Hoche, S; Hussein, M A; Becker, T
2015-03-01
The accuracy of density, reflection coefficient, and acoustic impedance determination via multiple reflection method was validated experimentally. The ternary system water-maltose-ethanol was used to execute a systematic, temperature dependent study over a wide range of densities and viscosities aiming an application as inline sensor in beverage industries. The validation results of the presented method and setup show root mean square errors of: 1.201E-3 g cm(-3) (±0.12%) density, 0.515E-3 (0.15%) reflection coefficient and 1.851E+3 kg s(-1) m(-2) (0.12%) specific acoustic impedance. The results of the diffraction corrected absorption showed an average standard deviation of only 0.12%. It was found that the absorption change shows a good correlation to concentration variations and may be useful for laboratory analysis of sufficiently pure liquids. The main part of the observed errors can be explained by the observed noise, temperature variation and the low signal resolution of 50 MHz. In particular, the poor signal-to-noise ratio of the second reflector echo was found to be a main accuracy limitation. Concerning the investigation of liquids the unstable properties of the reference material PMMA, due to hygroscopicity, were identified to be an additional, unpredictable source of uncertainty. While dimensional changes can be considered by adequate methodology, the impact of the time and temperature dependent water absorption on relevant reference properties like the buffer's sound velocity and density could not be considered and may explain part of the observed deviations. PMID:25465962
Lenhart, S. |; Protopopescu, V.; Yong, J.
1997-12-31
The authors apply optimal control techniques to find approximate solutions to an inverse problem for the acoustic wave equation. The inverse problem (assumed here to have a solution) is to determine the boundary reflection coefficient from partial measurements of the acoustic signal. The sought reflection coefficient is treated as a control and the goal--quantified by an approximate functional--is to drive the model solution close to the experimental data by adjusting this coefficient. The problem is solved by finding the optimal control that minimizes the approximate functional. Then by driving the cost of the control to zero one proves that the corresponding sequence of optimal controls represents a converging sequence of estimates for the solution of the inverse problem. Compared to classical regularization methods (e.g., Tikhonov coupled with optimization schemes), their approach yields: (1) a systematic procedure to solve inverse problems of identification type and (ii) an explicit expression for the approximations of the solution.
Červenka, Milan; Bednařík, Michal
2015-10-01
This work verifies the idea that in principle it is possible to reconstruct axial temperature distribution of fluid employing reflection or transmission of acoustic waves. It is assumed that the fluid is dissipationless and its density and speed of sound vary along the wave propagation direction because of the fluid temperature distribution. A numerical algorithm is proposed allowing for calculation of the temperature distribution on the basis of known frequency characteristics of reflection coefficient modulus. Functionality of the algorithm is illustrated on a few examples, its properties are discussed. PMID:26520344
Measurement and modelling of the reflection coefficient of an Acoustic Black Hole termination
NASA Astrophysics Data System (ADS)
Denis, V.; Gautier, F.; Pelat, A.; Poittevin, J.
2015-08-01
The flexural waves propagating in a beam can be efficiently absorbed if one extremity is tapered with a power law profile and covered by a thin layer of additional damping material. Such a termination induces the so-called "Acoustic Black Hole effect" (ABH): if the thickness decreases locally, flexural waves slow down and the amplitude of the displacement field increases, leading to efficient energy dissipation if an absorbing layer is placed where the thickness is minimum. This paper presents a specific study of the reflection coefficient of ABH beam terminations. A Kundt-like measurement method of the reflection coefficient of a beam termination is proposed. The method is validated using theoretical results in the case of a beam free end. Results for several ABH extremities show a clear decrease of the modulus of the reflection coefficient R. The phase of R due to the decreasing thickness profile is also investigated and is interpreted by defining a correction length for the tapered termination. These experimental results are compared with several models: geometrical acoustics based model, beam waveguide model and plate model.
ERIC Educational Resources Information Center
Greenslade, Thomas B., Jr.
1994-01-01
Discusses and provides an example of reflectivity approximation to determine whether reflection will occur. Provides a method to show thin-film interference on a projection screen. Also applies the reflectivity concepts to electromagnetic wave systems. (MVL)
NASA Astrophysics Data System (ADS)
Tohmyoh, Hironori; Sakamoto, Yuhei
2015-11-01
This paper reports on a technique to measure the acoustic properties of a thin polymer film utilizing the frequency dependence of the reflection coefficient of ultrasound reflected back from a system comprising a reflection plate, the film, and a material that covers the film. The frequency components of the echo reflected from the back of the plate, where the film is attached, take their minimum values at the resonant frequency, and from these frequency characteristics, the acoustic impedance, sound velocity, and the density of the film can be determined. We applied this technique to characterize an ion exchange membrane, which has high water absorbability, and successfully determined the acoustic properties of the membrane without getting it wet.
NASA Astrophysics Data System (ADS)
Chen, Jian; Bai, Xiaolong; Yang, Keji; Ju, Bing-Feng
2012-01-01
For inspection of mechanical properties and integrity of critical components such as integrated circuits or composite materials by acoustic methodology, it is imperative to evaluate their acoustic reflection coefficients, which are in close correlation with the elastic properties, thickness, density, and attenuation and interface adhesion of these layered structures. An experimental method based on angular spectrum to evaluate the acoustic coefficient as a function of the incident angle, θ, and frequency, ω, is presented with high frequency time-resolved acoustic microscopy. In order to achieve a high spatial resolution for evaluation of thin plates with thicknesses about one or two wavelengths, a point focusing transducer with a nominal center frequency of 25 MHz is adopted. By measuring the V(z, t) data in pulse mode, the reflection coefficient, R(θ, ω), can be reconstructed from its two-dimensional spectrum. It brings simplicity to experimental setup and measurement procedure since only single translation of the transducer in the vertical direction is competent for incident angle and frequency acquisition. It overcomes the disadvantages of the conventional methods requiring the spectroscopy for frequency scanning and/or ultrasonic goniometer for angular scanning. Two substrates of aluminum and Plexiglas and four stainless plates with various thicknesses of 100 μm, 150 μm, 200 μm, and 250 μm were applied. The acoustic reflection coefficients are consistent with the corresponding theoretical calculations. It opened the way of non-destructive methodology to evaluate the elastic and geometrical properties of very thin multi-layers structures simultaneously.
NASA Astrophysics Data System (ADS)
Bolton, J. S.; Gold, E.
1986-10-01
The authors have previously outlined a transient free field technique, based on cepstral analysis, for the measurement of acoustic reflection coefficients. In this paper are described laboratory acoustical measurements of the normal incidence reflection coefficient of an absorbent material: emphasis is placed on practical aspects of the technique. Specifically, the origin of extraction noise, which distorts the reflector impulse response as it appears in the power cepstrum, is discussed and means of reducing it are described and implemented. Secondly, a means of identifying and removing the time delay introduced when the reflector impulse response is copied from the cepstrum is described; this procedure eliminates the need for highly accurate measurements of path length difference. The absorbent material tested was a commercial partially reticulated polyurethane foam. Bonded to one side of the foam was an impermeable polyurethane membrane, and the foam was measured in two configurations: first with its film covered face uppermost, then with its uncovered face uppermost. The broad frequency range of the measurements made possible by the cepstral technique has given a good picture of the properties of this material. These results will be considered in detail in a subsequent publication.
Prisutova, Jevgenija; Horoshenkov, Kirill; Groby, Jean-Philippe; Brouard, Bruno
2014-12-01
The measurement of acoustic material characteristics using a standard impedance tube method is generally limited to the plane wave regime below the tube cut-on frequency. This implies that the size of the tube and, consequently, the size of the material specimen must remain smaller than a half of the wavelength. This paper presents a method that enables the extension of the frequency range beyond the plane wave regime by at least a factor of 3, so that the size of the material specimen can be much larger than the wavelength. The proposed method is based on measuring of the sound pressure at different axial locations and applying the spatial Fourier transform. A normal mode decomposition approach is used together with an optimization algorithm to minimize the discrepancy between the measured and predicted sound pressure spectra. This allows the frequency and angle dependent reflection and absorption coefficients of the material specimen to be calculated in an extended frequency range. The method has been tested successfully on samples of melamine foam and wood fiber. The measured data are in close agreement with the predictions by the equivalent fluid model for the acoustical properties of porous media. PMID:25480044
NASA Technical Reports Server (NTRS)
Kraft, R. E.
1996-01-01
A computational method to predict modal reflection coefficients in cylindrical ducts has been developed based on the work of Homicz, Lordi, and Rehm, which uses the Wiener-Hopf method to account for the boundary conditions at the termination of a thin cylindrical pipe. The purpose of this study is to develop a computational routine to predict the reflection coefficients of higher order acoustic modes impinging on the unflanged termination of a cylindrical duct. This effort was conducted wider Task Order 5 of the NASA Lewis LET Program, Active Noise Control of aircraft Engines: Feasibility Study, and will be used as part of the development of an integrated source noise, acoustic propagation, ANC actuator coupling, and control system algorithm simulation. The reflection coefficient prediction will be incorporated into an existing cylindrical duct modal analysis to account for the reflection of modes from the duct termination. This will provide a more accurate, rapid computation design tool for evaluating the effect of reflected waves on active noise control systems mounted in the duct, as well as providing a tool for the design of acoustic treatment in inlet ducts. As an active noise control system design tool, the method can be used preliminary to more accurate but more numerically intensive acoustic propagation models such as finite element methods. The resulting computer program has been shown to give reasonable results, some examples of which are presented. Reliable data to use for comparison is scarce, so complete checkout is difficult, and further checkout is needed over a wider range of system parameters. In future efforts the method will be adapted as a subroutine to the GEAE segmented cylindrical duct modal analysis program.
Reflection properties of gravito-acoustic waves
NASA Astrophysics Data System (ADS)
Jovanović, Gordana
2016-03-01
We derive the dispersion equation for gravito-acoustic waves in an isothermal gravitationally stratified nonmagnetized atmosphere. In this model, with constant sound speed, it is possible to derive analytically the equations for gravito-acoustic waves. The large value of the viscous Reynolds number in the solar atmosphere imply that the dissipative terms in HD (hydrodynamics) equations are negligible. We consider the plane boundary z = 0 between two isothermal atmosphere regions and using the boundary conditions we derive the equation for the reflection coeffcient of gravito-acoustic waves. For the frequencies much greater than acoustic cutoff frequency, the reflection coefficient of the acoustic waves modified by gravity is the same as in the case of the pure acoustic waves. Reflection coefficient for the gravity waves is very high, R ≈ 1.
Quantitative Ultrasound Imaging Using Acoustic Backscatter Coefficients.
NASA Astrophysics Data System (ADS)
Boote, Evan Jeffery
Current clinical ultrasound scanners render images which have brightness levels related to the degree of backscattered energy from the tissue being imaged. These images offer the interpreter a qualitative impression of the scattering characteristics of the tissue being examined, but due to the complex factors which affect the amplitude and character of the echoed acoustic energy, it is difficult to make quantitative assessments of scattering nature of the tissue, and thus, difficult to make precise diagnosis when subtle disease effects are present. In this dissertation, a method of data reduction for determining acoustic backscatter coefficients is adapted for use in forming quantitative ultrasound images of this parameter. In these images, the brightness level of an individual pixel corresponds to the backscatter coefficient determined for the spatial position represented by that pixel. The data reduction method utilized rigorously accounts for extraneous factors which affect the scattered echo waveform and has been demonstrated to accurately determine backscatter coefficients under a wide range of conditions. The algorithms and procedures used to form backscatter coefficient images are described. These were tested using tissue-mimicking phantoms which have regions of varying scattering levels. Another phantom has a fat-mimicking layer for testing these techniques under more clinically relevant conditions. Backscatter coefficient images were also formed of in vitro human liver tissue. A clinical ultrasound scanner has been adapted for use as a backscatter coefficient imaging platform. The digital interface between the scanner and the computer used for data reduction are described. Initial tests, using phantoms are presented. A study of backscatter coefficient imaging of in vivo liver was performed using several normal, healthy human subjects.
Multi-reflective acoustic wave device
Andle, Jeffrey C.
2006-02-21
An acoustic wave device, which utilizes multiple localized reflections of acoustic wave for achieving an infinite impulse response while maintaining high tolerance for dampening effects, is disclosed. The device utilized a plurality of electromechanically significant electrodes disposed on most of the active surface. A plurality of sensors utilizing the disclosed acoustic wave mode device are also described.
Reflective echo tomographic imaging using acoustic beams
Kisner, Roger; Santos-Villalobos, Hector J
2014-11-25
An inspection system includes a plurality of acoustic beamformers, where each of the plurality of acoustic beamformers including a plurality of acoustic transmitter elements. The system also includes at least one controller configured for causing each of the plurality of acoustic beamformers to generate an acoustic beam directed to a point in a volume of interest during a first time. Based on a reflected wave intensity detected at a plurality of acoustic receiver elements, an image of the volume of interest can be generated.
Frustrated total internal reflection acoustic field sensor
Kallman, Jeffrey S.
2000-01-01
A frustrated total internal reflection acoustic field sensor which allows the acquisition of the acoustic field over an entire plane, all at once. The sensor finds use in acoustic holography and acoustic diffraction tomography. For example, the sensor may be produced by a transparent plate with transparent support members tall enough to support one or more flexible membranes at an appropriate height for frustrated total internal reflection to occur. An acoustic wave causes the membrane to deflect away from its quiescent position and thus changes the amount of light that tunnels through the gap formed by the support members and into the membrane, and so changes the amount of light reflected by the membrane. The sensor(s) is illuminated by a uniform tight field, and the reflection from the sensor yields acoustic wave amplitude and phase information which can be picked up electronically or otherwise.
Diffuse reflection coefficient of a stratified sea.
Haltrin, V I
1999-02-20
A differential equation of a Riccati type for the diffuse reflection coefficient of a stratified sea is proposed. For a homogeneous sea with arbitrary inherent optical properties this equation is solved analytically. For an inhomogeneous sea it is solved approximately for any arbitrary stratification. The resulting equation expresses the diffuse reflection coefficient of the sea through vertical profiles of absorption and backscattering coefficients, bottom albedo, and sea depth. The results of calculations with this equation are compared with Monte Carlo computations. It was found that the precision of this approach is in the range of 15%. PMID:18305694
Modeling canopy reflectance and microwave backscattering coefficient
NASA Technical Reports Server (NTRS)
Goel, N. S.
1985-01-01
Various approaches to model canopy reflectance (CR) in the visible/infrared region and backscattering coefficient (BSC) in the microwave region are compared and contrasted. It is noted that BSC can be related to CR in the source direction (the 'hot spot' direction). By assuming a frequency dependent leaf reflectance and transmittance it is shown that the observed dependence of BSC on leaf area index, leaf angle distribution, angle of incidence, soil moisture content, and frequency can be simulated by a CR model. Thus both BSC and CR can, in principle, be calculated using a single model which has essentially the same parameters as many CR models do.
Solute concentration effect on osmotic reflection coefficient.
Adamski, R P; Anderson, J L
1983-01-01
A theory for the effect of concentration on osmotic reflection coefficient, correct to first order, was developed at the molecular level by considering the effect of solute-solute interactions on solute concentration and the fluid stress tensor within a solvent-filled pore. The solvent was modeled as a continuous fluid and potential energies between solute molecules and the pore wall were assumed to be pairwise additive. Although the theory is more general, calculations are presented only for excluded volume effects (hard-sphere for solute, hard-wall for pore). The relationship between the first-order concentration effect and the infinite dilution value of reflection coefficient appears to be geometry independent. The theory is discussed in light of experimental studies of osmotic flow that have recently appeared in the literature. PMID:6626681
Reflection and Scattering of Acoustical Waves from a Discontinuity in Absorption
NASA Astrophysics Data System (ADS)
Jones, J. P.; Leeman, S.; Nolan, E.; Lee, D.
The reflection and transmission of a plane acoustical wave from a planar boundary at the interface between two homogeneous media of different acoustical properties is a classical problem in acoustics that has served as a basis for many developments in acoustics for over 100 years. This problem, detailed in virtually every textbook on acoustics, provides us with the acoustical analogue to Snell's Law in optics and gives us correspondingly simple results. Classical acoustics predicts that a reflection from a boundary occurs only if the characteristic acoustical impedances of the two media are different. Here we show that a reflection also occurs if the media have the same impedances but different absorption coefficients. Our analysis yields some surprising results. For example, a reflection will occur at a discontinuity in absorption even if the impedance is uniform and continuous across the interface. In addition, a discontinuity in impedance at an interface between two media that have constant and equal, but non-zero absorption, results in a reflection coefficient that is dependent on absorption as well as impedance. In general, reflection coefficients now become frequency dependent. To experimentally test our results, we measured the reflection at the interface between water and castor oil, two liquids with similar impedances but very different absorption coefficients. Measurement of the reflection coefficient between 1 and 50 MHz demonstrated a frequency dependence that was in good agreement with our analysis.
Virtual reflections in electronic acoustic architecture
NASA Astrophysics Data System (ADS)
van Munster, Bjorn
2005-09-01
In the era of the ancient Greeks and Byzantines, the first attempts for increasing reverberation time are noted. In the 1950s, the Ambiophonic system accomplished this by means of an electronic device, for the first time. The early systems only increased the reverberation time by delaying the picked-up reverberation. With the introduction of multichannel feedback-based systems, the reverberation level also could be increased. Later, it was understood that it was important to also fill in the missing reflections, address reflection density, frequency dependence, etc. This resulted in the development of the SIAP concept. Current DSP technology led to the development of a processor whereby density, length, level, and the frequency content can be controlled for different areas in the same room or different rooms, leading to the concept of the acoustic server. electronic acoustic architecture has become the current state-of-the-art approach for solving acoustic deficiencies in, among others, rehearsal rooms, theaters, churches, and multipurpose venues. Incorporation of complementary passive acoustic solutions provides an optimum solution for all room problems. This paper discusses the utilization of virtual reflections in the new approach of electronic acoustic architecture for different environments. Measurements performed in the Sejong Performing Arts Centre, Seoul, South Korea, show the power of this approach.
Studying how flocculation affects acoustic reflection
NASA Astrophysics Data System (ADS)
Schultz, Colin
2013-06-01
In inland estuaries and shallow coastal waters, small particles of organic matter, such as organic waste and debris or bacteria, clump together to form an aggregate known as floc. Flocculated particles can span a range of sizes, from a few micrometers to a few millimeters, and the properties and concentration of floc have a strong influence on water quality. To infer the properties of floc particles, researchers have proposed using acoustic backscatter measurements, a common technique for estimating sediment concentrations. To do so, however, requires an understanding of how the properties of floc particles affect acoustic wave reflection.
Determination of decay coefficients for combustors with acoustic absorbers
NASA Technical Reports Server (NTRS)
Mitchell, C. E.; Espander, W. R.; Baer, M. R.
1972-01-01
An analytical technique for the calculation of linear decay coefficients in combustors with acoustic absorbers is presented. Tuned circumferential slot acoustic absorbers were designed for the first three transverse modes of oscillation, and decay coefficients for these absorbers were found as a function of backing distance for seven different chamber configurations. The effectiveness of the absorbers for off-design values of the combustion response and acoustic mode is also investigated. Results indicate that for tuned absorbers the decay coefficient increases approximately as the cube of the backing distance. For most off-design situations the absorber still provides a damping effect. However, if an absorber designed for some higher mode of oscillation is used to damp lower mode oscillations, a driving effect is frequently found.
Reciprocity in the scattering coefficients of acoustic waveguide modes.
Tong, Yuhui; Pan, Jie
2013-09-01
In this Letter, a proof is provided for the reciprocity between modal scattering coefficients of the acoustic waveguides connected by a junction enclosure. The result holds for all waveguide modes and for junction enclosures with locally reactive boundary conditions away from the interfaces between the junction and waveguides. Also provided is a physical interpretation of the reciprocity of the modal scattering coefficients. The scattering of two-dimensional waveguide modes by a right-angled bend in a rectangular duct is used as an illustrating example. PMID:23967907
Sensitivity of room acoustic parameters to changes in scattering coefficients
NASA Astrophysics Data System (ADS)
Rathsam, Jonathan; Wang, Lily M.
2001-05-01
This project uses the room acoustics computer modeling program, ODEON, to investigate the sensitivity of room acoustic parameters to changes in scattering coefficients. Particularly, the study is interested in determining if the results from certain room models are more sensitive to scattering coefficients than from other models, due to their geometry or absorption characteristics. If so, how can one quantify a model's susceptibility to being sensitive to scattering? Various models of three real spaces in Omaha, Nebraska are tested. The predicted reverberation, clarity, and spaciousness parameters are compared at various receiver locations, while the scattering coefficient of all surfaces is varied from 0 to 0.1, 0.3, 0.5, and 0.8. The resulting data are analyzed by frequency according to the (1) average absorption of the room; (2) magnitude variation of absorption within the room; (3) spatial distribution of absorption within the room; and (4) level of model detail. Initial results indicate that parameters studied may show more sensitivity to scattering coefficients in models that have a wider range of absorption values, more disparate distribution of absorption, and lower detail level. Various schemes that include these aspects are proposed for computing a model's sensitivity to changes in scattering.
Ultrasonic measurements of the reflection coefficient at a water/polyurethane foam interface.
Sagers, Jason D; Haberman, Michael R; Wilson, Preston S
2013-09-01
Measured ultrasonic reflection coefficients as a function of normal incidence angle are reported for several samples of polyurethane foam submerged in a water bath. Three reflection coefficient models are employed as needed in this analysis to approximate the measured data: (1) an infinite plane wave impinging on an elastic halfspace, (2) an infinite plane wave impinging on a single fluid layer overlying a fluid halfspace, and (3) a finite acoustic beam impinging on an elastic halfspace. The compressional wave speed in each sample is calculated by minimizing the sum of squared error (SSE) between the measured and modeled data. PMID:23968059
Manipulating Acoustic Wavefront by Inhomogeneous Impedance and Steerable Extraordinary Reflection
Zhao, Jiajun; Li, Baowen; Chen, Zhining; Qiu, Cheng-Wei
2013-01-01
We unveil the connection between the acoustic impedance along a flat surface and the reflected acoustic wavefront, in order to empower a wide wariety of novel applications in acoustic community. Our designed flat surface can generate double reflections: the ordinary reflection and the extraordinary one whose wavefront is manipulated by the proposed impedance-governed generalized Snell's law of reflection (IGSL). IGSL is based on Green's function and integral equation, instead of Fermat's principle for optical wavefront manipulation. Remarkably, via the adjustment of the designed specific acoustic impedance, extraordinary reflection can be steered for unprecedented acoustic wavefront while that ordinary reflection can be surprisingly switched on or off. The realization of the complex discontinuity of the impedance surface has been proposed using Helmholtz resonators. PMID:23985717
Manipulating acoustic wavefront by inhomogeneous impedance and steerable extraordinary reflection.
Zhao, Jiajun; Li, Baowen; Chen, Zhining; Qiu, Cheng-Wei
2013-01-01
We unveil the connection between the acoustic impedance along a flat surface and the reflected acoustic wavefront, in order to empower a wide wariety of novel applications in acoustic community. Our designed flat surface can generate double reflections: the ordinary reflection and the extraordinary one whose wavefront is manipulated by the proposed impedance-governed generalized Snell's law of reflection (IGSL). IGSL is based on Green's function and integral equation, instead of Fermat's principle for optical wavefront manipulation. Remarkably, via the adjustment of the designed specific acoustic impedance, extraordinary reflection can be steered for unprecedented acoustic wavefront while that ordinary reflection can be surprisingly switched on or off. The realization of the complex discontinuity of the impedance surface has been proposed using Helmholtz resonators. PMID:23985717
Manipulating Acoustic Wavefront by Inhomogeneous Impedance and Steerable Extraordinary Reflection
NASA Astrophysics Data System (ADS)
Zhao, Jiajun; Li, Baowen; Chen, Zhining; Qiu, Cheng-Wei
2013-08-01
We unveil the connection between the acoustic impedance along a flat surface and the reflected acoustic wavefront, in order to empower a wide wariety of novel applications in acoustic community. Our designed flat surface can generate double reflections: the ordinary reflection and the extraordinary one whose wavefront is manipulated by the proposed impedance-governed generalized Snell's law of reflection (IGSL). IGSL is based on Green's function and integral equation, instead of Fermat's principle for optical wavefront manipulation. Remarkably, via the adjustment of the designed specific acoustic impedance, extraordinary reflection can be steered for unprecedented acoustic wavefront while that ordinary reflection can be surprisingly switched on or off. The realization of the complex discontinuity of the impedance surface has been proposed using Helmholtz resonators.
Madelin, Guillaume; Grucker, Daniel; Franconi, Jean-Michel; Thiaudiere, Eric
2006-07-01
In this study, magnetic resonance imaging (MRI) is used to visualize acoustic streaming in liquids. A single-shot spin echo sequence (HASTE) with a saturation band perpendicular to the acoustic beam permits the acquisition of an instantaneous image of the flow due to the application of ultrasound. An average acoustic streaming velocity can be estimated from the MR images, from which the ultrasonic absorption coefficient and the bulk viscosity of different glycerol-water mixtures can be deduced. In the same way, this MRI method could be used to assess the acoustic field and time-average power of ultrasonic transducers in water (or other liquids with known physical properties), after calibration of a geometrical parameter that is dependent on the experimental setup. PMID:16650447
Coefficient of variation spectral analysis: An application to underwater acoustics
NASA Astrophysics Data System (ADS)
Herstein, P. D.; Laplante, R. F.
1983-05-01
Acoustic noise in the ocean is often described in terms of its power spectral density. Just as in other media, this noise consists of both narrowband and broadband frequency components. A major problem in the analysis of power spectral density measurements is distinguishing between narrowband spectral components of interest and contaminating narrowband components. In this paper, the use of coefficient of variation (Cv) spectrum is examined as an adjunct to the conventional power spectrum to distinguish narrowband components of interest from contaminating components. The theory of the Cv is presented. Coefficients for several classical input distributions are developed. It is shown that Cv spectra can be easily implemented as an adjunct procedure during the computation of the ensemble of averaged power spectra. Power and Cv spectra derived from actual at-sea sonobuoy measurements of deep ocean ambient noise separate narrowband components from narrowband lines of interest in the ensemble of averaged power spectra, these acoustic components of interest can be distinguished in the Cv spectra.
Reflection of acoustic wave from the elastic seabed with an overlying gassy poroelastic layer
NASA Astrophysics Data System (ADS)
Chen, Weiyun; Wang, Zhihua; Zhao, Kai; Chen, Guoxing; Li, Xiaojun
2015-10-01
Based on the multiphase poroelasticity theory, the reflection characteristics of an obliquely incident acoustic wave upon a plane interface between overlying water and a gassy marine sediment layer with underlying elastic solid seabed are investigated. The sandwiched gassy layer is modelled as a porous material with finite thickness, which is saturated by two compressible and viscous fluids (liquid and gas). The closed-form expression for the amplitude ratio of the reflected wave, called reflection coefficient, is derived theoretically according to the boundary conditions at the upper and lower interfaces in our proposed model. Using numerical calculation, the influences of layer thickness, incident angle, wave frequency and liquid saturation of sandwiched porous layer on the reflection coefficient are analysed, respectively. It is revealed that the reflection coefficient is closely associated with incident angle and sandwiched layer thickness. Moreover, in different frequency ranges, the dependence of the wave reflection characteristics on moisture (or gas) variations in the intermediate marine sediment layer is distinguishing.
On the distribution of seismic reflection coefficients and seismic amplitudes
Painter, S.; Paterson, L.; Beresford, G.
1995-07-01
Reflection coefficient sequences from 14 wells in Australia have a statistical character consistent with a non-Gaussian scaling noise model based on the Levy-stable family of probability distributions. Experimental histograms of reflection coefficients are accurately approximated by symmetric Levy-stable probability density functions with Levy index between 0.99 and 1.43. These distributions have the same canonical role in mathematical statistics as the Gaussian distribution, but they have slowly decaying tails and infinite moments. The distribution of reflection coefficients is independent of the spatial scale (statistically self-similar), and the reflection coefficient sequences have long-range dependence. These results suggest that the logarithm of seismic impedance can be modeled accurately using fractional Levy motion, which is a generalization of fractional Brownian motion. Synthetic seismograms produced from the authors` model for the reflection coefficients also have Levy-stable distributions. These isolations include transmission losses, the effects of reverberations, and the loss of resolution caused by band-limited wavelets, and suggest that actual seismic amplitudes with sufficient signal-to-noise ratio should also have a Levy-stable distribution. This prediction is verified using post-stack seismic data acquired in the Timor Sea and in the continental USA. However, prestack seismic amplitudes from the Timor Sea are nearly Gaussian. They attribute the difference between prestack and poststack data to the high level of measurement noise in the prestack data.
Protein osmotic pressure gradients and microvascular reflection coefficients.
Drake, R E; Dhother, S; Teague, R A; Gabel, J C
1997-08-01
Microvascular membranes are heteroporous, so the mean osmotic reflection coefficient for a microvascular membrane (sigma d) is a function of the reflection coefficient for each pore. Investigators have derived equations for sigma d based on the assumption that the protein osmotic pressure gradient across the membrane (delta II) does not vary from pore to pore. However, for most microvascular membranes, delta II probably does vary from pore to pore. In this study, we derived a new equation for sigma d. According to our equation, pore-to-pore differences in delta II increase the effect of small pores and decrease the effect of large pores on the overall membrane osmotic reflection coefficient. Thus sigma d for a heteroporous membrane may be much higher than previously derived equations indicate. Furthermore, pore-to-pore delta II differences increase the effect of plasma protein osmotic pressure to oppose microvascular fluid filtration. PMID:9277520
Acoustic Immittance, Absorbance, and Reflectance in the Human Ear Canal
Rosowski, John J.; Wilber, Laura Ann
2015-01-01
Ear canal measurements of acoustic immittance (a term that groups impedance and its inverse, admittance) and the related quantities of acoustic reflectance and power absorbance have been used to assess auditory function and aid in the differential diagnosis of conductive hearing loss for over 50 years. The change in such quantities after stimulation of the acoustic reflex also has been used in diagnosis. In this article, we define these quantities, describe how they are commonly measured, and discuss appropriate calibration procedures and standards necessary for accurate immittance/reflectance measurements.
On-Line Measurement of Lubricant Film Thickness Using Ultrasonic Reflection Coefficients
Drinkwater, B.W.; Dwyer-Joyce, R.S.; Harper, P.
2004-02-26
The ultrasonic reflectivity of a lubricant layer between two solid bodies depends on the ultrasonic frequency, the acoustic properties of the liquid and solid, and the layer thickness. In this paper, ultrasonic reflectivity measurements are used as a method for determining the thickness of lubricating films in bearing systems. An ultrasonic transducer is positioned on the outside of a bearing shell such that the wave is focused on the lubricant film layer. For a particular lubricant film the reflected pulse is processed to give a reflection coefficient spectrum. The lubricant film thickness is then obtained from either the layer stiffness or the resonant frequency. The method has been validated using static fluid wedges and the elastohydrodynamic film formed between a ball sliding on a flat. Film thickness values in the range 50-500 nm were recorded which agreed well with theoretical film formation predictions.
Choosing the averaging interval when calculating primary reflection coefficients from well logs
Walden, A.T.; Hosken, J.W.J.
1988-11-01
Most seismic data is processed using a sample interval of 4 ms two-way time (twt). The study of the statistical properties of primary reflection coefficients showed that the power spectrum of primaries can change noticeably when the logs are averaged over blocks of 0.5, 1 and 2 ms twt (block-averaging). What is a suitable block-averaging interval for producing broadband synthetics, and in particular how should the power spectrum of primaries be constructed when it is to be used to correct 4 ms sampled deconvolved seismic data for the effects of coloured primary reflectivity. In this paper the authors show that for a typical sonic log, a block-averaging interval of 1 ms twt should satisfy some important requirements. Firstly, it is demonstrated that if the reflection coefficients in an interval are not too large the effect of all the reflection impulses can be represented by another much sparser set at intervals of ..delta..t twt. The coefficient amplitudes are given by the differences in the logarithmic acoustic impedances, thus justifying block-averaging. However, a condition for this to hold up to the aliasing (Nyquist) frequency is that ..delta..t takes a maximum value of about 1 ms twt. Secondly, an event on a log should be represented in the seismic data. For this the acoustic impedance contrast must have sufficient lateral extent or continuity. By making some tentative suggestions on the relation between continuity and bed-thickness, a bed-thickness requirement of 0.15 m or more is obtained. Combining this requirement with the maximum number of beds allowable in an interval in order that multiple reflections do not contribute significantly to the reflections in the interval, again suggests a value of about 1 ms for the block-averaging interval.
Reflected wavefront manipulation based on ultrathin planar acoustic metasurfaces
Li, Yong; Liang, Bin; Gu, Zhong-ming; Zou, Xin-ye; Cheng, Jian-chun
2013-01-01
The introduction of metasurfaces has renewed the Snell's law and opened up new degrees of freedom to tailor the optical wavefront at will. Here, we theoretically demonstrate that the generalized Snell's law can be achieved for reflected acoustic waves based on ultrathin planar acoustic metasurfaces. The metasurfaces are constructed with eight units of a solid structure to provide discrete phase shifts covering the full 2π span with steps of π/4 by coiling up the space. By careful selection of the phase profiles in the transverse direction of the metasurfaces, some fascinating wavefront engineering phenomena are demonstrated, such as anomalous reflections, conversion of propagating waves into surface waves, planar aberration-free lens and nondiffracting Bessel beam generated by planar acoustic axicon. Our results could open up a new avenue for acoustic wavefront engineering and manipulations. PMID:23986034
Acoustic signalling reflects personality in a social mammal
Friel, Mary; Kunc, Hansjoerg P.; Griffin, Kym; Asher, Lucy; Collins, Lisa M.
2016-01-01
Social interactions among individuals are often mediated through acoustic signals. If acoustic signals are consistent and related to an individual's personality, these consistent individual differences in signalling may be an important driver in social interactions. However, few studies in non-human mammals have investigated the relationship between acoustic signalling and personality. Here we show that acoustic signalling rate is repeatable and strongly related to personality in a highly social mammal, the domestic pig (Sus scrofa domestica). Furthermore, acoustic signalling varied between environments of differing quality, with males from a poor-quality environment having a reduced vocalization rate compared with females and males from an enriched environment. Such differences may be mediated by personality with pigs from a poor-quality environment having more reactive and more extreme personality scores compared with pigs from an enriched environment. Our results add to the evidence that acoustic signalling reflects personality in a non-human mammal. Signals reflecting personalities may have far reaching consequences in shaping the evolution of social behaviours as acoustic communication forms an integral part of animal societies. PMID:27429775
Acoustic signalling reflects personality in a social mammal.
Friel, Mary; Kunc, Hansjoerg P; Griffin, Kym; Asher, Lucy; Collins, Lisa M
2016-06-01
Social interactions among individuals are often mediated through acoustic signals. If acoustic signals are consistent and related to an individual's personality, these consistent individual differences in signalling may be an important driver in social interactions. However, few studies in non-human mammals have investigated the relationship between acoustic signalling and personality. Here we show that acoustic signalling rate is repeatable and strongly related to personality in a highly social mammal, the domestic pig (Sus scrofa domestica). Furthermore, acoustic signalling varied between environments of differing quality, with males from a poor-quality environment having a reduced vocalization rate compared with females and males from an enriched environment. Such differences may be mediated by personality with pigs from a poor-quality environment having more reactive and more extreme personality scores compared with pigs from an enriched environment. Our results add to the evidence that acoustic signalling reflects personality in a non-human mammal. Signals reflecting personalities may have far reaching consequences in shaping the evolution of social behaviours as acoustic communication forms an integral part of animal societies. PMID:27429775
Distribution of reflection coefficients in absorbing chaotic microwave cavities.
Méndez-Sánchez, R A; Kuhl, U; Barth, M; Lewenkopf, C H; Stöckmann, H-J
2003-10-24
The distribution of reflection coefficients P(R) for chaotic microwave cavities with time-reversal symmetry is investigated in different absorption and antenna coupling regimes. For all regimes the agreement between experimental distributions and random-matrix theory predictions is very good, provided both the antenna coupling T(a) and the wall absorption strength T(w) are taken into account in an appropriate way. These parameters are determined by independent experimental quantities. PMID:14611349
Ma, Zhiyuan; Zhao, Yang; Luo, Zhongbing; Lin, Li
2014-04-01
The thermally grown oxide (TGO) growth at the interface of ceramic coating/bond coating in thermal barrier coatings (TBCs) was evaluated by ultrasonic reflection coefficient amplitude spectrum (URCAS). A theoretical analysis was performed about the influence of acoustic impedance match relationship between the ceramic coating and its adjacent media on URCAS. The immersion ultrasonic narrow pulse echo method was carried out on the TBC specimen before and after oxidation under 1050°C×1h for 15cycles. The resonant peaks of URCAS obtained before and after oxidation showed that TGO which generated between the ceramic coating and bond coating due to the oxidation, changed the acoustic impedance match between the ceramic coating and its adjacent media. This method is able to nondestructively characterize the generation of TGO in TBCs, and is important to practical engineering application. PMID:24359869
Ding, Juncai; Wu, Bin; He, Cunfu
2016-08-01
Compared with body waves, ultrasonic guided waves can provide more local characteristic information about the interface in the defect detection of adhesive structures. In the paper, the expressions of the reflection and transmission coefficients of the lowest SH mode (SH0) in multilayered plate-like adhesive structure were deduced on the basis of wave propagation controlling equations and tangential stiffness coefficient KT was contained in the expressions. Then, the expressions were compared with the previous results to verify their applicability and correctness. Then, aluminum/epoxy resin/aluminum adhesive structures were used to explore the effects of the changes in incident angle, frequency-thickness product and tangential stiffness coefficient on SH wave propagation characteristics in adhesive structures with different interface quality (perfect, weak bonding, and slip/debonding interfaces). The results showed that the propagation mode of SH wave in adhesive structures was mainly determined by the incident angle, frequency, adhesive layer thickness and tangential stiffness coefficient. With the increase in the frequency-thickness product, multi-order resonance is generated in the reflection and transmission coefficient curves of SH wave under the perfect and weak bonding interfaces. If proper values of the incident angle of acoustic waves and frequency-thickness product are selected, the perfect, weak bonding, and slip/debonding interfaces can be differentiated from each other, but the slip and debonding interfaces cannot be distinguished from each other. The study provides theoretical contribution to the detection of multilayered plate-like adhesive structure by SH wave. PMID:27236364
Scattering coefficients and gray-body factor for 1D BEC acoustic black holes: Exact results
NASA Astrophysics Data System (ADS)
Fabbri, Alessandro; Balbinot, Roberto; Anderson, Paul R.
2016-03-01
A complete set of exact analytic solutions to the mode equation is found in the region exterior to the acoustic horizon for a class of 1D Bose-Einstein condensate acoustic black holes. From these, analytic expressions for the scattering coefficients and gray-body factor are obtained. The results are used to verify previous predictions regarding the behaviors of the scattering coefficients and gray-body factor in the low-frequency limit.
Anomalous acoustic reflection on a sliding interface or a shear band.
Caroli, C; Velický, B
2003-06-01
We study the reflection of an acoustic plane wave from a steadily sliding planar interface with velocity-strengthening friction or a shear band in a confined granular medium. The corresponding acoustic impedance is utterly different from that of the static interface. In particular, the system being open, the energy of an in-plane polarized wave is no longer conserved, the work of the external pulling force being partitioned between frictional dissipation and gain (of either sign) of coherent acoustic energy. Large values of the friction coefficient favor energy gain, while velocity strengthening tends to suppress it. An interface with infinite elastic contrast (one rigid medium) and v-independent (Coulomb) friction exhibits spontaneous acoustic emission, as already shown by Nosonovsky and Adams [Int. J. Eng. Sci. 39, 1257 (2001)]. But this pathology is cured by a moderately large V strengthening of friction, or, for systems with not too large friction coefficients, by any finite elastic contrast. We show that (i) positive gain should be observable for rough-on-flat multicontact interfaces and (ii) a sliding shear band in a granular medium should give rise to sizable reflection, which opens a promising possibility for the detection of shear localization. PMID:16241215
Application of acoustic reflection tomography to sonar imaging.
Ferguson, Brian G; Wyber, Ron J
2005-05-01
Computer-aided tomography is a technique for providing a two-dimensional cross-sectional view of a three-dimensional object through the digital processing of many one-dimensional views (or projections) taken at different look directions. In acoustic reflection tomography, insonifying the object and then recording the backscattered signal provides the projection information for a given look direction (or aspect angle). Processing the projection information for all possible aspect angles enables an image to be reconstructed that represents the two-dimensional spatial distribution of the object's acoustic reflectivity function when projected on the imaging plane. The shape of an idealized object, which is an elliptical cylinder, is reconstructed by applying standard backprojection, Radon transform inversion (using both convolution and filtered backprojections), and direct Fourier inversion to simulated projection data. The relative merits of the various reconstruction algorithms are assessed and the resulting shape estimates compared. For bandpass sonar data, however, the wave number components of the acoustic reflectivity function that are outside the passband are absent. This leads to the consideration of image reconstruction for bandpass data. Tomographic image reconstruction is applied to real data collected with an ultra-wideband sonar transducer to form high-resolution acoustic images of various underwater objects when the sonar and object are widely separated. PMID:15957762
Linear-response reflection coefficient of the recorder air-jet amplifier.
Price, John C; Johnston, William A; McKinnon, Daniel D
2015-11-01
In a duct-flute such as the recorder, steady-state oscillations are controlled by two parameters, the blowing pressure and the frequency of the acoustic resonator. As in most feedback oscillators, the oscillation amplitude is determined by gain-saturation of the amplifier, and thus it cannot be controlled independently of blowing pressure and frequency unless the feedback loop is opened. In this work, the loop is opened by replacing the recorder body with a waveguide reflectometer: a section of transmission line with microphones, a signal source, and an absorbing termination. When the mean flow from the air-jet into the transmission line is not blocked, the air-jet amplifier is unstable to edge-tone oscillations through a feedback path that does not involve the acoustic resonator. When it is blocked, the air-jet is deflected somewhat outward and the system becomes stable. It is then possible to measure the reflection coefficient of the air-jet amplifier versus blowing pressure and acoustic frequency under linear response conditions, avoiding the complication of gain-saturation. The results provide a revealing test of flute drive models under the simplest conditions and with few unknown parameters. The strengths and weaknesses of flute drive models are discussed. PMID:26627801
Dispersionless Manipulation of Reflected Acoustic Wavefront by Subwavelength Corrugated Surface
Zhu, Yi-Fan; Zou, Xin-Ye; Li, Rui-Qi; Jiang, Xue; Tu, Juan; Liang, Bin; Cheng, Jian-Chun
2015-01-01
Free controls of optic/acoustic waves for bending, focusing or steering the energy of wavefronts are highly desirable in many practical scenarios. However, the dispersive nature of the existing metamaterials/metasurfaces for wavefront manipulation necessarily results in limited bandwidth. Here, we propose the concept of dispersionless wavefront manipulation and report a theoretical, numerical and experimental work on the design of a reflective surface capable of controlling the acoustic wavefront arbitrarily without bandwidth limitation. Analytical analysis predicts the possibility to completely eliminate the frequency dependence with a specific gradient surface which can be implemented by designing a subwavelength corrugated surface. Experimental and numerical results, well consistent with the theoretical predictions, have validated the proposed scheme by demonstrating a distinct phenomenon of extraordinary acoustic reflection within an ultra-broad band. For acquiring a deeper insight into the underlying physics, a simple physical model is developed which helps to interpret this extraordinary phenomenon and predict the upper cutoff frequency precisely. Generations of planar focusing and non-diffractive beam have also been exemplified. With the dispersionless wave-steering capability and deep discrete resolution, our designed structure may open new avenue to fully steer classical waves and offer design possibilities for broadband optical/acoustical devices. PMID:26077772
Dispersionless Manipulation of Reflected Acoustic Wavefront by Subwavelength Corrugated Surface.
Zhu, Yi-Fan; Zou, Xin-Ye; Li, Rui-Qi; Jiang, Xue; Tu, Juan; Liang, Bin; Cheng, Jian-Chun
2015-01-01
Free controls of optic/acoustic waves for bending, focusing or steering the energy of wavefronts are highly desirable in many practical scenarios. However, the dispersive nature of the existing metamaterials/metasurfaces for wavefront manipulation necessarily results in limited bandwidth. Here, we propose the concept of dispersionless wavefront manipulation and report a theoretical, numerical and experimental work on the design of a reflective surface capable of controlling the acoustic wavefront arbitrarily without bandwidth limitation. Analytical analysis predicts the possibility to completely eliminate the frequency dependence with a specific gradient surface which can be implemented by designing a subwavelength corrugated surface. Experimental and numerical results, well consistent with the theoretical predictions, have validated the proposed scheme by demonstrating a distinct phenomenon of extraordinary acoustic reflection within an ultra-broad band. For acquiring a deeper insight into the underlying physics, a simple physical model is developed which helps to interpret this extraordinary phenomenon and predict the upper cutoff frequency precisely. Generations of planar focusing and non-diffractive beam have also been exemplified. With the dispersionless wave-steering capability and deep discrete resolution, our designed structure may open new avenue to fully steer classical waves and offer design possibilities for broadband optical/acoustical devices. PMID:26077772
NASA Technical Reports Server (NTRS)
Hanson, Donald B.
1999-01-01
A reduced order modeling scheme has been developed for the unsteady acoustic and vortical coupling between blade rows of a turbomachine. The essential behavior of the system is governed by modal scattering coefficients (i.e., reflection and transmission coefficients) of the rotor, stator, inlet and nozzle, which are calculated as if they were connected to non-reflecting ducts. The objective of this report is to identify fundamental behavior of these scattering coefficients for a better understanding of the role of blade row reflection and transmission in noise generation. A 2D flat plate unsteady cascade model is used for the analysis with the expectation that the general behavior presented herein will carry over to models that include more realistic flow and geometry. It is shown that stators scatter input waves into many modes at the same frequency whereas rotors scatter on frequency, or harmonic order. Important cases are shown here the rotor reflection coefficient is greater than unity; a mode at blade passing frequency (BPF) traveling from the stator with unit sound power is reflected by the rotor with more than unit power at 2xBPF and 3xBPE Analysis is presented to explain this unexpected phenomenon. Scattering curves are presented in a format chosen for design use and for physical interpretation. To aid in interpretation of the curves, formulas are derived for special condition where waveforms are parallel to perpendicular to the rotor.
Design and Analysis of Underwater Acoustic Networks with Reflected Links
NASA Astrophysics Data System (ADS)
Emokpae, Lloyd
Underwater acoustic networks (UWANs) have applications in environmental state monitoring, oceanic profile measurements, leak detection in oil fields, distributed surveillance, and navigation. For these applications, sets of nodes are employed to collaboratively monitor an area of interest and track certain events or phenomena. In addition, it is common to find autonomous underwater vehicles (AUVs) acting as mobile sensor nodes that perform search-and-rescue missions, reconnaissance in combat zones, and coastal patrol. These AUVs are to work cooperatively to achieve a desired goal and thus need to be able to, in an ad-hoc manner, establish and sustain communication links in order to ensure some desired level of quality of service. Therefore, each node is required to adapt to environmental changes and be able to overcome broken communication links caused by external noise affecting the communication channel due to node mobility. In addition, since radio waves are quickly absorbed in the water medium, it is common for most underwater applications to rely on acoustic (or sound) rather than radio channels for mid-to-long range communications. However, acoustic channels pose multiple challenging issues, most notably the high transmission delay due to slow signal propagation and the limited channel bandwidth due to high frequency attenuation. Moreover, the inhomogeneous property of the water medium affects the sound speed profile while the signal surface and bottom reflections leads to multipath effects. In this dissertation, we address these networking challenges by developing protocols that take into consideration the underwater physical layer dynamics. We begin by introducing a novel surface-based reflection scheme (SBR), which takes advantage of the multipath effects of the acoustic channel. SBR works by using reflections from the water surface, and bottom, to establish non-line-of-sight (NLOS) communication links. SBR makes it possible to incorporate both line
Acoustic lens for marine seismic data multiple reflection noise reduction
Clark, W.H.
1986-11-25
This patent describes an apparatus for use in gathering seismic data in an area covered by a body of water having a surface, comprising: a seismic vessel; a seismic source towed by the seismic vessel for generating in the body of water an acoustic wave which will penetrate to and be reflected from at least one reflective horizon located below the body of water; a streamer towed by the seismic vessel in the body of water below its surface, including at least one hydrophone for detecting the acoustic wave reflected from at least one reflective horizon; a first gas dispensing tube and a second gas dispensing tube disposed in the water adjacent the vessel, the tubes each having a side wall and a plurality of perforations through the side wall for permitting gas bubbles to escape into the water; a first paravane attached to the first tube; a second paravane attached to the second tube; and control means connected to the first paravane and to the second paravane for controlling the position of the paravanes relative to the streamer.
Reconstructing surface wave profiles from reflected acoustic pulses.
Walstead, Sean P; Deane, Grant B
2013-05-01
Surface wave shapes are determined by analyzing underwater reflected acoustic signals. The acoustic signals (of nominal frequency 200 kHz) are forward scattered from the underside of surface waves that are generated in a wave tank and scaled to model smooth ocean swell. An inverse processing algorithm is designed and implemented to reconstruct the surface displacement profiles of the waves over one complete period. The inverse processing uses the surface scattered pulses collected at the receiver, an initial wave profile (two are considered), and a broadband forward scattering model based on Kirchhoff's diffraction formula to iteratively adjust the surface until it is considered optimized or reconstructed. Two physical length scales over which information can be known about the surface are confirmed. An outer length scale, the Fresnel zone surrounding each specular reflection point, is the only region where optimized surfaces resulting from each initial profile converge within a resolution set by the inner length scale, a quarter-wavelength of the acoustic pulse. The statistical confidence of each optimized surface is also highest within a Fresnel zone. Future design considerations are suggested such as an array of receivers that increases the region of surface reconstruction by a factor of 2 to 3. PMID:23654368
Characterization of Ion-Acoustic Wave Reflection Off A Plasma Chamber Wall
NASA Astrophysics Data System (ADS)
Berumen, Jorge; Chu, Feng; Hood, Ryan; Mattingly, Sean; Rogers, Anthony; Skiff, Fred
2015-11-01
We present an experimental characterization of the ion acoustic wave reflection coefficient off a plasma chamber wall. The experiment is performed in a cylindrical, magnetized, singly-ionized Argon inductively-coupled gas discharge plasma that is weakly collisional with typical conditions: n ~ 1010cm-3 Te ~ 3 eV and B ~ 1 kG. The main diagnostics are laser-induced fluorescence and Langmuir probe measurements. A survey of the ion velocity distribution function's zeroth and first order as well as density fluctuations at different wave excitation frequencies is obtained. Analysis of the reflection coefficient's dependence on the phase velocity and frequency of the wave is done through the characterization of waves utilizing Case-Van Kampen modes and the use of Morrison's G-transform. This research is supported by the Department of Energy under grant No. DOE DE-FG02-99ER54543.
Effect of Electron Reflection at the Anode on Ionization Coefficient
NASA Astrophysics Data System (ADS)
Takeda, Akihide; Ikuta, Nobuaki
2001-10-01
The ionization coefficient α is determined with the gradient of log I(I:ionization current) versus gap length d assuming the energy equilibrium over full gap space. However, the equilibrium in full space is difficult as well known. The α values in H2 reported by Haydon[1] and Satoh[2] show sudden breaking of increase with increase of reduced electric field E/p0 at less than 200 Vcm-1Torr. The relaxation of electron energy distribution in H2 is much slower than that in other gases due to the low values of inelastic cross sections in particular in high-energy range, accordingly in high E/p0 condition. Hayashi pointed out[3,4] that the breaking is due to the runaway of electrons. Many electrons are lost from the anode without sufficient ionization collisions with H_2. In such a situation, it is found that the electron reflection at the anode, the ratio is considerably large in practice, gives large increase in the measured values of α d. The effect of reflection on the values of α d in H2 with the change of E/p0 and p_0d will be reported. [1]S. C. Haydon and H. M. Stock: Aust. J. Phys. 24 pp.527-42(1966). [2]K. Satoh, T. Kudoh, T. Miki, M. Kawashima, H. Itoh and H. Tagashira: T. IEEE Jpn. 119-A pp.1136-41(1999) [3]M. Hayashi, M. Ohoka and A. Miwa: 18th ICPIG pp.14-15(1987) [4]M. Hayashi: 4th ICDG Vol.1 pp.195-198(1976)
Optimization of the acoustic absorption coefficients of certain functional absorbents
NASA Technical Reports Server (NTRS)
Pocsa, V.; Biborosch, L.; Veres, A.; Halpert, E.; Lorian, R.; Botos, T.
1974-01-01
The sound absorption coefficients of some functional absorbents (mineral wool plates) are determined by the reverberation chamber method. The influence of the angle of inclination of the sound absorbing material with respect to the surface to be treated is analyzed as well as the influence of the covering index, defined as the ratio of the designed area of a plate and the area of the treated surface belonging to another plate. As compared with the conventional method of applying sound-absorbing plates, the analyzed structures have a higher technological and economical efficiency. The optimum structure corresponds to an angle of inclination of 15 deg and a covering index of 0.8.
Acoustic speed and attenuation coefficient in sheep aorta measured at 5-9 MHz.
Fraser, Katharine H; Poepping, Tamie L; McNeilly, Alan; Megson, Ian L; Hoskins, Peter R
2006-06-01
B-mode ultrasound (US) images from blood vessels in vivo differ significantly from vascular flow phantom images. Phantoms with acoustic properties more closely matched to those of in vivo arteries may give better images. A method was developed for measuring the speed and attenuation coefficient of US over the range 5 to 9 MHz in samples of sheep aorta using a pulse-echo technique. The times-of-flight method was used with envelope functions to identify the reference points. The method was tested with samples of tissue-mimicking material of known acoustic properties. The tissue samples were stored in Krebs physiologic buffer solution and measured over a range of temperatures. At 37 degrees C, the acoustic speed and attenuation coefficient as a function of frequency in MHz were 1600 +/- 50 ms(-1) and 1.5 +/- 4f(0.94 +/- 1.3) dB cm(-1), respectively. PMID:16785018
Acoustical imaging of spheres above a reflecting surface
NASA Astrophysics Data System (ADS)
Chambers, David; Berryman, James
2003-04-01
An analytical study using the MUSIC method of subspace imaging is presented for the case of spheres above a reflecting boundary. The field scattered from the spheres and the reflecting boundary is calculated analytically, neglecting interactions between spheres. The singular value decomposition of the response matrix is calculated and the singular vectors divided into signal and noise subspaces. Images showing the estimated sphere locations are obtained by backpropagating the noise vectors using either the free space Green's function or the Green's function that incorporates reflections from the boundary. We show that the latter Green's function improves imaging performance after applying a normalization that compensates for the interference between direct and reflected fields. We also show that the best images are attained in some cases when the number of singular vectors in the signal subspace exceeds the number of spheres. This is consistent with previous analysis showing multiple eigenvalues of the time reversal operator for spherical scatterers [Chambers and Gautesen, J. Acoust. Soc. Am. 109 (2001)]. [Work performed under the auspices of the U.S. Department of Energy by the University of California, Lawrence Livermore National Laboratory under Contract No. W-7405-Eng-48.
NASA Astrophysics Data System (ADS)
Ohsaka, K.; Rednikov, A.; Sadhal, S. S.
2003-02-01
We present a technique that can be used to determine the thermal diffusivity coefficient of undercooled liquids, which exist at temperatures below their freezing points. The technique involves levitation of a small amount of liquid in a flattened drop shape using an acoustic levitator and heating it with a laser beam. The heated drop is then subjected to natural cooling by heat loss from the surface. Due to acoustic streaming, the heat loss mainly occurs through the equator section of the drop. The measured cooling rate in combination with a radial heat conduction model allows us to calculate the thermal diffusivity coefficient of the drop. We demonstrate the feasibility of the technique using glycerin drops as a model liquid. The technique is well suited if the thermal diffusivity coefficient of the liquid in the normal state (i.e., above the freezing point) is known or can be measured by conventional techniques.
Fracture identification based on remote detection acoustic reflection logging
NASA Astrophysics Data System (ADS)
Zhang, Gong; Li, Ning; Guo, Hong-Wei; Wu, Hong-Liang; Luo, Chao
2015-12-01
Fracture identification is important for the evaluation of carbonate reservoirs. However, conventional logging equipment has small depth of investigation and cannot detect rock fractures more than three meters away from the borehole. Remote acoustic logging uses phase-controlled array-transmitting and long sound probes that increase the depth of investigation. The interpretation of logging data with respect to fractures is typically guided by practical experience rather than theory and is often ambiguous. We use remote acoustic reflection logging data and high-order finite-difference approximations in the forward modeling and prestack reverse-time migration to image fractures. First, we perform forward modeling of the fracture responses as a function of the fracture-borehole wall distance, aperture, and dip angle. Second, we extract the energy intensity within the imaging area to determine whether the fracture can be identified as the formation velocity is varied. Finally, we evaluate the effect of the fracture-borehole distance, fracture aperture, and dip angle on fracture identification.
Air-ground interface: Surface waves, surface impedance and acoustic-to-seismic coupling coefficient
NASA Technical Reports Server (NTRS)
Daigle, Gilles; Embleton, Tony
1990-01-01
In atmospheric acoustics, the subject of surface waves has been an area of discussion for many years. The existence of an acoustic surface wave is now well established theoretically. The mathematical solution for spherical wave propagation above an impedance boundary includes the possibility of a contribution that possesses all the standard properties for a surface wave. Surface waves exist when the surface is sufficiently porous, relative to its acoustical resistance, that it can influence the airborne particle velocity near the surface and reduce the phase velocity of sound waves in air at the surface. This traps some of the sound energy in the air to remain near the surface as it propagates. Above porous grounds, the existence of surface waves has eluded direct experimental confirmation (pulse experiments have failed to show a separate arrival expected from the reduced phase speed) and indirect evidence for its existence has appeared contradictory. The experimental evidence for the existence of an acoustical surface wave above porous boundaries is reviewed. Recent measurements including pulse experiments are also described. A few years ago the acoustic impedance of a grass-covered surface was measured in the frequency range 30 to 300 Hz. Here, further measurements on the same site are discussed. These measurements include core samples, a shallow refractive survey to determine the seismic velocities, and measurements of the acoustic-to-seismic coupling coefficient.
Uncertainty estimation in seismo-acoustic reflection travel time inversion.
Dettmer, Jan; Dosso, Stan E; Holland, Charles W
2007-07-01
This paper develops a nonlinear Bayesian inversion for high-resolution seabed reflection travel time data including rigorous uncertainty estimation and examination of statistical assumptions. Travel time data are picked on seismo-acoustic traces and inverted for a layered sediment sound-velocity model. Particular attention is paid to picking errors which are often biased, correlated, and nonstationary. Non-Toeplitz data covariance matrices are estimated and included in the inversion along with unknown travel time offset (bias) parameters to account for these errors. Simulated experiments show that neglecting error covariances and biases can cause misleading inversion results with unrealistically high confidence. The inversion samples the posterior probability density and provides a solution in terms of one- and two-dimensional marginal probability densities, correlations, and credibility intervals. Statistical assumptions are examined through the data residuals with rigorous statistical tests. The method is applied to shallow-water data collected on the Malta Plateau during the SCARAB98 experiment. PMID:17614476
Microwave bulk-acoustic-wave reflection-grating resonators.
Oates, D E; Pan, J Y
1988-01-01
A technique for fabrication of bulk-acoustic-wave (BAW) resonators operating at fundamental frequencies between 1 and 10 GHz is presented. The resonators utilize a reflection grating made by optical holographic methods in iron-doped lithium niobate. Q factors of 30000 at 1 GHz have been demonstrated. Extension to Q of 10000 at 10 GHz appears feasible. Projected limitations to performance are discussed. The high Q at the high fundamental frequency directly results in low-phase noise. Phase-noise measurements of BAW resonator-stabilized oscillators operating at 1.14 GHz are presented. The single-sideband noise floor of <-140 dBc/Hz is shown to be in agreement with an analytical model. Projected improvements in the devices and circuits promise performance of <-160 dBc/Hz. PMID:18290157
Thermal diffusivity coefficient of glycerin determined on an acoustically levitated drop.
Ohsaka, K; Rednikov, A; Sadhal, S S
2002-10-01
We present a technique that can be used to determine the thermal diffusivity coefficient of undercooled liquids that exist at temperatures below their freezing points. The technique involves levitation of a small amount of liquid in the shape of a flattened drop using an acoustic levitator and heating it with a CO2 laser. The heated drop is then allowed to cool naturally by heat loss from the surface. Due to acoustic streaming, heat loss is highly non-uniform and appears to mainly occur at the drop circumference (equatorial region). This fact allows us to relate the heat loss rate with a heat transfer model to determine the thermal diffusion coefficient. We demonstrate the feasibility of the technique using glycerin drops as a model liquid. PMID:12446319
Mantsevich, S N
2016-08-01
Significant part of acousto-optic devices apply the acoustic beam reflection to arouse the desired type of acoustic mode propagating along the required direction in crystal. The influence of acoustic beam reflection process on the ultrasound field structure in the acousto-optic cell and the collinear acousto-optic diffraction characteristics is examined in this paper. The investigation is carried on the example of the collinear acousto-optic filter fabricated on the base of calcium molybdate crystal. It is shown that the reflection process changes the acoustic field structure and affects the acousto-optic filter transmission function shape and diffraction efficiency. PMID:27153373
Determining the nominal power transfer coefficient for passive surface acoustic wave devices
NASA Astrophysics Data System (ADS)
Timoshenko, A. N.; Palamarchuk, A. A.; Semenko, A. I.
1982-05-01
A method for calculating the nominal power transfer coefficient of passive SAW devices operating in a linear mode is described. Relations of practical importance are obtained, making it possible, on the basis of known characteristics of acousto-electric transducers and acoustic lines, to determine the losses incurred by devices when they are connected to radioelectronic equipment. The relations also permit an assessment of the uniformity of the amplitude-frequency characteristics of the devices.
Measurement of the absorption coefficient of acoustical materials using the sound intensity method
NASA Technical Reports Server (NTRS)
Atwal, Mahabir S.; Crocker, Malcolm J.
1987-01-01
In this study the possibility of using the two-microphone sound intensity technique to measure the normal incidence and the random incidence sound absorption coefficient was investigated. The normal incidence absorption coefficient was determined by measuring the intensity incidence on the sample and the intensity reflected by the sample placed in an anechoic chamber. The random incidence absorption coefficient was determined by measuring the intensity incident on the sample and the intensity reflected by the sample placed in a reverberation chamber. Absorption coefficient results obtained by the sound intensity technique were compared with standard techniques, namely the reverberation chamber and the standing wave tube. The major advantages of using the sound intensity technique are that it permits 'in situ' measurements and the absorption coefficient for a large range of frequencies can be obtained from a single measurement.
Influence of gas humidity on the reflection coefficient of multilayer dielectric mirrors.
Serdyukov, V I; Sinitsa, L N; Lugovskoi, A A
2016-06-10
The influence of water vapor on the reflection coefficient of multilayer mirrors was studied using a gas cell with multiple reflections from the mirrors. A strong change in the reflection coefficient of the mirrors (up to 0.9%) was found when water vapor under a pressure of 23 mbar was injected into the cell, which was interpreted as a change in the refraction index of the layers of multilayer coatings when water vapor penetrated into the porous coating structure. PMID:27409037
Two dimensional investigation of ion acoustic waves reflection from the sheath
Cartwright, K.L.; Birdsall, C.K.
1995-12-31
Preliminary results show that oblique ion waves propagate from the bulk plasma into and all the way through the sheath in both 1D and 2D simulation. These waves are launched from one side of the system with a AC voltage or a current source with a frequency less than the ion plasma frequency. The one and initial two dimensional PIC simulations show the details of densities, potentials, fields, particle moments and time-distance plots of the average density minus the instantaneous density. From the time-distance plot the direction and magnitude of the ion acoustic wave is measured. From this the coefficients of reflection and transmission as a function of the incident angle is calculated. The observations are compared with laboratory experiments and theory.
Determination of the Accommodation Coefficient Using Vapor/gas Bubble Dynamics in an Acoustic Field
NASA Technical Reports Server (NTRS)
Gumerov, Nail A.; Hsiao, Chao-Tsung; Goumilevski, Alexei G.; Allen, Jeff (Technical Monitor)
2001-01-01
Nonequilibrium liquid/vapor phase transformations can occur in superheated or subcooled liquids in fast processes such as in evaporation in a vacuum. The rate at which such a phase transformation occurs depends on the "condensation" or "accommodation" coefficient, Beta, which is a property of the interface. Existing measurement techniques for Beta are complex and expensive. The development of a relatively inexpensive and reliable technique for measurement of Beta for a wide range of substances and temperatures is of great practical importance. The dynamics of a bubble in an acoustic field strongly depends on the value of Beta. It is known that near the saturation temperature, small vapor bubbles grow under the action of an acoustic field due to "rectified heat transfer." This finding can be used as the basis for an effective measurement technique of Beta. We developed a theory of vapor bubble behavior in an isotropic acoustic wave and in a plane standing acoustic wave. A numerical code was developed which enables simulation of a variety of experimental situations and accurately takes into account slowly evolving temperature. A parametric study showed that the measurement of Beta can be made over a broad range of frequencies and bubble sizes. We found several interesting regimes and conditions which can be efficiently used for measurements of Beta. Measurements of Beta can be performed in both reduced and normal gravity environments.
On the subtraction method for in-situ reflection and diffusion coefficient measurements.
Robinson, Philip; Xiang, Ning
2010-03-01
The subtraction method is a technique critical to several important acoustic measurements. It involves subtracting a reference measurement including only direct sound from one with direct sound and a reflection, to isolate the reflection. The process is very sensitive to environmental conditions, such as changes in temperature, air movement, and microphone positioning. These variations cause small time differences between the reference and reflection measurements, which prevent complete subtraction of the direct sound; the residual direct sound then pollutes analysis of the isolated reflection. This work evaluates methods to compensate for differences to achieve minimal interference from the residual direct sound. PMID:20329814
NASA Astrophysics Data System (ADS)
Blackstock, David T.
1987-07-01
Research on four topics in nonlinear acoustics is described. (1) Dependence of three coefficients of nonlinearity for sea water on pressure, temperature, and density. Computation of the coefficients from a combination of theoretical and empirical relations is in progress. (2) Nonlinear, noncollinear interaction of sound waves. Three journal articles have been written, two on interaction in a rectangular waveguide and one on coefficient of nonlinearity for collinear and noncollinear interaction. (3) Reflection and refraction of finite amplitude sound at a plane interface between two fluids. A new form of Snell's law valid for waves of finite amplitude is derived. An experiment to test the implications of the new law is being carried out. (4) Scattering of sound by sound. The classical problem of the secondary radiation produced by interaction of two crossed sound beams is discussed. An experimental test of recent theoretical treatments is in preparation. A preliminary experiment is the measurement of the range dependence of finger lobes in the second harmonic radiation produced in the field of a monochromatically driven piston.
Directional Reflective Surface Formed via Gradient-Impeding Acoustic Meta-Surfaces
Song, Kyungjun; Kim, Jedo; Hur, Shin; Kwak, Jun-Hyuk; Lee, Seong-Hyun; Kim, Taesung
2016-01-01
Artificially designed acoustic meta-surfaces have the ability to manipulate sound energy to an extraordinary extent. Here, we report on a new type of directional reflective surface consisting of an array of sub-wavelength Helmholtz resonators with varying internal coiled path lengths, which induce a reflection phase gradient along a planar acoustic meta-surface. The acoustically reshaped reflective surface created by the gradient-impeding meta-surface yields a distinct focal line similar to a parabolic cylinder antenna, and is used for directive sound beamforming. Focused beam steering can be also obtained by repositioning the source (or receiver) off axis, i.e., displaced from the focal line. Besides flat reflective surfaces, complex surfaces such as convex or conformal shapes may be used for sound beamforming, thus facilitating easy application in sound reinforcement systems. Therefore, directional reflective surfaces have promising applications in fields such as acoustic imaging, sonic weaponry, and underwater communication. PMID:27562634
Directional Reflective Surface Formed via Gradient-Impeding Acoustic Meta-Surfaces.
Song, Kyungjun; Kim, Jedo; Hur, Shin; Kwak, Jun-Hyuk; Lee, Seong-Hyun; Kim, Taesung
2016-01-01
Artificially designed acoustic meta-surfaces have the ability to manipulate sound energy to an extraordinary extent. Here, we report on a new type of directional reflective surface consisting of an array of sub-wavelength Helmholtz resonators with varying internal coiled path lengths, which induce a reflection phase gradient along a planar acoustic meta-surface. The acoustically reshaped reflective surface created by the gradient-impeding meta-surface yields a distinct focal line similar to a parabolic cylinder antenna, and is used for directive sound beamforming. Focused beam steering can be also obtained by repositioning the source (or receiver) off axis, i.e., displaced from the focal line. Besides flat reflective surfaces, complex surfaces such as convex or conformal shapes may be used for sound beamforming, thus facilitating easy application in sound reinforcement systems. Therefore, directional reflective surfaces have promising applications in fields such as acoustic imaging, sonic weaponry, and underwater communication. PMID:27562634
ERIC Educational Resources Information Center
Cordon, Gabriela B.; Lagorio, M. Gabriela
2007-01-01
A biophysical-chemistry experiment, based on the reflectance spectroscopy for calculating the absorption and scattering coefficients of leaves is described. The results show that different plants species exhibit different values for both the coefficients because of their different pigment composition.
Zhang, Shuzeng; Li, Xiongbing; Jeong, Hyunjo Cho, Sungjong
2015-07-15
A novel method to determine acoustic parameters involved in measuring the nonlinearity parameter of fluids or solids is proposed. The approach is based on the measurement of fundamental and second harmonic pressures with a calibrated receiver, and on a nonlinear least squares data-fitting to multi-Gaussian beam (MGB) equations which explicitly define the attenuation and diffraction effects in the quasilinear regime. Results obtained in water validate the proposed method. The choice of suitable source pressure is discussed with regard to the quasilinear approximation involved. The attenuation coefficients are also acquired in nonlinear regime and their relations are discussed.
Acoustics Reflections of Full-Scale Rotor Noise Measurements in NFAC 40- by 80-Foot Wind Tunnel
NASA Technical Reports Server (NTRS)
Barbely, Natasha Lydia; Kitaplioglu, Cahit; Sim, Ben W.
2012-01-01
The objective of current research is to identify the extent of acoustic time history distortions due to wind tunnel wall reflections. Acoustic measurements from the recent full-scale Boeing-SMART rotor test (Fig. 2) will be used to illustrate the quality of noise measurement in the NFAC 40- by 80-Foot Wind Tunnel test section. Results will be compared to PSU-WOPWOP predictions obtained with and without adjustments due to sound reflections off wind tunnel walls. Present research assumes a rectangular enclosure as shown in Fig. 3a. The Method of Mirror Images7 is used to account for reflection sources and their acoustic paths by introducing mirror images of the rotor (i.e. acoustic source), at each and every wall surface, to enforce a no-flow boundary condition at the position of the physical walls (Fig. 3b). While conventional approach evaluates the "combined" noise from both the source and image rotor at a single microphone position, an alternative approach is used to simplify implementation of PSU-WOPWOP for this reflection analysis. Here, an "equivalent" microphone position is defined with respect to the source rotor for each mirror image that effectively renders the reflection analysis to be a one rotor, multiple microphones problem. This alternative approach has the advantage of allowing each individual "equivalent" microphone, representing the reflection pulse from the associated wall surface, to be adjusted by the panel absorption coefficient illustrated in Fig. 1a. Note that the presence of parallel wall surfaces requires an infinite number of mirror images (Fig. 3c) to satisfy the no-flow boundary conditions. In the present analysis, up to four mirror images (per wall surface) are accounted to achieve convergence in the predicted time histories
The reflection coefficient in stimulated parametric backscattering. [in laser-heated plasmas
NASA Technical Reports Server (NTRS)
Yu, C.; Hsu, H.
1977-01-01
The step-function approximation of the anomalous reflection coefficient in laser-induced parametric backscattering currently used in the theory of nonlinear laser plasma interactions is improved using a simple exponential derived from elliptic functions. The validity of the single-reflection analysis is reaffirmed.
The role of the reflection coefficient in precision measurement of ultrasonic attenuation
NASA Technical Reports Server (NTRS)
Generazio, E. R.
1984-01-01
Ultrasonic attenuation measurements using contact, pulse-echo techniques are sensitive to surface roughness and couplant thickness variations. This can reduce considerable inaccuracies in the measurement of the attenuation coefficient for broadband pulses. Inaccuracies arise from variations in the reflection coefficient at the buffer-couplant-sample interface. The reflection coefficient is examined as a function of the surface roughness and corresponding couplant thickness variations. Interrelations with ultrasonic frequency are illustrated. Reliable attenuation measurements are obtained only when the frequency dependence of the reflection coefficient is incorporated in signal analysis. Data are given for nickel 200 samples and a silicon nitride ceramic bar having surface roughness variations in the 0.3 to 3.0 microns range for signal bandwidths in the 50 to 100 MHz range.
The role of the reflection coefficient in precision measurement of ultrasonic attenuation
NASA Technical Reports Server (NTRS)
Generazio, E. R.
1985-01-01
Ultrasonic attenuation measurements using contact, pulse-echo techniques are sensitive to surface roughness and couplant thickness variations. This can reduce considerable inaccuracies in the measurement of the attenuation coefficient for broadband pulses. Inaccuracies arise from variations in the reflection coefficient at the buffer-couplant-sample interface. The reflection coefficient is examined as a function of the surface roughness and corresponding couplant thickness variations. Interrelations with ultrasonic frequency are illustrated. Reliable attenuation measurements are obtained only when the frequency dependence of the reflection coefficient is incorporated in signal analysis. Data are given for nickel 200 samples and a silicon nitride ceramic bar having surface roughness variations in the 0.3 to 3.0 microns range for signal bandwidths in the 50 to 100 MHz range.
Incidence-angle-dependent acoustic reflections from liquid-saturated porous solids
NASA Astrophysics Data System (ADS)
Bouzidi, Youcef; Schmitt, Douglas R.
2012-12-01
Angle of incidence amplitude variations of acoustic waves reflected from an interface is increasingly important in acoustic sea floor imaging and seismological studies. Such observations are almost solely interpreted assuming elastic wave theory. However, wave propagation through, and hence reflectivity from, liquid-saturated porous solids is complicated by the presence of the slow longitudinal (P2) wave. There have only been limited quantitative experimental tests of porous media reflectivity as a function of angle of incidence. Here, the acoustic reflectivity from a water-saturated porous plate is measured as a function of the angle of incidence using a specially developed ultrasonic reflectometer. The observed reflectivity agrees with that predicted using the Biot-type poroelastic theory; this work confirms the use of boundary conditions that allow fluid transfer across the reflecting interface. It is found that simpler elastic expressions based on equivalent-elastic solid cannot be reconciled with the observations.
NASA Astrophysics Data System (ADS)
Buchanan, James L.; Gilbert, Robert P.; Ou, Miao-jung Y.
2011-12-01
Estimating the parameters of an elastic or poroelastic medium from reflected or transmitted acoustic data is an important but difficult problem. Use of the Nelder-Mead simplex method to minimize an objective function measuring the discrepancy between some observable and its value calculated from a model for a trial set of parameters has been tried by several authors. In this paper, the difficulty with this direct approach, which is the existence of numerous local minima of the objective function, is documented for the in vitro experiment in which a specimen in a water tank is subject to an ultrasonic pulse. An indirect approach, based on the numerical solution of the equations for a set of ‘effective’ velocities and transmission coefficients, is then observed empirically to ameliorate the difficulties posed by the direct approach.
NASA Astrophysics Data System (ADS)
Deryabin, M. S.; Kasyanov, D. A.; Kurin, V. V.; Garasyov, M. A.
2016-05-01
We show that a significant energy redistribution occurs in the spectrum of reflected nonlinear waves, when an intense acoustic beam is reflected from an acoustically soft boundary, which manifests itself at short wave distances from a reflecting boundary. This effect leads to the appearance of extrema in the distributions of the amplitude and intensity of the field of the reflected acoustic beam near the reflecting boundary. The results of physical experiments are confirmed by numerical modeling of the process of transformation of nonlinear waves reflected from an acoustically soft boundary. Numerical modeling was performed by means of the Khokhlov—Zabolotskaya—Kuznetsov (KZK) equation.
NASA Astrophysics Data System (ADS)
Deryabin, M. S.; Kasyanov, D. A.; Kurin, V. V.; Garasyov, M. A.
2016-06-01
We show that a significant energy redistribution occurs in the spectrum of reflected nonlinear waves, when an intense acoustic beam is reflected from an acoustically soft boundary, which manifests itself at short wave distances from a reflecting boundary. This effect leads to the appearance of extrema in the distributions of the amplitude and intensity of the field of the reflected acoustic beam near the reflecting boundary. The results of physical experiments are confirmed by numerical modeling of the process of transformation of nonlinear waves reflected from an acoustically soft boundary. Numerical modeling was performed by means of the Khokhlov—Zabolotskaya—Kuznetsov (KZK) equation.
NASA Astrophysics Data System (ADS)
Jenerowicz, Agnieszka; Walczykowski, Piotr
2015-10-01
Monitoring of water environment and ecosystem, detecting water contaminants and understanding water quality parameters are most important tasks in water management and protection of whole aquatic environment. Detection of biological contaminants play a very important role in preserving human health and water management. To obtain accurate and precise results of determination of the level of biological contamination and to distinguish its type it is necessary to determine precisely spectral reflectance coefficients of several water biological pollutants with inter alia spectroradiometer. This paper presents a methodology and preliminary results of acquisition of spectral reflectance coefficients with different reference panels (e.g. with 5%, 20%, 50%, 80% and 96% of reflectivity) of several biological pollutants. The authors' main task was to measure spectral reflectance coefficients of different biological water pollutants with several reference panels and to select optimal reference standard, which would allow for distinguish different types of several biological contaminants. Moreover it was necessary to indicate the spectral range in which it is possible to discriminate investigated samples of biological contaminants. By conducting many series of measurements of several samples of different types of biological pollutants, authors had concluded how the reflectivity of reference panel influences the accuracy of acquisition of spectral reflectance coefficients. This research was crucial in order to be able to distinguish several types of biological pollutants and to determine the useful spectral range for detection of different kinds of biological contaminants with multispectral and hyperspectral imagery.
Measurement of reflection coefficients of organic and non-organic media and materials in UV spectrum
NASA Astrophysics Data System (ADS)
Klimkin, A. V.; Belov, V. V.; Vorobieva, L. P.; Prokopev, V. E.; Kurjak, A. V.; Sokovikov, V. G.
2015-12-01
Measurements of the diffuse reflection coefficients of organic and inorganic materials and media in solid, granular and liquid forms were made in the UV field of 230-400 nm. A single channel spectrometer with an integrating sphere was used. Relation between diffuse reflection coefficients and the structure and composition of the samples is discussed. These data allow us to estimate the prospect of machine vision systems application for the UV range in such areas as biology, geology, remote control of materials and media.
Decay of photoinduced oscillations of the optical reflection coefficient of bismuth
Semenov, A. L.
2013-07-15
A model describing the decay of photoinduced oscillations of the optical reflection coefficient R of bismuth is constructed, taking the crystal lattice anharmonicity into account. The decay time of oscillations of R is calculated as a function of the energy density of a laser pulse. The results of calculations explain the experimental data on the anomalously strong decay of oscillations of the optical reflection coefficient of bismuth (the decay time decreases by more than an order of magnitude with an increase in the laser pulse energy density from 0 to 4 mJ/cm{sup 2})
NASA Astrophysics Data System (ADS)
Muralidhar, Karthik; Li, Kwok Hung; George, Sapna
To attain good performance in an acoustic echo cancellation system, it is important to have a variable step size (VSS) algorithm as part of an adaptive filter. In this paper, we are concerned with the development of a VSS algorithm for a recently proposed subband affine projection (SAP) adaptive filter. Two popular VSS algorithms in the literature are the methods of delayed coefficients (DC) and variable regularization (VR). However, the merits and demerits of them are mutually exclusive. We propose a VSS algorithm* that is a hybrid of both methods and combines their advantages. An extensive study of the new algorithm in different scenarios like the presence double-talk (DT) during the transient phase of the adaptive filter, DT during steady state, and varying DT power is conducted and reasoning is given to support the observed behavior. The importance of the method of VR as part of a VSS algorithm is emphasized.
Nonlinear reflection and refraction of planar ion-acoustic plasma solitons
NASA Astrophysics Data System (ADS)
Nagasawa, T.; Nishida, Y.
1986-06-01
Experimental observations on the reflection and refraction of a planar ion-acoustic soliton from a metallic mesh electrode are performed in a uniform double-plasma device. Reflection and refraction angles are observed to depend on the incident wave amplitude, showing a nonlinear Snell's law.
The far field diffraction pattern for corner reflectors with complex reflection coefficients
NASA Technical Reports Server (NTRS)
Chang, R. F.; Currie, D. G.; Alley, C. O.; Pittman, M. E.
1970-01-01
The far field diffraction pattern of a geometrically perfect corner reflector is examined analytically for normally incident monochromatic light. The states of polarization and the complex amplitudes of the emerging light are expressed through transformation matrices in terms of those of the original incident light for each sextant of the face in a single coordinate system. The analytic expression of the total diffraction pattern is obtained for a circular face. This expression consists of three component functions in addition to the basic Airy function. The coefficient of each function is expressed in terms of complex coefficients of reflectance of the reflecting surface. Some numerical results for different reflecting surfaces, including total internal reflection, are presented. The iso-intensity contours of the diffraction pattern evaluated from the analytical expressions for an uncoated solid corner reflector are also presented along with the photographs of the pattern.
Mach stem formation in reflection and focusing of weak shock acoustic pulses.
Karzova, Maria M; Khokhlova, Vera A; Salze, Edouard; Ollivier, Sébastien; Blanc-Benon, Philippe
2015-06-01
The aim of this study is to show the evidence of Mach stem formation for very weak shock waves with acoustic Mach numbers on the order of 10(-3) to 10(-2). Two representative cases are considered: reflection of shock pulses from a rigid surface and focusing of nonlinear acoustic beams. Reflection experiments are performed in air using spark-generated shock pulses. Shock fronts are visualized using a schlieren system. Both regular and irregular types of reflection are observed. Numerical simulations are performed to demonstrate the Mach stem formation in the focal region of periodic and pulsed nonlinear beams in water. PMID:26093452
Seismic Rheological Model and Reflection Coefficients of the Brittle-Ductile Transition
NASA Astrophysics Data System (ADS)
Carcione, José M.; Poletto, Flavio
2013-12-01
It is well established that the upper—cooler—part of the crust is brittle, while deeper zones present ductile behaviour. In some cases, this brittle-ductile transition is a single seismic reflector with an associated reflection coefficient. We first develop a stress-strain relation including the effects of crust anisotropy, seismic attenuation and ductility in which deformation takes place by shear plastic flow. Viscoelastic anisotropy is based on the eigenstrain model and the Zener and Burgers mechanical models are used to model the effects of seismic attenuation, velocity dispersion, and steady-state creep flow, respectively. The stiffness components of the brittle and ductile media depend on stress and temperature through the shear viscosity, which is obtained by the Arrhenius equation and the octahedral stress criterion. The P- and S-wave velocities decrease as depth and temperature increase due to the geothermal gradient, an effect which is more pronounced for shear waves. We then obtain the reflection and transmission coefficients of a single brittle-ductile interface and of a ductile thin layer. The PP scattering coefficient has a Brewster angle (a sign change) in both cases, and there is substantial PS conversion at intermediate angles. The PP coefficient is sensitive to the layer thickness, unlike the SS coefficient. Thick layers have a well-defined Brewster angle and show higher reflection amplitudes. Finally, we compute synthetic seismograms in a homogeneous medium as a function of temperature.
A Simple Student Laboratory on Osmotic Flow, Osmotic Pressure, and the Reflection Coefficient.
ERIC Educational Resources Information Center
Feher, Joseph J.; Ford, George D.
1995-01-01
Describes a laboratory exercise containing a practical series of experiments that novice students can perform within two hours. The exercise provides a confirmation of van't Hoff's law while placing more emphasis on osmotic flow than pressure. Students can determine parameters such as the reflection coefficient which stress the interaction of both…
An improved six-port technique for measuring complex reflection coefficient
NASA Astrophysics Data System (ADS)
Rafal, M. D.
1980-03-01
Current realizations of the Six-Port technique for measuring the complex reflection coefficient require accurate information about the system calibration constants. An examination of the sensitivity of the solution of the reflection coefficient to calibration constants is undertaken. An improved set of design specifications is derived based on the sensitivity of the solution and constraints on power measurement accuracy. It has been recognized that the system equations for the Six-Port are an overdetermined set of equations. Previously, this overdeterminedness has not been used to reduce the sensitivity of the solution of the reflection coefficient to variation of the calibration constants. An algorithm is described which makes use of the extra calibration constants. A Fortran program is presented which implements the algorithm. A hardware realization based on the improved set of design specifications is described. The circuit operates at a center frequency of 900 MHz and performs over a 16% band of frequencies without recalibration. Errors in phase measurement for this Six-Port implementation are less than two degrees except at the band edges. Errors in magnitude measurement are less than 10% except for measurements of small values of reflection coefficient magnitude (0.3) for which errors are 20%.
NASA Astrophysics Data System (ADS)
Yang, H. Z.; Chen, Y. J.; Leong, S. H.; An, C. W.; Ye, K. D.; Hu, J. F.
2015-08-01
With increased interest in heat assisted magnetic recording (HAMR), the thermal reflection coefficient of HAMR media becomes more important, as it is related to the change of optical parameters of the media at different temperatures and can potentially be used for non-contact temperature measurement. In this report, we introduce a method to calibrate the thermal reflection coefficient of magnetic thin films by in situ measurement of the thermal reflectance as well as the magneto-optic Kerr effect (MOKE) signal from the media. In the measurement, we use one beam to locally heat up the media, while using a second beam, whose diameter and intensity is much smaller, to measure in situ the MOKE and thermal reflectance signal of the heated media. We characterize the media temperature by heating up the magnetic media with prewritten magnetic patterns in an ultra-high vacuum system and the resulting magnetic remanence in the prewritten area is measured by magnetic force microscopy. Thus the thermal reflection coefficient is measured by performing a pump-probe experiment, with the temperature calibrated at the zero thermoremanence temperature of the HAMR media, at which temperature all grains under test have reached Curie temperature. This method can be extended to comparative studies of the thermo-optical properties of magnetic thin films, whose magnetic properties are sensitive to temperature.
NASA Astrophysics Data System (ADS)
Orych, A.; Walczykowski, P.; Jenerowicz, A.; Zdunek, Z.
2014-11-01
Nowadays remote sensing plays a very important role in many different study fields, i.e. environmental studies, hydrology, mineralogy, ecosystem studies, etc. One of the key areas of remote sensing applications is water quality monitoring. Understanding and monitoring of the water quality parameters and detecting different water contaminants is an important issue in water management and protection of whole environment and especially the water ecosystem. There are many remote sensing methods to monitor water quality and detect water pollutants. One of the most widely used method for substance detection with remote sensing techniques is based on usage of spectral reflectance coefficients. They are usually acquired using discrete methods such as spectrometric measurements. These however can be very time consuming, therefore image-based methods are used more and more often. In order to work out the proper methodology of obtaining spectral reflectance coefficients from hyperspectral and multispectral images, it is necessary to verify the impact of cameras radiometric resolution on the accuracy of determination of them. This paper presents laboratory experiments that were conducted using two monochromatic XEVA video sensors (400-1700 nm spectral data registration) with two different radiometric resolutions (12 and 14 bits). In view of determining spectral characteristics from images, the research team used set of interferometric filters. All data collected with multispectral digital video cameras were compared with spectral reflectance coefficients obtained with spectroradiometer. The objective of this research is to find the impact of cameras radiometric resolution on reflectance values in chosen wavelength. The main topic of this study is the analysis of accuracy of spectral coefficients from sensors with different radiometric resolution. By comparing values collected from images acquired with XEVA sensors and with the curves obtained with spectroradiometer it
Echo thresholds for reflections from acoustically diffusive architectural surfaces.
Robinson, Philip W; Walther, Andreas; Faller, Christof; Braasch, Jonas
2013-10-01
When sound reflects from an irregular architectural surface, it spreads spatially and temporally. Extensive research has been devoted to prediction and measurement of diffusion, but less has focused on its perceptual effects. This paper examines the effect of temporal diffusion on echo threshold. There are several notable differences between the waveform of a reflection identical to the direct sound and one from an architectural surface. The onset and offset are damped and the energy is spread in time; hence, the reflection response has a lower peak amplitude, and is decorrelated from the direct sound. The perceptual consequences of these differences are previously undocumented. Echo threshold tests are conducted with speech and music signals, using direct sound and a simulated reflection that is either identical to the direct sound or has various degrees of diffusion. Results indicate that for a speech signal, diffuse reflections are less easily detectable as a separate auditory event than specular reflections of the same total energy. For a music signal, no differences are observed between the echo thresholds for reflections with and without temporal diffusion. Additionally, echo thresholds are found to be shorter for speech than for music, and shorter for spatialized than for diotic presentation of signals. PMID:24116414
NASA Astrophysics Data System (ADS)
Samatham, Ravikant; Jacques, Steven L.
2013-02-01
Different techniques have been developed to determine the optical properties of turbid media, which include collimated transmission, diffuse reflectance, adding-doubling and goniometry. While goniometry can be used to determine the anisotropy of scattering (g), other techniques are used to measure the absorption coefficient and reduced scattering coefficient (μs(1-g)). But separating scattering coefficient (μs) and anisotropy of scattering from reduced scattering coefficient has been tricky. We developed an algorithm to determine anisotropy of scattering from the depth dependent decay of reflectance-mode confocal scanning laser microscopy (rCSLM) data. This report presents the testing of the algorithm on tissue phantoms with different anisotropies (g = 0.127 to 0.868, at 488 nm wavelength). Tissue phantoms were made from polystyrene microspheres (6 sizes 0.1-0.5 μm dia.) dispersed in both aqueous solutions and agarose gels. Three dimensional images were captured. The rCSLM-signal followed an exponential decay as a function of depth of the focal volume, R(z)ρexp(-μz) where ρ (dimensionless, ρ = 1 for a mirror) is the local reflectivity and μ [cm-1] is the exponential decay constant. The theory was developed to uniquely map the experimentally determined μ and ρ into the optical scattering properties μs and g. The values of μs and g depend on the composition and microstructure of tissues, and allow characterization of a tissue.
NASA Astrophysics Data System (ADS)
Petruk, V. G.; Ivanov, A. P.; Kvaternyuk, S. M.; Barun, V. V.
2016-03-01
We have designed an experimental setup, based on two integrating spheres, that lets us measure the optical diffuse reflectance spectra (diffuse reflection coefficient vs. wavelength) of human skin quickly under clinical conditions in vivo. For the wavelength interval 520-1100 nm, we give the values of the diffuse reflection coefficient for healthy tissue, skin with a benign nevus, and skin with a malignant melanoma for a large group of test subjects. We experimentally established a number of wavelengths in the red-near IR region of the spectrum which can be used for early differential diagnosis of nevi and melanoma in patient cancer screening. According to the Kramer-Welch test, the probability of the diffuse reflection coefficient for skin with melanoma and a nevus having different distributions is >0.94, and at many wavelengths it is >0.999. By solving the inverse problem, we estimated the changes in a number of structural and biophysical parameters of the tissue on going from healthy skin to nevus and melanoma. The results obtained can provide a basis for developing a clinical approach to identifying the risk of malignant transformation of the skin before surgery and histological analysis of the tissue.
Franco, Ediguer E; Adamowski, Julio C; Buiochi, Flávio
2010-05-01
Real-time viscosity measurement remains a necessity for highly automated industry. To resolve this problem, many studies have been carried out using an ultrasonic shear wave reflectance method. This method is based on the determination of the complex reflection coefficient's magnitude and phase at the solid-liquid interface. Although magnitude is a stable quantity and its measurement is relatively simple and precise, phase measurement is a difficult task because of strong temperature dependence. A simplified method that uses only the magnitude of the reflection coefficient and that is valid under the Newtonian regimen has been proposed by some authors, but the obtained viscosity values do not match conventional viscometry measurements. In this work, a mode conversion measurement cell was used to measure glycerin viscosity as a function of temperature (15 to 25 degrees C) and corn syrup-water mixtures as a function of concentration (70 to 100 wt% of corn syrup). Tests were carried out at 1 MHz. A novel signal processing technique that calculates the reflection coefficient magnitude in a frequency band, instead of a single frequency, was studied. The effects of the bandwidth on magnitude and viscosity were analyzed and the results were compared with the values predicted by the Newtonian liquid model. The frequency band technique improved the magnitude results. The obtained viscosity values came close to those measured by the rotational viscometer with percentage errors up to 14%, whereas errors up to 96% were found for the single frequency method. PMID:20442023
NASA Technical Reports Server (NTRS)
Lei, Ning; Chiang, Kwo-Fu; Oudrari, Hassan; Xiong, Xiaoxiong
2011-01-01
Optical sensors aboard Earth orbiting satellites such as the next generation Visible/Infrared Imager/Radiometer Suite (VIIRS) assume that the sensors radiometric response in the Reflective Solar Bands (RSB) is described by a quadratic polynomial, in relating the aperture spectral radiance to the sensor Digital Number (DN) readout. For VIIRS Flight Unit 1, the coefficients are to be determined before launch by an attenuation method, although the linear coefficient will be further determined on-orbit through observing the Solar Diffuser. In determining the quadratic polynomial coefficients by the attenuation method, a Maximum Likelihood approach is applied in carrying out the least-squares procedure. Crucial to the Maximum Likelihood least-squares procedure is the computation of the weight. The weight not only has a contribution from the noise of the sensor s digital count, with an important contribution from digitization error, but also is affected heavily by the mathematical expression used to predict the value of the dependent variable, because both the independent and the dependent variables contain random noise. In addition, model errors have a major impact on the uncertainties of the coefficients. The Maximum Likelihood approach demonstrates the inadequacy of the attenuation method model with a quadratic polynomial for the retrieved spectral radiance. We show that using the inadequate model dramatically increases the uncertainties of the coefficients. We compute the coefficient values and their uncertainties, considering both measurement and model errors.
Grigorian, G. M.; Dyatko, N. A.; Kochetov, I. V.
2015-05-15
Radial profiles of the density of metastable atoms Ar({sup 3}P{sub 2}) in the positive column of a dc glow discharge in argon were measured. Gas-discharge glass tubes with clean inner surfaces and surfaces covered with a carbonitride or carbon film were utilized. The parameters of the discharge plasma under experimental conditions were calculated in the framework of a one-dimensional (along the tube radius) discharge model. The coefficient K of reflection of Ar({sup 3}P{sub 2}) atoms from the tube wall was estimated by comparing the measured and calculated density profiles. It is found that, for a clean tube wall, the coefficient of reflection is K = 0.4 ± 0.2, whereas for a wall covered with a carbonitride or carbon film, it is K < 0.2.
Theoretical calculations of the self-reflection coefficients for some species of ions
NASA Astrophysics Data System (ADS)
Luo, Z. M.; Gou, C.; Hou, Q.
2002-06-01
The bipartition model of ion transport has been applied to study the self-reflection coefficients of some species of ion beams which are normally incident to a surface. The computational results has been compared with the results taken from Eckstein and Biersack and the compilation data given by Thomas, Janev and Smith. It was found that there are in reasonable agreement between the results given by the bipartition model and the results given by Monte Carlo method.
NASA Astrophysics Data System (ADS)
Rohr, Kristin M. M.; Schmidt, Ulrike; Groschel-Becker, Henrike
1993-09-01
Reflection coefficients of the seafloor have been calculated from three multi-channel seismic reflection profiles across Middle Valley of the Juan de Fuca ridge. Seafloor reflection coefficients in this sedimented rift valley are high over an active hydrothermal vent and adjacent to major offset faults. Comparison of our measurements to drilling results from Leg 139 shows that high reflection coefficients over an active vent mound are produced by cemented sediments. Large reflection coefficients adjacent to major faults may have a similar origin and indicate that ongoing faulting creates pathways for hydrothermal fluids which alter the sediments and result in higher densities and velocities. Since 30 Hz seismic energy responds to the top 50 m of sediments, we are looking at the integrated response of hydrothermal alteration over tens of thousands of years. This is the first time seafloor reflection coefficients have been used to identify highly altered sediments in a region of deep-water hydrothermal activity.
NASA Astrophysics Data System (ADS)
Deckers, Elke; Claeys, Claus; Atak, Onur; Groby, Jean-Philippe; Dazel, Olivier; Desmet, Wim
2016-05-01
This paper presents an extension to the Wave Based Method to predict the absorption, reflection and transmission coefficients of a porous material with an embedded periodic set of inclusions. The porous unit cell is described using the Multi-Level methodology and by embedding Bloch-Floquet periodicity conditions in the weighted residual scheme. The dynamic pressure field in the semi-infinite acoustic domains is approximated using a novel wave function set that fulfils the Helmholtz equation, the Bloch-Floquet periodicity conditions and the Sommerfeld radiation condition. The method is meshless and computationally efficient, which makes it well suited for optimisation studies.
NASA Astrophysics Data System (ADS)
Suzuki, S.; Itoh, H.
2016-05-01
The diffusion coefficient of the metastable excited Ne(3P2) atom in neon, the reflection coefficient of Ne(3P2) at the surface of an electrode and the rate coefficient of Ne(3P2) for collisional quenching by Ne(1S0) were determined from the gas pressure dependence of the effective lifetime of Ne(3P2). The effective lifetime of Ne(3P2) was measured from the transient current after turning off the Ultraviolet (UV) light in a Townsend discharge. The observed transient current waveform was analysed by solving the diffusion equation for the metastable excited Ne(3P2) atom using the third kind of boundary condition. The rate coefficient of Ne(3P2) for collisional quenching by Ne(1S0) and the reflection coefficient were determined by a nonspectroscopic method for the first time in neon to the best of our knowledge and were (3.2 ± 0.4) × 10‑16 cm3 s‑1 and 0.10 ± 0.04, respectively. The obtained diffusion coefficient at 1 Torr was 177 ± 17 cm2 s‑1, which is consistent with the value reported by Dixon and Grant. Moreover, the present results are compared with the results of Phelps and were found to be in good agreement. We also discuss the deexcitation rate of Ne(3P2) at pressures of up to 60 Torr in comparison with previously reported values.
Sensitivity Enhanced Vital Sign Detection Based on Antenna Reflection Coefficient Variation.
An, Yong-Jun; Yun, Gi-Ho; Yook, Jong-Gwan
2016-04-01
This paper presents a vital sign detection sensor based on reflection coefficient variance from an antenna used in wireless communication devices. The near-field effect is estimated by performing 3D full-wave simulations using a dipole antenna and the magnitude variation of the reflection coefficient induced by human thorax movement due to heart and lungs is observed. The results support the possibility of vital sign detection based on the magnitude variation of the reflection coefficient from an antenna, which can be explained as a narrowband modulation scheme. In particular, a sensitivity enhancement method is proposed and analyzed, and experiments are carried out for heartbeat detection using a dipole antenna with the proposed system. Experimental results are compared between the direct detection and sensitivity enhancement detection schemes. FM signal is also applied to confirm that the proposed sensor works properly in conjunction with an existing communication system. The proposed cardiopulmonary detection sensor is implemented with off-the-shelf components at 2.4 GHz and excellent performance is obtained. PMID:25706824
Acoustic reflections in the water column of Krishna-Godavari offshore basin, Bay of Bengal.
Sinha, Satish K; Dewangan, Pawan; Sain, Kalachand
2016-05-01
Seismic oceanographic studies from various oceans worldwide have indicated that the acoustic reflections are mostly observed along thermal boundaries within the water column. However, the authors present a case study of seismic data from Krishna-Godavari Basin which shows that salinity variations also play an important role in the occurrence of water column reflections. The observed reflection is modeled using the reflectivity series derived from the salinity and temperature profiles from a nearby Conductivity-Temperature-Depth (CTD) location. Sensitivity analysis of temperature and salinity on soundspeed shows that the effect of salinity cannot be ignored for modeling acoustic reflections. The synthetic seismogram matches well with the observed reflection seismic data. Remarkable similarities between the reflection seismic and the salinity profile in the upper thermocline suggest the importance of salinity variations on the water column reflection. Furthermore, impedance inversion of the reflectivity data reveals several thermohaline structures in the water column. The origin of these thermohaline structures is largely unaddressed and may be attributed to the fresh water influx coming from Himalayan and Peninsular rivers or due to the presence of different water masses in the Indian Ocean which warrants a detailed study using concurrent seismic and CTD data. PMID:27250139
Measurement of acoustic impedance and reflectance in the human ear canal.
Voss, S E; Allen, J B
1994-01-01
The pressure reflectance R (omega) is the transfer function which may be defined for a linear one-port network by the ratio of the reflected complex pressure divided by the incident complex pressure. The reflectance is a function that is closely related to the impedance of the 1-port. The energy reflectance R (omega) is defined as magnitude of [R]2. It represents the ratio of reflected to incident energy. In the human ear canal the energy reflectance is important because it is a measure of the inefficiency of the middle ear and cochlea, and because of the insight provided by its simple frequency domain interpretation. One may characterize the ear canal impedance by use of the pressure reflectance and its magnitude, sidestepping the difficult problems of (a) the unknown canal length from the measurement point to the eardrum, (b) the complicated geometry of the drum, and (c) the cross-sectional area changes in the canal as a function of distance. Reported here are acoustic impedance measurements, looking into the ear canal, measured on ten young adults with normal hearing (ages 18-24). The measurement point in the canal was approximately 0.85 cm from the entrance of the canal. From these measurements, the pressure reflectance in the canal is computed and impedance and reflectance measurements from 0.1 to 15.0 kHz are compared among ears. The average reflectance and the standard deviation of the reflectance for the ten subjects have been determined. The impedance and reflectance of two common ear simulators, the Brüel & Kjaer 4157 and the Industrial Research Products DB-100 (Zwislocki) coupler are also measured and compared to the average human measurements. All measurements are made using controls that assure a uniform accuracy in the acoustic calibration across subjects. This is done by the use of two standard acoustic resistors whose impedances are known. From the experimental results, it is concluded that there is significant subject variability in the magnitude
Multi Reflection of Lamb Wave Emission in an Acoustic Waveguide Sensor
Schmitt, Martin; Olfert, Sergei; Rautenberg, Jens; Lindner, Gerhard; Henning, Bernd; Reindl, Leonhard Michael
2013-01-01
Recently, an acoustic waveguide sensor based on multiple mode conversion of surface acoustic waves at the solid—liquid interfaces has been introduced for the concentration measurement of binary and ternary mixtures, liquid level sensing, investigation of spatial inhomogenities or bubble detection. In this contribution the sound wave propagation within this acoustic waveguide sensor is visualized by Schlieren imaging for continuous and burst operation the first time. In the acoustic waveguide the antisymmetrical zero order Lamb wave mode is excited by a single phase transducer of 1 MHz on thin glass plates of 1 mm thickness. By contact to the investigated liquid Lamb waves propagating on the first plate emit pressure waves into the adjacent liquid, which excites Lamb waves on the second plate, what again causes pressure waves traveling inside the liquid back to the first plate and so on. The Schlieren images prove this multi reflection within the acoustic waveguide, which confirms former considerations and calculations based on the receiver signal. With this knowledge the sensor concepts with the acoustic waveguide sensor can be interpreted in a better manner. PMID:23447010
Reflection and refraction of acoustic waves at the interface between a gas and a disperse systems
NASA Astrophysics Data System (ADS)
Shagapov, V. Sh.; Sarapulova, V. V.
2015-09-01
The reflection and refraction of acoustic waves at different angles of incidence on the interface between a vapor-gas-droplet system and air are studied. From an analysis of analytical solutions, it has been found that in the case of incidence on the interface from the side of the vapor-gas-droplet medium, there is a critical angle of incidence at which the wave is completely reflected from the boundary, i.e., total internal reflection takes place. It is shown that for a certain angle of incidence on the interface both from the air side and from the mixture side and for a certain volume fraction of water in the disperse system, complete transmission of the acoustic wave through the medium is observed.
Method for Calculating the Optical Diffuse Reflection Coefficient for the Ocular Fundus
NASA Astrophysics Data System (ADS)
Lisenko, S. A.; Kugeiko, M. M.
2016-07-01
We have developed a method for calculating the optical diffuse reflection coefficient for the ocular fundus, taking into account multiple scattering of light in its layers (retina, epithelium, choroid) and multiple refl ection of light between layers. The method is based on the formulas for optical "combination" of the layers of the medium, in which the optical parameters of the layers (absorption and scattering coefficients) are replaced by some effective values, different for cases of directional and diffuse illumination of the layer. Coefficients relating the effective optical parameters of the layers and the actual values were established based on the results of a Monte Carlo numerical simulation of radiation transport in the medium. We estimate the uncertainties in retrieval of the structural and morphological parameters for the fundus from its diffuse reflectance spectrum using our method. We show that the simulated spectra correspond to the experimental data and that the estimates of the fundus parameters obtained as a result of solving the inverse problem are reasonable.
A robust method for determining calibration coefficients for VIIRS reflective solar bands
NASA Astrophysics Data System (ADS)
Ji, Qiang; McIntire, Jeffrey; Efremova, Boryana; Schwarting, Thomas; Oudrari, Hassan; Zeng, Jinan; Xiong, Xiaoxiong
2015-09-01
This paper presents a robust method for determining the calibration coefficients in polynomial calibration equations, and discusses the corresponding calibration uncertainties. An attenuator method that takes into account all measurements with and without an attenuator screen was used to restrict the impact of the absolute calibration of the light source. The originally proposed procedure attempts to simultaneously determine all unknowns nonlinearly using polynomial curve fitting. The newly proposed method divides the task into two simpler parts. For example, in the case of a quadratic calibration equation, the first part becomes a quadratic equation solely for the transmittance of attenuator, which has an analytical solution using three or four sets of measurements. Additionally, it is straightforward to determine the median value and the standard deviation of the transmittance from the solutions using all combinations of measured data points. In conjunction, the second part becomes a linear fit, with the ratio of the zeroth-order to first-order calibration coefficients as the intercept and the ratio of the second-order to first-order calibration coefficients as the slope. These ratios are unaffected by the absolute calibration of the light source and are then used in the calibration equation to calculate the first-order calibration coefficient. How the new method works is straightforward to visualize, which makes its results easier to verify. This is demonstrated using measurements from the Joint Polar Satellite System (JPSS) J1 Visible Infrared Imaging Radiometer Suite (VIIRS) reflective solar bands (RSB) pre-launch testing.
NASA Astrophysics Data System (ADS)
Imel, Adam; Miller, Brad; Holley, Wade; Baskaran, Durairaj; Mays, Jimmy; Dadmun, Mark
2015-03-01
The diffusion properties of nanoparticles in polymer nanocomposites are largely unknown and depend intimately on the dispersion of the nanoparticles. We examine the diffusion of soft, organic nanoparticles, which disperse in a polymer matrix due to the interpenetration of polymer chains and particles and the reduction in the depletion of entropy in the system. The impact of the presence of soft nanoparticles on the diffusion coefficient of polystyrene chains has recently been determined with neutron reflectivity. This was completed by monitoring the interdiffusion of deuterated and protonated polystyrene nanocomposite bilayers with and without the soft nanoparticles dispersed throughout both layers and extracting the diffusion coefficient from the one-dimensional solution to Fick's second law of diffusion. In this work, we extend this method to bilayer systems with only the soft nanoparticles as one of the layers and a linear deuterated polystyrene as an adjacent layer. The development of this method allows us to determine the tracer diffusion coefficient of the soft polystyrene nanoparticles for the first time by analyzing the mutual diffusion coefficient from Fick's second law and the fast and slow modes theories for diffusion.
Reconstructing surface wave profiles from reflected acoustic pulses using multiple receivers.
Walstead, Sean P; Deane, Grant B
2014-08-01
Surface wave shapes are determined by analyzing underwater reflected acoustic signals collected at multiple receivers. The transmitted signals are of nominal frequency 300 kHz and are reflected off surface gravity waves that are paddle-generated in a wave tank. An inverse processing algorithm reconstructs 50 surface wave shapes over a length span of 2.10 m. The inverse scheme uses a broadband forward scattering model based on Kirchhoff's diffraction formula to determine wave shapes. The surface reconstruction algorithm is self-starting in that source and receiver geometry and initial estimates of wave shape are determined from the same acoustic signals used in the inverse processing. A high speed camera provides ground-truth measurements of the surface wave field for comparison with the acoustically derived surface waves. Within Fresnel zone regions the statistical confidence of the inversely optimized surface profile exceeds that of the camera profile. Reconstructed surfaces are accurate to a resolution of about a quarter-wavelength of the acoustic pulse only within Fresnel zones associated with each source and receiver pair. Multiple isolated Fresnel zones from multiple receivers extend the spatial extent of accurate surface reconstruction while overlapping Fresnel zones increase confidence in the optimized profiles there. PMID:25096095
NASA Astrophysics Data System (ADS)
Song, Peng; Liu, Zhaolun; Zhang, Xiaobo; Tan, Jun; Xia, Dongming; Li, Jing; Zhu, Bo
2015-12-01
This paper introduces the fourth-order absorbing boundary condition (ABC) into staggered-grid finite difference forward modeling of the first-order stress-velocity acoustic equation, and develops a new method to optimize coefficients of the fourth-order ABC to further improve its overall absorbing effect. Theoretical analysis and the results of numerical tests demonstrate that the fourth-order ABC with optimized coefficients has much higher absorbing efficiency than both the conventional second-order and fourth-order ABCs without optimized coefficients, for waves with large incident angles. Compared with the perfectly matched layer (PML) with 40 layers, the fourth-order ABC not only has a much better absorbing effect, but also uses far less computer memory for calculation. We present the fourth-order ABC with optimized coefficients as an ideal artificial boundary for the simulation of the acoustic equation based on extensive and complex structure models. Supported by the Fundamental Research Funds for the Central Universities (201513005).
NASA Astrophysics Data System (ADS)
Alman, D. A.; Ruzic, D. N.; Brooks, J. N.
2001-10-01
Reflection coefficients of carbon and hydrocarbon molecules have been calculated with a molecular dynamics code. The code uses the Brenner hydrocarbon potential, an empirical many-body potential that can model the chemical bonding in small hydrocarbon molecules and graphite surfaces. A variety of incident energies and angles have been studied. Typical results for carbon show reflection coefficients 0.4 at thermal energy, decreasing to a minimum of 0.15 at 10-20 eV, and then increasing again. Distributed computing is used to distribute the work among 10-20 desktop PCs in the laboratory. The system consists of a client application run on all of the PCs and a single server machine that distributes work and compiles the results sent back from the clients. The client-server software is written in Java and requires no commercial software packages. Thus, the MD code benefits from multiprocessor-like speed-up at no additional cost by using the idle CPU cycles that would otherwise be wasted. These calculations represent an important improvement to the WBC code, which has been used to model surface erosion, core plasma contamination, and tritium codeposition in many fusion design studies and experiments.
NASA Astrophysics Data System (ADS)
Smagin, N. V.; Krutyansky, L. M.; Zelenova, Z. V.; Brysev, A. P.
2014-03-01
Acoustic absorption has been measured in a series of biological tissue specimens—porcine muscle, renal and fat tissues—by the standard insert-substitution method, as well as by ultrasonic phase conjugation. Comparison of the experimental results and revealed differences confirm the promise of using phase conjugate waves to measure acoustic losses in biological objects. It is demonstrated that in inhomogeneous tissues, the phase conjugation method makes it possible to obtain a more reliable estimate of dissipative losses.
NASA Astrophysics Data System (ADS)
Moyer, D.; Vandermierden, N.; Rausch, K.; De Luccia, F.
2014-09-01
A primary sensor on-board the Suomi-National Polar-orbiting Partnership (SNPP) spacecraft, the Visible Infrared Imaging Radiometer Suite (VIIRS) has 22 bands: 7 thermal emissive bands (TEBs), 14 reflective solar bands (RSBs) and a Day Night Band (DNB). The RSBs cover the spectral wavelengths between 0.412 to 2.25 μm and have three (I1-I3) 371m and eleven (M1-M11) 742m spatial resolution bands. A VIIRS Key Performance Parameter (KPP) is the Ocean Color/Chlorophyll (OCC) which uses moderate bands M1 (0.412μm) through M7's (0.865 μm) calibrated Science Data Records (SDRs). The RSB SDRs rely on prelaunch calibration coefficients which use a quadratic algorithm to convert the detector's response to calibrated radiance. This paper will evaluate the performance of these prelaunch calibration coefficients using SDR comparisons between bands with the same spectral characteristics: I2 with M7 (0.865 μm) and I3 with M10 (1.610 μm). Changes to the prelaunch calibration coefficient's offset term c0 to improve the SDR's performance at low radiance levels will also be discussed.
NASA Astrophysics Data System (ADS)
Singh, Mithun K.; Steenbergen, Wiendelt
2015-07-01
Reflection artifacts caused by acoustic reflectors is an important problem in reflection-mode photoacoustic imaging. The light absorbed by skin and superficial optical absorbers may produce high photoacoustic signals, which traverse into the tissue and get reflected from structures having different acoustic impedance. These reflected photoacoustic signals, when reconstructed may appear in the region of interest, which causes complications in interpreting the images. We propose a novel method to identify and reduce reflection artifacts in photoacoustic images by making use of PhotoAcoustic-guided Focused UltraSound [PAFUSion]. Our method ultrasonically mimics the photoacoustic image formation process and thus delivers a clinically feasible way to reduce reflection artifacts. Simulation and phantom measurement results are presented to demonstrate the validity and impact of this method. Results show that PAFUSion technique can identify and differentiate reflection signals from the signals of interest and thus foresees good potential for improving photoacoustic imaging of deep tissue.
Determining Spectral Reflectance Coefficients from Hyperspectral Images Obtained from Low Altitudes
NASA Astrophysics Data System (ADS)
Walczykowski, P.; Jenerowicz, A.; Orych, A.; Siok, K.
2016-06-01
Remote Sensing plays very important role in many different study fields, like hydrology, crop management, environmental and ecosystem studies. For all mentioned areas of interest different remote sensing and image processing techniques, such as: image classification (object and pixel- based), object identification, change detection, etc. can be applied. Most of this techniques use spectral reflectance coefficients as the basis for the identification and distinction of different objects and materials, e.g. monitoring of vegetation stress, identification of water pollutants, yield identification, etc. Spectral characteristics are usually acquired using discrete methods such as spectrometric measurements in both laboratory and field conditions. Such measurements however can be very time consuming, which has led many international researchers to investigate the reliability and accuracy of using image-based methods. According to published and ongoing studies, in order to acquire these spectral characteristics from images, it is necessary to have hyperspectral data. The presented article describes a series of experiments conducted using the push-broom Headwall MicroHyperspec A-series VNIR. This hyperspectral scanner allows for registration of images with more than 300 spectral channels with a 1.9 nm spectral bandwidth in the 380- 1000 nm range. The aim of these experiments was to establish a methodology for acquiring spectral reflectance characteristics of different forms of land cover using such sensor. All research work was conducted in controlled conditions from low altitudes. Hyperspectral images obtained with this specific type of sensor requires a unique approach in terms of post-processing, especially radiometric correction. Large amounts of acquired imagery data allowed the authors to establish a new post- processing approach. The developed methodology allowed the authors to obtain spectral reflectance coefficients from a hyperspectral sensor mounted on an
Ion-acoustic shocks with self-regulated ion reflection and acceleration
NASA Astrophysics Data System (ADS)
Malkov, M. A.; Sagdeev, R. Z.; Dudnikova, G. I.; Liseykina, T. V.; Diamond, P. H.; Papadopoulos, K.; Liu, C.-S.; Su, J. J.
2016-04-01
An analytic solution describing an ion-acoustic collisionless shock, self-consistently with the evolution of shock-reflected ions, is obtained. The solution extends the classic soliton solution beyond a critical Mach number, where the soliton ceases to exist because of the upstream ion reflection. The reflection transforms the soliton into a shock with a trailing wave and a foot populated by the reflected ions. The solution relates parameters of the entire shock structure, such as the maximum and minimum of the potential in the trailing wave, the height of the foot, as well as the shock Mach number, to the number of reflected ions. This relation is resolvable for any given distribution of the upstream ions. In this paper, we have resolved it for a simple "box" distribution. Two separate models of electron interaction with the shock are considered. The first model corresponds to the standard Boltzmannian electron distribution in which case the critical shock Mach number only insignificantly increases from M ≈1.6 (no ion reflection) to M ≈1.8 (substantial reflection). The second model corresponds to adiabatically trapped electrons. They produce a stronger increase, from M ≈3.1 to M ≈4.5 . The shock foot that is supported by the reflected ions also accelerates them somewhat further. A self-similar foot expansion into the upstream medium is described analytically.
Measurement of the acoustic reflectivity of sirenia (Florida manatees) at 171 kHz.
Jaffe, Jules S; Simonet, Fernando; Roberts, Paul L D; Bowles, Ann E
2007-01-01
The Florida manatee (Trichechus manatus latirostris) is an endangered sirenian. At present, its adult population (approximately 2200) seems stable, but tenuous. Manatee-boat collisions are a significant proportion (approximately 25%) of mortalities. Here, the potential use of active sonar for detecting manatees by quantifying sonic reflectivity is explored. In order to estimate reflectivity two methods were used. One method measured live reflections from captive animals using a carefully calibrated acoustic and co-registered optical system. The other method consisted of the analysis of animal tissue in order to obtain estimates of the sound speed and density and to predict reflectivity. The impedance measurement predicts that for a lateral view, the tissue reflectivity is close to 0.13, with a critical grazing angle of 28 degrees. Data measured from live animals indicate that substantial reflections can be recorded, however in many instances observed "empirical target strengths" were less than an experimentally dependent -48-dB threshold. Conclusions favor the hypothesis that the animals reflect substantial amounts of sound; however, the reflections can often be specular, and therefore impractical for observation by a manatee detection sonar operating at 171 kHz. PMID:17297771
Retrieval of diffuse attenuation coefficient in the China seas from surface reflectance.
Qiu, Zhongfeng; Wu, Tingting; Su, Yuanyuan
2013-07-01
Accurate estimation of the diffuse attenuation coefficient is important for our understanding the availability of light to underwater communities, which provide critical information for the China seas ecosystem. However, algorithm developments and validations of the diffuse attenuation coefficient in the China seas have been seldom performed before and therefore our knowledge on the quality of retrieval of the diffuse attenuate coefficient is poor. In this paper optical data at 306 sites collected in coastal waters of the China seas between July 2000 and February 2004 are used to evaluate three typical existing Kd(490) models. The in situ Kd(490) varied greatly among different sites from 0.029 m(-1) to 10.3 m(-1), with a mean of 0.92 ± 1.59 m(-1). Results show that the empirical model and the semi-analytical model significantly underestimate the Kd(490) value, with estimated mean values of 0.24 m(-1) and 0.5 m(-1), respectively. The combined model also shows significant differences when the in situ Kd(490) range from 0.2 m(-1) to 1 m(-1). Thus, the present study proposes that the three algorithms cannot be directly used to appropriately estimate Kd(490) in the turbid coastal waters of the China seas without a fine tuning for regional applications. In this paper, new Kd(490) algorithms are developed based on the semi-analytical retrieval of the absorption coefficient a(m(-1)) and the backscattering coefficient bb(m(-1)) from the reflectance at two wavelengths, 488 and 667 nm for the Moderate Resolution Imaging Spectroradiometer (MODIS) and 490 and 705 nm for the Medium Resolution Imaging Spectrometer (MERIS) applications, respectively. With the new approaches, the mean ratio and the relative percentage difference are 1.05 and 4.6%, respectively, based on an independent in situ data set. Furthermore, the estimates are reliable within a factor of 1.9 (95% confidence interval). Comparisons also show that the Kd(490) derived with the new algorithms are well correlated
Mathematical models for the reflection coefficients of dielectric half-spaces
NASA Technical Reports Server (NTRS)
Evans, D. D.
1973-01-01
The reflection coefficients at normal incidence are found for a large class of one-dimensionally inhomogeneous or stratified half-spaces, which contain a homogeneous half-space. The formulation of the problem involves a combination of the classical boundary value technique, and the nonclassical principle of invariant imbedding. Solutions are in closed form and expressible in terms of Bessel functions. All results are given in terms of the ratio of the distance between free space and the homogeneous half-space to the wavelength in vacuo. One special case is that of an arbitrary number of layers lying on a homogeneous half-space where the dielectric constant of each layer has a constant gradient. A number of other special cases, limiting cases, and generalizations are developed including one in which the thickness of the top layer obeys a probability distribution.
NASA Astrophysics Data System (ADS)
Thoma, Carsten Hilmar
1997-12-01
The coupling of stress and strain fields to electric fields present in anisotropic piezoelectric crystals makes them ideal for use as electromechanical transducers in a wide variety of applications. In recent years such crystals have been utilized to produce surface acoustic wave devices for signal processing applications, in which an applied metallic grating both transmits and receives, through the piezoelectric effect, electromechanical surface waves. The design of such interdigital transducers requires an accurate knowledge of wave propagation and reflection. The presence of the metal grating in addition to its ideal transduction function, by means of electrical and mechanical loading, also introduces a velocity shift as well as reflection into substrate surface waves. We seek to obtain a consistent formulation of the wave behavior due to the electrical and mechanical loading of the substrate crystal by the metallic grating. A perturbative solution up to second order in h//lambda is developed, where h is the maximum grating height and λ the acoustic wavelength. For the operating frequencies and physical parameters of modern surface acoustic wave devices such an analysis will provide an adequate description of device behavior in many cases, thereby circumventing the need for more computationally laborious methods. Numerical calculations are presented and compared with available experimental data.
NASA Astrophysics Data System (ADS)
Robinson, Philip W.
This thesis addresses the effect of reflections from diffusive architectural surfaces on the perception of echoes and on auditory spatial resolution. Diffusive architectural surfaces play an important role in performance venue design for architectural expression and proper sound distribution. Extensive research has been devoted to the prediction and measurement of the spatial dispersion. However, previous psychoacoustic research on perception of reflections and the precedence effect has focused on specular reflections. This study compares the echo threshold of specular reflections, against those for reflections from realistic architectural surfaces, and against synthesized reflections that isolate individual qualities of reflections from diffusive surfaces, namely temporal dispersion and spectral coloration. In particular, the activation of the precedence effect, as indicated by the echo threshold is measured. Perceptual tests are conducted with direct sound, and simulated or measured reflections with varying temporal dispersion. The threshold for reflections from diffusive architectural surfaces is found to be comparable to that of a specular re ection of similar energy rather than similar amplitude. This is surprising because the amplitude of the dispersed re ection is highly attenuated, and onset cues are reduced. This effect indicates that the auditory system is integrating re ection response energy dispersed over many milliseconds into a single stream. Studies on the effect of a single diffuse reflection are then extended to a full architectural enclosure with various surface properties. This research utilizes auralizations from measured and simulated performance venues to investigate spatial discrimination of multiple acoustic sources in rooms. It is found that discriminating the lateral arrangement of two sources is possible at narrower separation angles when reflections come from at rather than diffusive surfaces. Additionally, subjective impressions are
Gélat, Pierre; Shaw, Adam
2015-03-01
Total acoustic output power is an important parameter required by standards for most ultrasonic medical equipment including high-intensity focused ultrasound (HIFU) systems. Radiation force balances are routinely used; however, radiation force is not strictly dependent on the ultrasound power but, rather, on the wave momentum resolved in one direction. Consequently, measurements based on radiation force become progressively less accurate as the ultrasound wave deviates further from a true plane wave. HIFU transducers can be very strongly focused with F-numbers less than one: under these conditions, the uncertainty associated with use of the radiation force method becomes very significant. International Standards IEC 61161 and IEC 62555 suggest plane-wave correction factors for unfocused transducers radiating onto an ideal absorbing target and focusing corrections for focused transducers radiating onto ideal absorbing targets and onto conical reflecting targets (IEC 61161). Previous models have relied on calculations based on the Rayleigh integral, which is not strictly correct for curved sources. In the work described here, an approach combining finite element methods with a discretization of the Helmholtz equation was developed, making it possible to model the boundary condition at the structure/fluid interface more correctly. This has been used to calculate the relationship between radiation force and total power for both absorbing and conical reflecting targets for transducers ranging from planar to an F-number of 0.5 (hemispherical) and to compare with the recommendations of IEC 61161 and IEC 62555. PMID:25683223
Evaluation of several non-reflecting computational boundary conditions for duct acoustics
NASA Technical Reports Server (NTRS)
Watson, Willie R.; Zorumski, William E.; Hodge, Steve L.
1994-01-01
Several non-reflecting computational boundary conditions that meet certain criteria and have potential applications to duct acoustics are evaluated for their effectiveness. The same interior solution scheme, grid, and order of approximation are used to evaluate each condition. Sparse matrix solution techniques are applied to solve the matrix equation resulting from the discretization. Modal series solutions for the sound attenuation in an infinite duct are used to evaluate the accuracy of each non-reflecting boundary conditions. The evaluations are performed for sound propagation in a softwall duct, for several sources, sound frequencies, and duct lengths. It is shown that a recently developed nonlocal boundary condition leads to sound attenuation predictions considerably more accurate for short ducts. This leads to a substantial reduction in the number of grid points when compared to other non-reflecting conditions.
Ion-acoustic shocks with reflected ions: modelling and particle-in-cell simulations
NASA Astrophysics Data System (ADS)
Liseykina, T. V.; Dudnikova, G. I.; Vshivkov, V. A.; Malkov, M. A.
2015-10-01
> Non-relativistic collisionless shock waves are widespread in space and astrophysical plasmas and are known as efficient particle accelerators. However, our understanding of collisionless shocks, including their structure and the mechanisms whereby they accelerate particles, remains incomplete. We present here the results of numerical modelling of an ion-acoustic collisionless shock based on the one-dimensional kinetic approximation for both electrons and ions with a real mass ratio. Special emphasis is paid to the shock-reflected ions as the main driver of shock dissipation. The reflection efficiency, the velocity distribution of reflected particles and the shock electrostatic structure are studied in terms of the shock parameters. Applications to particle acceleration in geophysical and astrophysical shocks are discussed.
Reflection and transmission coefficients of a single layer in poroelastic media.
Corredor, Robiel Martinez; Santos, Juan E; Gauzellino, Patricia M; Carcione, José M
2014-06-01
Wave propagation in poroelastic media is a subject that finds applications in many fields of research, from geophysics of the solid Earth to material science. In geophysics, seismic methods are based on the reflection and transmission of waves at interfaces or layers. It is a relevant canonical problem, which has not been solved in explicit form, i.e., the wave response of a single layer, involving three dissimilar media, where the properties of the media are described by Biot's theory. The displacement fields are recast in terms of potentials and the boundary conditions at the two interfaces impose continuity of the solid and fluid displacements, normal and shear stresses, and fluid pressure. The existence of critical angles is discussed. The results are verified by taking proper limits-zero and 100% porosity-by comparison to the canonical solutions corresponding to single-phase solid (elastic) media and fluid media, respectively, and the case where the layer thickness is zero, representing an interface separating two poroelastic half-spaces. As examples, it was calculated the reflection and transmission coefficients for plane wave incident at a highly permeable and compliant fluid-saturated porous layer, and the case where the media are saturated with the same fluid. PMID:24907781
NASA Astrophysics Data System (ADS)
Dickinson, A. S.
2010-11-01
A quantum-reflection model is employed to calculate the rate coefficient for the Penning ionization of rubidium by cold metastable helium atoms in unpolarized collisions. Various results for the p-wave transmission coefficient on a 1/R6 long-range potential are discussed. The dispersion coefficient for the interaction of these atoms is estimated as 3540 au. The calculated value of the rate coefficient is about four times lower than the recently measured value (Byron et al 2010a Phys. Rev. A 81 013405) for this process when both atoms are held in magneto-optical traps.
NASA Technical Reports Server (NTRS)
Miles, J. H.
1975-01-01
A computer method for obtaining a rational function representation of an acoustic spectrum and for correcting reflection effects is introduced. The functional representation provides a means of compact storage of data and the nucleus of the data analysis method. The method is applied to noise from a full-scale externally blown flap system with a quiet 6:1 bypass ratio turbofan engine and a three-flap wing section designed to simulate the take-off condition of a conceptual STOL aircraft.
Hydraulic conductivity, albumin reflection and diffusion coefficients of pig mediastinal pleura.
Parameswaran, S; Brown, L V; Ibbott, G S; Lai-Fook, S J
1999-09-01
Hydraulic conductivity (L), albumin reflection coefficient (sigma), and albumin diffusion coefficient (D) were measured across pig mediastinal pleura. The tissue (7 mm diameter) was bonded between two chambers. Flow (Q) of lactated Ringer solution between the chambers was measured in turn at driving pressures (DeltaP) of 2, 4, and 6 cm H(2)O. Value of L was proportional to the slope of the Q-DeltaP curve. Then Q was measured in turn at three albumin osmotic pressure differences (Deltapi equivalent to -1, -2, and -3 g/dl albumin concentration difference, DeltaC) with DeltaP constant at either 2, 3, 4, or 6 cm H(2)O. From Starling's equation, magnitude of sigma was the slope of the Q-Deltapi curve divided by the slope of the Q-DeltaP curve. We measured the diffusion of 0, 2, 5, and 10 g/dl albumin with tracer (125)I-albumin. Tracer mass (M) that diffused across the pleura was measured for 10 h using a well-type NaI(T1) detector. D was calculated from the slope of the M-time curve. Values of L averaged 2.0 x 10(-8) cm(3). s(-1). dyne(-1) (n = 23). Values of sigma were small (0.02-0.05) and sigma increased as flow increased 20-fold. D (n = 24) increased 3-fold from 2.7 x 10(-8) cm(2)/s as DeltaC increased from 0 to 10 g/dl. The small values of sigma indicated that mediastinal pleura provided little restriction to the passage of protein. PMID:10458927
NASA Astrophysics Data System (ADS)
Diaz, Sandra; Chopra, Rajiv; Pichardo, Samuel
2012-11-01
In this work we present a model to calculate the acoustic pressure generated by the interaction of forward and reflected waves in the vicinity of a solid interface and compare it to experimental data. An experimental setup was designed to measure the forward and the combined forward-reflected acoustic fields produced by a solid interface. A 0.785mm-needle hydrophone was used to characterize the acoustic field produced by a 7.29MHz-ultrasound transducer focused at 6cm. The hydrophone was positioned perpendicularly to the sound propagation direction and moved between the transducer and a 9mm-thick acrylic sample using a robotic arm. Simulations were carried out using a modified Rayleigh-Sommerfeld integral that calculates the particle displacement over a reflecting surface. This particle displacement at the boundary of the interface is then used as an acoustic source to obtain the reflected particle displacement. The complex sum of the forward and reflected fields was compared to the experimental measurements. The measurements showed an interference pattern that increased the pressure amplitude in average 10.4% with peaks of up to 25.8%. The proposed model is able to represent the interference pattern produced by the reflected wave with an average absolute error of 3.4+/-0.54% and a maximal error of 5.6%. The comparison between the experimental measurements and the simulations indicates that the presented model predicts with good accuracy the acoustic field generated by ultrasound transducers facing a solid interface. This model can be used to foresee the outcome of therapeutic applications where the devices are used in proximity to a bone interface.
Safrai, Eli; Ishai, Paul Ben; Caduff, Andreas; Puzenko, Alexander; Polsman, Alexander; Agranat, Aharon J; Feldman, Yuri
2012-07-01
Recent work has demonstrated that the reflection coefficient of human skin in the frequency range from 95 to 110 GHz (W band) mirrors the temporal relaxation of stress induced by physical exercise. In this work, we extend these findings to show that in the event of a subtle trigger to stress, such as mental activity, a similar picture of response emerges. Furthermore, the findings are extended to cover not only the W band (75-110 GHz), but also the frequency band from 110 to 170 GHz (D band). We demonstrate that mental stress, induced by the Stroop effect and recorded by the galvanic skin response (GSR), can be correlated to the reflection coefficient in the aforementioned frequency bands. Intriguingly, a light physical stress caused by repeated hand gripping clearly showed an elevated stress level in the GSR signal, but was largely unnoted in the reflection coefficient in the D band. The implication of this observation requires further validation. PMID:22170380
NASA Astrophysics Data System (ADS)
Franco, Ediguer E.; Adamowski, Julio C.; Buiochi, Flávio
2012-05-01
This work implements the ultrasonic shear-wave reflectance method for viscosity measurements. A modeconversion device was used for the dynamic viscosity measurement of mineral oil, SAE 40 automotive oil and glycerin samples at room temperature and 1 MHz. A novel signals processing technique that calculates the reflection coefficient magnitude in a frequency band, instead of a single frequency, was employed, showing an important improvement on the measurement accuracy.
Permeability and reflection coefficients of urea and small amides in the human red cell.
Toon, M R; Solomon, A K
1996-09-01
Measurement of the transport parameters that govern the passage of urea and amides across the red cell membrane leads to important questions about transport of water. It had initially been thought that small protein channels, permeable to water and small solutes, traversed the membrane (see Solomon, 1987). Recently, however, very strong evidence has been presented that the 28 kDa protein, CHIP28, found in the red cell membrane, is the locus of the water channel (see Agre et al., 1993). CHIP28 transports water very rapidly but does not transport small nonelectrolytes such as urea. The irreversible thermodynamic parameter, sigma i, the reflection coefficient, is a measure of the relationship between the permeability of the solute and that of water. If a solute permeates by dissolution in the membrane, sigma i = 1.0; if it permeates by passage through an aqueous channel, sigma i < 1.0. For urea, Goldstein and Solomon (1960) found that sigma urea = 0.62 +/- 0.03 which meant that urea crosses the red cell membrane in a water-filled channel. This result and many subsequent observations that showed that sigma urea < 1.0 are at variance with the observation that CHIP28 is impermeable to urea. In view of this problem, we have made a new series of measurements of sigma i for urea and other small solutes by a different method, which obviates many of the criticisms Macey and Karan (1993) have made of our earlier method. The new method (Chen et al., 1988), which relies upon fluorescence of the intracellular dye, fluorescein sulfonate, leads to the corrected value, sigma urea,corr = 0.64 +/- 0.03 for ghosts, in good agreement with earlier data for red cells. Thus, the conclusion on irreversible thermodynamic and other grounds that urea and water share a common channel is in disagreement with the view that CHIP28 provides the sole channel for water entrance into the cell. PMID:8703203
Fan, Fan; Chen, Chun Cheng Andy; Zhang, Jin; Schreck, Carlos M N; Roman, Eric A; Williams, Jan M; Hirata, Takashi; Sharma, Mukut; Beard, Daniel A; Savin, Virginia J; Roman, Richard J
2015-12-15
This study describes a high-throughput fluorescence dilution technique to measure the albumin reflection coefficient (σAlb) of isolated glomeruli. Rats were injected with FITC-dextran 250 (75 mg/kg), and the glomeruli were isolated in a 6% BSA solution. Changes in the fluorescence of the glomerulus due to water influx in response to an imposed oncotic gradient was used to determine σAlb. Adjustment of the albumin concentration of the bath from 6 to 5, 4, 3, and 2% produced a 10, 25, 35, and 50% decrease in the fluorescence of the glomeruli. Pretreatment of glomeruli with protamine sulfate (2 mg/ml) or TGF-β1 (10 ng/ml) decreased σAlb from 1 to 0.54 and 0.48, respectively. Water and solute movement were modeled using Kedem-Katchalsky equations, and the measured responses closely fit the predicted behavior, indicating that loss of albumin by solvent drag or diffusion is negligible compared with the movement of water. We also found that σAlb was reduced by 17% in fawn hooded hypertensive rats, 33% in hypertensive Dahl salt-sensitive (SS) rats, 26% in streptozotocin-treated diabetic Dahl SS rats, and 21% in 6-mo old type II diabetic nephropathy rats relative to control Sprague-Dawley rats. The changes in glomerular permeability to albumin were correlated with the degree of proteinuria in these strains. These findings indicate that the fluorescence dilution technique can be used to measure σAlb in populations of isolated glomeruli and provides a means to assess the development of glomerular injury in hypertensive and diabetic models. PMID:26447220
Soleimani, Hassan; Abbas, Zulkifly; Yahya, Noorhana; Shameli, Kamyar; Soleimani, Hojjatollah; Shabanzadeh, Parvaneh
2012-01-01
The sol-gel method was carried out to synthesize nanosized Yttrium Iron Garnet (YIG). The nanomaterials with ferrite structure were heat-treated at different temperatures from 500 to 1000 °C. The phase identification, morphology and functional groups of the prepared samples were characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR), respectively. The YIG ferrite nanopowder was composited with polyvinylidene fluoride (PVDF) by a solution casting method. The magnitudes of reflection and transmission coefficients of PVDF/YIG containing 6, 10 and 13% YIG, respectively, were measured using rectangular waveguide in conjunction with a microwave vector network analyzer (VNA) in X-band frequencies. The results indicate that the presence of YIG in polymer composites causes an increase in reflection coefficient and decrease in transmission coefficient of the polymer. PMID:22942718
Cortisol levels in hair reflect behavioural reactivity of dogs to acoustic stimuli.
Siniscalchi, M; McFarlane, J R; Kauter, K G; Quaranta, A; Rogers, L J
2013-02-01
Cortisol levels in hair samples were examined in fourteen domestic dogs and related to the dogs' responses to different acoustic stimuli. Stimuli were playbacks of species-typical vocalizations recorded during three different situations ("disturbance", "isolation" and "play" barks) and the sounds of a thunderstorm. Hair samples were collected at 9:00 h and 17:00 h two weeks after the behavioural tests. Results showed that behavioural reactivity to playback of the various stimuli correlates with cortisol levels in hair samples collected at 9:00 h, and the same was the case for the separate measures of behaviour (i.e. hiding, running away, seeking attention from the tester, panting and lowering of the body posture). Hence, levels of cortisol in hair appear to reflect the dog's chronic state of emotional reactivity, or temperament. PMID:22449333
Nonlinear acoustics: Reflection and refraction, scattering of sound by sound, and periodic media
NASA Astrophysics Data System (ADS)
Blackstock, David T.
1988-07-01
Research on three topics in nonlinear acoustics is described: (1) reflection and refraction at a plane interface between two fluids. Previously a modified form of Snell's law was derived; theoretical work is underway to investigate assumptions on which the derivation was based, (2) scattering of sound by sound. Work on a single beam experiment and a crossed-beams experiment is in progress, and (3) propagation in periodic media. An experiment is being designed to measure finite-amplitude distortion in a plane wave tube loaded periodically with reactive branch elements. Other work, on noncollinear interaction and on biomedical ultrasonics, is described briefly. Two journal articles, five oral papers, and one technical report are listed.
Wang, Wenbo; He, Xingli; Ye, Zhi E-mail: jl2@bolton.ac.uk; Wang, Xiaozhi; Mayrhofer, Patrick M.; Gillinger, Manuel; Bittner, Achim; Schmid, Ulrich
2014-09-29
AlN and AlScN thin films with 27% scandium (Sc) were synthesized by DC magnetron sputtering deposition and used to fabricate surface acoustic wave (SAW) devices. Compared with AlN-based devices, the AlScN SAW devices exhibit much better transmission properties. Scandium doping results in electromechanical coupling coefficient, K{sup 2}, in the range of 2.0% ∼ 2.2% for a wide normalized thickness range, more than a 300% increase compared to that of AlN-based SAW devices, thus demonstrating the potential applications of AlScN in high frequency resonators, sensors, and high efficiency energy harvesting devices. The coupling coefficients of the present AlScN based SAW devices are much higher than that of the theoretical calculation based on some assumptions for AlScN piezoelectric material properties, implying there is a need for in-depth investigations on the material properties of AlScN.
Grate, J W; Kaganove, S N; Bhethanabotla, V R
1998-01-01
Apparent partition coefficients, K, for the sorption of toluene by four different polymer thin films on thickness shear mode (TSM) and surface acoustic wave (SAW) devices are compared. The polymers examined were poly(isobutylene) (PIB), poly(epichlorohydrin) (PECH), poly(butadiene) (PBD), and poly(dimethylsiloxane) (PDMS). Independent data on partition coefficients for toluene in these polymers were compiled for comparison, and TSM sensor measurements were made using both oscillator and impedance analysis methods. K values from SAW sensor measurements were about twice those calculated from TSM sensor measurements when the polymers were PIB and PECH, and they were also at least twice the values of the independent partition coefficient data, which is interpreted as indicating that the SAW sensor responds to polymer modulus changes as well as to mass changes. K values from SAW and TSM measurements were in agreement with each other and with independent data when the polymer was PBD. Similarly, K values from the PDMS-coated SAW sensor were not much larger than values from independent measurements. These results indicate that modulus effects were not contributing to the SAW sensor responses in the cases of PBD and PDMS. However, K values from the PDMS-coated TSM device were larger than the values from the SAW device or independent measurements, and the impedance analyzer results indicated that this sensor using our sample of PDMS at the applied thickness did not behave as a simple mass sensor. Differences in behavior among the test polymers on SAW devices are interpreted in terms of their differing viscoelastic properties. PMID:21644612
NASA Technical Reports Server (NTRS)
Barbely, Natasha L.; Sim, Ben W.; Kitaplioglu, Cahit; Goulding, Pat, II
2010-01-01
Difficulties in obtaining full-scale rotor low frequency noise measurements in wind tunnels are addressed via residual sound reflections due to non-ideal anechoic wall treatments. Examples illustrated with the Boeing-SMART rotor test in the National Full-Scale Aerodynamics Complex (NFAC) 40- by 80-Foot Wind Tunnel facility demonstrated that these reflections introduced distortions in the measured acoustic time histories that are not representative of free-field rotor noise radiation. A simplified reflection analysis, based on the method of images, is used to examine the sound measurement quality in such "less-than-anechoic" environment. Predictions of reflection-adjusted acoustic time histories are qualitatively shown to account for some of the spurious fluctuations observed in wind tunnel noise measurements
NASA Astrophysics Data System (ADS)
Nekuee, Seyed Amir Hossein; Akbari, Mahmood; Khavasi, Amin
2016-04-01
An accurate and fast method for guided modes extraction in monolayer colloidal crystals and their inverse replicas is presented. These three-dimensional structures are composed of a monolayer of spherical particles that can easily and simply be prepared by self-assembly method in close packed hexagonal lattices. In this work, we describe how the guided modes, even or odd modes and light cone boundary can be easily determined using phase variations of reflection and transmission coefficients. These coefficients are quickly calculated by Fourier modal method. The band structures are obtained for a monolayer of polystyrene particles and two-dimensional TiO2 inverse opal by this proposed method.
NASA Astrophysics Data System (ADS)
The acoustics research activities of the DLR fluid-mechanics department (Forschungsbereich Stroemungsmechanik) during 1988 are surveyed and illustrated with extensive diagrams, drawings, graphs, and photographs. Particular attention is given to studies of helicopter rotor noise (high-speed impulsive noise, blade/vortex interaction noise, and main/tail-rotor interaction noise), propeller noise (temperature, angle-of-attack, and nonuniform-flow effects), noise certification, and industrial acoustics (road-vehicle flow noise and airport noise-control installations).
NASA Astrophysics Data System (ADS)
Lemaire, Ph.; Georges, M.
1992-07-01
The propagation of light in linearly birefringent and optically active media, such as Bi 12SiO 20 crystals (BSO), has been widely studied by several workers. Various measurement methods of the electro-optic coefficient r41 have been described. One family of those methods consisting in measurement of the light polarization ellipticity after through the crystal has been analysed. Due to the high reflectivity of such crystals, we show that the effect of the secondary reflections can not be neglected. We present the theoretical description and analysis of this effect for one of these methods and we propose a corrective algorithm.
NASA Astrophysics Data System (ADS)
Errifaiy, Meriem; Naasse, Smail; Chahine, Chakib
2016-07-01
Our work presents an analytical study of the determination of the reflection coefficient during the interaction between the regular wave current and a horizontal plate. This study was done using the linearized potential flow theory with the evanescent modes model, while searching for complex solutions to the dispersion equation that are neither real pure nor imaginary pure. To validate the established model, it has been confronted with the experimental results of V. Rey and J. Touboul, in a first phase, and then compared to those of the numerical study by H.-X. Lin et al. Then, this model was used to study the effect of current on the reflection coefficient. xml:lang="fr"
Lawniczak, Michał; Hul, Oleh; Bauch, Szymon; Seba, Petr; Sirko, Leszek
2008-05-01
We present the results of an experimental and numerical study of the distribution of the reflection coefficient P(R) and the distributions of the imaginary P(v) and the real P(u) parts of the Wigner reaction K matrix for irregular fully connected hexagon networks (graphs) in the presence of strong absorption. In the experiment we used microwave networks, which were built of coaxial cables and attenuators connected by joints. In the numerical calculations experimental networks were described by quantum fully connected hexagon graphs. The presence of absorption introduced by attenuators was modeled by optical potentials. The distribution of the reflection coefficient P(R) and the distributions of the reaction K matrix were obtained from measurements and numerical calculations of the scattering matrix S of the networks and graphs, respectively. We show that the experimental and numerical results are in good agreement with the exact analytic ones obtained within the framework of random matrix theory. PMID:18643145
NASA Astrophysics Data System (ADS)
Aoyama, C.; Aoyama, S.
2014-12-01
The objective of this survey is to measure acoustical reflection from the methane plumes at close range by utilizing a remotely-operated vehicle, in order to quantify methane gas flux seeping out from shallow methane hydrates in the sea of japan. In the off-Joetsu area, we conducted acoustic survey for methane plumes distribution using quantitative echo sounder (Simrad EK60) and Multi beam echo sounder (SEABAT 8160) installed on R/V Natsushima, and then conducted underwater survey using ROV Hyper-Dolphin in the following methods, 1) Observing seafloor morphology, 2) Measurement methane discharge with a calibrated collecting equipment , 3) Measuring rising speed of methane bubbles with a ruler, 4) Collecting acoustic reflection data using quantitative echo sounder, 5) Observing rising methane bubbles. All processes in the underwater survey were recorded by a HD camera equipped on ROV, and those videos are used for after-cruise analysis. In the underwater survey by ROV, we found three methane plume points and successfully collected acoustic data which would detect each methane bubble. Based on videos and acoustic data obtained in this survey, detailed analysis conducted.
Grazing incidence reflection coefficients of rhodium, osmium, platinum, and gold from 50 to 300 A
NASA Technical Reports Server (NTRS)
Hettrick, M. C.; Edelstein, J.; Flint, S. A.
1985-01-01
Reflectance measurements were made of several metals illuminated from various angles with light at 14 wavelengths in the interval 46.5-283 A. The metals, Rh, Os, Pt and Au were deposited as 125 A films on a binding substrate through electron beam epitaxy. Measurements were made with a grazing incidence monochromator and a reflectometer. The data generally showed lowered reflectance with increasing angles of illumination and shorter wavelengths. The reflectance peak, however, was located at wavelengths of 100-160 A, particularly at large grazing incidences. The wavelengths correspond with the 5p to epsilon-d transition in all of the elements. Rh displayed the highest overall reflectance, and both Rh and Os were more efficient than Au or Pt.
Evaluation of the Reflection Coefficient of Microstrip Elements for Reflectarray Antennas
NASA Technical Reports Server (NTRS)
Rengarajan, Sembiam
2011-01-01
Basis functions were studied and identified that provide efficient and accurate solutions for the induced patch currents and the reflection phase in microstrip reflect arrays. The integral equation of an infinite array of microstrip elements in the form of patches or crossed dipoles excited by a uniform plane wave is solved by the method-of-moments. Efficient choices of entire domain basis functions that yield accurate results have been described.
NASA Astrophysics Data System (ADS)
Baek, Sang-In; Kim, Sung-Jo; Kim, Jong-Hyun
2015-09-01
Although the homeotropic alignment of liquid crystals is widely used in LCD TVs, no easy method exists to measure its anchoring coefficient. In this study, we propose an easy and convenient measurement technique in which a polarizing optical microscope is used in the reflective mode with an objective lens having a low depth of focus. All measurements focus on the reflection of light near the interface between the liquid crystal and alignment layer. The change in the reflected light is measured by applying an electric field. We model the response of the director of the liquid crystal to the electric field and, thus, the change in reflectance. By adjusting the extrapolation length in the calculation, we match the experimental and calculated results and obtain the anchoring coefficient. In our experiment, the extrapolation lengths were 0.31 ± 0.04 μm, 0.32 ± 0.08 μm, and 0.23 ± 0.05 μm for lecithin, AL-64168, and SE-5662, respectively.
Reflection and refraction of finite amplitude acoustic waves at a fluid-fluid interface
NASA Astrophysics Data System (ADS)
Cotaras, Frederick D.
1989-01-01
A theoretical investigation is presented of the nonlinear effects in reflection and refraction of plane finite-amplitude acoustic waves at an initially plane interface between two lossless fluids. In the first part, the terms in the equations of motion for a homogeneous, thermoviscous fluid with a single relaxation mechanism are rank ordered to determine the most important nonlinear and dissipation terms. The equations are then combined to form a general wave equation that includes the most important effects of nonlinearity and dissipation. In the second part, the terms in the boundary conditions between two lossless fluids are rank ordered to include the most important nonlinear effects. Subject to these boundary conditions, a solution of the lossless form of the aforementioned wave equation is obtained by way of second order perturbation expansion. The lossless form of the wave equation and the lossless boundary conditions are expanded, and the O (epsilon) and O (epsilon-sq) systems are solved in terms of a modified velocity potential. The analysis is performed for oblique incidence, and the boundary condition at the source is arbitrary. Effects examined include the finite displacement of the interface and the variation of the direction of the normal to the interface, both of which are caused by the motion of the interface as it responds to the incident sound.
Signal processing Model/Method for Recovering Acoustic Reflectivity of Spot Weld
Energy Science and Technology Software Center (ESTSC)
2005-09-08
empirically. For fast estimation of R using only observations beta(1, ..., T) a receiver state equation has been derived, and is attached as Eq. (3). This equation has the further advantage that the initial impulse S need not be known, rather it is estimated simultaneously. This is necessary because element failure and coupling can cause large variations in S. Constrained nonlinear least squares techniques can be applied to this equation to recover reflectivity (and initial impulse) [4]. In particular, the Gauss-Newton algorithm on the log of the sum of squared errors based on the receiver state equation is recommended. To summarize, it is the model described in Eqs. (2) and (3) that is novel, and that enables the recovery of acoustic reflectivity from the ultrasound signals. It has been verified that this reflectivity estimate provides a better indicator of weld veracity than other features previously derived from such signals.« less
Choo, Youngmin; Song, H C
2016-05-01
A computationally efficient, time-domain Helmholtz-Kirchhoff (H-K) integral was derived and applied to reconstructing surface wave profiles from reflected acoustic pulses [Walstead and Deane, J. Acoust. Soc. Am. 133, 2597-2611 (2013)]. However, the final form of the integral equation incorporating a stationary phase approximation contained a complex phase term exp(iπ/4), which cannot be treated as a simple time delay. In this work, a real time-domain H-K integral is presented that includes an additional Hilbert transform of the time-derivative of the transmitted pulse. Numerical simulation with a sinusoidal surface shows good agreement between the real time-domain formulation and exact H-K integral, while achieving a significant improvement in computational speed (e.g., 2 orders of magnitude). PMID:27250135
NASA Technical Reports Server (NTRS)
Goodman, Jerry R.; Grosveld, Ferdinand
2007-01-01
The acoustics environment in space operations is important to maintain at manageable levels so that the crewperson can remain safe, functional, effective, and reasonably comfortable. High acoustic levels can produce temporary or permanent hearing loss, or cause other physiological symptoms such as auditory pain, headaches, discomfort, strain in the vocal cords, or fatigue. Noise is defined as undesirable sound. Excessive noise may result in psychological effects such as irritability, inability to concentrate, decrease in productivity, annoyance, errors in judgment, and distraction. A noisy environment can also result in the inability to sleep, or sleep well. Elevated noise levels can affect the ability to communicate, understand what is being said, hear what is going on in the environment, degrade crew performance and operations, and create habitability concerns. Superfluous noise emissions can also create the inability to hear alarms or other important auditory cues such as an equipment malfunctioning. Recent space flight experience, evaluations of the requirements in crew habitable areas, and lessons learned (Goodman 2003; Allen and Goodman 2003; Pilkinton 2003; Grosveld et al. 2003) show the importance of maintaining an acceptable acoustics environment. This is best accomplished by having a high-quality set of limits/requirements early in the program, the "designing in" of acoustics in the development of hardware and systems, and by monitoring, testing and verifying the levels to ensure that they are acceptable.
NASA Astrophysics Data System (ADS)
Liu, Xu; Greenhalgh, Stewart
2014-09-01
Using Biot's poroelasticity theory, we derive expressions for the reflection and transmission coefficients for a plane shear wave incident on an interface separating two different poroelastic solids. The coefficients are formulated as a function of the wave incidence angle, frequency and rock properties. Specific cases calculated include the boundary between water-saturated sand and water-saturated sandstone and the gas-water interface in sand. The results show a very different interface response to that of an incident P wave. Plane SV wave incidence does not significantly excite the Biot slow P wave if the frequency of the wave is below the transition frequency. Above this frequency, an incident plane SV wave can generate a mode-converted slow Biot P wave which is actually a normal propagating wave and not highly attenuating as in the usual (diffusive) case. For an incident SV wave onto a gas-water interface, even at very high frequency, there is no significant Biot second P wave produced. For small incident angles, the gas-water interface is essentially transparent. With increasing angles, there can arise an unusual "definitive angle" in the reflection/transmission coefficient curves which is related to the change of fluid viscosity on both sides of the interface and provides a possible new means for underground fluid assessment.
Reflection coefficient of qP, qS and SH at a plane boundary between viscoelastic TTI media
NASA Astrophysics Data System (ADS)
Wang, Hongwei; Peng, Suping
2016-01-01
This paper introduces a calculation method for the effective elastic stiffness tensor matrix of the viscous-elastic TTI medium based on the Chapman theory. We then obtain the phase velocity formula and seismic wave polarization formula of the viscous-elastic TTI medium, by solving the Christoffel equation; solve the phase angle of reflection and transmission wave through the numerical method in accordance with the wave slowness ellipsoid; on the basis of this assumption, and assuming that qP, qS and SH waves occurred simultaneously at the viscous-elastic anisotropic interface, establish the sixth-order Zoeppritz equation in accordance with the boundary conditions; establish the models for the upper and lower media which are viscous-elastic HTI, TTI, etc., on the basis of the sixth-order Zoeppritz equation; and study the impact of fracture dip angle, azimuth angle and frequency on the reflection coefficient. From this we obtain the following conclusions: the reflection coefficient can identify the fracture strike and dip when any information pertaining to the media is unknown; dispersion phenomenon is obvious on the axial plane of symmetry and weakened in the plane vertical to the axial plane of symmetry; the vertical-incidence longitudinal wave can stimulate the qS wave when the dip angle is not 0° or 90° under the condition of coincidence between the symmetry planes of the upper and lower media; when the symmetry planes of the upper and lower media do not coincide and the dip angle is not 0° or 90°, then the vertical-incidence qP will stimulate the qS and SH waves at the same time; the dip angle can cause the reflection coefficient curve to have a more obvious dispersion phenomenon, while the included angle between the symmetry planes of the upper and lower media will weaken the dispersion except SH; and the intercept of reflection coefficient is affected by the fracture dip and included angle between the symmetry planes of the upper and lower media.
Spectral absorption coefficients of argon and silicon and spectral reflectivity of aluminum
NASA Technical Reports Server (NTRS)
Krascella, N. L.
1972-01-01
A theoretical investigation was conducted to estimate the spectral properties of argon as a function of pressure, temperature, and wave number. The spectral characteristics of the argon buffer gas exert a strong influence on radiative energy transfer in the in-reactor test configuration of the nuclear light bulb engine. An existing computer program was modified and used to calculate the spectral absorption coefficients of argon at total pressures of 50, 100, 250, 500, 750 and 1000 atm in the temperature interval between 1000 and 30,000 K. At each pressure and temperature, spectral properties were calculated for forty-seven wave numbers in the interval between 1000 and 1,000,000 cm/1. Estimates of the spectral absorption coefficients of silicon were made as part of an evaluation of silicon vapor as a possible buffer-gas seeding agent for the reference nuclear light bulb engine. Existing cross-section data were used to calculate the spectral characteristics of silicon at twenty-four temperatures in the interval between 2000 and 10,000 K.
NASA Technical Reports Server (NTRS)
Beatty, R. W.; Otosh, T. Y.
1978-01-01
Theoretical equations are derived for calculating the effects of local VSWR and reflection coefficient phase angle drifts on hydrogen maser frequency stability. Sample calculations made for a typical JPL maser show that under special load conditions, a VSWR drift of 0.000075/h or phase angle drive of 0.01 deg/h can produce a frequency drift of (10 to the -14th power f sub 0) Hz/h where f sub 0 is the maser frequency of approximately 1.42 x 10 to the 9th power Hz.
Rouseff, Daniel; Badiey, Mohsen; Song, Aijun
2009-11-01
The performance of a communications equalizer is quantified in terms of the number of acoustic paths that are treated as usable signal. The analysis uses acoustical and oceanographic data collected off the Hawaiian Island of Kauai. Communication signals were measured on an eight-element vertical array at two different ranges, 1 and 2 km, and processed using an equalizer based on passive time-reversal signal processing. By estimating the Rayleigh parameter, it is shown that all paths reflected by the sea surface at both ranges undergo incoherent scattering. It is demonstrated that some of these incoherently scattered paths are still useful for coherent communications. At range of 1 km, optimal communications performance is achieved when six acoustic paths are retained and all paths with more than one reflection off the sea surface are rejected. Consistent with a model that ignores loss from near-surface bubbles, the performance improves by approximately 1.8 dB when increasing the number of retained paths from four to six. The four-path results though are more stable and require less frequent channel estimation. At range of 2 km, ray refraction is observed and communications performance is optimal when some paths with two sea-surface reflections are retained. PMID:19894819
Test-bench system for a borehole azimuthal acoustic reflection imaging logging tool
NASA Astrophysics Data System (ADS)
Liu, Xianping; Ju, Xiaodong; Qiao, Wenxiao; Lu, Junqiang; Men, Baiyong; Liu, Dong
2016-06-01
The borehole azimuthal acoustic reflection imaging logging tool (BAAR) is a new generation of imaging logging tool, which is able to investigate stratums in a relatively larger range of space around the borehole. The BAAR is designed based on the idea of modularization with a very complex structure, so it has become urgent for us to develop a dedicated test-bench system to debug each module of the BAAR. With the help of a test-bench system introduced in this paper, test and calibration of BAAR can be easily achieved. The test-bench system is designed based on the client/server model. The hardware system mainly consists of a host computer, an embedded controlling board, a bus interface board, a data acquisition board and a telemetry communication board. The host computer serves as the human machine interface and processes the uploaded data. The software running on the host computer is designed based on VC++. The embedded controlling board uses Advanced Reduced Instruction Set Machines 7 (ARM7) as the micro controller and communicates with the host computer via Ethernet. The software for the embedded controlling board is developed based on the operating system uClinux. The bus interface board, data acquisition board and telemetry communication board are designed based on a field programmable gate array (FPGA) and provide test interfaces for the logging tool. To examine the feasibility of the test-bench system, it was set up to perform a test on BAAR. By analyzing the test results, an unqualified channel of the electronic receiving cabin was discovered. It is suggested that the test-bench system can be used to quickly determine the working condition of sub modules of BAAR and it is of great significance in improving production efficiency and accelerating industrial production of the logging tool.
NASA Technical Reports Server (NTRS)
Noever, D. A.; Rosenberger, F. E.
1989-01-01
A proposed experimental program to look at a series of vapor transport properties measured along solid and liquid surfaces is described. The research objectives proposed are: (1) with accuracy otherwise unobtainable on ground, to determine the coefficient of slip measured between gases and the surfaces of liquids and solids; (2) for the first time, to classify and tabulate dominant surface effects found for a variety of solids, particularly those crystalized by vapor transport; and (3) to extend understanding of settling rates predicted for cosmic dust and condensed vapor falling through planetary atmospheres. The method used to obtain these objectives, has aided, to an order of magnitude, understanding of various liquid-gas interfaces such as oil and water. But to date, no similar characterization has proved successful for solids or liquids of uncertain densities. Likewise, no data exist in either ground-based research or as part of a microgravity program that, when collected with the high accuracy expected in low gravity, could definitely settle outstanding questions in kinetic theory, molecular dynamics, and cosmic physics.
Pratson, Lincoln F.; Hutton, E.W.H.; Kettner, A.J.; Syvitski, J.P.M.; Hill, P.S.; George, D.A.; Milligan, T.G.
2007-01-01
Flood deposition and storm reworking of sediments on the inner shelf can change the mixture of grain sizes on the seabed and thus its porosity, bulk density, bulk compressional velocity and reflectivity. Whether these changes are significant enough to be detectable by repeat sub-bottom sonar surveys, however, is uncertain. Here the question is addressed through numerical modeling. Episodic flooding of a large versus small river over the course of a century are modeled with HYDROTREND using the drainage basin characteristics of the Po and Pescara Rivers (respectively). A similarly long stochastic record of storms offshore of both rivers is simulated from the statistics of a long-term mooring recording of waves in the western Adriatic Sea. These time series are then input to the stratigraphic model SEDFLUX2D, which simulates flood deposition and storm reworking on the inner shelf beyond the river mouths. Finally, annual changes in seabed reflectivity across these shelf regions are computed from bulk densities output by SEDFLUX2D and compressional sound speeds computed from mean seafloor grain size using the analytical model of Buckingham [1997. Theory of acoustic attenuation, dispersion, and pulse propagation in unconsolidated granular materials including marine sediments. Journal of the Acoustical Society of America 102, 2579-2596; 1998. Theory of compressional and shear waves in fluidlike marine sediments. Journal of the Acoustical Society of America 103, 288-299; 2000. Wave propagation, stress relaxation, and grain-tograin shearing in saturated, unconsolidated marine sediments. Journal of the Acoustical Society of America 108, 2796-2815]. The modeling predicts reflectivities that change from 9 dB for muds farther offshore, values that agree with reflectivity measurements for these sediment types. On local scales of ???100 m, however, maximum changes in reflectivity are <0.5 dB. So are most annual changes in reflectivity over all water depths modeled (i.e., 0-35 m
NASA Astrophysics Data System (ADS)
Pratson, Lincoln F.; Hutton, Eric W. H.; Kettner, Albert J.; Syvitski, James P. M.; Hill, Paul S.; George, Douglas A.; Milligan, Timothy G.
2007-02-01
Flood deposition and storm reworking of sediments on the inner shelf can change the mixture of grain sizes on the seabed and thus its porosity, bulk density, bulk compressional velocity and reflectivity. Whether these changes are significant enough to be detectable by repeat sub-bottom sonar surveys, however, is uncertain. Here the question is addressed through numerical modeling. Episodic flooding of a large versus small river over the course of a century are modeled with HYDROTREND using the drainage basin characteristics of the Po and Pescara Rivers (respectively). A similarly long stochastic record of storms offshore of both rivers is simulated from the statistics of a long-term mooring recording of waves in the western Adriatic Sea. These time series are then input to the stratigraphic model SEDFLUX2D, which simulates flood deposition and storm reworking on the inner shelf beyond the river mouths. Finally, annual changes in seabed reflectivity across these shelf regions are computed from bulk densities output by SEDFLUX2D and compressional sound speeds computed from mean seafloor grain size using the analytical model of Buckingham [1997. Theory of acoustic attenuation, dispersion, and pulse propagation in unconsolidated granular materials including marine sediments. Journal of the Acoustical Society of America 102, 2579-2596; 1998. Theory of compressional and shear waves in fluidlike marine sediments. Journal of the Acoustical Society of America 103, 288-299; 2000. Wave propagation, stress relaxation, and grain-tograin shearing in saturated, unconsolidated marine sediments. Journal of the Acoustical Society of America 108, 2796-2815]. The modeling predicts reflectivities that change from <12 dB for sands on the innermost shelf to >9 dB for muds farther offshore, values that agree with reflectivity measurements for these sediment types. On local scales of ˜100 m, however, maximum changes in reflectivity are <0.5 dB. So are most annual changes in reflectivity
NASA Astrophysics Data System (ADS)
Miyoshi, S.; Tokunaga, T.; Mogi, K.
2011-12-01
Many studies have shown that abnormally high pore pressure can be generated by the act of clay as semipermeable membrane. The reason is that surface electricity of smectite composing of clay generates the electric double layer in clay pores that ristricts the migration of ions. The act of clay as semipermeable membrane has not been understood quantitatively from the view points of the microscopic structure and the mineral compositions of clay. The authors have developed a laboratory apparatus and a numerical simulator to obtain the fundamental data for the quantitative understanding of the phenomena. In this study, the samples of a tarbidite and a clay of Niigata sedimentary basin were collected. The analysis of the microscopic structure and the mineralogy and the laboratory experiments to measure the reflection coefficient were done. The large part of pore radius of clay is less than 1.0μm while the pore radius of approximately 35% of the pore volume of tarbidite is more than 1.0μm. The XRD chart of the tarbidite does not show the peek of smectite while that of the clay shows it. Based on the data that the authors have obtained so far, it is suggested that there is a relationship between the reflection coefficient and the methylene blue adsorption of clay.
Nikolic, M.V. . E-mail: maria@mi.sanu.ac.yu; Paraskevopoulos, K.M.; Aleksic, O.S.; Zorba, T.T.; Savic, S.M.; Lukovic, D.T.
2007-08-07
Single phase complex spinel (Mn, Ni, Co, Fe){sub 3}O{sub 4} samples were sintered at 1050, 1200 and 1300 deg. C for 30 min and at 1200 deg. C for 120 min. Morphological changes of the obtained samples with the sintering temperature and time were analyzed by X-ray diffraction and scanning electron microscope (SEM). Room temperature far infrared reflectivity spectra for all samples were measured in the frequency range between 50 and 1200 cm{sup -1}. The obtained spectra for all samples showed the presence of the same oscillators, but their intensities increased with the sintering temperature and time in correlation with the increase in sample density and microstructure changes during sintering. The measured spectra were numerically analyzed using the Kramers-Kroenig method and the four-parameter model of coupled oscillators. Optical modes were calculated for six observed ionic oscillators belonging to the spinel structure of (Mn, Ni, Co, Fe){sub 3}O{sub 4} of which four were strong and two were weak.
NASA Astrophysics Data System (ADS)
Hachay, Olga; Dryagin, Veniamin; Igolkina, Galina; Khachay, Oleg
2013-04-01
It is provided a comparison of no equilibrium effects by independent hydro dynamical and seism acoustic influence on an oil layer. It is known, that by drainage and steeps the hysteresis effect on curves of the relative phase permeability in dependence from porous medium water saturation by some cycles of influence: drainage-steep-drainage is observed. In earlier papers the analysis of the seism acoustic monitoring data in regimes of phone radiation, response on the first influence of given frequency and on the second influence is developed. For the analysis of seism acoustic response in time on fixed intervals along the borehole an algorithm of phase diagrams of the state of many phase medium is suggested In that paper on the base of developed algorithm a new algorithm of analyze of space, but integral in time for equal observation periods changing by the method of phase diagram state of many phase medium in the oil layer is developed. The paper was supported by the Program of Presidium UB RAS 2012-2014. Key words: Oil and gas deposits, seism acoustic borehole monitoring data, new method of processing, reflection of no equilibrium two phase processes, heterogeneous media.
Zhang, Honghu
2006-04-01
The acoustical radiosity method is a computationally expensive acoustical simulation algorithm that assumes an enclosure with ideal diffuse reflecting boundaries. Miles observed that for such an enclosure, the sound energy decay of every point on the boundaries will gradually converge to exponential manner with a uniform decay rate. Therefore, the ratio of radiosity between every pair of points on the boundaries will converge to a constant, and the radiosity across the boundaries will approach a fixed distribution during the sound decay process, where radiosity is defined as the acoustic power per unit area leaving (or being received by) a point on a boundary. We call this phenomenon the "relaxation" of the sound field. In this paper, we study the relaxation in rooms of different shapes with different boundary absorptions. Criteria based on the relaxation of the sound field are proposed to terminate the costly and unnecessary radiosity computation in the later phase, which can then be replaced by a fast regression step to speed up the acoustical radiosity simulation. PMID:16642833
NASA Astrophysics Data System (ADS)
Le Gonidec, Yves; Gibert, Dominique
2007-05-01
The wavelet response is a multiscale method based on the continuous wavelet transform. We use it to characterize the acoustic reflectivity of a layer of glass beads with diameter d = 1 mm randomly arranged in water. The volumetric concentration is ϕ ≃ 63% of spherical inclusions. The wavelet response is measured over a large frequency range (100 kHz ≤ f ≤ 5 MHz) where five different acoustic regimes are identified on the basis of scattering phenomena. A strong decrease in the reflectivity occurs when the wavelength of the incident wave is twice the bead diameter, a situation where lateral scattering is dominant. The energy ratio of the ballistic and the coda parts of the wavelet response reveals a clear transition from a ballistic propagation regime to a diffusion regime where multiple scattering occurs. The experimental data are explained with an effective medium theory approach: the reflectivity data in the low-frequency domain of the spanned frequency range are correctly reproduced with quasi-static models. For higher frequencies, more sophisticated models accounting for multiple scattering must be used. The high-frequency part of the experimental reflectivity curve may be explained by strong multiple scattering at the top of the glass beads located at the surface of the layer and corresponds to the optical geometric limit.
Marangos, Orestes; Misra, Anil; Spencer, Paulette; Katz, J. Lawrence
2013-01-01
Composite restorations in modern restorative dentistry rely on the bond formed in the adhesive-infiltrated acid-etched dentin. The physical characteristics of etched dentin are, therefore, of paramount interest. However, characterization of the acid-etched zone in its natural state is fraught with problems stemming from a variety of sources including its narrow size, the presence of water, heterogeneity, and spatial scale dependency. We have developed a novel homotopic (same location) measurement methodology utilizing scanning acoustic microscopy (SAM). Homotopic measurements with SAM overcome the problems encountered by other characterization/ imaging methods. These measurements provide us with acoustic reflectance at the same location of both the pre- and post-etched dentin in its natural state. We have applied this methodology for in vitro measurements on dentin samples. Fourier spectra from acid-etched dentin showed amplitude reduction and shifts of the central frequency that were location dependent. Through calibration, the acoustic reflectance of acid-etched dentin was found to have complex and non-monotonic frequency dependence. These data suggest that acid-etching of dentin results in a near-surface graded layer of varying thickness and property gradations. The measurement methodology described in this paper can be applied to systematically characterize mechanical properties of heterogeneous soft layers and interfaces in biological materials. PMID:21429849
NASA Astrophysics Data System (ADS)
Maydanyuk, Sergei P.
In the paper the closed Friedmann-Robertson-Walker model with quantization in the presence of the positive cosmological constant and radiation is studied. For analysis of tunneling probability for birth of an asymptotically de Sitter, inflationary universe as a function of the radiation energy, a new definition of a "free" wave propagating inside strong fields is proposed. On such a basis, tunneling boundary condition is corrected, penetrability and reflection relative to the barrier are calculated in fully quantum stationary approach. For the first time nonzero interference between the incident and reflected waves has been taken into account which turns out to play important role inside cosmological potentials and could be explained by non-locality of barriers in quantum mechanics. Inside the whole region of radiation energy the tunneling probability for the birth of the inflationary universe is found to be close to its value obtained in the semiclassical approach. The reflection from the barrier is determined for the first time (which differs essentially on 1 at the energy of radiation close to the barrier height). The proposed method could be easily generalized on the cosmological models with barriers of arbitrary shape, as demonstrated for the FRW model with included Chaplygin gas. The result is stable for variations of the studied barriers, accuracy is found to be 11-18 digits for all coefficients and energies below the barrier height.
NASA Astrophysics Data System (ADS)
Wei, Jianwei; Lee, Zhongping; Ondrusek, Michael; Mannino, Antonio; Tzortziou, Maria; Armstrong, Roy
2016-03-01
The spectral slope of the absorption coefficient of colored dissolved and detrital material (CDM), Scdm (units: nm-1), is an important optical parameter for characterizing the absorption spectral shape of CDM. Although highly variable in natural waters, in most remote sensing algorithms, this slope is either kept as a constant or empirically modeled with multiband ocean color in the visible domain. In this study, we explore the potential of semianalytically retrieving Scdm with added ocean color information in the ultraviolet (UV) range between 360 and 400 nm. Unique features of hyperspectral remote sensing reflectance in the UV-visible wavelengths (360-500 nm) have been observed in various waters across a range of coastal and open ocean environments. Our data and analyses indicate that ocean color in the UV domain is particularly sensitive to the variation of the CDM spectral slope. Here, we used a synthesized dataset to show that adding UV wavelengths to the ocean color measurements will improve the retrieval of Scdm from remote sensing reflectance considerably, while the spectral band settings of past and current satellite ocean color sensors cannot fully account for the spectral variation of remote sensing reflectance. Results of this effort support the concept to include UV wavelengths in the next generation of satellite ocean color sensors.
NASA Astrophysics Data System (ADS)
Jaffe, J. S.; Ohman, M. D.; De Robertis, A.
A new instrument Optical-Acoustic Submersible Imaging System (OASIS) has been developed for three-dimensional acoustic tracking of zooplankton with concurrent optical imaging to verify the identity of the insonified organisms. OASIS also measures in situ target strengths (TS) of freely swimming zooplankton and nekton of known identity and 3-D orientation. The system consists of a three-dimensional acoustic imaging system (FishTV), a sensitive optical CCD camera with red-filtered strobe illumination, and ancillary oceanographic sensors. The sonar triggers the acquisition of an optical image when it detects the presence of a significant target in the precise location where the camera, strobe and sonar are co-registered. Acoustic TS can then be related to the optical image, which permits identification of the animal and its 3-D aspect. The system was recently deployed (August 1996) in Saanich Inlet, B.C., Canada. Motile zooplankton and nekton were imaged with no evidence of reaction to or avoidance of the OASIS instrument package. Target strengths of many acoustic reflectors were recorded in parallel with the optical images, triggered by the presence of an animal in the correct location of the sonar system. Inspection of the optical images, corroborated with zooplankton sampling with a MOCNESS net, revealed that the joint optically and acoustically sensed taxa at the site were the euphausiid Euphausia pacifica, the gammarid amphipod Orchomene obtusa, and a gadid fish. The simultaneous optical and acoustic images permitted an exact correlation of TS and taxa. Computer simulations from a model of the backscattered strength from euphausiids are in good agreement with the observed data.
Kanick, S. C.; Gamm, U. A.; Schouten, M.; Sterenborg, H. J. C. M.; Robinson, D. J.; Amelink, A.
2011-01-01
This paper presents a relationship between the intensity collected by a single fiber reflectance device (RSF) and the fiber diameter (dfib) and the reduced scattering coefficient ( μs′) and phase function (p(θ)) of a turbid medium. Monte Carlo simulations are used to identify and model a relationship between RSF and dimensionless scattering ( μs′dfib). For μs′dfib > 10 we find that RSF is insensitive to p(θ). A solid optical phantom is constructed with μs′ ≈ 220 mm−1 and is used to convert RSF of any turbid medium to an absolute scale. This calibrated technique provides accurate estimates of μs′ over a wide range ([0.05 – 8] mm−1) for a range of dfib ([0.2 – 1] mm). PMID:21698029
Coherent reflection from surface gravity water waves during reciprocal acoustic transmissions.
Badiey, Mohsen; Song, Aijun; Smith, Kevin B
2012-10-01
During a recent experiment in Kauai, Hawaii, reciprocal transmissions were conducted between two acoustic transceivers mounted on the seafloor at a depth of 100 m. The passage of moving surface wave crests was shown to generate focused and intense coherent acoustic returns, which had increasing or decreasing delay depending on the direction of propagation relative to the direction of surface wave crests. It is shown that a rough surface two-dimensional parabolic equation model with an evolving sea surface can produce qualitative agreement with data for the dynamic surface returns. PMID:23039567
NASA Technical Reports Server (NTRS)
Huff, R. G.
1984-01-01
Spectral analyses of static pressure fluctuations measured in turbine engine combustors at low engine speed show good agreement with theory. At idle speed the high pressure turbine is unchoked. Above idle speed the turbine chokes and a significant change in the shape of the measured combustor pressure spectrum is observed. A simplified theoretical model of the acoustic pressure generated in the combustor due to the turbulence-flame front interaction did not account for acoustic waves reflected from the turbine. By retaining this simplified combustion noise source model and adding a partial reflecting plane at the turbine and combustor inlet, a simple theoretical model was developed that reproduces the undulations in the combustor fluctuating pressure spectra. Plots of the theoretical combustor fluctuating pressure spectra are compared to the measured pressure spectra obtained from the CF6-50 turbofan engine over a range of engine operating speeds. The simplified combustion noise theory when modified by a simple turbine reflecting plane adequately accounts for the changes in measured combustor pressure spectra. It is further concluded that the shape of the pressure spectra downstream of the turbine, neglecting noise generated by the turbine itself, will be the combustion noise spectra unchanged except for the level reduction due to the energy blocked by the turbine.
NASA Astrophysics Data System (ADS)
Huff, R. G.
Spectral analyses of static pressure fluctuations measured in turbine engine combustors at low engine speed show good agreement with theory. At idle speed the high pressure turbine is unchoked. Above idle speed the turbine chokes and a significant change in the shape of the measured combustor pressure spectrum is observed. A simplified theoretical model of the acoustic pressure generated in the combustor due to the turbulence-flame front interaction did not account for acoustic waves reflected from the turbine. By retaining this simplified combustion noise source model and adding a partial reflecting plane at the turbine and combustor inlet, a simple theoretical model was developed that reproduces the undulations in the combustor fluctuating pressure spectra. Plots of the theoretical combustor fluctuating pressure spectra are compared to the measured pressure spectra obtained from the CF6-50 turbofan engine over a range of engine operating speeds. The simplified combustion noise theory when modified by a simple turbine reflecting plane adequately accounts for the changes in measured combustor pressure spectra. It is further concluded that the shape of the pressure spectra downstream of the turbine, neglecting noise generated by the turbine itself, will be the combustion noise spectra unchanged except for the level reduction due to the energy blocked by the turbine.
NASA Astrophysics Data System (ADS)
Huff, R. G.
1984-10-01
Spectral analyses of static pressure fluctuations measured in turbine engine combustors at low engine speed show good agreement with theory. At idle speed the high pressure turbine is unchoked. Above idle speed the turbine chokes and a significant change in the shape of the measured combustor pressure spectrum is observed. A simplified theoretical model of the acoustic pressure generated in the combustor due to the turbulence-flame front interaction did not account for acoustic waves reflected from the turbine. By retaining this simplified combustion noise source model and adding a partial reflecting plane at the turbine and combustor inlet, a simple theoretical model was developed that reproduces the undulations in the combustor fluctuating pressure spectra. Plots of the theoretical combustor fluctuating pressure spectra are compared to the measured pressure spectra obtained from the CF6-50 turbofan engine over a range of engine operating speeds. The simplified combustion noise theory when modified by a simple turbine reflecting plane adequately accounts for the changes in measured combustor pressure spectra. It is further concluded that the shape of the pressure spectra downstream of the turbine, neglecting noise generated by the turbine itself, will be the combustion noise spectra unchanged except for the level reduction due to the energy blocked by the turbine.
NASA Astrophysics Data System (ADS)
Jacques, S. L.; Samatham, R.; Phillips, K. G.
2011-03-01
Optical clearing of mouse dermis by glycerol was tested by reflectance-mode confocal microscopy (rCSLM) using 488- nm light. The reflectance signal R(z) was acquired as a function of the depth of the focus (z) within the upper 100 μm of freshly excised mouse dermis. The results specify the scattering coefficient (μs [cm-1]) and the anisotropy of scattering (g [dimensionless]). The absorption is too low to exert an effect. The results, published in Samatham et al., Journal of Innovative Optical Health Sciences 2010, 3(3):183-188, described how the clearing effect of glycerol was to increase g toward nearly 1.0, while having only a modest effect on μs. In other words, glycerol caused light scattering to become very forward-directed, but did not strongly alter the number of scattering events per unit length of photon path. This paper discusses the possible mechanism of action that is responsible for this clearing effect.
NASA Astrophysics Data System (ADS)
Karagiannis, Georgios T.; Grivas, Ioannis; Tsingotjidou, Anastasia; Apostolidis, Georgios K.; Grigoriadou, Ifigeneia; Dori, I.; Poulatsidou, Kyriaki-Nefeli; Doumas, Argyrios; Wesarg, Stefan; Georgoulias, Panagiotis
2015-03-01
Malignant melanoma is a form of skin cancer, with increasing incidence worldwide. Early diagnosis is crucial for the prognosis and treatment of the disease. The objective of this study is to develop a novel animal model of melanoma and apply a combination of the non-invasive imaging techniques acoustic microscopy, infrared (IR) and Raman spectroscopies, for the detection of developing tumors. Acoustic microscopy provides information about the 3D structure of the tumor, whereas, both spectroscopic modalities give qualitative insight of biochemical changes during melanoma development. In order to efficiently set up the final devices, propagation of ultrasonic and electromagnetic waves in normal skin and melanoma simulated structures was performed. Synthetic and grape-extracted melanin (simulated tumors), endermally injected, were scanned and compared to normal skin. For both cases acoustic microscopy with central operating frequencies of 110MHz and 175MHz were used, resulting to the tomographic imaging of the simulated tumor, while with the spectroscopic modalities IR and Raman differences among spectra of normal and melanin- injected sites were identified in skin depth. Subsequently, growth of actual tumors in an animal melanoma model, with the use of human malignant melanoma cells was achieved. Acoustic microscopy and IR and Raman spectroscopies were also applied. The development of tumors at different time points was displayed using acoustic microscopy. Moreover, the changes of the IR and Raman spectra were studied between the melanoma tumors and adjacent healthy skin. The most significant changes between healthy skin and the melanoma area were observed in the range of 900-1800cm-1 and 350-2000cm-1, respectively.
Near-field/far-field array manifold of an acoustic vector-sensor near a reflecting boundary.
Wu, Yue Ivan; Lau, Siu-Kit; Wong, Kainam Thomas
2016-06-01
The acoustic vector-sensor (a.k.a. the vector hydrophone) is a practical and versatile sound-measurement device, with applications in-room, open-air, or underwater. It consists of three identical uni-axial velocity-sensors in orthogonal orientations, plus a pressure-sensor-all in spatial collocation. Its far-field array manifold [Nehorai and Paldi (1994). IEEE Trans. Signal Process. 42, 2481-2491; Hawkes and Nehorai (2000). IEEE Trans. Signal Process. 48, 2981-2993] has been introduced into the technical field of signal processing about 2 decades ago, and many direction-finding algorithms have since been developed for this acoustic vector-sensor. The above array manifold is subsequently generalized for outside the far field in Wu, Wong, and Lau [(2010). IEEE Trans. Signal Process. 58, 3946-3951], but only if no reflection-boundary is to lie near the acoustic vector-sensor. As for the near-boundary array manifold for the general case of an emitter in the geometric near field, the far field, or anywhere in between-this paper derives and presents that array manifold in terms of signal-processing mathematics. Also derived here is the corresponding Cramér-Rao bound for azimuth-elevation-distance localization of an incident emitter, with the reflected wave shown to play a critical role on account of its constructive or destructive summation with the line-of-sight wave. The implications on source localization are explored, especially with respect to measurement model mismatch in maximum-likelihood direction finding and with regard to the spatial resolution between coexisting emitters. PMID:27369140
NASA Astrophysics Data System (ADS)
Schmeltz, M.; Froidefond, J.-M.; Jourdain, F.; Martiny, N.
2009-08-01
During the "Optic-Congo" oceanographic survey which took place in 2005 on board the "Beautemp-Beaupré" SHOM vessel, different optical measurements of the surface water were acquired using a TRIOS radiance sensor fixed onboard a mini-catamaran. Hydrological measurements (CTD, fluorescence, attenuation, scattering) and water samples were simultaneously collected in order to measure SPM, Chlorophyll-a and CDOM concentrations. Four types of surface water colours (blue, green-yellow, dark and brown) were identified. The main characteristics of these waters were the very low Chlorophyll-a concentrations for this period of the year (March), and the very high CDOM concentrations along the Congo coast, and particularly in the turbid plume of the Congo River. The attenuation and scattering measurements highlighted the predominance of organic matter at the water surface. These observations were documented using a beam electron microscope and by microanalysis. This data set was used to classify the water bodies along the Gabon and Congo coasts. We propose here to use the remote sensing reflectance (Rrs) measurements to invert the IOP (absorption (a) and backscattering (bb)) using the WASI numerical bio-optical model. The model is iterative: the Rrs WASI simulations are computed given initial values of ocean constituents' concentrations and iteratively adjusted to the Rrs in-situ measurements. The IOP computations are satisfying when the correlations between simulated and measured Rrs are optimized. Then, the attenuation coefficients (Kd) are computed from the IOP coefficients. These results are compared with measurements of Ku carried out during the survey.
NASA Astrophysics Data System (ADS)
Saulquin, Bertand; Hamdi, Anouar; Populus, Jacques; Loutier, Romain; Demaria, Julien; Mangin, Antoine; D'Andon, Odile Fanton
2010-12-01
Accurate estimations of the diffuse attenuation coefficient is critical to understand physical processes such as the heat transfer in the upper layer of the ocean and also biological processes such as phytoplankton photosynthesis in the ocean euphotic zone. Light availability in the water column and the seabed determine the euphotic zone and constraints the type and distribution of the algae species. The EuSeaMap project's aim is to characterize at a resolution of 250m the European infralitoral benthic zone, according to biology, physic and geology criteriums and using observations and models. Satellite observations of the diffuse attenuation coefficient of the downwelling spectral irradiance at wavelength 490 nm (Kd490) or the diffuse attenuation coefficient for the downwelling photosynthetically available radiation (KdPAR) is an effective method to provide large scale maps of these parameters at high spatial and temporal resolution. Several empirical and semi-analytical models are commonly used to derive the Kd490 and KdPAR maps from ocean colour satellite sensors such as the Medium Resolution Imaging Spectrometer Instrument (MERIS), the Sea- viewing Wide Field-of-view Sensor (SeaWiFS), and the Moderate Resolution Imaging Spectroradiometer (MODIS). Most of these existing empirical or semi- analytical models have been calibrated on open ocean waters and provide good results in these areas, but tend to underestimate the attenuation of light in coastal waters, our area of interest. We propose here a new estimation of the euphotic depth and the KdPAR for coastal European waters using MERIS reflectances at the resolution of 1km and 250 m. First, a semi-analytical model is used to estimate the Kd490, and in a second step, two relationships have been developed between the KdPAR and the Kd490 for respectively clear and turbid waters. Satellite-derived fields of Kd490 and the deduced KdPAR are validated using matchups collected over the world. Distribution maps of seabed
NASA Astrophysics Data System (ADS)
Desjouy, Cyril; Ollivier, Sébastien; Marsden, Olivier; Karzova, Maria; Blanc-Benon, Philippe
2016-02-01
The local interactions occurring between incident and reflected shock waves in the vicinity of rigid surfaces are investigated. Both regular and irregular — also called von Neumann — regimes of reflection are studied, via experimental and numerical simulations. Shock waves are produced experimentally with a 20 kV electrical spark source which allows the generation of spherically diverging acoustic shocks. The behaviour of the resulting weak acoustic shocks near rigid boundaries is visualized with a Schlieren optical technique which allows the spatial structure of the shocks to be studied. In particular, the evolution of the Mach stem forming above a flat surface is examined, and its height is observed to be directly linked to the angle of incidence and the pressure amplitude of the incident shock. The propagation of an acoustic shock between two parallel rigid boundaries is also studied. It is shown that the strong interactions between the Mach stems emerging from the two boundaries can lead to a drastic modification of the morphology of the acoustic field in the waveguide. Experimental results are compared to numerical results obtained from high-order finite-difference based simulations of the 2D Navier-Stokes equations. The good agreement between the experimental distribution of the acoustic field and numerical results suggests that numerical simulations are promising as a predictive tool to study nonlinear acoustic propagation of acoustic waves in complex geometrical configurations with rigid boundaries.
Acoustic characteristics of the medium with gradient change of impedance
NASA Astrophysics Data System (ADS)
Hu, Bo; Yang, Desen; Sun, Yu; Shi, Jie; Shi, Shengguo; Zhang, Haoyang
2015-10-01
The medium with gradient change of acoustic impedance is a new acoustic structure which developed from multiple layer structures. In this paper, the inclusion is introduced and a new set of equations is developed. It can obtain better acoustic properties based on the medium with gradient change of acoustic impedance. Theoretical formulation has been systematically addressed which demonstrates how the idea of utilizing this method. The sound reflection and absorption coefficients were obtained. At last, the validity and the correctness of this method are assessed by simulations. The results show that appropriate design of parameters of the medium can improve underwater acoustic properties.
Transmission and reflection of acoustic and entropy waves through a stator-rotor stage
NASA Astrophysics Data System (ADS)
Bauerheim, Michael; Duran, Ignacio; Livebardon, Thomas; Wang, Gaofeng; Moreau, Stéphane; Poinsot, Thierry
2016-07-01
The propagation of acoustic, entropy and vorticity waves through turbine stages is of significant interest in the field of core noise. In particular, entropy spots have been shown to generate significant noise when accelerated through turbine stages: the so-called indirect combustion noise. Analytical models for the propagation of acoustic, vorticity and entropy waves through a stator vane, developed since the seventies, are generally based on restrictive assumptions such as low frequency waves. In order to analyze such assumptions, the theory of Cumpsty and Marble is extended to rotating rows and applied to a 2D stator-rotor turbine stage. The theoretical transfer functions are then compared with numerical predictions from forced compressible Large-Eddy Simulations of a 2D stator-rotor configuration, using a fluid-fluid coupling strategy with an overset-grid method. The comparisons between the analytical model and the simulations are in good agreement. To improve the analytical predictions, the attenuation due to the entropy spot deformation through the stator vane or the rotor blade is then included, modeled either analytically or extracted from the mean flow of the simulations. The complete analytical model reveals a good agreement with 2D simulations, which allows the prediction and minimization of both direct and indirect noise at the design-stage without computation.
Reflection of an acoustic line source by an impedance surface with uniform flow
NASA Astrophysics Data System (ADS)
Brambley, E. J.; Gabard, G.
2014-10-01
An exact analytic solution is derived for the 2D acoustic pressure field generated by a time-harmonic line mass source located above an impedance surface with uniform grazing flow. Closed-form asymptotic solutions in the far field are also provided. The analysis is valid for both locally-reacting and nonlocally-reacting impedances, as is demonstrated by analyzing a nonlocally reacting effective impedance representing the presence of a thin boundary layer over the surface. The analytic solution may be written in a form suggesting a generalization of the method of images to account for the impedance surface. The line source is found to excite surface waves on the impedance surface, some of which may be leaky waves which contradict the assumption of decay away from the surface predicted in previous analyses of surface waves with flow. The surface waves may be treated either (correctly) as unstable waves or (artificially) as stable waves, enabling comparison with previous numerical or mathematical studies which make either of these assumptions. The computer code for evaluating the analytic solution and far-field asymptotics is provided in the supplementary material. It is hoped this work will provide a useful benchmark solution for validating 2D numerical acoustic codes.
NASA Astrophysics Data System (ADS)
Saito, Ikumi; Mizutani, Koichi; Wakatsuki, Naoto; Kawabe, Satoshi
2009-07-01
It is important to maintain an adequate indoor temperature for comfortable working conditions, improvement of the rate of production of farm goods grown in greenhouses, and for saving energy. Thus, it is necessary to measure the temperature distribution to realize efficient air-conditioning systems. However, we have to use many conventional instruments to measure the temperature distribution. We proposed a measurement system for vertical temperature distribution using a single pair of loudspeaker (SP) and microphone (MIC), and acoustic reflectors. This system consists of SP, MIC, and multiple acoustic reflectors, and it can be used to determine the temperature distribution from the mean temperature of the area bounded by two reflectors. In experiments, the vertical temperature distribution was measured using five sound probes in a large facility every 20 s for 24 h. From the results of this experiment, it was verified that this system can be used to measure the vertical temperature distribution from the mean temperature of each area bounded by two reflectors. This system could be used to measure the change in the temperature distribution over time. We constructed a simple system to measure the vertical temperature distribution.
Sun, Junqiang; Wang, Menghua
2015-11-01
The Visible Infrared Imaging Radiometer Suite (VIIRS) is now entering its fourth year of in-orbit global environmental observation and is producing a wide range of scientific output. The ocean color products in particular require a level of accuracy from the reflective solar bands (RSBs) that is a magnitude higher than the specification. In this work, we present an updated and completed core calibration pipeline that achieves the best sensor data records (SDR) to date and helps the ocean color products to reach maturity. We review the core calibration methodology of the RSBs and describe each essential input, including the solar diffuser stability monitor, the solar diffuser (SD), and lunar calibrations. Their associated issues, along with the successful mitigation and improved results, are described and presented. In particular, we illuminate the inaccuracy suffered due to the evolving angular dependence in the degradation of the on-board SD that impacts the heart of the RSB calibration, but also show that lunar-based calibration instead provides the correct long-term baseline for the successful restoration of the core methodology. The new look-up tables, which combine the coefficients from the SD-based and lunar-based calibrations, produce the optimal result, with an estimated accuracy of ∼0.2%. This hybrid approach highlights significant progress in the VIIRS RSB calibration and marks a completion of the core calibration result upon which other physical impacts or scientific issues can then be more accurately examined. We demonstrate the significant improvement and its impact on the ocean color products by comparing the current official output to the newly generated result. Lastly, we point out that this hybrid calibration coefficients scheme is made possible by a VIIRS design and layout change over its predecessor, the Moderate Resolution Imaging Spectroradiometer, that allows both the SD and the moon to be viewed by the RSB at the same angle of incidence
NASA Astrophysics Data System (ADS)
Karagiannis, Georgios; Apostolidis, Georgios; Georgoulias, Panagiotis
2016-03-01
Melanoma is a very malicious type of cancer as it metastasizes early and hence its late diagnosis leads to death. Consequently, early diagnosis of melanoma and its removal is considered the most effective way of treatment. We present a design of a high frequency acoustic microscopy and infrared reflectance system for the early detection of melanoma. Specifically, the identification of morphological changes related to carcinogenesis is required. In this work, we simulate of the propagation of the ultrasonic waves of the order of 100 MHz as well as of electromagnetic waves of the order of 100 THz in melanoma structures targeting to the estimation and optimization of the basic characteristics of the systems. The simulation results of the acoustic microscopy subsystem aim to provide information such as the geometry of the transducer, the center frequency of operation, the focal length where the power transmittance is optimum and the spot size in focal length. As far as the infrared is concerned the optimal frequency range and the spot illumination size of the external probe is provided. This information is next used to assemble a properly designed system which is applied to melanoma phantoms as well as real skin lesions. Finally, the measurement data are visualized to reveal the information of the experimented structures, proving noteworthy accuracy.
Hierlemann, A.; Hill, M.; Ricco, A.J.; Staton, A.W.; Thomas, R.C.
1999-01-11
We have developed instrumentation to enable the combination of surface acoustic wave (SAW) sensor measurements with direct, in-situ molecular spectroscopic measurements to understand the response of the SAW sensors with respect to the interfacial chemistry of surface-confined sensing films interacting with gas-phase analytes. Specifically, the instrumentation and software was developed to perform in-situ Fourier-transform infrared external-reflectance spectroscopy (FTIR-ERS) on operating SAW devices during dosing of their chemically modified surfaces with analytes. By probing the surface with IR spectroscopy during gas exposure, it is possible to understand in unprecedented detail the interaction processes between the sorptive SAW coatings and the gaseous analyte molecules. In this report, we provide details of this measurement system, and also demonstrate the utility of these combined measurements by characterizing the SAW and FTIR-ERS responses of organic thin-film sensor coatings interacting with gas-phase analytes.
NASA Technical Reports Server (NTRS)
Kleinstein, G. G.; Gunzburger, M. D.
1976-01-01
An integral conservation law for wave numbers is considered. In order to test the validity of the proposed conservation law, a complete solution for the reflection and transmission of an acoustic wave impinging normally on a material interface moving at a constant speed is derived. The agreement between the frequency condition thus deduced from the dynamic equations of motion and the frequency condition derived from the jump condition associated with the integral equation supports the proposed law as a true conservation law. Additional comparisons such as amplitude discontinuities and Snells' law in a moving media further confirm the stated proposition. Results are stated concerning frequency and wave number relations across a shock front as predicted by the proposed conservation law.
Pearce, D; Verkman, A S
1989-06-01
Two independent methods, induced osmosis and solvent drag, were used to determine the reflection coefficients for NaCl (sigma NaCl) in brush border and basolateral membrane vesicles isolated from rabbit proximal tubule. In the induced osmosis method, vesicles loaded with sucrose were subjected to varying inward NaCl gradients in a stopped-flow apparatus. sigma NaCl was determined from the osmolality of the NaCl solution required to cause no initial osmotic water flux as measured by light scattering (null point). By this method sigma NaCl was greater than 0.92 for both apical and basolateral membranes with best estimates of 1.0. sigma NaCl was determined by the solvent drag method using the Cl-sensitive fluorescent indicator, 6-methoxy-N-[3-sulfopropyl]quinolinium (SPQ), to detect the drag of Cl into vesicles by inward osmotic water movement caused by an outward osmotic gradient. sigma NaCl was determined by comparing experimental data with theoretical curves generated using the coupled flux equations of Kedem and Katchalsky. By this method we found that sigma NaCl was greater than 0.96 for apical and greater than 0.98 for basolateral membrane vesicles, with best estimates of 1.0 for both membranes. These results demonstrate that sigma NaCl for proximal tubule apical and basolateral membranes are near unity. Taken together with previous results, these data suggest that proximal tubule water channels are long narrow pores that exclude NaCl. PMID:2765660
NASA Astrophysics Data System (ADS)
Ghanbari, Keyvan; Khakian Ghomi, Mehdi; Mohammadi, Mohammad; Marbouti, Marjan; Tan, Le Minh
2016-08-01
The ionized atmosphere lying from 50 to 600 km above surface, known as ionosphere, contains high amount of electrons and ions. Very Low Frequency (VLF) radio waves with frequencies between 3 and 30 kHz are reflected from the lower ionosphere specifically D-region. A lot of applications in long range communications and navigation systems have been inspired by this characteristic of ionosphere. There are several factors which affect the ionization rate in this region, such as: time of day (presence of sun in the sky), solar zenith angle (seasons) and solar activities. Due to nonlinear response of ionospheric reflection coefficient to these factors, finding an accurate relation between these parameters and reflection coefficient is an arduous task. In order to model these kinds of nonlinear functionalities, some numerical methods are employed. One of these methods is artificial neural network (ANN). In this paper, the VLF radio wave data of 4 sudden ionospheric disturbance (SID) stations are given to a multi-layer perceptron ANN in order to simulate the variations of reflection coefficient of D region ionosphere. After training, validation and testing the ANN, outputs of ANN and observed values are plotted together for 2 random cases of each station. By evaluating the results using 2 parameters of pearson correlation coefficient and root mean square error, a satisfying agreement was found between ANN outputs and real observed data.
Innovative acoustic reflection imaging techniques and application to clinical breast tomography
NASA Astrophysics Data System (ADS)
Schmidt, Steve P.
Conventional ultrasound techniques use beam-formed, constant sound speed ray models for fast image reconstruction. However, these techniques are inadequate for the emerging new field of ultrasound tomography (UST). We present a new technique for reconstruction of reflection images from UST data. We have extended the planar Kirchhoff migration method used in geophysics, and combined it with sound speed and attenuation data obtained from the transmission signals to create reflection ultrasound images that are corrected for refractive and attenuative effects. The resulting techniques were applied to simulated numerical phantom data, physical phantom data and in-vivo breast data obtained with an experimental ring transducer prototype. Additionally, the ring transducer was customized to test compatibility with an existing ultrasound workstation. We were able to obtain independently recorded radio-frequency (RF) data for individual transmit-receive pair combinations for all 128 transducers. The signal data was then successfully reconstructed into reflection data using the Kirchhoff migration techniques. The results from the use of sound speed and attenuation corrections lead to significant improvements in image quality, particularly in dense tissues where the refractive and scattering effects are the greatest. The procedure was applied to a variety of breast densities and masses of different natures. The resulting reflection images successfully resolved boundaries and textures. The reflection characteristics of tomographic ultrasound maintain an indispensible position in the quantification of proper mass identification. The results of this project indicate the clinical significance of the invocation of properly compensated Kirchhoff based reconstruction method with the use of sound speed and attenuation parameters for the visualization and classification of masses and tissue.
Combination of acoustical radiosity and the image source method.
Koutsouris, Georgios I; Brunskog, Jonas; Jeong, Cheol-Ho; Jacobsen, Finn
2013-06-01
A combined model for room acoustic predictions is developed, aiming to treat both diffuse and specular reflections in a unified way. Two established methods are incorporated: acoustical radiosity, accounting for the diffuse part, and the image source method, accounting for the specular part. The model is based on conservation of acoustical energy. Losses are taken into account by the energy absorption coefficient, and the diffuse reflections are controlled via the scattering coefficient, which defines the portion of energy that has been diffusely reflected. The way the model is formulated allows for a dynamic control of the image source production, so that no fixed maximum reflection order is required. The model is optimized for energy impulse response predictions in arbitrary polyhedral rooms. The predictions are validated by comparison with published measured data for a real music studio hall. The proposed model turns out to be promising for acoustic predictions providing a high level of detail and accuracy. PMID:23742350
NASA Astrophysics Data System (ADS)
Keefe, Douglas H.; Zhao, Fei; Neely, Stephen T.; Gorga, Michael P.; Vohr, Betty R.
2003-01-01
This report describes the extent to which ear-canal acoustic admittance and energy reflectance (YR) in human neonates (1) predict otoacoustic emission (OAE) levels and auditory brainstem response (ABR) latencies, and (2) classify OAE and ABR responses as present or absent. Analyses are reported on a subset of ears in which hearing screening measurements were obtained previously [Norton et al., Ear. Hear. 21, 348-356 (2000a)]. Tests on 1405 ears included YR, distortion-product OAEs, transient-evoked OAEs, and ABR. Principal components analysis reduced the 33 YR variables to 5-7 factors. OAE levels decreased and ABR latencies increased with increasing high-frequency energy reflectance. Up to 28% of the variance in OAE levels and 12% of the variance in ABR wave-V latencies were explained by these factors. Thus, the YR response indirectly encodes information on inter-ear variations in forward and reverse middle-ear transmission. The YR factors classify OAEs with an area under the relative operating characteristic (ROC) curve as high as 0.79, suggesting that middle-ear dysfunction is partly responsible for the inability to record OAEs in some ears. The YR factors classified ABR responses less well, with ROC areas of 0.64 for predicting wave-V latency and 0.56 for predicting Fsp.
NASA Astrophysics Data System (ADS)
Jajodia, S.; Chimankar, O. P.; Kalambe, A.; Goswami, S. G.
2012-12-01
Amino acids are the building blocks of the proteins; their study provides important information, about the behaviour of larger biomolecules such as proteins. The properties of proteins such as their structure, solubility, denaturation, etc. are greatly influenced by electrolytes. Ultrasonic velocity and density values have been used for evaluation of thermal expansion coefficient and adiabatic compressibility for ternary systems (amino acid/salt + water) namely L-leucine / L-asparagine each in 1.5 M aqueous solution of NaCl used as solvent for various concentrations and at different temperatures (298.15K - 323.15K). Present paper reports the variation of various thermoacoustical parameters such as Moelwyn-Hughes parameter (C1), Beyer's non-linearity parameter (B/A), internal pressure (Pi), fractional free volume (f), available volume (Va), repulsive exponent (n), molecular constant (r), van der Waals' constant (b), Debye temperatue (θD), etc. have been computed from the thermal expansion coefficient with the change of concentration and temperature. The variations of all these parameters have been interpreted in terms of various intermolecular interactions such as strong, weak, charge transfer, complex formation, hydrogen bonding interaction. The structure making and breaking properties of the interacting components existing in proposed ternary systems. It shows the associating and dissociating tendency of the molecules of solute in solvent.The hetromolecular interactions are present in both the ternary systems.
The dyadic diffraction coefficient for a curved edge
NASA Technical Reports Server (NTRS)
Kouyoumjian, R. G.; Pathak, P. H.
1974-01-01
A compact dyadic diffraction coefficient for electromagnetic waves obliquely incident on a curved edge formed by perfectly conducting curved or plane surfaces is obtained. This diffraction coefficent remains valid in the transition regions adjacent to shadow and reflection boundaries, where the diffraction coefficients of Keller's original theory fail. The method is on Keller's method of the canonical problem, which in this case is the perfectly conducting wedge illuminated by plane, cylindrical, conical, and spherical waves. When the proper ray fixed coordinate system is introduced, the dyadic diffraction coefficient for the wedge is found to be the sum of only two dyads, and it is shown that this is also true for the dyadic diffraction coefficients of higher order edges. One dyad contains the acoustic soft diffraction coefficient; the other dyad contains the acoustic hard diffraction coefficient. The expressions for the acoustic wedge diffraction coefficients contain Fresnel integrals, which ensure that the total field is continuous at shadow and reflection boundaries. The diffraction coefficients have the same form for the different types of edge illumination; only the arguments of the Fresnel integrals are different. Since diffraction is a local phenomenon, and locally the curved edge structure is wedge shaped, this result is readily extended to the curved edge.
Wei, Jianwei; Lee, Zhongping
2015-02-01
The light absorption of phytoplankton and colored detrital matter (CDM), which includes contribution of gelbstoff and detrital matters, has distinctive yet overlapping features in the ultraviolet (UV) and visible domain. The CDM absorption (a(dg)) increases exponentially with decreasing wavelength while the absorption coefficient of phytoplankton (a(ph)) generally decreases toward the shorter bands for the range of 350-450 nm. It has long been envisioned that including ocean color measurements in the UV range may help the separation of these two components from the remotely sensed ocean color spectrum. An attempt is made in this study to provide an analytical assessment of this expectation. We started with the development of an absorption decomposition model [quasi-analytical algorithm (QAA)-UV], analogous to the QAA, that partitions the total absorption coefficient using information at bands 380 and 440 nm. Compared to the retrieval results relying on the absorption information at 410 and 440 nm of the original QAA, our analyses indicate that QAA-UV can improve the retrieval of a(ph) and a(dg), although the improvement in accuracy is not significant for values at 440 nm. The performance of the UV-based algorithm is further evaluated with in situ measurements. The limited improvement observed with the field measurements highlights that the separation of a(dg) and a(ph) is highly dependent on the accuracy of the ocean color measurements and the estimated total absorption coefficient. PMID:25967770
NASA Astrophysics Data System (ADS)
Tanaka, Satoru; Tkalčić, Hrvoje
2015-12-01
Frequency-dependent reflection coefficients of P waves at the inner core boundary (ICB) are estimated from the spectral ratios of PKiKP and PcP waves observed by the high-sensitivity seismograph network (Hi-net) in Japan. The corresponding PKiKP reflection locations at the ICB are distributed beneath the western Pacific. At frequencies where noise levels are sufficiently low, spectra of reflection coefficients show four distinct sets of characteristics: a flat spectrum, a spectrum with a significant spectral hole at approximately 1 or 3 Hz, a spectrum with a strong peak at approximately 2 or 3 Hz, and a spectrum containing both a sharp peak and a significant hole. The variety in observed spectra suggests complex lateral variations in ICB properties. To explain the measured differences in frequency characteristics of ICB reflection coefficients, we conduct 2D finite difference simulations of seismic wavefields near the ICB. The models tested in our simulations include a liquid layer and a solid layer above the ICB, as well as sinusoidal and spike-shaped ICB topography with varying heights and scale lengths. We find that the existence of a layer above the ICB can be excluded as a possible explanation for the observed spectra. Furthermore, we find that an ICB topographic model with wavelengths and heights of several kilometers is too extreme to explain our measurements. However, restricting the ICB topography to wavelengths and heights of 1.0-1.5 km can explain the observed frequency-related phenomena. The existence of laterally varying topography may be a sign of lateral variations in inner core solidification.
McKinney, W.R.; Palmer, C.
1997-09-01
The definition of the generalized optical path function for a grating or mirror with a single plane of symmetry is reviewed. The generalized optical path function is then expanded in a series of wavefront aberration terms using only a few lines of code in the Mathematica{trademark} scientific programming environment. The use of the algebraic capabilities of the Mathematica{trademark} environment allows straightforward calculation of aberration coefficients that would normally require considerable effort if undertaken by paper and pencil. In addition, the derivation can be carried out to higher order aberration terms, limited only by the capabilities of the computer platform used.
Curiel, Fernando; Vargas, William E; Barrera, Rubén G
2002-10-01
A spectral-projected gradient method and an extension of the Kubelka-Munk theory are applied to obtain the relevant parameters of the theory from measured diffuse reflectance spectra of pigmented samples illuminated with visible diffuse radiation. The initial estimate of the spectral dependence of the parameters, required by a recursive spectral-projected gradient method, was obtained by use of direct measurements and up-to-date theoretical estimates. We then tested the consistency of the Kubelka-Munk theory by repeating the procedure with samples of different thicknesses. PMID:12371558
A theoretical study of the feasibility of acoustical tweezers: Ray acoustics approach
NASA Astrophysics Data System (ADS)
Lee, Jungwoo; Ha, Kanglyeol; Shung, K. Kirk
2005-05-01
The optical tweezer has been found to have many biomedical applications in trapping macromolecules and cells. For the trapping mechanism, there has to be a sharp spatial change in axial optical intensity and the particle size must be much greater than the wavelength. Similar phenomenon may exist in acoustics. This work was undertaken to demonstrate theoretically that it is possible to acoustically trap particles near the focal point where most of the acoustic energy is concentrated if certain conditions are met. Acoustic force exerted on a fluid particle in ultrasonic fields is analyzed in a ray acoustics regime where the wavelength of acoustic beam is much smaller than the size of the particle. In order to apply the acoustical tweezer to manipulating macromolecules and cells whose size is in the order of a few microns or less, a prerequisite is that the ultrasound wavelength has to be much smaller than a few microns. In this paper, the analysis is therefore based on the field pattern produced by a strongly focused 100 MHz ultrasonic transducer with Gaussian intensity distribution. For the realization of acoustic trapping, negative axial radiation force has to be generated to pull a particle towards a focus. The fat particle considered for acoustic trapping in this paper has an acoustic impedance of 1.4 MRayls. The magnitude of the acoustic axial radiation force that has been calculated as the size of the fat particle is varied from 8λ to 14λ. In addition, both Fresnel coefficients at various positions are also calculated to assess the interaction of reflection and refraction and their relative contribution to the effect of the acoustical tweezer. The simulation results show that the feasibility of the acoustical tweezer depends on both the degree of acoustic impedance mismatch and the degree of focusing relative to the particle size. .
NASA Technical Reports Server (NTRS)
Lee, Zhong-Ping; Carder, Kendall L.
2001-01-01
A multi-band analytical (MBA) algorithm is developed to retrieve absorption and backscattering coefficients for optically deep waters, which can be applied to data from past and current satellite sensors, as well as data from hyperspectral sensors. This MBA algorithm applies a remote-sensing reflectance model derived from the Radiative Transfer Equation, and values of absorption and backscattering coefficients are analytically calculated from values of remote-sensing reflectance. There are only limited empirical relationships involved in the algorithm, which implies that this MBA algorithm could be applied to a wide dynamic range of waters. Applying the algorithm to a simulated non-"Case 1" data set, which has no relation to the development of the algorithm, the percentage error for the total absorption coefficient at 440 nm a (sub 440) is approximately 12% for a range of 0.012 - 2.1 per meter (approximately 6% for a (sub 440) less than approximately 0.3 per meter), while a traditional band-ratio approach returns a percentage error of approximately 30%. Applying it to a field data set ranging from 0.025 to 2.0 per meter, the result for a (sub 440) is very close to that using a full spectrum optimization technique (9.6% difference). Compared to the optimization approach, the MBA algorithm cuts the computation time dramatically with only a small sacrifice in accuracy, making it suitable for processing large data sets such as satellite images. Significant improvements over empirical algorithms have also been achieved in retrieving the optical properties of optically deep waters.
Azzam, R M A
2013-10-01
The complex Fresnel reflection coefficients r(p) and r(s) of p- and s-polarized light and their ratio ρ=r(p)/r(s) at the pseudo-Brewster angle (PBA) φ(pB) of a dielectric-conductor interface are evaluated for all possible values of the complex relative dielectric function ε=|ε|exp(-jθ)=ε(r)-jε(i), ε(i)>0 that share the same φ(pB). Complex-plane trajectories of r(p), r(s), and ρ at the PBA are presented at discrete values of φ(pB) from 5° to 85° in equal steps of 5° as θ is increased from 0° to 180°. It is shown that for φ(pB)>70° (high-reflectance metals in the IR) r(p) at the PBA is essentially pure negative imaginary and the reflection phase shift δ(p)=arg(r(p))≈-90°. In the domain of fractional optical constants (vacuum UV or light incidence from a high-refractive-index immersion medium) 0<φ(pB)<45° and r(p) is pure real negative (δ(p)=π) when θ=tan(-1)(√(cos(2φ(pB)))), and the corresponding locus of ε in the complex plane is obtained. In the limit of ε(i)=0, ε(r)<0 (interface between a dielectric and plasmonic medium) the total reflection phase shifts δ(p), δ(s), Δ=δ(p)-δ(s)=arg(ρ) are also determined as functions of φ(pB). PMID:24322852
NASA Astrophysics Data System (ADS)
Belov, V. V.; Tarasenkov, M. V.
2015-11-01
An algorithm for atmospheric correction of satellite images combining the consideration of the main factors influencing imaging and a number of techniques allowing the computational time to be decreased considerably is analyzed. On the example of a series of images of the South of the Tomsk Region recorded from 7/13/2013 to 7/17/2013 with the low atmospheric turbidity, a comparison of the results of atmospheric correction using the suggested algorithm with the results obtained using the NASA MOD09 algorithm is performed. The correction error is estimated under assumption of a linear change of the reflection coefficient from image to image. Our comparison demonstrates that the results of correction differ within the correction error.
NASA Astrophysics Data System (ADS)
Ward, A. J.; Pendry, J. B.
2000-06-01
In this paper we present an updated version of our ONYX program for calculating photonic band structures using a non-orthogonal finite difference time domain method. This new version employs the same transparent formalism as the first version with the same capabilities for calculating photonic band structures or causal Green's functions but also includes extra subroutines for the calculation of transmission and reflection coefficients. Both the electric and magnetic fields are placed onto a discrete lattice by approximating the spacial and temporal derivatives with finite differences. This results in discrete versions of Maxwell's equations which can be used to integrate the fields forwards in time. The time required for a calculation using this method scales linearly with the number of real space points used in the discretization so the technique is ideally suited to handling systems with large and complicated unit cells.
Malik, Hitendra K.; Tomar, Renu; Dahiya, Raj P.
2014-07-15
Modified Korteweg-de Vries (mKdV) equations are derived for the incident, reflected, and transmitted waves in order to examine the soliton reflection and its transmission through an inhomogeneous plasma comprising ions, dust grains with fluctuating charge and two types of electrons, namely nonisothermal electrons and isothermal electrons. All the mKdV equations are coupled at the point of reflection and solved for the reflected soliton. Unlike others, a relation is established between the velocity shifts of the incident, reflected and transmitted solitons, and based on a critical value of the shift of incident soliton the strengths of the soliton reflection and transmission are talked about. Conditions are obtained for the soliton reflection and its transmission, and a comparative study is made for the two cases of fixed and fluctuating charges on the dust grains.
NASA Technical Reports Server (NTRS)
Miles, J. H.
1974-01-01
A rational function is presented for the acoustic spectra generated by deflection of engine exhaust jets for under-the-wing and over-the-wing versions of externally blown flaps. The functional representation is intended to provide a means for compact storage of data and for data analysis. The expressions are based on Fourier transform functions for the Strouhal normalized pressure spectral density, and on a correction for reflection effects based on the N-independent-source model of P. Thomas extended by use of a reflected ray transfer function. Curve fit comparisons are presented for blown flap data taken from turbofan engine tests and from large scale cold-flow model tests. Application of the rational function to scrubbing noise theory is also indicated.
Estimating surface acoustic impedance with the inverse method.
Piechowicz, Janusz
2011-01-01
Sound field parameters are predicted with numerical methods in sound control systems, in acoustic designs of building and in sound field simulations. Those methods define the acoustic properties of surfaces, such as sound absorption coefficients or acoustic impedance, to determine boundary conditions. Several in situ measurement techniques were developed; one of them uses 2 microphones to measure direct and reflected sound over a planar test surface. Another approach is used in the inverse boundary elements method, in which estimating acoustic impedance of a surface is expressed as an inverse boundary problem. The boundary values can be found from multipoint sound pressure measurements in the interior of a room. This method can be applied to arbitrarily-shaped surfaces. This investigation is part of a research programme on using inverse methods in industrial room acoustics. PMID:21939599
NASA Astrophysics Data System (ADS)
El Hassouani, Y.; El Boudouti, E. H.; Djafari-Rouhani, B.; Aynaou, H.
2008-11-01
Using a Green’s function method, we present a comprehensive theoretical analysis of the propagation of sagittal acoustic waves in superlattices (SLs) made of alternating elastic solid and ideal fluid layers. This structure may exhibit very narrow pass bands separated by large stop bands. In comparison with solid-solid SLs, we show that the band gaps originate both from the periodicity of the system (Bragg-type gaps) and the transmission zeros induced by the presence of the solid layers immersed in the fluid. The width of the band gaps strongly depends on the thickness and the contrast between the elastic parameters of the two constituting layers. In addition to the usual crossing of subsequent bands, solid-fluid SLs may present a closing of the bands, giving rise to large gaps separated by flat bands for which the group velocity vanishes. Also, we give an analytical expression that relates the density of states and the transmission and reflection group delay times in finite-size systems embedded between two fluids. In particular, we show that the transmission zeros may give rise to a phase drop of π in the transmission phase, and therefore, a negative delta peak in the delay time when the absorption is taken into account in the system. A rule on the confined and surface modes in a finite SL made of N cells with free surfaces is demonstrated, namely, there are always N-1 modes in the allowed bands, whereas there is one and only one mode corresponding to each band gap. Finally, we present a theoretical analysis of the occurrence of omnidirectional reflection in a layered media made of alternating solid and fluid layers. We discuss the conditions for such a structure to exhibit total reflection of acoustic incident waves in a given frequency range for all incident angles. Also, we show how this structure can be used as an acoustic filter that may transmit selectively certain frequencies within the omnidirectional gaps. In particular, we show the possibility of
NASA Astrophysics Data System (ADS)
Keefe, Douglas H.; Gorga, Michael P.; Neely, Stephen T.; Zhao, Fei; Vohr, Betty R.
2003-01-01
This report describes relationships between middle-ear measurements of acoustic admittance and energy reflectance (YR) and measurements of hearing status using visual reinforcement audiometry in a neonatal hearing-screening population. Analyses were performed on 2638 ears in which combined measurements were obtained [Norton et al., Ear Hear. 21, 348-356 (2000)]. The measurements included distortion-product otoacoustic emissions (DPOAE), transient evoked otoacoustic emissions (TEOAE), and auditory brainstem responses (ABR). Models to predict hearing status using DPOAEs, TEOAEs, or ABRs were each improved by the addition of the YR factors as interactions, in which factors were calculated using factor loadings from Keefe et al. [J. Acoust. Soc. Am. 113, 389-406 (2003)]. This result suggests that information on middle-ear status improves the ability to predict hearing status. The YR factors were used to construct a middle-ear dysfunction test on 1027 normal-hearing ears in which DPOAE and TEOAE responses were either both present or both absent, the latter condition being viewed as indicative of middle-ear dysfunction. The middle-ear dysfunction test classified these ears with a nonparametric area (A) under the relative operating characteristic curve of A=0.86, and classified normal-hearing ears that failed two-stage hearing-screening tests with areas A=0.84 for DPOAE/ABR, and A=0.81 for TEOAE/ABR tests. The middle-ear dysfunction test adequately generalized to a new sample population (A=0.82).
Ahmad, Ahmad F.; Abbas, Zulkifly; Obaiys, Suzan J.; Ibrahim, Norazowa; Hashim, Mansor; Khaleel, Haider
2015-01-01
Bio-composites of oil palm empty fruit bunch (OPEFB) fibres and polycaprolactones (PCL) with a thickness of 1 mm were prepared and characterized. The composites produced from these materials are low in density, inexpensive, environmentally friendly, and possess good dielectric characteristics. The magnitudes of the reflection and transmission coefficients of OPEFB fibre-reinforced PCL composites with different percentages of filler were measured using a rectangular waveguide in conjunction with a microwave vector network analyzer (VNA) in the X-band frequency range. In contrast to the effective medium theory, which states that polymer-based composites with a high dielectric constant can be obtained by doping a filler with a high dielectric constant into a host material with a low dielectric constant, this paper demonstrates that the use of a low filler percentage (12.2%OPEFB) and a high matrix percentage (87.8%PCL) provides excellent results for the dielectric constant and loss factor, whereas 63.8% filler material with 36.2% host material results in lower values for both the dielectric constant and loss factor. The open-ended probe technique (OEC), connected with the Agilent vector network analyzer (VNA), is used to determine the dielectric properties of the materials under investigation. The comparative approach indicates that the mean relative error of FEM is smaller than that of NRW in terms of the corresponding S21 magnitude. The present calculation of the matrix/filler percentages endorses the exact amounts of substrate utilized in various physics applications. PMID:26474301
Ahmad, Ahmad F; Abbas, Zulkifly; Obaiys, Suzan J; Ibrahim, Norazowa; Hashim, Mansor; Khaleel, Haider
2015-01-01
Bio-composites of oil palm empty fruit bunch (OPEFB) fibres and polycaprolactones (PCL) with a thickness of 1 mm were prepared and characterized. The composites produced from these materials are low in density, inexpensive, environmentally friendly, and possess good dielectric characteristics. The magnitudes of the reflection and transmission coefficients of OPEFB fibre-reinforced PCL composites with different percentages of filler were measured using a rectangular waveguide in conjunction with a microwave vector network analyzer (VNA) in the X-band frequency range. In contrast to the effective medium theory, which states that polymer-based composites with a high dielectric constant can be obtained by doping a filler with a high dielectric constant into a host material with a low dielectric constant, this paper demonstrates that the use of a low filler percentage (12.2%OPEFB) and a high matrix percentage (87.8%PCL) provides excellent results for the dielectric constant and loss factor, whereas 63.8% filler material with 36.2% host material results in lower values for both the dielectric constant and loss factor. The open-ended probe technique (OEC), connected with the Agilent vector network analyzer (VNA), is used to determine the dielectric properties of the materials under investigation. The comparative approach indicates that the mean relative error of FEM is smaller than that of NRW in terms of the corresponding S21 magnitude. The present calculation of the matrix/filler percentages endorses the exact amounts of substrate utilized in various physics applications. PMID:26474301
Pavlikova, M I; Makarov, A K; Lyakso, E E
2015-08-01
The paper presented the possibility of recognition by adult the comfort and discomfort state of 3 and 6 months old infant's on the base of their vocalizations. The acoustic features of the vocalizations that are important for the recognition of the infant state of the characteristics of voice was described. It is shown that discomfort vocalizations differ from comfort ones on the basis of the average and maximum values of pitch, pitch values in the central and final part of the vocalization. A mathematical model is proposed and described a classification function signal of discomfort and comfort. Was found that the vocalizations of infants attributable adults with a probability of 0.75 and above the categories of comfort and discomfort with high reliability are recognized by the mathematical model based on a classification function. PMID:26591591
NASA Astrophysics Data System (ADS)
Mandal, Sudip; Yuan, Ding; Fang, Xia; Banerjee, Dipankar; Pant, Vaibhav; Van Doorsselaere, Tom
2016-09-01
Slow MHD waves are important tools for understanding coronal structures and dynamics. In this paper, we report a number of observations from the X-Ray Telescope (XRT) on board HINODE and Solar Dynamic Observatory/Atmospheric Imaging Assembly (AIA) of reflecting longitudinal waves in hot coronal loops. To our knowledge, this is the first report of this kind as seen from the XRT and simultaneously with the AIA. The wave appears after a micro-flare occurs at one of the footpoints. We estimate the density and temperature of the loop plasma by performing differential emission measure (DEM) analysis on the AIA image sequence. The estimated speed of propagation is comparable to or lower than the local sound speed, suggesting it to be a propagating slow wave. The intensity perturbation amplitude, in every case, falls very rapidly as the perturbation moves along the loop and eventually vanishes after one or more reflections. To check the consistency of such reflection signatures with the obtained loop parameters, we perform a 2.5D MHD simulation, which uses the parameters obtained from our observation as inputs, and perform forward modeling to synthesize AIA 94 Å images. Analyzing the synthesized images, we obtain the same properties of the observables as for the real observation. From the analysis we conclude that a footpoint heating can generate a slow wave which then reflects back and forth in the coronal loop before fading. Our analysis of the simulated data shows that the main agent for this damping is anisotropic thermal conduction.
NASA Astrophysics Data System (ADS)
Pazos, Daniel F. P.; Musafir, Ricardo E.; Avital, Eldad J.
2002-11-01
The precision of insertion loss prediction obtained by applying Kurze-Anderson formula to each of the four possible ray paths connecting source and observer in the presence of a reflecting ground, and computing interference appropriately, is discussed. To this end, the field behind the barrier, given by the method described, is compared to that obtained by solving numerically the continuity and momentum equations simultaneously, using the appropriate boundary conditions to account for the perfectly reflecting ground and the barrier. Analysis of the agreement of the interference patterns obtained in both cases, for pure tones and for octave bands, permits determining the range in which the much simpler ray method provides sufficient results. Calculations with the Kurze-Anderson formula are performed with Mathematica 4.0, while the numerical propagation code is written in Fortran.
Low frequency acoustic microscope
Khuri-Yakub, Butrus T.
1986-11-04
A scanning acoustic microscope is disclosed for the detection and location of near surface flaws, inclusions or voids in a solid sample material. A focused beam of acoustic energy is directed at the sample with its focal plane at the subsurface flaw, inclusion or void location. The sample is scanned with the beam. Detected acoustic energy specularly reflected and mode converted at the surface of the sample and acoustic energy reflected by subsurface flaws, inclusions or voids at the focal plane are used for generating an interference signal which is processed and forms a signal indicative of the subsurface flaws, inclusions or voids.
Quantifying Errors in Jet Noise Research Due to Microphone Support Reflection
NASA Technical Reports Server (NTRS)
Nallasamy, Nambi; Bridges, James
2002-01-01
The reflection coefficient of a microphone support structure used insist noise testing is documented through tests performed in the anechoic AeroAcoustic Propulsion Laboratory. The tests involve the acquisition of acoustic data from a microphone mounted in the support structure while noise is generated from a known broadband source. The ratio of reflected signal amplitude to the original signal amplitude is determined by performing an auto-correlation function on the data. The documentation of the reflection coefficients is one component of the validation of jet noise data acquired using the given microphone support structure. Finally. two forms of acoustic material were applied to the microphone support structure to determine their effectiveness in reducing reflections which give rise to bias errors in the microphone measurements.
NASA Astrophysics Data System (ADS)
Riobóo, Rafael J. Jiménez; Prieto, Carlos; Cuscó, Ramón; Artús, Lluís; Boney, Chris; Bensaoula, Abdelhak; Yamaguchi, Tomohiro; Nanishi, Yasushi
2013-05-01
Temperature-dependent surface acoustic wave (SAW) propagation velocity and temperature coefficient of frequency (TCF) have been determined for the first time in InxGa1-xN alloys by means of high-resolution Brillouin spectroscopy (HRBS). HRBS offers an alternative way of determining TCF. The obtained TCF values present a non-linear behavior with the In concentration. TCF of pure InN (-13.75 ppm/K) is similar to those of AlN and GaN (-19 and -17.7 ppm/K, respectively). InxGa1-xN samples exhibit frequency values that are very stable against temperature changes, which makes InxGa1-xN a good candidate for current SAW-based technological applications.
Homentcovschi, Dorel; Miles, Ronald N.
2008-01-01
An analysis is presented of the diffraction of a pressure wave by a periodic grating including the influence of the air viscosity. The direction of the incoming pressure wave is arbitrary. As opposed to the classical nonviscous case, the problem cannot be reduced to a plane problem having a definite 3-D character. The system of partial differential equations used for solving the problem consists of the compressible Navier-Stokes equations associated with no-slip boundary conditions on solid surfaces. The problem is reduced to a system of two hypersingular integral equations for determining the velocity components in the slits’ plane and a hypersingular integral equation for the normal component of velocity. These equations are solved by using Galerkin’s method with some special trial functions. The results can be applied in designing protective screens for miniature microphones realized in MEMS technology. In this case, the physical dimensions of the device are on the order of the viscous boundary layer so that the viscosity cannot be neglected. The analysis indicates that the openings in the screen should be on the order of 10 microns in order to avoid excessive attenuation of the signal. This paper also provides the variation of the transmission coefficient with frequency in the acoustical domain. PMID:19122753
Vestibular schwannoma; Tumor - acoustic; Cerebellopontine angle tumor; Angle tumor ... Acoustic neuromas have been linked with the genetic disorder neurofibromatosis type 2 (NF2). Acoustic neuromas are uncommon.
Simplified Rotation In Acoustic Levitation
NASA Technical Reports Server (NTRS)
Barmatz, M. B.; Gaspar, M. S.; Trinh, E. H.
1989-01-01
New technique based on old discovery used to control orientation of object levitated acoustically in axisymmetric chamber. Method does not require expensive equipment like additional acoustic drivers of precisely adjustable amplitude, phase, and frequency. Reflecting object acts as second source of sound. If reflecting object large enough, close enough to levitated object, or focuses reflected sound sufficiently, Rayleigh torque exerted on levitated object by reflected sound controls orientation of object.
NASA Astrophysics Data System (ADS)
Nakanishi, Hidekazu; Nakamura, Hiroyuki; Tsurunari, Tetsuya; Fujiwara, Joji; Hamaoka, Yosuke; Hashimoto, Ken-ya
2012-07-01
In this paper, we describe a suppression technique of transverse-mode spurious responses for a surface acoustic wave (SAW) resonator with a near zero temperature coefficient of frequency (TCF) on a SiO2/Al/LiNbO3 structure. We investigated the thinning of SiO2 on the dummy electrode region and studied how the transverse-mode responses change with remaining SiO2 thickness h on the dummy electrode region. As the results, we clarified that the remaining SiO2 thickness h on the dummy electrode region has an optimum value and could suppress the transverse-mode spurious responses completely when H and h are set at 0.35 λ and 0.20 λ, respectively. It was demonstrated that the selective SiO2 removal technique is effective to suppress transverse-mode spurious responses for SAW resonators employing the SiO2/Al/LiNbO3 structure for a wide range of SiO2 thicknesses, provided that the SiO2 thickness at the dummy electrode region is adjusted properly.
Investigation of ground reflection and impedance from flyover noise measurements
NASA Technical Reports Server (NTRS)
Chapkis, R. L.; Marsh, A. H.
1978-01-01
An extensive series of flyover noise tests was conducted for the primary purpose of studying meteorological effects on propagation of aircraft noise. The test airplane, a DC 9-10, flew several level-flight passes at various heights over a taxiway. Two microphone stations were located under the flight path. A total of 37 runs was selected for analysis and processed to obtain a consistant set of 1/3 octave band sound pressure levels at half-second intervals. The goal of the present study was to use the flyover noise data to deduce acoustical reflection coefficients and hence, acoustical impedances.
Modal decomposition method for acoustic impedance testing in square ducts.
Schultz, Todd; Cattafesta, Louis N; Sheplak, Mark
2006-12-01
Accurate duct acoustic propagation models are required to predict and reduce aircraft engine noise. These models ultimately rely on measurements of the acoustic impedance to characterize candidate engine nacelle liners. This research effort increases the frequency range of normal-incidence acoustic impedance testing in square ducts by extending the standard two-microphone method (TMM), which is limited to plane wave propagation, to include higher-order modes. The modal decomposition method (MDM) presented includes four normal modes in the model of the sound field, thus increasing the bandwidth from 6.7 to 13.5 kHz for a 25.4 mm square waveguide. The MDM characterizes the test specimen for normal- and oblique-incident acoustic impedance and mode scattering coefficients. The MDM is first formulated and then applied to the measurement of the reflection coefficient matrix for a ceramic tubular specimen. The experimental results are consistent with results from the TMM for the same specimen to within the 95% confidence intervals for the TMM. The MDM results show a series of resonances for the ceramic tubular material exhibiting a monotonic decrease in the resonant peaks of the acoustic resistance with increasing frequency, resembling a rigidly-terminated viscous tube, and also evidence of mode scattering is visible at the higher frequencies. PMID:17225402
NASA Astrophysics Data System (ADS)
Aoyama, C.
2013-12-01
Acoustic reflection depending on physical property differences among solid of methane hydrates and methane gas bubbles from seafloor and sea water.By sending ultrasonic waves from the transducer of an echo sounder or a sonar system through the water and measuring the echo of the back-scatterings from the methane hydrates or bubbles,it is possible that a visualized image of the methane plumes is displayed on the display of an echo sounder or a sonar system.Estimates of the amount of the methane plumes are extremely important for the global environment as part of the carbon cycle.The observations were carried out at Umitaka Spur and Joetsu knoll in the Sea of Japan every year since 2004. There are many methane plumes in the same ocean area. Thus, we investigate minutely about methane plumes in this study.In order to recognize estimates of the methane plumes, we observed the image of methane plumes using a remotely operated submarine vehicle (Hyper Dolphin, of the Japan Agency of Marine-Earth Science and Technology (JAMSTEC)), and captured the methane bubble using a funnel.We observe the images of the methane plumes seeping points on the seafloor taken by a high-definition camera loaded in the vehicle, measure the surfacing velocity of the gushed methane plumes, and compute the surfacing velocity of the gas and solid substance using a theoretical formula.The observation was carried out at Umitaka Spur in the Japan Sea. The depth was 1000 m and the seawater temperature was 0.3 C°.From 3 seeping points, we gathered 300ml of methane in 643 seconds in the funnel with an opening of 20 cm in diameter.If it is assumed that the seeping points are equally scattered in the area, the seeping volume per unit area is 5.4×104cm3 per hour, which is 4.7×102m3 per year.The experiment in the ocean revealed the followings.The methane hydrate particles that are seeping out from seafloor are solid substances just above the seafloor.In the studied ocean area, 7.7×104m3 of methane
Spinning mode acoustic radiation from the flight inlet
NASA Technical Reports Server (NTRS)
Moss, W. F.
1983-01-01
A mathematical model was developed for spinning mode acoustic radiation from a thick wall duct without flow. This model is based on a series of experiments (with and without flow). A nearly pure azimuthal spinning mode was isolated and then reflection coefficients and far field pressure (amplitude and phase) were measured. In our model the governing boundary value problem for the Helmholtz equation is first converted into an integral equation for the unknown acoustic pressure over a disk, S1, near the mouth of the duct and over the exterior surface, S2, of the duct. Assuming a pure azimuthal mode excitation, the azimuthal dependence is integrated out which yields an integral equation over the generator C1 of S1 and the generator C2 of S2. The sound pressure on C1 was approximated by a truncated modal expansion of the interior acoustic pressure. Piecewise linear spline approximation on C2 was used.
Imaging of Buried Archaeological Materials: The Reflection Properties of Archaeological Wood
NASA Astrophysics Data System (ADS)
Arnott, Stephanie H. L.; Dix, Justin K.; Best, Angus I.; Gregory, David J.
2005-06-01
Effective marine archaeological site management demands detailed information on not only the spatial distribution of artefacts but also the degradation state of the materials present. Although sonar methods have frequently been used in an attempt to detect buried wooden shipwrecks they are currently unable to indicate their degradation state. To assess the sensitivity of acoustic measurements to changes in the degradation state of such material, and hence the potential for sonars to quantify degradation, laboratory measurements of compressional wave velocity, as well as bulk density for oak and pine samples, in varying states of decay, were undertaken. These data enabled the calculation of theoretical reflection coefficients for such materials buried in various marine sediments. As wood degrades, the reflection coefficients become more negative, resulting in the hypothesis that the more degraded wood becomes, the easier it should be to detect. Typical reflection coefficients of the order of -0.43 and -0.52 for the most degraded oak and pine samples in sand are predicted. Conversely, for wood exposed to seawater the predicted reflection coefficients are large and positive for undegraded material (0.35 for oak, 0.18 for pine) and decrease to zero or slightly below for the most degraded samples. This indicates that exposed timbers, when heavily degraded, can be acoustically transparent and so undetectable by acoustic methods. Corroboration of these experimental results was provided through comparison with high resolution seismic reflection data that has been acquired over two shipwrecks.
NASA Astrophysics Data System (ADS)
Montes-Hugo, Martin; Xie, Huxiang
2015-10-01
The inversion of individual inherent optical properties (IOPs) is very challenging in optically complex waters and within the violet spectral range (i.e., 380-450 nm) due to the strong light attenuation caused by chromophoric dissolved organic matter, nonalgal particulates, and phytoplankton. Here we present a technique to better discriminate light absorption contributions due to phytoplankton based on a hybrid model (QAA-hybrid) that combines regional Saint Lawrence System estimates of IOPs derived from a quasi-analytical algorithm (hereafter QAA-SLE) and empirical relationships between salinity and IOPs. Preliminary results in the Saint Lawrence System during May 2000 and April 2001 showed that QAA-hybrid estimates of phytoplankton absorption coefficient at 443 nm have a smaller bias with respect to in situ measurements (root-mean-square deviation, RMSD = 0.156) than those derived from QAA-SLE (RMSD = 0.341). These results were valid for surface waters (i.e., 0-5 m depth) of the lower estuary with a salinity and chlorophyll-a concentration range of 22-28 psu and 2.1-13.8 mg m-3, respectively.
Optical and Acoustic Device Applications of Ferroelastic Crystals
NASA Astrophysics Data System (ADS)
Meeks, Steven Wayne
This dissertation presents the discovery of a means of creating uniformly periodic domain gratings in a ferroelastic crystal of neodymium pentaphosphate (NPP). The uniform and non-uniform domain structures which can be created in NPP have the potential applications as tunable active gratings for lasers, tunable diffraction gratings, tunable Bragg reflection gratings, tunable acoustic filters, optical modulators, and optical domain wall memories. The interaction of optical and acoustic waves with ferroelastic domain walls in NPP is presented in detail. Acoustic amplitude reflection coefficients from a single domain wall in NPP are much larger than other ferroelastic-ferroelectrics such as gadolinium molybdate (GMO). Domain walls of NPP are used to make two demonstration acoustic devices: a tunable comb filter and a tunable delay line. The tuning process is accomplished by moving the position of the reflecting surface (the domain wall). A theory of the reflection of optical waves from NPP domain walls is discussed. The optical reflection is due to a change in the polarization of the wave, and not a change in the index, as the wave crosses the domain wall. Theoretical optical power reflection coefficients show good agreement with the experimentally measured values. The largest optical reflection coefficient of a single domain wall is at a critical angle and is 2.2% per domain wall. Techniques of injecting periodic and aperiodic domain walls into NPP are presented. The nucleation process of the uniformly periodic domain gratings in NPP is described in terms of a newly-discovered domain structure, namely the ferroelastic bubble. A ferroelastic bubble is the elastic analogue to the well-known magnetic bubble. The period of the uniformly periodic domain grating is tunable from 100 to 0.5 microns and the grating period may be tuned relatively rapidly. The Bragg efficiency of these tunable gratings is 77% for an uncoated crystal. Several demonstration devices which use
A comparison of time domain boundary conditions for acoustic waves in wave guides
NASA Technical Reports Server (NTRS)
Banks, H. T.; Propst, G.; Silcox, R. J.
1991-01-01
Researchers consider several types of boundary conditions in the context of time domain models for acoustic waves. Experiments with four different duct terminations (hard wall, free radiation, foam, and wedge) were carried out in a wave duct from which reflection coefficients over a wide frequency range were measured. These reflection coefficients were used to estimate parameters in the time domain boundary conditions. A comparison of the relative merits of the models in describing the data is presented. Boundary conditions which yield a good fit of the model to the experimental data were found for all duct terminations except the wedge.
Hofler, Thomas J.; Wheatley, John C.; Swift, Gregory W.; Migliori, Albert
1988-01-01
An acoustic cooling engine with improved thermal performance and reduced internal losses comprises a compressible fluid contained in a resonant pressure vessel. The fluid has a substantial thermal expansion coefficient and is capable of supporting an acoustic standing wave. A thermodynamic element has first and second ends and is located in the resonant pressure vessel in thermal communication with the fluid. The thermal response of the thermodynamic element to the acoustic standing wave pumps heat from the second end to the first end. The thermodynamic element permits substantial flow of the fluid through the thermodynamic element. An acoustic driver cyclically drives the fluid with an acoustic standing wave. The driver is at a location of maximum acoustic impedance in the resonant pressure vessel and proximate the first end of the thermodynamic element. A hot heat exchanger is adjacent to and in thermal communication with the first end of the thermodynamic element. The hot heat exchanger conducts heat from the first end to portions of the resonant pressure vessel proximate the hot heat exchanger. The hot heat exchanger permits substantial flow of the fluid through the hot heat exchanger. The resonant pressure vessel can include a housing less than one quarter wavelength in length coupled to a reservoir. The housing can include a reduced diameter portion communicating with the reservoir. The frequency of the acoustic driver can be continuously controlled so as to maintain resonance.
Marlow, M. S.; Hart, P.E.; Carlson, P.R.; Childs, J. R.; Mann, D. M.; Anima, R.J.; Kayen, R.E.
1996-01-01
We collected high-resolution seismic reflection profiles in the southern part of San Francisco Bay in 1992 and 1993 to investigate possible Holocene faulting along postulated transbay bedrock fault zones. The initial analog records show apparent offsets of reflection packages along sharp vertical boundaries. These records were originally interpreted as showing a complex series of faults along closely spaced, sharp vertical boundaries in the upper 10 m (0.013 s two-way travel time) of Holocene bay mud. A subsequent survey in 1994 was run with a different seismic reflection system, which utilized a higher power source. This second system generated records with deeper penetration (max. 20 m, 0.026 s two-way travel time) and demonstrated that the reflections originally interpreted as fault offsets by faulting were actually laterally continuous reflection horizons. The pitfall in the original interpretations was caused by lateral variations in the amplitude brightness of reflection events, coupled with a long (greater than 15 ms) source signature of the low-power system. These effects combined to show apparent offsets of reflection packages along sharp vertical boundaries. These boundaries, as shown by the second system, in fact occur where the reflection amplitude diminishes abruptly on laterally continuous reflection events. This striking lateral variation in reflection amplitude is attributable to the localized presence of biogenic(?) gas.
a Reverse Flow Theorem and Acoustic Reciprocity in Compressible Potential Flows in Ducts
NASA Astrophysics Data System (ADS)
EVERSMAN, W.
2001-09-01
A reverse flow theorem for acoustic propagation in compressible potential flow has been obtained directly from the field equations without recourse to energy conservation arguments. A reciprocity theorem for the scattering matrix for the propagation of acoustic modes in a duct with either acoustically rigid walls or acoustically absorbing walls follows. It is found that for a source at a specific end of the duct, suitably scaled reflection matrices in direct and reverse flow have a reciprocal relationship. Scaled transmission matrices obtained for direct flow and reversed flow with simultaneous switching of source location from one end to the other also have a reciprocal relationship. A related reverse flow theorem specialized to one-dimensional acoustic propagation has also been obtained. Reciprocity relationships for the scattering coefficients for propagation are derived, and are found to be similar though much simpler than in the case of multi-mode propagation. In one-dimensional flow, reciprocal relations and power conservation arguments are used to show that scaled power reflection and transmission coefficients are invariant to flow reversal and switching of source location from one end of the duct to the other. Numerical verification of the reciprocal relationships is given in a companion paper.
Setting Time Measurement Using Ultrasonic Wave Reflection
Chung, Chul-Woo; Suraneni, Prannoy; Popovics, John S.; Struble, Leslie J.
2012-01-09
Ultrasonic shear wave reflection was used to investigate setting times of cement pastes by measuring the reflection coefficient at the interface between hydrating cement pastes of varying water-to-cement ratio and an ultrasonic buffer material. Several different buffer materials were employed, and the choice of buffer was seen to strongly affect measurement sensitivity; high impact polystyrene showed the highest sensitivity to setting processes because it had the lowest acoustic impedance value. The results show that ultrasonic shear-wave reflection can be used successfully to monitor early setting processes of cement paste with good sensitivity when such a very low impedance buffer is employed. Criteria are proposed to define set times, and the resulting initial and final set times agreed broadly with those determined using the standard penetration resistance test.
An acoustic neuroma is a benign tumor that develops on the nerve that connects the ear to the brain. ... can press against the brain, becoming life-threatening. Acoustic neuroma can be difficult to diagnose, because the ...
Transition section for acoustic waveguides
Karplus, H.H.B.
1975-10-28
A means of facilitating the transmission of acoustic waves with minimal reflection between two regions having different specific acoustic impedances is described comprising a region exhibiting a constant product of cross-sectional area and specific acoustic impedance at each cross-sectional plane along the axis of the transition region. A variety of structures that exhibit this feature is disclosed, the preferred embodiment comprising a nested structure of doubly reentrant cones. This structure is useful for monitoring the operation of nuclear reactors in which random acoustic signals are generated in the course of operation.
Acoustic communication in plant-animal interactions.
Schöner, Michael G; Simon, Ralph; Schöner, Caroline R
2016-08-01
Acoustic communication is widespread and well-studied in animals but has been neglected in other organisms such as plants. However, there is growing evidence for acoustic communication in plant-animal interactions. While knowledge about active acoustic signalling in plants (i.e. active sound production) is still in its infancy, research on passive acoustic signalling (i.e. reflection of animal sounds) revealed that bat-dependent plants have adapted to the bats' echolocation systems by providing acoustic reflectors to attract their animal partners. Understanding the proximate mechanisms and ultimate causes of acoustic communication will shed light on an underestimated dimension of information transfer between plants and animals. PMID:27423052
Evaluating the crop coefficient using spectral reflectance
Heilman, J. L.; Heilman, W. E.; Moore, Donald G.
1982-01-01
Significant linear relationships were found between PVI and percent cover (r2 = 0.911), and between Kc and percent cover (r2 = 0.815). In addition, the position of the PVl intersection on the soil background line changed as a result of soil moisture increases following irrigation, even at high percent cover. Thus, once experimental relationships between Kc and crop growth are established, a mean Kc can be determined from spectral estimates of stage of development and the soil background component of PVI can be used to adjust the mean K, for increased evaporation following irrigation because the ratio of actual to potential evapotranspiration will approach 1 when the soil surface is wet.
NASA Technical Reports Server (NTRS)
Steinetz, Bruce M. (Inventor)
2006-01-01
The invention relates to a sealing device having an acoustic resonator. The acoustic resonator is adapted to create acoustic waveforms to generate a sealing pressure barrier blocking fluid flow from a high pressure area to a lower pressure area. The sealing device permits noncontacting sealing operation. The sealing device may include a resonant-macrosonic-synthesis (RMS) resonator.
NASA Technical Reports Server (NTRS)
Steinetz, Bruce M. (Inventor)
2006-01-01
The invention relates to a sealing device having an acoustic resonator. The acoustic resonator is adapted to create acoustic waveforms to generate a sealing pressure barrier blocking fluid flow from a high pressure area to a lower pressure area. The sealing device permits noncontacting sealing operation. The sealing device may include a resonant-macrosonic-synthesis (RMS) resonator.
Reflection of drill-string extensional waves at the bit-rock contact
NASA Astrophysics Data System (ADS)
Poletto, Flavio; Malusa, Massimo
2002-06-01
Downward propagating extensional waves are partially reflected at the bit-rock contact. The evaluation of the reflection coefficient is important to obtain while drilling information about the acoustic properties of the formations. The scope of this work is to estimate the bit-rock reflection coefficient, assuming a flat drill bit in perfect contact with the formation. Using the low-frequency approximation, which holds when the wavelength is much larger than the lateral dimensions of the borehole, the drill-string is assumed to be a laterally free rod, and the formation an homogeneous and isotropic medium. This work shows that the reflection coefficient of the extensional waves depends, along with the elastic properties of the formation, on the ratio of the cross sections of the drill-string and borehole. The impedance of the drilled rock can be calculated from the measured reflection coefficient, which is related to the amplitude of waves produced in the string and in the formation by a working drill-bit. copyright 2002 Acoustical Society of America.
Ocean acoustic reverberation tomography.
Dunn, Robert A
2015-12-01
Seismic wide-angle imaging using ship-towed acoustic sources and networks of ocean bottom seismographs is a common technique for exploring earth structure beneath the oceans. In these studies, the recorded data are dominated by acoustic waves propagating as reverberations in the water column. For surveys with a small receiver spacing (e.g., <10 km), the acoustic wave field densely samples properties of the water column over the width of the receiver array. A method, referred to as ocean acoustic reverberation tomography, is developed that uses the travel times of direct and reflected waves to image ocean acoustic structure. Reverberation tomography offers an alternative approach for determining the structure of the oceans and advancing the understanding of ocean heat content and mixing processes. The technique has the potential for revealing small-scale ocean thermal structure over the entire vertical height of the water column and along long survey profiles or across three-dimensional volumes of the ocean. For realistic experimental geometries and data noise levels, the method can produce images of ocean sound speed on a smaller scale than traditional acoustic tomography. PMID:26723303
Sound absorption coefficient in situ: an alternative for estimating soil loss factors.
Freire, Rosane; Meletti de Abreu, Marco Henrique; Okada, Rafael Yuri; Soares, Paulo Fernando; GranhenTavares, Célia Regina
2015-01-01
The relationship between the sound absorption coefficient and factors of the Universal Soil Loss Equation (USLE) was determined in a section of the Maringá Stream basin, Paraná State, by using erosion plots. In the field, four erosion plots were built on a reduced scale, with dimensions of 2.0×12.5m. With respect to plot coverage, one was kept with bare soil and the others contained forage grass (Brachiaria), corn and wheat crops, respectively. Planting was performed without any type of conservation practice in an area with a 9% slope. A sedimentation tank was placed at the end of each plot to collect the material transported. For the acoustic system, pink noise was used in the measurement of the proposed monitoring, for collecting information on incident and reflected sound pressure levels. In general, obtained values of soil loss confirmed that 94.3% of material exported to the basin water came from the bare soil plot, 2.8% from the corn plot, 1.8% from the wheat plot, and 1.1% from the forage grass plot. With respect to the acoustic monitoring, results indicated that at 16kHz erosion plot coverage type had a significant influence on the sound absorption coefficient. High correlation coefficients were found in estimations of the A and C factors of the USLE, confirming that the acoustic technique is feasible for the determination of soil loss directly in the field. PMID:24972796
NASA Astrophysics Data System (ADS)
Yang, Zhaoju; Gao, Fei; Shi, Xihang; Lin, Xiao; Gao, Zhen; Chong, Yidong; Zhang, Baile
2015-03-01
The manipulation of acoustic wave propagation in fluids has numerous applications, including some in everyday life. Acoustic technologies frequently develop in tandem with optics, using shared concepts such as waveguiding and metamedia. It is thus noteworthy that an entirely novel class of electromagnetic waves, known as "topological edge states," has recently been demonstrated. These are inspired by the electronic edge states occurring in topological insulators, and possess a striking and technologically promising property: the ability to travel in a single direction along a surface without backscattering, regardless of the existence of defects or disorder. Here, we develop an analogous theory of topological fluid acoustics, and propose a scheme for realizing topological edge states in an acoustic structure containing circulating fluids. The phenomenon of disorder-free one-way sound propagation, which does not occur in ordinary acoustic devices, may have novel applications for acoustic isolators, modulators, and transducers.
Yang, Zhaoju; Gao, Fei; Shi, Xihang; Lin, Xiao; Gao, Zhen; Chong, Yidong; Zhang, Baile
2015-03-20
The manipulation of acoustic wave propagation in fluids has numerous applications, including some in everyday life. Acoustic technologies frequently develop in tandem with optics, using shared concepts such as waveguiding and metamedia. It is thus noteworthy that an entirely novel class of electromagnetic waves, known as "topological edge states," has recently been demonstrated. These are inspired by the electronic edge states occurring in topological insulators, and possess a striking and technologically promising property: the ability to travel in a single direction along a surface without backscattering, regardless of the existence of defects or disorder. Here, we develop an analogous theory of topological fluid acoustics, and propose a scheme for realizing topological edge states in an acoustic structure containing circulating fluids. The phenomenon of disorder-free one-way sound propagation, which does not occur in ordinary acoustic devices, may have novel applications for acoustic isolators, modulators, and transducers. PMID:25839273