the time domain electric field integral equation, the method of moments, and the thin-wire approximation. The method includes approximate treatment of resistance evolution due to lightning channel heating and the corona sheath of charge surrounding the lightning channel. Focusing our attention on preliminary breakdown in natural lightning by simulating stepwise channel extension with a simplified geometry, our simulation reproduces the broad features observed in data collected with the Huntsville Alabama Marx Meter Array. Some deviations in pulse shape details are evident, suggesting future work focusing on the detailed properties of the stepping mechanism. Key Points Preliminary breakdown pulses can be reproduced by simulated channel extension Channel heating and corona sheath formation are crucial to proper pulse shape Extension processes and channel orientation significantly affect observations PMID:26664815
Time-domain simulation of a guitar: model and method.
Derveaux, Grégoire; Chaigne, Antoine; Joly, Patrick; Bécache, Eliane
2003-12-01
This paper presents a three-dimensional time-domain numerical model of the vibration and acoustic radiation from a guitar. The model involves the transverse displacement of the string excited by a force pulse, the flexural motion of the soundboard, and the sound radiation. A specific spectral method is used for solving the Kirchhoff-Love's dynamic top plate model for a damped, heterogeneous orthotropic material. The air-plate interaction is solved with a fictitious domain method, and a conservative scheme is used for the time discretization. Frequency analysis is performed on the simulated sound pressure and plate velocity waveforms in order to evaluate quantitatively the transfer of energy through the various components of the coupled system: from the string to the soundboard and from the soundboard to the air. The effects of some structural changes in soundboard thickness and cavity volume on the produced sounds are presented and discussed. Simulations of the same guitar in three different cases are also performed: "in vacuo," in air with a perfectly rigid top plate, and in air with an elastic top plate. This allows comparisons between structural, acoustic, and structural-acoustic modes of the instrument. Finally, attention is paid to the evolution with time of the spatial pressure field. This shows, in particular, the complex evolution of the directivity pattern in the near field of the instrument, especially during the attack.
Time domain functional NIRS imaging for human brain mapping.
Torricelli, Alessandro; Contini, Davide; Pifferi, Antonio; Caffini, Matteo; Re, Rebecca; Zucchelli, Lucia; Spinelli, Lorenzo
2014-01-15
This review is aimed at presenting the state-of-the-art of time domain (TD) functional near-infrared spectroscopy (fNIRS). We first introduce the physical principles, the basics of modeling and data analysis. Basic instrumentation components (light sources, detection techniques, and delivery and collection systems) of a TD fNIRS system are described. A survey of past, existing and next generation TD fNIRS systems used for research and clinical studies is presented. Performance assessment of TD fNIRS systems and standardization issues are also discussed. Main strengths and weakness of TD fNIRS are highlighted, also in comparison with continuous wave (CW) fNIRS. Issues like quantification of the hemodynamic response, penetration depth, depth selectivity, spatial resolution and contrast-to-noise ratio are critically examined, with the help of experimental results performed on phantoms or in vivo. Finally we give an account on the technological developments that would pave the way for a broader use of TD fNIRS in the neuroimaging community.
Time domain reflectometry as a rock mass monitoring technique
Francke, J.L.; Terrill, L.J.; Allen, W.W.
1996-06-01
This paper describes the practices and methods used in a study of Time Domain Reflectometry (TDR) as an inexpensive deformation monitoring tool in underground excavations at the Waste Isolation Pilot Plant (WIPP). The WIPP is being developed near Carlsbad, New Mexico, for the disposal of transuranic nuclear wastes in bedded salt 655 m (2150 ft) below the surface. Data collected from WIPP geomechanical monitoring are used to characterize conditions, confirm design assumptions, and understand and predict the performance of the deep salt excavation. The geomechanical monitoring techniques ranging from inspection of observation boreholes to advanced radar surveys. In 1989 TDR was introduced as a monitoring tool with the installation of 12.7 mm (0.5 in) diameter TDR cables in the underground excavations. In 1993, a new TDR system was installed in a separate location. Based on experience with the previous installation, enhancements were implemented into the new TDR system that: (1) extended the period of performance by increasing cable diameter to 22. 2 mm (0.875 in), (2) increased accuracy in locating areas of deformation by aligning cables with nearby observation boreholes, and (3) improved data acquisition and analyses using a standard laptop computer, eliminating the chart recorder previously used. In summary, the results of a correlation between the TDR signatures to nearby observation boreholes and geomechanical instrumentation will be presented.
Towards next generation time-domain diffuse optics devices
NASA Astrophysics Data System (ADS)
Dalla Mora, Alberto; Contini, Davide; Arridge, Simon R.; Martelli, Fabrizio; Tosi, Alberto; Boso, Gianluca; Farina, Andrea; Durduran, Turgut; Martinenghi, Edoardo; Torricelli, Alessandro; Pifferi, Antonio
2015-03-01
Diffuse Optics is growing in terms of applications ranging from e.g. oximetry, to mammography, molecular imaging, quality assessment of food and pharmaceuticals, wood optics, physics of random media. Time-domain (TD) approaches, although appealing in terms of quantitation and depth sensibility, are presently limited to large fiber-based systems, with limited number of source-detector pairs. We present a miniaturized TD source-detector probe embedding integrated laser sources and single-photon detectors. Some electronics are still external (e.g. power supply, pulse generators, timing electronics), yet full integration on-board using already proven technologies is feasible. The novel devices were successfully validated on heterogeneous phantoms showing performances comparable to large state-of-the-art TD rack-based systems. With an investigation based on simulations we provide numerical evidence that the possibility to stack many TD compact source-detector pairs in a dense, null source-detector distance arrangement could yield on the brain cortex about 1 decade higher contrast as compared to a continuous wave (CW) approach. Further, a 3-fold increase in the maximum depth (down to 6 cm) is estimated, opening accessibility to new organs such as the lung or the heart. Finally, these new technologies show the way towards compact and wearable TD probes with orders of magnitude reduction in size and cost, for a widespread use of TD devices in real life.
THz Time-Domain Spectroscopy of Complex Interstellar Ice Analogs
NASA Astrophysics Data System (ADS)
Ioppolo, Sergio; McGuire, Brett A.; Allodi, Marco A.; de Vries, Xander; Finneran, Ian; Carroll, Brandon; Blake, Geoffrey
2014-06-01
It is generally accepted that complex organic molecules (COMs) form on the icy surface of interstellar grains. Our ability to identify interstellar complex species in the ices is affected by the limited number of laboratory analogs that can be compared to the huge amount of observational data currently coming from international astronomical facilities, such as the Herschel Space Observatory, SOFIA, and ALMA. We have recently constructed a new THz time-domain spectroscopy system to investigate the spectra of interstellar ice analogs in a range that fully covers the spectral bandwidth of the aforementioned facilities (0.3 - 7.5 THz). The system is coupled to a FT-IR spectrometer to monitor the ices in the mid-IR (4000 - 500 cm-1). This talk focuses on the laboratory investigation of the composition and structure of the bulk phases of interstellar ice analogs (i.e., H2O, CO2, CO, CH3OH, NH3, and CH4) compared to more complex molecules (e.g., HCOOH, CH3COOH, CH3CHO, (CH3)2CO, HCOOCH3, and HCOOC2H5). The ultimate goal of this research project is to provide the scientific community with an extensive THz ice database, which will allow quantitative studies of the ISM, and potentially guide future astronomical observations of species in the solid phase.
Time domain simulations of arm locking in LISA
NASA Astrophysics Data System (ADS)
Thorpe, J. I.; Maghami, P.; Livas, J.
2011-06-01
Arm locking is a proposed laser frequency stabilization technique for the Laser Interferometer Space Antenna (LISA), a gravitational-wave observatory sensitive in the milliHertz frequency band. Arm locking takes advantage of the geometric stability of the triangular constellation of three spacecraft that compose LISA to provide a frequency reference with a stability in the LISA measurement band that exceeds that available from a standard reference such as an optical cavity or molecular absorption line. We have implemented a time-domain simulation of a Kalman-filter-based arm-locking system that includes the expected limiting noise sources as well as the effects of imperfect a priori knowledge of the constellation geometry on which the design is based. We use the simulation to study aspects of the system performance that are difficult to capture in a steady-state frequency-domain analysis such as frequency pulling of the master laser due to errors in estimates of heterodyne frequency. We find that our implementation meets requirements on both the noise and dynamic range of the laser frequency with acceptable tolerances and that the design is sufficiently insensitive to errors in the estimated constellation geometry that the required performance can be maintained for the longest continuous measurement intervals expected for the LISA mission.
Seismic analysis of wind turbines in the time domain
NASA Astrophysics Data System (ADS)
Witcher, D.
2005-01-01
The analysis of wind turbine loading associated with earthquakes is clearly important when designing for and assessing the feasibility of wind farms in seismically active regions. The approach taken for such analysis is generally based on codified methods which have been developed for the assessment of seismic loads acting on buildings. These methods are not able to deal properly with the aeroelastic interaction of the dynamic motion of the wind turbine structure with either the wind loading acting on the rotor blades or the response of the turbine controller. This article presents an alternative approach, which is to undertake the calculation in the time domain. In this case a full aeroelastic model of the wind turbine subject to turbulent wind loading is further excited by ground motion corresponding to the earthquake. This capability has been introduced to the GH Bladed wind turbine simulation package. The software can be used to compute the combined wind and earthquake loading of a wind turbine given a definition of the external conditions for an appropriate series of load cases. This article discusses the method and presents example results. Copyright
Time-domain simulation of a guitar: Model and method
NASA Astrophysics Data System (ADS)
Derveaux, Grégoire; Chaigne, Antoine; Joly, Patrick; Bécache, Eliane
2003-12-01
This paper presents a three-dimensional time-domain numerical model of the vibration and acoustic radiation from a guitar. The model involves the transverse displacement of the string excited by a force pulse, the flexural motion of the soundboard, and the sound radiation. A specific spectral method is used for solving the Kirchhoff-Love's dynamic top plate model for a damped, heterogeneous orthotropic material. The air-plate interaction is solved with a fictitious domain method, and a conservative scheme is used for the time discretization. Frequency analysis is performed on the simulated sound pressure and plate velocity waveforms in order to evaluate quantitatively the transfer of energy through the various components of the coupled system: from the string to the soundboard and from the soundboard to the air. The effects of some structural changes in soundboard thickness and cavity volume on the produced sounds are presented and discussed. Simulations of the same guitar in three different cases are also performed: ``in vacuo,'' in air with a perfectly rigid top plate, and in air with an elastic top plate. This allows comparisons between structural, acoustic, and structural-acoustic modes of the instrument. Finally, attention is paid to the evolution with time of the spatial pressure field. This shows, in particular, the complex evolution of the directivity pattern in the near field of the instrument, especially during the attack.
An optimum PML for scattering problems in the time domain
NASA Astrophysics Data System (ADS)
Modave, Axel; Kameni, Abelin; Lambrechts, Jonathan; Delhez, Eric; Pichon, Lionel; Geuzaine, Christophe
2013-11-01
In electromagnetic compatibility, scattering problems are defined in an infinite spatial domain, while numerical techniques such as finite element methods require a computational domain that is bounded. The perfectly matched layer (PML) is widely used to simulate the truncation of the computational domain. However, its performance depends critically on an absorption function. This function is generally tuned by using case-dependent optimization procedures. In this paper, we will present some efficient functions that overcome any tuning. They will be compared using a realistic scattering benchmark solved with the Discontinuous Galerkin method. Contribution to the Topical Issue "Numelec 2012", Edited by Adel Razek.
Airborne geophysical surveys conducted in western Nebraska, 2010: contractor reports and data
,
2014-01-01
This report contains three contractor reports and data files for an airborne electromagnetic survey flown from June 28 to July 7, 2010. The first report; “SkyTEM Survey: Nebraska, USA, Data” describes data aquisition and processing from a time-domain electromagnetic and magnetic survey performed by SkyTEM Canada, Inc. (the North American SkyTEM subsidiary), in western Nebraska, USA. Digital data for this report are given in Appendix 1. The airborne geophysical data from the SkyTEM survey subsequently were processed and inverted by Aarhus Geophysics ApS, Aarhus, Denmark, to produce resistivity depth sections along each flight line. The result of that processing is described in two reports presented in Appendix 2, “Processing and inversion of SkyTEM data from USGS Area UTM–13” and “Processing and inversion of SkyTEM data from USGS Area UTM–14.” Funding for these surveys was provided by the North Platte Natural Resources District, the South Platte Natural Resources District, and the Twin Platte Natural Resources District, in Scottsbluff, Sidney, and North Platte, Nebraska, respectively. Any additional information concerning the geophysical data may be obtained from the U.S. Geological Survey Crustal Geophysics and Geochemistry Science Center, Denver Colorado.
NASA Astrophysics Data System (ADS)
Hu, Y.; Ji, Y.; Egbert, G. D.
2015-12-01
The fictitious time domain method (FTD), based on the correspondence principle for wave and diffusion fields, has been developed and used over the past few years primarily for marine electromagnetic (EM) modeling. Here we present results of our efforts to apply the FTD approach to land and airborne TEM problems which can reduce the computer time several orders of magnitude and preserve high accuracy. In contrast to the marine case, where sources are in the conductive sea water, we must model the EM fields in the air; to allow for topography air layers must be explicitly included in the computational domain. Furthermore, because sources for most TEM applications generally must be modeled as finite loops, it is useful to solve directly for the impulse response appropriate to the problem geometry, instead of the point-source Green functions typically used for marine problems. Our approach can be summarized as follows: (1) The EM diffusion equation is transformed to a fictitious wave equation. (2) The FTD wave equation is solved with an explicit finite difference time-stepping scheme, with CPML (Convolutional PML) boundary conditions for the whole computational domain including the air and earth , with FTD domain source corresponding to the actual transmitter geometry. Resistivity of the air layers is kept as low as possible, to compromise between efficiency (longer fictitious time step) and accuracy. We have generally found a host/air resistivity contrast of 10-3 is sufficient. (3)A "Modified" Fourier Transform (MFT) allow us recover system's impulse response from the fictitious time domain to the diffusion (frequency) domain. (4) The result is multiplied by the Fourier transformation （FT） of the real source current avoiding time consuming convolutions in the time domain. (5) The inverse FT is employed to get the final full waveform and full time response of the system in the time domain. In general, this method can be used to efficiently solve most time-domain EM
Wang, X G; Shang, X L; Lin, J
2016-05-01
Time-domain electromagnetic system can implement great depth detection. As for the electromagnetic system, the receiver utilized an air coil sensor, and the matching mode of the sensor employed the resistance matching method. By using the resistance matching method, the vibration of the coil in the time domain can be effectively controlled. However, the noise of the sensor, especially the noise at the resonance frequency, will be increased as well. In this paper, a novel design of a low noise induction coil sensor is proposed, and the experimental data and noise characteristics are provided. The sensor is designed based on the principle that the amplified voltage will be converted to current under the influence of the feedback resistance of the coil. The feedback loop around the induction coil exerts a magnetic field and sends the negative feedback signal to the sensor. The paper analyses the influence of the closed magnetic feedback loop on both the bandwidth and the noise of the sensor. The signal-to-noise ratio is improved dramatically.
The Time Domain Spectroscopic Survey: Variable Selection and Anticipated Results
NASA Astrophysics Data System (ADS)
Morganson, Eric; Green, Paul J.; Anderson, Scott F.; Ruan, John J.; Myers, Adam D.; Eracleous, Michael; Kelly, Brandon; Badenes, Carlos; Bañados, Eduardo; Blanton, Michael R.; Bershady, Matthew A.; Borissova, Jura; Nielsen Brandt, William; Burgett, William S.; Chambers, Kenneth; Draper, Peter W.; Davenport, James R. A.; Flewelling, Heather; Garnavich, Peter; Hawley, Suzanne L.; Hodapp, Klaus W.; Isler, Jedidah C.; Kaiser, Nick; Kinemuchi, Karen; Kudritzki, Rolf P.; Metcalfe, Nigel; Morgan, Jeffrey S.; Pâris, Isabelle; Parvizi, Mahmoud; Poleski, Radosław; Price, Paul A.; Salvato, Mara; Shanks, Tom; Schlafly, Eddie F.; Schneider, Donald P.; Shen, Yue; Stassun, Keivan; Tonry, John T.; Walter, Fabian; Waters, Chris Z.
2015-06-01
We present the selection algorithm and anticipated results for the Time Domain Spectroscopic Survey (TDSS). TDSS is an Sloan Digital Sky Survey (SDSS)-IV Extended Baryon Oscillation Spectroscopic Survey (eBOSS) subproject that will provide initial identification spectra of approximately 220,000 luminosity-variable objects (variable stars and active galactic nuclei across 7500 deg2 selected from a combination of SDSS and multi-epoch Pan-STARRS1 photometry. TDSS will be the largest spectroscopic survey to explicitly target variable objects, avoiding pre-selection on the basis of colors or detailed modeling of specific variability characteristics. Kernel Density Estimate analysis of our target population performed on SDSS Stripe 82 data suggests our target sample will be 95% pure (meaning 95% of objects we select have genuine luminosity variability of a few magnitudes or more). Our final spectroscopic sample will contain roughly 135,000 quasars and 85,000 stellar variables, approximately 4000 of which will be RR Lyrae stars which may be used as outer Milky Way probes. The variability-selected quasar population has a smoother redshift distribution than a color-selected sample, and variability measurements similar to those we develop here may be used to make more uniform quasar samples in large surveys. The stellar variable targets are distributed fairly uniformly across color space, indicating that TDSS will obtain spectra for a wide variety of stellar variables including pulsating variables, stars with significant chromospheric activity, cataclysmic variables, and eclipsing binaries. TDSS will serve as a pathfinder mission to identify and characterize the multitude of variable objects that will be detected photometrically in even larger variability surveys such as Large Synoptic Survey Telescope.
Integral ceramic superstructure evaluation using time domain optical coherence tomography
NASA Astrophysics Data System (ADS)
Sinescu, Cosmin; Bradu, Adrian; Topala, Florin I.; Negrutiu, Meda Lavinia; Duma, Virgil-Florin; Podoleanu, Adrian G.
2014-02-01
Optical Coherence Tomography (OCT) is a non-invasive low coherence interferometry technique that includes several technologies (and the corresponding devices and components), such as illumination and detection, interferometry, scanning, adaptive optics, microscopy and endoscopy. From its large area of applications, we consider in this paper a critical aspect in dentistry - to be investigated with a Time Domain (TD) OCT system. The clinical situation of an edentulous mandible is considered; it can be solved by inserting 2 to 6 implants. On these implants a mesostructure will be manufactured and on it a superstructure is needed. This superstructure can be integral ceramic; in this case materials defects could be trapped inside the ceramic layers and those defects could lead to fractures of the entire superstructure. In this paper we demonstrate that a TD-OCT imaging system has the potential to properly evaluate the presence of the defects inside the ceramic layers and those defects can be fixed before inserting the prosthesis inside the oral cavity. Three integral ceramic superstructures were developed by using a CAD/CAM technology. After the milling, the ceramic layers were applied on the core. All the three samples were evaluated by a TD-OCT system working at 1300 nm. For two of the superstructures evaluated, no defects were found in the most stressed areas. The third superstructure presented four ceramic defects in the mentioned areas. Because of those defects the superstructure may fracture. The integral ceramic prosthesis was send back to the dental laboratory to fix the problems related to the material defects found. Thus, TD-OCT proved to be a valuable method for diagnosing the ceramic defects inside the integral ceramic superstructures in order to prevent fractures at this level.
THE TIME DOMAIN SPECTROSCOPIC SURVEY: VARIABLE SELECTION AND ANTICIPATED RESULTS
Morganson, Eric; Green, Paul J.; Anderson, Scott F.; Ruan, John J.; Myers, Adam D.; Eracleous, Michael; Brandt, William Nielsen; Kelly, Brandon; Badenes, Carlos; Bañados, Eduardo; Blanton, Michael R.; Bershady, Matthew A.; Borissova, Jura; Burgett, William S.; Chambers, Kenneth; and others
2015-06-20
We present the selection algorithm and anticipated results for the Time Domain Spectroscopic Survey (TDSS). TDSS is an Sloan Digital Sky Survey (SDSS)-IV Extended Baryon Oscillation Spectroscopic Survey (eBOSS) subproject that will provide initial identification spectra of approximately 220,000 luminosity-variable objects (variable stars and active galactic nuclei across 7500 deg{sup 2} selected from a combination of SDSS and multi-epoch Pan-STARRS1 photometry. TDSS will be the largest spectroscopic survey to explicitly target variable objects, avoiding pre-selection on the basis of colors or detailed modeling of specific variability characteristics. Kernel Density Estimate analysis of our target population performed on SDSS Stripe 82 data suggests our target sample will be 95% pure (meaning 95% of objects we select have genuine luminosity variability of a few magnitudes or more). Our final spectroscopic sample will contain roughly 135,000 quasars and 85,000 stellar variables, approximately 4000 of which will be RR Lyrae stars which may be used as outer Milky Way probes. The variability-selected quasar population has a smoother redshift distribution than a color-selected sample, and variability measurements similar to those we develop here may be used to make more uniform quasar samples in large surveys. The stellar variable targets are distributed fairly uniformly across color space, indicating that TDSS will obtain spectra for a wide variety of stellar variables including pulsating variables, stars with significant chromospheric activity, cataclysmic variables, and eclipsing binaries. TDSS will serve as a pathfinder mission to identify and characterize the multitude of variable objects that will be detected photometrically in even larger variability surveys such as Large Synoptic Survey Telescope.
Exploration of the Time Domain With Palomar-Quest Survey
NASA Astrophysics Data System (ADS)
Djorgovski, Stanislav G.; Mahabal, A.; Drake, A.; Donalek, C.; Glikman, E.; Graham, M.; Williams, R.; Morton, T.; Bauer, A.; Baltay, C.; Rabinowitz, D.; Scalzo, R.; Nugent, P.; Palomar-Quest Survey Team
2009-01-01
Palomar-Quest (PQ) digital synoptic sky survey, conducted at the Samuel Oschin 48-inch telescope at Palomar Observatory, using the Yale Quest-2, 161-Megapixel, 112-CCD camera, is now complete. The survey covered > 15,000 deg2 multiple times (up to several tens of pointings), spanning a range of time baselines from minutes to years. The data were taken in a drift scan mode, in Johnson UBRI or Gunn griz filters. They are now supplemented by an even larger data set taken in the traditional point-and-stare mode, with a broad red bandpass, much of it taken by the JPL NEAT team, and processed at LBNL Nearby Supernova Factory. This joint data set offers unprecedented opportunities for exploration of time domain in astronomy. All transient sources detected in the course of real-time processing of the drift scan survey have been published immediately, using the VOEventNet system. In addtion to a very productive supernova search conducted in collaboration with the LBNL Nearby Supernova Factory, we have conducted several studies: (1) a real-time detection of transients and strong variables; (2) a systematic study of QSO variability; (3) studies of blazar variability, and blazar discovery using variability alone; (4) the astrophysical nature of the most variable sources on the high-latitude sky. Follow-up spectroscopy was obtained at the Palomar 200-inch Hale telescope for a number of sources. We will report preliminary results from some of these studies. Experience gained in the course of this survey should be useful for future synoptic sky surveys.
Time-Domain Studies as a Probe of Stellar Evolution
NASA Astrophysics Data System (ADS)
Miller, Adam Andrew
This dissertation focuses on the use of time-domain techniques to discover and characterize these rare astrophysical gems, while also addressing some gaps in our understanding of the earliest and latest stages of stellar evolution. The observational studies presented herein can be grouped into three parts: (i) the study of stellar death (supernovae); (ii) the study of stellar birth; and (iii) the use of modern machine-learning algorithms to discover and classify variable sources. I present observations of supernova (SN) 2006gy, the most luminous SN ever at the time of discovery, and the even-more luminous SN 2008es. Together, these two supernovae (SNe) demonstrate that core-collapse SNe can be significantly more luminous than thermonuclear type Ia SNe, and that there are multiple channels for producing these brilliant core-collapse explosions. For SN 2006gy I show that the progenitor star experienced violent, eruptive mass loss on multiple occasions during the centuries prior to explosion, a scenario that was completely unexpected within the cannon of massive-star evolution theory. I also present observations of SN 2008iy, one of the most unusual SNe ever discovered. Typical SNe take ≲3 weeks to reach peak luminosity; SN 2008iy exhibited a slow and steady rise for ˜400 days before reaching maximum brightness. The best explanation for such behavior is that the progenitor of SN 2008iy experienced an episodic phase of mass loss ˜100 yr prior to explosion. The three SNe detailed in this dissertation have altered our understanding of massive-star mass loss, namely, these SNe provide distinct evidence that post-main sequence mass loss, for at least some massive stars, occurs in sporatic fits, rather than being steady. They also demonstrate that core collapse is not restricted to the red supergiant and Wolf-Rayet stages of stellar evolution as theory predicted. Instead, some massive stars explode while in a luminous blue variable-like state. I also present
NASA Astrophysics Data System (ADS)
Bedrosian, P. A.; Burgess, M. K.; Bloss, B.; Ball, L. B.; Polster, S.; Densmore, J.; Martin, P.; Langenheim, V. E.; Jachens, R. C.
2011-12-01
In the Mojave Desert of the southwestern USA, groundwater is compartmentalized within a series of fault-bounded basins. As part of an effort to understand and manage groundwater resources in arid environments, the USGS is investigating basins within the Fort Irwin National Training Center through a combination of hydrologic, geophysical, and geochemical approaches. Airborne time-domain electromagnetic (TDEM) data were collected within the Leach Basin, a geologically complex, internally-drained basin bisected and flanked by a number of Quaternary faults, including the Garlock fault and the Death Valley fault zone. The airborne TDEM data provide subsurface constraints down to approximately 200 m depth, and show abrupt changes in earth response across faulted boundaries, reflecting the strong lateral resistivity contrast between igneous rocks and basin sediments. Intra-basin faults are additionally identified, and to a lesser extent faults within the igneous basement can be traced. The distribution of faults throughout the basin and within the subsurface can thus be directly obtained from the airborne data. These electrical discontinuities, however, present challenges for the laterally-constrained inversion approach we applied, and we present alternative approaches to inverting these data which honor the complexity of the region. We further outline a multivariate approach to fault identification which combines resistivity models, airborne magnetics, and surface topography. A resistivity stratigraphy has been developed using borehole geophysical logs, ground-based gravity, TDEM soundings, and lab resistivity measurements from nearby basins. The results are applied to the airborne resistivity models and used to trace aquifer hydrostratigraphy throughout the basin. Interpreted parameters include the depth to basement, the base of the primary aquifer, depth to water, and variations in groundwater salinity. Together with hydrologic investigations, these results are being
Wideband THz Time Domain Spectroscopy based on Optical Rectification and Electro-Optic Sampling
Tomasino, A.; Parisi, A.; Stivala, S.; Livreri, P.; Cino, A. C.; Busacca, A. C.; Peccianti, M.; Morandotti, R.
2013-01-01
We present an analytical model describing the full electromagnetic propagation in a THz time-domain spectroscopy (THz-TDS) system, from the THz pulses via Optical Rectification to the detection via Electro Optic-Sampling. While several investigations deal singularly with the many elements that constitute a THz-TDS, in our work we pay particular attention to the modelling of the time-frequency behaviour of all the stages which compose the experimental set-up. Therefore, our model considers the following main aspects: (i) pump beam focusing into the generation crystal; (ii) phase-matching inside both the generation and detection crystals; (iii) chromatic dispersion and absorption inside the crystals; (iv) Fabry-Perot effect; (v) diffraction outside, i.e. along the propagation, (vi) focalization and overlapping between THz and probe beams, (vii) electro-optic sampling. In order to validate our model, we report on the comparison between the simulations and the experimental data obtained from the same set-up, showing their good agreement. PMID:24173583
Liu, Wen-Tao; Li, Jing-Wen; Sun, Zhi-Hui
2010-03-01
Terahertz waves (THz, T-ray) lie between far-infrared and microwave in electromagnetic spectrum with frequency from 0.1 to 10 THz. Many chemical agent explosives show characteristic spectral features in the terahertz. Compared with conventional methods of detecting a variety of threats, such as weapons and chemical agent, THz radiation is low frequency and non-ionizing, and does not give rise to safety concerns. The present paper summarizes the latest progress in the application of terahertz time domain spectroscopy (THz-TDS) to chemical agent explosives. A kind of device on laser radar detecting and real time spectrum measuring was designed which measures the laser spectrum on the bases of Fourier optics and optical signal processing. Wedge interferometer was used as the beam splitter to wipe off the background light and detect the laser and measure the spectrum. The result indicates that 10 ns laser radar pulse can be detected and many factors affecting experiments are also introduced. The combination of laser radar spectrum detecting, THz-TDS, modern pattern recognition and signal processing technology is the developing trend of remote detection for chemical agent explosives.
Hot-Wiring Flare Stars: Optical Flare Rates and Properties from Time-Domain Surveys
NASA Astrophysics Data System (ADS)
Kowalski, A.
Flares are thought to result from the reconnection of magnetic fields in the upper layers (coronae) of stellar atmospheres. The highly dynamic atmospheric response produces radiation across the electromagnetic spectrum, from the radio to X-rays, on a range of timescales, from seconds to days. Due to their high flare rates and energies combined with a large contrast against the background quiescent emission, the low-mass M dwarfs are the primary target for studying flare rates in the Galaxy. However, high-precision monitoring campaigns using Kepler and the Hubble Space Telescope have recently revealed important information on the flare rates of earlier- type, more massive stars. In this talk, I will focus on the properties of flares and flare stars in the optical and near-ultraviolet wavelength regimes as revealed from time-domain surveys, such as the repeat observations of the Sloan Digital Sky Surveys Stripe 82. I will discuss the importance of spectroscopic follow-up characterization of the quiescent and flare emission, and I will highlight new radiative-hydrodynamic modeling results that have enhanced our understanding of impulsive phase U-band flare emission.
SAR image simulation in the time domain for moving ocean surfaces.
Yoshida, Takero; Rheem, Chang-Kyu
2013-04-02
This paper presents a fundamental simulation method to generate synthetic aperture radar (SAR) images for moving ocean surfaces. We have designed the simulation based on motion induced modulations and Bragg scattering, which are important features of ocean SAR images. The time domain simulation is able to obtain time series of microwave backscattering modulated by the orbital motions of ocean waves. Physical optics approximation is applied to calculate microwave backscattering. The computational grids are smaller than transmit microwave to demonstrate accurate interaction between electromagnetic waves and ocean surface waves. In this paper, as foundations for SAR image simulation of moving ocean surfaces, the simulation is carried out for some targets and ocean waves. The SAR images of stationary and moving targets are simulated to confirm SAR signal processing and motion induced modulation. Furthermore, the azimuth signals from the regular wave traveling to the azimuth direction also show the azimuthal shifts due to the orbital motions. In addition, incident angle dependence is simulated for irregular wind waves to compare with Bragg scattering theory. The simulation results are in good agreement with the theory. These results show that the simulation is applicable for generating numerical SAR images of moving ocean surfaces.
Quantitative analyses of tartaric acid based on terahertz time domain spectroscopy
NASA Astrophysics Data System (ADS)
Cao, Binghua; Fan, Mengbao
2010-10-01
Terahertz wave is the electromagnetic spectrum situated between microwave and infrared wave. Quantitative analysis based on terahertz spectroscopy is very important for the application of terahertz techniques. But how to realize it is still under study. L-tartaric acid is widely used as acidulant in beverage, and other food, such as soft drinks, wine, candy, bread and some colloidal sweetmeats. In this paper, terahertz time-domain spectroscopy is applied to quantify the tartaric acid. Two methods are employed to process the terahertz spectra of different samples with different content of tartaric acid. The first one is linear regression combining correlation analysis. The second is partial least square (PLS), in which the absorption spectra in the 0.8-1.4THz region are used to quantify the tartaric acid. To compare the performance of these two principles, the relative error of the two methods is analyzed. For this experiment, the first method does better than the second one. But the first method is suitable for the quantitative analysis of materials which has obvious terahertz absorption peaks, while for material which has no obvious terahertz absorption peaks, the second one is more appropriate.
NASA Astrophysics Data System (ADS)
Yu, Xuhui; Zhou, Deliang; Lu, Bin; Liu, Sufang; Pan, Ming
2015-10-01
In this paper, we demonstrate a distributed fence-perimeter intrusion detection system using a phase-sensitive optical time domain reflectometer (Φ-OTDR) with several advantages, such as high spatial resolution, large detection range, single-end measurement and immunity from electromagnetic interference. By the effort of generating a high-extinction-ratio optical pulse, optimizing the incident optical power and utilizing a differential algorithm, a home-made Φ-OTDR system, as a distributed vibration sensor, is implemented with a spatial resolution of 10 meter. Nowadays, a fence-perimeter intrusion detection system is desired for the security monitor. We set up a fence perimeter using a fiber cable containing only one fiber and a field experiment is carried out based on our Φ-OTDR system. Various vibration events are recorded and analyzed, including wind blowing, personal climbing and knocking. The experiment results reveal unique vibration characteristics of different events in the frequency domain and confirm the effectiveness of the homemade Φ-OTDR system in the application of the distributed fence-perimeter intrusion detection.
Time-Domain Analysis of Higher Order Mode Properties in an Open Cavity Retaining Axial Symmetry
NASA Astrophysics Data System (ADS)
Lin, S. Y.; Lin, M. C.
2016-10-01
Theoretical and computational research to accurately and efficiently determine higher order mode properties of an axially symmetrical open cavity has been pursued. Open cavities have been widely employed in gyrotrons for the generation of high-power millimeter, submillimeter, and THz waves. A standing wave forms in the main body of the cavity, and the open end allows the extraction of power generated by the electron beam wave interaction. On the other hand, microresonators, such as microspheres that have small effective volume of their whispering gallery modes (WGMs), high quality factors, and quasi insensitivity to conducting material boundaries can also be considered as open cavities since the WGMs are natural electromagnetic eigenmodes that are activated by external coherent signals. For these cavities, axial symmetry is usually retained. The CAVITY program developed by Professor K. R. Chu using Fortran allows the users to accurately and efficiently determine the resonant frequency, the quality factor, and the field profile for the TE modes of an open cavity. In this work, an extension of the CAVITY program using Mathematica, CAVITY-M, to perform time-domain analysis of higher order modes in open cavities retaining axial symmetry for wider applications such as those mentioned above has been carried out. The new CAVITY-M program developed using Mathematica is able to effectively analyze the higher order mode characteristics of a general open cavity with an axial symmetry, in addition to the traditional modes in a gyrotron cavity.
Time Domain Science and Fundamental Physics with the Next-generation Very Large Array
NASA Astrophysics Data System (ADS)
Demorest, Paul; Bower, Geoffrey C.; ngVLA Time Domain/Physics Science Working Group
2017-01-01
The Next-generation Very Large Array (ngVLA) is a design concept for a future large-area radio telescope under development by the NRAO and interested members of the scientific community. The approximate ngVLA specifications call for a frequency range of ~1--116 GHz, ten times the effective collecting area and moderately increased field of view versus the current VLA, and an array configuration consisting of a dense (~km-scale) array core with some baselines extending out to hundreds of km. This instrument will enable new discoveries in many diverse areas of research relevant to modern astronomy; our group has explored the impact the ngVLA will have in time domain astronomy and fundamental physics.Here we present several key science topics considered as part of this work. These include: Searching for and timing radio pulsars at the galactic center -- the frequency coverage and sensitivity of the ngVLA will allow detection of highly-scattered pulsars near Sgr A*. Monitoring these sources will permit unprecedented tests of general relativity. Detecting and characterizing explosive transient sources -- electromagnetic observations of gravitational-wave sources provide complementary information to the GW signals themselves. Observations across the wide frequency range spanned by the ngVLA are critical for energy calorimetry of these events. Finally, with sufficient long-baseline coverage, novel astrometric approaches to cosmology become possible, by watching the expansion of the universe in real time through correlated proper motions of many extragalactic radio sources.
Simulation of optical devices using parallel finite-difference time-domain method
NASA Astrophysics Data System (ADS)
Li, Kang; Kong, Fanmin; Mei, Liangmo; Liu, Xin
2005-11-01
This paper presents a new parallel finite-difference time-domain (FDTD) numerical method in a low-cost network environment to stimulate optical waveguide characteristics. The PC motherboard based cluster is used, as it is relatively low-cost, reliable and has high computing performance. Four clusters are networked by fast Ethernet technology. Due to the simplicity nature of FDTD algorithm, a native Ethernet packet communication mechanism is used to reduce the overhead of the communication between the adjacent clusters. To validate the method, a microcavity ring resonator based on semiconductor waveguides is chosen as an instance of FDTD parallel computation. Speed-up rate under different division density is calculated. From the result we can conclude that when the decomposing size reaches a certain point, a good parallel computing speed up will be maintained. This simulation shows that through the overlapping of computation and communication method and controlling the decomposing size, the overhead of the communication of the shared data will be conquered. The result indicates that the implementation can achieve significant speed up for the FDTD algorithm. This will enable us to tackle the larger real electromagnetic problem by the low-cost PC clusters.
Greene, Jethro H; Taflove, Allen
2003-10-01
We report the initial three-dimensional finite-difference time-domain modeling of a vertically coupled photonic racetrack. The modeling reveals details of the full suite of space-time behavior of electromagnetic-wave phenomena involved in guiding, coupling, multimoding, dispersion, and radiation. This behavior is not easily obtainable by analytical or full-vector frequency-domain methods, measurements of terminal properties, or near-field scanning optical microscopy.
Time-Domain Terahertz Computed Axial Tomography NDE System
NASA Technical Reports Server (NTRS)
Zimdars, David
2012-01-01
NASA has identified the need for advanced non-destructive evaluation (NDE) methods to characterize aging and durability in aircraft materials to improve the safety of the nation's airline fleet. 3D THz tomography can play a major role in detection and characterization of flaws and degradation in aircraft materials, including Kevlar-based composites and Kevlar and Zylon fabric covers for soft-shell fan containment where aging and durability issues are critical. A prototype computed tomography (CT) time-domain (TD) THz imaging system has been used to generate 3D images of several test objects including a TUFI tile (a thermal protection system tile used on the Space Shuttle and possibly the Orion or similar capsules). This TUFI tile had simulated impact damage that was located and the depth of damage determined. The CT motion control gan try was designed and constructed, and then integrated with a T-Ray 4000 control unit and motion controller to create a complete CT TD-THz imaging system prototype. A data collection software script was developed that takes multiple z-axis slices in sequence and saves the data for batch processing. The data collection software was integrated with the ability to batch process the slice data with the CT TD-THz image reconstruction software. The time required to take a single CT slice was decreased from six minutes to approximately one minute by replacing the 320 ps, 100-Hz waveform acquisition system with an 80 ps, 1,000-Hz waveform acquisition system. The TD-THZ computed tomography system was built from pre-existing commercial off-the-shelf subsystems. A CT motion control gantry was constructed from COTS components that can handle larger samples. The motion control gantry allows inspection of sample sizes of up to approximately one cubic foot (.0.03 cubic meters). The system reduced to practice a CT-TDTHz system incorporating a COTS 80- ps/l-kHz waveform scanner. The incorporation of this scanner in the system allows acquisition of 3D
Cable Damage Detection System and Algorithms Using Time Domain Reflectometry
Clark, G A; Robbins, C L; Wade, K A; Souza, P R
2009-03-24
This report describes the hardware system and the set of algorithms we have developed for detecting damage in cables for the Advanced Development and Process Technologies (ADAPT) Program. This program is part of the W80 Life Extension Program (LEP). The system could be generalized for application to other systems in the future. Critical cables can undergo various types of damage (e.g. short circuits, open circuits, punctures, compression) that manifest as changes in the dielectric/impedance properties of the cables. For our specific problem, only one end of the cable is accessible, and no exemplars of actual damage are available. This work addresses the detection of dielectric/impedance anomalies in transient time domain reflectometry (TDR) measurements on the cables. The approach is to interrogate the cable using time domain reflectometry (TDR) techniques, in which a known pulse is inserted into the cable, and reflections from the cable are measured. The key operating principle is that any important cable damage will manifest itself as an electrical impedance discontinuity that can be measured in the TDR response signal. Machine learning classification algorithms are effectively eliminated from consideration, because only a small number of cables is available for testing; so a sufficient sample size is not attainable. Nonetheless, a key requirement is to achieve very high probability of detection and very low probability of false alarm. The approach is to compare TDR signals from possibly damaged cables to signals or an empirical model derived from reference cables that are known to be undamaged. This requires that the TDR signals are reasonably repeatable from test to test on the same cable, and from cable to cable. Empirical studies show that the repeatability issue is the 'long pole in the tent' for damage detection, because it is has been difficult to achieve reasonable repeatability. This one factor dominated the project. The two-step model-based approach is
Monitoring moisture storage in trees using time domain reflectometry
Constantz, J.; Murphy, F.
1990-01-01
Laboratory and field tests were performed to examine the feasibility of using time domain reflectometry (TDR) to monitor changes in the moisture storage of the woody parts of trees. To serve as wave guides for the TDR signal, pairs of stainless steel rods (13 cm long, 0.32 cm in diameter, and 2.5 cm separation) were driven into parallel pilot holes drilled into the woody parts of trees, and a cable testing oscilloscope was used to determine the apparent dielectric constant. A laboratory calibration test was performed on two sapwood samples, so that the relation between the volumetric water content and the apparent dielectric constant of the sapwood could be determined over a range of water contents. The resulting calibration curve for these sapwood samples was significantly different than the general calibration curve used for soils, showing a smaller change in the apparent dielectric constant for a given change in the volumetric water content than is typical for soils. The calibration curve was used to estimate the average volumetric water content to a depth of 13 cm in living trees. One field experiment was conducted on an English walnut tree (Juglans regia) with a diameter of 40 cm, growing in a flood-irrigated orchard on a Hanford sandy loam near Modesto, California (U.S.A.). Rods were driven into the tree at about 50 cm above the soil surface and monitored hourly for the month of August, 1988. The moisture content determined by TDR showed a gradual decrease from 0.44 to 0.42 cm3 cm-3 over a two week period prior to flood irrigation, followed by a rapid rise to 0.47 cm3 cm-3 over a four day period after irrigation, then again a gradual decline approaching the next irrigation. A second field experiment was made on ten evergreen and deciduous trees with diameters ranging from 30 to 120 cm, growing in the foothills of the Coast Range of central California. Rods were driven into each tree at 50 to 100 cm above the soil surface and monitored on a biweekly to monthly
Monitoring moisture storage in trees using time domain reflectometry
NASA Astrophysics Data System (ADS)
Constantz, Jim; Murphy, Fred
1990-11-01
Laboratory and field tests were performed to examine the feasibility of using time domain reflectometry (TDR) to monitor changes in the moisture storage of the woody parts of trees. To serve as wave guides for the TDR signal, pairs of stainless steel rods (13 cm long, 0.32 cm in diameter, and 2.5 cm separation) were driven into parallel pilot holes drilled into the woody parts of trees, and a cable testing oscilloscope was used to determine the apparent dielectric constant. A laboratory calibration test was performed on two sapwood samples, so that the relation between the volumetric water content and the apparent dielectric constant of the sapwood could be determined over a range of water contents. The resulting calibration curve for these sapwood samples was significantly different than the general calibration curve used for soils, showing a smaller change in the apparent dielectric constant for a given change in the volumetric water content than is typical for soils. The calibration curve was used to estimate the average volumetric water content to a depth of 13 cm in living trees. One field experiment was conducted on an English walnut tree ( Juglans regia) with a diameter of 40 cm, growing in a flood-irrigated orchard on a Hanford sandy loam near Modesto, California (U.S.A.). Rods were driven into the tree at about 50 cm above the soil surface and monitored hourly for the month of August, 1988. The moisture content determined by TDR showed a gradual decrease from 0.44 to 0.42 cm 3 cm -3 over a two week period prior to flood irrigation, followed by a rapid rise to 0.47 cm 3 cm -3 over a four day period after irrigation, then again a gradual decline approaching the next irrigation. A second field experiment was made on ten evergreen and deciduous trees with diameters ranging from 30 to 120 cm, growing in the foothills of the Coast Range of central California. Rods were driven into each tree at 50 to 100 cm above the soil surface and monitored on a biweekly to
Finite-difference time-domain simulation of GPR data
NASA Astrophysics Data System (ADS)
Chen, How-Wei; Huang, Tai-Min
1998-10-01
Simulation of digital ground penetrating radar (GPR) wave propagation in two-dimensional (2-D) media is developed, tested, implemented, and applied using a time-domain staggered-grid finite-difference (FD) numerical method. Three types of numerical algorithms for constructing synthetic common-shot, constant-offset radar profiles based on an actual transmitter-to-receiver configuration and based on the exploding reflector concept are demonstrated to mimic different types of radar survey geometries. Frequency-dependent attenuation is also incorporated to account for amplitude decay and time shift in the recorded responses. The algorithms are based on an explicit FD solution to Maxwell's curl equations. In addition, the first-order TE mode responses of wave propagation phenomena are considered due to the operating frequency of current GPR instruments. The staggered-grid technique is used to sample the fields and approximate the spatial derivatives with fourth-order FDs. The temporal derivatives are approximated by an explicit second-order difference time-marching scheme. By combining paraxial approximation of the one-way wave equation ( A2) and the damping mechanisms (sponge filter), we propose a new composite absorbing boundary conditions (ABC) algorithm that effectively absorb both incoming and outgoing waves. To overcome the angle- and frequency-dependent characteristic of the absorbing behaviors, each ABC has two types of absorption mechanism. The first ABC uses a modified Clayton and Enquist's A2 condition. Moreover, a fixed and a floating A2 ABC that operates at one grid point is proposed. The second ABC uses a damping mechanism. By superimposing artificial damping and by alternating the physical attenuation properties and impedance contrast of the media within the absorbing region, those waves impinging on the boundary can be effectively attenuated and can prevent waves from reflecting back into the grid. The frequency-dependent characteristic of the damping
Quantitative modeling of ICRF antennas with integrated time domain RF sheath and plasma physics
NASA Astrophysics Data System (ADS)
Smithe, David N.; D'Ippolito, Daniel A.; Myra, James R.
2014-02-01
Significant efforts have been made to quantitatively benchmark the sheath sub-grid model used in our time-domain simulations of plasma-immersed antenna near fields, which includes highly detailed three-dimensional geometry, the presence of the slow wave, and the non-linear evolution of the sheath potential. We present both our quantitative benchmarking strategy, and results for the ITER antenna configuration, including detailed maps of electric field, and sheath potential along the entire antenna structure. Our method is based upon a time-domain linear plasma model [1], using the finite-difference electromagnetic Vorpal/Vsim software [2]. This model has been augmented with a non-linear rf-sheath sub-grid model [3], which provides a self-consistent boundary condition for plasma current where it exists in proximity to metallic surfaces. Very early, this algorithm was designed and demonstrated to work on very complicated three-dimensional geometry, derived from CAD or other complex description of actual hardware, including ITER antennas. Initial work with the simulation model has also provided a confirmation of the existence of propagating slow waves [4] in the low density edge region, which can significantly impact the strength of the rf-sheath potential, which is thought to contribute to impurity generation. Our sheath algorithm is based upon per-point lumped-circuit parameters for which we have estimates and general understanding, but which allow for some tuning and fitting. We are now engaged in a careful benchmarking of the algorithm against known analytic models and existing computational techniques [5] to insure that the predictions of rf-sheath voltage are quantitatively consistent and believable, especially where slow waves share in the field with the fast wave. Currently in progress, an addition to the plasma force response accounting for the sheath potential, should enable the modeling of sheath plasma waves, a predicted additional root to the dispersion
Quantitative modeling of ICRF antennas with integrated time domain RF sheath and plasma physics
Smithe, David N.; D'Ippolito, Daniel A.; Myra, James R.
2014-02-12
Significant efforts have been made to quantitatively benchmark the sheath sub-grid model used in our time-domain simulations of plasma-immersed antenna near fields, which includes highly detailed three-dimensional geometry, the presence of the slow wave, and the non-linear evolution of the sheath potential. We present both our quantitative benchmarking strategy, and results for the ITER antenna configuration, including detailed maps of electric field, and sheath potential along the entire antenna structure. Our method is based upon a time-domain linear plasma model, using the finite-difference electromagnetic Vorpal/Vsim software. This model has been augmented with a non-linear rf-sheath sub-grid model, which provides a self-consistent boundary condition for plasma current where it exists in proximity to metallic surfaces. Very early, this algorithm was designed and demonstrated to work on very complicated three-dimensional geometry, derived from CAD or other complex description of actual hardware, including ITER antennas. Initial work with the simulation model has also provided a confirmation of the existence of propagating slow waves in the low density edge region, which can significantly impact the strength of the rf-sheath potential, which is thought to contribute to impurity generation. Our sheath algorithm is based upon per-point lumped-circuit parameters for which we have estimates and general understanding, but which allow for some tuning and fitting. We are now engaged in a careful benchmarking of the algorithm against known analytic models and existing computational techniques to insure that the predictions of rf-sheath voltage are quantitatively consistent and believable, especially where slow waves share in the field with the fast wave. Currently in progress, an addition to the plasma force response accounting for the sheath potential, should enable the modeling of sheath plasma waves, a predicted additional root to the dispersion, existing at the
Computational Electronics and Electromagnetics
DeFord, J.F.
1993-03-01
The Computational Electronics and Electromagnetics thrust area is a focal point for computer modeling activities in electronics and electromagnetics in the Electronics Engineering Department of Lawrence Livermore National Laboratory (LLNL). Traditionally, they have focused their efforts in technical areas of importance to existing and developing LLNL programs, and this continues to form the basis for much of their research. A relatively new and increasingly important emphasis for the thrust area is the formation of partnerships with industry and the application of their simulation technology and expertise to the solution of problems faced by industry. The activities of the thrust area fall into three broad categories: (1) the development of theoretical and computational models of electronic and electromagnetic phenomena, (2) the development of useful and robust software tools based on these models, and (3) the application of these tools to programmatic and industrial problems. In FY-92, they worked on projects in all of the areas outlined above. The object of their work on numerical electromagnetic algorithms continues to be the improvement of time-domain algorithms for electromagnetic simulation on unstructured conforming grids. The thrust area is also investigating various technologies for conforming-grid mesh generation to simplify the application of their advanced field solvers to design problems involving complicated geometries. They are developing a major code suite based on the three-dimensional (3-D), conforming-grid, time-domain code DSI3D. They continue to maintain and distribute the 3-D, finite-difference time-domain (FDTD) code TSAR, which is installed at several dozen university, government, and industry sites.
Ground penetrating radar data analyzed in frequency and time domain for engineering issues
NASA Astrophysics Data System (ADS)
Capozzoli, Luigi; Giampaolo, Valeria; Votta, Mario; Rizzo, Enzo
2014-05-01
spectrum that allows a supplementary help to complete the information extracted in time-domain (dos Santos et al., 2014). The signal processing technique is based on a Fast Fourier Transform (FFT) that allows analyzing in frequency domain variations due to presence of anomalous bodies of different materials in the concrete and in the sand. Furthermore the data obtained in situ are compared with data extracted by theoretical simulation of e-m signal propagation built in Reflex-w software. There is a good agreement between simulated data and real data both in frequency domain both in time domain. So we have verified that frequency analysis can be adopted such as a useful tools to increase and complete information achieved in traditional way. Bibliography James S. Mellett (1995). Ground penetrating radar applications in engineering, environmental Management, and geology. Journal of Applied Geophysics. V. 33, Issues 1-3, January 1995, Pages 157-166 Proto, M.; Bavusi, M.; Bernini, R.; Bigagli, L.; Bost, M.; Bourquin, F.; Cottineau, L.-M.; Cuomo, V.; Vecchia, P.D.; Dolce, M.; Dumoulin, J.; Eppelbaum, L.; Fornaro, G.; Gustafsson, M.; Hugenschimdt, J.; Kaspersen, P.; Kim, H.; Lapenna, V.; Leggio, M.; Loperte, A.; Mazzetti, P.; Moroni, C.; Nativi, S.; Nordebo, S.; Pacini, F.; Palombo, A.; Pascucci, S.; Perrone, A.; Pignatti, S.; Ponzo, F.C.; Rizzo, E.; Soldovieri, F.; Taillade, F. Transport Infrastructure Surveillance and Monitoring by Electromagnetic Sensing: The ISTIMES Project. Sensors 2010, 10, 10620-10639 Vinicius Rafael N. dos Santos, Waleed Al-Nuaimy, Jorge Luís Porsani, Nina S. Tomita Hirata, Hamzah S. Alzubi (2014). Spectral analysis of ground penetrating radar signals in concrete, metallic and plastic targets. Journal of Applied Geophysics, V.100, January 2014, Pages 32-43
On the Analysis Methods for the Time Domain and Frequency Domain Response of a Buried Objects*
NASA Astrophysics Data System (ADS)
Poljak, Dragan; Šesnić, Silvestar; Cvetković, Mario
2014-05-01
There has been a continuous interest in the analysis of ground-penetrating radar systems and related applications in civil engineering [1]. Consequently, a deeper insight of scattering phenomena occurring in a lossy half-space, as well as the development of sophisticated numerical methods based on Finite Difference Time Domain (FDTD) method, Finite Element Method (FEM), Boundary Element Method (BEM), Method of Moments (MoM) and various hybrid methods, is required, e.g. [2], [3]. The present paper deals with certain techniques for time and frequency domain analysis, respectively, of buried conducting and dielectric objects. Time domain analysis is related to the assessment of a transient response of a horizontal straight thin wire buried in a lossy half-space using a rigorous antenna theory (AT) approach. The AT approach is based on the space-time integral equation of the Pocklington type (time domain electric field integral equation for thin wires). The influence of the earth-air interface is taken into account via the simplified reflection coefficient arising from the Modified Image Theory (MIT). The obtained results for the transient current induced along the electrode due to the transmitted plane wave excitation are compared to the numerical results calculated via an approximate transmission line (TL) approach and the AT approach based on the space-frequency variant of the Pocklington integro-differential approach, respectively. It is worth noting that the space-frequency Pocklington equation is numerically solved via the Galerkin-Bubnov variant of the Indirect Boundary Element Method (GB-IBEM) and the corresponding transient response is obtained by the aid of inverse fast Fourier transform (IFFT). The results calculated by means of different approaches agree satisfactorily. Frequency domain analysis is related to the assessment of frequency domain response of dielectric sphere using the full wave model based on the set of coupled electric field integral
NASA Technical Reports Server (NTRS)
Vinh, Hoang; Dwyer, Harry A.; Van Dam, C. P.
1992-01-01
The applications of two CFD-based finite-difference methods to computational electromagnetics are investigated. In the first method, the time-domain Maxwell's equations are solved using the explicit Lax-Wendroff scheme and in the second method, the second-order wave equations satisfying the Maxwell's equations are solved using the implicit Crank-Nicolson scheme. The governing equations are transformed to a generalized curvilinear coordinate system and solved on a body-conforming mesh using the scattered-field formulation. The induced surface current and the bistatic radar cross section are computed and the results are validated for several two-dimensional test cases involving perfectly-conducting scatterers submerged in transverse-magnetic plane waves.
Minowa, Yosuke; Fujii, Takashi; Nagai, Masaya; Ochiai, Tetsuyuki; Sakoda, Kazuaki; Hirao, Kazuyuki; Tanaka, Koichiro
2008-03-31
We established a novel method to evaluate effective optical constants by terahertz (THz) time domain spectroscopy and suggested a strict definition of optical constants and an expression for electromagnetic energy loss following the second law of thermodynamics. We deduced the effective optical constants of phosphor bronze wire grids in the THz region experimentally and theoretically. The results depend strongly on the polarization of the THz waves. When the electric field is parallel to the wires, we observed Drude-like electric permittivities with a plasma frequency reduced by a factor of 10(-3), whereas when the field is perpendicular, the sample behaved as a simple dielectric film. We also observed unexpected magnetic permeabilities, which originate from the non-resonant real magnetic response of finite size-conductors.
Brainard, James Robert; Tidwell, Vincent Carroll; Coplen, Amy K.; Ruby, Douglas Scott; Coombs, Jason R.; Wright, Jerome L.; Roberts, Jesse Daniel
2004-11-01
Time domain reflectometry (TDR) operates by propagating a radar frequency electromagnetic pulse down a transmission line while monitoring the reflected signal. As the electromagnetic pulse propagates along the transmission line, it is subject to impedance by the dielectric properties of the media along the transmission line (e.g., air, water, sediment), reflection at dielectric discontinuities (e.g., air-water or water-sediment interface), and attenuation by electrically conductive materials (e.g., salts, clays). Taken together, these characteristics provide a basis for integrated stream monitoring; specifically, concurrent measurement of stream stage, channel profile and aqueous conductivity. Here, we make novel application of TDR within the context of stream monitoring. Efforts toward this goal followed three critical phases. First, a means of extracting the desired stream parameters from measured TDR traces was required. Analysis was complicated by the fact that interface location and aqueous conductivity vary concurrently and multiple interfaces may be present at any time. For this reason a physically based multisection model employing the S11 scatter function and Cole-Cole parameters for dielectric dispersion and loss was developed to analyze acquired TDR traces. Second, we explored the capability of this multisection modeling approach for interpreting TDR data acquired from complex environments, such as encountered in stream monitoring. A series of laboratory tank experiments were performed in which the depth of water, depth of sediment, and conductivity were varied systematically. Comparisons between modeled and independently measured data indicate that TDR measurements can be made with an accuracy of {+-}3.4x10{sup -3} m for sensing the location of an air/water or water/sediment interface and {+-}7.4% of actual for the aqueous conductivity. Third, monitoring stations were sited on the Rio Grande and Paria rivers to evaluate performance of the TDR system
THE PSTD ALGORITHM: A TIME-DOMAIN METHOD REQUIRING ONLY TWO CELLS PER WAVELENGTH. (R825225)
A pseudospectral time-domain (PSTD) method is developed for solutions of Maxwell's equations. It uses the fast Fourier transform (FFT), instead of finite differences on conventional finite-difference-time-domain (FDTD) methods, to represent spatial derivatives. Because the Fourie...
A two-dimensional time domain near zone to far zone transformation
NASA Technical Reports Server (NTRS)
Luebbers, Raymond J.; Ryan, Deirdre; Beggs, John H.; Kunz, Karl S.
1991-01-01
A time domain transformation useful for extrapolating three dimensional near zone finite difference time domain (FDTD) results to the far zone was presented. Here, the corresponding two dimensional transform is outlined. While the three dimensional transformation produced a physically observable far zone time domain field, this is not convenient to do directly in two dimensions, since a convolution would be required. However, a representative two dimensional far zone time domain result can be obtained directly. This result can then be transformed to the frequency domain using a Fast Fourier Transform, corrected with a simple multiplicative factor, and used, for example, to calculate the complex wideband scattering width of a target. If an actual time domain far zone result is required, it can be obtained by inverse Fourier transform of the final frequency domain result.
A two-dimensional time domain near zone to far zone transformation
NASA Technical Reports Server (NTRS)
Luebbers, Raymond J.; Ryan, Deirdre; Beggs, John H.; Kunz, Karl S.
1991-01-01
In a previous paper, a time domain transformation useful for extrapolating 3-D near zone finite difference time domain (FDTD) results to the far zone was presented. In this paper, the corresponding 2-D transform is outlined. While the 3-D transformation produced a physically observable far zone time domain field, this is not convenient to do directly in 2-D, since a convolution would be required. However, a representative 2-D far zone time domain result can be obtained directly. This result can then be transformed to the frequency domain using a Fast Fourier Transform, corrected with a simple multiplicative factor, and used, for example, to calculate the complex wideband scattering width of a target. If an actual time domain far zone result is required it can be obtained by inverse Fourier transform of the final frequency domain result.
NASA Astrophysics Data System (ADS)
Amir, F.; Farrington, N.; Mitchell, C.; Missous, M.
2010-10-01
Simulated RF time-domain characteristics for advanced Gunn diodes with hot electron injection and sub-micron transit region lengths for use at frequencies over 100GHz are reported. The physical models used have been developed in SILVACO and are compared to measured results. The devices measured were originally fabricated to investigate the feasibility of GaAs Gunn diode oscillators capable of operating at D-band frequencies and ultimately intended for use in high power (multi-mW) Terahertz sources (~0.6THz) when used in conjunction with novel Schottky diode frequency multiplier technology. The device models created using SILVACO are described and the DC and time-domain results presented. The simulations were used to determine the shortest transit region length capable of producing sustained oscillation. The operation of resonant disk second harmonic Gunn diode oscillators is also discussed and accurate electromagnetic models created using Ansoft High Frequency Structure Simulator presented. Novel methods for combining small-signal frequency-domain electromagnetic simulations with time-domain device simulations in order to account for the significant interactions between the diode and oscillator circuit are described.
NASA Astrophysics Data System (ADS)
Catapano, Ilaria; Soldovieri, Francesco
2015-04-01
In the research field of art and archaeology, scientific observation and analysis are hugely demanded to gather as more information as possible on the materials and techniques used to create artworks as well as in previous restoration actions. In this frame, diagnostic tools exploiting electromagnetic waves deserve massive interest tanks to their ability to provide non-invasive and possibly contactless characterization of the investigated objects. Among the electromagnetic diagnostic technologies, those working at frequencies belonging to the 0.1-10 THz range are currently deserving an increased attention since THz waves are capable of penetrating into optically opaque materials (up to the preparation layers), without direct contact and by involving sufficiently low energy to be considered as perfectly non-invasive in practice [1,2]. Moreover, being THz non-ionizing radiations, a moderate exposure to them implies minor long term risks to the molecular stability of the historical artifact and humans. Finally, recent developments of THz technology have allowed the commercialization of compact, flexible and portable systems. One of them is the Fiber-Coupled Terahertz Time Domain System (FICO) developed by Z-Omega, acquired by the Institute of Electromagnetic Sensing of the Environment (IREA) in 2013. This system works in the range from 60GHz to 3THz with a waveform acquisition speed up to 500Hz, it is equipped with fiber optic coupled transmitting and receiving probes and, few months ago, has been potentiated by means of an automatic positioning system enabling to scan a 150mm x 150mm area. In the frame of the IREA research activities regarding cultural heritage, the FICO system is currently adopted to perform both spectroscopy and imaging, which are the two kind of analysis wherein THz technology can be profitably explored [3]. In particular, THz spectroscopy is used to distinguish different artists materials by exploiting their peculiar fingerprint in the absorption
NASA Technical Reports Server (NTRS)
Ryan, Deirdre A.; Luebbers, Raymond J.; Nguyen, Truong X.; Kunz, Karl S.; Steich, David J.
1992-01-01
Prediction of anechoic chamber performance is a difficult problem. Electromagnetic anechoic chambers exist for a wide range of frequencies but are typically very large when measured in wavelengths. Three dimensional finite difference time domain (FDTD) modeling of anechoic chambers is possible with current computers but at frequencies lower than most chamber design frequencies. However, two dimensional FDTD (2D-FTD) modeling enables much greater detail at higher frequencies and offers significant insight into compact anechoic chamber design and performance. A major subsystem of an anechoic chamber for which computational electromagnetic analyses exist is the reflector. First, an analysis of the quiet zone fields of a low frequency anechoic chamber produced by a uniform source and a reflector in two dimensions using the FDTD method is presented. The 2D-FDTD results are compared with results from a three dimensional corrected physical optics calculation and show good agreement. Next, a directional source is substituted for the uniform radiator. Finally, a two dimensional anechoic chamber geometry, including absorbing materials, is considered, and the 2D-FDTD results for these geometries appear reasonable.
NASA Astrophysics Data System (ADS)
Ribaudo, J. T.; Constable, C.
2010-12-01
The commercial finite element software FlexPDE has been successfully used to simulate electromagnetic induction in Earth's mantle and lithosphere and validated by several previously published results. Estimates of Earth's frequency-dependent electromagnetic response calculated from satellite data are known to be influenced by the local time of the observing frame. We use time-stepping methods scripted within FlexPDE to investigate the hypothesis that this bias results from the rotation of Earth through the asymmetric and highly variable magnetic field associated with the magnetospheric ring current. We evaluate local-time response functions at periods of a few hours to a few months. These are calculated from long 3-dimensional, time-domain simulations of geomagnetic induction and using the magnetic data similar to those gathered by low earth orbiting satellite missions. The spatial structure of the external field is imposed in the form of a time-varying spherical harmonic representation in a geomagnetic coordinate system that rotates with respect to Earth. The symmetric part of the field is controlled by the dipole (degree 1, order 0) term and the asymmetric part controlled by a quadrupole (degree 2, order 1) term. Time variations in the magnitude of the external field are controlled by a high-resolution magnetic index such as the new 1-minute USGS Dst, subsampled at 15 minute intervals.
NASA Astrophysics Data System (ADS)
Finn, C. A.; Deszcz-Pan, M.; Horton, R.; Breit, G.; John, D.
2007-12-01
High resolution helicopter-borne magnetic and electromagnetic (EM) data flown over the rugged, ice-covered, highly magnetic and mostly resistive volcanoes of Mount Rainier, Mount Adams and Mount Baker, along with rock property measurements, reveal the distribution of alteration, water and hydrothermal fluids that are essential to evaluating volcanic landslide hazards and understanding hydrothermal systems. Hydrothermally altered rocks, particularly if water saturated, can weaken stratovolcanoes, thereby increasing the potential for catastrophic sector collapses that can lead to far-traveled, destructive debris flows. Intense hydrothermal alteration significantly reduces the magnetization and resistivity of volcanic rock resulting in clear recognition of altered rock by helicopter magnetic and EM measurements. Magnetic and EM data, combined with geological mapping and rock property measurements, indicate the presence of appreciable thicknesses of hydrothermally altered rock west of the modern summit of Mount Rainier in the Sunset Amphitheater region, in the central core of Mount Adams north of the summit, and in much of the central cone of Mount Baker. We identify the Sunset Amphitheater region and steep cliffs at the western edge of the central altered zone at Mount Adams as likely sources for future debris flows. In addition, the EM data identified water-saturated rocks in the upper 100-200 m of the three volcanoes. The water-saturated zone could extend deeper, but is beyond the detection limits of the EM data. Water in hydrothermal fluids reacts with the volcanic rock to produce clay minerals. The formation of clay minerals and presence of free water reduces the effective stress, thereby increasing the potential for slope failure, and acts, with entrained melting ice, as a lubricant to transform debris avalanches into lahars. Therefore, knowing the distribution of water is also important for hazard assessments. Finally, modeling requires extremely low
Fourth Airborne Geoscience Workshop
NASA Technical Reports Server (NTRS)
1991-01-01
The focus of the workshop was on how the airborne community can assist in achieving the goals of the Global Change Research Program. The many activities that employ airborne platforms and sensors were discussed: platforms and instrument development; airborne oceanography; lidar research; SAR measurements; Doppler radar; laser measurements; cloud physics; airborne experiments; airborne microwave measurements; and airborne data collection.
As the surface clogs in permeable pavement systems, they lose effectiveness and require maintenance. There is limited direct guidance for determining when maintenance is needed to prevent surface runoff bypass. Research is being conducted using multiple time domain reflectomete...
Analysis of electron capture process in charge pumping sequence using time domain measurements
Hori, Masahiro Watanabe, Tokinobu; Ono, Yukinori; Tsuchiya, Toshiaki
2014-12-29
A method for analyzing the electron capture process in the charge pumping (CP) sequence is proposed and demonstrated. The method monitors the electron current in the CP sequence in time domain. This time-domain measurements enable us to directly access the process of the electron capture to the interface defects, which are obscured in the conventional CP method. Using the time-domain measurements, the rise time dependence of the capture process is systematically investigated. We formulate the capture process based on the rate equation and derive an analytic form of the current due to the electron capture to the defects. Based on the formula, the experimental data are analyzed and the capture cross section is obtained. In addition, the time-domain data unveil that the electron capture process completes before the electron channel opens, or below the threshold voltage in a low frequency range of the pulse.
A reevaluation of time domain reflectomery propagation time determination in soils
Technology Transfer Automated Retrieval System (TEKTRAN)
Time domain reflectometry (TDR) is an established method for the determination of apparent dielectric permittivity and water content in soils. Using current waveform interpretation procedures, signal attenuation and variation in dielectric media properties along the transmission line can significant...
Pulkkinen, Aki; Tarvainen, Tanja
2013-03-01
The radiative transfer equation (RTE) is widely accepted to accurately describe light transport in a medium with scattering particles, and it has been successfully applied as a light-transport model, for example, in diffuse optical tomography. Due to the computationally expensive nature of the RTE, most of these applications have been in the frequency domain. In this paper, an efficient solution method for the time-domain RTE is proposed. The method is based on solving the frequency-domain RTE at multiple modulation frequencies and using the Fourier-series representation of the radiance to obtain approximation of the time-domain solution. The approach is tested with simulations. The results show that the method can be used to obtain the solution of the time-domain RTE with good accuracy and with significantly fewer computational resources than are needed in the direct time-domain solution.
Assessment of Clogging Dynamics in Permeable Pavement Systems with Time Domain Reflectometers
Infiltration is a primary functional mechanism in green infrastructure stormwater controls. This study used time domain reflectometers (TDRs) to measure spatial infiltration and assess clogging dynamics of permeable pavement systems in Edison, NJ, and Louisville, KY. In 2009, t...
Windowing of THz time-domain spectroscopy signals: A study based on lactose
NASA Astrophysics Data System (ADS)
Vázquez-Cabo, José; Chamorro-Posada, Pedro; Fraile-Peláez, Francisco Javier; Rubiños-López, Óscar; López-Santos, José María; Martín-Ramos, Pablo
2016-05-01
Time-domain spectroscopy has established itself as a reference method for determining material parameters in the terahertz spectral range. This procedure requires the processing of the measured time-domain signals in order to estimate the spectral data. In this work, we present a thorough study of the properties of the signal windowing, a step previous to the parameter extraction algorithm, that permits to improve the accuracy of the results. Lactose has been used as sample material in the study.
Measurement of the Pulse Radiation of an IRA in Time Domain
NASA Astrophysics Data System (ADS)
Stadtler, Thiemo; Ter Haseborg, Jan Luiken; Sabath, Frank
For radiation of UWB pulses special Impulse Radiating Antennas (IRA) have been designed and are continuously improved. The measurement of its near field can help optimizing this antenna type. This paper presents a time domain scanner which is able to determine the transient near field. The so called double probe near field scanner can be employed to measure the two dimensional field distribution in time domain.
Maneuvering Simulation of Sea Fighter Using a Fast Nonlinear Time Domain Technique
2007-10-01
ultrasonic wave height sensors. Results Efforts to develop and mature a nonlinear comparing the 6-dof measured response of SeaFighter operating in sea... Nonlinear Time Domain Technique DISTRIBUTION: Approved for public release; distribution is unlimited. This paper is part of the following report: TITLE...Hydrodynamics Ann Arbor, Michigan, August 5-8, 2007 Maneuvering Simulation of Sea Fighter Using A Fast Nonlinear Time Domain Technique David E. Hess1, William
NASA Technical Reports Server (NTRS)
Ostheimer, W. D.
1972-01-01
Design techniques are presented applicable to nonminimum-phase systems. They are designed to handle plants with one right-half-plane zero which may vary, and any other variation of the plant parameters within known limits. The specifications that must be designed are given as a set of step response bounds in the time domain. A completed design will yield responses that stay within the time domain bounds at all times and utilize the entire region of allowed variation.
Revisiting the time domain induced polarization technique, from linearization to inversion
NASA Astrophysics Data System (ADS)
Kang, S.; Oldenburg, D.
2015-12-01
The induced polarization (IP) technique has been successful in mineral exploration, particularly for finding disseminated sulphide or porphyry deposits, but also in helping solve geotechnical and environmental problems. Electrical induced polarization (EIP) surveys use grounded electrodes and take measurements of the electric field while the current is both "on" and "off". Currently, 2D and 3D inversions of EIP data are generally carried out by first finding a background conductivity from the asymptotic "on-time" measurements. The DC resistivity problem is then linearized about that conductivity to obtain a linear relationship between the off-time data and the "pseudo-chargeability". The distribution of pseudo-chargeability in the earth is then interpreted within the context of the initial geoscience problem pursued. Despite its success, the current EIP implementation does have challenges. A fundamental assumption, that there is no electromagnetic induction (EM) effect, breaks down when the background is conductive. This is especially problematic in regions having conductive overburden. EM induction complicates, and sometimes overwhelms, the IP signal. To ameliorate this effect, we estimate the inductive signal, subtract it from the "off-time" data and invert the resultant IP data using the linearized formulation. We carefully examine the conditions under which this works. We also investigate the potential alterations to the linearized sensitivity function that are needed to allow a linearized inversion to be carried out. Inversions of EIP data recover a "chargeability" but this is not a uniquely defined quantity. There are multiple definitions of this property because there are a diverse number of ways in which an IP datum is defined. In time domain IP surveys, the data might be mV/V or a time-integrated voltage with units of ms. In reality however, data from an EIP survey have many time channels and each one can be inverted separately to produce a chargeability
ERIC Educational Resources Information Center
Ojala, Carl F.; Ojala, Eric J.
1987-01-01
Describes an activity in which students collect airborne particles using a common vacuum cleaner. Suggests ways for the students to convert their data into information related to air pollution and human health. Urges consideration of weather patterns when analyzing the results of the investigation. (TW)
NASA Technical Reports Server (NTRS)
1983-01-01
ATM (Airborne Thematic Mapper) was developed for NSTL (National Space Technology Companies) by Daedalus Company. It offers expanded capabilities for timely, accurate and cost effective identification of areas with prospecting potential. A related system is TIMS, Thermal Infrared Multispectral Scanner. Originating from Landsat 4, it is also used for agricultural studies, etc.
NASA Astrophysics Data System (ADS)
Spencer, E. A.; Russ, S.; Kerrigan, B.; Leggett, K.; Mullins, J.; Clark, D. C.; Mizell, J.; Gollapalli, R.; Vassiliadis, D.; Lusk, G. D.
2015-12-01
A plasma impedance probe is used to obtain plasma parameters in the ionosphere by measuring the magnitude, shape and location of resonances in the frequency spectrum when a probe structure is driven with RF excitation. The measured magnitude and phase response with respect to frequency can be analyzed via analytical and simulational means. We have designed and developed a new Time Domain Impedance Probe capable of making measurements of absolute electron density and electron neutral collision frequency at temporal and spatial resolutions not previously attained. A single measurement can be made in a time as short as 50 microseconds, which yields a spatial resolution of 0.35 meters for a satellite orbital velocity of 7 km/s. The method essentially consists of applying a small amplitude time limited voltage signal into a probe and measuring the resulting current response. The frequency bandwidth of the voltage signal is selected in order that the electron plasma resonances are observable. A prototype of the instrument will be flown in October 2015 on a NASA Undergraduate Student Instrument Progam (USIP) sounding rocket launched out of Wallops Flight Facility. To analyze the measurements, we use a Particle In Cell (PIC) kinetic simulation to calculate the impedance of a dipole antenna immersed in a plasma. The electromagnetic solver utilizes the Finite Difference Time Domain method, while the particle to grid and grid to particle interpolation schemes are standard. The plasma sheath formation electron flux into the dipole surface is not included. The bulk velocity of the plasma around the dipole is assumed to be zero. For completeness, the hot plasma and nonlinear effects of probe plasma interaction are explored, including the appearance of cyclotron harmonics. In this work the electron neutral collisions are simulated via a Poisson process approximation. Our results are compared to sounding rocket data from the NASA Tropical Storms mission in 2007, as well as the
NASA Astrophysics Data System (ADS)
Li, Jiusheng; Yao, Jianquan
2008-12-01
Recently, there has been a remarkable effort in employing terahertz (THz) spectroscopy for investigating material properties. Pulsed THz time-domain spectroscopy is a coherent technique, in which both the amplitude and the phase of a THz pulse are measured. Coherent detection enables direct calculations of both the imaginary and the real parts of the refractive index without using the Kramers-Kronig relations. In this letter, the terahertz absorption spectra and the refractive indices of olive oil were measured by using terahertz time-domain spectroscopy (THz-TDS) in the frequency range extending from 0.2 to 2.5 THz. The terahertz dielectric properties of olive oil were characterized by THz-TDS, and the consistency with the known parameters was identified. A novel iterative algorithm improves the existing data extraction algorithms and further enhances the accuracy of the parameter extraction for terahertz time-domain spectroscopy. The results obtained in this study suggest that the THz-TDS method is a useful tool for vegetable oils characterization in the far infrared region. This method can be applied not only to terahertz time-domain spectroscopy but also to any kind of optical constant measurement in the time domain.
A time-domain inverse technique for the localization and quantification of rotating sound sources
NASA Astrophysics Data System (ADS)
Zhang, Xiao-Zheng; Bi, Chuan-Xing; Zhang, Yong-Bin; Xu, Liang
2017-06-01
A time-domain inverse technique based on the time-domain equivalent source method is proposed for the localization and quantification of rotating sound sources. In this technique, the actual rotating sound sources are modeled by a series of rotating equivalent sources distributed on the source surface. The strengths of these equivalent sources are solved based on the exact transfer relationship between the measured pressure at the receiver time and the desired equivalent source strengths at the source time. Compared to the known time-domain rotating beamforming that just owns the function of source localization, the proposed inverse technique not only can locate rotating sources accurately but also can predict sound fields quantitatively. Moreover, due to the use of retarded time approach, the proposed inverse technique avoids the interpolation of measured pressure that is needed in the time-domain rotating beamforming, thus providing the ability of real-time calculation of source strengths. Numerical simulations and experiments examine the validity of the proposed technique and demonstrate its advantages of locating sources more accurately and enabling to predict sound fields quantitatively by comparing with the time-domain rotating beamforming.
Comparison of frequency-domain and time-domain rotorcraft vibration control methods
NASA Technical Reports Server (NTRS)
Gupta, N. K.
1984-01-01
Active control of rotor-induced vibration in rotorcraft has received significant attention recently. Two classes of techniques have been proposed. The more developed approach works with harmonic analysis of measured time histories and is called the frequency-domain approach. The more recent approach computes the control input directly using the measured time history data and is called the time-domain approach. The report summarizes the results of a theoretical investigation to compare the two approaches. Five specific areas were addressed: (1) techniques to derive models needed for control design (system identification methods), (2) robustness with respect to errors, (3) transient response, (4) susceptibility to noise, and (5) implementation difficulties. The system identification methods are more difficult for the time-domain models. The time-domain approach is more robust (e.g., has higher gain and phase margins) than the frequency-domain approach. It might thus be possible to avoid doing real-time system identification in the time-domain approach by storing models at a number of flight conditions. The most significant error source is the variation in open-loop vibrations caused by pilot inputs, maneuvers or gusts. The implementation requirements are similar except that the time-domain approach can be much simpler to implement if real-time system identification were not necessary.
Zhang, Xiao-Zheng; Bi, Chuan-Xing; Zhang, Yong-Bin; Xu, Liang
2011-09-01
Transient nearfield acoustic holography based on an interpolated time-domain equivalent source method (ESM) is proposed to reconstruct transient acoustic fields directly in the time domain. Since the equivalent source strengths solved by the traditional time-domain ESM formulation cannot be used to reconstruct the pressure on the source surface directly, an interpolation function is introduced to develop an interpolated time-domain ESM formulation which permits one to deduce an iterative reconstruction process. As the reconstruction process is ill-conditioned and especially there exists a cumulative effect of errors, the Tikhonov regularization is used to stabilize the process. Numerical examples of reconstructing transient acoustic fields from a baffled planar piston, an impulsively accelerating sphere and a cube box, respectively, demonstrate that the proposed method not only can effectively reconstruct transient acoustic fields in the time domain, but also can visualize acoustic fields in the space domain. And, in the first numerical example, the cumulative effect of errors and the validity of using the Tikhonov regularization to suppress the errors are described.
Remote sensing of soil moisture using airborne hyperspectral data
Technology Transfer Automated Retrieval System (TEKTRAN)
The Institute for Technology Development (ITD) has developed an airborne hyperspectral sensor system that collects electromagnetic reflectance data of the terrain. The system consists of sensors for three different sections of the electromagnetic spectrum; the Ultra-Violet (UV), Visible/Near Infrare...
Airborne space laser communication system and experiments
NASA Astrophysics Data System (ADS)
Li, Xiao-Ming; Zhang, Li-zhong; Meng, Li-Xin
2015-11-01
Airborne space laser communication is characterized by its high speed, anti-electromagnetic interference, security, easy to assign. It has broad application in the areas of integrated space-ground communication networking, military communication, anti-electromagnetic communication. This paper introduce the component and APT system of the airborne laser communication system design by Changchun university of science and technology base on characteristic of airborne laser communication and Y12 plan, especially introduce the high communication speed and long distance communication experiment of the system that among two Y12 plans. In the experiment got the aim that the max communication distance 144Km, error 10-6 2.5Gbps - 10-7 1.5Gbps capture probability 97%, average capture time 20s. The experiment proving the adaptability of the APT and the high speed long distance communication.
Numerical stability analysis of the pseudo-spectral analytical time-domain PIC algorithm
Godfrey, Brendan B.; Vay, Jean-Luc; Haber, Irving
2014-02-01
The pseudo-spectral analytical time-domain (PSATD) particle-in-cell (PIC) algorithm solves the vacuum Maxwell's equations exactly, has no Courant time-step limit (as conventionally defined), and offers substantial flexibility in plasma and particle beam simulations. It is, however, not free of the usual numerical instabilities, including the numerical Cherenkov instability, when applied to relativistic beam simulations. This paper derives and solves the numerical dispersion relation for the PSATD algorithm and compares the results with corresponding behavior of the more conventional pseudo-spectral time-domain (PSTD) and finite difference time-domain (FDTD) algorithms. In general, PSATD offers superior stability properties over a reasonable range of time steps. More importantly, one version of the PSATD algorithm, when combined with digital filtering, is almost completely free of the numerical Cherenkov instability for time steps (scaled to the speed of light) comparable to or smaller than the axial cell size.
Robust time-domain identification of mass stiffness, and damping matrices
NASA Technical Reports Server (NTRS)
Roemer, Michael J.; Mook, D. Joseph
1990-01-01
Accurate estimates of the mass, stiffness, and damping characteristics of a structure is necessary for determining the control laws best suited for active control methodologies. There are several modal identification techniques available for determining the frequencies, damping ratios, and mode shapes of a structure. However, modal identification methods in both the frequency and time domains have difficulties for certain circumstances. Frequency domain techniques which utilize the steady-state response from various harmonic inputs often encounter difficulties when the frequencies are closely distributed, the structure exhibits a high degree of damping, or the steady-state condition is hard to establish. Time domain techniques have produced successful results, but lack robustness with respect to measurement noise. In this paper, two identification techniques and an estimation method are combined to form a time-domain technique to accurately identify the mass, stiffness, and damping matrices from noisy measurements.
Time domain passivity controller for 4-channel time-delay bilateral teleoperation.
Rebelo, Joao; Schiele, Andre
2015-01-01
This paper presents an extension of the time-domain passivity control approach to a four-channel bilateral controller under the effects of time delays. Time-domain passivity control has been used successfully to stabilize teleoperation systems with position-force and position-position controllers; however, the performance with such control architectures is sub-optimal both with and without time delays. This work extends the network representation of the time-domain passivity controller to the four-channel architecture, which provides perfect transparency to the user without time delay. The proposed architecture is based on modelling the controllers as dependent voltage sources and using only series passivity controllers. The obtained results are shown on a one degree-of-freedom setup and illustrate the stabilization behaviour of the proposed controller when time delay is present in the communication channel.
Crystallization of amorphous lactose at high humidity studied by terahertz time domain spectroscopy
NASA Astrophysics Data System (ADS)
McIntosh, Alexander I.; Yang, Bin; Goldup, Stephen M.; Watkinson, Michael; Donnan, Robert S.
2013-02-01
We report the first use of terahertz time-domain spectroscopy (THz-TDS) to study the hydration and crystallization of an amorphous molecular solid at high humidity. Lactose in its amorphous and monohydrate forms exhibits different terahertz spectra due to the lack of long range order in the amorphous material. This difference allowed the transformation of amorphous lactose to its monohydrate form at high humidity to be studied in real time. Spectral fitting of frequency-domain data allowed kinetic data to be obtained and the crystallization was found to obey Avrami kinetics. Bulk changes during the crystallization could also be observed in the time-domain.
High-performance TDM demultiplexing of coherent Nyquist pulses using time-domain orthogonality.
Harako, Koudai; Otuya, David Odeke; Kasai, Keisuke; Hirooka, Toshihiko; Nakazawa, Masataka
2014-12-01
We propose a simple and high-performance scheme for demultiplexing coherent Nyquist TDM signals by photo-mixing on a photo-detector with Nyquist LO pulses. This scheme takes advantage of the time-domain orthogonality of Nyquist pulses, which enables high-SNR demultiplexing and homodyne detection simultaneously in spite of a strong overlap with adjacent pulses in the time domain. The feasibility of this scheme is demonstrated through a demultiplexing experiment employing 80 Gbaud, 64 QAM Nyquist pulse OTDM signals. This scheme exhibits excellent demultiplexing performance with a much simpler configuration than a conventional ultrafast all-optical sampling scheme.
NASA Astrophysics Data System (ADS)
Li, Li-juan; Wang, Sheng; Ren, Jiao-jiao; Zhou, Ming-xing; Zhao, Duo
2015-03-01
According to nondestructive testing principle for the terahertz time domain spectroscopy Imaging, using digital image processing techniques, through Terahertz time-domain spectroscopy system collected images and two-dimensional datas and using a range of processing methods, including selecting regions of interest, contrast enhancement, edge detection, and defects being detected. In the paper, Matlab programming is been use to defect recognition of Terahertz, by figuring out the pixels to determine defects defect area and border length, roundness, diameter size. Through the experiment of the qualitative analysis and quantitative calculation of Matlab image processing, this method of detection of defects of geometric dimension of the sample to get a better result.
Sparse temporal sampling for fast time-domain wide-field fluorescence molecular tomography
NASA Astrophysics Data System (ADS)
Yao, Ruoyang; Zhao, Lingling; Intes, Xavier
2016-03-01
Fluorescence Molecular Tomography (FMT) is a powerful optical imaging tool for preclinical research. Especially, its implementation with time-domain (TD) techniques allows lifetime multiplexing for simultaneously imaging multiple biomarkers and provides enhanced data sets for improved resolution and quantification compared to continuous wave (CW) and frequency domain (FD) methodologies. When performing time-domain reconstructions, one important aspect is the selection of a temporal sub-data set. Typically, such selection is performed a posteriori after dense temporal sampling during the acquisition. In this work, we investigate the potential to collect a priori sparse data sets for fast experimental acquisition without compromising FMT performances.
Statistical analysis in the Natural Time Domain of the seismicity in México
NASA Astrophysics Data System (ADS)
Ramírez-Rojas, A.; Moreno-Torres, L. R.; Flores-Marquez, E. L.
2012-04-01
This work deals in a statistical analysis performed in the natural time domain of the seismicity occurred in México within the period 2000-2011. The data set corresponds to the seismic activity recorded by the National Seismological Service (SSN). Our study is performed along the Mexican Pacific coast comprising the states of: Baja California, Jalisco, Michoacán, Guerrero, and Oaxaca. The preliminary results of the analysis of power spectrum, order parameter and entropy fluctuations in the natural time domain show good consistency with the natural time theory and the latest tectonic reported findings; this fact confirms the suspicions of different tectonic mechanisms as seism trigger.
a Time-Domain Method for Transonic Flutter Analysis with Multidirectional Coupled Vibrations
NASA Astrophysics Data System (ADS)
Guo, Tongqing; Lu, Zhiliang; Wu, Yongjian
Gridgen is employed for static multi-block grid generation. A rapid deforming technique is employed for dynamic grids. Flutters are numerically analyzed in the time domain with a coupled solution of unsteady Euler equations and structural equations of motion. Based on variable stiffness method of transonic flutter analysis, a time-domain method of transonic flutter analysis with multi-directional coupled vibrations is develpoed. For completeness, flutter characteristics of a wing model with winglets and an aircraft model with external stores are numerically analyzed.
Simple magneto-optic transition metal models for time-domain simulations.
Wolff, Christian; Rodríguez-Oliveros, Rogelio; Busch, Kurt
2013-05-20
Efficient modelling of the magneto-optic effects of transition metals such as nickel, cobalt and iron is a topic of growing interest within the nano-optics community. In this paper, we present a general discussion of appropriate material models for the linear dielectric properties for such metals, provide parameter fits and formulate the anisotropic response in terms of auxiliary differential equations suitable for time-domain simulations. We validate both our material models and their implementation by comparing numerical results obtained with the Discontinuous Galerkin time-domain (DGTD) method to analytical results and previously published experimental data.
A simple technique for high resolution time domain phase noise measurement
NASA Technical Reports Server (NTRS)
Reinhardt, V. S.; Donahoe, T.
1977-01-01
A new time domain phase comparator is described. The device uses a novel technique to allow time domain phase measurements to be made with period and time interval counters without the use of offset reference oscillators. The device uses a single reference oscillator and allows measurements with a phase resolution greater than the noise floor of the reference. Data is presented showing a phase resolution of 0.02ps at 5 MHz with a crystal reference. The device has application in measuring the phase stability of systems where approximate phase quadrature can be maintained.
PETERSEN SW
2010-12-02
Airborne electromagnetic (AEM) surveys were flown during fiscal year (FY) 2008 within the 600 Area in an attempt to characterize the underlying subsurface and to aid in the closure and remediation design study goals for the 200-PO-1 Groundwater Operable Unit (OU). The rationale for using the AEM surveys was that airborne surveys can cover large areas rapidly at relatively low costs with minimal cultural impact, and observed geo-electrical anomalies could be correlated with important subsurface geologic and hydrogeologic features. Initial interpretation of the AEM surveys indicated a tenuous correlation with the underlying geology, from which several anomalous zones likely associated with channels/erosional features incised into the Ringold units were identified near the River Corridor. Preliminary modeling resulted in a slightly improved correlation but revealed that more information was required to constrain the modeling (SGW-39674, Airborne Electromagnetic Survey Report, 200-PO-1 Groundwater Operable Unit, 600 Area, Hanford Site). Both time-and frequency domain AEM surveys were collected with the densest coverage occurring adjacent to the Columbia River Corridor. Time domain surveys targeted deeper subsurface features (e.g., top-of-basalt) and were acquired using the HeliGEOTEM{reg_sign} system along north-south flight lines with a nominal 400 m (1,312 ft) spacing. The frequency domain RESOLVE system acquired electromagnetic (EM) data along tighter spaced (100 m [328 ft] and 200 m [656 ft]) north-south profiles in the eastern fifth of the 200-PO-1 Groundwater OU (immediately adjacent to the River Corridor). The overall goal of this study is to provide further quantification of the AEM survey results, using ground based geophysical methods, and to link results to the underlying geology and/or hydrogeology. Specific goals of this project are as follows: (1) Test ground based geophysical techniques for the efficacy in delineating underlying geology; (2) Use ground
Time domain terahertz spectroscopy of semiconductor bulk and multiple quantum wells structures
NASA Astrophysics Data System (ADS)
Chen, Yue
A time-domain terahertz spectroscopic system with high source power (average power > 10 nW) and high signal-to- noise ratio (>104) was developed and used to study ultrafast electronic processes in semiconductor structures. The physics of the spectroscopy, the theoretical basis of the interferometry, the model of the electron-electromagnetic field interaction, and the principle of experimental data processing are presented. The first direct measurement of the intervalley scattering time in In 0.53Ga0.47As was performed. The intervalley scattering time constants obtained were τLΓ = 35 fs and τLΓ = 450 fs. The spectroscopic data showed that at low carrier density the carrier- carrier scattering is unimportant. The intervalley deformation potential was obtained from the measured intervalley scattering time constant τ LΓ. The transient conductivity was obtained using time-domain terahertz spectroscopy. The frequency dependent terahertz spectroscopy enabled us to uniquely determine the transient mobility and density. The transient electron mobility is ~5200 cm2/Vs, which is less than the Hall mobility. For large photocarrier densities, this discrepancy is attributed to the additional momentum relaxation associated with electron-hole scattering. Using pump pulses with wavelength of 810 run, the electron trapping time in low-temperature-grown GaAs was accurately determined. The measured trapping time is slightly larger than that observed from a band-edge pump- probe measurements. We argue that the terahertz technique provides the most reliable measure of carrier lifetime due to the unique interaction. The carrier dynamics of low-temperature-grown InGaAs bulk and InGaAs/InAlAs multiple quantum wells were investigated. We were able to differentiate the two dominant mechanisms in the electron decay process, trapping and recombination. A trapping time as fast as 1.3-2.6 ps was observed for photo-excited electrons. The effects of Be-doping and growth temperature on the
NASA Astrophysics Data System (ADS)
Wei, Xiao-Kun; Shao, Wei; Shi, Sheng-Bing; Zhang, Yong; Wang, Bing-Zhong
2015-07-01
An efficient conformal locally one-dimensional finite-difference time-domain (LOD-CFDTD) method is presented for solving two-dimensional (2D) electromagnetic (EM) scattering problems. The formulation for the 2D transverse-electric (TE) case is presented and its stability property and numerical dispersion relationship are theoretically investigated. It is shown that the introduction of irregular grids will not damage the numerical stability. Instead of the staircasing approximation, the conformal scheme is only employed to model the curve boundaries, whereas the standard Yee grids are used for the remaining regions. As the irregular grids account for a very small percentage of the total space grids, the conformal scheme has little effect on the numerical dispersion. Moreover, the proposed method, which requires fewer arithmetic operations than the alternating-direction-implicit (ADI) CFDTD method, leads to a further reduction of the CPU time. With the total-field/scattered-field (TF/SF) boundary and the perfectly matched layer (PML), the radar cross section (RCS) of two 2D structures is calculated. The numerical examples verify the accuracy and efficiency of the proposed method. Project supported by the National Natural Science Foundation of China (Grant Nos. 61331007 and 61471105).
Re, Rebecca; Martinenghi, Edoardo; Mora, Alberto Dalla; Contini, Davide; Pifferi, Antonio; Torricelli, Alessandro
2016-10-01
We report the development of a compact probe for time-domain (TD) functional near-infrared spectroscopy (fNIRS) based on a fast silicon photomultiplier (SiPM) that can be put directly in contact with the sample without the need of optical fibers for light collection. We directly integrated an avalanche signal amplification stage close to the SiPM, thus reducing the size of the detection channel and optimizing the signal immunity to electromagnetic interferences. The whole detection electronics was placed in a plastic screw holder compatible with the electroencephalography standard cap for measurement on brain or with custom probe holders. The SiPM is inserted into a transparent and insulating resin to avoid the direct contact of the scalp with the 100-V bias voltage. The probe was integrated in an instrument for TD fNIRS spectroscopy. The system was characterized on tissue phantoms in terms of temporal resolution, responsivity, linearity, and capability to detect deep absorption changes. Preliminary in vivo tests on adult volunteers were performed to monitor hemodynamic changes in the arm during a cuff occlusion and in the brain cortex during a motor task.
Riley, D.J.
1993-04-01
A technique to integrate a dense, locally non-uniform mesh into finite-difference time-domain (FDTD) codes is presented. The method is designed for the full-wave analysis of multi-material layers that are physically thin, but perhaps electrically thick. Such layers are often used for the purpose of suppressing electromagnetic reflections from conducting surfaces. Throughout the non-uniform local mesh, average values for the conductivity and permittivity are used, where as variations in permeability are accommodated by splitting H-field line integrals and enforcing continuity of the normal B field. A unique interpolation scheme provides accuracy and late-time stability for mesh discontinuities as large as 1000 to 1. Application is made to resistive sheets, the absorbing Salisbury screen, crosstalk on printed circuit boards, and apertures that are narrow both in width and depth with regard to a uniform cell. Where appropriate, comparisons are made with the MoM code CARLOS and transmission-line theory. The hybrid mesh formulation has been highly optimized for both vector and parallel-processing on Cray YMP architectures.
Ibrahim, T S; Lee, R; Baertlein, B A; Yu, Y; Robitaille, P M
2000-09-01
In this work, a finite difference time domain (FDTD) algorithm is validated at 1.5 tesla using the standard GE Signa quadrature head coil and a muscle phantom. The electrical characteristics of the birdcage head coil are then calculated for the linear and quadrature cases. Unlike previous computational analysis which assume idealized currents on the end rings and the struts of the resonator, a complete computational analysis is provided. This treatment considers the coupling between the resonator and the sample and includes a real coil excitation, a complete current derivation, and a thorough description of both B(1) fields and RF radiation. With this improvement, electromagnetic phenomena such as radiation, standing wave currents on the wires, and field inhomogeneities due to interactions between the coil and the load inside the coil are observed. At 200 MHz, it is demonstrated that this particular coil does not work well due to radiation and non-uniformities on the struts of the device. Also, at this frequency magnetic field inhomogeneities become large when the coil is loaded with a phantom.
NASA Astrophysics Data System (ADS)
Das, Y.
2006-05-01
The work reported in this paper is a part of on-going studies to clarify how and to what extent soil electromagnetic properties affect the performance of induction metal detectors widely used in humanitarian demining. This paper studies the specific case of the time-domain response of a small metallic sphere buried in a non-conducting soil half-space with frequency-dependent complex magnetic susceptibility. The sphere is chosen as a simple prototype for the small metal parts in low-metal landmines, while soil with dispersive magnetic susceptibility is a good model for some soils that are known to adversely affect the performance of metal detectors. The included analysis and computations extend previous work which has been done mostly in the frequency domain. Approximate theoretical expressions for weakly magnetic soils are found to fit the experimental data very well, which allowed the estimation of soil model parameters, albeit in an ad hoc manner. Soil signal is found to exceed target signal (due to an aluminum sphere of radius 0.0127 m) in many cases, even for the weakly magnetic Cambodian laterite used in the experiments. How deep a buried target is detected depends on many other factors in addition to the relative strength of soil and target signals. A general statement cannot thus be made regarding detectability of a target in soil based on the presented results. However, computational results complemented with experimental data extend the understanding of the effect that soil has on metal detectors.
Acousto-Optic Tunable Filter for Time-Domain Processing of Ultra-Short Optical Pulses,
The application of acousto - optic tunable filters for shaping of ultra-fast pulses in the time domain is analyzed and demonstrated. With the rapid...advance of acousto - optic tunable filter (AOTF) technology, the opportunity for sophisticated signal processing capabilities arises. AOTFs offer unique
NASA Technical Reports Server (NTRS)
Hu, Fang Q.; Pizzo, Michelle E.; Nark, Douglas M.
2016-01-01
Based on the time domain boundary integral equation formulation of the linear convective wave equation, a computational tool dubbed Time Domain Fast Acoustic Scattering Toolkit (TD-FAST) has recently been under development. The time domain approach has a distinct advantage that the solutions at all frequencies are obtained in a single computation. In this paper, the formulation of the integral equation, as well as its stabilization by the Burton-Miller type reformulation, is extended to cases of a constant mean flow in an arbitrary direction. In addition, a "Source Surface" is also introduced in the formulation that can be employed to encapsulate regions of noise sources and to facilitate coupling with CFD simulations. This is particularly useful for applications where the noise sources are not easily described by analytical source terms. Numerical examples are presented to assess the accuracy of the formulation, including a computation of noise shielding by a thin barrier motivated by recent Historical Baseline F31A31 open rotor noise shielding experiments. Furthermore, spatial resolution requirements of the time domain boundary element method are also assessed using point per wavelength metrics. It is found that, using only constant basis functions and high-order quadrature for surface integration, relative errors of less than 2% may be obtained when the surface spatial resolution is 5 points-per-wavelength (PPW) or 25 points-per-wavelength squared (PPW2).
Applications of time-domain spectroscopy to electron-phonon coupling dynamics at surfaces.
Matsumoto, Yoshiyasu
2014-10-01
Photochemistry is one of the most important branches in chemistry to promote and control chemical reactions. In particular, there has been growing interest in photoinduced processes at solid surfaces and interfaces with liquids such as water for developing efficient solar energy conversion. For example, photoinduced charge transfer between adsorbates and semiconductor substrates at the surfaces of metal oxides induced by photogenerated holes and electrons is a core process in photovoltaics and photocatalysis. In these photoinduced processes, electron-phonon coupling plays a central role. This paper describes how time-domain spectroscopy is applied to elucidate electron-phonon coupling dynamics at metal and semiconductor surfaces. Because nuclear dynamics induced by electronic excitation through electron-phonon coupling take place in the femtosecond time domain, the pump-and-probe method with ultrashort pulses used in time-domain spectroscopy is a natural choice for elucidating the electron-phonon coupling at metal and semiconductor surfaces. Starting with a phenomenological theory of coherent phonons generated by impulsive electronic excitation, this paper describes a couple of illustrative examples of the applications of linear and nonlinear time-domain spectroscopy to a simple adsorption system, alkali metal on Cu(111), and more complex photocatalyst systems.
Kemp, Jonathan A; Bilbao, Stefan; McMaster, James; Smith, Richard A
2013-08-01
Wave separation within a trumpet is presented using three high pressure microphones to measure pressure waves within the curved, constant cross-section tuning slide of the instrument while the instrument was being played by a virtuoso trumpet player. A closer inter-microphone spacing was possible in comparison to previous work through the use of time domain windowing on non-causal transfer functions and performing wave separation in the frequency domain. Time domain plots of the experimental wave separation were then compared to simulations using a physical model based on a time domain finite difference simulation of the trumpet bore coupled to a one mass, two degree of freedom lip model. The time domain and frequency spectra of the measured and synthesized sounds showed a similar profile, with the sound produced by the player showing broader spectral peaks in experimental data. Using a quality factor of 5 for the lip model was found to give greater agreement between the simulated and experimental starting transients in comparison to the values in the range 1-3 often assumed. Deviations in the spectral content and wave shape provide insights into the areas where future research may be directed in improving the accuracy of physical modeling synthesis.
Zhang, Xiao-Zheng; Thomas, Jean-Hugh; Bi, Chuan-Xing; Pascal, Jean-Claude
2012-10-01
A time-domain plane wave superposition method is proposed to reconstruct nonstationary sound fields. In this method, the sound field is expressed as a superposition of time convolutions between the estimated time-wavenumber spectrum of the sound pressure on a virtual source plane and the time-domain propagation kernel at each wavenumber. By discretizing the time convolutions directly, the reconstruction can be carried out iteratively in the time domain, thus providing the advantage of continuously reconstructing time-dependent pressure signals. In the reconstruction process, the Tikhonov regularization is introduced at each time step to obtain a relevant estimate of the time-wavenumber spectrum on the virtual source plane. Because the double infinite integral of the two-dimensional spatial Fourier transform is discretized directly in the wavenumber domain in the proposed method, it does not need to perform the two-dimensional spatial fast Fourier transform that is generally used in time domain holography and real-time near-field acoustic holography, and therefore it avoids some errors associated with the two-dimensional spatial fast Fourier transform in theory and makes possible to use an irregular microphone array. The feasibility of the proposed method is demonstrated by numerical simulations and an experiment with two speakers.
Time domain reflectometry waveform analysis with second order bounded mean oscillation
Technology Transfer Automated Retrieval System (TEKTRAN)
Tangent-line methods and adaptive waveform interpretation with Gaussian filtering (AWIGF) have been proposed for determining reflection positions of time domain reflectometry (TDR) waveforms. However, the accuracy of those methods is limited for short probe TDR sensors. Second order bounded mean osc...
Wang, Zhaojun; Zhou, Xiaoming
2016-12-01
The authors study the wave propagation in continuum acoustic metamaterials whose all or not all of the principal elements of the mass tensor or the scalar compressibility can be negative due to wave dispersion. Their time-domain wave characteristics are particularly investigated by the finite-difference time-domain (FDTD) method, in which algorithms for the Drude and Lorentz dispersion pertinent to acoustic metamaterials are provided necessarily. Wave propagation nature of anisotropic acoustic metamaterials with all admissible material parameters are analyzed in a general manner. It is found that anomalous negative refraction phenomena can appear in several dispersion regimes, and their unique time-domain signatures have been discovered by the FDTD modeling. It is further proposed that two different metamaterial layers with specially assigned dispersions could comprise a conjugate pair that permits wave propagation only at specific points in the wave vector space. The time-domain pulse simulation verifies that acoustic directive radiation capable of modulating radiation angle with the wave frequency can be realized with this conjugate pair. The study provides the detailed analysis of wave propagation in anisotropic and dispersive acoustic mediums, which makes a further step toward dispersion engineering and transient wave control through acoustic metamaterials.
Insensitivity of single particle time domain measurements to laser velocimeter 'Doppler ambiguity.'
NASA Technical Reports Server (NTRS)
Johnson, D. A.
1973-01-01
It is shown that single particle time domain measurements in high speed gas flows obtained by a laser velocimeter technique developed for use in wind tunnels are not affected by the so-called 'Doppler ambiguity.' A comparison of hot-wire anemometer and laser velocimeter measurements taken under similar flow conditions is used for the demonstration.
Design PID controllers for desired time-domain or frequency-domain response.
Zhang, Weidong; Xi, Yugeng; Yang, Genke; Xu, Xiaoming
2002-10-01
Practical requirements on the design of control systems, especially process control systems, are usually specified in terms of time-domain response, such as overshoot and rise time, or frequency-domain response, such as resonance peak and stability margin. Although numerous methods have been developed for the design of the proportional-integral-derivative (PID) controller, little work has been done in relation to the quantitative time-domain and frequency-domain responses. In this paper, we study the following problem: Given a nominal stable process with time delay, we design a suboptimal PID controller to achieve the required time-domain response or frequency-domain response for the nominal system or the uncertain system. An H(infinity) PID controller is developed based on optimal control theory and the parameters are derived analytically. Its properties are investigated and compared with that of two developed suboptimal controllers: an H2 PID controller and a Maclaurin PID controller. It is shown that all three controllers can provide the quantitative time-domain and frequency-domain responses.
NASA Technical Reports Server (NTRS)
Tranter, W. H.; Ziemer, R. E.; Fashano, M. J.
1975-01-01
This paper reviews the SYSTID technique for performance evaluation of communication systems using time-domain computer simulation. An example program illustrates the language. The inclusion of both Gaussian and impulse noise models make accurate simulation possible in a wide variety of environments. A very flexible postprocessor makes possible accurate and efficient performance evaluation.
Space–time domain velocity distributions in isotropic radiative transfer in two dimensions
NASA Astrophysics Data System (ADS)
Rossetto, Vincent
2017-04-01
We compute the exact solutions of the radiative transfer equation in two dimensions for isotropic scattering. The intensity and the radiance are given in the space–time domain when the source is punctual and isotropic or unidirectional. These analytical results are compared to Monte-Carlo simulations in four particular situations.
Time-domain Fresnel-to-Fraunhofer diffraction with photon echoes.
Ménager, L; Lorgeré, I; Gouët, J L; Mohan, R K; Kröll, S
1999-07-15
A photon echo experiment in Tm(3+):YAG is reported that shows, for the first time to the authors' knowledge, the time-domain equivalent of the transition from near- to far-field diffraction, including Talbot self-imaging effects. The experiment demonstrates the huge dispersion capability of photon echoes and opens the way to further exploration of space-time duality.
1997-03-01
to construct their computer codes (written largely in FORTRAN) to exploit this type of architecture. Towards the end of the 1980s, however, vector...for exploiting parallel architectures using both single and overset grids in conjunction with typical grid-based PDE solvers in general and FVTD...8217. Furthermore, it naturally exploits the means by which the electric and magnetic fields are related through the curl operators. Unfortunately, although stag
Passive microrheology in the effective time domain: analyzing time dependent colloidal dispersions.
Vyas, Bhavna M; Orpe, Ashish V; Kaushal, Manish; Joshi, Yogesh M
2016-10-21
We studied the aging dynamics of an aqueous suspension of LAPONITE®, a model time dependent soft glassy material, using a passive microrheology technique. This system is known to undergo physical aging during which its microstructure evolves progressively to explore lower free energy states. Optical microscopy is used to monitor the motion of micron-sized tracer probes embedded in a sample kept between two glass plates. The mean square displacements (MSD) obtained from the motion of the tracer particles show a systematic change from a purely diffusive behavior at short aging times to a subdiffusive behavior as the material ages. Interestingly, the MSDs at all the aging times as well as different LAPONITE® concentrations superpose remarkably to show a time-aging time master curve when the system is transformed from the real time domain to the effective time domain, which is obtained by rescaling the material clock to account for the age dependent relaxation time. The transformation of the master curve from the effective time domain to the real time domain leads to the prediction of the MSD in real time over a span of 5 decades when the measured data at individual aging times are only over 2 decades. Since the MSD obtained from microrheology is proportional to the creep compliance of a material, by using the Boltzmann superposition principle along with the convolution relation in the effective time domain, we predict the stress relaxation behavior of the system in real time. This work shows that the effective time approach applied to microrheology facilitates the prediction of long time creep and relaxation dynamics of a time dependent soft material by carrying out short time experiments at different aging times.
Time-domain imaging with quench-based fluorescent contrast agents
NASA Astrophysics Data System (ADS)
Akers, Walter J.; Solomon, Metasebya; Sudlow, Gail P.; Berezin, Mikhail; Achilefu, Samuel
2012-03-01
Quench-based probes utilize unique characteristics of fluorescence resonance energy transfer (FRET) to enhance contrast upon de-quenching. This mechanism has been used in a variety of molecular probes for imaging of cancer related enzyme activity such as matrix metalloproteinases, cathepsins and caspases. While non-fluorescent upon administration, fluorescence can be restored by separation of donor and acceptor, resulting in higher intensity in the presence of activator. Along with decreased quantum yield, FRET also results in altered fluorescence lifetime. Time-domain imaging can further enhance contrast and information yield from quench-based probes. We present in vivo time-domain imaging for detecting activation of quench-based probes. Quench-based probes utilize unique characteristics of fluorescence resonance energy transfer (FRET) to enhance contrast upon de-quenching. This mechanism has been used in a variety of molecular probes for imaging of cancer related enzyme activity such as matrix metalloproteinases, cathepsins and caspases. While non-fluorescent upon administration, fluorescence can be restored by separation of donor and acceptor, resulting in higher intensity in the presence of activator. Along with decreased quantum yield, FRET also results in altered fluorescence lifetime. Time-domain imaging can further enhance contrast and information yield from quench-based probes. We present in vivo time-domain imaging for detecting activation of quench-based probes. Time-domain diffuse optical imaging was performed to assess the FRET and quenching in living mice with orthotopic breast cancer. Tumor contrast enhancement was accompanied by increased fluorescence lifetime after administration of quenched probes selective for matrix metalloproteinases while no significant change was observed for non-quenched probes for integrin receptors. These results demonstrate the utility of timedomain imaging for detection of cancer-related enzyme activity in vivo.
NASA Astrophysics Data System (ADS)
Chiariotti, Paolo; Martarelli, Milena; Revel, Gian Marco
2014-07-01
This paper proposes the use of continuous scanning laser Doppler vibrometry (CSLDV) in time domain correlation techniques that aim at characterizing the structure-borne contributions of the noise emission of a mechanical system. The time domain correlation technique presented in this paper is based on the use of FIR (finite impulse response) filters obtained from the vibro-acoustic transfer matrix when vibration data are collected by laser Doppler vibrometry (LDV) exploited in continuous scan mode (CSLDV). The advantages, especially in terms of source decorrelation capabilities, related to the use of CSLDV for such purpose, with respect to standard discrete scan (SLDV), are discussed throughout the paper. To validate this approach, vibro-acoustic measurements were performed on a planetary gear motor for home appliances. The analysis of results is also supported by a simulation.
Feasibility investigation of general time-domain unsteady aerodynamics of rotors
NASA Technical Reports Server (NTRS)
Johnson, Wayne
1990-01-01
The feasibility of a general theory for the time-domain unsteady aerodynamics of helicopter rotors is investigated. The wake theory gives a linearized relation between the downwash and the wing bound circulation, in terms of the impulse response obtained directly in the time domain. This approach makes it possible to treat general wake configurations, including discrete wake vorticity with rolled-up and distorted geometry. The investigation establishes the approach for model order reduction; determines when a constrained identification method is needed; verifies the formulation of the theory for rolled-up, distorted trim wake geometry; and verifies the formulation of the theory for wake geometry perturbations. The basic soundness of the approach is demonstrated by the results presented. A research program to complete the development of the method is outlined. The result of this activity will be an approach for analyzing the aeroelastic stability and response of helicopter rotors, while retaining the important influence of the complicated rotor wake configuration.
Hori, Masahiro Watanabe, Tokinobu; Ono, Yukinori; Tsuchiya, Toshiaki
2015-01-26
To analyze the charge pumping (CP) sequence in detail, the source/drain electron current and the substrate hole current under the CP mode of transistors are simultaneously monitored in the time domain. Peaks are observed in both the electron and hole currents, which are, respectively, attributed to the electron emission from the interface defects and to the recombination with holes. The peak caused by the electron emission is found to consist of two components, strongly suggesting that the present time-domain measurement can enable us to resolve different kinds of interface defects. Investigating the correlation between the number of emitted and recombined electrons reveals that only one of the two components contributes to the CP current for the gate-pulse fall time from 6.25 × 10{sup −4} to 1.25 × 10{sup −2} s.
Scatterer size estimation using the center frequency assessed from ultrasound time domain data.
Erlöv, Tobias; Jansson, Tomas; Persson, Hans W; Cinthio, Magnus
2016-10-01
Scatterer size estimation is useful when characterizing tissue using ultrasound. In all previous studies on scatterer size, the estimations are performed in the frequency domain and are thus subjected to a trade off in time-frequency resolution. This study focused on the feasibility of estimating scatterer size in the time domain using only the ultrasound center frequency, assuming a Gaussian-shaped pulse. A model for frequency normalization was derived and the frequency-dependent attenuation was compensated. Five phantoms with well-defined sizes of spherical glass beads were made and scanned with two different linear array transducers with variable center frequencies. A strong correlation (r = 0.99, p < 10(-19)) between the backscattered center frequency and the product between the wave number and scatterer radius was demonstrated. On average the scatterer diameter was underestimated by 6% ± 24%. These results suggest that estimation of scatterer size is possible using only the center frequency assessed in the time domain.
Finite-difference time-domain simulation of thermal noise in open cavities
Andreasen, Jonathan; Cao Hui; Taflove, Allen; Kumar, Prem |; Cao Changqi
2008-02-15
A numerical model based on the finite-difference time-domain (FDTD) method is developed to simulate thermal noise in open cavities owing to output coupling. The absorbing boundary of the FDTD grid is treated as a blackbody, whose thermal radiation penetrates the cavity in the grid. The calculated amount of thermal noise in a one-dimensional dielectric cavity recovers the standard result of the quantum Langevin equation in the Markovian regime. Our FDTD simulation also demonstrates that in the non-Markovian regime the buildup of the intracavity noise field depends on the ratio of the cavity photon lifetime to the coherence time of thermal radiation. The advantage of our numerical method is that the thermal noise is introduced in the time domain without prior knowledge of cavity modes.
Single-shot terahertz time-domain spectroscopy in pulsed high magnetic fields
NASA Astrophysics Data System (ADS)
Noe, G. Timothy; Katayama, Ikufumi; Katsutani, Fumiya; Allred, James J.; Horowitz, Jeffrey A.; Sullivan, David M.; Zhang, Qi; Sekiguchi, Fumiya; Woods, Gary L.; Hoffmann, Matthias C.; Nojiri, Hiroyuki; Takeda, Jun; Kono, Junichiro
2016-12-01
We have developed a single-shot terahertz time-domain spectrometer to perform optical-pump/terahertz-probe experiments in pulsed, high magnetic fields up to 30 T. The single-shot detection scheme for measuring a terahertz waveform incorporates a reflective echelon to create time-delayed beamlets across the intensity profile of the optical gate beam before it spatially and temporally overlaps with the terahertz radiation in a ZnTe detection crystal. After imaging the gate beam onto a camera, we can retrieve the terahertz time-domain waveform by analyzing the resulting image. To demonstrate the utility of our technique, we measured cyclotron resonance absorption of optically excited carriers in the terahertz frequency range in intrinsic silicon at high magnetic fields, with results that agree well with published values.
Non-destructive inspections of illicit drugs in envelope using terahertz time-domain spectroscopy
NASA Astrophysics Data System (ADS)
Li, Ning; Shen, Jingling; Lu, Meihong; Jia, Yan; Sun, Jinhai; Liang, Laishun; Shi, Yanning; Xu, Xiaoyu; Zhang, Cunlin
2006-09-01
The absorption spectra of two illicit drugs, methylenedioxyamphetarnine (MDA) and methamphetamine (MA), within and without two conventional envelopes are studied using terahertz time-domain spectroscopy technique. The characteristic absorption spectra of MDA and MA are obtained in the range of 0.2 THz to 2.5 THz. MDA has an obvious absorption peak at 1.41 THz while MA has obvious absorption peaks at 1.23 THz, 1.67 THz, 1.84 THz and 2.43 THz. We find that the absorption peaks of MDA and MA within the envelopes are almost the same as those without the envelopes respectively although the two envelopes have some different absorption in THz waveband. This result indicates that the type of illicit drugs in envelopes can be determined by identifying their characteristic absorption peaks, and THz time-domain spectroscopy is one of the most powerful candidates for illicit drugs inspection.
Time domain averaging and correlation-based improved spectrum sensing method for cognitive radio
NASA Astrophysics Data System (ADS)
Li, Shenghong; Bi, Guoan
2014-12-01
Based on the combination of time domain averaging and correlation, we propose an effective time domain averaging and correlation-based spectrum sensing (TDA-C-SS) method used in very low signal-to-noise ratio (SNR) environments. With the assumption that the received signals from the primary users are deterministic, the proposed TDA-C-SS method processes the received samples by a time averaging operation to improve the SNR. Correlation operation is then performed with a correlation matrix to determine the existence of the primary signal in the received samples. The TDA-C-SS method does not need any prior information on the received samples and the associated noise power to achieve improved sensing performance. Simulation results are presented to show the effectiveness of the proposed TDA-C-SS method.
Small and Robotic Telescopes in the Era of Massive Time-Domain Surveys
NASA Astrophysics Data System (ADS)
Bode, M. F.; Vestrand, W. T.
2012-04-01
We have entered an era in time-domain astronomy in which the detected rate of explosive transients and important ephemeral states in persistent objects threatens to overwhelm the world's supply of traditional follow-up telescopes. As new, comprehensive time-domain surveys become operational and wide-field multi-messenger observatories come on-line, that problem will become more acute. The goal of this workshop was to foster discussion about how autonomous robotic telescopes and small-aperture conventional telescopes can be employed in the most effective ways to help deal with the coming deluge of scientifically interesting follow-up opportunities. Discussion topics included the role of event brokers, automated event triage, the establishment of cooperative global telescope networks, and real-time coordination of observations at geographically diverse sites. It therefore included brief overviews of the current diverse landscape of telescopes and their interactions, and also considered planned and potential new facilities and operating models.
Free-decay time-domain modal identification for large space structures
NASA Technical Reports Server (NTRS)
Kim, Hyoung M.; Vanhorn, David A.; Doiron, Harold H.
1992-01-01
Concept definition studies for the Modal Identification Experiment (MIE), a proposed space flight experiment for the Space Station Freedom (SSF), have demonstrated advantages and compatibility of free-decay time-domain modal identification techniques with the on-orbit operational constraints of large space structures. Since practical experience with modal identification using actual free-decay responses of large space structures is very limited, several numerical and test data reduction studies were conducted. Major issues and solutions were addressed, including closely-spaced modes, wide frequency range of interest, data acquisition errors, sampling delay, excitation limitations, nonlinearities, and unknown disturbances during free-decay data acquisition. The data processing strategies developed in these studies were applied to numerical simulations of the MIE, test data from a deployable truss, and launch vehicle flight data. Results of these studies indicate free-decay time-domain modal identification methods can provide accurate modal parameters necessary to characterize the structural dynamics of large space structures.
DEIMOS Spectroscopy of GALEX Time Domain Survey Tidal Disruption Event Candidates
NASA Astrophysics Data System (ADS)
Gezari, Suvi
2011-08-01
We propose for Keck II DEIMOS follow-up spectroscopy of extreme UV-flaring galaxies from the GALEX Time Domain Survey that are candidates for flares from the tidal disruption of stars around dormant supermassive black holes. GALEX has conducted an innovative dedicated survey in the time domain in the NUV, over a wide field of view (42 deg^2) with a cadence of 2 days to discover and characterize a wide range of UV variable and transient sources, including variable stars, quasars, active galactic nuclei, and Type II SNe. Here we propose for follow-up low-resolution spectroscopy of galaxies which demonstrated large amplitude UV flares to investigate their nature, and identify candidate tidal disruption events.
Analysis of wave packet motion in frequency and time domain: oxazine 1.
Braun, Markus; Sobotta, Constanze; Dürr, Regina; Pulvermacher, Horst; Malkmus, Stephan
2006-08-17
Wave packet motion in the laser dye oxazine 1 in methanol is investigated by spectrally resolved transient absorption spectroscopy. The spectral range of 600-690 nm was accessible by amplified broadband probe pulses covering the overlap region of ground-state bleach and stimulated emission signal. The influence of vibrational wave packets on the optical signal is analyzed in the frequency domain and the time domain. For the analysis in the frequency domain an algorithm is presented that accounts for interference effects of neighbored vibrational modes. By this method amplitude, phase and decay time of vibrational modes are retrieved as a function of probe wavelength and distortions due to neighbored modes are reduced. The analysis of the data in the time domain yields complementary information on the intensity, central wavelength, and spectral width of the optical bleach spectrum due to wave packet motion.
Time-domain measurement of optical transport in silicon micro-ring resonators.
Pernice, Wolfram H P; Li, Mo; Tang, Hong X
2010-08-16
We perform time-domain measurements of optical transport dynamics in silicon nano-photonic devices. Using pulsed optical excitation the thermal and carrier induced optical nonlinearities of micro-ring resonators are investigated, allowing for identification of their individual contributions. Under pulsed excitation build-up of free carriers and heat in the waveguides leads to a beating oscillation of the cavity resonance frequency. When employing a burst of pulse trains shorter than the carrier life-time, the slower heating effect can be separated from the faster carrier effect. Our scheme provides a convenient way to thermally stabilize optical resonators for high-power time-domain applications and nonlinear optical conversion.
Time-domain representation of frequency-dependent foundation impedance functions
Safak, E.
2006-01-01
Foundation impedance functions provide a simple means to account for soil-structure interaction (SSI) when studying seismic response of structures. Impedance functions represent the dynamic stiffness of the soil media surrounding the foundation. The fact that impedance functions are frequency dependent makes it difficult to incorporate SSI in standard time-history analysis software. This paper introduces a simple method to convert frequency-dependent impedance functions into time-domain filters. The method is based on the least-squares approximation of impedance functions by ratios of two complex polynomials. Such ratios are equivalent, in the time-domain, to discrete-time recursive filters, which are simple finite-difference equations giving the relationship between foundation forces and displacements. These filters can easily be incorporated into standard time-history analysis programs. Three examples are presented to show the applications of the method.
Adaptive time-domain filtering for real-time spectral discrimination in a Michelson interferometer.
Bhalotra, Sameer R; Kung, Helen L; Jiao, Yang; Miller, David A B
2002-07-01
We present a method of spectral discrimination that employs time-domain processing instead of the typical frequency-domain analysis and implement the method in a Michelson interferometer with a nonlinear mirror scan. The technique yields one analog output value per scan instead of a complete interferogram by directly filtering a measured scan with a reference function in the time domain. Such a procedure drastically reduces data-processing requirements downstream. Additionally, using prerecorded interferograms as references eliminates the need to compensate for scan nonlinearities, which broadens the field of usable components for implementation in miniaturized sensing systems. With our efficient use of known spectral signatures, we demonstrate real-time discrimination of 633- and 663-nm laser sources with a mirror scan length of 1 microm , compared with the Rayleigh criterion of 7 microm.
Applied Time Domain Stability Margin Assessment for Nonlinear Time-Varying Systems
NASA Technical Reports Server (NTRS)
Kiefer, J. M.; Johnson, M. D.; Wall, J. H.; Dominguez, A.
2016-01-01
The baseline stability margins for NASA's Space Launch System (SLS) launch vehicle were generated via the classical approach of linearizing the system equations of motion and determining the gain and phase margins from the resulting frequency domain model. To improve the fidelity of the classical methods, the linear frequency domain approach can be extended by replacing static, memoryless nonlinearities with describing functions. This technique, however, does not address the time varying nature of the dynamics of a launch vehicle in flight. An alternative technique for the evaluation of the stability of the nonlinear launch vehicle dynamics along its trajectory is to incrementally adjust the gain and/or time delay in the time domain simulation until the system exhibits unstable behavior. This technique has the added benefit of providing a direct comparison between the time domain and frequency domain tools in support of simulation validation. This technique was implemented by using the Stability Aerospace Vehicle Analysis Tool (SAVANT) computer simulation to evaluate the stability of the SLS system with the Adaptive Augmenting Control (AAC) active and inactive along its ascent trajectory. The gains for which the vehicle maintains apparent time-domain stability defines the gain margins, and the time delay similarly defines the phase margin. This method of extracting the control stability margins from the time-domain simulation is relatively straightforward and the resultant margins can be compared to the linearized system results. The sections herein describe the techniques employed to extract the time-domain margins, compare the results between these nonlinear and the linear methods, and provide explanations for observed discrepancies. The SLS ascent trajectory was simulated with SAVANT and the classical linear stability margins were evaluated at one second intervals. The linear analysis was performed with the AAC algorithm disabled to attain baseline stability
Gigahertz time-domain spectroscopy and imaging for non-destructive materials research and evaluation
Bulgarevich, Dmitry S.; Shiwa, Mitsuharu; Furuya, Takashi; Tani, Masahiko
2016-01-01
By using optical sampling with repetition frequency modulation of pump/probe laser pulses on photoconductive emitter/detector antennas, the high-speed time/frequency domain gigahertz imaging is reported due to the absence of opto-mechanical delay line in this optical scheme. The clear contrast for a 3-cm wide metal plate, which was placed behind a 5-cm thick concrete block, was observed with a 1 × 1 mm image pixilation. On average, it took only ~0.75 s per pixel/waveform acquisition/assignment with a 675 ps time-domain window. This could become a valuable non-destructive evaluation technique in gigahertz spectral range with all benefits of time-domain spectroscopy. PMID:27302877
Modeling XV-15 tilt-rotor aircraft dynamics by frequency and time-domain identification techniques
NASA Technical Reports Server (NTRS)
Tischler, Mark B.; Kaletka, Juergen
1987-01-01
Models of the open-loop hover dynamics of the XV-15 Tilt-Rotor Aircraft are extracted from flight data using two approaches: frequency domain and time-domain identification. Both approaches are reviewed and the identification results are presented and compared in detail. The extracted models are compared favorably, with the differences associated mostly with the inherent weighing of each technique. Step responses are used to show that the predictive capability of the models from both techniques is excellent. Based on the results of this study, the relative strengths and weaknesses of the frequency and time-domain techniques are summarized and a proposal for a coordinated parameter identification approach is presented.
Modeling XV-15 tilt-rotor aircraft dynamics by frequency and time-domain identification techniques
NASA Technical Reports Server (NTRS)
Tischler, Mark B.; Kaletka, Juergen
1986-01-01
Models of the open-loop hover dynamics of the XV-15 Tilt-Rotor Aircraft are extracted from flight data using two approaches: frequency-domain and time-domain identification. Both approaches are reviewed and the identification results are presented and compared in detail. The extracted models compare favorable, with the differences associated mostly with the inherent weighting of each technique. Step responses are used to show that the predictive capability of the models from both techniques is excellent. Based on the results of this study, the relative strengths and weaknesses of the frequency- and time-domain techniques are summarized, and a proposal for a coordinated parameter identification approach is presented.
Time-domain theory of gyrotron traveling wave amplifiers operating at grazing incidence
Ginzburg, N. S.; Sergeev, A. S.; Zotova, I. V.; Zheleznov, I. V.
2015-01-15
Time-domain theory of the gyrotron traveling wave tube (gyro-TWT) operating at grazing incidence has been developed. The theory is based on a description of wave propagation by a parabolic equation. The results of the simulations are compared with experimental results of the observation of subnanosecond pulse amplification in a gyro-TWT consisting of three gain sections separated by severs. The theory developed can also be used successfully for a description of amplification of monochromatic signals.
Time domain analysis of a gyrotron traveling wave amplifier with misaligned electron beam
Wang, Qiushi Peng, Shuyuan; Luo, Jirun
2014-08-15
This article develops a time-domain theory to study the beam-wave interaction in gyrotron traveling wave amplifier (gyro-TWA) with a misaligned electron beam. The effects of beam misalignment on the TE{sub 01} mode gyro-TWA operating at the fundamental are discussed. Numerical results show that the effect of misalignment is less obvious when the input power is larger, and the influences of misalignment on the stable gain and the stable time are basically opposite.
NASA Technical Reports Server (NTRS)
Beggs, John H.; Luebbers, Raymond J.; Kunz, Karl S.; Yee, Kane S.
1991-01-01
Surface impedance boundary conditions are employed to reduce the solution volume during the analysis of scattering from lossy dielectric objects. In a finite difference solution, they also can be utilized to avoid using small cells, made necessary by shorter wavelengths in conducting media, throughout the solution volume. A 1-D implementation for a surface impedance boundary condition for good conductors in the Finite Difference Time Domain (FDTD) technique.
Accurate finite-difference time-domain simulation of anisotropic media by subpixel smoothing.
Oskooi, Ardavan F; Kottke, Chris; Johnson, Steven G
2009-09-15
Finite-difference time-domain methods suffer from reduced accuracy when discretizing discontinuous materials. We previously showed that accuracy can be significantly improved by using subpixel smoothing of the isotropic dielectric function, but only if the smoothing scheme is properly designed. Using recent developments in perturbation theory that were applied to spectral methods, we extend this idea to anisotropic media and demonstrate that the generalized smoothing consistently reduces the errors and even attains second-order convergence with resolution.
Man-portable Vector Time Domain EMI Sensor and Discrimination Processing
2012-04-16
which designed and manufactured the laser system is sparse. After this successful calibration procedure , the positioning information from the laser system...not be construed as an official U.S. Government position, policy or decision, unless so designated by other documentation. SERDP project MR-1443...entitled “Man-portable Vector Time Domain EMI Sensor and Discrimination Processing” is complete. This report contains the final design , engineering
Comparison between pulsed terahertz time-domain imaging and continuous wave terahertz imaging
NASA Astrophysics Data System (ADS)
Karpowicz, Nicholas; Zhong, Hua; Xu, Jingzhou; Lin, Kuang-I.; Hwang, Jenn-Shyong; Zhang, X.-C.
2005-07-01
We report an evaluation of pulsed terahertz (THz) time-domain measurement and continuous wave (CW) terahertz measurement for non-destructive testing applications. The strengths and limitations of the modalities are explored via the example of the detection of defects in space shuttle foam insulation. It is decided that CW imaging allows for a more compact and simple system, while pulsed measurements yield a broader range of information.
NASA Technical Reports Server (NTRS)
Vaicaitis, R.
1986-01-01
The present paper reviews the basic concepts of nonlinear response of panels to surface flow and acoustic pressures, simulation of random processes, time domain solutions and the Monte Carlo Method. Applications of this procedure to the orbit-on-demand space vehicles, acoustic fatigue and composite materials are discussed. Numerical examples are included for a variety of nonlinear problems to illustrate the applicability of this method.
DANCING WITH THE ELECTRONS: TIME-DOMAIN AND CW IN VIVO EPR IMAGING
Subramanian, Sankaran; Krishna, Murali C.
2009-01-01
The progress in the development of imaging the distribution of unpaired electrons in living systems and the functional and the potential diagnostic dimensions of such an imaging process, using Electron Paramagnetic Resonance Imaging (EPRI), is traced from its origins with emphasis on our own work. The importance of EPR imaging stems from the fact that many paramagnetic probes show oxygen dependent spectral broadening. Assessment of in vivo oxygen concentration is an important factor in radiation oncology in treatment-planning and monitoring treatment-outcome. The emergence of narrow-line trairylmethyl based, bio-compatible spin probes has enabled the development of radiofrequency time-domain EPRI. Spectral information in time-domain EPRI can be achieved by generating a time sequence of T2* or T2 weighted images. Progress in CW imaging has led to the use of rotating gradients, more recently rapid scan with direct detection, and a combination of all the three. Very low field MRI employing Dynamic Nuclear polarization (Overhauser effect) is also employed for monitoring tumor hypoxia, and re-oxygenation in vivo. We have also been working on the co-registration of MRI and time domain EPRI on mouse tumor models at 300 MHz using a specially designed resonator assembly. The mapping of the unpaired electron distribution and unraveling the spectral characteristics by using magnetic resonance in presence of stationary and rotating gradients in indeed ‘dancing with the (unpaired) electrons’, metaphorically speaking. PMID:22025900
Time-Domain Simulation of Along-Track Interferometric SAR for Moving Ocean Surfaces.
Yoshida, Takero; Rheem, Chang-Kyu
2015-06-10
A time-domain simulation of along-track interferometric synthetic aperture radar (AT-InSAR) has been developed to support ocean observations. The simulation is in the time domain and based on Bragg scattering to be applicable for moving ocean surfaces. The time-domain simulation is suitable for examining velocities of moving objects. The simulation obtains the time series of microwave backscattering as raw signals for movements of ocean surfaces. In terms of realizing Bragg scattering, the computational grid elements for generating the numerical ocean surface are set to be smaller than the wavelength of the Bragg resonant wave. In this paper, the simulation was conducted for a Bragg resonant wave and irregular waves with currents. As a result, the phases of the received signals from two antennas differ due to the movement of the numerical ocean surfaces. The phase differences shifted by currents were in good agreement with the theoretical values. Therefore, the adaptability of the simulation to observe velocities of ocean surfaces with AT-InSAR was confirmed.
Optimal sensor placement for time-domain identification using a wavelet-based genetic algorithm
NASA Astrophysics Data System (ADS)
Mahdavi, Seyed Hossein; Razak, Hashim Abdul
2016-06-01
This paper presents a wavelet-based genetic algorithm strategy for optimal sensor placement (OSP) effective for time-domain structural identification. Initially, the GA-based fitness evaluation is significantly improved by using adaptive wavelet functions. Later, a multi-species decimal GA coding system is modified to be suitable for an efficient search around the local optima. In this regard, a local operation of mutation is introduced in addition with regeneration and reintroduction operators. It is concluded that different characteristics of applied force influence the features of structural responses, and therefore the accuracy of time-domain structural identification is directly affected. Thus, the reliable OSP strategy prior to the time-domain identification will be achieved by those methods dealing with minimizing the distance of simulated responses for the entire system and condensed system considering the force effects. The numerical and experimental verification on the effectiveness of the proposed strategy demonstrates the considerably high computational performance of the proposed OSP strategy, in terms of computational cost and the accuracy of identification. It is deduced that the robustness of the proposed OSP algorithm lies in the precise and fast fitness evaluation at larger sampling rates which result in the optimum evaluation of the GA-based exploration and exploitation phases towards the global optimum solution.
NASA Astrophysics Data System (ADS)
Zhou, T.; Ruppe, J.; Stanfield, P.; Nees, J.; Wilcox, R.; Galvanauskas, A.
2015-10-01
This paper describes novel time-domain multiplexing techniques that use various resonant cavity configurations for increasing pulse energy extraction per each parallel amplification channel of a coherently combined array. Two different techniques are presented: a so-called N2 coherent array combining technique, applicable to a periodic pulse train, and a coherent pulse stacking amplification (CPSA) technique, applicable to a pulse burst. The first technique is a coherent combining technique, which achieves simultaneous beam combining and time-domain pulse multiplexing/down-counting using traveling-wave Fabry-Perot type resonators. The second technique is purely a time-domain pulse multiplexing technique, used with either a single amplifier or an amplifier array, which uses traveling-wave Gires-Tourmois type resonators. The importance of these techniques is that they can enable stacking of very large number of pulses, thus increasing effective amplified-pulse duration potentially by 102 to 103 times, and reducing fiber array size by the corresponding factor. This could lead to very compact coherently combined arrays even for generating very high pulse energies in the range of 1 to 100 J.
Time Domains of the Hypoxic Ventilatory Response and Their Molecular Basis
Pamenter, Matthew E.; Powell, Frank L.
2016-01-01
Ventilatory responses to hypoxia vary widely depending on the pattern and length of hypoxic exposure. Acute, prolonged, or intermittent hypoxic episodes can increase or decrease breathing for seconds to years, both during the hypoxic stimulus, and also after its removal. These myriad effects are the result of a complicated web of molecular interactions that underlie plasticity in the respiratory control reflex circuits and ultimately control the physiology of breathing in hypoxia. Since the time domains of the physiological hypoxic ventilatory response (HVR) were identified, considerable research effort has gone toward elucidating the underlying molecular mechanisms that mediate these varied responses. This research has begun to describe complicated and plastic interactions in the relay circuits between the peripheral chemoreceptors and the ventilatory control circuits within the central nervous system. Intriguingly, many of these molecular pathways seem to share key components between the different time domains, suggesting that varied physiological HVRs are the result of specific modifications to overlapping pathways. This review highlights what has been discovered regarding the cell and molecular level control of the time domains of the HVR, and highlights key areas where further research is required. Understanding the molecular control of ventilation in hypoxia has important implications for basic physiology and is emerging as an important component of several clinical fields. PMID:27347896
A Time-Domain CMOS Oscillator-Based Thermostat with Digital Set-Point Programming
Chen, Chun-Chi; Lin, Shih-Hao
2013-01-01
This paper presents a time-domain CMOS oscillator-based thermostat with digital set-point programming [without a digital-to-analog converter (DAC) or external resistor] to achieve on-chip thermal management of modern VLSI systems. A time-domain delay-line-based thermostat with multiplexers (MUXs) was used to substantially reduce the power consumption and chip size, and can benefit from the performance enhancement due to the scaling down of fabrication processes. For further cost reduction and accuracy enhancement, this paper proposes a thermostat using two oscillators that are suitable for time-domain curvature compensation instead of longer linear delay lines. The final time comparison was achieved using a time comparator with a built-in custom hysteresis to generate the corresponding temperature alarm and control. The chip size of the circuit was reduced to 0.12 mm2 in a 0.35-μm TSMC CMOS process. The thermostat operates from 0 to 90 °C, and achieved a fine resolution better than 0.05 °C and an improved inaccuracy of ± 0.6 °C after two-point calibration for eight packaged chips. The power consumption was 30 μW at a sample rate of 10 samples/s. PMID:23385403
Time-domain characterization of the acoustic damping of a perforated liner with bias flow.
Zhong, Zhiyuan; Zhao, Dan
2012-07-01
Combustion instabilities are caused by the interaction of unsteady heat releases and acoustic waves. To mitigate combustion instabilities, perforated liners, typically subjected to a low Mach number bias flow (a cooling flow through perforated holes), are fitted along the bounding walls of a combustor. They dissipate the acoustic waves by generating vorticity at the rims of perforated apertures. To investigate the absorption of plane waves by a perforated liner with bias flow, a time-domain numerical model of a cylindrical lined duct is developed. The liners' damping mechanism is characterized by using a time-domain "compliance." The development of such time-domain compliance is based on simplified or unsimplified Rayleigh conductivity. Numerical simulations of two different configurations of lined duct systems are performed by combining a 1D acoustic wave model with the compliance model. Comparison is then made between the results from the present models, and those from the experiment and the frequency-domain model of previous investigation [Eldredge and Dowling, J. Fluid Mech. 485, 307-335(2003)]. Good agreement is observed. This confirms that the present model can be used to simulate the propagation and dissipation of acoustic plane waves in a lined duct in real-time.
Ultra-broadband THz time-domain spectroscopy of common polymers using THz air photonics.
D'Angelo, Francesco; Mics, Zoltán; Bonn, Mischa; Turchinovich, Dmitry
2014-05-19
Terahertz-range dielectric properties of the common polymers low-density polyethylene (LDPE), cyclic olefin/ethylene copolymer (TOPAS®), polyamide-6 (PA6), and polytetrafluoroethylene (PTFE or Teflon®) are characterized in the ultra-broadband frequency window 2-15 THz, using a THz time-domain spectrometer employing air-photonics for the generation and detection of single-cycle sub-50 fs THz transients. The time domain measurements provide direct access to both the absorption and refractive index spectra. The polymers LDPE and TOPAS® demonstrate negligible absorption and spectrally-flat refractive index across the entire spectroscopy window, revealing the high potential of these polymers for applications in THz photonics such as ultra-broadband polymer-based dielectric mirrors, waveguides, and fibers. Resonant high-frequency polar vibrational modes are observed and assigned in polymers PA6 and PTFE, and their dielectric functions in the complete frequency window 2-15 THz are theoretically reproduced. Our results demonstrate the potential of ultra-broadband air-photonics-based THz time domain spectroscopy as a valuable analytic tool for materials science.
A time-domain CMOS oscillator-based thermostat with digital set-point programming.
Chen, Chun-Chi; Lin, Shih-Hao
2013-01-29
This paper presents a time-domain CMOS oscillator-based thermostat with digital set-point programming [without a digital-to-analog converter (DAC) or external resistor] to achieve on-chip thermal management of modern VLSI systems. A time-domain delay-line-based thermostat with multiplexers (MUXs) was used to substantially reduce the power consumption and chip size, and can benefit from the performance enhancement due to the scaling down of fabrication processes. For further cost reduction and accuracy enhancement, this paper proposes a thermostat using two oscillators that are suitable for time-domain curvature compensation instead of longer linear delay lines. The final time comparison was achieved using a time comparator with a built-in custom hysteresis to generate the corresponding temperature alarm and control. The chip size of the circuit was reduced to 0.12 mm2 in a 0.35-mm TSMC CMOS process. The thermostat operates from 0 to 90 °C, and achieved a fine resolution better than 0.05 °C and an improved inaccuracy of ± 0.6 °C after two-point calibration for eight packaged chips. The power consumption was 30 µW at a sample rate of 10 samples/s.
Advanced Electromagnetic Methods for Aerospace Vehicles
NASA Technical Reports Server (NTRS)
Balanis, Constantine A.; Polycarpou, Anastasis; Birtcher, Craig R.; Georgakopoulos, Stavros; Han, Dong-Ho; Ballas, Gerasimos
1999-01-01
The imminent destructive threats of Lightning on helicopters and other airborne systems has always been a topic of great interest to this research grant. Previously, the lightning induced currents on the surface of the fuselage and its interior were predicted using the finite-difference time-domain (FDTD) method as well as the NEC code. The limitations of both methods, as applied to lightning, were identified and extensively discussed in the last meeting. After a thorough investigation of the capabilities of the FDTD, it was decided to incorporate into the numerical method a subcell model to accurately represent current diffusion through conducting materials of high conductivity and finite thickness. Because of the complexity of the model, its validity will be first tested for a one-dimensional FDTD problem. Although results are not available yet, the theory and formulation of the subcell model are presented and discussed here to a certain degree. Besides lightning induced currents in the interior of an aircraft, penetration of electromagnetic fields through apertures (e.g., windows and cracks) could also be devastating for the navigation equipment, electronics, and communications systems in general. The main focus of this study is understanding and quantifying field penetration through apertures. The simulation is done using the FDTD method and the predictions are compared with measurements and moment method solutions obtained from the NASA Langley Research Center. Cavity-backed slot (CBS) antennas or slot antennas in general have many applications in aircraft-satellite type of communications. These can be flushmounted on the surface of the fuselage and, therefore, they retain the aerodynamic shape of the aircraft. In the past, input impedance and radiation patterns of CBS antennas were computed using a hybrid FEM/MoM code. The analysis is now extended to coupling between two identical slot antennas mounted on the same structure. The predictions are performed
NASA Technical Reports Server (NTRS)
Lansing, Faiza S.; Rascoe, Daniel L.
1993-01-01
This paper presents a modified Finite-Difference Time-Domain (FDTD) technique using a generalized conformed orthogonal grid. The use of the Conformed Orthogonal Grid, Finite Difference Time Domain (GFDTD) enables the designer to match all the circuit dimensions, hence eliminating a major source o error in the analysis.
NASA Astrophysics Data System (ADS)
Fukunaga, Kaori; Ikari, Tomofumi; Iwai, Kikuko
2016-02-01
The terahertz pulsed time-domain imaging technique and near-infrared observation were applied to investigate an oil painting on canvas by Pablo Picasso. The multilayer structure is clearly observed in cross-sectional image by terahertz pulsed time-domain imaging, and particular Cubism style lines were revealed under newly painted area by near-infrared image.
Computational electronics and electromagnetics
Shang, C. C.
1997-02-01
The Computational Electronics and Electromagnetics thrust area at Lawrence Livermore National Laboratory serves as the focal point for engineering R&D activities for developing computer-based design, analysis, and tools for theory. Key representative applications include design of particle accelerator cells and beamline components; engineering analysis and design of high-power components, photonics, and optoelectronics circuit design; EMI susceptibility analysis; and antenna synthesis. The FY-96 technology-base effort focused code development on (1) accelerator design codes; (2) 3-D massively parallel, object-oriented time-domain EM codes; (3) material models; (4) coupling and application of engineering tools for analysis and design of high-power components; (5) 3-D spectral-domain CEM tools; and (6) enhancement of laser drilling codes. Joint efforts with the Power Conversion Technologies thrust area include development of antenna systems for compact, high-performance radar, in addition to novel, compact Marx generators. 18 refs., 25 figs., 1 tab.
Time Domain Tool Validation Using ARES I-X Flight Data
NASA Technical Reports Server (NTRS)
Hough, Steven; Compton, James; Hannan, Mike; Brandon, Jay
2011-01-01
The ARES I-X vehicle was launched from NASA's Kennedy Space Center (KSC) on October 28, 2009 at approximately 11:30 EDT. ARES I-X was the first test flight for NASA s ARES I launch vehicle, and it was the first non-Shuttle launch vehicle designed and flown by NASA since Saturn. The ARES I-X had a 4-segment solid rocket booster (SRB) first stage and a dummy upper stage (US) to emulate the properties of the ARES I US. During ARES I-X pre-flight modeling and analysis, six (6) independent time domain simulation tools were developed and cross validated. Each tool represents an independent implementation of a common set of models and parameters in a different simulation framework and architecture. Post flight data and reconstructed models provide the means to validate a subset of the simulations against actual flight data and to assess the accuracy of pre-flight dispersion analysis. Post flight data consists of telemetered Operational Flight Instrumentation (OFI) data primarily focused on flight computer outputs and sensor measurements as well as Best Estimated Trajectory (BET) data that estimates vehicle state information from all available measurement sources. While pre-flight models were found to provide a reasonable prediction of the vehicle flight, reconstructed models were generated to better represent and simulate the ARES I-X flight. Post flight reconstructed models include: SRB propulsion model, thrust vector bias models, mass properties, base aerodynamics, and Meteorological Estimated Trajectory (wind and atmospheric data). The result of the effort is a set of independently developed, high fidelity, time-domain simulation tools that have been cross validated and validated against flight data. This paper presents the process and results of high fidelity aerospace modeling, simulation, analysis and tool validation in the time domain.
Finite difference time domain analysis of microwave ferrite devices and mobile antenna systems
NASA Astrophysics Data System (ADS)
Yildirim, Bahadir Suleyman
This dissertation presents analysis and design of shielded mobile antenna systems and microwave ferrite devices using a finite-difference time-domain method. Novel shielded antenna structures suitable for cellular communications have been analyzed and designed with emphasize on reducing excessive radiated energy absorbed in user's head and hand, while keeping the antenna performance at its peak in the presence of user. These novel antennas include a magnetically shielded antenna, a dual-resonance shielded antenna and, a shorted and truncated microstrip antenna. The effect of magnetic coating on the performance of a shielded monopole antenna is studied extensively. A parametric study is performed to analyze the dual-resonance phenomenon observed in the dual-resonance shielded antenna, optimize the antenna design within the cellular communications band, and improve the antenna performance. Input impedance, near and far fields of the dual-resonance shielded antenna are calculated using the finite-difference time-domain method. Experimental validation is also presented. In addition, performance of a shorted and truncated microstrip antenna has been investigated over a wide range of substrate parameters and dimensions. Objectives of the research work also include development of a finite-difference time-domain technique to accurately model magnetically anisotropic media, including the effect of non-uniform magnetization within the finite-size ferrite material due to demagnetizing fields. A slow wave thin film isolator and a stripline disc junction circulator are analyzed. An extensive parametric study calculates wide-band frequency-dependent parameters of these devices for various device dimensions and material parameters. Finally, a ferrite-filled stripline configuration is analyzed to study the non- linear behaviour of ferrite by introducing a modified damping factor.
An optimization approach to multi-dimensional time domain acoustic inverse problems.
Gustafsson, M; He, S
2000-10-01
An optimization approach to a multi-dimensional acoustic inverse problem in the time domain is considered. The density and/or the sound speed are reconstructed by minimizing an objective functional. By introducing dual functions and using the Gauss divergence theorem, the gradient of the objective functional is found as an explicit expression. The parameters are then reconstructed by an iterative algorithm (the conjugate gradient method). The reconstruction algorithm is tested with noisy data, and these tests indicate that the algorithm is stable and robust. The computation time for the reconstruction is greatly improved when the analytic gradient is used.
Contact-free fault location and imaging with on-chip terahertz time-domain reflectometry.
Nagel, Michael; Michalski, Alexander; Kurz, Heinrich
2011-06-20
We demonstrate in a first experimental study the application of novel micro-machined optoelectronic probes for a time-domain reflectometry-based localization of discontinuities and faults in electronic structures at unprecedented resolution and accuracy (± 0.55 µm). Thanks to the THz-range bandwidth of our optoelectronic system--including the active probes used for pulse injection and detection--the spatial resolution and precision of high-end all-electronic detection systems is surpassed by more than one order of magnitude. The new analytic technology holds great promise for rapid and precise fault detection and location in advanced (3D) integrated semiconductor chips and packages.
Polarization-current-based, finite-difference time-domain, near-to-far-field transformation.
Zeng, Yong; Moloney, Jerome V
2009-05-15
A near-to-far-field transformation algorithm for three-dimensional finite-difference time-domain is presented in this Letter. This approach is based directly on the polarization current of the scatterer, not the scattered near fields. It therefore eliminates the numerical errors originating from the spatial offset of the E and H fields, inherent in the standard near-to-far-field transformation. The proposed method is validated via direct comparisons with the analytical Lorentz-Mie solutions of plane waves scattered by large dielectric and metallic spheres with strong forward-scattering lobes.
The design of circuit for THz time domain spectroscopy system based on asynchronous optical sampling
NASA Astrophysics Data System (ADS)
Wang, Ruike; Zhang, Mile; Li, Yihan; He, Jingsuo; Zhang, Cunlin; Cui, Hailin
2016-11-01
Terahertz time domain spectroscopy system (THz-TDS) is the most commonly means of measuring terahertz time-domain spectroscopy. The time delay between the pump and probe laser is an important technology to realize THz time domain spectrum measurement. The translation platform with two mirrors and the mechanical structure is the popular means to adjust the optical path difference between the pump and probe laser to get the time delay of femtosecond pulse. Because of the limit of the mechanical structure and the phase-locked amplifier, this technique can't scan spectrum fast. In order to obtain high quality signal, a long time will be taken to scan spectrum. So a more rapid and convenient time delay technology is required to Instead of the machine translation platform and accomplish the Rapid spectral measurement. Asynchronous optical sampling technique is a way to get the time delay by producing a very small frequency difference between the repetition frequency of two femtosecond lasers. The scanner time will be reduced, because of there is no waste of time, due to mechanical inertia, not only by using the asynchronous optical sampling method to replace the mechanical structure without the influence of vibration. It will greatly increase the degree of integration by using the fiber femtosecond laser and highly integrated circuit to realize optical asynchronous sampling. To solve the problem above, a terahertz time-domain spectroscopy system based on asynchronous sampling is designed in this thesis. The system is based of two femtosecond laser whose repetition frequency is 100MHz.In order to realize asynchronous sampling, the control circuit of the two lasers is the most important. This thesis focuses on the researching, designing and experiment of this circuit. Firstly, the circuit is designed overall. Then the selection of the key device and the designing of the circuit principle is done by myself. Secondly, the test of the circuit to phase locked the master and
Time-domain model of quantum-dot semiconductor optical amplifiers for wideband optical signals.
Puris, D; Schmidt-Langhorst, C; Lüdge, K; Majer, N; Schöll, E; Petermann, K
2012-11-19
We present a novel theoretical time-domain model for a quantum dot semiconductor optical amplifier, that allows to simulate subpicosecond pulse propagation including power-based and phase-based effects. Static results including amplified spontaneous emission spectra, continuous wave amplification, and four-wave mixing experiments in addition to dynamic pump-probe simulations are presented for different injection currents. The model uses digital filters to describe the frequency dependent gain and microscopically calculated carrier-carrier scattering rates for the interband carrier dynamics. It can be used to calculate the propagation of multiple signals with different wavelengths or one wideband signal with high bitrate.
Stoik, Christopher D; Bohn, Matthew J; Blackshire, James L
2008-10-13
Terahertz time domain spectroscopy (TDS) was assessed as a nondestructive evaluation technique for aircraft composites. Damage to glass fiber was studied including voids, delaminations, mechanical damage, and heat damage. Measurement of the material properties on samples with localized heat damage showed that burning did not change the refractive index or absorption coefficient noticeably; however, material blistering was detected. Voids were located by TDS transmissive imaging using amplitude and phase techniques. The depth of delaminations was measured via the timing of Fabry-Perot reflections after the main pulse. Evidence of bending stress damage and simulated hidden cracks was also detected with terahertz imaging.
NASA Astrophysics Data System (ADS)
Adhikari, Achyut; Dev, Kapil; Asundi, Anand
2016-11-01
Wire grid polarizers (WGP), are sub-wavelength gratings with applications in display projection system due to their compact size, wide field of view and long-term stability. Measurement and testing of these structures are important to optimize their use. This is done by first measuring the Mueller matrix of the WGP using a Mueller matrix polarimeter. Next the finite difference time domain (FDTD) method is used to simulate a similar Mueller matrix thus providing the period and step height of the WGP. This approach may lead to more generic determination of sub-wavelength structures including diffractive optical structures.
NASA Technical Reports Server (NTRS)
Beggs, John H.; Luebbers, Raymond J.; Kunz, Karl S.; Yee, Kane S.
1991-01-01
Surface impedance boundary conditions are used to reduce the solution volume during the analysis of scattering from lossy dielectric objects. In a finite difference solution, they also can be used to avoid using small cells, made necessary by shorter wavelengths in conducting media, throughout the solution volume. A one dimensional implementation is presented for a surface impedance boundary condition for good conductors in the Finite Difference Time Domain (FDTD) technique. In order to illustrate the FDTD surface impedance boundary condition, a planar air-lossy dielectric interface is considered.
Time domain modal identification/estimation of the mini-mast testbed
NASA Technical Reports Server (NTRS)
Roemer, Michael J.; Mook, D. Joseph
1991-01-01
The Mini-Mast is a 20 meter long 3-dimensional, deployable/retractable truss structure designed to imitate future trusses in space. Presented here are results from a robust (with respect to measurement noise sensitivity), time domain, modal identification technique for identifying the modal properties of the Mini-Mast structure even in the face of noisy environments. Three testing/analysis procedures are considered: sinusoidal excitation near resonant frequencies of the Mini-Mast, frequency response function averaging of several modal tests, and random input excitation with a free response period.
Studies in astronomical time series analysis. I - Modeling random processes in the time domain
NASA Technical Reports Server (NTRS)
Scargle, J. D.
1981-01-01
Several random process models in the time domain are defined and discussed. Attention is given to the moving average model, the autoregressive model, and relationships between and combinations of these models. Consideration is then given to methods for investigating pulse structure, procedures of model construction, computational methods, and numerical experiments. A FORTRAN algorithm of time series analysis has been developed which is relatively stable numerically. Results of test cases are given to study the effect of adding noise and of different distributions for the pulse amplitudes. A preliminary analysis of the light curve of the quasar 3C 272 is considered as an example.
An efficient stabilized boundary element formulation for 2D time-domain acoustics and elastodynamics
NASA Astrophysics Data System (ADS)
Soares, D.; Mansur, W. J.
2007-07-01
The present paper describes a procedure that improves efficiency, stability and reduces artificial energy dissipation of the standard time-domain direct boundary element method (BEM) for acoustics and elastodynamics. Basically, the developed procedure modifies the boundary element convolution-related vector, being very easy to implement into existing codes. A stabilization parameter is introduced into the recent-in-time convolution operations and the operations related to the distant-in-time convolution contributions are approximated by matrix interpolations. As it is shown in the numerical examples presented at the end of the text, the proposed formulation substantially reduces the BEM computational cost, as well as its numerical instabilities.
Quantitative analysis of the mixtures of illicit drugs using terahertz time-domain spectroscopy
NASA Astrophysics Data System (ADS)
Jiang, Dejun; Zhao, Shusen; Shen, Jingling
2008-03-01
A method was proposed to quantitatively inspect the mixtures of illicit drugs with terahertz time-domain spectroscopy technique. The mass percentages of all components in a mixture can be obtained by linear regression analysis, on the assumption that all components in the mixture and their absorption features be known. For illicit drugs were scarce and expensive, firstly we used common chemicals, Benzophenone, Anthraquinone, Pyridoxine hydrochloride and L-Ascorbic acid in the experiment. Then illicit drugs and a common adulterant, methamphetamine and flour, were selected for our experiment. Experimental results were in significant agreement with actual content, which suggested that it could be an effective method for quantitative identification of illicit drugs.
Nonlinear time-domain cochlear model for transient stimulation and human otoacoustic emission
Verhulst, Sarah; Dau, Torsten; Shera, Christopher A.
2012-01-01
This paper describes the implementation and performance of a nonlinear time-domain model of the cochlea for transient stimulation and human otoacoustic emission generation. The nonlinearity simulates compressive growth of measured basilar-membrane impulse responses. The model accounts for reflection and distortion-source otoacoustic emissions (OAEs) and simulates spontaneous OAEs through manipulation of the middle-ear reflectance. The model was calibrated using human psychoacoustical and otoacoustic tuning parameters. It can be used to investigate time-dependent properties of cochlear mechanics and the generator mechanisms of otoacoustic emissions. Furthermore, the model provides a suitable preprocessor for human auditory perception models where realistic cochlear excitation patterns are desired. PMID:23231114
An Explicit Time-Domain Hybrid Formulation Based on the Unified Boundary Condition
Madsen, N; Fasenfest, B J; White, D; Stowell, M; Jandhyala, V; Pingenot, J; Champagne, N J; Rockway, J D
2007-02-28
An approach to stabilize the two-surface, time domain FEM/BI hybrid by means of a unified boundary condition is presented. The first-order symplectic finite element formulation [1] is used along with a version of the unified boundary condition of Jin [2] reformulated for Maxwell's first-order equations in time to provide both stability and accuracy over the first-order ABC. Several results are presented to validate the numerical solutions. In particular the dipole in a free-space box is analyzed and compared to the Dirchlet boundary condition of Ziolkowski and Madsen [3] and to a Neuman boundary condition approach.
Characteristics of chiral and racemic ketoprofen drugs using terahertz time-domain spectroscopy
NASA Astrophysics Data System (ADS)
Du, Yong; Liu, Jianjun; Hong, Zhi
2013-08-01
Absorption spectra of chiral S-(+)- and racemic RS-ketoprofen pharmaceutical molecules in crystalline form were recorded in the terahertz region between 6 and 66 cm-1 (0.2 ~ 2.0 THz) by using time-domain terahertz spectroscopic (THz-TDS) measurement. Different distinctive absorption features were observed which are strikingly sensitive to the change of subtle conformational structures within such isostructural crystal molecules. The results suggest that the THz-TDS technique can be definitely used for distinguishing between chiral and racemic compounds in pharmaceutical and biological fields.
Brunner, Fabian D J; Schneider, Arno; Günter, Peter
2009-11-09
We present a versatile terahertz time-domain spectrometer which allows reflection measurements at normal incidence and double pass transmission measurements in a single experimental setup. Two different modes for transmission measurements are demonstrated for precise measurements of transparent high or low refractive index materials, respectively. The refractive indices and absorption coefficients of cesium iodide, potassium bromide, sodium chloride, polytetrafluoroethylene (PTFE, Teflon), and silicon have been measured in the frequency range between 1.4 and 4.7 THz. The parameters of the Lorentz oscillator functions describing the phonon polariton dispersions of CsI and KBr have been determined.
Interferometric distributed sensing system with phase optical time-domain reflectometry
NASA Astrophysics Data System (ADS)
Wang, Chen; Shang, Ying; Liu, Xiaohui; Wang, Chang; Wang, Hongzhong; Peng, Gangding
2016-11-01
We demonstrate a distributed optical fiber sensing system based on the Michelson interferometer of the phase sensitive optical time domain reflectometer (φ-OTDR) for acoustic measurement. Phase, amplitude, frequency response, and location information can be directly obtained at the same time by using the passive 3×3 coupler demodulation. We also set an experiment and successfully restore the acoustic information. Meanwhile, our system has preliminary realized acoustic-phase sensitivity around -150 dB (re rad/μPa) in the experiment.
Fra Angelico's painting technique revealed by terahertz time-domain imaging (THz-TDI)
NASA Astrophysics Data System (ADS)
Koch Dandolo, Corinna Ludovica; Picollo, Marcello; Cucci, Costanza; Jepsen, Peter Uhd
2016-10-01
We have investigated with terahertz time-domain imaging (THz-TDI) the well-known Lamentation over the dead Christ panel painting (San Marco Museum, Florence) painted by Fra Giovanni Angelico within 1436 and 1441. The investigation provided a better understanding of the construction and gilding technique used by the eminent artist, as well as the plastering technique used during the nineteenth-century restoration intervention. The evidence obtained from THz-TDI scans was correlated with the available documentation on the preservation history of the art piece. Erosion and damages documented for the wooden support, especially in the lower margin, found confirmation in the THz-TD images.
Gastric Emptying Assessment in Frequency and Time Domain Using Bio-impedance: Preliminary Results
NASA Astrophysics Data System (ADS)
Huerta-Franco, R.; Vargas-Luna, M.; Hernández, E.; Córdova, T.; Sosa, M.; Gutiérrez, G.; Reyes, P.; Mendiola, C.
2006-09-01
The impedance assessment to measure gastric emptying and in general gastric activity has been reported since 1985. The physiological interpretation of these measurements, is still under research. This technique usually uses a single frequency, and the conductivity parameter. The frequency domain and the Fourier analysis of the time domain behavior of the gastric impedance in different gastric conditions (fasting state, and after food administration) has not been explored in detail. This work presents some insights of the potentiality of these alternative methodologies to measure gastric activity.
Morrison, John L.
2001-04-24
Leaks are detected in a multi-layered geomembrane liner by a two-dimensional time domain reflectometry (TDR) technique. The TDR geomembrane liner is constructed with an electrically conductive detection layer positioned between two electrically non-conductive dielectric layers, which are each positioned between the detection layer and an electrically conductive reference layer. The integrity of the TDR geomembrane liner is determined by generating electrical pulses within the detection layer and measuring the time delay for any reflected electrical energy caused by absorption of moisture by a dielectric layer.
Time domain reflectometry (TDR) instrumentation used for in-situ plasma vitrification
Tarpley, J.
1997-09-08
An application of TDR (Time Domain Reflectometry) was developed and demonstrated for use with the in-situ plasma vitrification (ISPV) environmental restoration project. The technique was simple, using an inexpensive sacrificial TDR probe made out of ordinary coaxial cable. This technique proved its viability for field operation in support of the vitrification process. This presentation will detail the design, construction, operation and field results of the TDR instrumentation that was developed and used in this project. Other practical applications of this technology will be suggested.
Time Domain Identification of an Optimal Control Pilot Model with Emphasis on the Objective Function
NASA Technical Reports Server (NTRS)
Schmidt, D. K.
1982-01-01
A method for the identification of the pilot's control compensation using time domain techniques is proposed. From this information we hope to infer a quadratic cost function, supported by the data, that represents a reasonable expression for the pilot's control objective in the task being performed, or an inferred piloting strategy. The objectives for this method are: (1) obtain a better understanding of the fundamental piloting techniques in complex tasks, such as landing approach; (2) the development of a metric measurable in simulations and flight test that correlate with subjective pilot opinion; and (3) to further validate pilot models and pilot vehicle analysis methods.
Time domain and frequency domain design techniques for model reference adaptive control systems
NASA Technical Reports Server (NTRS)
Boland, J. S., III
1971-01-01
Some problems associated with the design of model-reference adaptive control systems are considered and solutions to these problems are advanced. The stability of the adapted system is a primary consideration in the development of both the time-domain and the frequency-domain design techniques. Consequentially, the use of Liapunov's direct method forms an integral part of the derivation of the design procedures. The application of sensitivity coefficients to the design of model-reference adaptive control systems is considered. An application of the design techniques is also presented.
Characterization of crystal transformation in the solid-state by terahertz time-domain spectroscopy
NASA Astrophysics Data System (ADS)
Ge, Min; Wang, Wenfeng; Zhao, Hongwei; Zhang, Zengyan; Yu, Xiaohan; Li, Wenxin
2007-08-01
Terahertz time-domain spectroscopy (THz-TDS) was utilized to investigate crystal transformation between p-benzoquinone and p-dihydroxybenzene in the solid-state. This process can be clearly visualized by THz spectral patterns of the pure starting compounds and the products at different conditions. The observed results were further confirmed by characteristic X-ray powder diffraction and mid-infrared spectra. The extent of crystal-to-crystal transformation was quantified by the absorption intensity ratio according to the Beer-Lambert law. THz-TDS was demonstrated to be a promising and complementary method in analyzing solid-state reactions.
Numerical modeling of wind turbine aerodynamic noise in the time domain.
Lee, Seunghoon; Lee, Seungmin; Lee, Soogab
2013-02-01
Aerodynamic noise from a wind turbine is numerically modeled in the time domain. An analytic trailing edge noise model is used to determine the unsteady pressure on the blade surface. The far-field noise due to the unsteady pressure is calculated using the acoustic analogy theory. By using a strip theory approach, the two-dimensional noise model is applied to rotating wind turbine blades. The numerical results indicate that, although the operating and atmospheric conditions are identical, the acoustical characteristics of wind turbine noise can be quite different with respect to the distance and direction from the wind turbine.
Distributed hot-wire anemometry based on Brillouin optical time-domain analysis.
Wylie, Michael T V; Brown, Anthony W; Colpitts, Bruce G
2012-07-02
A distributed hot-wire anemometer based on Brillouin optical time-domain analysis is presented. The anemometer is created by passing a current through a stainless steel tube fibre bundle and monitoring Brillouin frequency changes in the presence of airflow. A wind tunnel is used to provide laminar airflow while the device response is calibrated against theoretical models. The sensitivity equation for this anemometer is derived and discussed. Airspeeds from 0 m/s to 10 m/s are examined, and the results show that a Brillouin scattering based distributed hot-wire anemometer is feasible.
Terahertz time-domain spectroscopy for monitoring the curing of dental composites
Schwerdtfeger, Michael; Lippert, Sina; Koch, Martin; Berg, Andreas; Katletz, Stefan; Wiesauer, Karin
2012-01-01
We apply terahertz (THz) time-domain spectroscopy for monitoring the curing process of three different light-curing dental composites. Exact knowledge of the sample thickness is required for a precise determination of the THz dielectric parameters, as the materials exhibit shrinkage when they are cured. We find very small but significant changes of the THz refractive index and absorption coefficient during stepwise light exposure. The changes in the refractive index are correlated with changes in the density of the materials. Furthermore, the refractive index and the sample thickness are found to give the most reliable result for monitoring the curing process of the dental composites. PMID:23162722
Time domain solutions of Maxwell's equations using a finite-volume formulation
Noack, R.W.
1991-01-01
A new method for solving Maxwell's equations in the time domain was developed. The method approximates the integral form of the time-dependent Maxwell's equations using a finite-volume formulation. The method utilizes a staggered mesh and requires boundary conditions on the electric field or the magnetic field but not both. Predictions from the present method were compared to exact solutions for a full three-dimensional calculation of a sphere and experimental measurements for a generic missile body. These comparisons show that the method is capable of accurately solving the time-dependent Maxwell's equations and yields accurate predictions of the radar cross section for arbitrary geometries.
Distributed acoustic mapping based on interferometry of phase optical time-domain reflectometry
NASA Astrophysics Data System (ADS)
Wang, Chang; Wang, Chen; Shang, Ying; Liu, Xiaohui; Peng, Gangding
2015-07-01
We demonstrate the design and characterization of a distributed optical fiber sensing system based on Michelson interferometer of the phase sensitive optical time domain reflectometer (φ-OTDR) for acoustic measurement. Phase, amplitude, frequency response and location information can be directly obtained at the same time by using the passive 3×3 coupler demodulation. In order to simulate sound profiles of seismic or hydroacoustic imaging, experiments on detection of multiple piezoelectric transducers (PZT) are carried out. The result shows that our system can well demodulate different acoustic sources with different intensities.
Realization of a time-domain Fresnel lens with coherent control.
Degert, Jérôme; Wohlleben, Wendel; Chatel, Béatrice; Motzkus, Marcus; Girard, Bertrand
2002-11-11
Perturbative chirped pulse excitation leads to oscillations of the excited state amplitude. These coherent transients are governed by interferences between resonant and off-resonant contributions. Control mechanisms in both frequency and time domain are used to modify these dynamics. First, by applying a phase step in the spectrum, we manipulate the phase of the oscillations. By direct analogy with Fresnel zone lenses, we then conceive highly phase-amplitude modulated pulse shapes that slice destructive interferences out of the excitation time structure and enhance the final population.
Morris, John L.
1998-11-09
Leaks are detected in a multi-layered geomembrane liner by a two-dimensional time domain reflectometry (TDR) technique. The TDR geomembrane liner is constructed with an electrically conductive detection layer positioned between two electrically non-conductive dielectric layers, which are each positioned between the detection layer and an electrically conductive reference layer. The integrity of the TDR geomembrane liner is determined by generating electrical pulses within the detection layer and measuring the time delay for any reflected electrical energy caused by absorption of moisture by a dielectric layer.
Linearity of Air-Biased Coherent Detection for Terahertz Time-Domain Spectroscopy
NASA Astrophysics Data System (ADS)
Wang, Tianwu; Iwaszczuk, Krzysztof; Wrisberg, Emil Astrup; Denning, Emil Vosmar; Jepsen, Peter Uhd
2016-06-01
The performance of air-biased coherent detection (ABCD) in a broadband two-color laser-induced air plasma system for terahertz time-domain spectroscopy (THz-TDS) has been investigated. Fundamental parameters of the ABCD detection, including signal-to-noise ratio (SNR), dynamic range (DR), and linearity of detection have been characterized. Moreover, the performance of a photomultiplier tube (PMT) and an avalanche photodiode (APD) as photodetector in the ABCD have been compared. We have observed nonlinear behavior of PMT detector, which leads to artificial gain factor in TDS spectroscopy. The APD turns out to have superior linearity and three times higher dynamic compared to the PMT.
Improving the performance of time-domain pulsed echo laser profile using tunable lens.
Jie, Cao; Cheng, Yang; Hao, Qun; Zhang, Fanghua; Zhang, Kaiyu; Li, Xiao; Li, Kun; Peng, Yuxin
2017-04-03
We theoretically and experimentally examined the effects of the different positions between receiving lens (RL) and detector, namely, defocus, off-axis, and tilt, on the time-domain pulsed echo laser profile (TDPELP). Results show that distortions including saturation and broadening of TDPELP are obtained, regardless of the position between RL and detector. Thus, we adjust the focal length of RL to successfully obtain an optimal TDPELP using tunable lens under extreme situations, such as too strong or too weak intensity of the TDPELP.
Analysis of drugs-of-abuse and explosives using terahertz time-domain and Raman spectroscopy
NASA Astrophysics Data System (ADS)
Burnett, Andrew; Fan, Wenhui; Upadhya, Prashanth; Cunningham, John; Linfield, Edmund; Davies, Giles; Edwards, Howell; Munshi, Tasnim; O'Neil, Andrew
2006-02-01
We demonstrate that, through coherent measurement of the transmitted terahertz electric fields, broadband (0.3-8THz) time-domain spectroscopy can be used to measure far-infrared vibrational modes of a range of illegal drugs and high explosives that are of interest to the forensic and security services. Our results show that these absorption features are highly sensitive to the structural and spatial arrangement of the molecules. Terahertz frequency spectra are also compared with high-resolution low-frequency Raman spectra to assist in understanding the low frequency inter- and intra-molecular vibrational modes of the molecules.
Spherical Wave Propagation in a Poroelastic Medium with Infinite Permeability: Time Domain Solution
Ozyazicioglu, Mehmet
2014-01-01
Exact time domain solutions for displacement and porepressure are derived for waves emanating from a pressurized spherical cavity, in an infinitely permeable poroelastic medium with a permeable boundary. Cases for blast and exponentially decaying step pulse loadings are considered; letter case, in the limit as decay constant goes to zero, also covers the step (uniform) pressure. Solutions clearly show the propagation of the second (slow) p-wave. Furthermore, Biot modulus Q is shown to have a pronounced influence on wave propagation characteristics in poroelastic media. Results are compared with solutions in classical elasticity theory. PMID:24701190
NASA Technical Reports Server (NTRS)
Adamovsky, Grigory; Piltch, Nancy D.
1986-01-01
A fiber-optic thermometer based on temperature dependent absorption in Nd(3+) doped glass is demonstrated over the 298-573 K range. A broadband detection technique allows the use of the complete spectrum of a pulse modulated light emitting diode. A fiber-optic recirculating loop is employed to construct a reference channel in the time domain by generating a train of pulses from one initial pulse. A theoretical model is developed, and experimental data are shown to compare well with the theory. Possible sources of error and instability are identified, and ways to enhance the performance of the system are proposed.
A RF time domain approach for electric arcs detection and localization systems
NASA Astrophysics Data System (ADS)
Deacu, Daniela; Tamas, Razvan; Petrescu, Teodor; Paun, Mirel; Anchidin, Liliana; Algiu, Madalina
2016-12-01
In this paper we propose a new method for detection and localization of electric arcs by using two ultra-wide band (UWB) antennas together with data processing in the time-domain. The source of electric arcs is localized by computing an average on the inter-correlation functions of the signals received on two channels. By calculating the path length difference to the antennas, the direction of the electric arcs is then found. The novelty of the method consists in the spatial averaging in order to reduce the incertitude caused by the finite sampling rate.
Generalized computer-aided discrete time domain modeling and analysis of dc-dc converters
NASA Technical Reports Server (NTRS)
Lee, F. C.; Iwens, R. P.; Yu, Y.; Triner, J. E.
1977-01-01
A generalized discrete time domain modeling and analysis technique is presented for all types of switching regulators using any type of duty-cycle controller, and operating in both continuous and discontinuous inductor current. State space techniques are employed to derive an equivalent nonlinear discrete time model that describes the converter exactly. The system is linearized about its equilibrium state to obtain a linear discrete time model for small signal performance evaluations, such as stability, audiosusceptibility and transient response. The analysis makes extensive use of the digital computer as an analytical tool. It is universal, exact and easy to use.
Vibrational frequencies of anti-diabetic drug studied by terahertz time-domain spectroscopy
NASA Astrophysics Data System (ADS)
Du, S. Q.; Li, H.; Xie, L.; Chen, L.; Peng, Y.; Zhu, Y. M.; Li, H.; Dong, P.; Wang, J. T.
2012-04-01
By using terahertz time-domain spectroscopy, the absorption spectra of seven anti-diabetic pills have been investigated. For gliquidone, glipizide, gliclazide, and glimepiride, an obvious resonance peak is found at 1.37 THz. Furthermore, to overcome the limit of density functional theory that can analyze the normal mode frequencies of the ground state of organic material, we also present a method that relies on pharmacophore recognition, from which we can obtain the resonance peak at 1.37 THz can be attributed to the vibration of sulfonylurea group. The results indicate that the veracity of density functional theory can be increased by combining pharmacophore recognition.
Development of a Time Domain Fluorimeter for Fluorescent Lifetime Multiplexing Analysis
Weissleder, Ralph; Mahmood, Umar
2009-01-01
We show that a portable, inexpensive USB-powered time domain fluorimeter (TDF) and analysis scheme were developed for use in evaluating a new class of fluorescent lifetime multiplexed dyes. Fluorescent proteins, organic dyes, and quantum dots allow the labeling of more and more individual features within biological systems, but the wide absorption and emission spectra of these fluorophores limit the number of distinct processes which may be simultaneously imaged using spectral separation alone. By additionally separating reporters in a second dimension, fluorescent lifetime multiplexing provides a means to multiply the number of available imaging channels. PMID:19830273
Time-domain study on reproducibility of laser-based soft-error simulation
NASA Astrophysics Data System (ADS)
Itsuji, Hiroaki; Kobayashi, Daisuke; Lourenco, Nelson E.; Hirose, Kazuyuki
2017-04-01
Studied is the soft error issue, which is a circuit malfunction caused by ion-radiation-induced noise currents. We have developed a laser-based soft-error simulation system to emulate the noise and evaluate its reproducibility in the time domain. It is found that this system, which utilizes a two-photon absorption process, can reproduce the shape of ion-induced transient currents, which are assumed to be induced from neutrons at the ground level. A technique used to extract the initial carrier structure inside the device is also presented.
Torsional vibrational modes of tryptophan studied by terahertz time-domain spectroscopy.
Yu, B; Zeng, F; Yang, Y; Xing, Q; Chechin, A; Xin, X; Zeylikovich, I; Alfano, R R
2004-03-01
The low-frequency torsional modes, index of refraction, and absorption of a tryptophan film and pressed powders from 0.2 to 2.0 THz (6.6-66 cm(-1)) were measured by terahertz time-domain spectroscopy at room temperature. It was found that there were two dominated torsional vibrational modes at around 1.435 and 1.842 THz. The associated relaxation lifetimes ( approximately 1 ps) for these modes of the tryptophan molecule were measured. Using a density-functional calculation, the origins of the observed torsional vibrations were assigned to the chain and ring of the tryptophan molecule.
Nonlinear time-domain cochlear model for transient stimulation and human otoacoustic emission.
Verhulst, Sarah; Dau, Torsten; Shera, Christopher A
2012-12-01
This paper describes the implementation and performance of a nonlinear time-domain model of the cochlea for transient stimulation and human otoacoustic emission generation. The nonlinearity simulates compressive growth of measured basilar-membrane impulse responses. The model accounts for reflection and distortion-source otoacoustic emissions (OAEs) and simulates spontaneous OAEs through manipulation of the middle-ear reflectance. The model was calibrated using human psychoacoustical and otoacoustic tuning parameters. It can be used to investigate time-dependent properties of cochlear mechanics and the generator mechanisms of otoacoustic emissions. Furthermore, the model provides a suitable preprocessor for human auditory perception models where realistic cochlear excitation patterns are desired.