Sound field reproduction as an equivalent acoustical scattering problem.
Fazi, Filippo Maria; Nelson, Philip A
2013-11-01
Given a continuous distribution of acoustic sources, the determination of the source strength that ensures the synthesis of a desired sound field is shown to be identical to the solution of an equivalent acoustic scattering problem. The paper begins with the presentation of the general theory that underpins sound field reproduction with secondary sources continuously arranged on the boundary of the reproduction region. The process of reproduction by a continuous source distribution is modeled by means of an integral operator (the single layer potential). It is then shown how the solution of the sound reproduction problem corresponds to that of an equivalent scattering problem. Analytical solutions are computed for two specific instances of this problem, involving, respectively, the use of a secondary source distribution in spherical and planar geometries. The results are shown to be the same as those obtained with analyses based on High Order Ambisonics and Wave Field Synthesis, respectively, thus bringing to light a fundamental analogy between these two methods of sound reproduction. Finally, it is shown how the physical optics (Kirchhoff) approximation enables the derivation of a high-frequency simplification for the problem under consideration, this in turn being related to the secondary source selection criterion reported in the literature on Wave Field Synthesis.
NASA Astrophysics Data System (ADS)
Sapega, V. F.; Belitsky, V. I.; Ruf, T.; Fuchs, H. D.; Cardona, M.; Ploog, K.
1992-12-01
A strong increase of low-frequency Raman scattering has been observed in GaAs/AlxGa1-xAs multiple quantum wells in magnetic fields up to 14 T. The spectra, consisting of background scattering, folded acoustic phonons, and additional features, show resonant behavior with respect to the laser frequency and the strength of the magnetic field. The broad background, usually related to geminate recombination, has its origin in a continuum of Raman processes with the emission of longitudinal-acoustic phonons where crystal momentum is not conserved. Such processes can become dominant when interface fluctuations allow for resonant scattering in individual quantum wells only. Thus phonons with all possible energies contribute to the background scattering efficiency. The observed folded longitudinal-acoustic phonons are in good agreement with calculated frequencies. Additional features, detected in all samples measured, are attributed to local vibrational modes tied to the gaps at the folded Brillouin-zone center and edge. Other peculiarities observed correspond to modes localized at crossings of the folded longitudinal- and transverse-acoustic branches inside the Brillouin zone. The appearance of these local modes is attributed to fluctuations in the well and barrier thicknesses of the quantum wells.
Scattered acoustic field above a grating of non-parallel rectangular cavities
NASA Astrophysics Data System (ADS)
Khanfir, A.; Faiz, A.; Ducourneau, J.; Chatillon, J.; Lami, S. Skali
2016-01-01
Geometric or acoustical irregularities induces acoustic scattering. In this paper, a generalization of the model proposed by Khanfir et al. [8] (Journal of Sound and Vibration 332 (4) (2013)) to determine the scattered acoustic field above gratings of parallel rectangular cavities is developed, addressing the case of gratings of non-parallel rectangular cavities. The results provided by the model were compared both to numerical results, obtained with the finite element method, and to experimental ones. The observed agreement between the analytical predictions and the numerical and experimental results supports the validity of the proposed model. The coupling between the different cavities was investigated, in order to attain an explanation for its dependence on frequency and on the spacing between cavities.
Fischell, Erin M; Schmidt, Henrik
2015-12-01
One of the long term goals of autonomous underwater vehicle (AUV) minehunting is to have multiple inexpensive AUVs in a harbor autonomously classify hazards. Existing acoustic methods for target classification using AUV-based sensing, such as sidescan and synthetic aperture sonar, require an expensive payload on each outfitted vehicle and post-processing and/or image interpretation. A vehicle payload and machine learning classification methodology using bistatic angle dependence of target scattering amplitudes between a fixed acoustic source and target has been developed for onboard, fully autonomous classification with lower cost-per-vehicle. To achieve the high-quality, densely sampled three-dimensional (3D) bistatic scattering data required by this research, vehicle sampling behaviors and an acoustic payload for precision timed data acquisition with a 16 element nose array were demonstrated. 3D bistatic scattered field data were collected by an AUV around spherical and cylindrical targets insonified by a 7-9 kHz fixed source. The collected data were compared to simulated scattering models. Classification and confidence estimation were shown for the sphere versus cylinder case on the resulting real and simulated bistatic amplitude data. The final models were used for classification of simulated targets in real time in the LAMSS MOOS-IvP simulation package [M. Benjamin, H. Schmidt, P. Newman, and J. Leonard, J. Field Rob. 27, 834-875 (2010)].
Fischell, Erin M; Schmidt, Henrik
2015-12-01
One of the long term goals of autonomous underwater vehicle (AUV) minehunting is to have multiple inexpensive AUVs in a harbor autonomously classify hazards. Existing acoustic methods for target classification using AUV-based sensing, such as sidescan and synthetic aperture sonar, require an expensive payload on each outfitted vehicle and post-processing and/or image interpretation. A vehicle payload and machine learning classification methodology using bistatic angle dependence of target scattering amplitudes between a fixed acoustic source and target has been developed for onboard, fully autonomous classification with lower cost-per-vehicle. To achieve the high-quality, densely sampled three-dimensional (3D) bistatic scattering data required by this research, vehicle sampling behaviors and an acoustic payload for precision timed data acquisition with a 16 element nose array were demonstrated. 3D bistatic scattered field data were collected by an AUV around spherical and cylindrical targets insonified by a 7-9 kHz fixed source. The collected data were compared to simulated scattering models. Classification and confidence estimation were shown for the sphere versus cylinder case on the resulting real and simulated bistatic amplitude data. The final models were used for classification of simulated targets in real time in the LAMSS MOOS-IvP simulation package [M. Benjamin, H. Schmidt, P. Newman, and J. Leonard, J. Field Rob. 27, 834-875 (2010)]. PMID:26723332
NASA Astrophysics Data System (ADS)
Rajabi, Majid
2016-05-01
The method of wave function expansion is adopted to study the three dimensional scattering of a plane progressive harmonic acoustic wave incident upon an arbitrarily thick-walled helically filament-wound composite cylindrical shell submerged in and filled with compressible ideal fluids. An approximate laminate model in the context of the so-called state-space formulation is employed for the construction of T-matrix solution to solve for the unknown modal scattering coefficients. Considering the nonaxisymmetric wave propagation phenomenon in anisotropic cylindrical components and following the resonance scattering theory which determines the resonance and background scattering fields, the stimulated resonance frequencies of the shell are isolated and classified due to their fundamental mode of excitation, overtone and style of propagation along the cylindrical axis (i.e., clockwise or anticlockwise propagation around the shell) and are identified as the helically circumnavigating waves.
Acoustic scattering by multiple elliptical cylinders using collocation multipole method
NASA Astrophysics Data System (ADS)
Lee, Wei-Ming
2012-05-01
This paper presents the collocation multipole method for the acoustic scattering induced by multiple elliptical cylinders subjected to an incident plane sound wave. To satisfy the Helmholtz equation in the elliptical coordinate system, the scattered acoustic field is formulated in terms of angular and radial Mathieu functions which also satisfy the radiation condition at infinity. The sound-soft or sound-hard boundary condition is satisfied by uniformly collocating points on the boundaries. For the sound-hard or Neumann conditions, the normal derivative of the acoustic pressure is determined by using the appropriate directional derivative without requiring the addition theorem of Mathieu functions. By truncating the multipole expansion, a finite linear algebraic system is derived and the scattered field can then be determined according to the given incident acoustic wave. Once the total field is calculated as the sum of the incident field and the scattered field, the near field acoustic pressure along the scatterers and the far field scattering pattern can be determined. For the acoustic scattering of one elliptical cylinder, the proposed results match well with the analytical solutions. The proposed scattered fields induced by two and three elliptical-cylindrical scatterers are critically compared with those provided by the boundary element method to validate the present method. Finally, the effects of the convexity of an elliptical scatterer, the separation between scatterers and the incident wave number and angle on the acoustic scattering are investigated.
Modelling of the acoustic field of a multi-element HIFU array scattered by human ribs
NASA Astrophysics Data System (ADS)
Gélat, Pierre; ter Haar, Gail; Saffari, Nader
2011-09-01
The efficacy of high-intensity focused ultrasound (HIFU) for the treatment of a range of different cancers, including those of the liver, prostate and breast, has been demonstrated. As a non-invasive focused therapy, HIFU offers considerable advantages over techniques such as chemotherapy and surgical resection in terms of reduced risk of harmful side effects. Despite this, there are a number of significant challenges which currently hinder its widespread clinical application. One of these challenges is the need to transmit sufficient energy through the rib cage to induce tissue necrosis in the required volume whilst minimizing the formation of side lobes. Multi-element random-phased arrays are currently showing great promise in overcoming the limitations of single-element transducers. Nevertheless, successful treatment of a patient with liver tumours requires a thorough understanding of the way in which the ultrasonic pressure field from a HIFU array is scattered by the rib cage. In order to address this, a boundary element approach based on a generalized minimal residual (GMRES) implementation of the Burton-Miller formulation was used in conjunction with phase conjugation techniques to focus the field of a 256-element random HIFU array behind human ribs at locations requiring intercostal and transcostal treatment. Simulations were carried out on a 3D mesh of quadratic pressure patches generated using CT scan anatomical data for adult ribs 9-12 on the right side. The methodology was validated on spherical and cylindrical scatterers. Field calculations were also carried out for idealized ribs, consisting of arrays of strip-like scatterers, demonstrating effects of splitting at the focus. This method has the advantage of fully accounting for the effect of scattering and diffraction in 3D under continuous wave excitation.
Modelling of the acoustic field of a multi-element HIFU array scattered by human ribs.
Gélat, Pierre; Ter Haar, Gail; Saffari, Nader
2011-09-01
The efficacy of high-intensity focused ultrasound (HIFU) for the treatment of a range of different cancers, including those of the liver, prostate and breast, has been demonstrated. As a non-invasive focused therapy, HIFU offers considerable advantages over techniques such as chemotherapy and surgical resection in terms of reduced risk of harmful side effects. Despite this, there are a number of significant challenges which currently hinder its widespread clinical application. One of these challenges is the need to transmit sufficient energy through the rib cage to induce tissue necrosis in the required volume whilst minimizing the formation of side lobes. Multi-element random-phased arrays are currently showing great promise in overcoming the limitations of single-element transducers. Nevertheless, successful treatment of a patient with liver tumours requires a thorough understanding of the way in which the ultrasonic pressure field from a HIFU array is scattered by the rib cage. In order to address this, a boundary element approach based on a generalized minimal residual (GMRES) implementation of the Burton-Miller formulation was used in conjunction with phase conjugation techniques to focus the field of a 256-element random HIFU array behind human ribs at locations requiring intercostal and transcostal treatment. Simulations were carried out on a 3D mesh of quadratic pressure patches generated using CT scan anatomical data for adult ribs 9-12 on the right side. The methodology was validated on spherical and cylindrical scatterers. Field calculations were also carried out for idealized ribs, consisting of arrays of strip-like scatterers, demonstrating effects of splitting at the focus. This method has the advantage of fully accounting for the effect of scattering and diffraction in 3D under continuous wave excitation.
Acoustic Scattering from Compact Bubble Clouds.
NASA Astrophysics Data System (ADS)
Schindall, Jeffrey Alan
In this study, a simple model describing the low -frequency scattering properties of high void fraction bubble clouds in both the free field and near the ocean surface is developed. This model, which is based on an effective medium approximation and acoustically compact scatters, successfully predicts the results of the bubble cloud scattering experiment carried out at Lake Seneca in New York state for frequencies consistent with the model assumptions (Roy et al., 1992). The introduction of the surface is facilitated by the method of images and is subject to the same constraint of low-acoustic frequency imposed by the compact scatterer assumption. This model is not intended to serve as an exact replicate of oceanic bubble cloud scattering. The model herein was kept simple by design, for only then can the complex physical behavior be expressed in a simple analytical form. Simple, analytic theories facilitate the exploration of parameter space, and more importantly serve to illuminate the underlying physics.
An invariance theorem in acoustic scattering theory
NASA Astrophysics Data System (ADS)
Ha-Duong, T.
1996-10-01
Karp's theorem states that if the far-field pattern corresponding to the scattering of a time-harmonic acoustic plane wave by a sound-soft obstacle is invariant under the group of orthogonal transformations in 0266-5611/12/5/007/img1 (rotations in 0266-5611/12/5/007/img2), then the scatterer is a sphere (circle). The theorem is generalized to the case where the invariant group of the far field pattern is only a subgroup of the orthogonal group, and for a class of mixed boundary conditions.
NASA Astrophysics Data System (ADS)
Ouyang, Wei; Mao, Weijian; Li, Xuelei; Li, Wuqun
2014-08-01
Sound velocity inversion problem based on scattering theory is formulated in terms of a nonlinear integral equation associated with scattered field. Because of its nonlinearity, in practice, linearization algorisms (Born/single scattering approximation) are widely used to obtain an approximate inversion solution. However, the linearized strategy is not congruent with seismic wave propagation mechanics in strong perturbation (heterogeneous) medium. In order to partially dispense with the weak perturbation assumption of the Born approximation, we present a new approach from the following two steps: firstly, to handle the forward scattering by taking into account the second-order Born approximation, which is related to generalized Radon transform (GRT) about quadratic scattering potential; then to derive a nonlinear quadratic inversion formula by resorting to inverse GRT. In our formulation, there is a significant quadratic term regarding scattering potential, and it can provide an amplitude correction for inversion results beyond standard linear inversion. The numerical experiments demonstrate that the linear single scattering inversion is only good in amplitude for relative velocity perturbation () of background media up to 10 %, and its inversion errors are unacceptable for the perturbation beyond 10 %. In contrast, the quadratic inversion can give more accurate amplitude-preserved recovery for the perturbation up to 40 %. Our inversion scheme is able to manage double scattering effects by estimating a transmission factor from an integral over a small area, and therefore, only a small portion of computational time is added to the original linear migration/inversion process.
Nonlinear ion acoustic waves scattered by vortexes
NASA Astrophysics Data System (ADS)
Ohno, Yuji; Yoshida, Zensho
2016-09-01
The Kadomtsev-Petviashvili (KP) hierarchy is the archetype of infinite-dimensional integrable systems, which describes nonlinear ion acoustic waves in two-dimensional space. This remarkably ordered system resides on a singular submanifold (leaf) embedded in a larger phase space of more general ion acoustic waves (low-frequency electrostatic perturbations). The KP hierarchy is characterized not only by small amplitudes but also by irrotational (zero-vorticity) velocity fields. In fact, the KP equation is derived by eliminating vorticity at every order of the reductive perturbation. Here, we modify the scaling of the velocity field so as to introduce a vortex term. The newly derived system of equations consists of a generalized three-dimensional KP equation and a two-dimensional vortex equation. The former describes 'scattering' of vortex-free waves by ambient vortexes that are determined by the latter. We say that the vortexes are 'ambient' because they do not receive reciprocal reactions from the waves (i.e., the vortex equation is independent of the wave fields). This model describes a minimal departure from the integrable KP system. By the Painlevé test, we delineate how the vorticity term violates integrability, bringing about an essential three-dimensionality to the solutions. By numerical simulation, we show how the solitons are scattered by vortexes and become chaotic.
Inverse potential scattering in duct acoustics.
Forbes, Barbara J; Pike, E Roy; Sharp, David B; Aktosun, Tuncay
2006-01-01
The inverse problem of the noninvasive measurement of the shape of an acoustical duct in which one-dimensional wave propagation can be assumed is examined within the theoretical framework of the governing Klein-Gordon equation. Previous deterministic methods developed over the last 40 years have all required direct measurement of the reflectance or input impedance but now, by application of the methods of inverse quantum scattering to the acoustical system, it is shown that the reflectance can be algorithmically derived from the radiated wave. The potential and area functions of the duct can subsequently be reconstructed. The results are discussed with particular reference to acoustic pulse reflectometry.
Nonlinear scattering of acoustic waves by vibrating obstacles
NASA Astrophysics Data System (ADS)
Piquette, J. C.
1983-06-01
The problem of the generation of sum- and difference-frequency waves produced via the scattering of an acoustic wave by an obstacle whose surface vibrates harmonically was studied both theoretically and experimentally. The theoretical approach involved solving the nonlinear wave equation, subject to appropriate boundary conditions, by the use of a perturbation expansion of the fields and a Green's function method. In addition to ordinary rigid-body scattering, Censor predicted nongrowing waves at frequencies equal to the sum and to the difference of the frequencies of the primary waves. The solution to the nonlinear wave equation also yields scattered waves at the sum and difference frequencies. However, the nonlinearity of the medium causes these waves to grow with increasing distance from the scatter's surface and, after a very small distance, dominate those predicted by Censor. The simple-source formulation of the second-order nonlinear wave equation for a lossless fluid medium has been derived for arbitrary primary wave fields. This equation was used to solve the problem of nonlinear scattering of acoustic waves by a vibrating obstacle for three geometries: (1) a plane-wave scattering by a vibrating plane, (2) cylindrical-wave scattering by a vibrating cylinder, and (3) plane-wave scattering by a vibrating cylinder. Successful experimental validation of the theory was inhibited by previously unexpected levels of nonlinearity in the hydrophones used. Such high levels of hydrophone nonlinearity appeared in hydrophones that, by their geometry of construction, were expected to be fairly linear.
Inverse Scattering Problems for Acoustic Waves in AN Inhomogeneous Medium.
NASA Astrophysics Data System (ADS)
Kedzierawski, Andrzej Wladyslaw
1990-01-01
This dissertation considers the inverse scattering problem of determining either the absorption of sound in an inhomogeneous medium or the surface impedance of an obstacle from a knowledge of the far-field patterns of the scattered fields corresponding to many incident time -harmonic plane waves. First, we consider the inverse problem in the case when the scattering object is an inhomogeneous medium with complex refraction index having compact support. Our approach to this problem is the orthogonal projection method of Colton-Monk (cf. The inverse scattering problem for time acoustic waves in an inhomogeneous medium, Quart. J. Mech. Appl. Math. 41 (1988), 97-125). After that, we prove the analogue of Karp's Theorem for the scattering of acoustic waves through an inhomogeneous medium with compact support. We then generalize some of these results to the case when the inhomogeneous medium is no longer of compact support. If the acoustic wave penetrates the inhomogeneous medium by only a small amount then the inverse medium problem leads to the inverse obstacle problem with an impedance boundary condition. We solve the inverse impedance problem of determining the surface impedance of an obstacle of known shape by using both the methods of Kirsch-Kress and Colton-Monk (cf. R. Kress, Linear Integral Equations, Springer-Verlag, New York, 1989).
A time domain sampling method for inverse acoustic scattering problems
NASA Astrophysics Data System (ADS)
Guo, Yukun; Hömberg, Dietmar; Hu, Guanghui; Li, Jingzhi; Liu, Hongyu
2016-06-01
This work concerns the inverse scattering problems of imaging unknown/inaccessible scatterers by transient acoustic near-field measurements. Based on the analysis of the migration method, we propose efficient and effective sampling schemes for imaging small and extended scatterers from knowledge of time-dependent scattered data due to incident impulsive point sources. Though the inverse scattering problems are known to be nonlinear and ill-posed, the proposed imaging algorithms are totally "direct" involving only integral calculations on the measurement surface. Theoretical justifications are presented and numerical experiments are conducted to demonstrate the effectiveness and robustness of our methods. In particular, the proposed static imaging functionals enhance the performance of the total focusing method (TFM) and the dynamic imaging functionals show analogous behavior to the time reversal inversion but without solving time-dependent wave equations.
Acoustic scattering from microfibers of Parylene C
NASA Astrophysics Data System (ADS)
Chindam, Chandraprakash; Lakhtakia, Akhlesh; Awadelkarim, Osama O.; Orfali, Wasim
2014-10-01
The acoustic scattering characteristics of ˜10 μ m-long microfibers of Parylene C embedded in water were investigated, towards the eventual goal of designing polymeric sculptured thin films for biomedical applications. The chosen microfibers were upright circular-cylindrical, slanted circular-cylindrical, chevronic, and helical in shape. A combination of numerical and analytical techniques was adopted to examine the scattering of plane waves in a spectral regime spanning the lower few eigenfrequencies of the microfibers. Certain maximums in the spectrums of the forward and back scattering efficiencies arise from the phenomenon of creeping waves. The same phenomenon affects the total scattering efficiency in some instances. The spectrums of all efficiencies exhibit the geometric symmetry of a microfiber in relation to the direction of propagation of the incident plane wave. Similarities in the shapes of the slanted circular-cylindrical and the chevronic microfibers are reflected in the spectrums of their scattering efficiencies. A highly compliant microfiber has shorter and broader peaks than a less compliant microfiber in the spectrums of the total scattering efficiency. The proper design of polymeric sculptured thin films will benefit from the knowledge gained of the directions of maximum scattering from individual microfibers.
Support minimized inversion of acoustic and elastic wave scattering
Safaeinili, A.
1994-04-24
This report discusses the following topics on support minimized inversion of acoustic and elastic wave scattering: Minimum support inversion; forward modelling of elastodynamic wave scattering; minimum support linearized acoustic inversion; support minimized nonlinear acoustic inversion without absolute phase; and support minimized nonlinear elastic inversion.
Acoustic asymmetric transmission based on time-dependent dynamical scattering
Wang, Qing; Yang, Yang; Ni, Xu; Xu, Ye-Long; Sun, Xiao-Chen; Chen, Ze-Guo; Feng, Liang; Liu, Xiao-ping; Lu, Ming-Hui; Chen, Yan-Feng
2015-01-01
An acoustic asymmetric transmission device exhibiting unidirectional transmission property for acoustic waves is extremely desirable in many practical scenarios. Such a unique property may be realized in various configurations utilizing acoustic Zeeman effects in moving media as well as frequency-conversion in passive nonlinear acoustic systems and in active acoustic systems. Here we demonstrate a new acoustic frequency conversion process in a time-varying system, consisting of a rotating blade and the surrounding air. The scattered acoustic waves from this time-varying system experience frequency shifts, which are linearly dependent on the blade’s rotating frequency. Such scattering mechanism can be well described theoretically by an acoustic linear time-varying perturbation theory. Combining such time-varying scattering effects with highly efficient acoustic filtering, we successfully develop a tunable acoustic unidirectional device with 20 dB power transmission contrast ratio between two counter propagation directions at audible frequencies. PMID:26038886
Acoustic scattering from phononic crystals with complex geometry.
Kulpe, Jason A; Sabra, Karim G; Leamy, Michael J
2016-05-01
This work introduces a formalism for computing external acoustic scattering from phononic crystals (PCs) with arbitrary exterior shape using a Bloch wave expansion technique coupled with the Helmholtz-Kirchhoff integral (HKI). Similar to a Kirchhoff approximation, a geometrically complex PC's surface is broken into a set of facets in which the scattering from each facet is calculated as if it was a semi-infinite plane interface in the short wavelength limit. When excited by incident radiation, these facets introduce wave modes into the interior of the PC. Incorporation of these modes in the HKI, summed over all facets, then determines the externally scattered acoustic field. In particular, for frequencies in a complete bandgap (the usual operating frequency regime of many PC-based devices and the requisite operating regime of the presented theory), no need exists to solve for internal reflections from oppositely facing edges and, thus, the total scattered field can be computed without the need to consider internal multiple scattering. Several numerical examples are provided to verify the presented approach. Both harmonic and transient results are considered for spherical and bean-shaped PCs, each containing over 100 000 inclusions. This facet formalism is validated by comparison to an existing self-consistent scattering technique.
Novel limiting circle theory in acoustic wave scattering and absorption
NASA Astrophysics Data System (ADS)
Huang, Changzheng
Wave scattering theory is the basis for many key technologies that have important military and commercial applications. The familiar examples are radar, sonar, and various ultrasound instruments commonly used in remote sensing, target identification, non-destructive evaluation, medical diagnosis, and many other areas. Their mathematical model involves the solution of the so- called inverse scattering problem where an incident wave is used to probe a remote or inaccessible object. From the scattered field measurement, the shape and/or the material composition of the object can be determined. A new wave scattering theory, termed limiting circle theory (LCT), has been developed in this dissertation based on a novel approach of decomposing the wave scattering matrix. LCT has rigorously proved that the scattered wave field from any penetrable object (of cylinder and sphere geometries) is composed of three contributions: a rigid background, a soft background, and a pure resonance. This is a significant modification to the existing resonance scattering theory (RST) which states that the scattered field is made up of only two components: a proper background (either rigid or soft), and a pure resonance. LCT formalism led to the discovery of the limiting circle patterns associated with all normal modes or partial waves. These patterns provide a clear understanding of the resonance behavior such as the resonance period and the resonance intensity. The analytical LCT approach could also be the key to solving the background problems for shell structures that have remained unsolved for many years in acoustics.
Experimental Demonstration of Underwater Acoustic Scattering Cancellation
Rohde, Charles A.; Martin, Theodore P.; Guild, Matthew D.; Layman, Christopher N.; Naify, Christina J.; Nicholas, Michael; Thangawng, Abel L.; Calvo, David C.; Orris, Gregory J.
2015-01-01
We explore an acoustic scattering cancellation shell for buoyant hollow cylinders submersed in a water background. A thin, low-shear, elastic coating is used to cancel the monopole scattering from an air-filled, neutrally buoyant steel shell for all frequencies where the wavelength is larger than the object diameter. By design, the uncoated shell also has an effective density close to the aqueous background, independently canceling its dipole scattering. Due to the significantly reduced monopole and dipole scattering, the compliant coating results in a hollow cylindrical inclusion that is simultaneously impedance and sound speed matched to the water background. We demonstrate the proposed cancellation method with a specific case, using an array of hollow steel cylinders coated with thin silicone rubber shells. These experimental results are matched to finite element modeling predictions, confirming the scattering reduction. Additional calculations explore the optimization of the silicone coating properties. Using this approach, it is found that scattering cross-sections can be reduced by 20 dB for all wavelengths up to k0a = 0.85. PMID:26282067
Acoustic orbital angular momentum transfer to matter by chiral scattering
NASA Astrophysics Data System (ADS)
Wunenburger, Régis; Israel Vazquez Lozano, Juan; Brasselet, Etienne
2015-10-01
We report on orbital angular momentum exchange between sound and matter mediated by a non-dissipative chiral scattering process. An experimental demonstration is made possible by irradiating a three-dimensional printed, spiral-shaped chiral object with an incident ultrasonic beam carrying zero orbital angular momentum. Chiral refraction is shown to impart a nonzero orbital angular momentum to the scattered field and to rotate the object. This result constitutes a proof of concept of a novel kind of acoustic angular manipulation of matter.
Numerical solution of acoustic scattering by finite perforated elastic plates
NASA Astrophysics Data System (ADS)
Cavalieri, A. V. G.; Wolf, W. R.; Jaworski, J. W.
2016-04-01
We present a numerical method to compute the acoustic field scattered by finite perforated elastic plates. A boundary element method is developed to solve the Helmholtz equation subjected to boundary conditions related to the plate vibration. These boundary conditions are recast in terms of the vibration modes of the plate and its porosity, which enables a direct solution procedure. A parametric study is performed for a two-dimensional problem whereby a cantilevered perforated elastic plate scatters sound from a point quadrupole near the free edge. Both elasticity and porosity tend to diminish the scattered sound, in agreement with previous work considering semi-infinite plates. Finite elastic plates are shown to reduce acoustic scattering when excited at high Helmholtz numbers k0 based on the plate length. However, at low k0, finite elastic plates produce only modest reductions or, in cases related to structural resonance, an increase to the scattered sound level relative to the rigid case. Porosity, on the other hand, is shown to be more effective in reducing the radiated sound for low k0. The combined beneficial effects of elasticity and porosity are shown to be effective in reducing the scattered sound for a broader range of k0 for perforated elastic plates.
Microparticle and Cell Characterization Using Acoustic Scattering.
NASA Astrophysics Data System (ADS)
Roos, Mark Schaefer
A technique is presented for measuring physical properties of particles with radii from one to five microns. Tone bursts of 30 MHz center frequency are scattered by single particles as they are carried by a coaxial jet flow past three focused acoustic transducers (one sender and two receivers). The scattered pressure is measured simultaneously at two angles, which allows the compressibility and density of the particles to be calculated given the volume of the particles and the density and compressibility of the host liquid using Rayleigh's theory for long wavelength acoustic scattering. Because the particles are measured one at a time, statistical distributions of their properties may be determined. The device is calibrated using particles whose properties are known. A study was conducted on human red blood cells in hosts of different tonicity. Density and compressibility values obtained in these experiments are compared with a model accounting for changes in red cell properties due to variations in cell water content. Other studies were conducted using polystyrene and polystyrene divinylbenzene spheres. This technique is well suited to in vitro measurement of properties of biological cells. Applications are discussed, with emphasis on the study of red blood cells.
Low frequency acoustic and electromagnetic scattering
NASA Technical Reports Server (NTRS)
Hariharan, S. I.; Maccamy, R. C.
1986-01-01
This paper deals with two classes of problems arising from acoustics and electromagnetics scattering in the low frequency stations. The first class of problem is solving Helmholtz equation with Dirichlet boundary conditions on an arbitrary two dimensional body while the second one is an interior-exterior interface problem with Helmholtz equation in the exterior. Low frequency analysis show that there are two intermediate problems which solve the above problems accurate to 0(k/2/ log k) where k is the frequency. These solutions greatly differ from the zero frequency approximations. For the Dirichlet problem numerical examples are shown to verify the theoretical estimates.
Low frequency acoustic and electromagnetic scattering
NASA Technical Reports Server (NTRS)
Hariharan, S. I.; Maccamy, R. C.
1983-01-01
This paper deals with two classes of problems arising from acoustics and electromagnetics scattering in the low frequency stations. The first class of problem is solving Helmholtz equation with Dirichlet boundary conditions on an arbitrary two dimensional body while the second one is an interior-exterior interface problem with Helmholtz equation in the exterior. Low frequency analysis show that there are two intermediate problems which solve the above problems accurate to 0(k(2) log k) where k is the frequency. These solutions greatly differ from the zero frequency approximations. For the Dirichlet problem numerical examples are shown to verify the theoretical estimates.
NASA Astrophysics Data System (ADS)
Rajabi, Majid
2016-09-01
In the present work as the second part of the research work on wave propagation characteristics of helically orthotropic cylindrical shells, the main aim is to use the developed solution for resonance isolation and identification of an air-filled and water submerged Graphite/Epoxy cylindrical shell and quantitative sensitivity analysis of excited resonance frequencies to the perturbation in the material's elastic constants. The physical justifications are presented for the singular features associated with the stimulated resonance frequencies according to their style of propagation and polarization, induced stress-strain fields and wave type. For evaluation purposes, the wave propagation characteristics of the anisotropic shell and the far-field form function amplitude of a limiting case are considered and good agreement with the solutions available in the literature is established.
Inverse scattering problems for acoustic waves in an inhomogeneous medium
NASA Astrophysics Data System (ADS)
Kedzierawski, Andrzej Wladyslaw
The inverse scattering problem is considered of determining either the absorption of sound in an inhomogeneous medium or the surface impedance of an obstacle from a knowledge of the far field patterns of the scattered field corresponding to many incident time-harmonic plane waves. First, the inverse problem is studied in the case when the scattering object is an inhomogeneous medium with complex refractive index having compact support. The approach to this problem is the orthogonal projection method of Colton-Monk (1988). After that, the analogue is proven of Karp's Theorem for the scattering of acoustic waves through an inhomogeneous medium with compact support. Some of these results are then generalized to the case when the inhomogeneous medium is no longer of compact support. If the acoustic wave penetrates the inhomogeneous medium by only a small amount then the inverse medium problem leads to the inverse obstacle problem with an impedance boundary condition. The inverse impedance problem is solved of determining the surface impedance of an obstacle of known shape by using both the methods of Kirsch-Kress and Colton-Monk (1989).
NASA Astrophysics Data System (ADS)
Wei, Qi; Cheng, Ying; Liu, Xiao-jun
2012-07-01
We present a three-dimensional acoustic concentrator capable of significantly enhancing the sound intensity in the compressive region with scattering cancellation, imaging, and mirage effects. The concentrator shell is built by isotropic gradient negative-index materials, which together with an exterior host medium slab constructs a pair of complementary media. The enhancement factor, which can approach infinity by tuning the geometric parameters, is always much higher than that of a traditional concentrator made by positive-index materials with the same size. The acoustic scattering theory is applied to derive the pressure field distribution of the concentrator, which is consistent with the numerical full-wave simulations. The inherent acoustic impedance match at the interfaces of the shell as well as the inverse processes of “negative refraction—progressive curvature—negative refraction” for arbitrary sound rays can exactly cancel the scattering of the concentrator. In addition, the concentrator shell can also function as an acoustic spherical magnifying superlens, which produces a perfect image with the same shape, with bigger geometric and acoustic parameters located at a shifted position. Then some acoustic mirages are observed whereby the waves radiated from (scattered by) an object located in the center region may seem to be radiated from (scattered by) its image. Based on the mirage effect, we further propose an intriguing acoustic transformer which can transform the sound scattering pattern of one object into another object at will with arbitrary geometric, acoustic, and location parameters.
Flow velocity measurement with the nonlinear acoustic wave scattering
NASA Astrophysics Data System (ADS)
Didenkulov, Igor; Pronchatov-Rubtsov, Nikolay
2015-10-01
A problem of noninvasive measurement of liquid flow velocity arises in many practical applications. To this end the most often approach is the use of the linear Doppler technique. The Doppler frequency shift of signal scattered from the inhomogeneities distributed in a liquid relatively to the emitted frequency is proportional to the sound frequency and velocities of inhomogeneities. In the case of very slow flow one needs to use very high frequency sound. This approach fails in media with strong sound attenuation because acoustic wave attenuation increases with frequency and there is limit in increasing sound intensity, i.e. the cavitation threshold. Another approach which is considered in this paper is based on the method using the difference frequency Doppler Effect for flows with bubbles. This method is based on simultaneous action of two high-frequency primary acoustic waves with closed frequencies on bubbles and registration of the scattered by bubbles acoustic field at the difference frequency. The use of this method is interesting since the scattered difference frequency wave has much lower attenuation in a liquid. The theoretical consideration of the method is given in the paper. The experimental examples confirming the theoretical equations, as well as the ability of the method to be applied in medical diagnostics and in technical applications on measurement of flow velocities in liquids with strong sound attenuation is described. It is shown that the Doppler spectrum form depends on bubble concentration velocity distribution in the primary acoustic beams crossing zone that allows one to measure the flow velocity distribution.
Flow velocity measurement with the nonlinear acoustic wave scattering
Didenkulov, Igor; Pronchatov-Rubtsov, Nikolay
2015-10-28
A problem of noninvasive measurement of liquid flow velocity arises in many practical applications. To this end the most often approach is the use of the linear Doppler technique. The Doppler frequency shift of signal scattered from the inhomogeneities distributed in a liquid relatively to the emitted frequency is proportional to the sound frequency and velocities of inhomogeneities. In the case of very slow flow one needs to use very high frequency sound. This approach fails in media with strong sound attenuation because acoustic wave attenuation increases with frequency and there is limit in increasing sound intensity, i.e. the cavitation threshold. Another approach which is considered in this paper is based on the method using the difference frequency Doppler Effect for flows with bubbles. This method is based on simultaneous action of two high-frequency primary acoustic waves with closed frequencies on bubbles and registration of the scattered by bubbles acoustic field at the difference frequency. The use of this method is interesting since the scattered difference frequency wave has much lower attenuation in a liquid. The theoretical consideration of the method is given in the paper. The experimental examples confirming the theoretical equations, as well as the ability of the method to be applied in medical diagnostics and in technical applications on measurement of flow velocities in liquids with strong sound attenuation is described. It is shown that the Doppler spectrum form depends on bubble concentration velocity distribution in the primary acoustic beams crossing zone that allows one to measure the flow velocity distribution.
Numerical Simulations of Radar Acoustic Scattering
NASA Astrophysics Data System (ADS)
Boluriaan, Said; Morris, Philip J.
1998-11-01
Wake vortices are produced by the lifting surfaces of all aircraft. The vortex created by a large aircraft can have a catastrophic effect on a small plane following closely behind. A vortex detection system would not only increase airport productivity by allowing adaptive spacing, but would also increase the safety of all aircraft operating around the airport by alerting controllers to hazardous conditions that might exist near the runways. In the present research, one and two-dimensional models have been considered for the study of wake vortex detection using a Radar Acoustic Sounding System (RASS). The permittivity perturbation caused by the vortex is modeled as a traveling wave with a Gaussian envelope and a variable propagation speed. The model equations are solved numerically. The one-dimensional model is also solved analytically. The main problem with a time domain simulation is the number of samples required to resolve the Doppler shift. Even for a 1D model with a typical scatterer size, the CPU time required to run the code is far beyond the currently available computer resources. One way to make the time domain simulation feasible is to recast the governing differential equation in order to remove the carrier frequency and solve only for the frequency shift in the scattered wave. The numerical stability characteristics of the resulting equation with complex coefficients are discussed. In order to validate the numerical scheme, the code is run for a fictitious speed of light.
Topics in electromagnetic, acoustic, and potential scattering theory
NASA Astrophysics Data System (ADS)
Nuntaplook, Umaporn
With recent renewed interest in the classical topics of both acoustic and electromagnetic aspects for nano-technology, transformation optics, fiber optics, metamaterials with negative refractive indices, cloaking and invisibility, the topic of time-independent scattering theory in quantum mechanics is becoming a useful field to re-examine in the above contexts. One of the key areas of electromagnetic theory scattering of plane electromagnetic waves --- is based on the properties of the refractive indices in the various media. It transpires that the refractive index of a medium and the potential in quantum scattering theory are intimately related. In many cases, understanding such scattering in radially symmetric media is sufficient to gain insight into scattering in more complex media. Meeting the challenge of variable refractive indices and possibly complicated boundary conditions therefore requires accurate and efficient numerical methods, and where possible, analytic solutions to the radial equations from the governing scalar and vector wave equations (in acoustics and electromagnetic theory, respectively). Until relatively recently, researchers assumed a constant refractive index throughout the medium of interest. However, the most interesting and increasingly useful cases are those with non-constant refractive index profiles. In the majority of this dissertation the focus is on media with piecewise constant refractive indices in radially symmetric media. The method discussed is based on the solution of Maxwell's equations for scattering of plane electromagnetic waves from a dielectric (or "transparent") sphere in terms of the related Helmholtz equation. The main body of the dissertation (Chapters 2 and 3) is concerned with scattering from (i) a uniform spherical inhomogeneity embedded in an external medium with different properties, and (ii) a piecewise-uniform central inhomogeneity in the external medium. The latter results contain a natural generalization of
Acoustic build-up in on-chip stimulated Brillouin scattering
Wolff, C.; Steel, M. J.; Eggleton, B. J.; Poulton, C. G.
2015-01-01
We investigate the role of the spatial evolution of the acoustic field in stimulated Brillouin scattering processes in short high-gain structures. When the gain is strong enough that the gain length becomes comparable to the acoustic wave decay length of order 100 microns, standard approximations treating the acoustic field as a local response no longer apply. Treating the acoustic evolution more accurately, we find that the backward SBS gain of sub-millimetre long waveguides is significantly reduced from the value obtained by the conventional treatment because the acoustic mode requires several decay lengths to build up to its nominal value. In addition, the corresponding resonance line is broadened with the development of side bands. In contrast, we argue that intra-mode forward SBS is not expected to show these effects. Our results have implications for several recent proposals and experiments on high-gain stimulated Brillouin scattering in short semiconductor waveguides. PMID:26338720
Cloaking of an acoustic sensor using scattering cancellation
NASA Astrophysics Data System (ADS)
Guild, Matthew D.; Alù, Andrea; Haberman, Michael R.
2014-07-01
In this Letter, a bilaminate acoustic cloak designed using scattering cancellation methods is applied to the case of an acoustic sensor consisting of a hollow piezoelectric shell with mechanical absorption. The bilaminate cloak provides 20-50 dB reduction in scattering strength relative to the uncloaked configuration over the typical range of operation for an acoustic sensor, retains its ability to sensing acoustic pressure signals, and remains within the physical bounds of a passive absorber. Further, the cloak is shown to increase the range of frequencies over which there is nearly perfect phase fidelity between the acoustic signal and the voltage generated by the sensor. The feasibility of achieving the necessary fluid layer properties is demonstrated using sonic crystals with the use of readily available acoustic materials.
Preconditioned iterative methods for inhomogeneous acoustic scattering applications
NASA Astrophysics Data System (ADS)
Sifuentes, Josef
This thesis develops and analyzes efficient iterative methods for solving discretizations of the Lippmann--Schwinger integral equation for inhomogeneous acoustic scattering. Analysis and numerical illustrations of the spectral properties of the scattering problem demonstrate that a significant portion of the spectrum is approximated well on coarse grids. To exploit this, I develop a novel restarted GMRES method with adaptive deflation preconditioning based on spectral approximations on multiple grids. Much of the literature in this field is based on exact deflation, which is not feasible for most practical computations. This thesis provides an analytical framework for general approximate deflation methods and suggests a way to rigorously study a host of inexactly-applied preconditioners. Approximate deflation algorithms are implemented for scattering through thin inhomogeneities in photonic band gap problems. I also develop a short term recurrence for solving the one dimensional version of the problem that exploits the observation that the integral operator is a low rank perturbation of a self-adjoint operator. This method is based on strategies for solving Schur complement problems, and provides an alternative to a recent short term recurrence algorithm for matrices with such structure that we show to be numerically unstable for this application. The restarted GMRES method with adaptive deflation preconditioning over multiple grids, as well as the short term recurrence method for operators with low rank skew-adjoint parts, are very effective for reducing both the computational time and computer memory required to solve acoustic scattering problems. Furthermore, the methods are sufficiently general to be applicable to a wide class of problems.
Multiscale analysis of the acoustic scattering by many scatterers of impedance type
NASA Astrophysics Data System (ADS)
Challa, Durga Prasad; Sini, Mourad
2016-06-01
We are concerned with the acoustic scattering problem, at a frequency {κ}, by many small obstacles of arbitrary shapes with impedance boundary condition. These scatterers are assumed to be included in a bounded domain {Ω} in {{R}^3} which is embedded in an acoustic background characterized by an eventually locally varying index of refraction. The collection of the scatterers {D_m, m=1,ldots,M} is modeled by four parameters: their number M, their maximum radius a, their minimum distance d and the surface impedances {λ_m, m=1,ldots,M}. We consider the parameters M, d and {λ_m}'s having the following scaling properties: {M:=M(a)=O(a^{-s}), d:=d(a)≈ a^t} and {λ_m:=λ_m(a)=λ_{m,0}a^{-β}}, as {a→ 0}, with non negative constants s, t and {β} and complex numbers {λ_{m, 0}}'s with eventually negative imaginary parts. We derive the asymptotic expansion of the far-fields with explicit error estimate in terms of a, as {a→ 0}. The dominant term is the Foldy-Lax field corresponding to the scattering by the point-like scatterers located at the centers {z_m}'s of the scatterers {D_m}'s with {λ_m \\vert partial D_m\\vert} as the related scattering coefficients. This asymptotic expansion is justified under the following conditions a ≤ a_0, \\vert Re (λ_{m,0})\\vert ≥ λ_-,quad \\vertλ_{m,0}\\vert ≤ λ_+,quad β < 1,quad 0 ≤ s ≤2-β,quads/3 ≤ t and the error of the approximation is {C a^{3-2β-s}}, as {a → 0}, where the positive constants {a_0, λ_-,λ_+} and C depend only on the a priori uniform bounds of the Lipschitz characters of the obstacles {D_m}'s and the ones of {M(a)a^s} and {d(a)/a^t}. We do not assume the periodicity in distributing the small scatterers. In addition, the scatterers can be arbitrary close since t can be arbitrary large, i.e., we can handle the mesoscale regime. Finally, for spherical scatterers, we can also allow the limit case {β=1} with a slightly better error of the approximation.
Acoustic Force Density Acting on Inhomogeneous Fluids in Acoustic Fields.
Karlsen, Jonas T; Augustsson, Per; Bruus, Henrik
2016-09-01
We present a theory for the acoustic force density acting on inhomogeneous fluids in acoustic fields on time scales that are slow compared to the acoustic oscillation period. The acoustic force density depends on gradients in the density and compressibility of the fluid. For microfluidic systems, the theory predicts a relocation of the inhomogeneities into stable field-dependent configurations, which are qualitatively different from the horizontally layered configurations due to gravity. Experimental validation is obtained by confocal imaging of aqueous solutions in a glass-silicon microchip. PMID:27661695
Acoustic Force Density Acting on Inhomogeneous Fluids in Acoustic Fields.
Karlsen, Jonas T; Augustsson, Per; Bruus, Henrik
2016-09-01
We present a theory for the acoustic force density acting on inhomogeneous fluids in acoustic fields on time scales that are slow compared to the acoustic oscillation period. The acoustic force density depends on gradients in the density and compressibility of the fluid. For microfluidic systems, the theory predicts a relocation of the inhomogeneities into stable field-dependent configurations, which are qualitatively different from the horizontally layered configurations due to gravity. Experimental validation is obtained by confocal imaging of aqueous solutions in a glass-silicon microchip.
Acoustical scattering cross section of gas bubbles under dual-frequency acoustic excitation.
Zhang, Yuning; Li, Shengcai
2015-09-01
The acoustical scattering cross section is a paramount parameter determining the scattering ability of cavitation bubbles when they are excited by the incident acoustic waves. This parameter is strongly related with many important applications of acoustic cavitation including facilitating the reaction of chemical process, boosting bubble sonoluminescence, and performing non-invasive therapy and drug delivery. In present paper, both the analytical and numerical solutions of acoustical scattering cross section of gas bubbles under dual-frequency excitation are obtained. The validity of the analytical solution is shown with demonstrating examples. The nonlinear characteristics (e.g., harmonics, subharmonics and ultraharmonics) of the scattering cross section curve under dual-frequency approach are investigated. Compared with single-frequency approach, the dual-frequency approach displays more resonances termed as "combination resonances" and could promote the acoustical scattering cross section significantly within a much broader range of bubble sizes due to the generation of more resonances. The influence of several paramount parameters (e.g., acoustic pressure amplitude, power allocations between two acoustic components, and the ratio of the frequencies) in the dual-frequency system on the predictions of scattering cross section has been discussed.
Acoustic and elastic multiple scattering and radiation from cylindrical structures
NASA Astrophysics Data System (ADS)
Amirkulova, Feruza Abdukadirovna
Multiple scattering (MS) and radiation of waves by a system of scatterers is of great theoretical and practical importance and is required in a wide variety of physical contexts such as the implementation of "invisibility" cloaks, the effective parameter characterization, and the fabrication of dynamically tunable structures, etc. The dissertation develops fast, rapidly convergent iterative techniques to expedite the solution of MS problems. The formulation of MS problems reduces to a system of linear algebraic equations using Graf's theorem and separation of variables. The iterative techniques are developed using Neumann expansion and Block Toeplitz structure of the linear system; they are very general, and suitable for parallel computations and a large number of MS problems, i.e. acoustic, elastic, electromagnetic, etc., and used for the first time to solve MS problems. The theory is implemented in Matlab and FORTRAN, and the theoretical predictions are compared to computations obtained by COMSOL. To formulate the MS problem, the transition matrix is obtained by analyzing an acoustic and an elastic single scattering of incident waves by elastic isotropic and anisotropic solids. The mathematical model of wave scattering from multilayered cylindrical and spherical structures is developed by means of an exact solution of dynamic 3D elasticity theory. The recursive impedance matrix algorithm is derived for radially heterogeneous anisotropic solids. An explicit method for finding the impedance in piecewise uniform, transverse-isotropic material is proposed; the solution is compared to elasticity theory solutions involving Buchwald potentials. Furthermore, active exterior cloaking devices are modeled for acoustic and elastic media using multipole sources. A cloaking device can render an object invisible to some incident waves as seen by some external observer. The active cloak is generated by a discrete set of multipole sources that destructively interfere with an
Arbitrary scattering of an acoustical Bessel beam by a rigid spheroid with large aspect-ratio
NASA Astrophysics Data System (ADS)
Gong, Zhixiong; Li, Wei; Mitri, Farid G.; Chai, Yingbin; Zhao, Yao
2016-11-01
In this paper, the T-matrix (null-field) method is applied to investigate the acoustic scattering by a large-aspect-ratio rigid spheroid immersed in a non-viscous fluid under the illumination of an unbounded zeroth-order Bessel beam with arbitrary orientation. Based on the proposed method, a MATLAB software package is constructed accordingly, and then verified and validated to compute the acoustic scattering by a rigid oblate or prolate spheroid in the Bessel beam. Several numerical examples are carried out to investigate the novel phenomenon of acoustic scattering by spheroids in Bessel beams with arbitrary incidence, with particular emphasis on the aspect ratio (i.e. the ratio of the polar radius over the equatorial radius of the spheroid), the half-cone angle of Bessel beam, the dimensionless frequency, as well as the angle of incidence. The quasi-periodic oscillations are observed in the plots of the far-field backscattering form function modulus versus the dimensionless frequency, owing to the interference between the specular reflection and the Franz wave circumnavigating the spheroid in the surrounding fluid. Furthermore, the 3D far-field scattering directivity patterns at end-on incidence and 2D polar plots at arbitrary angles of incidence are exhibited, which could provide new insights into the physical mechanisms of Bessel beam scattering by flat or elongated spheroid. This research work may provide an impetus for the application of acoustic Bessel beam in engineering practices.
NASA Astrophysics Data System (ADS)
Kim, Tae Hyun; Ko, Jae-Hyeon; Kojima, Seiji
2013-03-01
Relaxor-based ferroelectric Pb[(Mg1/3Nb2/3)1-x Tix]O3 (PMN-xPT) single crystals have attracted great attention because of their exceptionally strong piezoelectric properties. This peculiar characteristic was attributed to the rotation of polarization directions and structural complexity. In this study, the phase transition behaviors of PMN-17PT single crystals have been investigated under an electric field applied along [001] by micro-Brillouin scattering. PMN-17PT single crystals were grown by the modified Bridgeman method. The two (001) surfaces were Au-coated to apply the electric field, and the coating was thin enough to allow the incident beam to transmit without much loss. The electric field of different values was applied to the sample along the [001] direction, and the Brillouin scattering spectrum was measured under both field-heating (FH) and field-cooling (FC) conditions. The electric field of 1kV/cm induced a new longitudinal acoustic (LA) mode component along with a broad Brillouin peak evolving continuously from the paraelectric phase during both FC and FH processes. This was attributed to the remnant polar nanoregions that were not aligned under the electric field due to quenched random fields. However, the splitting of the LA mode did not appear when the electric field was over 2kV/cm indicating a clear structural phase transition. This research was supported in part by the Marubun Research Promotion Foundation and Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (2010-0010497).
Kinetic Enhancement of Raman Backscatter, and Electron Acoustic Thomson Scatter
Strozzi, D J; Williams, E A; Langdon, A B; Bers, A
2006-09-01
1-D Eulerian Vlasov-Maxwell simulations are presented which show kinetic enhancement of stimulated Raman backscatter (SRBS) due to electron trapping in regimes of heavy linear Landau damping. The conventional Raman Langmuir wave is transformed into a set of beam acoustic modes [L. Yin et al., Phys. Rev. E 73, 025401 (2006)]. For the first time, a low phase velocity electron acoustic wave (EAW) is seen developing from the self-consistent Raman physics. Backscatter of the pump laser off the EAW fluctuations is reported and referred to as electron acoustic Thomson scatter. This light is similar in wavelength to, although much lower in amplitude than, the reflected light between the pump and SRBS wavelengths observed in single hot spot experiments, and previously interpreted as stimulated electron acoustic scatter [D. S. Montgomery et al., Phys. Rev. Lett. 87, 155001 (2001)]. The EAW observed in our simulations is strongest well below the phase-matched frequency for electron acoustic scatter, and therefore the EAW is not produced by it. The beating of different beam acoustic modes is proposed as the EAW excitation mechanism, and is called beam acoustic decay. Supporting evidence for this process, including bispectral analysis, is presented. The linear electrostatic modes, found by projecting the numerical distribution function onto a Gauss-Hermite basis, include beam acoustic modes (some of which are unstable even without parametric coupling to light waves) and a strongly-damped EAW similar to the observed one. This linear EAW results from non-Maxwellian features in the electron distribution, rather than nonlinearity due to electron trapping.
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.
Broadband acoustic scattering measurements of underwater unexploded ordnance (UXO).
Bucaro, J A; Houston, B H; Saniga, M; Dragonette, L R; Yoder, T; Dey, S; Kraus, L; Carin, L
2008-02-01
In order to evaluate the potential for detection and identification of underwater unexploded ordnance (UXO) by exploiting their structural acoustic response, we carried out broadband monostatic scattering measurements over a full 360 degrees on UXO's (two mortar rounds, an artillery shell, and a rocket warhead) and false targets (a cinder block and a large rock). The measurement band, 1-140 kHz, includes a low frequency structural acoustics region in which the wavelengths are comparable to or larger than the target characteristic dimensions. In general, there are aspects that provide relatively high target strength levels ( approximately -10 to -15 dB), and from our experience the targets should be detectable in this structural acoustics band in most acoustic environments. The rigid body scattering was also calculated for one UXO in order to highlight the measured scattering features involving elastic responses. The broadband scattering data should be able to support feature-based separation of UXO versus false targets and identification of various classes of UXO as well.
Analytical modeling of the acoustic field during a direct field acoustic test.
Stasiunas, Eric Carl; Rouse, Jerry W.; Mesh, Mikhail
2010-12-01
The acoustic field generated during a Direct Field Acoustic Test (DFAT) has been analytically modeled in two space dimensions using a properly phased distribution of propagating plane waves. Both the pure-tone and broadband acoustic field were qualitatively and quantitatively compared to a diffuse acoustic field. The modeling indicates significant non-uniformity of sound pressure level for an empty (no test article) DFAT, specifically a center peak and concentric maxima/minima rings. This spatial variation is due to the equivalent phase among all propagating plane waves at each frequency. The excitation of a simply supported slender beam immersed within the acoustic fields was also analytically modeled. Results indicate that mid-span response is dependent upon location and orientation of the beam relative to the center of the DFAT acoustic field. For a diffuse acoustic field, due to its spatial uniformity, mid-span response sensitivity to location and orientation is nonexistent.
Acoustic scattering by benthic and planktonic shelled animals.
Stanton, T K; Chu, D; Wiebe, P H; Eastwood, R L; Warren, J D
2000-08-01
Acoustic backscattering measurements and associated scattering modeling were recently conducted on a type of benthic shelled animal that has a spiral form of shell (Littorina littorea). Benthic and planktonic shelled animals with this shape occur on the seafloor and in the water column, respectively, and can be a significant source of acoustic scattering in the ocean. Modeling of the scattering properties allows reverberation predictions to be made for sonar performance predictions as well as for detection and classification of animals for biological and ecological applications. The studies involved measurements over the frequency range 24 kHz to 1 MHz and all angles of orientation in as small as 1 degree increments. This substantial data set is quite revealing of the physics of the acoustic scattering by these complex shelled bodies and served as a basis for the modeling. Specifically, the resonance structure of the scattering was strongly dependent upon angle of orientation and could be traced to various types of rays (e.g., subsonic Lamb waves and rays entering the opercular opening). The data are analyzed in both the frequency and time domain (compressed pulse processing) so that dominant scattering mechanisms could be identified. Given the complexity of the animal body (irregular elastic shell with discontinuities), approximate scattering models are used with only the dominant scattering properties retained. Two models are applied to the data, both approximating the body as a deformed sphere: (1) an averaged form of the exact modal-series-based solution for the spherical shell, which is used to estimate the backscattering by a deformed shell averaged over all angles of orientation, and produces reasonably accurate predictions over all k1a(esr) (k1 is the acoustic wave number of the surrounding water and a(esr) is the equivalent spherical radius of the body), and (2) a ray-based formula which is used to estimate the scattering at fixed angle of orientation, but
Field Fluctuation Spectroscopy in a Reverberant Cavity with Moving Scatterers
NASA Astrophysics Data System (ADS)
de Rosny, Julien; Roux, Philippe; Fink, Mathias; Page, J. H.
2003-03-01
We report a study of transient ultrasonic waves inside a reverberant cavity containing moving scatterers. We show that the elastic mean free path and the dynamics of the scatterers govern the evolution of the autocorrelation of acoustic wave field. A parallel is established between these results and a closely related technique, diffusing acoustic wave spectroscopy. Excellent agreement is found between experiment and theory for a moving stainless steel ball in a water tank, thereby elucidating the underlying physics, and a potential application, fish monitoring inside aquariums, is demonstrated.
Nikolaeva, Anastasiia V. Kryzhanovsky, Maxim A.; Tsysar, Sergey A.; Kreider, Wayne; Sapozhnikov, Oleg A.
2015-10-28
Acoustic radiation force is a nonlinear acoustic effect caused by the transfer of wave momentum to absorbing or scattering objects. This phenomenon is exploited in modern ultrasound metrology for measurement of the acoustic power radiated by a source and is used for both therapeutic and diagnostic sources in medical applications. To calculate radiation force an acoustic hologram can be used in conjunction with analytical expressions based on the angular spectrum of the measured field. The results of an experimental investigation of radiation forces in two different cases are presented in this paper. In one case, the radiation force of an obliquely incident ultrasound beam on a large absorber (which completely absorbs the beam) is considered. The second case concerns measurement of the radiation force on a spherical target that is small compared to the beam diameter.
NASA Astrophysics Data System (ADS)
Nikolaeva, Anastasiia V.; Kryzhanovsky, Maxim A.; Tsysar, Sergey A.; Kreider, Wayne; Sapozhnikov, Oleg A.
2015-10-01
Acoustic radiation force is a nonlinear acoustic effect caused by the transfer of wave momentum to absorbing or scattering objects. This phenomenon is exploited in modern ultrasound metrology for measurement of the acoustic power radiated by a source and is used for both therapeutic and diagnostic sources in medical applications. To calculate radiation force an acoustic hologram can be used in conjunction with analytical expressions based on the angular spectrum of the measured field. The results of an experimental investigation of radiation forces in two different cases are presented in this paper. In one case, the radiation force of an obliquely incident ultrasound beam on a large absorber (which completely absorbs the beam) is considered. The second case concerns measurement of the radiation force on a spherical target that is small compared to the beam diameter.
Finite Element Prediction of Acoustic Scattering and Radiation from Submerged Elastic Structures
NASA Technical Reports Server (NTRS)
Everstine, G. C.; Henderson, F. M.; Lipman, R. R.
1984-01-01
A finite element formulation is derived for the scattering and radiation of acoustic waves from submerged elastic structures. The formulation uses as fundamental unknowns the displacement in the structure and a velocity potential in the field. Symmetric coefficient matrices result. The outer boundary of the fluid region is terminated with an approximate local wave-absorbing boundary condition which assumes that outgoing waves are locally planar. The finite element model is capable of predicting only the near-field acoustic pressures. Far-field sound pressure levels may be determined by integrating the surface pressures and velocities over the wet boundary of the structure using the Helmholtz integral. Comparison of finite element results with analytic results show excellent agreement. The coupled fluid-structure problem may be solved with general purpose finite element codes by using an analogy between the equations of elasticity and the wave equation of linear acoustics.
Acoustic Scattering in Flexible Waveguide Involving Step Discontinuity
Afzal, Muhammad; Nawaz, Rab; Ayub, Muhammad; Wahab, Abdul
2014-01-01
In this paper, the propagation and scattering of acoustic waves in a flexible wave-guide involving step discontinuity at an interface is considered. The emerging boundary value problem is non-Sturm-Liouville and is solved by employing a hybrid mode-matching technique. The physical scattering process and attenuation of duct modes versus frequency regime and change of height is studied. Moreover, the mode-matching solution is validated through a series of numerical experiments by testifying the power conservation identity and matching interface conditions. PMID:25084019
Acoustic scattering from mud volcanoes and carbonate mounds.
Holland, Charles W; Weber, Thomas C; Etiope, Giuseppe
2006-12-01
Submarine mud volcanoes occur in many parts of the world's oceans and form an aperture for gas and fluidized mud emission from within the earth's crust. Their characteristics are of considerable interest to the geology, geophysics, geochemistry, and underwater acoustics communities. For the latter, mud volcanoes are of interest in part because they pose a potential source of clutter for active sonar. Close-range (single-interaction) scattering measurements from a mud volcano in the Straits of Sicily show scattering 10-15 dB above the background. Three hypotheses were examined concerning the scattering mechanism: (1) gas entrained in sediment at/near mud volcano, (2) gas bubbles and/or particulates (emitted) in the water column, (3) the carbonate bio-construction covering the mud volcano edifice. The experimental evidence, including visual, acoustic, and nonacoustic sensors, rules out the second hypothesis (at least during the observation time) and suggests that, for this particular mud volcano the dominant mechanism is associated with carbonate chimneys on the mud volcano. In terms of scattering levels, target strengths of 4-14 dB were observed from 800 to 3600 Hz for a monostatic geometry with grazing angles of 3-5 degrees. Similar target strengths were measured for vertically bistatic paths with incident and scattered grazing angles of 3-5 degrees and 33-50 degrees, respectively. PMID:17225386
Acoustic scattering from mud volcanoes and carbonate mounds.
Holland, Charles W; Weber, Thomas C; Etiope, Giuseppe
2006-12-01
Submarine mud volcanoes occur in many parts of the world's oceans and form an aperture for gas and fluidized mud emission from within the earth's crust. Their characteristics are of considerable interest to the geology, geophysics, geochemistry, and underwater acoustics communities. For the latter, mud volcanoes are of interest in part because they pose a potential source of clutter for active sonar. Close-range (single-interaction) scattering measurements from a mud volcano in the Straits of Sicily show scattering 10-15 dB above the background. Three hypotheses were examined concerning the scattering mechanism: (1) gas entrained in sediment at/near mud volcano, (2) gas bubbles and/or particulates (emitted) in the water column, (3) the carbonate bio-construction covering the mud volcano edifice. The experimental evidence, including visual, acoustic, and nonacoustic sensors, rules out the second hypothesis (at least during the observation time) and suggests that, for this particular mud volcano the dominant mechanism is associated with carbonate chimneys on the mud volcano. In terms of scattering levels, target strengths of 4-14 dB were observed from 800 to 3600 Hz for a monostatic geometry with grazing angles of 3-5 degrees. Similar target strengths were measured for vertically bistatic paths with incident and scattered grazing angles of 3-5 degrees and 33-50 degrees, respectively.
Axisymmetric scattering of an acoustical Bessel beam by a rigid fixed spheroid.
Mitri, Farid G
2015-10-01
Based on the partial-wave series expansion (PWSE) method in spherical coordinates, a formal analytical solution for the acoustic scattering of a zeroth-order Bessel acoustic beam centered on a rigid fixed (oblate or prolate) spheroid is provided. The unknown scattering coefficients of the spheroid are determined by solving a system of linear equations derived for the Neumann boundary condition. Numerical results for the modulus of the backscattered pressure (θ = π) in the near field and the backscattering form function in the far field for both prolate and oblate spheroids are presented and discussed, with particular emphasis on the aspect ratio (i.e., the ratio of the major axis over the minor axis of the spheroid), the half-cone angle of the Bessel beam, and the dimensionless frequency. The plots display periodic oscillations (versus the dimensionless frequency) because of the interference of specularly reflected waves in the backscattering direction with circumferential Franz' waves circumnavigating the surface of the spheroid in the surrounding fluid. Moreover, the 3-D directivity patterns illustrate the near- and far-field axisymmetric scattering. Investigations in underwater acoustics, particle levitation, scattering, and the detection of submerged elongated objects and other related applications utilizing Bessel waves would benefit from the results of the present study. PMID:26470043
Surprises and anomalies in acoustical and optical scattering and radiation forces
NASA Astrophysics Data System (ADS)
Marston, Philip L.
2015-09-01
Experiments on radiation torques and negative radiation forces by various researchers display how the underlying wave-field geometry influences radiation forces. Other situations strongly influenced by wave-field geometry include high-order caustics present in light-scattering patterns of objects as simple as oblate drops of water or oblate bubbles of air in water. Related theoretical and experimental investigations are considered. Acoustic scattering enhancements associated with various guided waves are also examined. These include guided waves having negative group velocities and guided wave radiating wavefronts having a vanishing Gaussian curvature.
Relation between near field and far field acoustic measurements
NASA Technical Reports Server (NTRS)
Bies, D. A.; Scharton, T. D.
1974-01-01
Several approaches to the problem of determining the far field directivity of an acoustic source located in a reverberant environment, such as a wind tunnel, are investigated analytically and experimentally. The decrease of sound pressure level with distance is illustrated; and the spatial extent of the hydrodynamic and geometric near fields, the far field, and the reverberant field are described. A previously-prosposed analytical technique for predicting the far field directivity of the acoustic source on the basis of near field data is investigated. Experiments are conducted with small acoustic sources and an analysis is performed to determine the variation with distance from the source of the directionality of the sound field. A novel experiment is conducted in which the sound pressure measured at various distances from an acoustic driver located in the NASA Ames 40 x 80 ft wind tunnel is crosscorrelated with the driver excitation voltage.
Detection of nonlinear picosecond acoustic pulses by time-resolved Brillouin scattering
Gusev, Vitalyi E.
2014-08-14
In time-resolved Brillouin scattering (also called picosecond ultrasonic interferometry), the time evolution of the spatial Fourier component of an optically excited acoustic strain distribution is monitored. The wave number is determined by the momentum conservation in photon-phonon interaction. For linear acoustic waves propagating in a homogeneous medium, the detected time-domain signal of the optical probe transient reflectivity shows a sinusoidal oscillation at a constant frequency known as the Brillouin frequency. This oscillation is a result of heterodyning the constant reflection from the sample surface with the Brillouin-scattered field. Here, we present an analytical theory for the nonlinear reshaping of a propagating, finite amplitude picosecond acoustic pulse, which results in a time-dependence of the observed frequency. In particular, we examine the conditions under which this information can be used to study the time-evolution of the weak-shock front speed. Depending on the initial strain pulse parameters and the time interval of its nonlinear transformation, our theory predicts the detected frequency to either be monotonically decreasing or oscillating in time. We support these theoretical predictions by comparison with available experimental data. In general, we find that picosecond ultrasonic interferometry of nonlinear acoustic pulses provides access to the nonlinear acoustic properties of a medium spanning most of the GHz frequency range.
Haynes, Mark; Verweij, Sacha A. M.; Moghaddam, Mahta; Carson, Paul L.
2014-01-01
A self-contained source characterization method for commercial ultrasound probes in transmission acoustic inverse scattering is derived and experimentally tested. The method is based on modified scattered field volume integral equations that are linked to the source-scattering transducer model. The source-scattering parameters are estimated via pair-wise transducer measurements and the nonlinear inversion of an acoustic propagation model that is derived. This combination creates a formal link between the transducer characterization and the inverse scattering algorithm. The method is tested with two commercial ultrasound probes in a transmission geometry including provisions for estimating the probe locations and aligning a robotic rotator. The transducer characterization results show that the nonlinear inversion fit the measured data well. The transducer calibration and inverse scattering algorithm are tested on simple targets. Initial images show that the recovered contrasts are physically consistent with expected values. PMID:24569251
Acoustic scattering of a Bessel vortex beam by a rigid fixed spheroid
NASA Astrophysics Data System (ADS)
Mitri, F. G.
2015-12-01
Partial-wave series representation of the acoustic scattering field of high-order Bessel vortex beams by rigid oblate and prolate spheroids using the modal matching method is developed. The method, which is applicable to slightly elongated objects at low-to-moderate frequencies, requires solving a system of linear equations which depends on the partial-wave index n and the order of the Bessel vortex beam m using truncated partial-wave series expansions (PWSEs), and satisfying the Neumann boundary condition for a rigid immovable surface in the least-squares sense. This original semi-analytical approach developed for Bessel vortex beams is demonstrated for finite oblate and prolate spheroids, where the mathematical functions describing the spheroidal geometry are written in a form involving single angular (polar) integrals that are numerically computed. The transverse (θ = π / 2) and 3D scattering directivity patterns are evaluated in the far-field for both prolate and oblate spheroids, with particular emphasis on the aspect ratio (i.e., the ratio of the major axis over the minor axis of the spheroid) not exceeding 3:1, the half-cone angle β and order m of the Bessel vortex beam, as well as the dimensionless size parameter kr0. Periodic oscillations in the magnitude plots of the far-field scattering form function are observed, which result from the interference of the reflected waves with the circumferential (Franz') waves circumnavigating the surface of the spheroid in the surrounding fluid. Moreover, the 3D directivity patterns illustrate the far-field scattering from the spheroid, that vanishes in the forward (θ = 0) and backward (θ = π) directions. Particular applications in underwater acoustics and scattering, acoustic levitation and the detection of submerged elongated objects using Bessel vortex waves to name a few, would benefit from the results of the present investigation.
On the spatial bandwidth of scattered fields
NASA Astrophysics Data System (ADS)
Bucci, Ovidio M.; Franceschetti, Giorgio
1987-12-01
The concept of spatial bandwidth of scattered electromagnetic fields is introduced. It is shown that the scattered fields are almost space-bandlimited functions. The effective bandwidth W is introduced and evaluated for a very general scattering system, as well as the error made using functions bandlimited to values greater than the effective bandwidth (w greater than W) for representing the scattered field. The effective bandwidth is very simply related to the maximum dimension of the scattering system; the error drops to negligible values for modest increases of w compared to W, in the case of large scatterers. Consequences of these general results are stressed.
Representation theorems and Green's function retrieval for scattering in acoustic media.
Vasconcelos, Ivan; Snieder, Roel; Douma, Huub
2009-09-01
Reciprocity theorems for perturbed acoustic media are provided in the form of convolution- and correlation-type theorems. These reciprocity relations are particularly useful in the general treatment of both forward and inverse-scattering problems. Using Green's functions to describe perturbed and unperturbed waves in two distinct wave states, representation theorems for scattered waves are derived from the reciprocity relations. While the convolution-type theorems can be manipulated to obtain scattering integrals that are analogous to the Lippmann-Schwinger equation, the correlation-type theorems can be used to retrieve the scattering response of the medium by cross correlations. Unlike previous formulations of Green's function retrieval, the extraction of scattered-wave responses by cross correlations does not require energy equipartitioning. Allowing for uneven energy radiation brings experimental advantages to the retrieval of fields scattered by remote lossless and/or attenuative scatterers. These concepts are illustrated with a number of examples, including analytic solutions to a one-dimensional scattering problem, and a numerical example in the context of seismic waves recorded on the ocean bottom. PMID:19905236
Electromagnetic wave scattering by an external field
NASA Astrophysics Data System (ADS)
Sannikov, S. S.
1995-08-01
The quantum electrodynamics of bilocal fields is used to calculate the triangular Feynman diagrams describing the elastic scattering of a classical electromagnetic wave by an external Coulomb field. The total contribution of the diagrams is nonzero because of the violation of both the Furry theorem (CP or T symmetries) and the Ward identities. The cross section for this scattering process is found for low and high energies. A comparison with Compton scattering and Euler—Heisenberg scattering is given.
A boundary integral approach to the scattering of nonplanar acoustic waves by rigid bodies
NASA Technical Reports Server (NTRS)
Gallman, Judith M.; Myers, M. K.; Farassat, F.
1990-01-01
The acoustic scattering of an incident wave by a rigid body can be described by a singular Fredholm integral equation of the second kind. This equation is derived by solving the wave equation using generalized function theory, Green's function for the wave equation in unbounded space, and the acoustic boundary condition for a perfectly rigid body. This paper will discuss the derivation of the wave equation, its reformulation as a boundary integral equation, and the solution of the integral equation by the Galerkin method. The accuracy of the Galerkin method can be assessed by applying the technique outlined in the paper to reproduce the known pressure fields that are due to various point sources. From the analysis of these simpler cases, the accuracy of the Galerkin solution can be inferred for the scattered pressure field caused by the incidence of a dipole field on a rigid sphere. The solution by the Galerkin technique can then be applied to such problems as a dipole model of a propeller whose pressure field is incident on a rigid cylinder. This is the groundwork for modeling the scattering of rotating blade noise by airplane fuselages.
NASA Astrophysics Data System (ADS)
Annamalai, Subramanian; Parmar, Manoj; Balachandar, S.
2013-11-01
Particles when subjected to acoustic waves experience a time-averaged second-order force known as the acoustic radiation force, which is of prime importance in the fields of microfluidics and acoustic levitation. Here, the acoustic radiation force on a rigid spherical particle in a viscous compressible medium due to progressive and standing waves is considered. The relevant length scales include: particle radius (a), acoustic wavelength (λ) and viscous penetration depth (δ). While a / λ and a / δ are arbitrary, δ << λ . A farfield derivation approach has been used in determining the radiated force. Expressing the flow-field as a sum of the incident and scattered fields, an analytical expression for the force is obtained as a summation over infinite series (monopole, dipole and higher sources). These results indicate that the contributions from monopole, dipole and their cross-interaction are sufficient to describe the acoustic radiation force. Subsequently, the monopole and dipole strengths are represented in terms of the particle surface and volume averages of the incoming velocity. This generalization allows one to evaluate the radiation force for an incoming wave of any functional form. However acoustic streaming effects are neglected.
Seismic scattering of low-grazing-angle acoustic waves incident on the seafloor
NASA Astrophysics Data System (ADS)
Greaves, Robert John
The goal of this thesis is to develop a methodology to interpret sound scattered from the seafloor in terms of seafloor structure and subseafloor geological properties. Specifically, this work has been directed towards the interpretation of matched-filtered, beamformed monostatic acoustic reverberation data acquired on the west flank of the Mid-Atlantic Ridge when the seafloor is insonified by a band-limited, low-grazing-angle acoustic pulse. This research is based on the hypothesis that observed backscatter signals are produced by a combination of seafloor (interface) scattering and subseafloor (volume) scattering from structure having variations at scale lengths similar to the wavelength of the insonifying acoustic field. Analysis of monostatic reverberation data acquired during the Site A experiment (Run 1) of the Acoustic Reverberation Special Research Program 1993 Acoustics Cruise suggests that the scattered signals cannot be accounted for quantitatively in terms of large- scale slope, even though a strong correspondence between high intensity backscatter and seafloor ridges is observed. In order to investigate and quantify the actual sources of seafloor scattering, a numerical modeling study of seafloor models is undertaken using a finite- difference solution to the elastic wave equation. Geological data available at Site A and published reports describing geological properties of similar deep ocean crustal regions are used to develop a realistic seafloor model for the study area with realistic constraints on elastic parameters. Wavelength-scale heterogeneity in each model, in the form of seafloor roughness and subseafloor volume heterogeneity is defined using stochastic distributions with Gaussian autocorrelations. These distributions are quantified by their correlation lengths and standard deviation in amplitude. In order to incorporate all seafloor structure in a single parameterization of seafloor scattering, large-scale slope and wavelength
A fast and stable solver for acoustic scattering problems based on the nonuniform grid approach.
Chernokozhin, Evgeny; Brick, Yaniv; Boag, Amir
2016-01-01
A fast and stable boundary element method (BEM) algorithm for solving external problems of acoustic scattering by impenetrable bodies is developed. The method employs the Burton-Miller integral equation, which provides stable convergence of iterative solvers, and a generalized multilevel nonuniform grid (MLNG) algorithm for fast evaluation of field integrals. The MLNG approach is used here for the removal of computational bottlenecks involved with repeated matrix-vector multiplications as well as for the low-order basis function regularization of the hyper-singular integral kernel. The method is used for calculating the fields scattered by large acoustic scatterers, including nonconvex bodies with piece-wise smooth surfaces. As a result, the algorithm is capable of accurately incorporating high-frequency effects such as creeping waves and multiple-edges diffractions. In all cases, stable convergence of the method is observed. High accuracy of the method is demonstrated by comparison with the traditional BEM solution. The computational complexity of the method in terms of both the computation time and storage is estimated in practical computations and shown to be close to the asymptotic O(N log N) dependence. PMID:26827041
The inverse problem of acoustic wave scattering by an air-saturated poroelastic cylinder.
Ogam, Erick; Fellah, Z E A; Baki, Paul
2013-03-01
The efficient use of plastic foams in a diverse range of structural applications like in noise reduction, cushioning, and sleeping mattresses requires detailed characterization of their permeability and deformation (load-bearing) behavior. The elastic moduli and airflow resistance properties of foams are often measured using two separate techniques, one employing mechanical vibration methods and the other, flow rates of fluids based on fluid mechanics technology, respectively. A multi-parameter inverse acoustic scattering problem to recover airflow resistivity (AR) and mechanical properties of an air-saturated foam cylinder is solved. A wave-fluid saturated poroelastic structure interaction model based on the modified Biot theory and plane-wave decomposition using orthogonal cylindrical functions is employed to solve the inverse problem. The solutions to the inverse problem are obtained by constructing the objective functional given by the total square of the difference between predictions from the model and scattered acoustic field data acquired in an anechoic chamber. The value of the recovered AR is in good agreement with that of a slab sample cut from the cylinder and characterized using a method employing low frequency transmitted and reflected acoustic waves in a long waveguide developed by Fellah et al. [Rev. Sci. Instrum. 78(11), 114902 (2007)].
The inverse problem of acoustic wave scattering by an air-saturated poroelastic cylinder.
Ogam, Erick; Fellah, Z E A; Baki, Paul
2013-03-01
The efficient use of plastic foams in a diverse range of structural applications like in noise reduction, cushioning, and sleeping mattresses requires detailed characterization of their permeability and deformation (load-bearing) behavior. The elastic moduli and airflow resistance properties of foams are often measured using two separate techniques, one employing mechanical vibration methods and the other, flow rates of fluids based on fluid mechanics technology, respectively. A multi-parameter inverse acoustic scattering problem to recover airflow resistivity (AR) and mechanical properties of an air-saturated foam cylinder is solved. A wave-fluid saturated poroelastic structure interaction model based on the modified Biot theory and plane-wave decomposition using orthogonal cylindrical functions is employed to solve the inverse problem. The solutions to the inverse problem are obtained by constructing the objective functional given by the total square of the difference between predictions from the model and scattered acoustic field data acquired in an anechoic chamber. The value of the recovered AR is in good agreement with that of a slab sample cut from the cylinder and characterized using a method employing low frequency transmitted and reflected acoustic waves in a long waveguide developed by Fellah et al. [Rev. Sci. Instrum. 78(11), 114902 (2007)]. PMID:23464016
NASA Technical Reports Server (NTRS)
Turc, Catalin; Anand, Akash; Bruno, Oscar; Chaubell, Julian
2011-01-01
We present a computational methodology (a novel Nystrom approach based on use of a non-overlapping patch technique and Chebyshev discretizations) for efficient solution of problems of acoustic and electromagnetic scattering by open surfaces. Our integral equation formulations (1) Incorporate, as ansatz, the singular nature of open-surface integral-equation solutions, and (2) For the Electric Field Integral Equation (EFIE), use analytical regularizes that effectively reduce the number of iterations required by iterative linear-algebra solution based on Krylov-subspace iterative solvers.
Numerical method to compute acoustic scattering effect of a moving source.
Song, Hao; Yi, Mingxu; Huang, Jun; Pan, Yalin; Liu, Dawei
2016-01-01
In this paper, the aerodynamic characteristic of a ducted tail rotor in hover has been numerically studied using CFD method. An analytical time domain formulation based on Ffowcs Williams-Hawkings (FW-H) equation is derived for the prediction of the acoustic velocity field and used as Neumann boundary condition on a rigid scattering surface. In order to predict the aerodynamic noise, a hybrid method combing computational aeroacoustics with an acoustic thin-body boundary element method has been proposed. The aerodynamic results and the calculated sound pressure levels (SPLs) are compared with the known method for validation. Simulation results show that the duct can change the value of SPLs and the sound directivity. Compared with the isolate tail rotor, the SPLs of the ducted tail rotor are smaller at certain azimuth. PMID:27610323
Numerical method to compute acoustic scattering effect of a moving source.
Song, Hao; Yi, Mingxu; Huang, Jun; Pan, Yalin; Liu, Dawei
2016-01-01
In this paper, the aerodynamic characteristic of a ducted tail rotor in hover has been numerically studied using CFD method. An analytical time domain formulation based on Ffowcs Williams-Hawkings (FW-H) equation is derived for the prediction of the acoustic velocity field and used as Neumann boundary condition on a rigid scattering surface. In order to predict the aerodynamic noise, a hybrid method combing computational aeroacoustics with an acoustic thin-body boundary element method has been proposed. The aerodynamic results and the calculated sound pressure levels (SPLs) are compared with the known method for validation. Simulation results show that the duct can change the value of SPLs and the sound directivity. Compared with the isolate tail rotor, the SPLs of the ducted tail rotor are smaller at certain azimuth.
Fourth-order acoustic torque in intense sound fields
NASA Technical Reports Server (NTRS)
Wang, T. G.; Kanber, H.; Olli, E. E.
1978-01-01
The observation of a fourth-order acoustic torque in intense sound fields is reported. The torque was determined by measuring the acoustically induced angular deflection of a polished cylinder suspended by a torsion fiber. This torque was measured in a sound field of amplitude greater than that in which first-order acoustic torque has been observed.
NASA Technical Reports Server (NTRS)
Meyer, Harold D.
1999-01-01
This second volume of Acoustic Scattering by Three-Dimensional Stators and Rotors Using the SOURCE3D Code provides the scattering plots referenced by Volume 1. There are 648 plots. Half are for the 8750 rpm "high speed" operating condition and the other half are for the 7031 rpm "mid speed" operating condition.
Tuning Mie scattering resonances in soft materials with magnetic fields.
Brunet, Thomas; Zimny, Kevin; Mascaro, Benoit; Sandre, Olivier; Poncelet, Olivier; Aristégui, Christophe; Mondain-Monval, Olivier
2013-12-27
An original approach is proposed here to reversibly tune Mie scattering resonances occurring in random media by means of external low induction magnetic fields. This approach is valid for both electromagnetic and acoustic waves. The experimental demonstration is supported by ultrasound experiments performed on emulsions made of fluorinated ferrofluid spherical droplets dispersed in a Bingham fluid. We show that the electromagnet-induced change of droplet shape into prolate spheroids, with a moderate aspect ratio of 2.5, drastically affects the effective properties of the disordered medium. Its effective acoustic attenuation coefficient is shown to vary by a factor of 5, by controlling both the flux density and orientation of the applied magnetic field.
Tuning Mie scattering resonances in soft materials with magnetic fields.
Brunet, Thomas; Zimny, Kevin; Mascaro, Benoit; Sandre, Olivier; Poncelet, Olivier; Aristégui, Christophe; Mondain-Monval, Olivier
2013-12-27
An original approach is proposed here to reversibly tune Mie scattering resonances occurring in random media by means of external low induction magnetic fields. This approach is valid for both electromagnetic and acoustic waves. The experimental demonstration is supported by ultrasound experiments performed on emulsions made of fluorinated ferrofluid spherical droplets dispersed in a Bingham fluid. We show that the electromagnet-induced change of droplet shape into prolate spheroids, with a moderate aspect ratio of 2.5, drastically affects the effective properties of the disordered medium. Its effective acoustic attenuation coefficient is shown to vary by a factor of 5, by controlling both the flux density and orientation of the applied magnetic field. PMID:24483797
Brillouin light scattering from surface acoustic waves in a subwavelength-diameter optical fibre
Beugnot, Jean-Charles; Lebrun, Sylvie; Pauliat, Gilles; Maillotte, Hervé; Laude, Vincent; Sylvestre, Thibaut
2014-01-01
Brillouin scattering in optical fibres is a fundamental interaction between light and sound with important implications ranging from optical sensors to slow and fast light. In usual optical fibres, light both excites and feels shear and longitudinal bulk elastic waves, giving rise to forward-guided acoustic wave Brillouin scattering and backward-stimulated Brillouin scattering. In a subwavelength-diameter optical fibre, the situation changes dramatically, as we here report with the first experimental observation of Brillouin light scattering from surface acoustic waves. These Rayleigh-type surface waves travel the wire surface at a specific velocity of 3,400 m s−1 and backscatter the light with a Doppler shift of about 6 GHz. As these acoustic resonances are sensitive to surface defects or features, surface acoustic wave Brillouin scattering opens new opportunities for various sensing applications, but also in other domains such as microwave photonics and nonlinear plasmonics. PMID:25341638
NASA Technical Reports Server (NTRS)
Kolaini, Ali R.; Doty, Benjamin; Chang, Zensheu
2012-01-01
The aerospace industry has been using two methods of acoustic testing to qualify flight hardware: (1) Reverberant Acoustic Test (RAT), (2) Direct Field Acoustic Test (DFAT). The acoustic field obtained by RAT is generally understood and assumed to be diffuse, expect below Schroeder cut-of frequencies. DFAT method of testing has some distinct advantages over RAT, however the acoustic field characteristics can be strongly affected by test setup such as the speaker layouts, number and location of control microphones and control schemes. In this paper the following are discussed based on DEMO tests performed at APL and JPL: (1) Acoustic wave interference patterns and acoustic standing waves, (2) The structural responses in RAT and DFAT.
NASA Astrophysics Data System (ADS)
Tchahame, Joël. Cabrel; Sylvestre, Thibaut; Phan Huy, Kien; Kudlinski, Alexandre; Laude, Vincent; Beugnot, Jean-Charles
2016-04-01
Light propagation in small-core photonic crystal fibers enables tight optical confinement over long propagation lengths to enhance light-matter interactions. Not only can photonic crystal fibers compress light spatially, they also provide a tunable means to control light-hypersound interactions. By exploring Brillouin light scattering in a small-core and high air-filling fraction microstructured fiber, we report the observation of Brillouin scattering from surface acoustic waves at lower frequencies than standard Brillouin scattering from bulk acoustic waves. This effect could find potential applications for optical sensing technologies that exploit surface acoustic waves.
Reversibility of scattered fields (Conference Presentation)
NASA Astrophysics Data System (ADS)
Zhou, Renjie; Kim, Taewoo; Popescu, Gabriel
2016-03-01
In recent years, tremendous efforts have been spent on deep tissue imaging using phase conjugation, a technique used to undo the effects of light scattering in a thick tissue. Despite the early debates between Yariv and Wolf, it is still not well understood physically how deep can a field propagate into biological tissue and still be phase conjugated. In order to answer this question, we developed a light scattering theory to describe the evolution of the phase associated with a field scattered by a thick tissue block. The multiple scattering through the sample is simplified to a series of single scattering through consecutive thin tissue slices. With this theory, we identify the limits of the phase conjugation operation and recover the previous results by Yariv and Wolf, which asserts that phase conjugation is rooted in small angle approximation. Importantly, we discover the fundamental principle that rules phase conjugation: the mean axial wavenumber of a field progressively decreases to zero as it scatters multiple times. At this point, phase becomes a spatially random variable and phase conjugation becomes impossible. This result describes a fundamental phenomenon: the interaction between a deterministic object and a deterministic field can result in a random scattered field. We show that this phenomenon is rooted into Heisenberg's uncertainty principle.
Droplet Vaporization In A Levitating Acoustic Field
NASA Technical Reports Server (NTRS)
Ruff, G. A.; Liu, S.; Ciobanescu, I.
2003-01-01
Combustion experiments using arrays of droplets seek to provide a link between single droplet combustion phenomena and the behavior of complex spray combustion systems. Both single droplet and droplet array studies have been conducted in microgravity to better isolate the droplet interaction phenomena and eliminate or reduce the effects of buoyancy-induced convection. In most experiments involving droplet arrays, the droplets are supported on fibers to keep them stationary and close together before the combustion event. The presence of the fiber, however, disturbs the combustion process by introducing a source of heat transfer and asymmetry into the configuration. As the number of drops in a droplet array increases, supporting the drops on fibers becomes less practical because of the cumulative effect of the fibers on the combustion process. To eliminate the effect of the fiber, several researchers have conducted microgravity experiments using unsupported droplets. Jackson and Avedisian investigated single, unsupported drops while Nomura et al. studied droplet clouds formed by a condensation technique. The overall objective of this research is to extend the study of unsupported drops by investigating the combustion of well-characterized drop clusters in a microgravity environment. Direct experimental observations and measurements of the combustion of droplet clusters would provide unique experimental data for the verification and improvement of spray combustion models. In this work, the formation of drop clusters is precisely controlled using an acoustic levitation system so that dilute, as well as dense clusters can be created and stabilized before combustion in microgravity is begun. While the low-gravity test facility is being completed, tests have been conducted in 1-g to characterize the effect of the acoustic field on the vaporization of single and multiple droplets. This is important because in the combustion experiment, the droplets will be formed and
Acoustic field and array response uncertainties in stratified ocean media.
Hayward, Thomas J; Dhakal, Sagar
2012-07-01
The change-of-variables theorem of probability theory is applied to compute acoustic field and array beam power probability density functions (pdfs) in uncertain ocean environments represented by stratified, attenuating ocean waveguide models. Computational studies for one and two-layer waveguides investigate the functional properties of the acoustic field and array beam power pdfs. For the studies, the acoustic parameter uncertainties are represented by parametric pdfs. The field and beam response pdfs are computed directly from the parameter pdfs using the normal-mode representation and the change-of-variables theorem. For two-dimensional acoustic parameter uncertainties of sound speed and attenuation, the field and beam power pdfs exhibit irregular functional behavior and singularities associated with stationary points of the mapping, defined by acoustic propagation, from the parameter space to the field or beam power space. Implications for the assessment of orthogonal polynomial expansion and other methods for computing acoustic field pdfs are discussed.
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.
Rausch, Anne; Fischer, André; Kings, Nancy; Bake, Friedrich; Roehle, Ingo
2012-07-01
Rayleigh scattering is a measurement technique applicable for the determination of density distributions in various technical or natural flows. The current sensitivity limits of the Rayleigh scattering technique were investigated experimentally. It is shown that it is possible to measure density oscillations caused by acoustic pressure oscillations noninvasively and directly. Acoustical standing waves in a rectangular duct were investigated using Rayleigh scattering and compared to microphone measurements. The comparison showed a sensitivity of the Rayleigh scattering technique of 75 Pa (7·10(-4) kg/m(3)) and a precision of 14 Pa (1·10(-4) kg/m(3)). Therefore, it was also shown that Rayleigh scattering is applicable for acoustic measurements. PMID:22743495
Resolving the Location of Acoustic Point Sources Scattered Due to the Presence of a Skull Phantom
NASA Astrophysics Data System (ADS)
Sadler, J.; Shapoori, K.; Malyarenko, E.; DiCarlo, A.; Dech, J.; Severin, F.; Maev, R. Gr.
This paper considers resolving the location of a foreign object in the brain without the removal of the skull bone by detecting and processing the acoustic waves emitted from the foreign object modeled as point source. The variable thickness of the skull bone causes propagation acoustic waves to be scattered in such a manner that the acoustic wave undergoes a variable time delay relative to its entry point on the skull. Matched filtering can be used to detect the acoustic wave front, the time delay variations of the skull can be corrected for, and matched filtering time reversal algorithms can then detect the location of the acoustic source. This process is examined experimentally in a water tank system containing an acoustic source, custom-made skull phantom, and receiver. The apparatus is arranged in transmission mode so that the acoustic waves are emitted from the source, scattered by the phantom, and then received by a second transducer. The skull phantom has been designed so that the acoustic properties (velocity, density, and attenuation correspond approximately to those of a typical human skull. In addition, the phantom has been molded so that the surface closest to the acoustic source has smoothly oscillating ridges and valleys and a flat outer surface, approximately modeling a real-world skull bone. The data obtained from the experiment is processed to detect and extract the scattered acoustic wave front and correct for the time of flight variations in the skull. This re-creates the approximate wave front of a point source, whose location can be resolved via a matched filtering time reversal algorithm. The results of this process are examined for cases where there is no phantom present (no scattering), and with the phantom present. Comparison of these results shows a correlation between the calculated locations of the acoustic source and the expected location.
Küsel, Elizabeth T; Ratilal, Purnima
2009-04-01
The effect of incident field refraction on the scattered field from vertically extended cylindrical targets is investigated. A theoretical model for the total scattered field from a cylindrical target in a range-dependent ocean waveguide is developed from Green's theorem. The locally scattered field on the target surface is estimated as a function of the incident field by applying the appropriate boundary conditions on continuity of acoustic pressure and normal velocity, making the model applicable to general penetrable cylinders. The model can account for depth dependence in medium sound speed and hence refraction in the incident field along the target depth. Numerical implementation is done for a passive acoustic reflector, a long cylindrical air-filled rubber hose, often deployed vertically in experiments to provide calibration and charting consistency for wide-area active sonar systems. Analysis with the model indicates that refraction in the incident field along the target depth must be taken into account to accurately estimate the scattered field level from vertically extended cylindrical targets. It is demonstrated that the standard Ingenito waveguide target scattering model, which assumes that the incident field is planar along the target extent, can lead to significant errors of 10 dB or more in estimating the scattered field level.
A Advanced Boundary Element Formulation for Acoustic Radiation and Scattering in Three Dimensions.
NASA Astrophysics Data System (ADS)
Soenarko, Benjamin
A computational method is presented for determining acoustic fields produced by arbitrary shaped three-dimensional bodies. The formulation includes both radiation and scattering problems. In particular an isoparametric element formulation is introduced in which both the surface geometry and the acoustic variables on the surface of the body are represented by second order shape functions within the local coordinate system. A general result for the surface velocity potential and the exterior field is derived. This result is applicable to non-smooth bodies, i.e. it includes the case where the surface may have a non-unique normal (e.g. at the edge of a cube). Test cases are shown involving spherical, cylindrical and cubical geometry for both radiation and scattering problems. The present formulation is also extended to include half-space problems in which the effect of the reflected wave from an infinite plane is taken into account. By selecting an appropriate Green's function, the surface integral over the plane is nullified; thus all the computational efforts can be performed only on the radiating or scattering body at issue and thereby greatly simplify the solution. A special formulation involving axisymmetric bodies and boundary conditions is also presented. For this special case, the surface integrals are reduced to line integrals and an integral over the angle of revolution. The integration over the angle is performed partly analytically in terms of elliptic integrals and partly numerically using simple Gaussian quadrature formula. Since the rest of the integrals involve only line integrals along the generator of the body, any discretization scheme can be easily obtained to achieve a desired degree of accuracy in evaluating these integrals.
Chen, Xin; Parker, David S; Singh, David J
2013-01-01
We present first principles calculations of the phonon dispersions of \\BiTe and discuss these in relation to the acoustic phonon interface scattering in ceramics. The phonon dispersions show agreement with what is known from neutron scattering for the optic modes. We find a difference between the generalized gradient approximation and local density results for the acoustic branches. This is a consequence of an artificial compression of the van der Waals bonded gaps in the \\BiTe structure when using the generalized gradient approximation. As a result local density approximation calculations provide a better description of the phonon dispersions in Bi$_{2}$Te$_{3}$. A key characteristic of the acoustic dispersions is the existence of a strong anisotropy in the velocities. We develop a model for interface scattering in ceramics with acoustic wave anisotropy and apply this to \\BiTe and compare with PbTe and diamond.
Acoustic vibrations contribute to the diffuse scatter produced by ribosome crystals.
Polikanov, Yury S; Moore, Peter B
2015-10-01
The diffuse scattering pattern produced by frozen crystals of the 70S ribosome from Thermus thermophilus is as highly structured as it would be if it resulted entirely from domain-scale motions within these particles. However, the qualitative properties of the scattering pattern suggest that acoustic displacements of the crystal lattice make a major contribution to it.
Acoustic vibrations contribute to the diffuse scatter produced by ribosome crystals
Polikanov, Yury S.; Moore, Peter B.
2015-01-01
The diffuse scattering pattern produced by frozen crystals of the 70S ribosome from Thermus thermophilus is as highly structured as it would be if it resulted entirely from domain-scale motions within these particles. However, the qualitative properties of the scattering pattern suggest that acoustic displacements of the crystal lattice make a major contribution to it. PMID:26457426
Air bubbles in water: a strongly multiple scattering medium for acoustic waves.
Kafesaki, M; Penciu, R S; Economou, E N
2000-06-26
Using a newly developed multiple scattering scheme, we calculate band structure and transmission properties for acoustic waves propagating in bubbly water. We prove that the multiple scattering effects are responsible for the creation of wide gaps in the transmission even in the presence of strong positional and size disorder.
Sound field inside acoustically levitated spherical drop
NASA Astrophysics Data System (ADS)
Xie, W. J.; Wei, B.
2007-05-01
The sound field inside an acoustically levitated small spherical water drop (radius of 1mm) is studied under different incident sound pressures (amplitude p0=2735-5643Pa). The transmitted pressure ptr in the drop shows a plane standing wave, which varies mainly in the vertical direction, and distributes almost uniformly in the horizontal direction. The maximum of ptr is always located at the lowermost point of the levitated drop. Whereas the secondary maximum appears at the uppermost point if the incident pressure amplitude p0 is higher than an intermediate value (3044Pa), in which there exists a pressure nodal surface in the drop interior. The value of the maximum ptr lies in a narrow range of 2489-3173Pa, which has a lower limit of 2489Pa when p0=3044Pa. The secondary maximum of ptr is rather small and only remarkable at high incident pressures.
Nonlinear Raman-Type Acoustic Scattering in Three-Phase Marine Sediments
NASA Astrophysics Data System (ADS)
Pushkina, N. I.
2001-03-01
Stimulated Raman-type acoustic scattering by bubble oscillations in three-phase marine sediments, which consist of a solid frame, the pore water, and air bubbles, is considered. A model is developed for the case of the bubbles surrounded by water. The acoustic properties of the sediments are described on the basis of the Biot theory of sound propagation in a fluid-saturated porous medium. Nonlinear wave equations are obtained for marine sediments containing air bubbles. Expressions for the nonlinear scattering coefficient and the threshold intensity of the exciting sound wave are derived. A possibility of an experimental observation of the scattering process is discussed.
NASA Astrophysics Data System (ADS)
Suzumura, Yukio
2003-08-01
Convex tilted rear walls in a stage enclosure, an array of circular columns installed in front of walls, and triangular reflectors above the stage were newly adopted as scattering obstacles in an acoustic design of Tsuyama Music Cultural Hall, called ``Bell Fole‸t Tsuyama.'' The fundamental shape of the hall was designed using the theory of subjective preference. To calculate the effects of scattered reflections on a sound field in a real concert hall is extremely laborious. For this reason, the evaluation of effects of scattered reflections on the sound field in the hall was made experimentally by use of a
Bugay, A. N.; Sazonov, S. V.
2008-08-15
A new mechanism is proposed for continuous frequency down-conversion of acoustic waves propagating in a paramagnetic crystal at a low temperature in an applied magnetic field. A transverse hypersonic pulse generating a carrier-free longitudinal strain pulse via nonlinear effects is scattered by the generated pulse. This leads to a Stokes shift in the transverse hypersonic wave proportional to its intensity, and both pulses continue to propagate in the form of a mode-locked soliton. As the transverse-pulse frequency is Stokes shifted, its spectrum becomes narrower. This process can be effectively implemented only if the linear group velocity of the transverse hypersonic pulse equals the phase velocity of the longitudinal strain wave. These velocities are renormalized by spin-phonon coupling and can be made equal by adjusting the magnitude of the applied magnetic field. The transverse structure of the soliton depends on the sign of the group velocity dispersion of the transverse component. When the dispersion is positive, planar solitons can develop whose transverse component has a topological defect of dark vortex type and longitudinal component has a hole. In the opposite case, the formation of two-component acoustic 'bullets' or vortices localized in all directions is possible.
Nonlinear Bubble Interactions in Acoustic Pressure Fields
NASA Technical Reports Server (NTRS)
Barbat, Tiberiu; Ashgriz, Nasser; Liu, Ching-Shi
1996-01-01
The systems consisting of a two-phase mixture, as clouds of bubbles or drops, have shown many common features in their responses to different external force fields. One of particular interest is the effect of an unsteady pressure field applied to these systems, case in which the coupling of the vibrations induced in two neighboring components (two drops or two bubbles) may result in an interaction force between them. This behavior was explained by Bjerknes by postulating that every body that is moving in an accelerating fluid is subjected to a 'kinetic buoyancy' equal with the product of the acceleration of the fluid multiplied by the mass of the fluid displaced by the body. The external sound wave applied to a system of drops/bubbles triggers secondary sound waves from each component of the system. These secondary pressure fields integrated over the surface of the neighboring drop/bubble may result in a force additional to the effect of the primary sound wave on each component of the system. In certain conditions, the magnitude of these secondary forces may result in significant changes in the dynamics of each component, thus in the behavior of the entire system. In a system containing bubbles, the sound wave radiated by one bubble at the location of a neighboring one is dominated by the volume oscillation mode and its effects can be important for a large range of frequencies. The interaction forces in a system consisting of drops are much smaller than those consisting of bubbles. Therefore, as a first step towards the understanding of the drop-drop interaction subject to external pressure fluctuations, it is more convenient to study the bubble interactions. This paper presents experimental results and theoretical predictions concerning the interaction and the motion of two levitated air bubbles in water in the presence of an acoustic field at high frequencies (22-23 KHz).
NASA Technical Reports Server (NTRS)
Kolaini, Ali R.; Doty, Benjamin; Chang, Zensheu
2012-01-01
Loudspeakers have been used for acoustic qualification of spacecraft, reflectors, solar panels, and other acoustically responsive structures for more than a decade. Limited measurements from some of the recent speaker tests used to qualify flight hardware have indicated significant spatial variation of the acoustic field within the test volume. Also structural responses have been reported to differ when similar tests were performed using reverberant chambers. To address the impact of non-uniform acoustic field on structural responses, a series of acoustic tests were performed using a flat panel and a 3-ft cylinder exposed to the field controlled by speakers and repeated in a reverberant chamber. The speaker testing was performed using multi-input-single-output (MISO) and multi-input-multi-output (MIMO) control schemes with and without the test articles. In this paper the spatial variation of the acoustic field due to acoustic standing waves and their impacts on the structural responses in RAT and DFAT (both using MISO and MIMO controls for DFAT) are discussed in some detail.
Distorted Coulomb field of the scattered electron
Thomsen, H. D.; Esberg, J.; Andersen, K. K.; Lund, M. D.; Knudsen, H.; Uggerhoej, U. I.; Sona, P.; Mangiarotti, A.; Ketel, T. J.; Dizdar, A.; Ballestrero, S.; Connell, S. H.
2010-03-01
Experimental results for the radiation emission from ultrarelativistic electrons in targets of 0.03%-5% radiation length is presented. For the thinnest targets, the radiation emission is in accordance with the Bethe-Heitler formulation of bremsstrahlung, the target acting as a single scatterer. In this regime, the radiation intensity is proportional to the thickness. As the thickness increases, the distorted Coulomb field of the electron that is the result of the first scattering events, leads to a suppressed radiation emission per interaction, upon subsequent scattering events. In that case, the radiation intensity becomes proportional to a logarithmic function of the thickness, due to the suppression. Eventually, once the target becomes sufficiently thick, the entire radiation process becomes influenced by multiple scattering and the radiation intensity is again proportional to the thickness, but with a different constant of proportionality. The observed logarithmic thickness dependence of radiation intensity at intermediate values of the thickness can be directly interpreted as a manifestation of the distortion of the electron Coulomb field resulting from a scattering event. The Landau-Pomeranchuk-Migdal effect is explored with high primary energy using materials with low nuclear charge (Z). Also, targets that should give rise to the claimed interference effect in high-energy radiation emission from a structured target of thin foils are investigated.
Diversity of acoustic streaming in a rectangular acoustofluidic field.
Tang, Qiang; Hu, Junhui
2015-04-01
Diversity of acoustic streaming field in a 2D rectangular chamber with a traveling wave and using water as the acoustic medium is numerically investigated by the finite element method. It is found that the working frequency, the vibration excitation source length, and the distance and phase difference between two separated symmetric vibration excitation sources can cause the diversity in the acoustic streaming pattern. It is also found that a small object in the acoustic field results in an additional eddy, and affects the eddy size in the acoustic streaming field. In addition, the computation results show that with an increase of the acoustic medium's temperature, the speed of the main acoustic streaming decreases first and then increases, and the angular velocity of the corner eddies increases monotonously, which can be clearly explained by the change of the acoustic dissipation factor and shearing viscosity of the acoustic medium with temperature. Commercialized FEM software COMSOL Multiphysics is used to implement the computation tasks, which makes our method very easy to use. And the computation method is partially verified by an established analytical solution.
Xie, Weifeng; Fan, Chenglei; Yang, Chunli; Lin, Sanbao
2016-03-01
As a newly developed arc welding method, power ultrasound has been successfully introduced into arc and weld pool during ultrasonic wave-assisted arc welding process. The advanced process for molten metals can be realized by utilizing additional ultrasonic field. Under the action of the acoustic wave, the plasma arc as weld heat source is regulated and its characteristics make an obvious change. Compared with the conventional arc, the ultrasonic wave-assisted arc plasma is bound significantly and becomes brighter. To reveal the dependence of the acoustic binding force on acoustic field parameters, a two-dimensional acoustic field model for ultrasonic wave-assisted arc welding device is established. The influences of the radiator height, the central pore radius, the radiator radius, and curvature radius or depth of concave radiator surface are discussed using the boundary element method. Then the authors analyze the resonant mode by this relationship curve between acoustic radiation power and radiator height. Furthermore, the best acoustic binding ability is obtained by optimizing the geometric parameters of acoustic radiator. In addition, three concave radiator surfaces including spherical cap surface, paraboloid of revolution, and rotating single curved surface are investigated systematically. Finally, both the calculation and experiment suggest that, to obtain the best acoustic binding ability, the ultrasonic wave-assisted arc welding setup should be operated under the first resonant mode using a radiator with a spherical cap surface, a small central pore, a large section radius and an appropriate curvature radius.
Xie, Weifeng; Fan, Chenglei; Yang, Chunli; Lin, Sanbao
2016-03-01
As a newly developed arc welding method, power ultrasound has been successfully introduced into arc and weld pool during ultrasonic wave-assisted arc welding process. The advanced process for molten metals can be realized by utilizing additional ultrasonic field. Under the action of the acoustic wave, the plasma arc as weld heat source is regulated and its characteristics make an obvious change. Compared with the conventional arc, the ultrasonic wave-assisted arc plasma is bound significantly and becomes brighter. To reveal the dependence of the acoustic binding force on acoustic field parameters, a two-dimensional acoustic field model for ultrasonic wave-assisted arc welding device is established. The influences of the radiator height, the central pore radius, the radiator radius, and curvature radius or depth of concave radiator surface are discussed using the boundary element method. Then the authors analyze the resonant mode by this relationship curve between acoustic radiation power and radiator height. Furthermore, the best acoustic binding ability is obtained by optimizing the geometric parameters of acoustic radiator. In addition, three concave radiator surfaces including spherical cap surface, paraboloid of revolution, and rotating single curved surface are investigated systematically. Finally, both the calculation and experiment suggest that, to obtain the best acoustic binding ability, the ultrasonic wave-assisted arc welding setup should be operated under the first resonant mode using a radiator with a spherical cap surface, a small central pore, a large section radius and an appropriate curvature radius. PMID:26558995
Nondestructive acoustic electric field probe apparatus and method
Migliori, Albert
1982-01-01
The disclosure relates to a nondestructive acoustic electric field probe and its method of use. A source of acoustic pulses of arbitrary but selected shape is placed in an oil bath along with material to be tested across which a voltage is disposed and means for receiving acoustic pulses after they have passed through the material. The received pulses are compared with voltage changes across the material occurring while acoustic pulses pass through it and analysis is made thereof to determine preselected characteristics of the material.
Simulation of Acoustic Scattering from a Trailing Edge
NASA Technical Reports Server (NTRS)
Singer, Bart A.; Brentner, Kenneth S.; Lockhard, David P.; Lilley, Geoffrey M.
1999-01-01
Three model problems were examined to assess the difficulties involved in using a hybrid scheme coupling flow computation with the the Ffowcs Williams and Hawkings equation to predict noise generated by vortices passing over a sharp edge. The results indicate that the Ffowcs Williams and Hawkings equation correctly propagates the acoustic signals when provided with accurate flow information on the integration surface. The most difficult of the model problems investigated inviscid flow over a two-dimensional thin NACA airfoil with a blunt-body vortex generator positioned at 98 percent chord. Vortices rolled up downstream of the blunt body. The shed vortices possessed similarities to large coherent eddies in boundary layers. They interacted and occasionally paired as they convected past the sharp trailing edge of the airfoil. The calculations showed acoustic waves emanating from the airfoil trailing edge. Acoustic directivity and Mach number scaling are shown.
MODE CONVERSION BETWEEN DIFFERENT RADIAL ORDERS FOR SOLAR ACOUSTIC WAVES SCATTERED BY SUNSPOTS
Zhao, Hui; Chou, Dean-Yi
2013-11-20
We study the mode conversion between different radial orders for solar acoustic waves interacting with sunspots. Solar acoustic waves are modified in the presence of sunspots. The modification in the wave can be viewed as that the sunspot, excited by the incident wave, generates the scattered wave, and the scattered wave is added to the incident wave to form the total wave inside and around the sunspot. The wavefunction of the acoustic wave on the solar surface is computed from the cross-correlation function. The wavefunction of the scattered wave is obtained by subtracting the wavefunction of the incident wave from that of the total wave. We use the incident waves of radial order n = 0-5 to measure the scattered wavefunctions from n to another radial order n' for NOAAs 11084 and 11092. The strength of scattered waves decreases rapidly with |Δn|, where Δn ≡ n' – n. The scattered waves of Δn = ±1 are visible for n ≤ 1, and significant for n ≥ 2. For the scattered wave of Δn = ±2, only few cases are visible. None of the scattered waves of Δn = ±3 are visible. The properties of scattered waves for Δn = 0 and Δn ≠ 0 are different. The scattered wave amplitude relative to the incident wave amplitude decreases with n for Δn = 0, while it increases with n for Δn ≠ 0. The scattered wave amplitudes of Δn = 0 are greater for the larger sunspot, while those of Δn ≠ 0 are insensitive to the sunspot size.
NASA Astrophysics Data System (ADS)
Lyons, Anthony Patrick
1995-11-01
There has been little work on developing and testing seafloor volume scattering models and on the characterization of such volumes because of the complexity of the medium and the paucity of high resolution ground truth data. This dissertation addresses the different physical mechanisms responsible for backscattering from a seafloor volume and their relative importance. This was accomplished by: (1) examining and adapting theoretical and numerical techniques for predicting volume backscatter from seafloor environments in the frequency range from 5-50 kHz, (2) characterizing the physical properties of the seafloor volume that control acoustic backscatter in selected environmental regimes by using the high resolution techniques of CT scanning and p-wave logging and casting these descriptions in a form useful for scattering models, and (3) comparing model results constrained by ground truth information with acoustic data sets obtained in different seafloor environments in order to isolate physical scattering mechanisms which dominate scattering and to examine the effectiveness of the characterization and modeling components of this research. Specifically, a layered, gassy sediment and a sandy, shell hash sediment were examined. The gassy sediment was analyzed by using a continuum model for scattering from the surrounding sediment and a non-spherical bubble model for scattering from the included gas features. Simulations carried out with the bubble model showed that bubble scattering will dominate continuum scattering in soft mud containing gas bubbles. Results of calculations using the bubble scattering model compare well with data taken with the Naval Research Laboratory's Acoustic Sediment Classification System. The comparisons also show that bubbles smaller than those which could be found with CT scanning methods might be important at higher acoustic frequencies. The shell hash sediment was examined by using a single scattering model for the shell pieces instead of
Scattering reduction of an acoustically hard cylinder covered with layered pentamode metamaterials.
Boisvert, Jeffrey E; Scandrett, Clyde L; Howarth, Thomas R
2016-06-01
Transformational acoustics offers the theoretical possibility of cloaking obstacles within fluids, provided metamaterials having continuously varying bulk moduli and densities can be found or constructed. Realistically, materials with the proper, continuously varying anisotropies do not presently exist. However, discretely layered cloaks having constant material parameters within each layer may be a viable alternative in practice. The present work considers a range of cloaks, from those comprised of fluid layers that are isotropic in bulk moduli with anisotropic density (inertial cloaks) to those having anisotropic bulk moduli and isotropic density (pentamode cloaks). In this paper an analytical solution is obtained for the case of plane wave scattering from a submerged rigid cylinder covered with a multilayered cylindrical cloak composed of discrete anisotropic fluid layers. An investigation of the parameter space defining such cloaks is undertaken with the goal of minimizing the far-field scattered pressure, using layer constituent anisotropic properties (density and bulk modulus) constrained to lie within reasonable ranges relative to those of water.
Scattering reduction of an acoustically hard cylinder covered with layered pentamode metamaterials.
Boisvert, Jeffrey E; Scandrett, Clyde L; Howarth, Thomas R
2016-06-01
Transformational acoustics offers the theoretical possibility of cloaking obstacles within fluids, provided metamaterials having continuously varying bulk moduli and densities can be found or constructed. Realistically, materials with the proper, continuously varying anisotropies do not presently exist. However, discretely layered cloaks having constant material parameters within each layer may be a viable alternative in practice. The present work considers a range of cloaks, from those comprised of fluid layers that are isotropic in bulk moduli with anisotropic density (inertial cloaks) to those having anisotropic bulk moduli and isotropic density (pentamode cloaks). In this paper an analytical solution is obtained for the case of plane wave scattering from a submerged rigid cylinder covered with a multilayered cylindrical cloak composed of discrete anisotropic fluid layers. An investigation of the parameter space defining such cloaks is undertaken with the goal of minimizing the far-field scattered pressure, using layer constituent anisotropic properties (density and bulk modulus) constrained to lie within reasonable ranges relative to those of water. PMID:27369167
Non-contact transportation using near-field acoustic levitation
Ueha; Hashimoto; Koike
2000-03-01
Near-field acoustic levitation, where planar objects 10 kg in weight can levitate stably near the vibrating plate, is successfully applied both to non-contact transportation of objects and to a non-contact ultrasonic motor. Transporting apparatuses and an ultrasonic motor have been fabricated and their characteristics measured. The theory of near-field acoustic levitation both for a piston-like sound source and a flexural vibration source is also briefly described. PMID:10829622
Field Measurement of the Acoustic Nonlinearity Parameter in Turbine Blades
NASA Technical Reports Server (NTRS)
Hinton, Yolanda L.; Na, Jeong K.; Yost, William T.; Kessel, Gregory L.
2000-01-01
Nonlinear acoustics techniques were used to measure fatigue in turbine blades in a power generation plant. The measurements were made in the field using a reference based measurement technique, and a reference sample previously measured in the laboratory. The acoustic nonlinearity parameter showed significant increase with fatigue in the blades, as indicated by service age and areas of increased stress. The technique shows promise for effectively measuring fatigue in field applications and predicting subsequent failures.
NASA Astrophysics Data System (ADS)
Follett, R. K.; Delettrez, J. A.; Edgell, D. H.; Henchen, R. J.; Katz, J.; Myatt, J. F.; Froula, D. H.
2016-11-01
Collective Thomson scattering is a technique for measuring the plasma conditions in laser-plasma experiments. Simultaneous measurements of ion-acoustic and electron plasma-wave spectra were obtained using a 263.25-nm Thomson-scattering probe beam. A fully reflective collection system was used to record light scattered from electron plasma waves at electron densities greater than 1021 cm-3, which produced scattering peaks near 200 nm. An accurate analysis of the experimental Thomson-scattering spectra required accounting for plasma gradients, instrument sensitivity, optical effects, and background radiation. Practical techniques for including these effects when fitting Thomson-scattering spectra are presented and applied to the measured spectra to show the improvements in plasma characterization.
Difference-frequency generation in nonlinear scattering of acoustic waves by a rigid sphere.
Silva, Glauber T; Bandeira, Anderson
2013-02-01
In this paper, the partial-wave expansion method is applied to describe the difference-frequency pressure generated in a nonlinear scattering of two acoustic waves with an arbitrary wavefront by means of a rigid sphere. Particularly, the difference-frequency generation is analyzed in the nonlinear scattering with a spherical scatterer involving two intersecting plane waves in the following configurations: collinear, crossing at right angles, and counter-propagating. For the sake of simplicity, the plane waves are assumed to be spatially located in a spherical region which diameter is smaller than the difference-frequency wavelength. Such arrangements can be experimentally accomplished in vibro-acoustography and nonlinear acoustic tomography techniques. It turns out to be that when the sphere radius is of the order of the primary wavelengths, and the downshift ratio (i.e. the ratio between the fundamental frequency and the difference-frequency) is larger than five, difference-frequency generation is mostly due to a nonlinear interaction between the primary scattered waves. The exception to this is the collinear scattering for which the nonlinear interaction of the primary incident waves is also relevant. In addition, the difference-frequency scattered pressure in all scattering configurations decays as r(-1)lnr and 1/r, where r is the radial distance from the scatterer to the observation point.
Particle Cloud Flames in Acoustic Fields
NASA Technical Reports Server (NTRS)
Berlad, A. L.; Tangirala, V.; Ross, H.; Facca, L.
1990-01-01
Results are presented on a study of flames supported by clouds of particles suspended in air, at pressures about 100 times lower than normal. In the experiment, an acoustic driver (4-in speaker) placed at one end of a closed tube, 0.75-m long and 0.05 m in diameter, disperses a cloud of lycopodium particles during a 0.5-sec powerful acoustic burst. Properties of the particle cloud and the flame were recorded by high-speed motion pictures and optical transmission detectors. Novel flame structures were observed, which owe their features to partial confinement, which encourages flame-acoustic interactions, segregation of particle clouds into laminae, and penetration of the flame's radiative flux density into the unburned particle-cloud regimes. Results of these experiments imply that, for particles in confined spaces, uncontrolled fire and explosion may be a threat even if the Phi(0) values are below some apparent lean limit.
Initial Integration of Noise Prediction Tools for Acoustic Scattering Effects
NASA Technical Reports Server (NTRS)
Nark, Douglas M.; Burley, Casey L.; Tinetti, Ana; Rawls, John W.
2008-01-01
This effort provides an initial glimpse at NASA capabilities available in predicting the scattering of fan noise from a non-conventional aircraft configuration. The Aircraft NOise Prediction Program, Fast Scattering Code, and the Rotorcraft Noise Model were coupled to provide increased fidelity models of scattering effects on engine fan noise sources. The integration of these codes led to the identification of several keys issues entailed in applying such multi-fidelity approaches. In particular, for prediction at noise certification points, the inclusion of distributed sources leads to complications with the source semi-sphere approach. Computational resource requirements limit the use of the higher fidelity scattering code to predict radiated sound pressure levels for full scale configurations at relevant frequencies. And, the ability to more accurately represent complex shielding surfaces in current lower fidelity models is necessary for general application to scattering predictions. This initial step in determining the potential benefits/costs of these new methods over the existing capabilities illustrates a number of the issues that must be addressed in the development of next generation aircraft system noise prediction tools.
Temperature dependence of Brillouin light scattering spectra of acoustic phonons in silicon
Olsson, Kevin S.; Klimovich, Nikita; An, Kyongmo; Sullivan, Sean; Weathers, Annie; Shi, Li E-mail: elaineli@physics.utexas.edu; Li, Xiaoqin E-mail: elaineli@physics.utexas.edu
2015-02-02
Electrons, optical phonons, and acoustic phonons are often driven out of local equilibrium in electronic devices or during laser-material interaction processes. The need for a better understanding of such non-equilibrium transport processes has motivated the development of Raman spectroscopy as a local temperature sensor of optical phonons and intermediate frequency acoustic phonons, whereas Brillouin light scattering (BLS) has recently been explored as a temperature sensor of low-frequency acoustic phonons. Here, we report the measured BLS spectra of silicon at different temperatures. The origins of the observed temperature dependence of the BLS peak position, linewidth, and intensity are examined in order to evaluate their potential use as temperature sensors for acoustic phonons.
NASA Astrophysics Data System (ADS)
Robertsson, Johan O. A.; Levander, Alan; Holliger, Klaus
1996-02-01
Quantitative modeling of bottom-interacting ocean acoustic waves is complicated by the long propagation ranges and by the complexity of the scattering targets. We employ a two-dimensional (2-D) hybrid technique combining Gaussian beam, finite difference, and Kirchhoff integral solutions of the wave equation to simulate ocean acoustic experiments within half of a convergence zone in the SOFAR channel. The 2-D modeling approach is reasonable due to the one-dimensional (1-D) velocity distribution in the water column and the strong lineation of the seafloor morphology parallel to the mid-ocean ridges. Full-waveform modeling of ocean acoustic data requires that the topography and the material properties of the seafloor are available at scales that are several orders of magnitude smaller than typical bathymetric sampling rates. We have therefore investigated the effects on the ocean acoustic response of a stochastic interpolation scheme used to generate seafloor models. For typical grazing angles of the incident wave field (approximately 5°-20°), we found that different stochastic realizations of the same seafloor segment (sampled at 200 m) yield an intrinsic uncertainty of the order of 3-8 dB in amplitude and 0.1-0.3 s in time for individual prominent events in the reverberant acoustic field. Hybrid simulations are compared to beam-formed ocean acoustic data collected during the Acoustic Reverberation Special Research Program (ARSRP) cruises. Side lobe noise in the observed acoustic data is simulated by adding band-limited white noise at -30 dB relative to the maximum intensity in the synthetic data. Numerical simulations can be limited to the response of only one of the mirror azimuth beams provided that the experimental geometry is suitably chosen. For the 2-D approximation to be valid, the cross-range resolution of the observed data must be smaller than the characteristic scale of seafloor lineations, and the beams of interest must be approximately perpendicular to
NASA Technical Reports Server (NTRS)
Lyell, Margaret J.
1992-01-01
The development of acoustic levitation systems has provided a technology with which to undertake droplet studies as well as do containerless processing experiments in a microgravity environment. Acoustic levitation chambers utilize radiation pressure forces to position/manipulate the drop. Oscillations can be induced via frequency modulation of the acoustic wave, with the modulated acoustic radiation vector acting as the driving force. To account for tangential as well as radial forcing, it is necessary that the viscous effects be included in the acoustic field. The method of composite expansions is employed in the determination of the acoustic field with viscous effects.
NASA Astrophysics Data System (ADS)
Yoder, Timothy J.
2000-05-01
The solutions for acoustic scattering from objects in separable geometries along with the associated fluid- structure interactions are well established. Closed-form solutions to these problems have either interpretations such as resonance scattering theory, or some limiting situations that provide insight into the physical processes that occur. In contrast, most acoustical scattering problems do not have closed-form solutions. Numerical solutions, like finite and boundary element methods, allow researchers to obtain solutions from scattering problems with more complicated geometries; unfortunately, these methods of solution are limited in that they lack the kind of interpretation that provides insight into the physical processes that occur. It is only through the systematic analysis of the large volume of data produced by numerical solutions that this insight is gained. One way to gain this insight is to analyze the monostatic dependence of echoes in the time-frequency domain. However, traditional three-dimensional graphical analysis of time-frequency signals that vary as a function of a third parameter (the monostatic dependence) does not display all of the signals' information content because two marginals, of this distribution (the time and frequency representations) contain information that is lost in the visual representation of the time-frequency domain. This information is lost because the uncertainty principal prevents simultaneous display of the time and frequency information via a time-frequency transform, and because humans do not possess the innate ability to perform the transforms that extract the information. The problem of how to systematically analyze monostatic scattering data in the time-frequency domain and how to visually display all of the data's information content is overcome by introducing a time-frequency-parameter graphical analysis technique. This technique is applied to farfield acoustic scattering from finite, elastic, cylindrical
Characterization of Biological Cells by Inverse Acoustic Scattering and Electrozone Sensing.
NASA Astrophysics Data System (ADS)
Chen, Xucai
A technique is presented which characterizes biological cells by their mechanical descriptors: size, compressibility and density. The experimental apparatus consists of two acoustic transducers and an electrozone sensor submerged in a bath of conducting host fluid. Diluted biological cells are convected through the apparatus by a coaxial jet. An individual cell passes through the electrozone where its volume is measured by the Coulter principle, and then through the confocal region of the two acoustic transducers. One acoustic transducer sends out tone bursts at a center frequency of 30 MHz and detects a back-scattered signal from the cell while the other transducer detects the scattered signal at 90^circ. Thus the volume, the 90^circ scattering function, and the 180^circ scattering function are recorded for each cell. The acoustic scattering functions are then inverted to provide the compressibility and density of that cell. Statistics of the mechanical properties for human red and white blood cells are generated and displayed. The size, compressibility and density of both normal and abnormal red blood cells are reported. By modeling a cell as an immiscible mixture of protein and saline solution, perfect mixture laws for compressibility and density are derived and confirmed by experimental results. With the mixture laws established, the mean corpuscular hemoglobin concentration (MCHC) is inferred from the compressibility and density data for red blood cells. Using only the data from the 180^circ back-scattered signal, different white cell subgroups are successfully distinguished by their locations in the two dimensional histograms of their mechanical descriptors.
NASA Astrophysics Data System (ADS)
Lacombe, R.; Föller, S.; Jasor, G.; Polifke, W.; Aurégan, Y.; Moussou, P.
2013-09-01
The identification of the aero-acoustic scattering matrix of an orifice in a duct is achieved by computational fluid dynamics. The methodology first consists in performing a large eddy simulation of a turbulent compressible flow, with superimposed broadband acoustic excitations. After extracting time series of acoustic data with a specific filter, system identification techniques are applied. They allow us to determine the components of the acoustic scattering matrix of the orifice. Following the same procedure, a previous paper determines the scattering features of a sudden area expansion. In the present paper, the focus is on whistling orifices. The whistling ability of the tested orifice is evaluated by deriving the acoustic power balance from the scattering matrix. Comparisons with experiments at two different Mach numbers show a good agreement. The potential whistling frequency range is well predicted in terms of frequency and amplitude.
Acoustic field distribution of sawtooth wave with nonlinear SBE model
Liu, Xiaozhou Zhang, Lue; Wang, Xiangda; Gong, Xiufen
2015-10-28
For precise prediction of the acoustic field distribution of extracorporeal shock wave lithotripsy with an ellipsoid transducer, the nonlinear spheroidal beam equations (SBE) are employed to model acoustic wave propagation in medium. To solve the SBE model with frequency domain algorithm, boundary conditions are obtained for monochromatic and sawtooth waves based on the phase compensation. In numerical analysis, the influence of sinusoidal wave and sawtooth wave on axial pressure distributions are investigated.
Near-specular acoustic scattering from a buried submarine mud volcano.
Gerig, Anthony L; Holland, Charles W
2007-12-01
Submarine mud volcanoes are objects that form on the seafloor due to the emission of gas and fluidized sediment from the Earth's interior. They vary widely in size, can be exposed or buried, and are of interest to the underwater acoustics community as potential sources of active sonar clutter. Coincident seismic reflection data and low frequency bistatic scattering data were gathered from one such buried mud volcano located in the Straits of Sicily. The bistatic data were generated using a pulsed piston source and a 64-element horizontal array, both towed over the top of the volcano. The purpose of this work was to appropriately model low frequency scattering from the volcano using the bistatic returns, seismic bathymetry, and knowledge of the general geoacoustic properties of the area's seabed to guide understanding and model development. Ray theory, with some approximations, was used to model acoustic propagation through overlying layers. Due to the volcano's size, scattering was modeled using geometric acoustics and a simple representation of volcano shape. Modeled bistatic data compared relatively well with experimental data, although some features remain unexplained. Results of an inversion for the volcano's reflection coefficient indicate that it may be acoustically softer than expected. PMID:18247739
Near-specular acoustic scattering from a buried submarine mud volcano.
Gerig, Anthony L; Holland, Charles W
2007-12-01
Submarine mud volcanoes are objects that form on the seafloor due to the emission of gas and fluidized sediment from the Earth's interior. They vary widely in size, can be exposed or buried, and are of interest to the underwater acoustics community as potential sources of active sonar clutter. Coincident seismic reflection data and low frequency bistatic scattering data were gathered from one such buried mud volcano located in the Straits of Sicily. The bistatic data were generated using a pulsed piston source and a 64-element horizontal array, both towed over the top of the volcano. The purpose of this work was to appropriately model low frequency scattering from the volcano using the bistatic returns, seismic bathymetry, and knowledge of the general geoacoustic properties of the area's seabed to guide understanding and model development. Ray theory, with some approximations, was used to model acoustic propagation through overlying layers. Due to the volcano's size, scattering was modeled using geometric acoustics and a simple representation of volcano shape. Modeled bistatic data compared relatively well with experimental data, although some features remain unexplained. Results of an inversion for the volcano's reflection coefficient indicate that it may be acoustically softer than expected.
Can different media generate scattered field with identical spectral coherence?
NASA Astrophysics Data System (ADS)
Wang, Tao; Jiang, Zhenfei; Ji, Xiaoling; Zhao, Daomu
2016-03-01
The possibility for different media to generate scattered field with identical spectral coherence is discussed. It is shown that two random media, with different characters of correlation function, may generate scattered field with identical spectral coherence property. An example of light waves on scattering from Gaussian-Schell model media is discussed, and a condition for identical spectral coherence of the far-zone scattered field is obtained.
Gong, Zheng; Chen, Tianrun; Ratilal, Purnima; Makris, Nicholas C
2013-11-01
An analytical model derived from normal mode theory for the accumulated effects of range-dependent multiple forward scattering is applied to estimate the temporal coherence of the acoustic field forward propagated through a continental-shelf waveguide containing random three-dimensional internal waves. The modeled coherence time scale of narrow band low-frequency acoustic field fluctuations after propagating through a continental-shelf waveguide is shown to decay with a power-law of range to the -1/2 beyond roughly 1 km, decrease with increasing internal wave energy, to be consistent with measured acoustic coherence time scales. The model should provide a useful prediction of the acoustic coherence time scale as a function of internal wave energy in continental-shelf environments. The acoustic coherence time scale is an important parameter in remote sensing applications because it determines (i) the time window within which standard coherent processing such as matched filtering may be conducted, and (ii) the number of statistically independent fluctuations in a given measurement period that determines the variance reduction possible by stationary averaging.
Yin, Jie; Tao, Chao Cai, Peng; Liu, Xiaojun
2015-06-08
Acoustically inhomogeneous mediums with multiple scattering are often the nightmare of photoacoustic tomography. In order to break this limitation, a photoacoustic tomography scheme combining ultrasound interferometry and time reversal is proposed to achieve images in acoustically scattering medium. An ultrasound interferometry is developed to determine the unknown Green's function of strong scattering tissue. Using the determined Greens' function, a time-reversal process is carried out to restore images behind an acoustically inhomogeneous layer from the scattering photoacoustic signals. This method effectively decreases the false contrast, noise, and position deviation of images induced by the multiple scattering. Phantom experiment is carried out to validate the method. Therefore, the proposed method could have potential value in extending the biomedical applications of photoacoustic tomography in acoustically inhomogeneous tissue.
Standing wave pressure fields generated in an acoustic levitation chamber
NASA Astrophysics Data System (ADS)
Hancock, Andrew; Allen, John S.; Kruse, Dustin E.; Dayton, Paul A.; Kargel, Christian M.; Insana, Michael F.
2001-05-01
We are developing an acoustic levitation chamber for measuring adhesion force strengths among biological cells. Our research has four phases. Phase I, presented here, is concerned with the design and construction of a chamber for trapping cell-sized microbubbles with known properties in acoustic standing waves, and examines the theory that describes the standing wave field. A cylindrical chamber has been developed to generate a stable acoustic standing wave field. The pressure field was mapped using a 0.4-mm needle hydrophone, and experiments were performed using 100 micron diameter unencapsulated air bubbles, 9 micron diameter isobutane-filled microbubbles, and 3 micron diameter decafluorobutane (C4F10)-filled microbubbles, confirming that the net radiation force from the standing wave pressure field tends to band the microbubbles at pressure antinodes, in accordance with theory.
Guided acoustic and optical waves in silicon-on-insulator for Brillouin scattering and optomechanics
NASA Astrophysics Data System (ADS)
Sarabalis, Christopher J.; Hill, Jeff T.; Safavi-Naeini, Amir H.
2016-10-01
We numerically study silicon waveguides on silica showing that it is possible to simultaneously guide optical and acoustic waves in the technologically important silicon on insulator (SOI) material system. Thin waveguides, or fins, exhibit geometrically softened mechanical modes at gigahertz frequencies with phase velocities below the Rayleigh velocity in glass, eliminating acoustic radiation losses. We propose slot waveguides on glass with telecom optical frequencies and strong radiation pressure forces resulting in Brillouin gains on the order of 500 and 50 000 W-1m-1 for backward and forward Brillouin scattering, respectively.
Lepper, Paul A; D'Spain, Gerald L
2007-08-01
The performance of traditional techniques of passive localization in ocean acoustics such as time-of-arrival (phase differences) and amplitude ratios measured by multiple receivers may be degraded when the receivers are placed on an underwater vehicle due to effects of scattering. However, knowledge of the interference pattern caused by scattering provides a potential enhancement to traditional source localization techniques. Results based on a study using data from a multi-element receiving array mounted on the inner shroud of an autonomous underwater vehicle show that scattering causes the localization ambiguities (side lobes) to decrease in overall level and to move closer to the true source location, thereby improving localization performance, for signals in the frequency band 2-8 kHz. These measurements are compared with numerical modeling results from a two-dimensional time domain finite difference scheme for scattering from two fluid-loaded cylindrical shells. Measured and numerically modeled results are presented for multiple source aspect angles and frequencies. Matched field processing techniques quantify the source localization capabilities for both measurements and numerical modeling output.
NASA Astrophysics Data System (ADS)
Mitri, F. G.
2015-11-01
Using the partial-wave series expansion method in cylindrical coordinates, a formal analytical solution for the acoustical scattering of a 2D cylindrical quasi-Gaussian beam with an arbitrary angle of incidence θi, focused on a rigid elliptical cylinder in a non-viscous fluid, is developed. The cylindrical focused beam expression is an exact solution of the Helmholtz equation. The scattering coefficients for the elliptical cylinder are determined by forcing the expression of the total (incident + scattered) field to satisfy the Neumann boundary condition for a rigid immovable surface, and performing the product of matrices involving an inversion procedure. Computations for the matrices elements require a single numerical integration procedure for each partial-wave mode. Numerical results are performed with particular emphasis on the focusing properties of the incident beam and its angle of incidence with respect to the major axis a of the ellipse as well as the aspect ratio a/b where b is the minor axis (assuming a > b). The method is validated and verified against previous results obtained via the T-matrix for plane waves. The present analysis is the first to consider an acoustical beam on an elliptic cylinder of variable cross-section as opposed to plane waves of infinite extent. Other 2D non-spherical and Chebyshev surfaces are mentioned that may be examined throughout this analytical formalism assuming a small deformation parameter ɛ.
Mitri, F. G.
2015-11-14
Using the partial-wave series expansion method in cylindrical coordinates, a formal analytical solution for the acoustical scattering of a 2D cylindrical quasi-Gaussian beam with an arbitrary angle of incidence θ{sub i}, focused on a rigid elliptical cylinder in a non-viscous fluid, is developed. The cylindrical focused beam expression is an exact solution of the Helmholtz equation. The scattering coefficients for the elliptical cylinder are determined by forcing the expression of the total (incident + scattered) field to satisfy the Neumann boundary condition for a rigid immovable surface, and performing the product of matrices involving an inversion procedure. Computations for the matrices elements require a single numerical integration procedure for each partial-wave mode. Numerical results are performed with particular emphasis on the focusing properties of the incident beam and its angle of incidence with respect to the major axis a of the ellipse as well as the aspect ratio a/b where b is the minor axis (assuming a > b). The method is validated and verified against previous results obtained via the T-matrix for plane waves. The present analysis is the first to consider an acoustical beam on an elliptic cylinder of variable cross-section as opposed to plane waves of infinite extent. Other 2D non-spherical and Chebyshev surfaces are mentioned that may be examined throughout this analytical formalism assuming a small deformation parameter ε.
Tunneling effects in resonant acoustic scattering of an air bubble in unbounded water.
Simão, André G; Guimarães, Luiz G
2016-01-01
The problem of acoustic scattering of a gaseous spherical bubble immersed within unbounded liquid surrounding is considered in this work. The theory of partial wave expansion related to this problem is revisited. A physical model based on the analogy between acoustic scattering and potential scattering in quantum mechanics is proposed to describe and interpret the acoustical natural oscillation modes of the bubble, namely, the resonances. In this context, a physical model is devised in order to describe the air water interface and the implications of the high density contrast on the various regimes of the scattering resonances. The main results are presented in terms of resonance lifetime periods and quality factors. The explicit numerical calculations are undertaken through an asymptotic analysis considering typical bubble dimensions and underwater sound wavelengths. It is shown that the resonance periods are scaled according to the Minnaert's period, which is the short lived resonance mode, called breathing mode of the bubble. As expected, resonances with longer lifetimes lead to impressive cavity quality Q-factor ranging from 1010 to 105. The present theoretical findings lead to a better understanding of the energy storage mechanism in a bubbly medium. PMID:27331803
Modified electron acoustic field and energy applied to observation data
NASA Astrophysics Data System (ADS)
Abdelwahed, H. G.; El-Shewy, E. K.
2016-08-01
Improved electrostatic acoustic field and energy have been debated in vortex trapped hot electrons and fluid of cold electrons with pressure term plasmas. The perturbed higher-order modified-Korteweg-de Vries equation (PhomKdV) has been worked out. The effect of trapping and electron temperatures on the electro-field and energy properties in auroral plasmas has been inspected.
NASA Astrophysics Data System (ADS)
Sveshnikov, B. V.; Bagdasaryan, A. S.
2016-08-01
We develop a physical model allowing one to analyze reflection of the inhomogeneous beams of surface acoustic waves from metal strips in a planar waveguide on the piezoelectric substrate. Analytical relationships for determining the coefficients of scattering and mutual conversion of the transverse waveguide modes during their interaction with the spatially limited Bragg reflectors are obtained. The waveguide-reflector characteristics are shown to depend on the ratio of the waveguide aperture to its maximum value for which only the fundamental transverse mode is excited. It is established that the developed model strictly corresponds to the energy conservation law, i.e., in the absence of dissipation, the power of the inhomogeneous beam, which is incident on the finite reflector, is equal to the total power of all the scattered fields of the discrete and continuous waveguide spectra.
NASA Astrophysics Data System (ADS)
Ariza, A.; Landeira, J. M.; Escánez, A.; Wienerroither, R.; Aguilar de Soto, N.; Røstad, A.; Kaartvedt, S.; Hernández-León, S.
2016-05-01
Diel vertical migration (DVM) facilitates biogeochemical exchanges between shallow waters and the deep ocean. An effective way of monitoring the migrant biota is by acoustic observations although the interpretation of the scattering layers poses challenges. Here we combine results from acoustic observations at 18 and 38 kHz with limited net sampling in order to unveil the origin of acoustic phenomena around the Canary Islands, subtropical northeast Atlantic Ocean. Trawling data revealed a high diversity of fishes, decapods and cephalopods (152 species), although few dominant species likely were responsible for most of the sound scattering in the region. We identified four different acoustic scattering layers in the mesopelagic realm: (1) at 400-500 m depth, a swimbladder resonance phenomenon at 18 kHz produced by gas-bearing migrant fish such as Vinciguerria spp. and Lobianchia dofleini, (2) at 500-600 m depth, a dense 38 kHz layer resulting primarily from the gas-bearing and non-migrant fish Cyclothone braueri, and to a lesser extent, from fluid-like migrant fauna also inhabiting these depths, (3) between 600 and 800 m depth, a weak signal at both 18 and 38 kHz ascribed either to migrant fish or decapods, and (4) below 800 m depth, a weak non-migrant layer at 18 kHz which was not sampled. All the dielly migrating layers reached the epipelagic zone at night, with the shorter-range migrations moving at 4.6 ± 2.6 cm s - 1 and the long-range ones at 11.5 ± 3.8 cm s - 1. This work reduces uncertainties interpreting standard frequencies in mesopelagic studies, while enhances the potential of acoustics for future research and monitoring of the deep pelagic fauna in the Canary Islands.
Field-Deployable Acoustic Digital Systems for Noise Measurement
NASA Technical Reports Server (NTRS)
Shams, Qamar A.; Wright, Kenneth D.; Lunsford, Charles B.; Smith, Charlie D.
2000-01-01
Langley Research Center (LaRC) has for years been a leader in field acoustic array measurement technique. Two field-deployable digital measurement systems have been developed to support acoustic research programs at LaRC. For several years, LaRC has used the Digital Acoustic Measurement System (DAMS) for measuring the acoustic noise levels from rotorcraft and tiltrotor aircraft. Recently, a second system called Remote Acquisition and Storage System (RASS) was developed and deployed for the first time in the field along with DAMS system for the Community Noise Flight Test using the NASA LaRC-757 aircraft during April, 2000. The test was performed at Airborne Airport in Wilmington, OH to validate predicted noise reduction benefits from alternative operational procedures. The test matrix was composed of various combinations of altitude, cutback power, and aircraft weight. The DAMS digitizes the acoustic inputs at the microphone site and can be located up to 2000 feet from the van which houses the acquisition, storage and analysis equipment. Digitized data from up to 10 microphones is recorded on a Jaz disk and is analyzed post-test by microcomputer system. The RASS digitizes and stores acoustic inputs at the microphone site that can be located up to three miles from the base station and can compose a 3 mile by 3 mile array of microphones. 16-bit digitized data from the microphones is stored on removable Jaz disk and is transferred through a high speed array to a very large high speed permanent storage device. Up to 30 microphones can be utilized in the array. System control and monitoring is accomplished via Radio Frequency (RF) link. This paper will present a detailed description of both systems, along with acoustic data analysis from both systems.
NASA Astrophysics Data System (ADS)
Neuville, C.; Tassin, V.; Pesme, D.; Monteil, M.-C.; Masson-Laborde, P.-E.; Baccou, C.; Fremerye, P.; Philippe, F.; Seytor, P.; Teychenné, D.; Seka, W.; Katz, J.; Bahr, R.; Depierreux, S.
2016-06-01
The indirect-drive scheme to inertial confinement fusion uses a large number of laser beams arranged in a symmetric angular distribution. Collective laser plasma instabilities can therefore develop that couple all the incident laser waves located in a cone to the daughter wave growing along the cone symmetry axis [D. F. DuBois et al., Phys. Fluids B 4, 241 (1992)]. With complementary diagnostics of Thomson scattering and of the scattered light, we demonstrate the occurrence of collective stimulated Brillouin sidescattering driving collective acoustic waves in indirect-drive experiments.
Neuville, C; Tassin, V; Pesme, D; Monteil, M-C; Masson-Laborde, P-E; Baccou, C; Fremerye, P; Philippe, F; Seytor, P; Teychenné, D; Seka, W; Katz, J; Bahr, R; Depierreux, S
2016-06-10
The indirect-drive scheme to inertial confinement fusion uses a large number of laser beams arranged in a symmetric angular distribution. Collective laser plasma instabilities can therefore develop that couple all the incident laser waves located in a cone to the daughter wave growing along the cone symmetry axis [D. F. DuBois et al., Phys. Fluids B 4, 241 (1992)]. With complementary diagnostics of Thomson scattering and of the scattered light, we demonstrate the occurrence of collective stimulated Brillouin sidescattering driving collective acoustic waves in indirect-drive experiments. PMID:27341238
Observation of cavitation bubbles and acoustic streaming in high intensity ultrasound fields
NASA Astrophysics Data System (ADS)
Uemura, Yuuki; Sasaki, Kazuma; Minami, Kyohei; Sato, Toshio; Choi, Pak-Kon; Takeuchi, Shinichi
2015-07-01
We observed the behavior of acoustic cavitation by sonochemical luminescence and ultrasound B-mode imaging with ultrasound diagnostic equipment in a standing-wave ultrasound field and focused ultrasound field. Furthermore, in order to investigate the influence of acoustic streaming on acoustic cavitation bubbles, we performed flow analysis of the sound field using particle image velocimetry. We found that acoustic cavitation bubbles are stirred by circulating acoustic streaming and local vortexes occurring in the water tank of the standing-wave ultrasound exposure system. We considered that the acoustic cavitation bubbles are carried away by acoustic streaming due to the high ultrasound pressure in the focused ultrasound field.
Saikia, P.
1981-07-01
The spectrum of stimulated Brillouin scattering from an inhomogeneous moving laser plasma is analyzed. The damping of acoustic waves and scattered electromagnetic waves is taken into account. Spectra are derived for various scattering angles and for various radii of the laser beam. For all observation angles the center of the spectral line is at an unshifted frequency. As the observation angle increases, the width of the red wing in the spectrum increases. The intensity of the scattered light is very anisotropic.
On noninvasive assessment of acoustic fields acting on the fetus
NASA Astrophysics Data System (ADS)
Antonets, V. A.; Kazakov, V. V.
2014-05-01
The aim of this study is to verify a noninvasive technique for assessing the characteristics of acoustic fields in the audible range arising in the uterus under the action of maternal voice, external sounds, and vibrations. This problem is very important in view of actively developed methods for delivery of external sounds to the uterus: music, maternal voice recordings, sounds from outside the mother's body, etc., that supposedly support development of the fetus at the prenatal stage psychologically and cognitively. However, the parameters of acoustic signals have been neither measured nor normalized, which may be dangerous for the fetus and hinder actual assessment of their impact on fetal development. The authors show that at frequencies below 1 kHz, acoustic pressure in the uterus may be measured noninvasively using a hydrophone placed in a soft capsule filled with liquid. It was found that the acoustic field at frequencies up to 1 kHz arising in the uterus under the action of an external sound field has amplitude-frequency parameters close to those of the external field; i.e., the external field penetrates the uterus with hardly any difficulty.
NASA Astrophysics Data System (ADS)
Yang, Hai-Bin; Li, Yue; Zhao, Hong-Gang; Wen, Ji-Hong; Wen, Xi-Sen
2014-10-01
The acoustic properties of anechoic layers with a singly periodic array of cylindrical scatterers are investigated. A method combined plane wave expansion and finite element analysis is extended for out-of-plane incidence. The reflection characteristics of the anechoic layers with cavities and locally resonant scatterers are discussed. The backing is a steel plate followed by an air half space. Under this approximate zero transmission backing condition, the reflection reduction is induced by the absorption enhancement. The absorption mechanism is explained by the scattering/absorption cross section of the isolated scatterer. Three types of resonant modes which can induce efficient absorption are revealed. Due to the fact that the frequencies of the resonant modes are related to the size of the scatterers, anechoic layers with scatterers of mixed size can broaden the absorption band. A genetic optimization algorithm is adopted to design the anechoic layer with scatterers of mixed size at a desired frequency band from 2 kHz to 10 kHz for normal incidence, and the influence of the incident angle is also discussed.
NASA Astrophysics Data System (ADS)
Voronovich, Alexander G.; Ostashev, Vladimir E.
2003-04-01
In our previous paper [J. Acoust. Soc. Am. 112, 2232], we obtained a time dependence of the horizontal refraction angle (HRA) of acoustic signals propagating over a range of about 4000 km in the ocean. This dependence was computed by processing of acoustic signals recorded during the North Pacific Acoustic Laboratory (NPAL) experiment using a ray-type approach. In the present paper, we consider the results obtained in signal processing of the same data using a modal approach. In this approach, the acoustic field is represented as a sum of local acoustic modes with amplitudes depending on a frequency and arrival angle. We obtained a time dependence of HRA for a time interval of about a year. Time evolution of HRA exhibits long-period variations which could be associated with seasonal trends in the sound speed profiles. The results are consistent with those obtained by the ray approach. Different horizontal angles within arrivals were impossible to resolve due to sound scattering by internal waves. A theoretical estimate of the angular width of the acoustic signals in a horizontal plane was obtained. It appears to be consistent with the observed variance of HRA data. [Work supported by ONR.] a)J. A. Colosi, B. D. Cornuelle, B. D. Dushaw, M. A. Dzieciuch, B. M. Howe, J. A. Mercer, R. C. Spindel, and P. F. Worcester.
NASA Astrophysics Data System (ADS)
Buscombe, D.; Grams, P. E.; Kaplinski, M. A.
2013-12-01
Bed sediment classification using backscatter intensities from multibeam echosounder (MBES) systems in rivers is attractive due to its high coverage and resolution, limited costs compared to conventional sampling, and the potential combination of bathymetric and bottom sediment mapping in one instrument. Sediment classification by means of hydro-acoustic remote sensing is becoming an established discipline in oceanography. A number of techniques have been proposed, none of which has become the preferred method. In rivers, however, the field is relatively new and faces challenges not typically encountered in deep ocean settings. For example, river beds tend to have larger mean and maximum slopes than typical seabeds. Shallow water depths not only make MBES deployments more difficult, but also make the size of the beam footprint on the bed small which can lead to relatively noisy backscatter data. In particular, sediments can more heterogeneous in terms of: 1) range of particle sizes (both in a given area and over an entire mapped reach); 2) range of grain size over proximal bedform fields; 3) superimposed bedforms; and 4) abrupt sedimentological transitions over small scales. This sediment heterogeneity means grain-size usually changes along swath, which has a number of implications for existing sediment classification methods which use the distribution of backscatter intensities over all acoustic beams. We discuss these implications with reference to MBES data collected from the Colorado River in Grand Canyon, Arizona. We analyze the scale-dependence of probability density functions (PDF) of measured elevations in different sedimentological settings, which reveals the appropriate spatial scale at which to apply acoustic scattering theories. We also discuss the joint PDF of elevation and backscatter over different scales as a means by which to create an adaptive gridding scheme in which each grid is scaled appropriately, in situations with rapidly changing
Characterizing riverbed sediment using high-frequency acoustics 1: spectral properties of scattering
Buscombe, Daniel D.; Grams, Paul E.; Kaplinski, Matt A.
2014-01-01
Bed-sediment classification using high-frequency hydro-acoustic instruments is challenging when sediments are spatially heterogeneous, which is often the case in rivers. The use of acoustic backscatter to classify sediments is an attractive alternative to analysis of topography because it is potentially sensitive to grain-scale roughness. Here, a new method is presented which uses high-frequency acoustic backscatter from multibeam sonar to classify heterogeneous riverbed sediments by type (sand, gravel,rock) continuously in space and at small spatial resolution. In this, the first of a pair of papers that examine the scattering signatures from a heterogeneous riverbed, methods are presented to construct spatially explicit maps of spectral properties from geo-referenced point clouds of geometrically and radiometrically corrected echoes. Backscatter power spectra are computed to produce scale and amplitude metrics that collectively characterize the length scales of stochastic measures of riverbed scattering, termed ‘stochastic geometries’. Backscatter aggregated over small spatial scales have spectra that obey a power-law. This apparently self-affine behavior could instead arise from morphological- and grain-scale roughnesses over multiple overlapping scales, or riverbed scattering being transitional between Rayleigh and geometric regimes. Relationships exist between stochastic geometries of backscatter and areas of rough and smooth sediments. However, no one parameter can uniquely characterize a particular substrate, nor definitively separate the relative contributions of roughness and acoustic impedance (hardness). Combinations of spectral quantities do, however, have the potential to delineate riverbed sediment patchiness, in a data-driven approach comparing backscatter with bed-sediment observations (which is the subject of part two of this manuscript).
A field-deployable digital acoustic measurement system
NASA Technical Reports Server (NTRS)
Gray, David L.; Wright, Kenneth D., II; Rowland, Wayne D.
1991-01-01
A field deployable digital acoustic measurement system was developed to support acoustic research programs at the Langley Research Center. The system digitizes the acoustic inputs at the microphone, which can be located up to 1000 feet from the van which houses the acquisition, storage, and analysis equipment. Digitized data from up to 12 microphones is recorded on high density 8mm tape and is analyzed post-test by a microcomputer system. Synchronous and nonsynchronous sampling is available with maximum sample rates of 12,500 and 40,000 samples per second respectively. The high density tape storage system is capable of storing 5 gigabytes of data at transfer rates up to 1 megabyte per second. System overall dynamic range exceeds 83 dB.
Theoretical and experimental examination of near-field acoustic levitation.
Nomura, Hideyuki; Kamakura, Tomoo; Matsuda, Kazuhisa
2002-04-01
A planar object can be levitated stably close to a piston sound source by making use of acoustic radiation pressure. This phenomenon is called near-field acoustic levitation [Y. Hashimoto et al., J. Acoust. Soc. Am. 100, 2057-2061 (1996)]. In the present article, the levitation distance is predicted theoretically by numerically solving basic equations in a compressible viscous fluid subject to the appropriate initial and boundary conditions. Additionally, experiments are carried out using a 19.5-kHz piston source with a 40-mm aperture and various aluminum disks of different sizes. The measured levitation distance agrees well with the theory, which is different from a conventional theory, and the levitation distance is not inversely proportional to the square root of the surface density of the levitated disk in a strict sense. PMID:12002842
Sound field simulation and acoustic animation in urban squares
NASA Astrophysics Data System (ADS)
Kang, Jian; Meng, Yan
2005-04-01
Urban squares are important components of cities, and the acoustic environment is important for their usability. While models and formulae for predicting the sound field in urban squares are important for their soundscape design and improvement, acoustic animation tools would be of great importance for designers as well as for public participation process, given that below a certain sound level, the soundscape evaluation depends mainly on the type of sounds rather than the loudness. This paper first briefly introduces acoustic simulation models developed for urban squares, as well as empirical formulae derived from a series of simulation. It then presents an acoustic animation tool currently being developed. In urban squares there are multiple dynamic sound sources, so that the computation time becomes a main concern. Nevertheless, the requirements for acoustic animation in urban squares are relatively low compared to auditoria. As a result, it is important to simplify the simulation process and algorithms. Based on a series of subjective tests in a virtual reality environment with various simulation parameters, a fast simulation method with acceptable accuracy has been explored. [Work supported by the European Commission.
Love, Richard H
2013-11-01
In the 1970s a model of resonant scattering from a swimbladder-bearing fish was developed. The fish was modeled as an air bubble, representing a swimbladder, encased in a viscous spherical shell, representing the fish flesh. This model has been used successfully to correlate acoustic scattering data with fish information in a number of ocean locations. Recently, questions have arisen about viscous damping of the flesh and the thickness of the shell [K. Baik, J. Acoust. Soc. Am. 133, 5-8 (2013)]. This Letter responds to those questions and provides practical insight into the model's use.
Love, Richard H
2013-11-01
In the 1970s a model of resonant scattering from a swimbladder-bearing fish was developed. The fish was modeled as an air bubble, representing a swimbladder, encased in a viscous spherical shell, representing the fish flesh. This model has been used successfully to correlate acoustic scattering data with fish information in a number of ocean locations. Recently, questions have arisen about viscous damping of the flesh and the thickness of the shell [K. Baik, J. Acoust. Soc. Am. 133, 5-8 (2013)]. This Letter responds to those questions and provides practical insight into the model's use. PMID:24180749
Weak scattering of scalar and electromagnetic random fields
NASA Astrophysics Data System (ADS)
Tong, Zhisong
This dissertation encompasses several studies relating to the theory of weak potential scattering of scalar and electromagnetic random, wide-sense statistically stationary fields from various types of deterministic or random linear media. The proposed theory is largely based on the first Born approximation for potential scattering and on the angular spectrum representation of fields. The main focus of the scalar counterpart of the theory is made on calculation of the second-order statistics of scattered light fields in cases when the scattering medium consists of several types of discrete particles with deterministic or random potentials. It is shown that the knowledge of the correlation properties for the particles of the same and different types, described with the newly introduced pair-scattering matrix, is crucial for determining the spectral and coherence states of the scattered radiation. The approach based on the pair-scattering matrix is then used for solving an inverse problem of determining the location of an "alien" particle within the scattering collection of "normal" particles, from several measurements of the spectral density of scattered light. Weak scalar scattering of light from a particulate medium in the presence of optical turbulence existing between the scattering centers is then approached using the combination of the Born's theory for treating the light interaction with discrete particles and the Rytov's theory for light propagation in extended turbulent medium. It is demonstrated how the statistics of scattered radiation depend on scattering potentials of particles and the power spectra of the refractive index fluctuations of turbulence. This theory is of utmost importance for applications involving atmospheric and oceanic light transmission. The second part of the dissertation includes the theoretical procedure developed for predicting the second-order statistics of the electromagnetic random fields, such as polarization and linear momentum
Oscillations of a deformed liquid drop in an acoustic field
NASA Astrophysics Data System (ADS)
Shi, Tao; Apfel, Robert E.
1995-07-01
The oscillations of an axially symmetric liquid drop in an acoustic standing wave field in air have been studied using the boundary integral method. The interaction between the drop oscillation and sound field has been included in this analysis. Our computations focus on the frequency shift of small-amplitude oscillations of an acoustically deformed drop typical of a drop levitated in air. In the presence or absence of gravity, the trend and the magnitude of the frequency shift have been given in terms of drop size, drop deformation, and the strength of the sound field. Our calculations are compared with experiments performed on the United States Microgravity Laboratory (USML-1) and with ground-based measurements, and are found to be in good agreement within the accuracy of the experimental data.
Control of acoustic absorption in one-dimensional scattering by resonant scatterers
NASA Astrophysics Data System (ADS)
Merkel, A.; Theocharis, G.; Richoux, O.; Romero-García, V.; Pagneux, V.
2015-12-01
We experimentally report perfect acoustic absorption through the interplay of the inherent losses and transparent modes with high Q factor. These modes are generated in a two-port, one-dimensional waveguide, which is side-loaded by isolated resonators of moderate Q factor. In symmetric structures, we show that in the presence of small inherent losses, these modes lead to coherent perfect absorption associated with one-sided absorption slightly larger than 0.5. In asymmetric structures, near perfect one-sided absorption is possible (96%) with a deep sub-wavelength sample ( λ / 28 , where λ is the wavelength of the sound wave in the air). The control of strong absorption by the proper tuning of the radiation leakage of few resonators with weak losses will open possibilities in various wave-control devices.
Nonasymptotic analysis of relativistic electron scattering in the Coulomb field
NASA Astrophysics Data System (ADS)
Feranchuk, I. D.; Skoromnik, O. D.
2010-11-01
It is shown that the conventional Born series for relativistic electron scattering in the Coulomb field cannot be used for calculating the scattering characteristics. The differential cross section at small scattering angles is found on the basis of the Furry-Sommerfeld-Maue solution of the Dirac equation. Propagation of the electron wave packet is considered in order to separate the incident and scattered fluxes. It is shown that the total scattering cross section proves to be finite but depends on the distance r between the scattering center and the observation point. It is also shown that the polarization characteristics of the scattered beam are changed due to the long-range character of the Coulomb potential. The results can be important because Coulomb scattering is often used for normalization of experimental data in high-energy physics.
Doc, Jean-Baptiste; Conoir, Jean-Marc; Marchiano, Régis; Fuster, Daniel
2016-04-01
The weakly nonlinear propagation of acoustic waves in monodisperse bubbly liquids is investigated numerically. A hydrodynamic model based on the averaged two-phase fluid equations is coupled with the Rayleigh-Plesset equation to model the dynamics of bubbles at the local scale. The present model is validated in the linear regime by comparing with the Foldy approximation. The analysis of the pressure signals in the linear regime highlights two resonance frequencies: the Minnaert frequency and a multiple scattering resonance that strongly depends on the bubble concentration. For weakly nonlinear regimes, the generation of higher harmonics is observed only for the Minnaert frequency. Linear combinations between the Minnaert harmonics and the multiple scattering resonance are also observed. However, the most significant effect observed is the appearance of softening-hardening effects that share some similarities with those observed for sandstones or cracked materials. These effects are related to the multiple scattering resonance. Downward or upward resonance frequency shifts can be observed depending on the characteristic of the incident wave when increasing the excitation amplitude. It is shown that the frequency shift can be explained assuming that the acoustic wave velocity depends on a law different from those usually encountered for sandstones or cracked materials.
Doc, Jean-Baptiste; Conoir, Jean-Marc; Marchiano, Régis; Fuster, Daniel
2016-04-01
The weakly nonlinear propagation of acoustic waves in monodisperse bubbly liquids is investigated numerically. A hydrodynamic model based on the averaged two-phase fluid equations is coupled with the Rayleigh-Plesset equation to model the dynamics of bubbles at the local scale. The present model is validated in the linear regime by comparing with the Foldy approximation. The analysis of the pressure signals in the linear regime highlights two resonance frequencies: the Minnaert frequency and a multiple scattering resonance that strongly depends on the bubble concentration. For weakly nonlinear regimes, the generation of higher harmonics is observed only for the Minnaert frequency. Linear combinations between the Minnaert harmonics and the multiple scattering resonance are also observed. However, the most significant effect observed is the appearance of softening-hardening effects that share some similarities with those observed for sandstones or cracked materials. These effects are related to the multiple scattering resonance. Downward or upward resonance frequency shifts can be observed depending on the characteristic of the incident wave when increasing the excitation amplitude. It is shown that the frequency shift can be explained assuming that the acoustic wave velocity depends on a law different from those usually encountered for sandstones or cracked materials. PMID:27106317
Weber, Thomas C; Lutcavage, Molly E; Schroth-Miller, Madeline L
2013-06-01
Schools of Atlantic bluefin tuna (Thunnus thynnus) can exhibit highly organized spatial structure within the school. This structure was quantified for dome shaped schools using both aerial imagery collected from a commercial spotter plane and 400 kHz multibeam echo sounder data collected on a fishing vessel in 2009 in Cape Cod Bay, MA. Observations from one school, containing an estimated 263 fish within an approximately ellipsoidal volume of 1900 m(3), were used to seed an acoustic model that estimated the school target strength at frequencies between 10 and 2000 Hz. The fish's swimbladder resonance was estimated to occur at approximately 50 Hz. The acoustic model examined single and multiple scattering solutions and also a completely incoherent summation of scattering responses from the fish. Three levels of structure within the school were examined, starting with fish locations that were constrained by the school boundaries but placed according to a Poisson process, then incorporating a constraint on the distance to the nearest neighbor, and finally adding a constraint on the bearing to the nearest neighbor. Results suggest that both multiple scattering and spatial organization within the school should be considered when estimating the target strength of schools similar to the ones considered here. PMID:23742334
Collins, David J; Ma, Zhichao; Ai, Ye
2016-05-17
Concentration and separation of particles and biological specimens are fundamental functions of micro/nanofluidic systems. Acoustic streaming is an effective and biocompatible way to create rapid microscale fluid motion and induce particle capture, though the >100 MHz frequencies required to directly generate acoustic body forces on the microscale have traditionally been difficult to generate and localize in a way that is amenable to efficient generation of streaming. Moreover, acoustic, hydrodynamic, and electrical forces as typically applied have difficulty manipulating specimens in the submicrometer regime. In this work, we introduce highly focused traveling surface acoustic waves (SAW) at high frequencies between 193 and 636 MHz for efficient and highly localized production of acoustic streaming vortices on microfluidic length scales. Concentration occurs via a novel mechanism, whereby the combined acoustic radiation and streaming field results in size-selective aggregation in fluid streamlines in the vicinity of a high-amplitude acoustic beam, as opposed to previous acoustic radiation induced particle concentration where objects typically migrate toward minimum pressure locations. Though the acoustic streaming is induced by a traveling wave, we are able to manipulate particles an order of magnitude smaller than possible using the traveling wave force alone. We experimentally and theoretically examine the range of particle sizes that can be captured in fluid streamlines using this technique, with rapid particle concentration demonstrated down to 300 nm diameters. We also demonstrate that locations of trapping and concentration are size-dependent, which is attributed to the combined effects of the acoustic streaming and acoustic forces.
Plateau structures in potential scattering in a strong laser field
Cerkic, A.; Milosevic, D.B.
2004-11-01
Electron-atom scattering in a strong laser field is analyzed using the strong-field approximation and modeling elastic scattering of electrons by atoms with a realistic analytical potential derived from an independent-particle model. The results that include both direct scattering and scattering with a repeated scattering (rescattering) are presented. In the latter case, in the intermediate step of the process, the electron can absorb the energy from the laser field and additional plateau structures appear. The features of these plateaus and their cutoffs are analyzed for various incident electron energies and scattering angles, for different laser intensities, and for various atomic gases. The boundaries of these plateaus are compared with classical estimates.
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.
Laval nozzle as an acoustic analogue of a massive field
NASA Astrophysics Data System (ADS)
Cuyubamba, M. A.
2013-10-01
We study a gas flow in the Laval nozzle, which is a convergent-divergent tube that has a sonic point in its throat. We show how to obtain the appropriate form of the tube, so that the acoustic perturbations of the gas flow in it satisfy any given wave-like equation. With the help of the proposed method we find the Laval nozzle, which is an acoustic analogue of the massive scalar field in the background of the Schwarzschild black hole. This gives us a possibility to observe in a laboratory the quasinormal ringing of the massive scalar field, which, for special set of the parameters, can have infinitely long-living oscillations in its spectrum.
NASA Astrophysics Data System (ADS)
Mori, Kazuyoshi; Ogasawara, Hanako; Nakamura, Toshiaki; Tsuchiya, Takenobu; Endoh, Nobuyuki
2012-07-01
We have already designed and fabricated an aspherical lens with an aperture diameter of 1.0 m to develop a prototype system for ambient noise imaging (ANI). It has also been verified that this acoustic lens realizes a directional resolution, which is a beam width of 1° at the center frequency of 120 kHz over the field of view from -7 to +7°. In this study, a sea trial of silent target detection using the prototype ANI system was conducted under only natural ocean ambient noise at Uchiura Bay, in November of 2010. There were many transients in the received sound. These transients were classified roughly into directly received noises and target scatterings. We proposed a classification method to extract transients of only target scatterings. By analyzing transients extracted as target scatterings, it was verified that the power spectrum density levels of the on-target directions were greater than those of the off-target directions in the higher frequency band over 60 kHz. These results showed that the targets are successfully detected under natural ocean ambient noise, mainly generated by snapping shrimps.
NASA Astrophysics Data System (ADS)
Titovich, Alexey S.; Norris, Andrew N.
2015-03-01
A thin infinitely long elastic shell is stiffened by J in number identical lengthwise ribs distributed uniformly around the circumference and joined to a rod in the center. The 2D model of the substructure is a rigid central mass supported by J axisymmetrically placed linear springs. The response of the shell-spring-mass system is quite different from a fluid filled shell or that of a solid cylinder due to the discrete number of contact points which couple the displacement of the shell at different locations. Exterior acoustic scattering due to normal plane wave incidence is solved in closed form for arbitrary J. The scattering matrix associated with the normal mode solution displays a simple structure, composed of distinct sub-matrices which decouple the incident and scattered fields into J families. The presence of a spring-mass substructure causes resonances which are shown to be related to the subsonic shell flexural waves, and an approximate analytic expression is derived for the quasi-flexural resonance frequencies. Numerical simulations indicate that the new solution for J ≥ 3 springs results in a complicated scattering response for plane wave incidence. As the number of springs becomes large enough, the total scattering cross-section is asymptotically zero at low frequencies and slightly increased compared to the empty shell at moderate frequencies due to the added stiffness and mass. It is also observed that the sensitivity to the angle of incidence diminishes as the number of springs is increased. This system can be tuned by selecting the shell thickness, spring stiffness and added mass to yield desired quasi-static effective properties making it a candidate element for graded index sonic crystals.
Field tests of acoustic telemetry for a portable coastal observatory
Martini, M.; Butman, B.; Ware, J.; Frye, D.
2006-01-01
Long-term field tests of a low-cost acoustic telemetry system were carried out at two sites in Massachusetts Bay. At each site, an acoustic Doppler current profiler mounted on a bottom tripod was fitted with an acoustic modem to transmit data to a surface buoy; electronics mounted on the buoy relayed these data to shore via radio modem. The mooring at one site (24 m water depth) was custom-designed for the telemetry application, with a custom designed small buoy, a flexible electro-mechanical buoy to mooring joint using a molded chain connection to the buoy, quick-release electro-mechanical couplings, and dual hydrophones suspended 7 m above the bottom. The surface buoy at the second site (33 m water depth) was a U.S. Coast Guard (USCG) channel buoy fitted with telemetry electronics and clamps to hold the hydrophones. The telemetry was tested in several configurations for a period of about four years. The custom-designed buoy and mooring provided nearly error-free data transmission through the acoustic link under a variety of oceanographic conditions for 261 days at the 24 m site. The electro mechanical joint, cables and couplings required minimal servicing and were very reliable, lasting 862 days deployed before needing repairs. The acoustic communication results from the USCG buoy were poor, apparently due to the hard cobble bottom, noise from the all-steel buoy, and failure of the hydrophone assembly. Access to the USCG buoy at sea required ideal weather. ??2006 IEEE.
Direct Field and Reverberant Chamber Acoustic Test Comparisons
NASA Technical Reports Server (NTRS)
OConnell, Michael
2007-01-01
Reverberant and direct acoustic test comparisons were analyzed in this viewgraph presentation. The acoustic test data set includes: 1) CloudSat antenna subjected to PF reverberant chamber acoustic test; 2) CloudSat subjected to a PF direct speaker acoustic test; and 3) DAWN flight spacecraft subjected to PF direct speaker and a workmanship reverberant chamber acoustic test.
Measurements of high-frequency acoustic scattering from glacially eroded rock outcrops.
Olson, Derek R; Lyons, Anthony P; Sæbø, Torstein O
2016-04-01
Measurements of acoustic backscattering from glacially eroded rock outcrops were made off the coast of Sandefjord, Norway using a high-frequency synthetic aperture sonar (SAS) system. A method by which scattering strength can be estimated from data collected by a SAS system is detailed, as well as a method to estimate an effective calibration parameter for the system. Scattering strength measurements from very smooth areas of the rock outcrops agree with predictions from both the small-slope approximation and perturbation theory, and range between -33 and -26 dB at 20° grazing angle. Scattering strength measurements from very rough areas of the rock outcrops agree with the sine-squared shape of the empirical Lambertian model and fall between -30 and -20 dB at 20° grazing angle. Both perturbation theory and the small-slope approximation are expected to be inaccurate for the very rough area, and overestimate scattering strength by 8 dB or more for all measurements of very rough surfaces. Supporting characterization of the environment was performed in the form of geoacoustic and roughness parameter estimates. PMID:27106331
Measurements of high-frequency acoustic scattering from glacially eroded rock outcrops.
Olson, Derek R; Lyons, Anthony P; Sæbø, Torstein O
2016-04-01
Measurements of acoustic backscattering from glacially eroded rock outcrops were made off the coast of Sandefjord, Norway using a high-frequency synthetic aperture sonar (SAS) system. A method by which scattering strength can be estimated from data collected by a SAS system is detailed, as well as a method to estimate an effective calibration parameter for the system. Scattering strength measurements from very smooth areas of the rock outcrops agree with predictions from both the small-slope approximation and perturbation theory, and range between -33 and -26 dB at 20° grazing angle. Scattering strength measurements from very rough areas of the rock outcrops agree with the sine-squared shape of the empirical Lambertian model and fall between -30 and -20 dB at 20° grazing angle. Both perturbation theory and the small-slope approximation are expected to be inaccurate for the very rough area, and overestimate scattering strength by 8 dB or more for all measurements of very rough surfaces. Supporting characterization of the environment was performed in the form of geoacoustic and roughness parameter estimates.
Stevens, Lewis L; Orler, E Bruce; Dattelbaum, Dana M; Ahart, Muhtar; Hemley, Russell J
2007-09-14
The acoustic properties of three polymer elastomers, a cross-linked poly(dimethylsiloxane) (Sylgard 184), a cross-linked terpolymer poly(ethylene-vinyl acetate-vinyl alcohol), and a segmented thermoplastic poly(ester urethane) copolymer (Estane 5703), have been measured from ambient pressure to approximately 12 GPa by using Brillouin scattering in high-pressure diamond anvil cells. The Brillouin-scattering technique is a powerful tool for aiding in the determination of equations of state for a variety of materials, but to date has not been applied to polymers at pressures exceeding a few kilobars. For the three elastomers, both transverse and longitudinal acoustic modes were observed, though the transverse modes were observed only at elevated pressures (>0.7 GPa) in all cases. From the Brillouin frequency shifts, longitudinal and transverse sound speeds were calculated, as were the C(11) and C(12) elastic constants, bulk, shear, and Young's moduli, and Poisson's ratios, and their respective pressure dependencies. P-V isotherms were then constructed, and fit to several empirical/semiempirical equations of state to extract the isothermal bulk modulus and its pressure derivative for each material. Finally, the lack of shear waves observed for any polymer at ambient pressure, and the pressure dependency of their appearance is discussed with regard to instrumental and material considerations.
NASA Astrophysics Data System (ADS)
Stevens, Lewis L.; Orler, E. Bruce; Dattelbaum, Dana M.; Ahart, Muhtar; Hemley, Russell J.
2007-09-01
The acoustic properties of three polymer elastomers, a cross-linked poly(dimethylsiloxane) (Sylgard® 184), a cross-linked terpolymer poly(ethylene-vinyl acetate-vinyl alcohol), and a segmented thermoplastic poly(ester urethane) copolymer (Estane® 5703), have been measured from ambient pressure to approximately 12GPa by using Brillouin scattering in high-pressure diamond anvil cells. The Brillouin-scattering technique is a powerful tool for aiding in the determination of equations of state for a variety of materials, but to date has not been applied to polymers at pressures exceeding a few kilobars. For the three elastomers, both transverse and longitudinal acoustic modes were observed, though the transverse modes were observed only at elevated pressures (>0.7GPa) in all cases. From the Brillouin frequency shifts, longitudinal and transverse sound speeds were calculated, as were the C11 and C12 elastic constants, bulk, shear, and Young's moduli, and Poisson's ratios, and their respective pressure dependencies. P-V isotherms were then constructed, and fit to several empirical/semiempirical equations of state to extract the isothermal bulk modulus and its pressure derivative for each material. Finally, the lack of shear waves observed for any polymer at ambient pressure, and the pressure dependency of their appearance is discussed with regard to instrumental and material considerations.
Near-Field Acoustical Characterization of Clustered Rocket Engines
NASA Technical Reports Server (NTRS)
Kandula, Max; Vu, Bruce T.; Lindsay Halie K.
2005-01-01
This paper presents an approach for the prediction and characterization of the near-field acoustic levels from closely-spaced clustered rocket engines. The calculations are based on the method proposed by Eldred, wherein the flowfield from the clustered rockets is divided into two zones. Zone 1 contains the isolated nozzles which produce noise independently, and extends up to a distance where the individual flows completely mix to form an equivalent single nozzle flow. Zone 2 is occupied by the single mixed stream starting from the station where the jets merge. The acoustic fields from the two zones are computed separately on the basis of the NASA-SP method of Eldred developed for a single equivalent nozzle. A summation of the spectra for the two zones yields the total effective sound pressure level for the clustered engines. Under certain conditions of nozzle spacing and flow parameters, the combined sound pressure level spectrum for the clustered nozzles displays a double peak. Test cases are presented here to demonstrate the importance of hydrodynamic interactions responsible for the double peak in the sound spectrum in the case of clustered rocket nozzles, and the role of ground reflections in the case of non-interfering jets. A graphics interface (Rocket Acoustic Prediction Tool) has been developed to take into account the effects of clustered nozzles and ground reflections.
Acoustic source localization in mixed field using spherical microphone arrays
NASA Astrophysics Data System (ADS)
Huang, Qinghua; Wang, Tong
2014-12-01
Spherical microphone arrays have been used for source localization in three-dimensional space recently. In this paper, a two-stage algorithm is developed to localize mixed far-field and near-field acoustic sources in free-field environment. In the first stage, an array signal model is constructed in the spherical harmonics domain. The recurrent relation of spherical harmonics is independent of far-field and near-field mode strengths. Therefore, it is used to develop spherical estimating signal parameter via rotational invariance technique (ESPRIT)-like approach to estimate directions of arrival (DOAs) for both far-field and near-field sources. In the second stage, based on the estimated DOAs, simple one-dimensional MUSIC spectrum is exploited to distinguish far-field and near-field sources and estimate the ranges of near-field sources. The proposed algorithm can avoid multidimensional search and parameter pairing. Simulation results demonstrate the good performance for localizing far-field sources, or near-field ones, or mixed field sources.
Naqvi, S A; Sarfaraz, M; Holmes, T; Yu, C X; Li, X A
2001-07-01
The frequent blocking of the irradiated volume in intensity modulated radiation therapy (IMRT) makes the head-scatter fraction of the incident photon fluence more significant than that in conventional therapy with open fields. On the other hand. certain collimator configurations block scatter photons directed to a given observation point while allowing primary photons to be transmitted. The 'anomalous blocking' makes the primary field a poor indicator of the scatter fluence. Since large MU-to-cGy ratios in IMRT can magnify head-scatter uncertainties, it becomes necessary to accurately model both the effective scatter source and the collimator structure that limits the scatter reaching the irradiated volume. First we obtain a dual-source model, using a Taylor series expansion to derive the effective scatter source distribution from the data measured for the Elekta SL20 linac equipped with a multi-leaf collimator (MLC). Then, using a raytracing algorithm, we calculate the transmission of scatter rays from the effective scatter source plane to points in the patient plane. The method can account for the anomalous blocking of scatter by the MLC leaves and the backup diaphragms. For a variety of collimator settings tested, the calculations agree with measurements to an accuracy of 0.002psi10 x 10, where psi10 x 10 is the total (primary + scatter) photon fluence of an open 10 x 10 cm2 field for the same MU delivered. Although the significance of collimator structure in IMRT depends strongly on fields shapes employed for the delivery, potential cumulative errors on the order of a few per cent can be avoided in fluence calculations if the proposed method is used. PMID:11474941
Single layer planar near-field acoustic holography for compact sources and a parallel reflector
NASA Astrophysics Data System (ADS)
Zea, Elias; Lopez Arteaga, Ines
2016-10-01
We consider the problem of planar near-field acoustic holography (PNAH) and introduce a new reconstruction method that can be used to process single layer pressure measurements performed in the presence of a reflective surface that is parallel to the measurement plane. The method is specially tailored for compact sources, or for problems in which the scattered field due to the source can be neglected. The approach consists in formulating a seismic model (WRW model) in wavenumber-space and employ it for sound source reconstructions. The proposed method is validated with numerical and experimental data, and, although the most accurate results are obtained when an estimate of the surface impedance is known beforehand, we show that it can substantially improve the reconstruction performance with respect to that of free-field PNAH.
The inverse problem of an impenetrable sound-hard body in acoustic scattering
NASA Astrophysics Data System (ADS)
Olshansky, Yaakov; Turkel, Eli
2008-11-01
We study the inverse problem of recovering the scatterer shape from the far-field pattern(FFP) of the scattered wave in presence of noise. This problem is ill-posed and is usually addressed via regularization. Instead, a direct approach to denoise the FFP using wavelet technique is proposed by us. We are interested in methods that deal with the scatterer of the general shape which may be described by a finite number of parameters. To study the effectiveness of the technique we concentrate on simple bodies such as ellipses, where the analytic solution to the forward scattering problem is known. The shape parameters are found based on a least-square error estimator. Two cases with the FFP corrupted by Gaussian noise and/or computational error from a finite element method are considered. We also consider the case where only partial data is known in the far field.
Field-theoretical description of deep inelastic scattering
Geyer, B.; Robaschik, D.; Wieczorek, E.
1980-01-01
The most important theoretical notions concerning deep inelastic scattering are reviewed. Topics discussed are the model-independent approach, which is based on the general principles of quantum field theory, the application of quantum chromodynamics to deep inelastic scattering, approaches based on the quark--parton model, the light cone algebra, and conformal invariance, and also investigations in the framework of perturbation theory.
The near-field acoustic levitation of high-mass rotors
Hong, Z. Y.; Lü, P.; Geng, D. L.; Zhai, W.; Yan, N.; Wei, B.
2014-10-15
Here we demonstrate that spherical rotors with 40 mm diameter and 0-1 kg mass can be suspended more than tens of micrometers away from an ultrasonically vibrating concave surface by near-field acoustic radiation force. Their rotating speeds exceed 3000 rpm. An acoustic model has been developed to evaluate the near-field acoustic radiation force and the resonant frequencies of levitation system. This technique has potential application in developing acoustic gyroscope.
The near-field acoustic levitation of high-mass rotors.
Hong, Z Y; Lü, P; Geng, D L; Zhai, W; Yan, N; Wei, B
2014-10-01
Here we demonstrate that spherical rotors with 40 mm diameter and 0-1 kg mass can be suspended more than tens of micrometers away from an ultrasonically vibrating concave surface by near-field acoustic radiation force. Their rotating speeds exceed 3000 rpm. An acoustic model has been developed to evaluate the near-field acoustic radiation force and the resonant frequencies of levitation system. This technique has potential application in developing acoustic gyroscope. PMID:25362441
The near-field acoustic levitation of high-mass rotors
NASA Astrophysics Data System (ADS)
Hong, Z. Y.; Lü, P.; Geng, D. L.; Zhai, W.; Yan, N.; Wei, B.
2014-10-01
Here we demonstrate that spherical rotors with 40 mm diameter and 0-1 kg mass can be suspended more than tens of micrometers away from an ultrasonically vibrating concave surface by near-field acoustic radiation force. Their rotating speeds exceed 3000 rpm. An acoustic model has been developed to evaluate the near-field acoustic radiation force and the resonant frequencies of levitation system. This technique has potential application in developing acoustic gyroscope.
Hesford, Andrew J.; Tillett, Jason C.; Astheimer, Jeffrey P.; Waag, Robert C.
2014-01-01
Accurate and efficient modeling of ultrasound propagation through realistic tissue models is important to many aspects of clinical ultrasound imaging. Simplified problems with known solutions are often used to study and validate numerical methods. Greater confidence in a time-domain k-space method and a frequency-domain fast multipole method is established in this paper by analyzing results for realistic models of the human breast. Models of breast tissue were produced by segmenting magnetic resonance images of ex vivo specimens into seven distinct tissue types. After confirming with histologic analysis by pathologists that the model structures mimicked in vivo breast, the tissue types were mapped to variations in sound speed and acoustic absorption. Calculations of acoustic scattering by the resulting model were performed on massively parallel supercomputer clusters using parallel implementations of the k-space method and the fast multipole method. The efficient use of these resources was confirmed by parallel efficiency and scalability studies using large-scale, realistic tissue models. Comparisons between the temporal and spectral results were performed in representative planes by Fourier transforming the temporal results. An RMS field error less than 3% throughout the model volume confirms the accuracy of the methods for modeling ultrasound propagation through human breast. PMID:25096103
Effects of Horizontal Magnetic Fields on Acoustic Travel Times
NASA Astrophysics Data System (ADS)
Jain, Rekha
2007-02-01
Local helioseismology techniques seek to probe the subsurface magnetic fields and flows by observing waves that emerge at the solar surface after passing through these inhomogeneities. Active regions on the surface of the Sun are distinguished by their strong magnetic fields, and techniques such as time-distance helioseismology can provide a useful diagnostic for probing these structures. Above the active regions, the fields fan out to create a horizontal magnetic canopy. We investigate the effect of a uniform horizontal magnetic field on the travel time of acoustic waves by considering vertical velocity in a simple plane-parallel adiabatically stratified polytrope. It is shown that such fields can lower the upper turning point of p-modes and hence influence their travel time. It is found that acoustic waves reflected from magnetically active regions have travel times up to a minute less than for waves similarly reflected in quiet regions. It is also found that sound speeds are increased below the active regions. These findings are consistent with time-distance measurements.
Plate Scattering Visualization: Images, Near Fields, Currents, and Far Field Patterns
NASA Technical Reports Server (NTRS)
Shaeffer, John; Hom, Kam
2004-01-01
This paper presents a case study of a simple yet robust target for demonstration of the EM visualization process. A five lambda square plate exhibits many scattering mechanisms depending on excitation angle and polarization: specular scattering, leading and trailing edge diffraction, traveling wave, and edge wave scattering. Bistatic k space radiation images, currents maps, and near scattered / total fields are examined for each of these scattering mechanisms.
NASA Astrophysics Data System (ADS)
Ressler, Patrick H.
2002-11-01
A 153 kHz narrowband acoustic Doppler current profiler (ADCP) was used to measure volume backscattering strength ( Sv) during a deepwater oceanographic survey of cetacean and seabird habitat in the northeastern Gulf of Mexico. Sv was positively related to zooplankton and micronekton biomass (wet displacement volume) in 'sea-truth' net hauls made with a 1 m 2 Multiple Opening-Closing Net Environmental Sensing System (MOCNESS). A subset of these MOCNESS tows was used to explore the relationship between the numerical densities of various taxonomic categories of zooplankton and the ADCP backscatter signal. Crustaceans, small fish, and fragments of non-gas-bearing siphonophores in the net samples all showed significant, positive correlations with the acoustic signal, while other types of gelatinous zooplankton, pteropod and atlantid molluscs, and gas-filled siphonophore floats showed no significant correlation with Sv. Previously published acoustic scattering models for zooplankton were used to calculate expected scattering for several general zooplankton types and sizes for comparison with the field data. Even though gelatinous material often made up a large fraction of the total biomass, crustaceans, small fish, and pteropods were most likely the important scatterers. Since only crustacean and small fish densities were significantly correlated with Sv, it is suggested that Sv at 153 kHz can be used as a relative proxy for the abundance of these organisms in the Gulf of Mexico.
Microwave scattering properties of snow fields
NASA Technical Reports Server (NTRS)
Angelakos, D. J.
1977-01-01
Experimental results were presented showing backscatter dependence on frequency, angle of incidence, snow wetness, and frequency modulation. Theoretical studies were made of the inverse scattering problem yielding some preliminary results concerning the determination of the dielectric constant of the snow layer. The experimental results lead to the following conclusions: (1) snow layering affects backscatter; (2) layer response was significant up to 45 degrees of incidence; (3) wetness modifies snow layer effects; and (4) frequency modulation masks the layer response.
Acoustic and Cavitation Fields of Shock Wave Therapy Devices
NASA Astrophysics Data System (ADS)
Chitnis, Parag V.; Cleveland, Robin O.
2006-05-01
Extracorporeal shock wave therapy (ESWT) is considered a viable treatment modality for orthopedic ailments. Despite increasing clinical use, the mechanisms by which ESWT devices generate a therapeutic effect are not yet understood. The mechanistic differences in various devices and their efficacies might be dependent on their acoustic and cavitation outputs. We report acoustic and cavitation measurements of a number of different shock wave therapy devices. Two devices were electrohydraulic: one had a large reflector (HMT Ossatron) and the other was a hand-held source (HMT Evotron); the other device was a pneumatically driven device (EMS Swiss DolorClast Vet). Acoustic measurements were made using a fiber-optic probe hydrophone and a PVDF hydrophone. A dual passive cavitation detection system was used to monitor cavitation activity. Qualitative differences between these devices were also highlighted using a high-speed camera. We found that the Ossatron generated focused shock waves with a peak positive pressure around 40 MPa. The Evotron produced peak positive pressure around 20 MPa, however, its acoustic output appeared to be independent of the power setting of the device. The peak positive pressure from the DolorClast was about 5 MPa without a clear shock front. The DolorClast did not generate a focused acoustic field. Shadowgraph images show that the wave propagating from the DolorClast is planar and not focused in the vicinity of the hand-piece. All three devices produced measurable cavitation with a characteristic time (cavitation inception to bubble collapse) that varied between 95 and 209 μs for the Ossatron, between 59 and 283 μs for the Evotron, and between 195 and 431 μs for the DolorClast. The high-speed camera images show that the cavitation activity for the DolorClast is primarily restricted to the contact surface of the hand-piece. These data indicate that the devices studied here vary in acoustic and cavitation output, which may imply that the
ADE-FDTD Scattered-Field Formulation for Dispersive Materials.
Kong, Soon-Cheol; Simpson, Jamesina J; Backman, Vadim
2008-01-01
This Letter presents a scattered-field formulation for modeling dispersive media using the finite-difference time-domain (FDTD) method. Specifically, the auxiliary differential equation method is applied to Drude and Lorentz media for a scattered field FDTD model. The present technique can also be applied in a straightforward manner to Debye media. Excellent agreement is achieved between the FDTD-calculated and exact theoretical results for the reflection coefficient in half-space problems.
Modeling of spray combustion in an acoustic field
Dubey, R.K.; McQuay, M.Q.; Carvalho, J.A. Jr.
1998-07-01
Combustion characteristics of an ethanol flame in a Rijke-tube, pulse combustor was theoretically studied to analyze the effects of injection velocity, burner location, droplet size distribution, surrounding gas velocity, and droplet phase difference on Sauter-mean diameter. The effects of these parameters were studied at first (80 Hz), second (160 Hz), and third (240 Hz) acoustic modes with steady (no oscillations) case as reference. The sound pressure level was kept constant at 150 decibels for all theoretical simulations. The simulation frequencies and sound pressure level was selected to match the actual conditions inside the rector. For all simulations, actual droplet size and velocity distributions, as experimentally measured using a phase-Doppler particle analyzer, at the injector exit were used. Significant effects on spray size distributions were found when the burning droplets were placed at the locations corresponding to the maximum acoustic velocity amplitude. Also, for both simulations and experimental results, the Sauter-mean diameters were higher for oscillating conditions compared to steady value because small droplets burn faster under an acoustic field and therefore, Sauter-mean diameter, which is biased towards larger droplets, increases.
Upscaling behavioural studies to the field using acoustic telemetry.
Hellström, Gustav; Klaminder, Jonatan; Jonsson, Micael; Fick, Jerker; Brodin, Tomas
2016-01-01
Laboratory-based behavioural assays are often used in ecotoxicological studies to assess the environmental risk of aquatic contaminants. While results from such laboratory-based risk assessments may be difficult to extrapolate to natural environments, technological advancements over the past decade now make it possible to perform risk assessments through detailed studies of exposed individuals in natural settings. Acoustic telemetry is a technology to monitor movement and behaviour of aquatic organism in oceans, lakes, and rivers. The technology allows for tracking of multiple individuals simultaneously with very high temporal and spatial resolution, with the option to incorporate sensors to measure various physiological and environmental parameters. Although frequently used in fisheries research, aquatic ecotoxicology has been slow to adopt acoustic telemetry as a tool in field-based studies. This mini-review intends to introduce acoustic telemetry to aquatic ecotoxicologists, focusing on the potential of the technology to bridge the gap between laboratory assays and natural behaviours when making toxicological risk assessments. PMID:26683267
Acoustic experience shapes female mate choice in field crickets
Bailey, Nathan W; Zuk, Marlene
2008-01-01
Female choice can drive the evolution of extravagant male traits. In invertebrates, the influence of prior social experience on female choice has only recently been considered. To better understand the evolutionary implications of experience-mediated plasticity in female choice, we investigated the effect of acoustic experience during rearing on female responsiveness to male song in the field cricket Teleogryllus oceanicus. Acoustic experience has unique biological relevance in this species: a morphological mutation has rendered over 90 per cent of males on the Hawaiian island of Kauai silent in fewer than 20 generations, impeding females' abilities to locate potential mates. Females reared in silent conditions mimicking Kauai were less discriminating of male calling song and more responsive to playbacks, compared with females that experienced song during rearing. Our results to our knowledge, are the first demonstration of long-term effects of acoustic experience in an arthropod, and suggest that female T. oceanicus may be able to compensate for the reduced availability of long-range male sexual signals by increasing their responsiveness to the few remaining signallers. Understanding the adaptive significance of experience-mediated plasticity in female choice provides insight into processes that facilitate rapid evolutionary change and shape sexual selection pressure in natural populations. PMID:18700205
NASA Astrophysics Data System (ADS)
Mao, Yijun; Xu, Chen; Qi, Datong
2015-02-01
A vector aeroacoustics method is developed to analyze the acoustic energy flow path from the rotating source. In this method, the instantaneous and time-averaged active acoustic intensity vectors are evaluated from the time-domain and frequency-domain acoustic pressure and acoustic velocity formulations, respectively. With the above method, the acoustic intensity vectors and the acoustic energy streamlines are visualized to investigate the propagation feature of the noise radiated from the monopole and dipole point sources and the rotor in subsonic rotation. The result reveals that a portion of the acoustic energy spirals many circles before moving towards the far field, and another portion of the acoustic energy firstly flows inward along the radial direction and then propagates along the axial direction. Further, an acoustic black hole exists in the plane of source rotation, from which the acoustic energy cannot escape once the acoustic energy flows into it. Moreover, by visualizing the acoustic intensity field around the rotating sources, the acoustic-absorption performance of the acoustic liner built in the casing and centerbody is discussed.
Interior near-field acoustical holography in flight.
Williams, E G; Houston, B H; Herdic, P C; Raveendra, S T; Gardner, B
2000-10-01
In this paper boundary element methods (BEM) are mated with near-field acoustical holography (NAH) in order to determine the normal velocity over a large area of a fuselage of a turboprop airplane from a measurement of the pressure (hologram) on a concentric surface in the interior of the aircraft. This work represents the first time NAH has been applied in situ, in-flight. The normal fuselage velocity was successfully reconstructed at the blade passage frequency (BPF) of the propeller and its first two harmonics. This reconstructed velocity reveals structure-borne and airborne sound-transmission paths from the engine to the interior space.
NASA Astrophysics Data System (ADS)
Wang, T.; Ke, M.; Qiu, C.; Liu, Z.
2016-06-01
We present the design for an acoustic system that can achieve particle trapping and transport using the acoustic force field above a phononic crystal plate. The phononic crystal plate comprised a thin brass plate with periodic slits alternately embedded with two kinds of elastic inclusions. Enhanced acoustic transmission and localized acoustic fields were achieved when the structure was excited by external acoustic waves. Because of the different resonant frequencies of the two elastic inclusions, the acoustic field could be controlled via the working frequency. Particles were transported between adjacent traps under the influence of the adjustable acoustic field. This device provides a new and versatile avenue for particle manipulation that would complement other means of particle manipulation.
Kaina, Nadège; Lemoult, Fabrice; Fink, Mathias; Lerosey, Geoffroy
2015-09-01
Metamaterials, man-made composite media structured on a scale much smaller than a wavelength, offer surprising possibilities for engineering the propagation of waves. One of the most interesting of these is the ability to achieve superlensing--that is, to focus or image beyond the diffraction limit. This originates from the left-handed behavior--the property of refracting waves negatively--that is typical of negative index metamaterials. Yet reaching this goal requires the design of 'double negative' metamaterials, which act simultaneously on the permittivity and permeability in electromagnetics, or on the density and compressibility in acoustics; this generally implies the use of two different kinds of building blocks or specific particles presenting multiple overlapping resonances. Such a requirement limits the applicability of double negative metamaterials, and has, for example, hampered any demonstration of subwavelength focusing using left-handed acoustic metamaterials. Here we show that these strict conditions can be largely relaxed by relying on media that consist of only one type of single resonant unit cell. Specifically, we show with a simple yet general semi-analytical model that judiciously breaking the symmetry of a single negative metamaterial is sufficient to turn it into a double negative one. We then demonstrate that this occurs solely because of multiple scattering of waves off the metamaterial resonant elements, a phenomenon often disregarded in these media owing to their subwavelength patterning. We apply our approach to acoustics and verify through numerical simulations that it allows the realization of negative index acoustic metamaterials based on Helmholtz resonators only. Finally, we demonstrate the operation of a negative index acoustic superlens, achieving subwavelength focusing and imaging with spot width and resolution 7 and 3.5 times better than the diffraction limit, respectively. Our findings have profound implications for the
NASA Technical Reports Server (NTRS)
Golubev, Vladimir; Mankbadi, Reda R.; Dahl, Milo D.; Kiraly, L. James (Technical Monitor)
2002-01-01
This paper provides preliminary results of the study of the acoustic radiation from the source model representing spatially-growing instability waves in a round jet at high speeds. The source model is briefly discussed first followed by the analysis of the produced acoustic directivity pattern. Two integral surface techniques are discussed and compared for prediction of the jet acoustic radiation field.
Theoretical evaluation of the acoustic field in an ultrasonic bioreactor.
Louw, Tobias M; Subramanian, Anuradha; Viljoen, Hendrik J
2015-06-01
Ultrasound-assisted bioreactors that provide mechanical conditioning to cells have broad applicability in tissue engineering, but biological experiments with ultrasound are very sensitive to environmental conditions. A mathematical model was developed to complement experimental measurements, as well as to describe ultrasonic fields existing in regions where measurements are impossible, specifically, within microporous tissue engineering scaffolds. The model uniquely combines Biot theory to predict the ultrasonic field in the scaffold with an electromechanical transducer model to couple the mechanical stimulation experienced by cells to the external electrical input. In the specific example examined here, cells immobilized on scaffolds are subjected to different forms of ultrasonic stimulation due to the formation of standing wave fields and vertical high-pressure bands. The model confirms the sensitivity of the supplied acoustic power to the liquid level in sonobioreactors and identifies the input electrical impedance as a method of detecting resonance effects.
Acoustic phonons in chrysotile asbestos probed by high-resolution inelastic x-ray scattering
Mamontov, Eugene; Vakhrushev, S. B.; Kumzerov, Yu. A,; Alatas, A.
2009-01-01
Acoustic phonons in an individual, oriented fiber of chrysotile asbestos (chemical formula Mg{sub 3}Si{sub 2}O{sub 5}(OH){sub 4}) were observed at room temperature in the inelastic x-ray measurement with a very high (meV) resolution. The x-ray scattering vector was aligned along [1 0 0] direction of the reciprocal lattice, nearly parallel to the long axis of the fiber. The latter coincides with [1 0 0] direction of the direct lattice and the axes of the nano-channels. The data were analyzed using a damped harmonic oscillator model. Analysis of the phonon dispersion in the first Brillouin zone yielded the longitudinal sound velocity of (9200 {+-} 600) m/s.
Stimulated scattering of a whistler wave off ion-cyclotron and ion-acoustic modes in a dusty plasma
Annou, R.; Tripathi, V.K.
1998-01-01
A whistler wave propagating through a magnetized dusty plasma undergoes stimulated Brillioun scattering off ion-cyclotron and ion-acoustic modes. The dust has little effect on nonlinear coupling. However, it reduces the growth rate by introducing linear damping on the low-frequency modes. {copyright} {ital 1998 American Institute of Physics.}
Resonant raman scattering and dispersion of polar optical and acoustic phonons in hexagonal inn
Davydov, V. Yu. Klochikhin, A. A.; Smirnov, A. N.; Strashkova, I. Yu.; Krylov, A. S.; Lu Hai; Schaff, William J.; Lee, H.-M.; Hong, Y.-L.; Gwo, S.
2010-02-15
It is shown that a study of the dependence of impurity-related resonant first-order Raman scattering on the frequency of excitation light makes it possible to observe the dispersion of polar optical and acoustic branches of vibrational spectrum in hexagonal InN within a wide range of wave vectors. It is established that the wave vectors of excited phonons are uniquely related to the energy of excitation photon. Frequencies of longitudinal optical phonons E{sub 1}(LO) and A{sub 1}(LO) in hexagonal InN were measured in the range of excitation-photon energies from 2.81 to 1.17 eV and the frequencies of longitudinal acoustic phonons were measured in the range 2.81-1.83 eV of excitation-photon energies. The obtained dependences made it possible to extrapolate the dispersion of phonons A{sub 1}(LO) and E{sub 1}(LO) to as far as the point {Gamma} in the Brillouin zone and estimate the center-band energies of these phonons (these energies have not been uniquely determined so far).
Field studies in architectural acoustics using Tablet PCs
NASA Astrophysics Data System (ADS)
Boye, Daniel
2005-04-01
Core requirements for the sciences within the liberal arts curriculum challenge students to become directly involved in scientific study. These requirements seek to develop scientifically literate leaders and members of society. Formal laboratory periods are not usually associated with these courses. Thus, conceptual discovery and quantitative experimentation must take place outside of the classroom. Physics 115: Musical Technology at Davidson College is such a course and contains a section dealing with architectural acoustics. Field studies in the past have been an awkward and cumbersome activity, especially for non-science majors. The emerging technology of Tablet PCs overcomes many of the problems of mobile data acquisition and analysis, and allows the students to determine the locations of the rooms to be studied. The impulse method for determining reverberation time is used and compared with calculations based on room size and absorption media. The use of Tablet PCs and the publicly available freeware Audacity in field studies investigating architectural acoustics will be discussed. [Work supported in part by the Associated Colleges of the South through their Technology Fellowship program.
Nonstationary random acoustic and electromagnetic fields as wave diffusion processes
NASA Astrophysics Data System (ADS)
Arnaut, L. R.
2007-07-01
We investigate the effects of relatively rapid variations of the boundaries of an overmoded cavity on the stochastic properties of its interior acoustic or electromagnetic field. For quasi-static variations, this field can be represented as an ideal incoherent and statistically homogeneous isotropic random scalar or vector field, respectively. A physical model is constructed showing that the field dynamics can be characterized as a generalized diffusion process. The Langevin-It\\hato and Fokker-Planck equations are derived and their associated statistics and distributions for the complex analytic field, its magnitude and energy density are computed. The energy diffusion parameter is found to be proportional to the square of the ratio of the standard deviation of the source field to the characteristic time constant of the dynamic process, but is independent of the initial energy density, to first order. The energy drift vanishes in the asymptotic limit. The time-energy probability distribution is in general not separable, as a result of nonstationarity. A general solution of the Fokker-Planck equation is obtained in integral form, together with explicit closed-form solutions for several asymptotic cases. The findings extend known results on statistics and distributions of quasi-stationary ideal random fields (pure diffusions), which are retrieved as special cases. A summary of selected results in this paper appeared in [1].
Bi, Chuan-Xing; Chen, Xin-Zhao; Chen, Jian
2008-03-01
A technique for separating sound fields using two closely spaced parallel measurement surfaces and based on equivalent source method is proposed. The method can separate wave components crossing two measurement surfaces in opposite directions, which makes nearfield acoustic holography (NAH) applications in a field where there exist sources on the two sides of the hologram surface, in a reverberant field or in a scattered field, possible. The method is flexible in applications, simple in computation, and very easy to implement. The measurement surfaces can be arbitrarily shaped, and they are not restricted to be regular as in the traditional field separation technique. And, because the method performs field separation calculations directly in the spatial domain-not in the wave number domain--it avoids the errors and limitations (the window effects, etc.) associated with the traditional field separation technique based on the spatial Fourier transform method. In the paper, a theoretical description is first given, and the performance of the proposed field separation technique and its application in NAH are then evaluated through experiments.
Turnbull, D.; Li, S.; Morozov, A.; Suckewer, S.
2012-08-15
In a Raman plasma amplifier, the aim is to create plasma conditions in which Raman backscattering is the fastest growing instability, outrunning all competing effects so that it is possible to amplify and compress a laser beam to unprecedented unfocused intensities by utilizing that instability. However, achieving high efficiencies via this scheme has proven very difficult experimentally. Recent data show the simultaneous occurrence of stimulated Raman scattering (SRS), stimulated Brillouin scattering (SBS), and stimulated electron-acoustic scattering (SEAS). The appearance of SEAS is indicative of strong particle trapping, the existence of which is hard to justify without highlighting the interplay between SRS and SBS.
Spurious fields in time domain computations of scattering problems
NASA Technical Reports Server (NTRS)
Kangro, Urve; Nicolaides, Roy
1995-01-01
In this paper two-dimensional electromagnetic scattering problems with a time-periodic incident field are considered. The scatterer is a perfect conductor, and an artificial boundary condition is used. The large time behavior of solutions, depending on (divergence-free) initial conditions, is characterized. It turns out that in addition to the expected time-periodic solution the limiting solution may also contain a spurious stationary field. The source of the stationary field is explained and equations describing it are obtained. Several avoidance strategies are discussed, and numerical comparisons of these techniques are given.
Impurity entanglement through electron scattering in a magnetic field
NASA Astrophysics Data System (ADS)
Metavitsiadis, Alexandros; Dillenschneider, Raoul; Eggert, Sebastian
2014-04-01
We study the entanglement of magnetic impurities in an environment of electrons through successive scattering while an external magnetic field is applied. We show that the dynamics of the problem can be approximately described by a reduced model of three interacting spins, which reveals an intuitive view on how spins can be entangled by controlled electron scattering. The role of the magnetic field is rather crucial. Depending on the initial state configuration, the magnetic field can either increase or decrease the resulting entanglement but more importantly it can allow the impurities to be maximally entangled.
The applicability of Brillouin scattering to flow field diagnostics
NASA Technical Reports Server (NTRS)
Laiosa, J.; Lederman, S.
1979-01-01
To fill the void between turbulence theory and experiment; particularly in the flow fields consisting of monatomic gases, for example in wind tunnels, means of measuring fluctuating quantities are needed. In the area of density fluctuation measurement, the optical method of Brillouin scattering was suggested. This was based on the theory, that the Brillouin scattered intensity is proportional to a function of density. In this investigation the potential of this method as a diagnostic tool was studied. Here the density fluctuations in gases were sought. Continuous wave lasers and interferometers were used as the primary illuminating source and scattered light filters respectively.
Nonlinear electron acoustic waves in presence of shear magnetic field
Dutta, Manjistha; Khan, Manoranjan; Ghosh, Samiran; Chakrabarti, Nikhil
2013-12-15
Nonlinear electron acoustic waves are studied in a quasineutral plasma in the presence of a variable magnetic field. The fluid model is used to describe the dynamics of two temperature electron species in a stationary positively charged ion background. Linear analysis of the governing equations manifests dispersion relation of electron magneto sonic wave. Whereas, nonlinear wave dynamics is being investigated by introducing Lagrangian variable method in long wavelength limit. It is shown from finite amplitude analysis that the nonlinear wave characteristics are well depicted by KdV equation. The wave dispersion arising in quasineutral plasma is induced by transverse magnetic field component. The results are discussed in the context of plasma of Earth's magnetosphere.
Field Assessment of Acoustic-Doppler Based Discharge Measurements
Mueller, D.S.; ,
2002-01-01
The use of equipment based on the Doppler principle for measuring water velocity and computing discharge is common within the U.S. Geological Survey (USGS). The instruments and software have changed appreciably during the last 5 years; therefore, the USGS has begun a field validation of the instruments currently (2002) available for making discharge measurements from a moving boat in streams of various sizes. Instruments manufactured by SonTek/YSI2 and RD Instruments, Inc. were used to collect discharge data at five different sites. One or more traditional discharge measurements were made by the use of a Price AA current meter and standard USGS procedures with the acoustic instruments at each site during data collection. The discharges measured with the acoustic instruments were compared with the discharges measured with Price AA meters and the current USGS stage-discharge rating for each site. The mean discharges measured by each acoustic instrument were within 5 percent of the Price AA-based measurement and (or) discharge from the stage-discharge rating. Additional analysis of the data collected indicates that the coefficient of variation of the discharge measurements consistently was less for the RD Instruments, Inc. Rio Grandes than it was for the SonTek/YSI RiverSurveyors. The bottom-tracking referenced measurement had a lower coefficient of variation than the differentially corrected global positioning system referenced measurements. It was observed that the higher frequency RiverSurveyors measured a moving bed more often than the lower frequency Rio Grandes. The detection of a moving bed caused RiverSurveyors to be consistently biased low when referenced to bottom tracking. Differentially corrected global positioning system data may be used to remove the bias observed in the bottom-tracking referenced measurements.
Iodine-starch clathrate complexes in low-field acoustic fields
NASA Astrophysics Data System (ADS)
Fadeev, G. N.; Boldyrev, V. S.; Ermolaeva, V. I.; Eliseeva, N. M.
2013-01-01
Experimental data on the kinetics of formation and decomposition of iodine-starch clathrate complexes (amyloiodine and amylopectoiodine) in low-frequency (5-45 Hz) acoustic fields are reported. The biological activity of these compounds suggests their use as a model of biocatalysts, in which iodine represents the coenzyme active group and starch homopolysaccharides (amylopectin and amylose) represents the apoenzyme.
Douma, Huub; Vasconcelos, Ivan; Snieder, Roel
2011-05-01
By analyzing correlation-type reciprocity theorems for wavefields in perturbed media, it is shown that the correlation-type reciprocity theorem for the scattered field is the progenitor of the generalized optical theorem. This reciprocity theorem, in contrast to the generalized optical theorem, allows for inhomogeneous background properties and does not make use of a far-field condition. This theorem specializes to the generalized optical theorem when considering a finite-size scatterer embedded in a homogeneous background medium and when utilizing the far-field condition. Moreover, it is shown that the reciprocity theorem for the scattered field is responsible for the cancellation of non-physical (spurious) arrivals in seismic interferometry, and as such provides the mathematical description of such arrivals. Even though here only acoustic waves are treated, the presented treatment is not limited to such wavefields and can be generalized to general wavefields. Therefore, this work provides the framework for deriving equivalents of the generalized optical theorem for general wavefields. PMID:21568381
Acoustic scattering by circular cylinders of various aspect ratios. [pressure gradient microphones
NASA Technical Reports Server (NTRS)
Maciulaitis, A.
1979-01-01
The effects of acoustic scattering on the useful frequency range of pressure gradient microphones were investigated experimentally between ka values of 0.407 and 4.232 using two circular cylindrical models (L/D = 0.5 and 0.25) having a 25 cm outside diameter. Small condenser microphones, attached to preamplifiers by flexible connectors, were installed from inside the cylindrical bodies, and flush mounted on the exterior surface of the cylinders. A 38 cm diameter woofer in a large speaker enclosure was used as the sound source. Surface pressure augmentation and phase differences were computed from measured data for various sound wave incidence angles. Results are graphically compared with theoretical predictions supplied by NASA for ka = 0.407, 2.288, and 4.232. All other results are tabulated in the appendices. With minor exceptions, the experimentally determined pressure augmentations agreed within 0.75 dB with theoretical predictions. The agreement for relative phase angles was within 5 percent without any exceptions. Scattering parameter variations with ka and L/D ratio, as computed from experimental data, are also presented.
Some far-field acoustics characteristics of the XV-15 tilt-rotor aircraft
NASA Technical Reports Server (NTRS)
Golub, Robert A.; Conner, David A.; Becker, Lawrence E.; Rutledge, C. Kendall; Smith, Rita A.
1990-01-01
Far-field acoustics tests have been conducted on an instrumented XV-15 tilt-rotor aircraft. The purpose of these acoustic measurements was to create an encompassing, high confidence (90 percent), and accurate (-1.4/ +1/8 dB theoretical confidence interval) far-field acoustics data base to validate ROTONET and other current rotorcraft noise prediction computer codes. This paper describes the flight techniques used, with emphasis on the care taken to obtain high-quality far-field acoustic data. The quality and extensiveness of the data base collected are shown by presentation of ground acoustic contours for level flyovers for the airplane flight mode and for several forward velocities and nacelle tilts for the transition mode and helicopter flight mode. Acoustic pressure time-histories and fully analyzed ensemble averaged far-field data results (spectra) are shown for each of the ground contour cases.
Mott scattering in an elliptically polarized laser field
Attaourti, Y.; Manaut, B.; Taj, S.
2004-08-01
We study Mott scattering in the presence of a strong elliptically polarized field. Using the first Born approximation and the Dirac-Volkov states for the electron, we obtain an analytic formula for the unpolarized differential cross section. This generalizes the results found for the linearly polarized field by Li et al. [ 67, 063409 (2003)] and for the circularly polarized field by Attaourti and Manaut [ 68, 067401 (2003)].
Numerical derivation of forces on particles and agglomerates in a resonant acoustic field
NASA Astrophysics Data System (ADS)
Knoop, Claas; Fritsching, Udo
2013-10-01
Particles and agglomerates are investigated in gaseous acoustic flow fields. Acoustic fields exert forces on solid objects, which can influence the shape of the exposed bodies, even to the point of breakage of the structures. Motivated by experimentally observed breakage of agglomerates in an acoustic levitator (f = 20 kHz), a numerical study is presented that derives the acoustic forces on a complex model agglomerate from the pressure and velocity fields of a resonant standing ultrasound wave, calculated by computational fluid dynamics (CFD). It is distinguished between the drag and lift/lateral forces on the overall agglomerate and on the different primary particles of the model.
Mott scattering of polarized electrons in a strong laser field
Manaut, B.; Taj, S.; Attaourti, Y.
2005-04-01
We present analytical and numerical results of the relativistic calculation of the transition matrix element S{sub fi} and differential cross sections for Mott scattering of initially polarized Dirac particles (electrons) in the presence of a strong laser field with linear polarization. We use exact Dirac-Volkov wave functions to describe the dressed electrons and the collision process is treated in the first Born approximation. The influence of the laser field on the degree of polarization of the scattered electron is reported.
Analytic expression for in-field scattered light distribution
NASA Astrophysics Data System (ADS)
Peterson, Gary L.
2004-01-01
Light that is scattered from lenses and mirrors in an optical system produces a halo of stray light around bright objects within the field of view. The angular distribution of scattered light from any one component is usually described by the Harvey model. This paper presents analytic expressions for the scattered irradiance at a focal plane from optical components that scatter light in accordance with the Harvey model. It is found that the irradiance is independent of the location of an optical element within the system, provided the element is not located at or near an intermediate image plane. It is also found that the irradiance has little or no dependence on the size of the element.
Orbital motions of bubbles in an acoustic field
NASA Astrophysics Data System (ADS)
Shirota, Minori; Yamashita, Ko; Inamura, Takao
2012-09-01
This experimental study aims to clarify the mechanism of orbital motion of two oscillating bubbles in an acoustic field. Trajectory of the orbital motion on the wall of a spherical levitator was observed using a high-speed video camera. Because of a good repeatability in volume oscillation of bubbles, we were also able to observe the radial motion driven at 24 kHz by stroboscopic like imaging technique. The orbital motions of bubbles raging from 0.13 to 0.18 mm were examined with different forcing amplitude and in different viscous oils. As a result, we found that pairs of bubbles revolve along an elliptic orbit around the center of mass of the bubbles. We also found that the two bubbles perform anti-phase radial oscillation. Although this radial oscillation should result in a repulsive secondary Bjerknes force, the bubbles kept a constant separate distance of about 1 mm, which indicates the existence of centripetal primary Bjerknes force.
Convergent acoustic field of view in echolocating bats.
Jakobsen, Lasse; Ratcliffe, John M; Surlykke, Annemarie
2013-01-01
Most echolocating bats exhibit a strong correlation between body size and the frequency of maximum energy in their echolocation calls (peak frequency), with smaller species using signals of higher frequency than larger ones. Size-signal allometry or acoustic detection constraints imposed on wavelength by preferred prey size have been used to explain this relationship. Here we propose the hypothesis that smaller bats emit higher frequencies to achieve directional sonar beams, and that variable beam width is critical for bats. Shorter wavelengths relative to the size of the emitter translate into more directional sound beams. Therefore, bats that emit their calls through their mouths should show a relationship between mouth size and wavelength, driving smaller bats to signals of higher frequency. We found that in a flight room mimicking a closed habitat, six aerial hawking vespertilionid species (ranging in size from 4 to 21 g, ref. 5) produced sonar beams of extraordinarily similar shape and volume. Each species had a directivity index of 11 ± 1 dB (a half-amplitude angle of approximately 37°) and an on-axis sound level of 108 ± 4 dB sound pressure level referenced to 20 μPa root mean square at 10 cm. Thus all bats adapted their calls to achieve similar acoustic fields of view. We propose that the necessity for high directionality has been a key constraint on the evolution of echolocation, which explains the relationship between bat size and echolocation call frequency. Our results suggest that echolocation is a dynamic system that allows different species, regardless of their body size, to converge on optimal fields of view in response to habitat and task.
Risk of a second cancer from scattered radiation in acoustic neuroma treatment
NASA Astrophysics Data System (ADS)
Yoon, Myonggeun; Lee, Hyunho; Sung, Jiwon; Shin, Dongoh; Park, Sungho; Chung, Weon Kuu; Jahng, Geon-Ho; Kim, Dong Wook
2014-06-01
The present study aimed to compare the risk of a secondary cancer from scattered and leakage doses in patients receiving intensity-modulated radiotherapy (IMRT), volumetric modulated arc therapy (VMAT), and stereotactic radiosurgery (SRS). Four acoustic neuroma patients were treated with IMRT, VMAT, or SRS. Their excess relative risk (ERR), excess absolute risk (EAR), and lifetime attributable risk (LAR) of a secondary cancer were estimated using the corresponding secondary doses measured at various organs by using radio-photoluminescence glass dosimeters (RPLGD) placed inside a humanoid phantom. When a prescription dose was delivered in the planning target volume of the 4 patients, the average organ equivalent doses (OED) at the thyroid, lung, liver, bowel, bladder, prostate (or ovary), and rectum were 14.6, 1.7, 0.9, 0.8, 0.6, 0.6, and 0.6 cGy, respectively, for IMRT whereas they were 19.1, 1.8, 2.0, 0.6, 0.4, 0.4, and 0.4 cGy, respectively, for VMAT, and 22.8, 4.6, 1.4, 0.7, 0.5, 0.5, and 0.5 cGy, respectively, for SRS. The OED decreased as the distance from the primary beam increased. The thyroid received the highest OED compared to other organs. A lifetime attributable risk evaluation estimated that more than 0.03% of acoustic neuroma (AN) patients would get radiation-induced cancer within 20 years of receiving radiation therapy. The organ with the highest radiation-induced cancer risk after radiation treatment for AN was the thyroid. We found that the LAR could be increased by the transmitted dose from the primary beam. No modality-specific difference in radiation-induced cancer risk was observed in our study.
Upcoming new international measurement standards in the field of building acoustics
NASA Astrophysics Data System (ADS)
Goydke, Hans
2002-11-01
The extensively completed revision of most of the ISO measurement standards in building acoustics mainly initiated by the European Commissions demand for harmonized standards emphasized the insight that the main goal to avoid trade barriers between the countries can only be reached when the standards sufficiently and comprehensively cover the field when they are related to the actual state of the art and when they are sufficiently related to practice. In modern architecture one can observe the rapid change in the use of building materials, for instance regarding the use of glass. Lightweight constructions as well as heavyweight building elements with additional linings are increasingly in common use and unquestionably there are consequences to be considered regarding the ascertainment of sound insulation properties. Besides others, International Standardization is unsatisfactory regarding the assessment of noise in buildings from waste water installations, in the low frequency area and in general regarding the expression of uncertainty of measurements. Intensity measurements in building acoustics, rainfall noise assessment, estimation of sound insulation, impulse response measurement methods, assessment of sound scattering are examples of upcoming standards.
Acoustic assisted, field-induced strain in ferromagnetic shape memory alloys
NASA Astrophysics Data System (ADS)
Peterson, Bradley W.; Feuchtwanger, Jorge; Chambers, Joshua M.; Bono, David; Hall, Steven R.; Allen, Samuel M.; O'Handley, Robert C.
2004-06-01
A technique has been developed that uses acoustic energy to assist a magnetic field in driving twin boundary motion in a NiMnGa single crystal. Acoustic assisted magnetic-field-induced strain has been observed to increase the magnetic-field-induced strain response by up to one order of magnitude. This effect is most pronounced for magnetic field drives near the twin boundary threshold field. Increasing frequency of the acoustic wave input is shown to increase strain up to about 4 kHz after which there is a small decline in FSMA strain for higher frequencies.
Coulomb field scattering in Born-Infeld electrodynamics
Tennant, Daniel
2011-02-15
In the context of Born-Infeld electrodynamics, the electromagnetic fields interact with each other via their nonlinear couplings. A calculation will be performed where an incoming electromagnetic plane wave scatters off a Coulomb field in the geometrical optics approximation. In addition to finding the first-order angle of deflection, exact solutions for the trajectory will also be found. The possibility of electromagnetic bound states will be discussed.
NASA Astrophysics Data System (ADS)
Guillermin, R.; Lasaygues, P.; Sessarego, J. P.; Wirgin, A.
2000-12-01
This paper is concerned with the reconstruction, from measured (synthetic and experimental) data, of a 2D penetrable fluid-like cylindrical object of arbitrary cross-section imbedded in a fluid-like (sediment) half-space separated by a plane interface from another fluid half-space (deep water) wherein propagates a plane acoustic interrogating wave. The Green theorem is used to provide (1) a domain integral representation (DIR) of the scattered field and (2) a domain integral equation (DIE) for the pressure field in a test region containing the object. Both the DIE and DIR are discretized by collocation, thereby leading to a linear system of equations for the discretized pressure in the test region and a linear transform for the discretized pressure outside the test region. This is the means adopted herein for generating synthetic scattered field data. The inverse problem is linearized by replacing the (unknown) field in the test region by the (known) field which is established in the water/sediment system in the absence of the object. Using this Born approximation and minimizing the discrepancy between the measured and model scattered fields gives rise to a linear system of equations for the (unknown) discretized index-of-refraction contrast function in the test region. Due to its ill conditioned nature, the linear system is solved by a singular value decomposition technique. Images of the index-of-refraction contrast representation of the object obtained by inversion of both simulated and experimentally measured scattered field data are presented and compared.
Inverse elastic surface scattering with near-field data
NASA Astrophysics Data System (ADS)
Li, Peijun; Wang, Yuliang; Zhao, Yue
2015-03-01
Consider the scattering of a time-harmonic plane wave by a one-dimensional periodic surface. A novel computational method is proposed for solving the inverse elastic surface scattering problem by using the near-field data. Above the surface, the space is filled with a homogeneous and isotropic elastic medium, while the space below the surface is assumed to be elastically rigid. Given an incident field, the inverse problem is to reconstruct the surface from the displacement of the wave field at a horizontal line above the surface. This paper is a nontrivial extension of the authors’ recent work on near-field imaging of the Helmholtz equation and the Maxwell equation to the more complicated Navier equation due to coexistence of the compressional and shear waves that propagate at different speed. Based on the Helmholtz decomposition, the wave field is decomposed into its compressional and shear parts by using two scalar potential functions. The transformed field expansion is then applied to each component and a coupled recurrence relation is obtained for their power series expansions. By solving the coupled system in the frequency domain, simple and explicit reconstruction formulas are derived for two types of measurement data. The method requires only a single illumination with a fixed frequency and incident angle. Numerical experiments show that it is simple, effective, and efficient to reconstruct the scattering surfaces with subwavelength resolution. The research was supported in part by the NSF grant DMS-1151308.
Malhotra, M.
1996-12-31
Finite-element discretizations of time-harmonic acoustic wave problems in exterior domains result in large sparse systems of linear equations with complex symmetric coefficient matrices. In many situations, these matrix problems need to be solved repeatedly for different right-hand sides, but with the same coefficient matrix. For instance, multiple right-hand sides arise in radiation problems due to multiple load cases, and also in scattering problems when multiple angles of incidence of an incoming plane wave need to be considered. In this talk, we discuss the iterative solution of multiple linear systems arising in radiation and scattering problems in structural acoustics by means of a complex symmetric variant of the BL-QMR method. First, we summarize the governing partial differential equations for time-harmonic structural acoustics, the finite-element discretization of these equations, and the resulting complex symmetric matrix problem. Next, we sketch the special version of BL-QMR method that exploits complex symmetry, and we describe the preconditioners we have used in conjunction with BL-QMR. Finally, we report some typical results of our extensive numerical tests to illustrate the typical convergence behavior of BL-QMR method for multiple radiation and scattering problems in structural acoustics, to identify appropriate preconditioners for these problems, and to demonstrate the importance of deflation in block Krylov-subspace methods. Our numerical results show that the multiple systems arising in structural acoustics can be solved very efficiently with the preconditioned BL-QMR method. In fact, for multiple systems with up to 40 and more different right-hand sides we get consistent and significant speed-ups over solving the systems individually.
Chu, Dezhang; Lawson, Gareth L; Wiebe, Peter H
2016-05-01
The linear inversion commonly used in fisheries and zooplankton acoustics assumes a constant inversion kernel and ignores the uncertainties associated with the shape and behavior of the scattering targets, as well as other relevant animal parameters. Here, errors of the linear inversion due to uncertainty associated with the inversion kernel are quantified. A scattering model-based nonlinear inversion method is presented that takes into account the nonlinearity of the inverse problem and is able to estimate simultaneously animal abundance and the parameters associated with the scattering model inherent to the kernel. It uses sophisticated scattering models to estimate first, the abundance, and second, the relevant shape and behavioral parameters of the target organisms. Numerical simulations demonstrate that the abundance, size, and behavior (tilt angle) parameters of marine animals (fish or zooplankton) can be accurately inferred from the inversion by using multi-frequency acoustic data. The influence of the singularity and uncertainty in the inversion kernel on the inversion results can be mitigated by examining the singular values for linear inverse problems and employing a non-linear inversion involving a scattering model-based kernel. PMID:27250181
Collective Thomson scattering measurements of the Ion Acoustic Decay Instability. Final report
Mizuno, K.; DeGroot, J.S.; Drake, R.P.; Seka, W.
1993-12-31
We have developed an uv collective Thomson scattering system for plasma produced by a short wavelength laser. The Ion Acoustic Decay Instabilities are studied in a large ({approximately}mm) scale, hot ({approximately}keV) plasma, which is relevant to a direct-driven laser fusion plasma. The IADI primary decay process is measured by the CTS. We used a random phase plate to minimize the non uniform irradiation of the interaction laser. Nevertheless, the threshold of the most unstable mode driven by the IADI is quite low. The measured threshold value agrees favorably with the theoretical value of the large scale plasma. We have also shown that the CTS from the IADI can be a good tool for measuring a local electron temperature. The measured results agree reasonably with the SAGE computer calculations. We used the real part of the wave (frequency) to estimate T{sub e}. The real part is, in general, reliable compared to the imaginary part such as the damping, and the growth rates. We have shown that the IADI can be easily excited in a large scale, hot plasma. The IADI has potentially important applications to direct drive laser fusion, and also critical surface diagnostic.
NASA Technical Reports Server (NTRS)
Hu, Fang Q.; Pizzo, Michelle E.; Nark, Douglas M.
2016-01-01
Based on the time domain boundary integral equation formulation of the linear convective wave equation, a computational tool dubbed Time Domain Fast Acoustic Scattering Toolkit (TD-FAST) has recently been under development. The time domain approach has a distinct advantage that the solutions at all frequencies are obtained in a single computation. In this paper, the formulation of the integral equation, as well as its stabilization by the Burton-Miller type reformulation, is extended to cases of a constant mean flow in an arbitrary direction. In addition, a "Source Surface" is also introduced in the formulation that can be employed to encapsulate regions of noise sources and to facilitate coupling with CFD simulations. This is particularly useful for applications where the noise sources are not easily described by analytical source terms. Numerical examples are presented to assess the accuracy of the formulation, including a computation of noise shielding by a thin barrier motivated by recent Historical Baseline F31A31 open rotor noise shielding experiments. Furthermore, spatial resolution requirements of the time domain boundary element method are also assessed using point per wavelength metrics. It is found that, using only constant basis functions and high-order quadrature for surface integration, relative errors of less than 2% may be obtained when the surface spatial resolution is 5 points-per-wavelength (PPW) or 25 points-per-wavelength squared (PPW2).
Time-frequency analysis of the bistatic acoustic scattering from a spherical elastic shell.
Anderson, Shaun D; Sabra, Karim G; Zakharia, Manell E; Sessarego, Jean-Pierre
2012-01-01
The development of low-frequency sonar systems, using, for instance, a network of autonomous systems in unmanned vehicles, provides a practical means for bistatic measurements (i.e., when the source and receiver are widely separated) allowing for multiple viewpoints of the target of interest. Time-frequency analysis, in particular, Wigner-Ville analysis, takes advantage of the evolution time dependent aspect of the echo spectrum to differentiate a man-made target, such as an elastic spherical shell, from a natural object of the similar shape. A key energetic feature of fluid-loaded and thin spherical shell is the coincidence pattern, also referred to as the mid-frequency enhancement (MFE), that results from antisymmetric Lamb-waves propagating around the circumference of the shell. This article investigates numerically the bistatic variations of the MFE with respect to the monostatic configuration using the Wigner-Ville analysis. The observed time-frequency shifts of the MFE are modeled using a previously derived quantitative ray theory by Zhang et al. [J. Acoust. Soc. Am. 91, 1862-1874 (1993)] for spherical shell's scattering. Additionally, the advantage of an optimal array beamformer, based on joint time delays and frequency shifts is illustrated for enhancing the detection of the MFE recorded across a bistatic receiver array when compared to a conventional time-delay beamformer.
Burton-Miller-type singular boundary method for acoustic radiation and scattering
NASA Astrophysics Data System (ADS)
Fu, Zhuo-Jia; Chen, Wen; Gu, Yan
2014-08-01
This paper proposes the singular boundary method (SBM) in conjunction with Burton and Miller's formulation for acoustic radiation and scattering. The SBM is a strong-form collocation boundary discretization technique using the singular fundamental solutions, which is mathematically simple, easy-to-program, meshless and introduces the concept of source intensity factors (SIFs) to eliminate the singularities of the fundamental solutions. Therefore, it avoids singular numerical integrals in the boundary element method (BEM) and circumvents the troublesome placement of the fictitious boundary in the method of fundamental solutions (MFS). In the present method, we derive the SIFs of exterior Helmholtz equation by means of the SIFs of exterior Laplace equation owing to the same order of singularities between the Laplace and Helmholtz fundamental solutions. In conjunction with the Burton-Miller formulation, the SBM enhances the quality of the solution, particularly in the vicinity of the corresponding interior eigenfrequencies. Numerical illustrations demonstrate efficiency and accuracy of the present scheme on some benchmark examples under 2D and 3D unbounded domains in comparison with the analytical solutions, the boundary element solutions and Dirichlet-to-Neumann finite element solutions.
An immersed boundary computational model for acoustic scattering problems with complex geometries.
Sun, Xiaofeng; Jiang, Yongsong; Liang, An; Jing, Xiaodong
2012-11-01
An immersed boundary computational model is presented in order to deal with the acoustic scattering problem by complex geometries, in which the wall boundary condition is treated as a direct body force determined by satisfying the non-penetrating boundary condition. Two distinct discretized grids are used to discrete the fluid domain and immersed boundary, respectively. The immersed boundaries are represented by Lagrangian points and the direct body force determined on these points is applied on the neighboring Eulerian points. The coupling between the Lagrangian points and Euler points is linked by a discrete delta function. The linearized Euler equations are spatially discretized with a fourth-order dispersion-relation-preserving scheme and temporal integrated with a low-dissipation and low-dispersion Runge-Kutta scheme. A perfectly matched layer technique is applied to absorb out-going waves and in-going waves in the immersed bodies. Several benchmark problems for computational aeroacoustic solvers are performed to validate the present method.
NASA Astrophysics Data System (ADS)
Denis, V.; Pelat, A.; Gautier, F.
2016-02-01
The so-called "acoustic black hole" (ABH) effect is a passive vibration control technique based on the flexural waves properties in thin structure of varying thickness. A usual implementation consists in using a plate with tapered extremity with a power-law profile, covered with a thin damping layer. The inhomogeneity of the structure leads to a decrease of flexural wave speed and an increase of their amplitude, therefore resulting in an efficient energy dissipation if damping layer is placed where the thickness is minimal. The manufacture of an efficient extremity is difficult because of the small thickness, and often generates imperfections and tearing. Moreover, previous works suggest that multiple flexural modes are propagating across the width of the ABH tip. A model of an ABH multimodal waveguide taking into account an imperfect termination is developed. It shows that an elementary imperfection can affect the reflection coefficient of the extremity and reduce it. Scattering and propagation properties of the extremity are also studied. An incident mode excites several modes that are localised in the tapered region and local resonances explain the drops in the reflection coefficient. Experimental evidence of the influence of the imperfection on the reflection coefficient is provided. A key result of the paper is that manufacturing imperfections are not detrimental to the ABH effect.
Baik, Kyungmin; Dudley, Christopher; Marston, Philip L
2011-12-01
When synthetic aperture sonar (SAS) is used to image elastic targets in water, subtle features can be present in the images associated with the dynamical response of the target being viewed. In an effort to improve the understanding of such responses, as well as to explore alternative image processing methods, a laboratory-based system was developed in which targets were illuminated by a transient acoustic source, and bistatic responses were recorded by scanning a hydrophone along a rail system. Images were constructed using a relatively conventional bistatic SAS algorithm and were compared with images based on supersonic holography. The holographic method is a simplification of one previously used to view the time evolution of a target's response [Hefner and Marston, ARLO 2, 55-60 (2001)]. In the holographic method, the space-time evolution of the scattering was used to construct a two-dimensional image with cross range and time as coordinates. Various features for vertically hung cylindrical targets were interpreted using high frequency ray theory. This includes contributions from guided surface elastic waves, as well as transmitted-wave features and specular reflection.
Acoustic scattering by elastic cylinders of elliptical cross-section and splitting up of resonances
Ancey, S. Bazzali, E. Gabrielli, P. Mercier, M.
2014-05-21
The scattering of a plane acoustic wave by an infinite elastic cylinder of elliptical cross section is studied from a modal formalism by emphasizing the role of the symmetries. More precisely, as the symmetry is broken in the transition from the infinite circular cylinder to the elliptical one, the splitting up of resonances is observed both theoretically and experimentally. This phenomenon can be interpreted using group theory. The main difficulty stands in the application of this theory within the framework of the vectorial formalism in elastodynamics. This method significantly simplifies the numerical treatment of the problem, provides a full classification of the resonances, and gives a physical interpretation of the splitting up in terms of symmetry breaking. An experimental part based on ultrasonic spectroscopy complements the theoretical study. A series of tank experiments is carried out in the case of aluminium elliptical cylinders immersed in water, in the frequency range 0 ≤ kr ≤ 50, where kr is the reduced wave number in the fluid. The symmetry is broken by selecting various cylinders of increasing eccentricity. More precisely, the greater the eccentricity, the higher the splitting up of resonances is accentuated. The experimental results provide a very good agreement with the theoretical ones, the splitting up is observed on experimental form functions, and the split resonant modes are identified on angular diagrams.
NASA Astrophysics Data System (ADS)
Sovardi, Carlo; Jaensch, Stefan; Polifke, Wolfgang
2016-09-01
A numerical method to concurrently characterize both aeroacoustic scattering and noise sources at a duct singularity is presented. This approach combines Large Eddy Simulation (LES) with techniques of System Identification (SI): In a first step, a highly resolved LES with external broadband acoustic excitation is carried out. Subsequently, time series data extracted from the LES are post-processed by means of SI to model both acoustic propagation and noise generation. The present work studies the aero-acoustic characteristics of an orifice placed in a duct at low flow Mach numbers with the "LES-SI" method. Parametric SI based on the Box-Jenkins mathematical structure is employed, with a prediction error approach that utilizes correlation analysis of the output residuals to avoid overfitting. Uncertainties of model parameters due to the finite length of times series are quantified in terms of confidence intervals. Numerical results for acoustic scattering matrices and power spectral densities of broad-band noise are validated against experimental measurements over a wide range of frequencies below the cut-off frequency of the duct.
NASA Astrophysics Data System (ADS)
Powell, Jesse R.; Ohman, Mark D.
2015-05-01
We report cross-frontal changes in the characteristics of plankton proxy variables measured by autonomous Spray ocean gliders operating within the Southern California Current System (SCCS). A comparison of conditions across the 154 positive frontal gradients (i.e., where density of the surface layer decreased in the offshore direction) identified from six years of continuous measurements showed that waters on the denser side of the fronts typically showed higher Chl-a fluorescence, shallower euphotic zones, and higher acoustic backscatter than waters on the less dense side. Transitions between these regions were relatively abrupt. For positive fronts the amplitude of Diel Vertical Migration (DVM), inferred from a 3-beam 750 kHz acoustic Doppler profiler, increased offshore of fronts and covaried with optical transparency of the water column. Average interbeam variability in acoustic backscatter also changed across many positive fronts within 3 depth strata (0-150 m, 150-400 m, and 400-500 m), revealing a front-related change in the acoustic scattering characteristics of the assemblages. The extent of vertical stratification of distinct scattering assemblages was also more pronounced offshore of positive fronts. Depth-stratified zooplankton samples collected by Mocness nets corroborated the autonomous measurements, showing copepod-dominated assemblages and decreased zooplankton body sizes offshore and euphausiid-dominated assemblages with larger median body sizes inshore of major frontal features.
Evanescent-wave scattering in near-field optical microscopy.
Wannemacher, R; Quinten, M; Pack, A
1999-01-01
Extended Mie theory is used to investigate the scattering and extinction of evanescent waves by small spherical particles and aggregates of such particles. Metallic, dielectric and metal-coated dielectric particles are taken into consideration. In contrast to plane-wave excitation, p- and s-polarized spectra differ in the case of evanescent waves due to the inherent asymmetry of both polarizations. Furthermore, contributions from higher multipoles are strongly enhanced, compared with plane-wave excitation, and the enhancement factors are polarization dependent. The corresponding changes in the scattering and extinction spectra are most pronounced in cases where higher multipoles exhibit resonances in the spectral range considered. This applies, for example, to morphological resonances of dielectric particles with size parameters > 1. The effect of the surface, where the evanescent wave is generated by total internal reflection, on the scattering and extinction spectra is investigated via numerical field calculations employing the multiple multipole method. In an application to apertureless near-field optical microscopy, the variation of the scattered power is calculated when a silicon particle is scanned across a silver particle in the evanescent field.
Dynamics of Dollard asymptotic variables. Asymptotic fields in Coulomb scattering
NASA Astrophysics Data System (ADS)
Morchio, G.; Strocchi, F.
2016-03-01
Generalizing Dollard’s strategy, we investigate the structure of the scattering theory associated to any large time reference dynamics UD(t) allowing for the existence of Møller operators. We show that (for each scattering channel) UD(t) uniquely identifies, for t →±∞, asymptotic dynamics U±(t); they are unitary groups acting on the scattering spaces, satisfy the Møller interpolation formulas and are interpolated by the S-matrix. In view of the application to field theory models, we extend the result to the adiabatic procedure. In the Heisenberg picture, asymptotic variables are obtained as LSZ-like limits of Heisenberg variables; their time evolution is induced by U±(t), which replace the usual free asymptotic dynamics. On the asymptotic states, (for each channel) the Hamiltonian can by written in terms of the asymptotic variables as H = H±(qout/in,pout/in), H±(q,p) the generator of the asymptotic dynamics. As an application, we obtain the asymptotic fields ψout/in in repulsive Coulomb scattering by an LSZ modified formula; in this case, U±(t) = U0(t), so that ψout/in are free canonical fields and H = H0(ψout/in).
The Dynamics of Vapor Bubbles in Acoustic Pressure Fields
NASA Technical Reports Server (NTRS)
Hao, Y.; Prosperetti, A.
1999-01-01
In spite of a superficial similarity with gas bubbles, the intimate coupling between dynamical and thermal processes confers to oscillating vapor bubbles some unique characteristics. This paper examines numerically the validity of some asymptotic-theory predictions such as the existence of two resonant radii and a limit size for a given sound amplitude and frequency. It is found that a small vapor bubble in a sound field of sufficient amplitude grows quickly through resonance and continues to grow thereafter at a very slow rate, seemingly indefinitely. Resonance phenomena therefore play a role for a few cycles at most, and reaching a limit size-if one exists at all-is found to require far more than several tens of thousands of cycles. It is also found that some small bubbles may grow or collapse depending on the phase of the sound field. The model accounts in detail for the thermo-fluid-mechanic processes in the vapor. In the second part of the paper, an approximate formulation valid for bubbles small with respect to the thermal penetration length in the vapor is derived and its accuracy examined, The present findings have implications for acoustically enhanced boiling heat transfer and other special applications such as boiling in microgravity.
NASA Astrophysics Data System (ADS)
Bemis, K. G.; Rona, P. A.; Santilli, K.; Dastur, J.; Silver, D.
2004-12-01
Optical and acoustic scattering from particles in a seafloor hydrothermal plume can be related if the particle properties and scattering mechanisms are known. We assume Rayleigh backscattering of sound and Mie forward scattering of light. We then use the particle concentrations implicit in the observed acoustic backscatter intensity to recreate the optical image a camera would see given a particular lighting level. The motivation for this study is to discover what information on particle size and composition in the buoyant plume can be inferred from a comparison of the calculated optical images (based on acoustic data) with actual video images from the acoustic acquisition cruise and the IMAX film "Volcanoes of the Deep Sea" (Stephen Low Productions, Inc.). Because the geologists, biologists and oceanographers involved in the study of seafloor hydrothermal plumes all "see" plumes in different ways, an additional motivation is to create more realistic plume images from the acoustic data. By using visualization techniques, with realistic lighting models, we can convert the plume image from mechanical waves (sound) to electromagnetic waves (light). The resulting image depends on assumptions about the particle size distribution and composition. Conversion of the volume scattering coefficients from Rayleigh to Mie scattering is accomplished by an extinction scale factor that depends on the wavelengths of light and sound and on the average particle size. We also make an adjustment to the scattered light based on the particles reflectivity (albedo) and color. We present a series of images of acoustic data for Grotto Plume, Main Endeavour Field (within the Endeavour ISS Site) using both realistic lighting models and traditional visualization techniques to investigate the dependence of the images on assumptions about particle composition and size. Sensitivity analysis suggests that the visibility of the buoyant plume increases as the intensity of supplied light increases
Thomson scattering in magnetic fields. [of white dwarf stars
NASA Technical Reports Server (NTRS)
Whitney, Barbara
1989-01-01
The equation of transfer in Thomson scattering atmospheres with magnetic fields is solved using Monte Carlo methods. Two cases, a plane parallel atmosphere with a magnetic field perpendicular to the atmosphere, and a dipole star, are investigated. The wavelength dependence of polarization from plane-parallel atmosphere is qualitatively similar to that observed in the magnetic white dwarf Grw+70 deg 8247, and the field strength determined by the calculation, 320 MG, is quantitatively similar to that determined from the line spectrum. The dipole model does not resemble the data as well as the single plane-parallel atmosphere.
NASA Astrophysics Data System (ADS)
Yang, Yang; Li, Xiukun
2016-06-01
Separation of the components of rigid acoustic scattering by underwater objects is essential in obtaining the structural characteristics of such objects. To overcome the problem of rigid structures appearing to have the same spectral structure in the time domain, time-frequency Blind Source Separation (BSS) can be used in combination with image morphology to separate the rigid scattering components of different objects. Based on a highlight model, the separation of the rigid scattering structure of objects with time-frequency distribution is deduced. Using a morphological filter, different characteristics in a Wigner-Ville Distribution (WVD) observed for single auto term and cross terms can be simplified to remove any cross-term interference. By selecting time and frequency points of the auto terms signal, the accuracy of BSS can be improved. An experimental simulation has been used, with changes in the pulse width of the transmitted signal, the relative amplitude and the time delay parameter, in order to analyzing the feasibility of this new method. Simulation results show that the new method is not only able to separate rigid scattering components, but can also separate the components when elastic scattering and rigid scattering exist at the same time. Experimental results confirm that the new method can be used in separating the rigid scattering structure of underwater objects.
NASA Astrophysics Data System (ADS)
Shiiba, Michihisa; Okada, Nagaya; Kurosawa, Minoru; Takeuchi, Shinichi
2016-07-01
Novel anticavitation hydrophones were fabricated by depositing a hydrothermally synthesized lead zirconate titanate polycrystalline film at the back of a titanium front plate. These anticavitation hydrophones were not damaged by the measurement of the acoustic field formed by a high-intensity focused ultrasound (HIFU) device. Their sensitivity was improved by approximately 20 dB over that of the conventional anticavitation hydrophone by modifying their basic structure and materials. The durability of the anticavitation hydrophone that we fabricated was compared by exposing it to a high-intensity acoustic field at the focal point of the HIFU field and in the water tank of an ultrasound cleaner. Therefore, the effect of the surface of the titanium front plate on acoustic cavitation was investigated by exposing such a surface to the high-intensity acoustic field. We found that the fabricated anticavitation hydrophone was robust and was not damaged easily, even in the focused acoustic field where acoustic cavitation occurs.
Li, Faqi; Zeng, Deping; He, Min; Wang, Zhibiao E-mail: wangzhibiao@haifu.com.cn; Song, Dan; Lei, Guangrong; Lin, Zhou; Zhang, Dong E-mail: wangzhibiao@haifu.com.cn; Wu, Junru
2015-12-15
Resolution of high intensity focused ultrasound (HIFU) focusing is limited by the wave diffraction. We have developed a spherical cavity transducer with two open ends to improve the focusing precision without sacrificing the acoustic intensity (App Phys Lett 2013; 102: 204102). This work aims to theoretically and experimentally investigate the frequency dependence of the acoustic field generated from the spherical cavity transducer with two open ends. The device emits high intensity ultrasound at the frequency ranging from 420 to 470 kHz, and the acoustic field is measured by a fiber optic probe hydrophone. The measured results shows that the spherical cavity transducer provides high acoustic intensity for HIFU treatment only in its resonant modes, and a series of resonant frequencies can be choosen. Furthermore, a finite element model is developed to discuss the frequency dependence of the acoustic field. The numerical simulations coincide well with the measured results.
An effective field theory for forward scattering and factorization violation
NASA Astrophysics Data System (ADS)
Rothstein, Ira Z.; Stewart, Iain W.
2016-08-01
Starting with QCD, we derive an effective field theory description for forward scattering and factorization violation as part of the soft-collinear effective field theory (SCET) for high energy scattering. These phenomena are mediated by long distance Glauber gluon exchanges, which are static in time, localized in the longitudinal distance, and act as a kernel for forward scattering where | t| ≪ s. In hard scattering, Glauber gluons can induce corrections which invalidate factorization. With SCET, Glauber exchange graphs can be calculated explicitly, and are distinct from graphs involving soft, collinear, or ultrasoft gluons. We derive a complete basis of operators which describe the leading power effects of Glauber exchange. Key ingredients include regulating light-cone rapidity singularities and subtractions which prevent double counting. Our results include a novel all orders gauge invariant pure glue soft operator which appears between two collinear rapidity sectors. The 1-gluon Feynman rule for the soft operator coincides with the Lipatov vertex, but it also contributes to emissions with ≥ 2 soft gluons. Our Glauber operator basis is derived using tree level and one-loop matching calculations from full QCD to both SCETII and SCETI. The one-loop amplitude's rapidity renormalization involves mixing of color octet operators and yields gluon Reggeization at the amplitude level. The rapidity renormalization group equation for the leading soft and collinear functions in the forward scattering cross section are each given by the BFKL equation. Various properties of Glauber gluon exchange in the context of both forward scattering and hard scattering factorization are described. For example, we derive an explicit rule for when eikonalization is valid, and provide a direct connection to the picture of multiple Wilson lines crossing a shockwave. In hard scattering operators Glauber subtractions for soft and collinear loop diagrams ensure that we are not sensitive to
Improving Classroom Acoustics (ICA): A Three-Year FM Sound Field Classroom Amplification Study.
ERIC Educational Resources Information Center
Rosenberg, Gail Gegg; Blake-Rahter, Patricia; Heavner, Judy; Allen, Linda; Redmond, Beatrice Myers; Phillips, Janet; Stigers, Kathy
1999-01-01
The Improving Classroom Acoustics (ICA) special project was designed to determine if students' listening and learning behaviors improved as a result of an acoustical environment enhanced through the use of FM sound field classroom amplification. The 3-year project involved 2,054 students in 94 general education kindergarten, first-, and…
Modified ion-acoustic solitary waves in plasmas with field-aligned shear flows
Saleem, H.; Haque, Q.
2015-08-15
The nonlinear dynamics of ion-acoustic waves is investigated in a plasma having field-aligned shear flow. A Korteweg-deVries-type nonlinear equation for a modified ion-acoustic wave is obtained which admits a single pulse soliton solution. The theoretical result has been applied to solar wind plasma at 1 AU for illustration.
Modified ion-acoustic solitary waves in plasmas with field-aligned shear flows
NASA Astrophysics Data System (ADS)
Saleem, H.; Ali, S.; Haque, Q.
2015-08-01
The nonlinear dynamics of ion-acoustic waves is investigated in a plasma having field-aligned shear flow. A Koeteweg-deVries-type nonlinear equation for a modified ion-acoustic wave is obtained which admits a single pulse soliton solution. The theoretical result has been applied to solar wind plasma at 1 AU for illustration.
NASA Technical Reports Server (NTRS)
Sepcenko, Valentin
1989-01-01
This report is an aid to designers of structures with large area-to-mass ratios that are subject to high acoustic pressures during rocket launches. A means is provided for determining generalized modal loads using AJ-coefficients. AJ-coefficients are a measure of a vibroacoustic coupling between the structure and the acoustic field.
Williams, Kevin L; Kargl, Steven G; Thorsos, Eric I; Burnett, David S; Lopes, Joseph L; Zampolli, Mario; Marston, Philip L
2010-06-01
Understanding acoustic scattering from objects placed on the interface between two media requires incorporation of scattering off the interface. Here, this class of problems is studied in the particular context of a 61 cm long, 30.5 cm diameter solid aluminum cylinder placed on a flattened sand interface. Experimental results are presented for the monostatic scattering from this cylinder for azimuthal scattering angles from 0 degrees to 90 degrees and frequencies from 1 to 30 kHz. In addition, synthetic aperture sonar (SAS) processing is carried out. Next, details seen within these experimental results are explained using insight derived from physical acoustics. Subsequently, target strength results are compared to finite-element (FE) calculations. The simplest calculation assumes that the source and receiver are at infinity and uses the FE result for the cylinder in free space along with image cylinders for approximating the target/interface interaction. Then the effect of finite geometries and inclusion of a more complete Green's function for the target/interface interaction is examined. These first two calculations use the axial symmetry of the cylinder in carrying out the analysis. Finally, the results from a three dimensional FE analysis are presented and compared to both the experiment and the axially symmetric calculations.
Scattering detection of a solenoidal Poynting vector field.
Fardad, Shima; Salandrino, Alessandro; Samadi, Akbar; Heinrich, Matthias; Chen, Zhigang; Christodoulides, Demetrios N
2016-08-01
The Poynting vector S plays a central role in electrodynamics as it is directly related to the power and the momentum carried by an electromagnetic wave. In the presence of multiple electromagnetic waves with different polarizations and propagation directions, the Poynting vector may exhibit solenoidal components which are not associated to any power flow. Here, we demonstrate theoretically and experimentally that the presence of such solenoidal components has physical consequences, and it is not a mere artifact of the gauge invariance of S. In particular, we identify a simple field configuration displaying solenoidal components of S and theoretically show that a judiciously designed scatterer can act as a "Poynting vector detector" which when immersed in such field distribution would experience a transverse optical force orthogonal to the incidence plane. We experimentally validate our theoretical predictions by observing a pronounced asymmetry in the scattering pattern of a spherical nanoparticle. PMID:27472632
Acoustic temperature measurement in a rocket noise field.
Giraud, Jarom H; Gee, Kent L; Ellsworth, John E
2010-05-01
A 1 μm diameter platinum wire resistance thermometer has been used to measure temperature fluctuations generated during a static GEM-60 rocket motor test. Exact and small-signal relationships between acoustic pressure and acoustic temperature are derived in order to compare the temperature probe output with that of a 3.18 mm diameter condenser microphone. After preliminary plane wave tests yielded good agreement between the transducers within the temperature probe's ∼2 kHz bandwidth, comparison between the temperature probe and microphone data during the motor firing show that the ±∼3 K acoustic temperature fluctuations are a significant contributor to the total temperature variations.
Longwave scattering effects on fluxes in broken cloud fields
Takara, E.E.; Ellingson, R.G.
1996-04-01
The optical properties of clouds in the radiative energy balance are important. Most works on the effects of scattering have been in the shortwave; but longwave effects can be significant. In this work, the fluxes above and below a single cloud layer are presented, along with the errors in assuming flat black plate clouds or black clouds. The predicted fluxes are the averaged results of analysis of several fields with the same cloud amount.
NASA Astrophysics Data System (ADS)
Guoyan, Liu; Kun, Gao; Xuefeng, Liu; Guoqiang, Ni
2016-10-01
We report the simulation and measurement results of near field spatial scattering spectra around nanoparticles. Our measurement and simulations results have indicated that Parametric Indirect Microscopic Imaging can image the near field spatial scattering to a much larger distance from the scattering source of the particle under measurement whereas this part of spatial scattering was lost in the conventional microscopy. Both FDTD modeling and measurement provided evidence that parameters of indirect optical wave vector have higher sensitivity to near field scattering.
NASA Astrophysics Data System (ADS)
Zakharov, A. V.; Voloshinov, V. B.
2016-09-01
Influence of acoustic anisotropy on acousto-optic interaction in optically and acoustically anisotropic media is theoretically and experimentally studied. A specific type of acousto-optic diffraction is analyzed with allowance for the phase-matching conditions for two diffraction maxima. Analytical expressions for the phase-mismatch parameters versus the angle between the phase and group velocities of acoustic wave are derived. Light intensity in the diffraction peaks is numerically calculated, and experimental data on the diffraction in the paratellurite crystal at an acoustic walk-off angle of 54° are presented.
NASA Technical Reports Server (NTRS)
Meyer, Harold D.
1999-01-01
This report provides a study of rotor and stator scattering using the SOURCE3D Rotor Wake/Stator Interaction Code. SOURCE3D is a quasi-three-dimensional computer program that uses three-dimensional acoustics and two-dimensional cascade load response theory to calculate rotor and stator modal reflection and transmission (scattering) coefficients. SOURCE3D is at the core of the TFaNS (Theoretical Fan Noise Design/Prediction System), developed for NASA, which provides complete fully coupled (inlet, rotor, stator, exit) noise solutions for turbofan engines. The reason for studying scattering is that we must first understand the behavior of the individual scattering coefficients provided by SOURCE3D, before eventually understanding the more complicated predictions from TFaNS. To study scattering, we have derived a large number of scattering curves for vane and blade rows. The curves are plots of output wave power divided by input wave power (in dB units) versus vane/blade ratio. Some of these plots are shown in this report. All of the plots are provided in a separate volume. To assist in understanding the plots, formulas have been derived for special vane/blade ratios for which wavefronts are either parallel or normal to rotor or stator chords. From the plots, we have found that, for the most part, there was strong transmission and weak reflection over most of the vane/blade ratio range for the stator. For the rotor, there was little transmission loss.
Axial acoustic radiation force on a sphere in Gaussian field
Wu, Rongrong; Liu, Xiaozhou Gong, Xiufen
2015-10-28
Based on the finite series method, the acoustical radiation force resulting from a Gaussian beam incident on a spherical object is investigated analytically. When the position of the particles deviating from the center of the beam, the Gaussian beam is expanded as a spherical function at the center of the particles and the expanded coefficients of the Gaussian beam is calculated. The analytical expression of the acoustic radiation force on spherical particles deviating from the Gaussian beam center is deduced. The acoustic radiation force affected by the acoustic frequency and the offset distance from the Gaussian beam center is investigated. Results have been presented for Gaussian beams with different wavelengths and it has been shown that the interaction of a Gaussian beam with a sphere can result in attractive axial force under specific operational conditions. Results indicate the capability of manipulating and separating spherical spheres based on their mechanical and acoustical properties, the results provided here may provide a theoretical basis for development of single-beam acoustical tweezers.
The potential of effective field theory in NN scattering
NASA Astrophysics Data System (ADS)
Beane, S. R.; Cohen, T. D.; Phillips, D. R.
1998-03-01
We study an effective field theory of interacting nucleons at distances much greater than the pion's Compton wavelength. In this regime the NN potential is conjectured to be the sum of a delta function and its derivatives. The question we address is whether this sum can be consistently truncated at a given order in the derivative expansion, and systematically improved by going to higher orders. Regularizing the Lippmann-Schwinger equation using a cutoff we find that the cutoff can be taken to infinity only if the effective range is negative. A positive effective range — which occurs in nature — requires that the cutoff be kept finite and below the scale of the physics which has been integrated out, i.e. O( mπ). Comparison of cutoff schemes and dimensional regularization reveals that the physical scattering amplitude is sensitive to the choice of regulator. Moreover, we show that the presence of some regulator scale, a feature absent in dimensional regularization, is essential if the effective field theory of NN scattering is to be useful. We also show that one can define a procedure where finite cutoff dependence in the scattering amplitude is removed order by order in the effective potential. However, the characteristic momentum in the problem is given by the cutoff, and not by the external momentum. It follows that in the presence of a finite cutoff there is no small parameter in the effective potential, and consequently no systematic truncation of the derivative expansion can be made. We conclude that there is no effective field theory of NN scattering with nucleons alone.
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.
Reeder, D Benjamin
2016-01-01
The estuarine environment often hosts a salt wedge, the stratification of which is a function of the tide's range and speed of advance, river discharge volumetric flow rate, and river mouth morphology. Competing effects of temperature and salinity on sound speed in this stratified environment control the degree of acoustic refraction occurring along an acoustic path. A field experiment was carried out in the Columbia River Estuary to test the hypothesis: the estuarine salt wedge is acoustically observable in terms of low-to-mid-frequency acoustic propagation. Linear frequency-modulated acoustic signals in the 500-2000 Hz band were transmitted during the advance and retreat of the salt wedge during May 27-29, 2013. Results demonstrate that the salt wedge front is the dominant physical mechanism controlling acoustic propagation in this environment: received signal energy is relatively stable before and after the passage of the salt wedge front when the acoustic path consists of a single medium (either entirely fresh water or entirely salt water), and suffers a 10-15 dB loss and increased variability during salt wedge front passage. Physical parameters and acoustic propagation modeling corroborate and inform the acoustic observations. PMID:26827001
Xu, Tailin; Soto, Fernando; Gao, Wei; Dong, Renfeng; Garcia-Gradilla, Victor; Magaña, Ernesto; Zhang, Xueji; Wang, Joseph
2015-02-18
The collective behavior of biological systems has inspired efforts toward the controlled assembly of synthetic nanomotors. Here we demonstrate the use of acoustic fields to induce reversible assembly of catalytic nanomotors, controlled swarm movement, and separation of different nanomotors. The swarming mechanism relies on the interaction between individual nanomotors and the acoustic field, which triggers rapid migration and assembly around the nearest pressure node. Such on-demand assembly of catalytic nanomotors is extremely fast and reversible. Controlled movement of the resulting swarm is illustrated by changing the frequency of the acoustic field. Efficient separation of different types of nanomotors, which assemble in distinct swarming regions, is illustrated. The ability of acoustic fields to regulate the collective behavior of catalytic nanomotors holds considerable promise for a wide range of practical applications. PMID:25634724
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.
NASA Astrophysics Data System (ADS)
Muromets, A. V.; Trushin, A. S.
Influence of acoustic field structure on polarization characteristics of acousto-optic interaction is investigated. It is shown that inhomogeneity of acoustic field and mechanism of ultrasound excitation causes changes in values of acousto-optic figure of merit for ordinary and extraordinary light beams in comparison with theoretic values. The theoretic values were derived under assumption that acoustic wave is homogeneous. Experimental analysis was carried out in acousto-optic cell based on lithium niobate crystal where the acoustic wave propagates at the angle 13 degrees to Z axis of the crystal. We used three different methods of ultrasound generation in the crystal: by means of external piezotransducer, by interdigital transducer and by two sets of electrodes placed on top of the crystal surface. In the latter case, the first pair of the electrodes was directed along X crystal axis, while the second pair of the electrodes was directed orthogonally to X crystal axis and the direction of ultrasound. Obtained values for diffraction efficiencies for ordinary and extraordinary polarized optical beams were qualitatively different which may be caused by spatial inhomogeneity of the generated acoustic waves in the crystal. Structure of acoustic field generated by these sets of electrodes was examined by laser probing. We performed the analysis of the acoustic field intensity using acousto-optic method. A relation of diffraction efficiencies for ordinary and extraordinary light waves was measured during each iteration of the laser probing.
Investigation of Acoustic Fields for the Cassini Spacecraft: Reverberant Versus Launch Environments
NASA Technical Reports Server (NTRS)
Hughes, William O.; McNelis, Anne M.; Himelblau, Harry
2000-01-01
The characterization and understanding of the acoustic field within a launch vehicle's payload fairing (PLF) is critical to the qualification of a spacecraft and ultimately to the success of its mission. Acoustic measurements taken recently for the Cassini mission have allowed unique opportunities to advance the aerospace industry's knowledge in this field. Prior to its launch, the expected liftoff acoustic environment of the spacecraft was investigated in a full-scale acoustic test of a Titan IV PLF and Cassini simulator in a reverberant test chamber. A major goal of this acoustic ground test was to quantify and verify the noise reduction performance of special barrier blankets that were designed especially to reduce the Cassirii acoustic environment. This paper will describe both the ground test and flight measurements, and compare the Cassini acoustic environment measured during launch with that measured earlier in the ground test. Special emphasis will be given to the noise reduction performance of the barrier blankets and to the acoustic coherence measured within the PLF.
Towards the optimisation of acoustic fields for ablative therapies of tumours in the upper abdomen
NASA Astrophysics Data System (ADS)
Gélat, P.; ter Haar, G.; Saffari, N.
2013-08-01
The efficacy of high intensity focused ultrasound (HIFU) for the non-invasive treatment of cancer has been demonstrated for a range of different cancers including those of the liver, kidney, prostate and breast. As a non-invasive focused therapy, HIFU offers considerable advantages over other techniques such as chemotherapy and surgical resection, in terms of its non-invasiveness and low risk of harmful side effects. There is, however, a number of significant challenges which currently hinder its widespread clinical application. One of these challenges is the need to transmit sufficient energy through the ribcage to induce tissue necrosis at the required foci whilst minimising the formation of side lobes and sparing healthy tissue. Ribs both absorb and reflect ultrasound strongly. As such, a common side effect of focusing ultrasound in regions located behind the rib cage is the overheating of bone and surrounding tissue, which can lead to skin burns. Successful treatment of a patient with tumours in the upper abdomen therefore requires a thorough understanding of the way acoustic and thermal energy are deposited. This is likely to rely on a treatment planning procedure in which optimal source velocity distributions are obtained so as to maximise a dose quantity at the treatment sites, whilst ensuring that this quantity does not exceed a specified threshold at other field locations, particularly on the surface of the ribs. Previously, a boundary element approach based on a Generalised Minimal Residual (GMRES) implementation of the Burton-Miller formulation was developed to predict the field of a multi-element HIFU array scattered by human ribs, the topology of which was obtained from CT scan data [1]. This work describes the reformulation of the boundary element equations as a least-squares minimisation problem with non-linear constraints. The methodology was subsequently tested at an excitation frequency of 100 kHz on a spherical multi-element array in the presence
Research of microwave scattering properties of snow fields
NASA Technical Reports Server (NTRS)
Angelakos, D. J.
1978-01-01
The results obtained in the research program of microwave scattering properties of snow fields are presented. Experimental results are presented showing backscatter dependence on frequency (5.8-8.0 GHz), angle of incidence (0-60 degrees), snow wetness (time of day), and frequency modulation (0-500 MHz). Theoretical studies are being made of the inverse scattering problem yielding some preliminary results concerning the determination of the dielectric constant of the snow layer. The experimental results lead to the following conclusions: snow layering affects backscatter, layer response is significant up to 45 degrees of incidence, wetness modifies snow layer effects, frequency modulation masks the layer response, and for the proper choice of probing frequency and for nominal snow depths, it appears to be possible to measure the effective dielectric constant and the corresponding water content of a snow pack.
A compact neutron scatter camera for field deployment.
Goldsmith, John E M; Gerling, Mark D; Brennan, James S
2016-08-01
We describe a very compact (0.9 m high, 0.4 m diameter, 40 kg) battery operable neutron scatter camera designed for field deployment. Unlike most other systems, the configuration of the sixteen liquid-scintillator detection cells are arranged to provide omnidirectional (4π) imaging with sensitivity comparable to a conventional two-plane system. Although designed primarily to operate as a neutron scatter camera for localizing energetic neutron sources, it also functions as a Compton camera for localizing gamma sources. In addition to describing the radionuclide source localization capabilities of this system, we demonstrate how it provides neutron spectra that can distinguish plutonium metal from plutonium oxide sources, in addition to the easier task of distinguishing AmBe from fission sources. PMID:27587113
Radiography by selective detection of scatter field velocity components
NASA Technical Reports Server (NTRS)
Jacobs, Alan M. (Inventor); Dugan, Edward T. (Inventor); Shedlock, Daniel (Inventor)
2007-01-01
A reconfigurable collimated radiation detector, system and related method includes at least one collimated radiation detector. The detector has an adjustable collimator assembly including at least one feature, such as a fin, optically coupled thereto. Adjustments to the adjustable collimator selects particular directions of travel of scattered radiation emitted from an irradiated object which reach the detector. The collimated detector is preferably a collimated detector array, where the collimators are independently adjustable. The independent motion capability provides the capability to focus the image by selection of the desired scatter field components. When an array of reconfigurable collimated detectors is provided, separate image data can be obtained from each of the detectors and the respective images cross-correlated and combined to form an enhanced image.
A compact neutron scatter camera for field deployment
NASA Astrophysics Data System (ADS)
Goldsmith, John E. M.; Gerling, Mark D.; Brennan, James S.
2016-08-01
We describe a very compact (0.9 m high, 0.4 m diameter, 40 kg) battery operable neutron scatter camera designed for field deployment. Unlike most other systems, the configuration of the sixteen liquid-scintillator detection cells are arranged to provide omnidirectional (4π) imaging with sensitivity comparable to a conventional two-plane system. Although designed primarily to operate as a neutron scatter camera for localizing energetic neutron sources, it also functions as a Compton camera for localizing gamma sources. In addition to describing the radionuclide source localization capabilities of this system, we demonstrate how it provides neutron spectra that can distinguish plutonium metal from plutonium oxide sources, in addition to the easier task of distinguishing AmBe from fission sources.
Lift-Off Acoustics Prediction of Clustered Rocket Engines in the Near Field
NASA Technical Reports Server (NTRS)
Vu, Bruce; Plotkin, Ken
2010-01-01
This slide presentation presents a method of predicting acoustics during lift-off of the clustered rocket engines in the near field. Included is a definition of the near field, and the use of deflectors and shielding. There is discussion about the use of PAD, a software system designed to calculate the acoustic levels from the lift of of clustered rocket enginee, including updates to extend the calculation to directivity, water suppression, and clustered nozzles.
Acoustic Field Calculation of Ultrasonic Linear Phased Array Transducers with Curve Surface
NASA Astrophysics Data System (ADS)
Xu, Chunguang; Wang, Lijiu; Xiao, Dingguo; Zhou, Shiyuan
2011-06-01
The focus law and acoustic field computation method about circular arc linear phased array have been discussed in the paper. Acoustic field of transducers is given by the use of the coordinate transformation and an approximation with rectangle element instead of circular arc element, and was validated using Rayleigh-Sommerfeld Integral and nonparallel multiple Gaussian beam model respectively. The results of two methods match well.
NASA Astrophysics Data System (ADS)
Gaebler, Peter J.; Eulenfeld, Tom; Wegler, Ulrich
2015-12-01
In this study, frequency-dependent seismic scattering and intrinsic attenuation parameters for the crustal structure beneath the W-Bohemia/Vogtland swarm earthquake region close to the border of Czech Republic and Germany are estimated. Synthetic seismogram envelopes are modelled using elastic and acoustic radiative transfer theory. Scattering and absorption parameters are determined by fitting these synthetic envelopes to observed seismogram envelopes from 14 shallow local events from the October 2008 W-Bohemia/Vogtland earthquake swarm. The two different simulation approaches yield similar results for the estimated crustal parameters and show a comparable frequency dependence of both transport mean free path and intrinsic absorption path length. Both methods suggest that intrinsic attenuation is dominant over scattering attenuation in the W-Bohemia/Vogtland region for the investigated epicentral distance range and frequency bands from 3 to 24 Hz. Elastic simulations of seismogram envelopes suggest that forward scattering is required to explain the data, however, the degree of forward scattering is not resolvable. Errors in the parameter estimation are smaller in the elastic case compared to results from the acoustic simulations. The frequency decay of the transport mean free path suggests a random medium described by a nearly exponential autocorrelation function. The fluctuation strength and correlation length of the random medium cannot be estimated independently, but only a combination of the parameters related to the transport mean free path of the medium can be computed. Furthermore, our elastic simulations show, that using our numerical method, it is not possible to resolve the value of the mean free path of the random medium.
Theory of weak scattering of stochastic electromagnetic fields from deterministic and random media
Tong Zhisong; Korotkova, Olga
2010-09-15
The theory of scattering of scalar stochastic fields from deterministic and random media is generalized to the electromagnetic domain under the first-order Born approximation. The analysis allows for determining the changes in spectrum, coherence, and polarization of electromagnetic fields produced on their propagation from the source to the scattering volume, interaction with the scatterer, and propagation from the scatterer to the far field. An example of scattering of a field produced by a {delta}-correlated partially polarized source and scattered from a {delta}-correlated medium is provided.
NASA Astrophysics Data System (ADS)
Mamou, Jonathan; Oelze, Michael L.; O'Brien, William D.; Zachary, James F.
2001-05-01
Accurate estimates of scatterer parameters (size and acoustic concentration) are beneficial adjuncts to characterize disease from ultrasonic backscatterer measurements. An estimation technique was developed to obtain parameter estimates from the Fourier transform of the spatial autocorrelation function (SAF). A 3D impedance map (3DZM) is used to obtain the SAF of tissue. 3DZMs are obtained by aligning digitized light microscope images from histologic preparations of tissue. Estimates were obtained for simulated 3DZMs containing spherical scatterers randomly located: relative errors were less than 3%. Estimates were also obtained from a rat fibroadenoma and a 4T1 mouse mammary tumor (MMT). Tissues were fixed (10% neutral-buffered formalin), embedded in paraffin, serially sectioned and stained with H&E. 3DZM results were compared to estimates obtained independently against ultrasonic backscatter measurements. For the fibroadenoma and MMT, average scatterer diameters were 91 and 31.5 μm, respectively. Ultrasonic measurements yielded average scatterer diameters of 105 and 30 μm, respectively. The 3DZM estimation scheme showed results similar to those obtained by the independent ultrasonic measurements. The 3D impedance maps show promise as a powerful tool to characterize ultrasonic scattering sites of tissue. [Work supported by the University of Illinois Research Board.
Acoustic temperature measurement in a rocket noise field.
Giraud, Jarom H; Gee, Kent L; Ellsworth, John E
2010-05-01
A 1 μm diameter platinum wire resistance thermometer has been used to measure temperature fluctuations generated during a static GEM-60 rocket motor test. Exact and small-signal relationships between acoustic pressure and acoustic temperature are derived in order to compare the temperature probe output with that of a 3.18 mm diameter condenser microphone. After preliminary plane wave tests yielded good agreement between the transducers within the temperature probe's ∼2 kHz bandwidth, comparison between the temperature probe and microphone data during the motor firing show that the ±∼3 K acoustic temperature fluctuations are a significant contributor to the total temperature variations. PMID:21117711
NASA Astrophysics Data System (ADS)
Zhou, Deng
2016-10-01
The dispersion relation of geodesic acoustic modes with a magnetic perturbation in the tokamak plasma with an equilibrium radial electric field was derived. The dispersion relation was analyzed for very low field strength. The mode frequency decreases with increasing field strength, which is different from the electrostatic geodesic acoustic mode. There exists an m = 1 magnetic component that is very low when the radial electric field is absent. The ratio between the m = 1 and m = 2 magnetic components increases with strength of the radial electric field for low Mach numbers.
Harland, Andy R; Petzing, Jon N; Tyrer, John R
2004-01-01
Localized changes in the density of water induced by the presence of an acoustic field cause perturbations in the localized refractive index. This relationship has given rise to a number of nonperturbing optical metrology techniques for recording measurement parameters from underwater acoustic fields. A method that has been recently developed involves the use of a Laser Doppler Vibrometer (LDV) targeted at a fixed, nonvibrating, plate through an underwater acoustic field. Measurements of the rate of change of optical pathlength along a line section enable the identification of the temporal and frequency characteristics of the acoustic wave front. This approach has been extended through the use of a scanning LDV, which facilitates the measurement of a range of spatially distributed parameters. A mathematical model is presented that relates the distribution of pressure amplitude and phase in a planar wave front with the rate of change of optical pathlength measured by the LDV along a specifically orientated laser line section. Measurements of a 1 MHz acoustic tone burst generated by a focused transducer are described and the results presented. Graphical depictions of the acoustic power and phase distribution recorded by the LDV are shown, together with images representing time history during the acoustic wave propagation.
Hu, Yuxiang; Zhou, Haoran; Lu, Jing; Qiu, Xiaojun
2016-08-01
Beamformers enable a microphone array to capture acoustic signals from a sound source with high signal to noise ratio in a noisy environment, and the linear microphone array is of particular importance, in practice, due to its simplicity and easy implementation. A linear microphone array sometimes is used near some scattering objects, which affect its beamforming performance. This paper develops a numerical model with a linear microphone array near a rigid sphere for both far-field plane wave and near-field sources. The effects of the scatterer on two typical beamformers, i.e., the delay-and-sum beamformer and the superdirective beamformer, are investigated by both simulations and experiments. It is found that the directivity factor of both beamformers improves due to the increased equivalent array aperture when the size of the array is no larger than that of the scatter. With the increase of the array size, the directivity factor tends to deteriorate at high frequencies because of the rising side-lobes. When the array size is significantly larger than that of the scatterer, the scattering has hardly any influence on the beamforming performance. PMID:27586725
An improved method for the calculation of Near-Field Acoustic Radiation Modes
NASA Astrophysics Data System (ADS)
Liu, Zu-Bin; Maury, Cédric
2016-02-01
Sensing and controlling Acoustic Radiation Modes (ARMs) in the near-field of vibrating structures is of great interest for broadband noise reduction or enhancement, as ARMs are velocity distributions defined over a vibrating surface, that independently and optimally contribute to the acoustic power in the acoustic field. But present methods only provide far-field ARMs (FFARMs) that are inadequate for the acoustic near-field problem. The Near-Field Acoustic Radiation Modes (NFARMs) are firstly studied with an improved numerical method, the Pressure-Velocity method, which rely on the eigen decomposition of the acoustic transfers between the vibrating source and a conformal observation surface, including sound pressure and velocity transfer matrices. The active and reactive parts of the sound power are separated and lead to the active and reactive ARMs. NFARMs are studied for a 2D baffled beam and for a 3D baffled plate, and so as differences between the NFARMS and the classical FFARMs. Comparisons of the NFARMs are analyzed when varying frequency and observation distance to the source. It is found that the efficiencies and shapes of the optimal active ARMs are independent on the distance while that of the reactive ones are distinctly related on.
Applications of digital holography in visualized measurement of acoustic and flow fields
NASA Astrophysics Data System (ADS)
Zhao, Jianlin; Li, Enpu; Sun, Weiwei; Di, Jianglei
2010-03-01
Digital holography allows recording the hologram using digitally imaging devices such as CCD, and reconstructing the holographic image by numerically simulating the diffraction of the hologram. Its main advantages are by which one can directly obtain the complex amplitude distribution of the object field, so that more impersonally measure the detail information of the object field, such as the distribution of the refractive index changing in crystals induced by light irradiation, deformation of the object surface, particle distribution, as well as acoustic field, flow field and temperature distribution in air. In this paper, we summarize the principle and some of our experimental results on the applications of digital holography in visualized measurement of acoustic standing wave (acoustic levitation field), plasma plume and water flow (Karman vortex street) fields.
Applications of digital holography in visualized measurement of acoustic and flow fields
NASA Astrophysics Data System (ADS)
Zhao, Jianlin; Li, Enpu; Sun, Weiwei; di, Jianglei
2009-12-01
Digital holography allows recording the hologram using digitally imaging devices such as CCD, and reconstructing the holographic image by numerically simulating the diffraction of the hologram. Its main advantages are by which one can directly obtain the complex amplitude distribution of the object field, so that more impersonally measure the detail information of the object field, such as the distribution of the refractive index changing in crystals induced by light irradiation, deformation of the object surface, particle distribution, as well as acoustic field, flow field and temperature distribution in air. In this paper, we summarize the principle and some of our experimental results on the applications of digital holography in visualized measurement of acoustic standing wave (acoustic levitation field), plasma plume and water flow (Karman vortex street) fields.
Measuring the complex field scattered by single submicron particles
Potenza, Marco A. C. Sanvito, Tiziano
2015-11-15
We describe a method for simultaneous measurements of the real and imaginary parts of the field scattered by single nanoparticles illuminated by a laser beam, exploiting a self-reference interferometric scheme relying on the fundamentals of the Optical Theorem. Results obtained with calibrated spheres of different materials are compared to the expected values obtained through a simplified analytical model without any free parameters, and the method is applied to a highly polydisperse water suspension of Poly(D,L-lactide-co-glycolide) nanoparticles. Advantages with respect to existing methods and possible applications are discussed.
Direct-field acoustic testing of a flight system : logistics, challenges, and results.
Stasiunas, Eric Carl; Gurule, David Joseph; Babuska, Vit; Skousen, Troy J.
2010-10-01
Before a spacecraft can be considered for launch, it must first survive environmental testing that simulates the launch environment. Typically, these simulations include vibration testing performed using an electro-dynamic shaker. For some spacecraft however, acoustic excitation may provide a more severe loading environment than base shaker excitation. Because this was the case for a Sandia Flight System, it was necessary to perform an acoustic test prior to launch in order to verify survival due to an acoustic environment. Typically, acoustic tests are performed in acoustic chambers, but because of scheduling, transportation, and cleanliness concerns, this was not possible. Instead, the test was performed as a direct field acoustic test (DFAT). This type of test consists of surrounding a test article with a wall of speakers and controlling the acoustic input using control microphones placed around the test item, with a closed-loop control system. Obtaining the desired acoustic input environment - proto-flight random noise input with an overall sound pressure level (OASPL) of 146.7 dB-with this technique presented a challenge due to several factors. An acoustic profile with this high OASPL had not knowingly been obtained using the DFAT technique prior to this test. In addition, the test was performed in a high-bay, where floor space and existing equipment constrained the speaker circle diameter. And finally, the Flight System had to be tested without contamination of the unit, which required a contamination bag enclosure of the test unit. This paper describes in detail the logistics, challenges, and results encountered while performing a high-OASPL, direct-field acoustic test on a contamination-sensitive Flight System in a high-bay environment.
Applications of effective field theory to electron scattering
NASA Astrophysics Data System (ADS)
Diaconescu, Luca Radu
In this work two calculations are presented. In the first, we compute the vector analyzing power (VAP) for the elastic scattering of transversely polarized electrons from protons at low energies, using an effective theory of electrons, protons, and photons. We study all contributions through second order in E/M, where E and M are the electron energy and nucleon mass, respectively. The leading order VAP arises from the imaginary part of the interference of one- and two-photon exchange amplitudes. Sub-leading contributions are generated by the nucleon magnetic moment and charge radius, as well as recoil corrections to the leading-order amplitude. Working to second order in E/M), we obtain a prediction for A_n that is free of unknown parameters and that agrees with the recent measurement of the VAP in backward angle electron proton scattering. In the second part of this thesis the longitudinal asymmetry due to Z exchange is calculated in quasi-elastic electron-deuteron scattering at momentum transfers |Q^2| of about 0.1 GeV^2 relevant for the SAMPLE experiment. The deuteron and pn scattering-state wave functions are obtained from solutions of a Schrodinger equation with the Argonne v18 potential. Electromagnetic and weak neutral one- and two-nucleon currents are included in the calculation. The two-nucleon currents of pion range are shown to be identical to those derived in Effective Field Theory. The results indicate that two-body contributions to the asymmetry are small (about 0.2%) around the quasi-elastic peak, but become relatively more significant (about 3%) in the high-energy wing of the quasi-elastic peak.
Recovering the Green's function from field-field correlations in an open scattering medium (L)
NASA Astrophysics Data System (ADS)
Derode, Arnaud; Larose, Eric; Tanter, Mickael; de Rosny, Julien; Tourin, Arnaud; Campillo, Michel; Fink, Mathias
2003-06-01
The possibility of recovering the Green's function from the field-field correlations of coda waves in an open multiple scattering medium is investigated. The argument is based on fundamental symmetries of reciprocity, time-reversal invariance, and the Helmholtz-Kirchhoff theorem. A criterion is defined, indicating how sources should be placed inside an open medium in order to recover the Green's function between two passive receivers. The case of noise sources is also discussed. Numerical experiments of ultrasonic wave propagation in a multiple scattering medium are presented to support the argument.
NATO TG-53: acoustic detection of weapon firing joint field experiment
NASA Astrophysics Data System (ADS)
Robertson, Dale N.; Pham, Tien; Scanlon, Michael V.; Srour, Nassy; Reiff, Christian G.; Sim, Leng K.; Solomon, Latasha; Thompson, Dorothea F.
2006-05-01
In this paper, we discuss the NATO Task Group 53 (TG-53) acoustic detection of weapon firing field joint experiment at Yuma Proving Ground during 31 October to 4 November 2005. The participating NATO countries include France, the Netherlands, UK and US. The objectives of the joint experiments are: (i) to collect acoustic signatures of direct and indirect firings from weapons such as sniper, mortar, artillery and C4 explosives and (ii) to share signatures among NATO partners from a variety of acoustic sensing platforms on the ground and in the air distributed over a wide area.
Adaptive algorithm for active control of high-amplitude acoustic field in resonator
NASA Astrophysics Data System (ADS)
Červenka, M.; Bednařík, M.; Koníček, P.
2008-06-01
This work is concerned with suppression of nonlinear effects in piston-driven acoustic resonators by means of two-frequency driving technique. An iterative adaptive algorithm is proposed to calculate parameters of the driving signal in order that amplitude of the second harmonics of the acoustic pressure is minimized. Functionality of the algorithm is verified firstly by means of numerical model and secondly, it is used in real computer-controlled experiment. The numerical and experimental results show that the proposed algorithm can be successfully used for generation of high-amplitude shock-free acoustic field in resonators.
NASA Astrophysics Data System (ADS)
Bhuyan, M.; Panda, R. N.; Routray, T. R.; Patra, S. K.
2010-12-01
In the framework of relativistic mean field (RMF) theory, we have calculated the density distribution of protons and neutrons for Ca40,42,44,48 with NL3 and G2 parameter sets. The microscopic proton-nucleus optical potentials for p+Ca40,42,44,48 systems are evaluated from the Dirac nucleon-nucleon scattering amplitude and the density of the target nucleus using relativistic-Love-Franey and McNeil-Ray-Wallace parametrizations. We have estimated the scattering observables, such as the elastic differential scattering cross section, analyzing power and the spin observables with the relativistic impulse approximation (RIA). The results have been compared with the experimental data for a few selective cases and we find that the use of density as well as the scattering matrix parametrizations are crucial for the theoretical prediction.
Bhuyan, M.; Panda, R. N.; Routray, T. R.; Patra, S. K.
2010-12-15
In the framework of relativistic mean field (RMF) theory, we have calculated the density distribution of protons and neutrons for {sup 40,42,44,48}Ca with NL3 and G2 parameter sets. The microscopic proton-nucleus optical potentials for p+{sup 40,42,44,48}Ca systems are evaluated from the Dirac nucleon-nucleon scattering amplitude and the density of the target nucleus using relativistic-Love-Franey and McNeil-Ray-Wallace parametrizations. We have estimated the scattering observables, such as the elastic differential scattering cross section, analyzing power and the spin observables with the relativistic impulse approximation (RIA). The results have been compared with the experimental data for a few selective cases and we find that the use of density as well as the scattering matrix parametrizations are crucial for the theoretical prediction.
Determination of near and far field acoustics for advanced propeller configurations
NASA Technical Reports Server (NTRS)
Korkan, K. D.; Jaeger, S. M.; Kim, J. H.
1989-01-01
A method has been studied for predicting the acoustic field of the SR-3 transonic propfan using flow data generated by two versions of the NASPROP-E computer code. Since the flow fields calculated by the solvers include the shock-wave system of the propeller, the nonlinear quadrupole noise source term is included along with the monopole and dipole noise sources in the calculation of the acoustic near field. Acoustic time histories in the near field are determined by transforming the azimuthal coordinate in the rotating, blade-fixed coordinate system to the time coordinate in a nonrotating coordinate system. Fourier analysis of the pressure time histories is used to obtain the frequency spectra of the near-field noise.
Thermo acoustic study of carbon nanotubes in near and far field: Theory, simulation, and experiment
NASA Astrophysics Data System (ADS)
Asadzadeh, S. S.; Moosavi, A.; Huynh, C.; Saleki, O.
2015-03-01
Carbon nanotube webs exhibit interesting properties when used as thermo-acoustic projectors. This work studies thermo-acoustic effect of these sound sources both in near and far field regions. Based on two alternative forms of the energy equation, we have developed a straightforward formula for calculation of pressure field, which is consistent with experimental data in far field. Also we have solved full 3-D governing equations using numerical methods. Our three-dimensional simulation and experimental data show pressure waves are highly affected by dimensions of sound sources in near field due to interference effects. However, generation of sound waves in far field is independent of projectors area surface. Energy analysis for free standing Thermo-Acoustic (TA) sound sources show that aerogel TA sound sources like CNT based projectors could act more efficiently compared to the other sources in delivering more than 75% of alternative input energy to the medium gas up to a frequency of 1 MHz.
Investigating the motion of particles in an ultrasonic acoustic wave field using PIV/PTV
NASA Astrophysics Data System (ADS)
Nobes, David S.; Setayeshgar, Alireza; Lipsett, Michael G.; Koch, Charles R.
2012-05-01
The influence of a multi-wavelength acoustic standing wave field on the motion of micron-sized particles is experimentally investigated using particle image velocimetry/particle tracking velocimetry (PIV/PTV) to examine existing theories describing the radiation force on particles. An ultrasonic acoustic wave is introduced into a column chamber containing a mixture of distilled water and a disperse population of spherical particles. In this system the acoustic field is aligned with gravity to form horizontal bands of particles, which are also influenced by buoyancy and drag forces. Accounting for these forces with the acoustic radiation pressure, the motion of an individual particle is modeled. There is a good agreement between the pattern of the particles motion in experimental results and the predicted single particle motion; however, due to the concentration of particles in the experiment, a difference is observed in the maximum value of the velocity of the particles in the experiment and in the single particle model.
Scaling laws in NMR scattering via dipolar fields.
Brown, S M; Sen, P N; Cory, D G
2002-01-01
Breaking translational symmetry in magnetostatics imparts a scale dependence that is commonly investigated in physics (W. Warren et al., 1993, Science 262, 2005-2008). An interesting and important example arises in nuclear magnetic resonance studies involving the dipolar mean field of adjacent nuclear spins where the scattering (transfer of spatial spin gratings) via intermolecular macroscopic fields carries a signature of the local spatial distribution of the spin density. For arbitrary geometry, the inverse problem of extracting this spin distribution from experiments is intractable. Here we point out a simple, universal crossover in the scaling behavior at the sample's characteristic length scale, xi, of the species fluctuations in the sample along the measurement direction. This behavior is observed experimentally in an oil-water emulsion, an important representation of complex, heterogeneous, soft matter. PMID:11820836
Acoustic radiation force due to arbitrary incident fields on spherical particles in soft tissue
Treweek, Benjamin C. Ilinskii, Yurii A.; Zabolotskaya, Evgenia A.; Hamilton, Mark F.
2015-10-28
Acoustic radiation force is of interest in a wide variety of biomedical applications ranging from tissue characterization (e.g. elastography) to tissue treatment (e.g. high intensity focused ultrasound, kidney stone fragment removal). As tissue mechanical properties are reliable indicators of tissue health, the former is the focus of the present contribution. This is accomplished through an investigation of the acoustic radiation force on a spherical scatterer embedded in tissue. Properties of both the scatterer and the surrounding tissue are important in determining the magnitude and the direction of the force. As these properties vary, the force computation shows changes in magnitude and direction, which may enable more accurate noninvasive determination of tissue properties.
Acoustic radiation force due to arbitrary incident fields on spherical particles in soft tissue
NASA Astrophysics Data System (ADS)
Treweek, Benjamin C.; Ilinskii, Yurii A.; Zabolotskaya, Evgenia A.; Hamilton, Mark F.
2015-10-01
Acoustic radiation force is of interest in a wide variety of biomedical applications ranging from tissue characterization (e.g. elastography) to tissue treatment (e.g. high intensity focused ultrasound, kidney stone fragment removal). As tissue mechanical properties are reliable indicators of tissue health, the former is the focus of the present contribution. This is accomplished through an investigation of the acoustic radiation force on a spherical scatterer embedded in tissue. Properties of both the scatterer and the surrounding tissue are important in determining the magnitude and the direction of the force. As these properties vary, the force computation shows changes in magnitude and direction, which may enable more accurate noninvasive determination of tissue properties.
NASA Astrophysics Data System (ADS)
Burov, V. A.; Grishina, I. M.; Lapshenkina, O. I.; Morozov, S. A.; Rumyantseva, O. D.; Sukhov, E. G.
2003-11-01
In the ultrasonic diagnostics of small-size neoplasms of biological tissues at the earliest stage of their development, an efficient way to eliminate the distorting influence of high-contrast or large inhomogeneities of the biological medium is to apply the iterative technique. A simple approach is proposed, which makes it possible with only two iteration steps to achieve an efficient focusing of the tomograph array. At the first step, the unknown distribution of the large-scale inhomogeneities of sound velocity and absorption over the scatterer is reconstructed, where the large-scale inhomogeneities are those whose size exceeds several wavelengths. At the second step, the fine structure of the scatterer is reconstructed against the large-scale background, which can be performed with a high accuracy owing to the evaluation of the background at the first step. The possibility of simultaneous reconstruction of the large-scale and fine structures by the noniterative Grinevich-Novikov algorithm is considered as an alternative. This algorithm reconstructs in an explicit form two-dimensional refractive-absorbing acoustic scatterers of almost arbitrary shape and strength. Taking into account the effects of multiple scattering, this algorithm provides resolution of the fine structure almost as good as that achieved in reconstructing the same structure against an undistorting homogeneous background. The results of numerical simulations of both algorithms are presented.
Polymer coating of glass microballoons levitated in a focused acoustic field
NASA Technical Reports Server (NTRS)
Young, A. T.; Lee, M. C.; Feng, I.-A.; Elleman, D. D.; Wang, T. G.
1982-01-01
Inertial confinement fusion (ICF) glass microballoons (GMBs) levitated in a focusing radiator acoustic device can be coated with liquid materials by deploying the liquid into the levitation field with a stepped-horn atomizer. The GMB can be forced to the center of the coating liquid with a strong acoustically generated centering force. Water solutions of organic polymers, UV-curable liquid organic monomers, and paraffin waxes have been used to prepare solid coatings on the surface of GMBs using this technique.
Polymer coating of glass microballoons levitated in a focused acoustic field
Young, A.T.; Lee, M.C.; Feng, I.A.; Elleman, D.D.; Wang, T.G.
1981-01-01
Inertial confinement fusion (ICF) glass microballoons (GMBs) levitated in a focusing radiator acoustic device can be coated with liquid materials by deploying the liquid into the levitation field with a stepped-horn atomizer. The GMB can be forced to the center of the coating liquid with a strong acoustically generated centering force. Water solutions of organic polymers, uv-curable liquid organic monomers, and paraffin waxes have been used to prepare solid coatings on the surface of GMBs using this technique.
Customization of the acoustic field produced by a piezoelectric array through interelement delays
Chitnis, Parag V.; Barbone, Paul E.; Cleveland, Robin O.
2008-01-01
A method for producing a prescribed acoustic pressure field from a piezoelectric array was investigated. The array consisted of 170 elements placed on the inner surface of a 15 cm radius spherical cap. Each element was independently driven by using individual pulsers each capable of generating 1.2 kV. Acoustic field customization was achieved by independently controlling the time when each element was excited. The set of time delays necessary to produce a particular acoustic field was determined by using an optimization scheme. The acoustic field at the focal plane was simulated by using the angular spectrum method, and the optimization searched for the time delays that minimized the least squared difference between the magnitudes of the simulated and desired pressure fields. The acoustic field was shaped in two different ways: the −6 dB focal width was increased to different desired widths and the ring-shaped pressure distributions of various prescribed diameters were produced. For both cases, the set of delays resulting from the respective optimization schemes were confirmed to yield the desired pressure distributions by using simulations and measurements. The simulations, however, predicted peak positive pressures roughly half those obtained from the measurements, which was attributed to the exclusion of nonlinearity in the simulations. PMID:18537369
NASA Astrophysics Data System (ADS)
Zimmerman, Robert Allen
Zooplankton and micronekton which cause a density discontinuity with the surrounding seawater reflect acoustic energy. This acoustic backscatter intensity (ABI) was measured using a vessel mounted 153 kHz acoustic Doppler current profiler. The ABI was used to describe vertical migration and distribution of sound scatterers in several mesoscale hydrographic features commonly found in the Gulf of Mexico: cold-core rings (CCRs), warm-core Loop Current eddies (LCEs) and the Loop Current (LC). The present paradigm contends that cold- core (cyclonic) features are mesoscale areas of enhanced production due to an influx of new nitrogen to surface waters as a result of divergent flow. The null hypothesis which was tested in this study was that the acoustic signatures of these features were not significantly different from one another. Clear diel differences in all of the features and a robust, positive correlation between ABI and plankton and micronekton wet displacement volume collected in MOCNESS tows in the upper 100 m of the water column were observed. During the day, ABI in CCRs was significantly greater than in LCEs and in the LC with regards to the upper 200 m. However, ABI in the LCEs and LC were not significantly different from each other. During the night, the ABI in the upper 50 m of the CCRs was significantly greater than that in the LCEs and the LC. However, there were no differences between features when ABI at night was summed for the entire upper 200 m, due to substantial vertical migrations of organisms into the upper 200 m of the water column at night. Two LCEs were revisited at an age of 8-9 months after their initial acoustic transects. The null hypothesis that there would be no significant difference in integrated ABI when the LCEs were resampled was rejected: both LCEs showed a reduction in integrated ABI over the upper 200 m. Further investigations into the faunal changes of these features are warranted, but the ADCP should continue to be a useful
Near-Field Imaging with Sound: An Acoustic STM Model
NASA Astrophysics Data System (ADS)
Euler, Manfred
2012-10-01
The invention of scanning tunneling microscopy (STM) 30 years ago opened up a visual window to the nano-world and sparked off a bunch of new methods for investigating and controlling matter and its transformations at the atomic and molecular level. However, an adequate theoretical understanding of the method is demanding; STM images can be considered quantum theory condensed into a pictorial representation. A hands-on model is presented for demonstrating the imaging principles in introductory teaching. It uses sound waves and computer visualization to create mappings of acoustic resonators. The macroscopic simile is made possible by quantum-classical analogies between matter and sound waves. Grounding STM in acoustic experience may help to make the underlying quantum concepts such as tunneling less abstract to students.
Numerical Analysis of the Acoustic Field of Tip-Clearance Flow
NASA Astrophysics Data System (ADS)
Alavi Moghadam, S. M.; M. Meinke Team; W. Schröder Team
2015-11-01
Numerical simulations of the acoustic field generated by a shrouded axial fan are studied by a hybrid fluid-dynamics-acoustics method. In a first step, large-eddy simulations are performed to investigate the dynamics of tip clearance flow for various tip gap sizes and to determine the acoustic sources. The simulations are performed for a single blade out of five blades with periodic boundary conditions in the circumferential direction on a multi-block structured mesh with 1.4 ×108 grid points. The turbulent flow is simulated at a Reynolds number of 9.36 ×105 at undisturbed inflow condition and the results are compared with experimental data. The diameter and strength of the tip vortex increase with the tip gap size, while simultaneously the efficiency of the fan decreases. In a second step, the acoustic field on the near field is determined by solving the acoustic perturbation equations (APE) on a mesh for a single blade consisting of approx. 9.8 ×108 grid points. The overall agreement of the pressure spectrum and its directivity with measurements confirm the correct identification of the sound sources and accurate prediction of the acoustic duct propagation. The results show that the longer the tip gap size the higher the broadband noise level. Senior Scientist, Institute of Aerodynamics, RWTH Aachen University.
Application of 30-MHz acoustic scattering to the study of human red blood cells
Roos, M.S.; Apfel, R.E.; Wardlaw, S.C.
1988-04-01
A technique for simultaneously measuring the scattering amplitude of individual particles at two angles is applied to human red blood cells. Using a Rayleigh scattering model, the density and compressibility of the cells may be determined given a priori knowledge of their volume. A calibration method relying on measurements of the bulk properties of particle suspensions is described. Red cell properties in hypotonic and hypertonic hosts are compared with a homogeneous mixture model, and a linear relation between hemoglobin content and scattering amplitude at a 90 deg scattering angle is established.
Progress in the Understanding of Narrow Directional Scattering over Agricultural Fields
NASA Astrophysics Data System (ADS)
Wegmuller, U.; Santoro, M.; Mattia, F.; Balenzano, A.; Satalino, G.; Marzahn, P.; Fischer, G.; Ludwig, R.; Floury, N.
2010-12-01
Results achieved in a comprehensive study on directional microwave scattering over agricultural fields are presented. Major progress presented includes the much improved experimental evidence achieved and significant improvements in the understanding of the scatter phenomenon through the presented scatter model. Good progress is also made in the detection of directional scattering. It is concluded that directional scattering is relevant for applications and cannot just be ignored.
Modelling acoustic scattering, sound speed, and attenuation in gassy soft marine sediments.
Mantouka, A; Dogan, H; White, P R; Leighton, T G
2016-07-01
A model for nonlinear gas bubble pulsation in marine sediments is presented. This model is then linearized to determine the resonance frequency and the damping terms for linear radial oscillations. The linear model is then used to predict the effects that such bubble pulsations will have on the sound speed and attenuation of acoustic waves propagating in gassy marine sediment. The results are compared for monodisperse populations against the predictions of a model of Anderson and Hampton and, furthermore, the additional abilities of the model introduced in this paper are discussed. These features include the removal of the sign ambiguities in the expressions, the straightforward implementation for acoustic propagation through polydisperse bubble populations, the capability to estimate bubble size distributions through a full acoustic inversion, and the capability to predict nonlinear effects. PMID:27475152
Wu, Sean F; Moondra, Manmohan; Beniwal, Ravi
2015-04-01
The Helmholtz equation least squares (HELS)-based nearfield acoustical holography (NAH) is utilized to analyze panel acoustic contributions toward the acoustic field inside the interior region of an automobile. Specifically, the acoustic power flows from individual panels are reconstructed, and relative contributions to sound pressure level and spectrum at any point of interest are calculated. Results demonstrate that by correlating the acoustic power flows from individual panels to the field acoustic pressure, one can correctly locate the panel allowing the most acoustic energy transmission into the vehicle interior. The panel on which the surface acoustic pressure amplitude is the highest should not be used as indicative of the panel responsible for the sound field in the vehicle passenger compartment. Another significant advantage of this HELS-based NAH is that measurements of the input data only need to be taken once by using a conformal array of microphones in the near field, and ranking of panel acoustic contributions to any field point can be readily performed. The transfer functions between individual panels of any vibrating structure to the acoustic pressure anywhere in space are calculated not measured, thus significantly reducing the time and effort involved in panel acoustic contributions analyses.
Prediction of the acoustic and bubble fields in insonified freeze-drying vials.
Louisnard, O; Cogné, C; Labouret, S; Montes-Quiroz, W; Peczalski, R; Baillon, F; Espitalier, F
2015-09-01
The acoustic field and the location of cavitation bubble are computed in vials used for freeze-drying, insonified from the bottom by a vibrating plate. The calculations rely on a nonlinear model of sound propagation in a cavitating liquid [Louisnard, Ultrason. Sonochem., 19, (2012) 56-65]. Both the vibration amplitude and the liquid level in the vial are parametrically varied. For low liquid levels, a threshold amplitude is required to form a cavitation zone at the bottom of the vial. For increasing vibration amplitudes, the bubble field slightly thickens but remains at the vial bottom, and the acoustic field saturates, which cannot be captured by linear acoustics. On the other hand, increasing the liquid level may promote the formation of a secondary bubble structure near the glass wall, a few centimeters below the free liquid surface. These predictions suggest that rather complex acoustic fields and bubble structures can arise even in such small volumes. As the acoustic and bubble fields govern ice nucleation during the freezing step, the final crystal's size distribution in the frozen product may crucially depend on the liquid level in the vial. PMID:25800984
Jiao, Junjie; He, Yong; Yasui, Kyuichi; Kentish, Sandra E; Ashokkumar, Muthupandian; Manasseh, Richard; Lee, Judy
2015-01-01
In this study, the coalescence time between two contacting sub-resonance size bubbles was measured experimentally under an acoustic pressure ranging from 10kPa to 120kPa, driven at a frequency of 22.4kHz. The coalescence time obtained under sonication was much longer compared to that calculated by the film drainage theory for a free bubble surface without surfactants. It was found that under the influence of an acoustic field, the coalescence time could be probabilistic in nature, exhibiting upper and lower limits of coalescence times which are prolonged when both the maximum surface approach velocity and secondary Bjerknes force increases. The size of the two contacting bubbles is also important. For a given acoustic pressure, bubbles having a larger average size and size difference were observed to exhibit longer coalescence times. This could be caused by the phase difference between the volume oscillations of the two bubbles, which in turn affects the minimum film thickness reached between the bubbles and the film drainage time. These results will have important implications for developing film drainage theory to account for the effect of bubble translational and volumetric oscillations, bubble surface fluctuations and microstreaming.
Full-Field Imaging of GHz Film Bulk Acoustic Resonator Motion
Telschow, Kenneth Louis; Deason, Vance Albert; Cottle, David Lynn; Larson III, J. D.
2003-10-01
A full-field view laser ultrasonic imaging method has been developed that measures acoustic motion at a surface without scanning. Images are recorded at normal video frame rates by using dynamic holography with photorefractive interferometric detection. By extending the approach to ultra high frequencies, an acoustic microscope has been developed that is capable of operation at gigahertz frequency and micron length scales. Both acoustic amplitude and phase are recorded, allowing full calibration and determination of phases to within a single arbitrary constant. Results are presented of measurements at frequencies of 800-900 MHz, illustrating a multitude of normal mode behavior in electrically driven thin film acoustic resonators. Coupled with microwave electrical impedance measurements, this imaging mode provides an exceptionally fast method for evaluation of electric-to-acoustic coupling of these devices and their performance. Images of 256 /spl times/ 240 pixels are recorded at 18 fps rates synchronized to obtain both in-phase and quadrature detection of the acoustic motion. Simple averaging provides sensitivity to the subnanometer level at each pixel calibrated over the image using interferometry. Identification of specific acoustic modes and their relationship to electrical impedance characteristics show the advantages and overall high speed of the technique.
Full-Field Imaging of Acoustic Motion at Nanosecond Time and Micron Length Scales
Telschow, Kenneth Louis; Deason, Vance Albert; Cottle, David Lynn; Larson III, John D.
2002-10-01
A full-field view laser ultrasonic imaging method has been developed that measures acoustic motion at a surface without scanning. Images are recorded at normal video frame rates by employing dynamic holography using photorefractive interferometric detection. By extending the approach to ultra high frequencies, an acoustic microscope has been developed capable of operation on the nanosecond time and micron length scales. Both acoustic amplitude and phase are recorded allowing full calibration and determination of phases to within a single arbitrary constant. Results are presented of measurements at frequencies at 800-900 MHz illustrating a multitude of normal mode behavior in electrically driven thin film acoustic resonators. Coupled with microwave electrical impedance measurements, this imaging mode provides an exceptionally fast method for evaluation of electric to acoustic coupling and performance of these devices. Images of 256x240 pixels are recorded at 18Hz rates synchronized to obtain both in-phase and quadrature detection of the acoustic motion. Simple averaging provides sensitivity to the subnanometer level calibrated over the image using interferometry. Identification of specific acoustic modes and their relationship to electrical impedance characteristics show the advantages and overall high speed of the technique.
Recovery of burner acoustic source structure from far-field sound spectra
NASA Technical Reports Server (NTRS)
Mahan, J. R.; Jones, J. D.
1984-01-01
A method is presented that permits the thermal-acoustic efficiency spectrum in a long turbulent burner to be recovered from the corresponding far-field sound spectrum. An acoustic source/propagation model is used based on the perturbation solution of the equations describing the unsteady one-dimensional flow of an inviscid ideal gas with a distributed heat source. The technique is applied to a long cylindrical hydrogen-flame burner operating over power levels of 4.5-22.3 kW. The results show that the thermal-acoustic efficiency at a given frequency, defined as the fraction of the total burner power converted to acoustic energy at that frequency, is rather insensitive to burner power, having a maximum value on the order of 10 to the -4th at 150 Hz and rolling off steeply with increasing frequency. Evidence is presented that acoustic agitation of the flame at low frequencies enhances the mixing of the unburned fuel and air with the hot products of combustion. The paper establishes the potential of the technique as a useful tool for characterizing the acoustic source structure in any burner, such as a gas turbine combustor, for which a reasonable acoustic propagation model can be postulated.
NASA Astrophysics Data System (ADS)
Carlson, Arthur W.
1987-05-01
An upper bound of (ñe/ne) <10-4 for frequencies and wavenumbers relevant to the lower-hybrid-drift (LHD) instability is set on fluctuations in field-reversed configurations (FRC's) produced by TRX-2 [Fusion Techn. 9, 48 (1986)]. LHD is a well-studied microinstability that is often invoked to explain particle loss rates in FRC's. The conventional technique of CO2 laser scattering with heterodyne detection is here modified to compensate for severe refraction. The calibration of the system is verified by scattering from acoustic waves in salt. The measured bound is two orders of magnitude below both the fluctuation level usually predicted and the level needed to account for observed particle loss rates. Electron collisionality is identified as the most likely LHD stabilization mechanism. Some alternative explanations of anomalous loss rates are discussed.
Daeva, S.G.; Setukha, A.V.
2015-03-10
A numerical method for solving a problem of diffraction of acoustic waves by system of solid and thin objects based on the reduction the problem to a boundary integral equation in which the integral is understood in the sense of finite Hadamard value is proposed. To solve this equation we applied piecewise constant approximations and collocation methods numerical scheme. The difference between the constructed scheme and earlier known is in obtaining approximate analytical expressions to appearing system of linear equations coefficients by separating the main part of the kernel integral operator. The proposed numerical scheme is tested on the solution of the model problem of diffraction of an acoustic wave by inelastic sphere.
Muir, Thomas G; Costley, R Daniel; Sabatier, James M
2014-01-01
Finite element methods are utilized to model and compare the use of both a remote loudspeaker and a vertical shaker in the generation of sound and shear and interface waves in an elastic solid containing an imbedded elastic scatterer, which is resonant. Results for steady state and transient insonification are presented to illustrate excitation, propagation, and scattering mechanisms and effects. Comparisons of acoustic and vibratory excitation of the solid interface are made, with a view towards remote sensing of induced vibratory motion through optical measurement of the ground interface motion above the imbedded inclusion. Some advantages of the acoustic excitation method for exciting plate mode resonances in the target are observed. PMID:24437744
Muir, Thomas G; Costley, R Daniel; Sabatier, James M
2014-01-01
Finite element methods are utilized to model and compare the use of both a remote loudspeaker and a vertical shaker in the generation of sound and shear and interface waves in an elastic solid containing an imbedded elastic scatterer, which is resonant. Results for steady state and transient insonification are presented to illustrate excitation, propagation, and scattering mechanisms and effects. Comparisons of acoustic and vibratory excitation of the solid interface are made, with a view towards remote sensing of induced vibratory motion through optical measurement of the ground interface motion above the imbedded inclusion. Some advantages of the acoustic excitation method for exciting plate mode resonances in the target are observed.
Generalizations of Karp's theorem to elastic scattering theory
NASA Astrophysics Data System (ADS)
Tuong, Ha-Duong
Karp's theorem states that if the far field pattern corresponding to the scattering of a time-harmonic acoustic plane wave by a sound-soft obstacle in R2 is invariant under the group of rotations, then the scatterer is a circle. The theorem is generalized to the elastic scattering problems and the axisymmetric scatterers in R3.
Reciprocity principle for scattered fields from discontinuities in waveguides.
Pau, Annamaria; Capecchi, Danilo; Vestroni, Fabrizio
2015-01-01
This study investigates the scattering of guided waves from a discontinuity exploiting the principle of reciprocity in elastodynamics, written in a form that applies to waveguides. The coefficients of reflection and transmission for an arbitrary mode can be derived as long as the principle of reciprocity is satisfied at the discontinuity. Two elastodynamic states are related by the reciprocity. One is the response of the waveguide in the presence of the discontinuity, with the scattered fields expressed as a superposition of wave modes. The other state is the response of the waveguide in the absence of the discontinuity oscillating according to an arbitrary mode. The semi-analytical finite element method is applied to derive the needed dispersion relation and wave mode shapes. An application to a solid cylinder with a symmetric double change of cross-section is presented. This model is assumed to be representative of a damaged rod. The coefficients of reflection and transmission of longitudinal waves are investigated for selected values of notch length and varying depth.
Source fields reconstruction with 3D mapping by means of the virtual acoustic volume concept
NASA Astrophysics Data System (ADS)
Forget, S.; Totaro, N.; Guyader, J. L.; Schaeffer, M.
2016-10-01
This paper presents the theoretical framework of the virtual acoustic volume concept and two related inverse Patch Transfer Functions (iPTF) identification methods (called u-iPTF and m-iPTF depending on the chosen boundary conditions for the virtual volume). They are based on the application of Green's identity on an arbitrary closed virtual volume defined around the source. The reconstruction of sound source fields combines discrete acoustic measurements performed at accessible positions around the source with the modal behavior of the chosen virtual acoustic volume. The mode shapes of the virtual volume can be computed by a Finite Element solver to handle the geometrical complexity of the source. As a result, it is possible to identify all the acoustic source fields at the real surface of an irregularly shaped structure and irrespective of its acoustic environment. The m-iPTF method is introduced for the first time in this paper. Conversely to the already published u-iPTF method, the m-iPTF method needs only acoustic pressure and avoids particle velocity measurements. This paper is focused on its validation, both with numerical computations and by experiments on a baffled oil pan.
Design of acoustic logging signal source of imitation based on field programmable gate array
NASA Astrophysics Data System (ADS)
Zhang, K.; Ju, X. D.; Lu, J. Q.; Men, B. Y.
2014-08-01
An acoustic logging signal source of imitation is designed and realized, based on the Field Programmable Gate Array (FPGA), to improve the efficiency of examining and repairing acoustic logging tools during research and field application, and to inspect and verify acoustic receiving circuits and corresponding algorithms. The design of this signal source contains hardware design and software design,and the hardware design uses an FPGA as the control core. Four signals are made first by reading the Random Access Memory (RAM) data which are inside the FPGA, then dealing with the data by digital to analog conversion, amplification, smoothing and so on. Software design uses VHDL, a kind of hardware description language, to program the FPGA. Experiments illustrate that the ratio of signal to noise for the signal source is high, the waveforms are stable, and also its functions of amplitude adjustment, frequency adjustment and delay adjustment are in accord with the characteristics of real acoustic logging waveforms. These adjustments can be used to imitate influences on sonic logging received waveforms caused by many kinds of factors such as spacing and span of acoustic tools, sonic speeds of different layers and fluids, and acoustic attenuations of different cementation planes.
Dark matter effective field theory scattering in direct detection experiments
Schneck, K.
2015-05-01
We examine the consequences of the effective field theory (EFT) of dark matter–nucleon scattering for current and proposed direct detection experiments. Exclusion limits on EFT coupling constants computed using the optimum interval method are presented for SuperCDMS Soudan, CDMS II, and LUX, and the necessity of combining results from multiple experiments in order to determine dark matter parameters is discussed. We demonstrate that spectral differences between the standard dark matter model and a general EFT interaction can produce a bias when calculating exclusion limits and when developing signal models for likelihood and machine learning techniques. We also discuss the implications of the EFT for the next-generation (G2) direct detection experiments and point out regions of complementarity in the EFT parameter space.
Dark matter effective field theory scattering in direct detection experiments
Schneck, K.
2015-05-01
We examine the consequences of the effective field theory (EFT) of dark matter–nucleon scattering for current and proposed direct detection experiments. Exclusion limits on EFT coupling constants computed using the optimum interval method are presented for SuperCDMS Soudan, CDMS II, and LUX, and the necessity of combining results from multiple experiments in order to determine dark matter parameters is discussed. We demonstrate that spectral differences between the standard dark matter model and a general EFT interaction can produce a bias when calculating exclusion limits and when developing signal models for likelihood and machine learning techniques. We also discuss the implicationsmore » of the EFT for the next-generation (G2) direct detection experiments and point out regions of complementarity in the EFT parameter space.« less
Dark matter effective field theory scattering in direct detection experiments
NASA Astrophysics Data System (ADS)
Schneck, K.; Cabrera, B.; Cerdeño, D. G.; Mandic, V.; Rogers, H. E.; Agnese, R.; Anderson, A. J.; Asai, M.; Balakishiyeva, D.; Barker, D.; Basu Thakur, R.; Bauer, D. A.; Billard, J.; Borgland, A.; Brandt, D.; Brink, P. L.; Bunker, R.; Caldwell, D. O.; Calkins, R.; Chagani, H.; Chen, Y.; Cooley, J.; Cornell, B.; Crewdson, C. H.; Cushman, P.; Daal, M.; Di Stefano, P. C. F.; Doughty, T.; Esteban, L.; Fallows, S.; Figueroa-Feliciano, E.; Godfrey, G. L.; Golwala, S. R.; Hall, J.; Harris, H. R.; Hofer, T.; Holmgren, D.; Hsu, L.; Huber, M. E.; Jardin, D. M.; Jastram, A.; Kamaev, O.; Kara, B.; Kelsey, M. H.; Kennedy, A.; Leder, A.; Loer, B.; Lopez Asamar, E.; Lukens, P.; Mahapatra, R.; McCarthy, K. A.; Mirabolfathi, N.; Moffatt, R. A.; Morales Mendoza, J. D.; Oser, S. M.; Page, K.; Page, W. A.; Partridge, R.; Pepin, M.; Phipps, A.; Prasad, K.; Pyle, M.; Qiu, H.; Rau, W.; Redl, P.; Reisetter, A.; Ricci, Y.; Roberts, A.; Saab, T.; Sadoulet, B.; Sander, J.; Schnee, R. W.; Scorza, S.; Serfass, B.; Shank, B.; Speller, D.; Toback, D.; Upadhyayula, S.; Villano, A. N.; Welliver, B.; Wilson, J. S.; Wright, D. H.; Yang, X.; Yellin, S.; Yen, J. J.; Young, B. A.; Zhang, J.; SuperCDMS Collaboration
2015-05-01
We examine the consequences of the effective field theory (EFT) of dark matter-nucleon scattering for current and proposed direct detection experiments. Exclusion limits on EFT coupling constants computed using the optimum interval method are presented for SuperCDMS Soudan, CDMS II, and LUX, and the necessity of combining results from multiple experiments in order to determine dark matter parameters is discussed. We demonstrate that spectral differences between the standard dark matter model and a general EFT interaction can produce a bias when calculating exclusion limits and when developing signal models for likelihood and machine learning techniques. We also discuss the implications of the EFT for the next-generation (G2) direct detection experiments and point out regions of complementarity in the EFT parameter space.
Dark matter effective field theory scattering in direct detection experiments
Schneck, K.; Cabrera, B.; Cerdeño, D. G.; Mandic, V.; Rogers, H. E.; Agnese, R.; Anderson, A. J.; Asai, M.; Balakishiyeva, D.; Barker, D.; Basu Thakur, R.; Bauer, D. A.; Billard, J.; Borgland, A.; Brandt, D.; Brink, P. L.; Bunker, R.; Caldwell, D. O.; Calkins, R.; Chagani, H.; Chen, Y.; Cooley, J.; Cornell, B.; Crewdson, C. H.; Cushman, P.; Daal, M.; Di Stefano, P. C. F.; Doughty, T.; Esteban, L.; Fallows, S.; Figueroa-Feliciano, E.; Godfrey, G. L.; Golwala, S. R.; Hall, J.; Harris, H. R.; Hofer, T.; Holmgren, D.; Hsu, L.; Huber, M. E.; Jardin, D. M.; Jastram, A.; Kamaev, O.; Kara, B.; Kelsey, M. H.; Kennedy, A.; Leder, A.; Loer, B.; Lopez Asamar, E.; Lukens, P.; Mahapatra, R.; McCarthy, K. A.; Mirabolfathi, N.; Moffatt, R. A.; Morales Mendoza, J. D.; Oser, S. M.; Page, K.; Page, W. A.; Partridge, R.; Pepin, M.; Phipps, A.; Prasad, K.; Pyle, M.; Qiu, H.; Rau, W.; Redl, P.; Reisetter, A.; Ricci, Y.; Roberts, A.; Saab, T.; Sadoulet, B.; Sander, J.; Schnee, R. W.; Scorza, S.; Serfass, B.; Shank, B.; Speller, D.; Toback, D.; Upadhyayula, S.; Villano, A. N.; Welliver, B.; Wilson, J. S.; Wright, D. H.; Yang, X.; Yellin, S.; Yen, J. J.; Young, B. A.; Zhang, J.
2015-05-18
We examine the consequences of the effective field theory (EFT) of dark matter-nucleon scattering for current and proposed direct detection experiments. Exclusion limits on EFT coupling constants computed using the optimum interval method are presented for SuperCDMS Soudan, CDMS II, and LUX, and the necessity of combining results from multiple experiments in order to determine dark matter parameters is discussed. Here. we demonstrate that spectral differences between the standard dark matter model and a general EFT interaction can produce a bias when calculating exclusion limits and when developing signal models for likelihood and machine learning techniques. In conclusion, we discuss the implications of the EFT for the next-generation (G2) direct detection experiments and point out regions of complementarity in the EFT parameter space.
Thermally induced secondary atomization of droplet in an acoustic field
NASA Astrophysics Data System (ADS)
Basu, Saptarshi; Saha, Abhishek; Kumar, Ranganathan
2012-01-01
We study the thermal effects that lead to instability and break up in acoustically levitated vaporizing fuel droplets. For selective liquids, atomization occurs at the droplet equator under external heating. Short wavelength [Kelvin-Helmholtz (KH)] instability for diesel and bio-diesel droplets triggers this secondary atomization. Vapor pressure, latent heat, and specific heat govern the vaporization rate and temperature history, which affect the surface tension gradient and gas phase density, ultimately dictating the onset of KH instability. We develop a criterion based on Weber number to define a condition for the inception of secondary atomization.
Orthogonal acoustical factors of a sound field in a bamboo forest.
Sakai, H; Shibata, S; Ando, Y
2001-06-01
To investigate the acoustical quality of a sound field in a bamboo forest, acoustical measurements were conducted to obtain orthogonal acoustical factors of the sound field. These results are compared with previous results for a sound field in an ordinary forest [H. Sakai, S. Sato, and Y. Ando, J. Acoust. Soc. Am. 104, 1491-1497 (1998)]. The IACC, which is defined as a maximum value of the normalized interaural cross-correlation function between signals at the ears, was 0.07 (4 kHz) and 0.16 (2 kHz) at positions 20 and 40 m from the source, respectively. These values are much better than those in the previously investigated forest. The measured subsequent reverberation time Tsub was up to 1.5 s in the frequency range above 1 kHz at the position 40 m from the source. For certain music sources with higher frequency components, therefore, sound fields in a bamboo forest have excellent acoustic properties.
NASA Astrophysics Data System (ADS)
Fujii, Ayaka; Wakatsuki, Naoto; Mizutani, Koichi
2016-01-01
A method of suppressing sound radiation to the far field of a near-field acoustic communication system using an evanescent sound field is proposed. The amplitude of the evanescent sound field generated from an infinite vibrating plate attenuates exponentially with increasing a distance from the surface of the vibrating plate. However, a discontinuity of the sound field exists at the edge of the finite vibrating plate in practice, which broadens the wavenumber spectrum. A sound wave radiates over the evanescent sound field because of broadening of the wavenumber spectrum. Therefore, we calculated the optimum distribution of the particle velocity on the vibrating plate to reduce the broadening of the wavenumber spectrum. We focused on a window function that is utilized in the field of signal analysis for reducing the broadening of the frequency spectrum. The optimization calculation is necessary for the design of window function suitable for suppressing sound radiation and securing a spatial area for data communication. In addition, a wide frequency bandwidth is required to increase the data transmission speed. Therefore, we investigated a suitable method for calculating the sound pressure level at the far field to confirm the variation of the distribution of sound pressure level determined on the basis of the window shape and frequency. The distribution of the sound pressure level at a finite distance was in good agreement with that obtained at an infinite far field under the condition generating the evanescent sound field. Consequently, the window function was optimized by the method used to calculate the distribution of the sound pressure level at an infinite far field using the wavenumber spectrum on the vibrating plate. According to the result of comparing the distributions of the sound pressure level in the cases with and without the window function, it was confirmed that the area whose sound pressure level was reduced from the maximum level to -50 dB was
Spatiotemporal Imaging of the Acoustic Field Emitted by a Single Copper Nanowire
NASA Astrophysics Data System (ADS)
Jean, Cyril; Belliard, Laurent; Cornelius, Thomas W.; Thomas, Olivier; Pennec, Yan; Cassinelli, Marco; Toimil-Molares, Maria Eugenia; Perrin, Bernard
2016-10-01
The monochromatic and geometrically anisotropic acoustic field generated by 400 nm and 120 nm diameter copper nanowires simply dropped on a 10 $\\mu$m silicon membrane is investigated in transmission using three-dimensional time-resolved femtosecond pump-probe experiments. Two pump-probe time-resolved experiments are carried out at the same time on both side of the silicon substrate. In reflection, the first radial breathing mode of the nanowire is excited and detected. In transmission, the longitudinal and shear waves are observed. The longitudinal signal is followed by a monochromatic component associated with the relaxation of the nanowire's first radial breathing mode. Finite Difference Time Domain (FDTD) simulations are performed and accurately reproduce the diffracted field. A shape anisotropy resulting from the large aspect ratio of the nanowire is detected in the acoustic field. The orientation of the underlying nanowires is thus acoustically deduced.
NASA Astrophysics Data System (ADS)
Nero, R. W.; Magnuson, J. J.; Brandt, S. B.; Stanton, T. K.; Jech, J. M.
1990-06-01
The spatial distribution of biological scatterers within the Gulf Stream front is inferred from an analysis of patch statistics obtained from digitally recorded backscattering data. Acoustic data were collected along 10 transects perpendicular to the front using a downward-looking 70 kHz echosounder. Patches were defined using an algorithm selected to search for finescale patches from within 200 × 900 element (approx. 200 m depth × 24 km length) integrated echo data. Based on principal component analyses of 17 patch parameters, we identified the third most important component as a measure of "acoustic roughness" (containing the coefficient of variance and coefficient of roughness of the integrated echo independent of echo intensity). This third component was a good descriptor of differences among patches within scattering layers and between water masses. It is independent of echo strength and patch size which constitute the first two components. We interpret higher acoustic roughness within patches to indicate a more contagious (clumped) distribution of animals within those patches. Classification of patches on acoustic roughness showed that patches were often acoustically different from distant neighbors but more similar to neighbors within the same scattering layer or region. We infer that finescale layers are made up of small patches of like animals exhibiting a similar spatial arrangement throughout the layer. Cross-stream differences in acoustic roughness indicate a greater number of solitary scatterers occur within the slope water than within the Gulf Stream. Acoustic roughness is also reduced at night when compared with day, indicating that the ascent of vertical migrators into the near-surface waters (<200 m) results in a more dispersed spatial pattern.
Active control of acoustic pressure fields using smart material technologies
NASA Technical Reports Server (NTRS)
Banks, H. T.; Smith, R. C.
1993-01-01
An overview describing the use of piezoceramic patches in reducing noise in a structural acoustics setting is presented. The passive and active contributions due to patches which are bonded to an Euler-Bernoulli beam or thin shell are briefly discussed and the results are incorporated into a 2-D structural acoustics model. In this model, an exterior noise source causes structural vibrations which in turn lead to interior noise as a result of nonlinear fluid/structure coupling mechanism. Interior sound pressure levels are reduced via patches bonded to the flexible boundary (a beam in this case) which generate pure bending moments when an out-of-phase voltage is applied. Well-posedness results for the infinite dimensional system are discussed and a Galerkin scheme for approximating the system dynamics is outlined. Control is implemented by using linear quadratic regulator (LQR) optimal control theory to calculate gains for the linearized system and then feeding these gains back into the nonlinear system of interest. The effectiveness of this strategy for this problem is illustrated in an example.
Flow Field and Acoustic Predictions for Three-Stream Jets
NASA Technical Reports Server (NTRS)
Simmons, Shaun Patrick; Henderson, Brenda S.; Khavaran, Abbas
2014-01-01
Computational fluid dynamics was used to analyze a three-stream nozzle parametric design space. The study varied bypass-to-core area ratio, tertiary-to-core area ratio and jet operating conditions. The flowfield solutions from the Reynolds-Averaged Navier-Stokes (RANS) code Overflow 2.2e were used to pre-screen experimental models for a future test in the Aero-Acoustic Propulsion Laboratory (AAPL) at the NASA Glenn Research Center (GRC). Flowfield solutions were considered in conjunction with the jet-noise-prediction code JeNo to screen the design concepts. A two-stream versus three-stream computation based on equal mass flow rates showed a reduction in peak turbulent kinetic energy (TKE) for the three-stream jet relative to that for the two-stream jet which resulted in reduced acoustic emission. Additional three-stream solutions were analyzed for salient flowfield features expected to impact farfield noise. As tertiary power settings were increased there was a corresponding near nozzle increase in shear rate that resulted in an increase in high frequency noise and a reduction in peak TKE. As tertiary-to-core area ratio was increased the tertiary potential core elongated and the peak TKE was reduced. The most noticeable change occurred as secondary-to-core area ratio was increased thickening the secondary potential core, elongating the primary potential core and reducing peak TKE. As forward flight Mach number was increased the jet plume region decreased and reduced peak TKE.
Scattering of a Hermite-Gaussian beam field by a chiral sphere.
Yokota, M; He, S; Takenaka, T
2001-07-01
Scattering of a Hermite-Gaussian beam field by a chiral sphere is analyzed. A Hermite-Gaussian beam field is expressed as a superposition of multipole fields at complex-source points. Electromagnetic fields are expanded in terms of the spherical vector wave functions. The unknown expansion coefficients for the scattered field and the internal field are determined by the boundary conditions. As numerical examples, the scattered near fields of the beam incidence are calculated, and the effects of the chirality and the radius of the chiral sphere on the fields are examined. The results for a Gaussian beam incidence are also compared with those of a plane-wave incidence.
Second harmonic acoustic responses induced in matter by quasi continuous radiofrequency fields
NASA Astrophysics Data System (ADS)
Kellnberger, Stephan; Omar, Murad; Sergiadis, George; Ntziachristos, Vasilis
2013-10-01
We subjected conductive matter and tissue to intermittent continuous-wave radiofrequency fields and investigated whether acoustic responses could be recorded. By placing samples in the near-field of the excitation, we observed frequency-domain acoustic responses from tissues responding to CW radiofrequency excitation. Frequency analysis revealed the generation of 2nd harmonic mechanical waves. This discovery of non-linear responses can lead to alternative measurement concepts of CW radiofrequency deposition in matter and tissues. We offer the theoretical mainframe and discuss sensing applications involving the direct measurement of second harmonic responses representative of CW RF energy deposition in matter.
Geodesic acoustic modes in tokamak plasmas with a radial equilibrium electric field
Zhou, Deng
2015-09-15
The dispersion relation of geodesic acoustic modes in the tokamak plasma with an equilibrium radial electric field is derived and analyzed. Multiple branches of eigenmodes have been found, similar to the result given by the fluid model with a poloidal mass flow. Frequencies and damping rates of both the geodesic acoustic mode and the sound wave increase with respect to the strength of radial electric field, while the frequency and the damping rate of the lower frequency branch slightly decrease. Possible connection to the experimental observation is discussed.
The optimization of acoustic fields for ablative therapies of tumours in the upper abdomen.
Gélat, P; Ter Haar, G; Saffari, N
2012-12-21
High intensity focused ultrasound (HIFU) enables highly localized, non-invasive tissue ablation and its efficacy has been demonstrated in the treatment of a range of cancers, including those of the kidney, prostate and breast. HIFU offers the ability to treat deep-seated tumours locally, and potentially bears fewer side effects than more invasive treatment modalities such as resection, chemotherapy and ionizing radiation. There remains however a number of significant challenges which currently hinder its widespread clinical application. One of these challenges is the need to transmit sufficient energy through the ribcage to ablate tissue at the required foci whilst minimizing the formation of side lobes and sparing healthy tissue. Ribs both absorb and reflect ultrasound strongly. This sometimes results in overheating of bone and overlying tissue during treatment, leading to skin burns. Successful treatment of a patient with tumours in the upper abdomen therefore requires a thorough understanding of the way acoustic and thermal energy is deposited. Previously, a boundary element approach based on a Generalized Minimal Residual (GMRES) implementation of the Burton-Miller formulation was developed to predict the field of a multi-element HIFU array scattered by human ribs, the topology of which was obtained from CT scan data (Gélat et al 2011 Phys. Med. Biol. 56 5553-81). The present paper describes the reformulation of the boundary element equations as a least-squares minimization problem with nonlinear constraints. The methodology has subsequently been tested at an excitation frequency of 1 MHz on a spherical multi-element array in the presence of ribs. A single array-rib geometry was investigated on which a 50% reduction in the maximum acoustic pressure magnitude on the surface of the ribs was achieved with only a 4% reduction in the peak focal pressure compared to the spherical focusing case. This method was then compared with a binarized apodization approach
The optimization of acoustic fields for ablative therapies of tumours in the upper abdomen
NASA Astrophysics Data System (ADS)
Gélat, P.; ter Haar, G.; Saffari, N.
2012-12-01
High intensity focused ultrasound (HIFU) enables highly localized, non-invasive tissue ablation and its efficacy has been demonstrated in the treatment of a range of cancers, including those of the kidney, prostate and breast. HIFU offers the ability to treat deep-seated tumours locally, and potentially bears fewer side effects than more invasive treatment modalities such as resection, chemotherapy and ionizing radiation. There remains however a number of significant challenges which currently hinder its widespread clinical application. One of these challenges is the need to transmit sufficient energy through the ribcage to ablate tissue at the required foci whilst minimizing the formation of side lobes and sparing healthy tissue. Ribs both absorb and reflect ultrasound strongly. This sometimes results in overheating of bone and overlying tissue during treatment, leading to skin burns. Successful treatment of a patient with tumours in the upper abdomen therefore requires a thorough understanding of the way acoustic and thermal energy is deposited. Previously, a boundary element approach based on a Generalized Minimal Residual (GMRES) implementation of the Burton-Miller formulation was developed to predict the field of a multi-element HIFU array scattered by human ribs, the topology of which was obtained from CT scan data (Gélat et al 2011 Phys. Med. Biol. 56 5553-81). The present paper describes the reformulation of the boundary element equations as a least-squares minimization problem with nonlinear constraints. The methodology has subsequently been tested at an excitation frequency of 1 MHz on a spherical multi-element array in the presence of ribs. A single array-rib geometry was investigated on which a 50% reduction in the maximum acoustic pressure magnitude on the surface of the ribs was achieved with only a 4% reduction in the peak focal pressure compared to the spherical focusing case. This method was then compared with a binarized apodization approach
Cryogen free high magnetic field sample environment for neutron scattering
NASA Astrophysics Data System (ADS)
Down, R. B. E.; Kouzmenko, G.; Kirichek, O.; Wotherspoon, R.; Brown, J.; Bowden, Z. A.
2010-11-01
Cryogenic equipment can be found in the majority of neutron scattering experiments. Recent increases in liquid helium cost caused by global helium supply problems lead to significant concern about affordability of conventional cryogenic equipment. However the latest progress in cryo-cooler technology offers a new generation of cryogenic systems in which the cryogen consumption can be significantly reduced and in some cases completely eliminated. These systems also offer the advantage of operational simplicity, require less space than conventional cryogen-cooled systems and can significantly improve user safety. At the ISIS facility it is possible to substitute conventional cryostats with cryogen free systems. Such systems are based on the pulse tube refrigerator (PTR) which possesses no cold moving parts. Oxford Instruments in collaboration with ISIS have developed new high magnetic field sample environment equipment based on re-condensing technology. This project includes 9T wide angle chopper magnet for spectrometry and 14T magnet for diffraction. The main advantage of these systems is that all magnet operating procedures, for example cooling, running up to the field and quenching remain the same as for a standard magnet in a bath cryostat. This approach also provides a homogeneous temperature distribution, which is crucial for optimum magnet performance.
Field installation of an acoustic slug-detection system
Dhulesia, H.; Bernicot, M.; Romanet, T.
1997-02-01
A pipeline operating in the slug flow regime creates high fluctuations in gas and liquid flow rates at the outlet. The detection of slugs and the estimation of their length and velocity are necessary to minimize the upsets in the operation of downstream process facilities. A new method based on the acoustic principle has been developed by Total and Syminex with two variants--passive and active. The passive method gives the slug length and velocity, whereas the active method also gives the fluid density. The prototype of this system has been installed permanently on a 20-in. multiphase pipeline in Argentina. As this system detects the slugs and determines their characteristics approximately 2 minutes before they arrive at the first-stage separator, the operators take appropriate action in the case of arrival of an excessively long slug and, thus, avoid possible shutdowns. At a later stage, an automatic adjustment of the process control valves will be realized.
Design of Scattering Scanning Near-Field Optical Microscope
NASA Astrophysics Data System (ADS)
Schrecongost, Dustin
The primary objective of this work is to construct a fully functional scattering type Scanning Near-field Optical Microscope (s-SNOM), and to understand the working mechanisms behind it. An s-SNOM is an instrument made up of two separate instruments working in unison. One instrument is a scanning optical microscope focusing light onto a raster scanning sample surface combined with an interferometer set up. The second instrument is an Atomic Force Microscope (AFM) operating in noncontact mode. The AFM uses a small probe that interacts with the raster scanning sample surface to map out the topography of the of the sample surface. An s-SNOM uses both of these instruments simultaneously by focusing the light of the optical microscope onto the probe of the AFM. This probe acts as a nano-antenna and confines the light allowing for light-matter interaction to be inferred far below the resolution of the diffraction limit of light. This specific s-SNOM system is unique to others by having a controllable environment. It is high vacuum compatible and variable temperature. In addition, it is efficient at collecting scattered light due to the focusing objective being a partial elliptical mirror which collects 360° of light around the major axis. This s-SNOM system will be used for direct imaging of surface plasmons. Intended works are inducing surface plasmons on InSe thin films, and seeing the enhancement effect of introducing Au nano-rods. Also dielectric properties of materials will be interpreted such as the metal to insulator phase transition of NbO2.
NASA Astrophysics Data System (ADS)
Bolghasi, Alireza; Ghadimi, Parviz; Chekab, Mohammad A. Feizi
2016-09-01
The aim of the present study is to improve the capabilities and precision of a recently introduced Sea Surface Acoustic Simulator (SSAS) developed based on optimization of the Helmholtz-Kirchhoff-Fresnel (HKF) method. The improved acoustic simulator, hereby known as the Modified SSAS (MSSAS), is capable of determining sound scattering from the sea surface and includes an extended Hall-Novarini model and optimized HKF method. The extended Hall-Novarini model is used for considering the effects of sub-surface bubbles over a wider range of radii of sub-surface bubbles compared to the previous SSAS version. Furthermore, MSSAS has the capability of making a three-dimensional simulation of scattered sound from the rough bubbly sea surface with less error than that of the Critical Sea Tests (CST) experiments. Also, it presents scattered pressure levels from the rough bubbly sea surface based on various incident angles of sound. Wind speed, frequency, incident angle, and pressure level of the sound source are considered as input data, and scattered pressure levels and scattering coefficients are provided. Finally, different parametric studies were conducted on wind speeds, frequencies, and incident angles to indicate that MSSAS is quite capable of simulating sound scattering from the rough bubbly sea surface, according to the scattering mechanisms determined by Ogden and Erskine. Therefore, it is concluded that MSSAS is valid for both scattering mechanisms and the transition region between them that are defined by Ogden and Erskine.
NASA Astrophysics Data System (ADS)
Bolghasi, Alireza; Ghadimi, Parviz; Chekab, Mohammad A. Feizi
2016-08-01
The aim of the present study is to improve the capabilities and precision of a recently introduced Sea Surface Acoustic Simulator (SSAS) developed based on optimization of the Helmholtz-Kirchhoff-Fresnel (HKF) method. The improved acoustic simulator, hereby known as the Modified SSAS (MSSAS), is capable of determining sound scattering from the sea surface and includes an extended Hall-Novarini model and optimized HKF method. The extended Hall-Novarini model is used for considering the effects of sub-surface bubbles over a wider range of radii of sub-surface bubbles compared to the previous SSAS version. Furthermore, MSSAS has the capability of making a three-dimensional simulation of scattered sound from the rough bubbly sea surface with less error than that of the Critical Sea Tests (CST) experiments. Also, it presents scattered pressure levels from the rough bubbly sea surface based on various incident angles of sound. Wind speed, frequency, incident angle, and pressure level of the sound source are considered as input data, and scattered pressure levels and scattering coefficients are provided. Finally, different parametric studies were conducted on wind speeds, frequencies, and incident angles to indicate that MSSAS is quite capable of simulating sound scattering from the rough bubbly sea surface, according to the scattering mechanisms determined by Ogden and Erskine. Therefore, it is concluded that MSSAS is valid for both scattering mechanisms and the transition region between them that are defined by Ogden and Erskine.
NASA Astrophysics Data System (ADS)
Bowman, D. C.; Lees, J. M.; Taddeucci, J.; Graettinger, A. H.; Sonder, I.; Valentine, G.
2014-12-01
We investigate the processes that give rise to complex acoustic signals during volcanic blasts by monitoring buried chemical explosions with infrasound and audio range microphones, strong motion sensors, and high speed imagery. Acoustic waveforms vary with scaled depth of burial (SDOB, units in meters per cube root of joules), ranging from high amplitude, impulsive, gas expansion dominated signals at low SDOB to low amplitude, longer duration, ground motion dominated signals at high SDOB. Typically, the sudden upward acceleration of the substrate above the blast produces the first acoustic arrival, followed by a second pulse due to the eruption of pressurized gas at the surface. Occasionally, a third overpressure occurs when displaced material decelerates upon impact with the ground. The transition between ground motion dominated and gas release dominated acoustics ranges between 0.0038-0.0018 SDOB, respectively. For example, one explosion registering an SDOB=0.0031 produced two overpressure pulses of approximately equal amplitude, one due to ground motion, the other to gas release. Recorded volcano infrasound has also identified distinct ground motion and gas release components during explosions at Sakurajima, Santiaguito, and Karymsky volcanoes. Our results indicate that infrasound records may provide a proxy for the depth and energy of these explosions. Furthermore, while magma fragmentation models indicate the possibility of several explosions during a single vulcanian eruption (Alidibirov, Bull Volc., 1994), our results suggest that a single explosion can also produce complex acoustic signals. Thus acoustic records alone cannot be used to distinguish between single explosions and multiple closely-spaced blasts at volcanoes. Results from a series of lateral blasts during the 2014 field experiment further indicates whether vent geometry can produce directional acoustic radiation patterns like those observed at Tungarahua volcano (Kim et al., GJI, 2012). Beside
Schlieren imaging of the standing wave field in an ultrasonic acoustic levitator
NASA Astrophysics Data System (ADS)
Rendon, Pablo Luis; Boullosa, Ricardo R.; Echeverria, Carlos; Porta, David
2015-11-01
We consider a model of a single axis acoustic levitator consisting of two cylinders immersed in air and directed along the same axis. The first cylinder has a flat termination and functions as a sound emitter, and the second cylinder, which is simply a refector, has the side facing the first cylinder cut out by a spherical surface. By making the first cylinder vibrate at ultrasonic frequencies a standing wave is produced in the air between the cylinders which makes it possible, by means of the acoustic radiation pressure, to levitate one or several small objects of different shapes, such as spheres or disks. We use schlieren imaging to observe the acoustic field resulting from the levitation of one or several objects, and compare these results to previous numerical approximations of the field obtained using a finite element method. The authors acknowledge financial support from DGAPA-UNAM through project PAPIIT IN109214.
Field support, data analysis and associated research for the acoustic grenade sounding program
NASA Technical Reports Server (NTRS)
Barnes, T. G.; Bullard, E. R.
1976-01-01
Temperature and horizontal winds in the 30 to 90 km altitude range of the upper atmosphere, were determined by acoustic grenade soundings conducted at Wallops Island, Virginia and Kourou, French Guiana. Field support provided at these locations included deployment of the large area microphone system, supervision, maintenance and operation of sound ranging stations; and coordination of activities. Data analysis efforts included the analysis of field data to determine upper atmospheric meteorological parameters. Profiles for upper atmospheric temperature, wind and density are provided in plots and tables for each of the acoustic grenade soundings conducted during the contract period. Research efforts were directed toward a systematic comparison of temperature data from acoustic grenade with other meteorological sensor probes in the upper atmosphere.
Mizuno, K.; DeGroot, J.S.; Seka, W.; Drake, R.P.
1992-08-01
We have developed 5-channel collective Thomson scattering system to measure the ion acoustic wave excited by the ion acoustic wave decay instabilities. The multichannel collective Thomson scattering technique was established with 4{omega} probe laser beam using GDL laser system at LLE, Univ. of Rochester. We have obtained the ionic charge state Z by measuring the second harmonic emission from the ion acoustic decay instability. The LASNEX computer simulation calculations have been carried out. The experimental results agree very well with the LASNEX computer simulation results with the flux number f=0.l. In high power laser regime, the spectrum become broad, and the {Delta}{gamma} decreases indicating that the turbulent like spectrum is observed. In order to understand the experimental results, we have developed a theory to study absorption of laser and heat transport. This new theory includes the temporal evolution of the heat conduction region. The results agree with flux-limited hydrodynamic simulations.
Mizuno, K.; DeGroot, J.S. ); Seka, W. . Lab. of Laser Energetics); Drake, R.P. )
1992-01-01
We have developed 5-channel collective Thomson scattering system to measure the ion acoustic wave excited by the ion acoustic wave decay instabilities. The multichannel collective Thomson scattering technique was established with 4{omega} probe laser beam using GDL laser system at LLE, Univ. of Rochester. We have obtained the ionic charge state Z by measuring the second harmonic emission from the ion acoustic decay instability. The LASNEX computer simulation calculations have been carried out. The experimental results agree very well with the LASNEX computer simulation results with the flux number f=0.l. In high power laser regime, the spectrum become broad, and the {Delta}{gamma} decreases indicating that the turbulent like spectrum is observed. In order to understand the experimental results, we have developed a theory to study absorption of laser and heat transport. This new theory includes the temporal evolution of the heat conduction region. The results agree with flux-limited hydrodynamic simulations.
Chen, Tao; Fan, Tingbo; Zhang, Wei; Qiu, Yuanyuan; Tu, Juan E-mail: dzhang@nju.edu.cn; Guo, Xiasheng; Zhang, Dong E-mail: dzhang@nju.edu.cn
2014-03-21
Prediction and measurement of the acoustic field emitted from a high intensity focused ultrasound (HIFU) is essential for the accurate ultrasonic treatment. In this study, the acoustic field generated from a strongly focused HIFU transmitter was characterized by a combined experiment and simulation method. The spheroidal beam equation (SBE) was utilized to describe the nonlinear sound propagation. The curve of the source pressure amplitude versus voltage excitation was determined by fitting the measured ratio of the second harmonic to the fundamental component of the focal waveform to the simulation result; finally, the acoustic pressure field generated by the strongly focused HIFU transmitter was predicted by using the SBE model. A commercial fiber optic probe hydrophone was utilized to measure the acoustic pressure field generated from a 1.1 MHz HIFU transmitter with a large half aperture angle of 30°. The maximum measured peak-to-peak pressure was up to 72 MPa. The validity of this combined approach was confirmed by the comparison between the measured results and the calculated ones. The results indicate that the current approach might be useful to describe the HIFU field. The results also suggest that this method is not valid for low excitations owing to low sensitivity of the second harmonic.
Wall, Alan T; Gee, Kent L; Neilsen, Tracianne B; McKinley, Richard L; James, Michael M
2016-04-01
The identification of acoustic sources is critical to targeted noise reduction efforts for jets on high-performance tactical aircraft. This paper describes the imaging of acoustic sources from a tactical jet using near-field acoustical holography techniques. The measurement consists of a series of scans over the hologram with a dense microphone array. Partial field decomposition methods are performed to generate coherent holograms. Numerical extrapolation of data beyond the measurement aperture mitigates artifacts near the aperture edges. A multisource equivalent wave model is used that includes the effects of the ground reflection on the measurement. Multisource statistically optimized near-field acoustical holography (M-SONAH) is used to reconstruct apparent source distributions between 20 and 1250 Hz at four engine powers. It is shown that M-SONAH produces accurate field reconstructions for both inward and outward propagation in the region spanned by the physical hologram measurement. Reconstructions across the set of engine powers and frequencies suggests that directivity depends mainly on estimated source location; sources farther downstream radiate at a higher angle relative to the inlet axis. At some frequencies and engine powers, reconstructed fields exhibit multiple radiation lobes originating from overlapped source regions, which is a phenomenon relatively recently reported for full-scale jets. PMID:27106340
Choi, Min Joo; Doh, Doeg Hee; Hwang, Tae Gyu; Cho, Chu Hyun; Paeng, Dong Guk; Rim, Gun Hee; Coleman, A J
2006-02-01
This study considers the acoustic streaming in water produced by a lithotripsy pulse. Particle image velocimetry (PIV) method was employed to visualize the acoustic streaming produced by an electromagnetic shock wave generator using video images of the light scattering particles suspended in water. Visualized streaming features including several local peaks and vortexes around or at the beam focus were easily seen with naked eyes over all settings of the lithotripter from 10 to 18 kV. Magnitudes of the peak streaming velocity measured vary in the range of 10-40 mm s(-1) with charging voltage settings. Since the streaming velocity was estimated on the basis of a series of the video images of particles averaged over 1/60s, the time resolution limited by the video frame rate which is 1-2 orders of magnitude larger than driving acoustic activities, measured velocities are expected to be underestimated and were shown a similar order of magnitude lower than those calculated from a simple theoretical consideration. Despite such an underestimation, it was shown that, as predicted by theory, the magnitude of the streaming velocity measured by the present PIV method was proportional to acoustic intensity. In particular it has almost a linear correlation with peak negative pressures (r=0.98683, p=0.0018). PMID:16376400
Bafile, Ubaldo; Guarini, Eleonora
2006-06-15
In the Q range where inelastic x-ray and neutron scattering are applied to the study of acoustic collective excitations in fluids, various models of the dynamic structure factor S(Q,{omega}) generalize in different ways the results obtained from linearized-hydrodynamics theory in the Q{yields}0 limit. Here we show that the models most commonly fitted to experimental S(Q,{omega}) spectra can be given a unified formulation. In this way, direct comparisons among the results obtained by fitting different models become now possible to a much larger extent than ever. We also show that a consistent determination of the dispersion curve and of the propagation Q range of the excitations is possible, whichever model is used. We derive an exact formula which describes in all cases the dispersion curve and allows for the first quantitative understanding of its shape, by assigning specific and distinct roles to the various structural, thermal, and damping effects that determine the Q dependence of the mode frequencies. The emerging picture describes the acoustic modes as Q-dependent harmonic oscillators whose characteristic frequency is explicitly renormalized in an exact way by the relaxation processes, which also determine, through the widths of both the inelastic and the elastic lines, the whole shape of collective-excitation spectra.
Elhanaoui, Abdelkader; Aassif, Elhoucein; Maze, Gérard; Décultot, Dominique
2016-02-01
The present paper studies the acoustic signal backscattered by an air-filled copper–solid polymer two-layer cylindrical tube immersed in water. The work is done from the calculation of the backscattered pressure, an inverse Fourier Transform, which allows us to obtain an impulse signal. Smoothed pseudo Wigner–Ville and Concentrated spectrogram representations have been chosen to analyze the scattering phenomenon. For reduced frequencies ranging from 0.1 to 200, the resonance trajectories and time–frequency images have shown the presence of the guided waves. The bifurcation of the A0 wave into the A0(-) and the A0(+) waves has also been observed. The authors provide the phase and the group velocities of guided waves and investigate the differences between curves. The findings are then compared with those obtained for the copper and the solid polymer one-layer cylindrical tubes. Group velocity values have also been extracted from smoothed pseudo Wigner–Ville and Concentrated spectrogram time–frequency images. A good agreement with the theory has, therefore, been observed. The study of acoustic backscattering by a copper–solid polymer two-layer tube has revealed the interaction and the coupling of guided waves, specially the presence of a pseudo A1 wave; which is a very interesting, remarkable phenomenon. PMID:26601563
NASA Astrophysics Data System (ADS)
Bafile, Ubaldo; Guarini, Eleonora; Barocchi, Fabrizio
2006-06-01
In the Q range where inelastic x-ray and neutron scattering are applied to the study of acoustic collective excitations in fluids, various models of the dynamic structure factor S(Q,ω) generalize in different ways the results obtained from linearized-hydrodynamics theory in the Q→0 limit. Here we show that the models most commonly fitted to experimental S(Q,ω) spectra can be given a unified formulation. In this way, direct comparisons among the results obtained by fitting different models become now possible to a much larger extent than ever. We also show that a consistent determination of the dispersion curve and of the propagation Q range of the excitations is possible, whichever model is used. We derive an exact formula which describes in all cases the dispersion curve and allows for the first quantitative understanding of its shape, by assigning specific and distinct roles to the various structural, thermal, and damping effects that determine the Q dependence of the mode frequencies. The emerging picture describes the acoustic modes as Q -dependent harmonic oscillators whose characteristic frequency is explicitly renormalized in an exact way by the relaxation processes, which also determine, through the widths of both the inelastic and the elastic lines, the whole shape of collective-excitation spectra.
Bafile, Ubaldo; Guarini, Eleonora; Barocchi, Fabrizio
2006-06-01
In the Q range where inelastic x-ray and neutron scattering are applied to the study of acoustic collective excitations in fluids, various models of the dynamic structure factor S(Q, omega) generalize in different ways the results obtained from linearized-hydrodynamics theory in the Q-->0 limit. Here we show that the models most commonly fitted to experimental S(Q, omega) spectra can be given a unified formulation. In this way, direct comparisons among the results obtained by fitting different models become now possible to a much larger extent than ever. We also show that a consistent determination of the dispersion curve and of the propagation Q range of the excitations is possible, whichever model is used. We derive an exact formula which describes in all cases the dispersion curve and allows for the first quantitative understanding of its shape, by assigning specific and distinct roles to the various structural, thermal, and damping effects that determine the Q dependence of the mode frequencies. The emerging picture describes the acoustic modes as Q-dependent harmonic oscillators whose characteristic frequency is explicitly renormalized in an exact way by the relaxation processes, which also determine, through the widths of both the inelastic and the elastic lines, the whole shape of collective-excitation spectra. PMID:16906814
NASA Astrophysics Data System (ADS)
Zhang, Zhiyao; Zhou, Xiaojun; Liang, Rui; Qin, Zujun; Liu, Yong
2009-07-01
Buffer performance of a 2.5 Gb/s bit stream with non-return-to-zero format is investigated based on acoustic excitation by stimulated Brillouin scattering in an As 2Se 3 fiber. The storage process and the retrieval process of the bit stream are separately controlled by a "Write" pulse and a "Read" pulse. The research results show that the output signal-to-noise ratio and the readout efficiency of the buffer are agreeable, and the pulse distortion is low, if both the "Write" and the "Read" pulses are with high enough peak power and spectrum wider than that of the signal pulse. Buffering of a consecutive 10-bit-long 2.5 Gb/s NRZ bit stream has also been demonstrated in the As 2Se 3 fiber with length of only 0.5 m. The storage of a long bit stream, such as the data packet containing about 1000 bits in the telecommunications, is limited by the high loss in the As 2Se 3 fiber. However, the development of the special optical fiber with high Brillouin gain coefficient, long acoustic lifetime and low loss can make this technology applicable for all-optical buffering in high speed optical networks.
Dynamics of a spherical particle in an acoustic field: A multiscale approach
Xie, Jin-Han Vanneste, Jacques
2014-10-15
A rigid spherical particle in an acoustic wave field oscillates at the wave period but has also a mean motion on a longer time scale. The dynamics of this mean motion is crucial for numerous applications of acoustic microfluidics, including particle manipulation and flow visualisation. It is controlled by four physical effects: acoustic (radiation) pressure, streaming, inertia, and viscous drag. In this paper, we carry out a systematic multiscale analysis of the problem in order to assess the relative importance of these effects depending on the parameters of the system that include wave amplitude, wavelength, sound speed, sphere radius, and viscosity. We identify two distinguished regimes characterised by a balance among three of the four effects, and we derive the equations that govern the mean particle motion in each regime. This recovers and organises classical results by King [“On the acoustic radiation pressure on spheres,” Proc. R. Soc. A 147, 212–240 (1934)], Gor'kov [“On the forces acting on a small particle in an acoustical field in an ideal fluid,” Sov. Phys. 6, 773–775 (1962)], and Doinikov [“Acoustic radiation pressure on a rigid sphere in a viscous fluid,” Proc. R. Soc. London A 447, 447–466 (1994)], clarifies the range of validity of these results, and reveals a new nonlinear dynamical regime. In this regime, the mean motion of the particle remains intimately coupled to that of the surrounding fluid, and while viscosity affects the fluid motion, it plays no part in the acoustic pressure. Simplified equations, valid when only two physical effects control the particle motion, are also derived. They are used to obtain sufficient conditions for the particle to behave as a passive tracer of the Lagrangian-mean fluid motion.
Stokes parameters for Thomson scattering in a strong magnetic field with radiation damping
NASA Astrophysics Data System (ADS)
Chou, Chih-Kang; Chen, Hui-Hwa
1990-12-01
The effect of a strong magnetic field on Thomson scattering is investigated taking into account radiation damping by using the Abraham-Lorentz equation instead of the Newton-Lorentz equation. The Stokes parameters for Thomson scattering are computed in terms of the state of polarization of the incident wave, the electron-cyclotron frequency, the angle of incidence, and the angle of scattering. It is noted that the Stokes parameters for the scattered radiation show resonance structures.
Short-range order and near-field effects on optical scattering and structural coloration
Liew, S.F.; Forster, J.; Noh, H.; Schreck, C.F.; Saranathan, V.; Lu, X.; Yang, L.; Prum, Richard O.; OHern, C.S.; Dufresne, E.R.; Cao, H.
2012-03-26
We have investigated wavelength-dependent light scattering in biomimetic structures with short-range order. Coherent backscattering experiments are performed to measure the transport mean free path over a wide wavelength range. Overall scattering strength is reduced significantly due to short-range order and near-field effects. Our analysis explains why single scattering of light is dominant over multiple scattering in similar biological structures and is responsible for color generation.
Short-range Order and Near-field Effects on Optical Scattering and Structural Coloration
S Liew; J Forster; H Noh; C Schreck; V Saranathan; X Lu; L Yang; E Dufresne; H Cao; et al.
2011-12-31
We have investigated wavelength-dependent light scattering in biomimetic structures with short-range order. Coherent backscattering experiments are performed to measure the transport mean free path over a wide wavelength range. Overall scattering strength is reduced significantly due to short-range order and near-field effects. Our analysis explains why single scattering of light is dominant over multiple scattering in similar biological structures and is responsible for color generation.
Experimental evidence of the effect of heat flux on thomson scattering off ion acoustic waves
Amiranoff; Baton; Huller; Malka; Modena; Mounaix; Galloudec; Rousseaux; Salvati
2000-02-01
Thomson self-scattering measurements are performed in a preionized helium gas jet plasma at different locations along the laser propagation direction. A systematic and important variation of the intensity ratio between the blue and the red ion spectral components is observed, depending on whether the location of the probed region is in front of or behind the focal plane. A simple theoretical calculation of Thomson scattering shows that this behavior can be qualitatively understood in terms of a deformation of the electron distribution function due to the return current correlated with the classical thermal heat flux. PMID:11046481
Shaping acoustic fields as a toolset for microfluidic manipulations in diagnostic technologies.
Reboud, Julien; Bourquin, Yannyk; Wilson, Rab; Pall, Gurman S; Jiwaji, Meesbah; Pitt, Andrew R; Graham, Anne; Waters, Andrew P; Cooper, Jonathan M
2012-09-18
Ultrasonics offers the possibility of developing sophisticated fluid manipulation tools in lab-on-a-chip technologies. Here we demonstrate the ability to shape ultrasonic fields by using phononic lattices, patterned on a disposable chip, to carry out the complex sequence of fluidic manipulations required to detect the rodent malaria parasite Plasmodium berghei in blood. To illustrate the different tools that are available to us, we used acoustic fields to produce the required rotational vortices that mechanically lyse both the red blood cells and the parasitic cells present in a drop of blood. This procedure was followed by the amplification of parasitic genomic sequences using different acoustic fields and frequencies to heat the sample and perform a real-time PCR amplification. The system does not require the use of lytic reagents nor enrichment steps, making it suitable for further integration into lab-on-a-chip point-of-care devices. This acoustic sample preparation and PCR enables us to detect ca. 30 parasites in a microliter-sized blood sample, which is the same order of magnitude in sensitivity as lab-based PCR tests. Unlike other lab-on-a-chip methods, where the sample moves through channels, here we use our ability to shape the acoustic fields in a frequency-dependent manner to provide different analytical functions. The methods also provide a clear route toward the integration of PCR to detect pathogens in a single handheld system. PMID:22949692
Shaping acoustic fields as a toolset for microfluidic manipulations in diagnostic technologies
Reboud, Julien; Bourquin, Yannyk; Wilson, Rab; Pall, Gurman S.; Jiwaji, Meesbah; Pitt, Andrew R.; Graham, Anne; Waters, Andrew P.; Cooper, Jonathan M.
2012-01-01
Ultrasonics offers the possibility of developing sophisticated fluid manipulation tools in lab-on-a-chip technologies. Here we demonstrate the ability to shape ultrasonic fields by using phononic lattices, patterned on a disposable chip, to carry out the complex sequence of fluidic manipulations required to detect the rodent malaria parasite Plasmodium berghei in blood. To illustrate the different tools that are available to us, we used acoustic fields to produce the required rotational vortices that mechanically lyse both the red blood cells and the parasitic cells present in a drop of blood. This procedure was followed by the amplification of parasitic genomic sequences using different acoustic fields and frequencies to heat the sample and perform a real-time PCR amplification. The system does not require the use of lytic reagents nor enrichment steps, making it suitable for further integration into lab-on-a-chip point-of-care devices. This acoustic sample preparation and PCR enables us to detect ca. 30 parasites in a microliter-sized blood sample, which is the same order of magnitude in sensitivity as lab-based PCR tests. Unlike other lab-on-a-chip methods, where the sample moves through channels, here we use our ability to shape the acoustic fields in a frequency-dependent manner to provide different analytical functions. The methods also provide a clear route toward the integration of PCR to detect pathogens in a single handheld system. PMID:22949692
Adaptive plasticity in wild field cricket's acoustic signaling.
Bertram, Susan M; Harrison, Sarah J; Thomson, Ian R; Fitzsimmons, Lauren P
2013-01-01
Phenotypic plasticity can be adaptive when phenotypes are closely matched to changes in the environment. In crickets, rhythmic fluctuations in the biotic and abiotic environment regularly result in diel rhythms in density of sexually active individuals. Given that density strongly influences the intensity of sexual selection, we asked whether crickets exhibit plasticity in signaling behavior that aligns with these rhythmic fluctuations in the socio-sexual environment. We quantified the acoustic mate signaling behavior of wild-caught males of two cricket species, Gryllus veletis and G. pennsylvanicus. Crickets exhibited phenotypically plastic mate signaling behavior, with most males signaling more often and more attractively during the times of day when mating activity is highest in the wild. Most male G. pennsylvanicus chirped more often and louder, with shorter interpulse durations, pulse periods, chirp durations, and interchirp durations, and at slightly higher carrier frequencies during the time of the day that mating activity is highest in the wild. Similarly, most male G. veletis chirped more often, with more pulses per chirp, longer interpulse durations, pulse periods, and chirp durations, shorter interchirp durations, and at lower carrier frequencies during the time of peak mating activity in the wild. Among-male variation in signaling plasticity was high, with some males signaling in an apparently maladaptive manner. Body size explained some of the among-male variation in G. pennsylvanicus plasticity but not G. veletis plasticity. Overall, our findings suggest that crickets exhibit phenotypically plastic mate attraction signals that closely match the fluctuating socio-sexual context they experience.
Field performance of an acoustic scour-depth monitoring system
Mason, Jr., Robert R.; Sheppard, D. Max
1994-01-01
The Herbert C. Bonner Bridge over Oregon Inlet serves as the only land link between Bodie and Hatteras Islands, part of the Outer Banks of North Carolina. Periodic soundings over the past 30 years have documented channel migration, local scour, and deposition at several pilings that support the bridge. In September 1992, a data-collection system was installed to permit the off-site monitoring of scour at 16 bridge pilings. The system records channel-bed elevations at 15-minute intervals and transmits the data to a satellite receiver. A cellular phone connection also permits downloading and reviewing of the data as they are being collected. A digitally recording, acoustic fathometer is the main component of the system. In November 1993, current velocity, water-surface elevation, wave characteristics, and water temperature measuring instruments were also deployed at the site. Several performance problems relating to the equipment and to the harsh marine environment have not been resolved, but the system has collected and transmitted reliable scour-depth and water-level data.
Bioacoustic Field Research: A Primer to Acoustic Analyses and Playback Experiments With Primates
FISCHER, JULIA; NOSER, RAHEL; HAMMERSCHMIDT, KURT
2013-01-01
Acoustic analyses of primate vocalizations as well as playback experiments are staple methods in primatology. Acoustic analyses have been used to investigate the influence of factors such as individuality, context, sex, age, and size on variation in calls. More recent studies have expanded our knowledge on the effects of phylogenetic relatedness and the structure of primate vocal repertoires in general. Complementary playback experiments allow direct testing of hypotheses regarding the attribution of meaning to calls, the cognitive mechanisms underpinning responses, and/or the adaptive value of primate behavior. After briefly touching on the historical background of this field of research, we first provide an introduction to recording primate vocalizations and discuss different approaches to describe primate calls in terms of their temporal and spectral properties. Second, we present a tutorial regarding the preparation, execution, and interpretation of field playback experiments, including a review of studies that have used such approaches to investigate the responses to acoustic variation in calls including the integration of contextual and acoustic information, recognition of kin and social relationships, and social knowledge. Based on the review of the literature and our own experience, we make a number of recommendations regarding the most common problems and pitfalls. The power of acoustic analyses typically hinges on the quality of the recordings and the number of individuals represented in the sample. Playback experiments require profound knowledge of the natural behavior of the animals for solid interpretation; experiments should be conducted sparingly, to avoid habituation of the subjects to the occurrence of the calls; experimenter-blind designs chosen whenever possible; and researchers should brace themselves for long periods of waiting times until the appropriate moments to do the experiment arise. If all these aspects are considered, acoustic analyses
NASA Astrophysics Data System (ADS)
Fatone, Lorella; Recchioni, Maria Cristina; Zirilli, Francesco
2006-05-01
In this paper we propose a highly parallelizable numerical method for time dependent acoustic scattering problems involving realistic smart obstacles hit by incoming waves having wavelengths small compared with the characteristic dimension of the obstacles. A smart obstacle is an obstacle that when hit by an incoming wave tries to pursue a goal circulating on its boundary a pressure current. In particular we consider obstacles whose goal is to be undetectable and we refer to them as furtive obstacles. These scattering problems are modelled as optimal control problems for the wave equation. We validate the method proposed to solve the optimal control problem considered on some test problems where a "smart" simplified version of the NASA space shuttle is hit by incoming waves with small wavelengths compared to its characteristic dimension. That is we consider test problems with ratio between the characteristic dimension of the obstacle and wavelength of the time harmonic component of the incoming wave up to approximately one hundred. The website: http://www.econ.univpm.it/recchioni/w14 contains animations and virtual reality applications showing some numerical experiments relative to the problems studied in this paper.
Acoustic streaming field structure. Part II. Examples that include boundary-driven flow.
Bradley, Charles
2012-01-01
In this paper three simple acoustic streaming problems are presented and solved. The purpose of the paper is to demonstrate the use of a previously published streaming model by Bradley [J. Acoust. Soc. Am. 100(3), 1399-1408 (1996)] and illustrate, with concrete examples, some of the features of streaming flows that were predicted by the general model. In particular, the problems are intended to demonstrate cases in which the streaming field boundary condition at the face of the radiator has a nontrivial lateral dc velocity component. Such a boundary condition drives a steady solenoidal flow just like a laterally translating boundary drives Couette flow.
Dynamics of single inclusions in channels with constrictions in the acoustic field
NASA Astrophysics Data System (ADS)
Maksimov, A. Yu.; Gubaidullin, A. A.
2016-10-01
The process of mobilization of viscous droplets, trapped in the channel with a sinusoidal constriction under the influence of an external acoustic field have been studied. The dependence of the amplitude of acoustic impact from the frequency has been found. The problem of the free longitudinal oscillations of a droplet in the absence of viscous friction forces in the channels with the constrictions was considered. The influence of surface tension, droplet volume and shape of constrictions on the natural frequency of the longitudinal oscillations of a droplet pinned at the constriction of the capillary were studied.
Ivakin, Anatoliy N
2016-07-01
A perturbation approach to roughness scattering and reverberation in range-dependent environments is developed treating each interface as a superposition of a smooth reference interface, which may include large-scale deterministic features (such as bathymetry changes), and small compared to the acoustic wavelength vertical deviations from this interface that are considered as random roughness perturbations. The reference interface is assumed to be smooth enough to allow analytic or numerical solution for the field in the vicinity of this interface that can then be used in perturbation theory. Expressions for both the reverberation field and average reverberation intensity in a general case of an arbitrary number of rough interfaces are obtained in a form convenient for numerical simulations. In the case of long-range ocean reverberation, several approximations for these expressions are developed, relevant to various environmental scenarios and different types of interfaces: sea-surface, water-sediment interface, buried sediment interfaces, and bottom basement. The results are presented in a simple form and provide a direct relationship of the reverberation intensity with three critical characteristics defined at each interface: (1) local spectrum of roughness, (2) local contrast of acoustic parameters, and (3) two-way full-field transmission intensity calculated taking into account only large-scale changes of the environment.
Imaging of transient surface acoustic waves by full-field photorefractive interferometry
Xiong, Jichuan; Xu, Xiaodong E-mail: christ.glorieux@fys.kuleuven.be; Glorieux, Christ E-mail: christ.glorieux@fys.kuleuven.be; Matsuda, Osamu; Cheng, Liping
2015-05-15
A stroboscopic full-field imaging technique based on photorefractive interferometry for the visualization of rapidly changing surface displacement fields by using of a standard charge-coupled device (CCD) camera is presented. The photorefractive buildup of the space charge field during and after probe laser pulses is simulated numerically. The resulting anisotropic diffraction upon the refractive index grating and the interference between the polarization-rotated diffracted reference beam and the transmitted signal beam are modeled theoretically. The method is experimentally demonstrated by full-field imaging of the propagation of photoacoustically generated surface acoustic waves with a temporal resolution of nanoseconds. The surface acoustic wave propagation in a 23 mm × 17 mm area on an aluminum plate was visualized with 520 × 696 pixels of the CCD sensor, yielding a spatial resolution of 33 μm. The short pulse duration (8 ns) of the probe laser yields the capability of imaging SAWs with frequencies up to 60 MHz.
Adaptive Plasticity in Wild Field Cricket’s Acoustic Signaling
Bertram, Susan M.; Harrison, Sarah J.; Thomson, Ian R.; Fitzsimmons, Lauren P.
2013-01-01
Phenotypic plasticity can be adaptive when phenotypes are closely matched to changes in the environment. In crickets, rhythmic fluctuations in the biotic and abiotic environment regularly result in diel rhythms in density of sexually active individuals. Given that density strongly influences the intensity of sexual selection, we asked whether crickets exhibit plasticity in signaling behavior that aligns with these rhythmic fluctuations in the socio-sexual environment. We quantified the acoustic mate signaling behavior of wild-caught males of two cricket species, Gryllus veletis and G. pennsylvanicus. Crickets exhibited phenotypically plastic mate signaling behavior, with most males signaling more often and more attractively during the times of day when mating activity is highest in the wild. Most male G. pennsylvanicus chirped more often and louder, with shorter interpulse durations, pulse periods, chirp durations, and interchirp durations, and at slightly higher carrier frequencies during the time of the day that mating activity is highest in the wild. Similarly, most male G. veletis chirped more often, with more pulses per chirp, longer interpulse durations, pulse periods, and chirp durations, shorter interchirp durations, and at lower carrier frequencies during the time of peak mating activity in the wild. Among-male variation in signaling plasticity was high, with some males signaling in an apparently maladaptive manner. Body size explained some of the among-male variation in G. pennsylvanicus plasticity but not G. veletis plasticity. Overall, our findings suggest that crickets exhibit phenotypically plastic mate attraction signals that closely match the fluctuating socio-sexual context they experience. PMID:23935965
Characterization of the Acoustic Field in Marine Environments with Anthropogenic Noise
NASA Astrophysics Data System (ADS)
Guan, Shane
Most animals inhabit the aquatic environment are acoustical-oriented, due to the physical characteristics of water that favors sound transmission. Many aquatic animals depend on underwater sound to navigate, communicate, find prey, and avoid predators. The degradation of underwater acoustic environment due to human activities is expected to affected these animals' well-being and survival at the population level. This dissertation presents three original studies on the characteristics and behavior of underwater sound fields in three unique marine environments with anthropogenic noises. The first study examines the soundscape of the Chinese white dolphin habitat in Taiwan. Acoustic recordings were made at two coastal shallow water locations, Yunlin and Waisanding, in 2012. Results show that croaker choruses are dominant sound sources in the 1.2--2.4 kHz frequency band for both locations at night, and noises from container ships in the 150--300 Hz frequency band define the relative higher broadband sound levels at Yunlin. Results also illustrate interrelationships among different biotic, abiotic, and anthropogenic elements that shape the fine-scale soundscape in a coastal environment. The second study investigates the inter-pulse sound field during an open-water seismic survey in coastal shallow waters of the Arctic. The research uses continuous acoustic recordings collected from one bottom-mounted hydrophone deployed in the Beaufort Sea in summer 2012. Two quantitative methods were developed to examine the inter-pulse sound field characteristics and its dependence on source distances. Results show that inter-pulse sound field could raise the ambient noise floor by as much as 9 dB, depending on ambient condition and source distance. The third study examines the inter-ping sound field of simulated mid-frequency active sonar in deep waters off southern California in 2013 and 2014. The study used drifting acoustic recorder buoys to collect acoustic data during sonar
Field evaluation of boat-mounted acoustic Doppler instruments used to measure streamflow
Mueller, D.S.; ,
2003-01-01
The use of instruments based on the Doppler principle for measuring water velocity and computing discharge is common within the U.S. Geological Survey (USGS). The instruments and software have changed appreciably during the last 5 years; therefore, the USGS has begun field validation of the instruments used to make discharge measurements from a moving boat. Instruments manufactured by SonTek/YSI and RD Instruments, Inc. were used to collect discharge data at five different sites. One or more traditional discharge measurements were made using a Price AA current meter and standard USGS procedures concurrent with the acoustic instruments at each site. Discharges measured with the acoustic instruments were compared with discharges measured with Price AA current meters and the USGS stage-discharge rating for each site. The mean discharges measured by each acoustic instrument were within 5 percent of the Price AA-based measurement and (or) discharge from the stage-discharge rating.
Wisniewska, Danuta M; Ratcliffe, John M; Beedholm, Kristian; Christensen, Christian B; Johnson, Mark; Koblitz, Jens C; Wahlberg, Magnus; Madsen, Peter T
2015-01-01
Toothed whales use sonar to detect, locate, and track prey. They adjust emitted sound intensity, auditory sensitivity and click rate to target range, and terminate prey pursuits with high-repetition-rate, low-intensity buzzes. However, their narrow acoustic field of view (FOV) is considered stable throughout target approach, which could facilitate prey escape at close-range. Here, we show that, like some bats, harbour porpoises can broaden their biosonar beam during the terminal phase of attack but, unlike bats, maintain the ability to change beamwidth within this phase. Based on video, MRI, and acoustic-tag recordings, we propose this flexibility is modulated by the melon and implemented to accommodate dynamic spatial relationships with prey and acoustic complexity of surroundings. Despite independent evolution and different means of sound generation and transmission, whales and bats adaptively change their FOV, suggesting that beamwidth flexibility has been an important driver in the evolution of echolocation for prey tracking.
Alibakhshi, Mohammad A.; Kracht, Jonathan M.; Cleveland, Robin O.; Filoux, Erwan; Ketterling, Jeffrey A.
2013-01-01
Piezopolymer-based hydrophone arrays consisting of 20 elements were fabricated and tested for use in measuring the acoustic field from a shock-wave lithotripter. The arrays were fabricated from piezopolymer films and were mounted in a housing to allow submersion into water. The motivation was to use the array to determine how the shot-to-shot variability of the spark discharge in an electrohydraulic lithotripter affects the resulting focused acoustic field. It was found that the dominant effect of shot-to-shot variability was to laterally shift the location of the focus by up to 5 mm from the nominal acoustic axis of the lithotripter. The effect was more pronounced when the spark discharge was initiated with higher voltages. The lateral beamwidth of individual, instantaneous shock waves were observed to range from 1.5 mm to 24 mm. Due to the spatial variation of the acoustic field, the average of instantaneous beamwidths were observed to be 1 to 2 mm narrower than beamwidths determined from traditional single-point measurements that average the pressure measured at each location before computing beamwidth. PMID:23654419
Measurement of transient acoustic fields using a single-shot pressure-sensitive paint system.
Disotell, Kevin J; Gregory, James W
2011-07-01
A pressure-sensitive paint (PSP) system capable of measuring high-frequency acoustic fields with non-periodic, acoustic-level pressure changes is described. As an optical measurement technique, PSP provides the experimenter with a global distribution of pressure on a painted surface. To demonstrate frequency response and enhanced sensitivity to pressure changes, a PSP system consisting of a polymer∕ceramic matrix binder with platinum tetra(pentafluorophenyl) porphyrin (PtTFPP) as the oxygen probe was applied to a wall inside an acoustic resonance cavity excited at 1.3 kHz. A data acquisition technique based on the luminescent decay lifetime of the oxygen sensors excited by a single pulse of light afforded the ability to capture instantaneous pressure fields with no phase-averaging. Superimposed wave-like structures were observed with a wavelength corresponding to a 4.7% difference from the theoretical value for a sound wave emanating from the speaker. High sound pressure cases upwards of 145 dB (re 20 μPa) exhibited skewed nodal lines attributed to a nonlinear acoustic field. The lowest sound pressure level of 125.4 dB--corresponding to an amplitude of 52.7 Pa, or approximately 0.05% of standard sea-level atmospheric pressure--showed that the paint could resolve the spatial details of the mode shape at the given resonance condition.
Measurement of transient acoustic fields using a single-shot pressure-sensitive paint system
NASA Astrophysics Data System (ADS)
Disotell, Kevin J.; Gregory, James W.
2011-07-01
A pressure-sensitive paint (PSP) system capable of measuring high-frequency acoustic fields with non-periodic, acoustic-level pressure changes is described. As an optical measurement technique, PSP provides the experimenter with a global distribution of pressure on a painted surface. To demonstrate frequency response and enhanced sensitivity to pressure changes, a PSP system consisting of a polymer/ceramic matrix binder with platinum tetra(pentafluorophenyl) porphyrin (PtTFPP) as the oxygen probe was applied to a wall inside an acoustic resonance cavity excited at 1.3 kHz. A data acquisition technique based on the luminescent decay lifetime of the oxygen sensors excited by a single pulse of light afforded the ability to capture instantaneous pressure fields with no phase-averaging. Superimposed wave-like structures were observed with a wavelength corresponding to a 4.7% difference from the theoretical value for a sound wave emanating from the speaker. High sound pressure cases upwards of 145 dB (re 20 μPa) exhibited skewed nodal lines attributed to a nonlinear acoustic field. The lowest sound pressure level of 125.4 dB—corresponding to an amplitude of 52.7 Pa, or approximately 0.05% of standard sea-level atmospheric pressure—showed that the paint could resolve the spatial details of the mode shape at the given resonance condition.
Jiao, Junjie; He, Yong; Leong, Thomas; Kentish, Sandra E; Ashokkumar, Muthupandian; Manasseh, Richard; Lee, Judy
2013-10-17
When subjected to an ultrasonic standing-wave field, cavitation bubbles smaller than the resonance size migrate to the pressure antinodes. As bubbles approach the antinode, they also move toward each other and either form a cluster or coalesce. In this study, the translational trajectory of two bubbles moving toward each other in an ultrasonic standing wave at 22.4 kHz was observed using an imaging system with a high-speed video camera. This allowed the speed of the approaching bubbles to be measured for much closer distances than those reported in the prior literature. The trajectory of two approaching bubbles was modeled using coupled equations of radial and translational motions, showing similar trends with the experimental results. We also indirectly measured the secondary Bjerknes force by monitoring the acceleration when bubbles are close to each other under different acoustic pressure amplitudes. Bubbles begin to accelerate toward each other as the distance between them gets shorter, and this acceleration increases with increasing acoustic pressure. The current study provides experimental data that validates the theory on the movement of bubbles and forces acting between them in an acoustic field that will be useful in understanding bubble coalescence in an acoustic field.
Measurement of transient acoustic fields using a single-shot pressure-sensitive paint system.
Disotell, Kevin J; Gregory, James W
2011-07-01
A pressure-sensitive paint (PSP) system capable of measuring high-frequency acoustic fields with non-periodic, acoustic-level pressure changes is described. As an optical measurement technique, PSP provides the experimenter with a global distribution of pressure on a painted surface. To demonstrate frequency response and enhanced sensitivity to pressure changes, a PSP system consisting of a polymer∕ceramic matrix binder with platinum tetra(pentafluorophenyl) porphyrin (PtTFPP) as the oxygen probe was applied to a wall inside an acoustic resonance cavity excited at 1.3 kHz. A data acquisition technique based on the luminescent decay lifetime of the oxygen sensors excited by a single pulse of light afforded the ability to capture instantaneous pressure fields with no phase-averaging. Superimposed wave-like structures were observed with a wavelength corresponding to a 4.7% difference from the theoretical value for a sound wave emanating from the speaker. High sound pressure cases upwards of 145 dB (re 20 μPa) exhibited skewed nodal lines attributed to a nonlinear acoustic field. The lowest sound pressure level of 125.4 dB--corresponding to an amplitude of 52.7 Pa, or approximately 0.05% of standard sea-level atmospheric pressure--showed that the paint could resolve the spatial details of the mode shape at the given resonance condition. PMID:21806232
NASA Astrophysics Data System (ADS)
Lu, Wenbo; Jiang, Weikang; Yuan, Guoqing; Yan, Li
2013-05-01
Vibration signal analysis is the main technique in machine condition monitoring or fault diagnosis, whereas in some cases vibration-based diagnosis is restrained because of its contact measurement. Acoustic-based diagnosis (ABD) with non-contact measurement has received little attention, although sound field may contain abundant information related to fault pattern. A new scheme of ABD for gearbox based on near-field acoustic holography (NAH) and spatial distribution features of sound field is presented in this paper. It focuses on applying distribution information of sound field to gearbox fault diagnosis. A two-stage industrial helical gearbox is experimentally studied in a semi-anechoic chamber and a lab workshop, respectively. Firstly, multi-class faults (mild pitting, moderate pitting, severe pitting and tooth breakage) are simulated, respectively. Secondly, sound fields and corresponding acoustic images in different gearbox running conditions are obtained by fast Fourier transform (FFT) based NAH. Thirdly, by introducing texture analysis to fault diagnosis, spatial distribution features are extracted from acoustic images for capturing fault patterns underlying the sound field. Finally, the features are fed into multi-class support vector machine for fault pattern identification. The feasibility and effectiveness of our proposed scheme is demonstrated on the good experimental results and the comparison with traditional ABD method. Even with strong noise interference, spatial distribution features of sound field can reliably reveal the fault patterns of gearbox, and thus the satisfactory accuracy can be obtained. The combination of histogram features and gray level gradient co-occurrence matrix features is suggested for good diagnosis accuracy and low time cost.
Vibration of a single microcapsule with a hard plastic shell in an acoustic standing wave field.
Koyama, Daisuke; Kotera, Hironori; Kitazawa, Natsuko; Yoshida, Kenji; Nakamura, Kentaro; Watanabe, Yoshiaki
2011-04-01
Observation techniques for measuring the small vibration of a single microcapsule of tens of nanometers in an acoustic standing wave field are discussed. First, simultaneous optical observation of a microbubble vibration by two methods is investigated, using a high-speed video camera, which permits two-dimensional observation of the bubble vibration, and a laser Doppler vibrometer (LDV), which can observe small bubble vibration amplitudes at high frequency. Bubbles of tens of micrometers size were trapped at the antinode of an acoustic standing wave generated in an observational cell. Bubble vibration at 27 kHz could be observed and the experimental results for the two methods showed good agreement. The radial vibration of microcapsules with a hard plastic shell was observed using the LDV and the measurement of the capsule vibration with radial oscillation amplitude of tens of nanometers was successful. The acoustic radiation force acting on microcapsules in the acoustic standing wave was measured from the trapped position of the standing wave and the radial oscillation amplitude of the capsules was estimated from the theoretical equation of the acoustic radiation force, giving results in good agreement with the LDV measurements. The radial oscillation amplitude of a capsule was found to be proportional to the amplitude of the driving sound pressure. A larger expansion ratio was observed for capsules closer to the resonance condition under the same driving sound pressure and frequency.
Popa, Alexandru
2011-08-15
We prove that the analytical expression of the intensity of the relativistic Thomson scattered field for a system composed of an electron interacting with a plane electromagnetic field can be written in the form of a composite periodic function of only one variable, that is, the phase of the incident field. This property is proved without using any approximation in the most general case in which the field is elliptically polarized, the initial phase of the incident field and the initial velocity of the electron are taken into consideration, and the direction in which the radiation is scattered is arbitrary. This property leads to an exact method for calculating the angular and spectral distributions of the scattered field, which reveals a series of physical details of these distributions, such as their dependence on the components of the initial electron velocity. Since the phase of the field is a relativistic invariant, it follows that the periodicity property is also valid when the analysis is made in the inertial system in which the initial velocity of the electron is zero in the case of interactions between very intense electromagnetic fields and relativistic electrons. Consequently, the calculation method can be used for the evaluation of properties of backscattered hard radiations generated by this type of interaction. The theoretical evaluations presented in this paper are in good agreement with the experimental data from literature.
Antifade sonar employs acoustic field diversity to recover signals from multipath fading
Lubman, D.
1996-04-01
Co-located pressure and particle motion (PM) hydrophones together with four-channel diversity combiners may be used to recover signals from multipath fading. Multipath fading is important in both shallow and deep water propagation and can be an important source of signal loss. The acoustic field diversity concept arises from the notion of conservation of signal energy and the observation that in rooms at least, the total acoustic energy density is the sum of potential energy (scalar field-sound pressure) and kinetic energy (vector field-sound PM) portions. One pressure hydrophone determines acoustic potential energy density at a point. In principle, three PM sensors (displacement, velocity, or acceleration) directed along orthogonal axes describe the kinetic energy density at a point. For a single plane wave, the time-averaged potential and kinetic field energies are identical everywhere. In multipath interference, however, potential and kinetic field energies at a point are partitioned unequally, depending mainly on relative signal phases. Thus, when pressure signals are in deep fade, abundant kinetic field signal energy may be available at that location. Performance benefits require a degree of uncorrelated fading between channels. The expectation of nearly uncorrelated fading is motivated from room theory. Performance benefits for sonar limited by independent Rayleigh fading are suggested by analogy to antifade radio. Average SNR can be improved by several decibels, holding time on target is multiplied manifold, and the bit error rate for data communication is reduced substantially. {copyright} {ital 1996 American Institute of Physics.}
Every, Arthur G; Amulele, George M
2002-03-01
The angular spectrum method is applied to calculating the acoustic field of a liquid-coupled focusing transducer in an anisotropic slab-shaped solid with surfaces normal to the axis of the transducer. The stationary phase approximation (SPA) is used to determine the dominant contributions to this field and calculate the echo signals produced by waves that have been reflected off the rear surface of the solid. The dominant features of this field and of the echoes are reproduced well by a hybrid ray method devised to simulate the finite point-spread function of the lens. Both approaches in the paraxial approximation yield a split focus for each wave polarization branch for a general direction of the surface normal. Echo arrival times and amplitudes calculated by the two methods are in good agreement. The hybrid ray method is shown to be particularly suited to handling multiple stationary phase points within the angular spectrum of the incident field and stationary phase points not associated with the normally incident ray, and should be useful for dealing with scattering from cracks and other defects. Pulse echo calculations for different crystallographic directions in a nickel-based superalloy are shown to be in good agreement with measurements carried out on single crystal specimens of the alloy. PMID:12322879
Every, Arthur G; Amulele, George M
2002-03-01
The angular spectrum method is applied to calculating the acoustic field of a liquid-coupled focusing transducer in an anisotropic slab-shaped solid with surfaces normal to the axis of the transducer. The stationary phase approximation (SPA) is used to determine the dominant contributions to this field and calculate the echo signals produced by waves that have been reflected off the rear surface of the solid. The dominant features of this field and of the echoes are reproduced well by a hybrid ray method devised to simulate the finite point-spread function of the lens. Both approaches in the paraxial approximation yield a split focus for each wave polarization branch for a general direction of the surface normal. Echo arrival times and amplitudes calculated by the two methods are in good agreement. The hybrid ray method is shown to be particularly suited to handling multiple stationary phase points within the angular spectrum of the incident field and stationary phase points not associated with the normally incident ray, and should be useful for dealing with scattering from cracks and other defects. Pulse echo calculations for different crystallographic directions in a nickel-based superalloy are shown to be in good agreement with measurements carried out on single crystal specimens of the alloy.
On multiple scattering in acoustic media: a deterministic Ray Tracing method for random structures.
Brigante, M
2013-03-01
The paper is devoted to computer and experimental simulation of US (ultrasonic) signal propagation in acoustic solids with micro-structure. Any change in the percentage of flaws or pores influences considerably the value of the ultrasonic wave speed. The theoretical analysis is based upon the Ray Tracing algorithm. We calculate numerically the full path of each ray from the transmitter to the receiver, in its multiple reflections between the surfaces of the internal obstacles. The natural experiments are performed in a water basin with some arrays of equal metallic round rods. This simulates the US evaluation of the mechanical properties of concrete. The computer modeling allows us to construct the envelope of the US signal registered at the receiving transducer. Then we simulate the dependence of the wave speed versus porosity. There is a sufficiently good accordance between numerical and experimental results.
Scatter radiation intensities around full-field digital mammography units.
Judge, M A; Keavey, E; Phelan, N
2013-01-01
The aim of this study was to investigate the scatter radiation intensity around digital mammography systems and apply these data to standard shielding calculations to reveal whether shielding design of existing breast screening rooms is adequate for the use of digital mammography systems. Three digital mammography systems from GE Healthcare, Hologic and Philips were employed in the study. A breast-equivalent phantom was imaged under clinical workload conditions and scatter radiation intensities around the digital mammography systems were measured for a range of angles in three planes using an ionisation chamber. The results were compared with those from previous studies of film-screen systems. It may be deduced from the results that scattering in the backward direction is significant for all three systems, while scattering in the forward direction can be significant for some planes around the GE and Hologic systems. Measurements at typical clinical settings on each system revealed the Philips system to have markedly lower scatter radiation intensities than the other systems. Substituting the measured scattered radiation intensity into shielding calculations yielded barrier requirements similar to those already in place at the screening centres operating these systems. Current radiation protection requirements based on film-screen technology remain sufficient when applied to rooms with digital mammography installations and no alteration is required to the structural shielding.
Acoustic structures in the near-field from clustered rocket nozzles
NASA Astrophysics Data System (ADS)
Canchero, Andres; Tinney, Charles E.; Murray, Nathan E.; Ruf, Joseph H.
2014-11-01
The plume and acoustic field produced by a cluster of two and four rocket nozzles is visualized by way of retroreflective shadowgraphy. Steady state and transient operations (startup/shutdown) were conducted in the fully-anechoic chamber and open jet facility of The University of Texas at Austin. The laboratory scale rocket nozzles comprise thrust-optimized parabolic contours, which during start-up, experience free shock separated flow, restricted shock separated flow and an end-effects regime prior to flowing full. Shadowgraphy images with synchronized surveys of the acoustic loads produced in close vicinity to the rocket clusters and wall static pressure profiles are first compared with several RANS simulations during steady operations. A Proper Orthogonal Decomposition of various regions in the shadowgraphy images is then performed to elucidate the prominent features residing in the supersonic annular flow region, the acoustic near field and the interaction zone that resides between the nozzle plumes. POD modes are used to detect propagation paths of the acoustic waves and shock cell structures in the supersonic shear layer. Spectral peak frequencies on the propagation paths are associated with the shock cell length, which are responsible for generating broadband shock noise. Aerospace Engineering & Engineering Mechanics.
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.
NASA Astrophysics Data System (ADS)
Røstad, Anders; Kaartvedt, Stein; Aksnes, Dag L.
2016-07-01
We make a comparison of the mesopelagic sound scattering layers (SLs) in two contrasting optical environments; the clear Red Sea and in murkier coastal waters of Norway (Masfjorden). The depth distributions of the SL in Masfjorden are shallower and narrower than those of the Red Sea. This difference in depth distribution is consistent with the hypothesis that the organisms of the SL distribute according to similar light comfort zones (LCZ) in the two environments. Our study suggest that surface and underwater light measurements ranging more than 10 orders of magnitude is required to assess the controlling effects of light on SL structure and dynamics.
Applications of whole field interferometry in mechanics and acoustics
NASA Astrophysics Data System (ADS)
Molin, Nils-Erik
1999-07-01
A description is given of fringe formation in holographic interferometry, in electronic speckle pattern interferometry, in electro-optic or TV holography and for a newly developed system for pulsed TV-holography. A numerical example, which simulates the equations describing the different techniques, is included. A strain measuring system using defocused digital speckle photography is described. Experiments showing mode shapes of musical instruments, transient bending wave propagation in beams and plates as well as sound pressure fields in air are included.
Source signature and acoustic field of seismic physical modeling
NASA Astrophysics Data System (ADS)
Lin, Q.; Jackson, C.; Tang, G.; Burbach, G.
2004-12-01
As an important tool of seismic research and exploration, seismic physical modeling simulates the real world data acquisition by scaling the model, acquisition parameters, and some features of the source generated by a transducer. Unlike the numerical simulation where a point source is easily satisfied, the transducer can't be made small enough for approximating the point source in physical modeling, therefore yield different source signature than the sources applied in the field data acquisition. To better understand the physical modeling data, characterizing the wave field generated by ultrasonic transducers is desirable and helpful. In this study, we explode several aspects of source characterization; including their radiation pattern, directivity, sensitivity and frequency response. We also try to figure out how to improve the acquired data quality, such as minimize ambient noise, use encoded chirp to prevent ringing, apply deterministic deconvolution to enhance data resolution and t-P filtering to remove linear events. We found that the transducer and their wave field, the modeling system performance, as well as material properties of the model and their coupling conditions all play roles in the physical modeling data acquisition.
Calculation of electromagnetic fields in the near-field region of a moving scattering object
NASA Astrophysics Data System (ADS)
Vogel, M. H.
1990-07-01
The problem of scattering of electromagnetic fields by perfectly conducting, moving objects is solved with the Lorentz transformation and the plane wave formulation. Apart from the physical optics approximation, the solution is exact. The result is subsequently applied to the special case of monostatic reflection by an object that moves slowly with respect to the velocity of light. The result can be used to predict the time dependent reflection from an aircraft that passes the antenna of a proximity fuze, and the optimum fuze algorithm can be selected.
NASA Astrophysics Data System (ADS)
Liu, Yuxiang; Barnett, Alex H.
2016-11-01
We present a high-order accurate boundary-based solver for three-dimensional (3D) frequency-domain scattering from a doubly-periodic grating of smooth axisymmetric sound-hard or transmission obstacles. We build the one-obstacle solution operator using separation into P azimuthal modes via the FFT, the method of fundamental solutions (with N proxy points lying on a curve), and dense direct least-squares solves; the effort is O (N3 P) with a small constant. Periodizing then combines fast multipole summation of nearest neighbors with an auxiliary global Helmholtz basis expansion to represent the distant contributions, and enforcing quasiperiodicity and radiation conditions on the unit cell walls. Eliminating the auxiliary coefficients, and preconditioning with the one-obstacle solution operator, leaves a well-conditioned square linear system that is solved iteratively. The solution time per incident wave is then O (NP) at fixed frequency. Our scheme avoids singular quadratures, periodic Green's functions, and lattice sums, and its convergence rate is unaffected by resonances within obstacles. We include numerical examples such as scattering from a grating of period 13 λ × 13 λ comprising highly-resonant sound-hard "cups" each needing NP = 64800 surface unknowns, to 10-digit accuracy, in half an hour on a desktop.
James, Kevin R; Dowling, David R
2008-09-01
In underwater acoustics, the accuracy of computational field predictions is commonly limited by uncertainty in environmental parameters. An approximate technique for determining the probability density function (PDF) of computed field amplitude, A, from known environmental uncertainties is presented here. The technique can be applied to several, N, uncertain parameters simultaneously, requires N+1 field calculations, and can be used with any acoustic field model. The technique implicitly assumes independent input parameters and is based on finding the optimum spatial shift between field calculations completed at two different values of each uncertain parameter. This shift information is used to convert uncertain-environmental-parameter distributions into PDF(A). The technique's accuracy is good when the shifted fields match well. Its accuracy is evaluated in range-independent underwater sound channels via an L(1) error-norm defined between approximate and numerically converged results for PDF(A). In 50-m- and 100-m-deep sound channels with 0.5% uncertainty in depth (N=1) at frequencies between 100 and 800 Hz, and for ranges from 1 to 8 km, 95% of the approximate field-amplitude distributions generated L(1) values less than 0.52 using only two field calculations. Obtaining comparable accuracy from traditional methods requires of order 10 field calculations and up to 10(N) when N>1.
NASA Astrophysics Data System (ADS)
Bagayev, Sergey N.; Zakharov, Vladimir N.; Orlov, Valery A.; Obraztsov, Yury D.; Panov, Sergey V.; Fomin, Yury N.
2003-09-01
In this paper, experimental results of investigations of the physical mechanism of transcapillary exchange by the method of phase sensitive laser spectroscopy of light scattering are presented. Acoustic oscillations of the walls of microvessels (arterioles, capillaries, and venules) which provide transcapillary exchange have been detected for the first time.
High-energy scatterings in infinite-derivative field theory and ghost-free gravity
NASA Astrophysics Data System (ADS)
Talaganis, Spyridon; Mazumdar, Anupam
2016-07-01
In this paper, we will consider scattering diagrams in the context of infinite-derivative theories. First, we examine a finite-order, higher-derivative scalar field theory and find that we cannot eliminate the growth of scattering diagrams for large external momenta. Then, we employ an infinite-derivative scalar toy model and obtain that the external momentum dependence of scattering diagrams is convergent as the external momenta become very large. In order to eliminate the external momentum growth, one has to dress the bare vertices of the scattering diagrams by considering renormalised propagator and vertex loop corrections to the bare vertices. Finally, we investigate scattering diagrams in the context of a scalar toy model which is inspired by a ghost-free and singularity-free infinite-derivative theory of gravity, where we conclude that infinite derivatives can eliminate the external momentum growth of scattering diagrams and make the scattering diagrams convergent in the ultraviolet.
Underwater Acoustic Matched Field Imaging Based on Compressed Sensing
Yan, Huichen; Xu, Jia; Long, Teng; Zhang, Xudong
2015-01-01
Matched field processing (MFP) is an effective method for underwater target imaging and localizing, but its performance is not guaranteed due to the nonuniqueness and instability problems caused by the underdetermined essence of MFP. By exploiting the sparsity of the targets in an imaging area, this paper proposes a compressive sensing MFP (CS-MFP) model from wave propagation theory by using randomly deployed sensors. In addition, the model’s recovery performance is investigated by exploring the lower bounds of the coherence parameter of the CS dictionary. Furthermore, this paper analyzes the robustness of CS-MFP with respect to the displacement of the sensors. Subsequently, a coherence-excluding coherence optimized orthogonal matching pursuit (CCOOMP) algorithm is proposed to overcome the high coherent dictionary problem in special cases. Finally, some numerical experiments are provided to demonstrate the effectiveness of the proposed CS-MFP method. PMID:26457708
Underwater Acoustic Matched Field Imaging Based on Compressed Sensing.
Yan, Huichen; Xu, Jia; Long, Teng; Zhang, Xudong
2015-01-01
Matched field processing (MFP) is an effective method for underwater target imaging and localizing, but its performance is not guaranteed due to the nonuniqueness and instability problems caused by the underdetermined essence of MFP. By exploiting the sparsity of the targets in an imaging area, this paper proposes a compressive sensing MFP (CS-MFP) model from wave propagation theory by using randomly deployed sensors. In addition, the model's recovery performance is investigated by exploring the lower bounds of the coherence parameter of the CS dictionary. Furthermore, this paper analyzes the robustness of CS-MFP with respect to the displacement of the sensors. Subsequently, a coherence-excluding coherence optimized orthogonal matching pursuit (CCOOMP) algorithm is proposed to overcome the high coherent dictionary problem in special cases. Finally, some numerical experiments are provided to demonstrate the effectiveness of the proposed CS-MFP method. PMID:26457708
Riabov, V A
2008-01-01
A model of the acoustic field of interfering reflections from steel cylinders was developed. Analysis of the model showed the availability of great potential resources for a decrease of the influence of unwanted echoes and hence for increasing the signal-to-clatter ratio. The conformity of the available models of the echolocation hearing of the dolphin to the acoustic field of the clatter was considered. The participation of mandidle mental foramens in conducting the echo to the cochlea was considered. In this case the hearing aperture is determined by the dimensions of mental foramens, while the hearing base is determined by the distance between the mental foramens of the left and right mandible halves. There are good reasons to believe that the optimal dimensions of the aperture and the base of echolocation hearing of Odontoceti essentially increase the effectiveness of defense of their sonar from reverberation.
Field theory for zero sound and ion acoustic wave in astrophysical matter
NASA Astrophysics Data System (ADS)
Gabadadze, Gregory; Rosen, Rachel A.
2016-02-01
We set up a field theory model to describe the longitudinal low-energy modes in high density matter present in white dwarf stars. At the relevant scales, ions—the nuclei of oxygen, carbon, and helium—are treated as heavy pointlike spin-0 charged particles in an effective field theory approach, while the electron dynamics is described by the Dirac Lagrangian at the one-loop level. We show that there always exists a longitudinal gapless mode in the system irrespective of whether the ions are in a plasma, crystal, or quantum liquid state. For certain values of the parameters, the gapless mode can be interpreted as a zero sound mode and, for other values, as an ion acoustic wave; we show that the zero sound and ion acoustic wave are complementary to each other. We discuss possible physical consequences of these modes for properties of white dwarfs.
NASA Technical Reports Server (NTRS)
Parasarathy, R.; Karamcheti, K.
1972-01-01
The Lighthill method was the basic procedure used to analyze the sound field associated with a vortex of modified strength interacting with an airfoil. A free vortex interacting with an airfoil in uniform motion was modeled in order to determine the sound field due to all the acoustic sources, not only on the airfoil surfaces (dipoles), but also the ones distributed on the perturbed flow field (quadrupoles) due to the vortex-airfoil interaction. Because inviscid flow is assumed in the study of the interaction, the quadrupoles considered in the perturbed flow field are entirely due to an unsteady flow field. The effects of airfoil thickness on the second radiation are examined by using a symmetric Joukowski airfoil for the vortex-airfoil interaction. Sound radiation in a plane, far field simplification, and computation of the sound field are discussed.
Jiang, Liang; Liu, Fengbing; Chen, Haosheng; Wang, Jiadao; Chen, Darong
2012-03-01
The dynamics and acoustic emission of two interacting cavitation bubbles exposed to strong acoustic fields with a frequency of 515 KHz are investigated numerically in this paper. After comparing the dynamics of a single bubble excited by the given pressure waves, bubbles with ambient radii of 2 and 5 μm were chosen to be studied to discuss the influence of the mutual bubble-bubble interaction on the dynamic behaviors and acoustic emission of the bubbles. The results show that, aside from the external driving pressure waves, the interaction between the bubbles imposes an extra nonlinear effect on the oscillations of the bubbles and that the dynamics of the smaller bubble could be suppressed gradually with the enhancement of this mutual interaction by decreasing the distance between the bubbles. Moreover, the improvement in the oscillation nonlinearity of the bubbles due to the change in the ambient circumstance could readily be observed from the frequency spectra of the bubbles' acoustic emission, which interprets the change by exhibiting an appropriate development of the subharmonics, the ultraharmonics, and the broadband component.
Visualizing flow fields using acoustic Doppler current profilers and the Velocity Mapping Toolbox
Jackson, P. Ryan
2013-01-01
The purpose of this fact sheet is to provide examples of how the U.S. Geological Survey is using acoustic Doppler current profilers for much more than routine discharge measurements. These instruments are capable of mapping complex three-dimensional flow fields within rivers, lakes, and estuaries. Using the Velocity Mapping Toolbox to process the ADCP data allows detailed visualization of the data, providing valuable information for a range of studies and applications.
Not Available
1987-06-01
The Acoustics site study plan describes a field program which characterizes existing sound levels, determines the area's sound propagation characteristics, and monitors the project-related sound emissions. The plan describes for each study: the need for the study, study design, data management and use, schedule, and quality assurance requirements. These studies will provide data needed to satisfy requirements contained in, or derived from, the Salt Repository Requirements Document. 37 refs., 9 figs., 3 tabs.
NASA Astrophysics Data System (ADS)
Ko, Jae-Hyeon; Ko, Young Ho; Kim, Kwang Joo
2014-06-01
The determination of the equation of state (EOS) of amorphous materials is very important for fundamental understanding of the glass transition and applications as well. Simultaneous observation of both longitudinal and transverse acoustic modes by Brillouin scattering spectroscopy has been one of the major methods to obtain EOS of amorphous materials. However, the transverse acoustic mode is hardly seen from some of the amorphous polymers, which makes it difficult to derive EOS. The temperature and pressure dependences of the acoustic properties of amorphous ethylene-vinyl acetate (EVA) copolymer were measured by using high-pressure Brillouin scattering spectroscopy. The temperature variation induced large changes in the frequency shift and linewidth of the longitudinal acoustic mode due to strong coupling between the structural relaxation process and the propagating density fluctuations. The residual linewidth in the glassy state was attributed to the remnant intramolecular motions of EVA, the activation energy of which was estimated to be ∼3.30 ± 0.27 kcal/mol. The pressure-density relationship of EVA could be obtained for the first time by measuring the refractive index and using the Lorentz-Lorenz equation. The density and the refractive index exhibited monotonic increase up to approximately 12 GPa. The strong reduction of the acoustic damping at low pressures below ∼3 GPa was attributed to the collapsing free volume in EVA. The present study clearly shows that measuring the refractive index by high-pressure Brillouin spectroscopy may be an alternative method to get the EOS of polymeric materials whose transverse acoustic mode is too weak to be observed.
Intermediate regime of charged particle scattering in the field-reversal configuration
Shustov, P. I. Yushkov, E. V.; Artemyev, A. V.
2015-12-15
In this paper, we investigate the charged particle scattering in the magnetic field configuration with stretched magnetic field lines. This scattering results from the violation of the adiabaticity of charged particle motion in the region with the strong gradient of the magnetic field. We consider the intermediate regime of charged particle dynamics, when the violation of the adiabaticity is significant enough, but particle motion is not chaotic. We demonstrate and describe the significant scattering of particles with large adiabatic invariants (magnetic moment). We discuss a possible application of obtained results for description of the peculiarities of pitch-angle diffusion of relativistic electrons in the Earth radiation belts.
Methods And Systems For Using Reference Images In Acoustic Image Processing
Moore, Thomas L.; Barter, Robert Henry
2005-01-04
A method and system of examining tissue are provided in which a field, including at least a portion of the tissue and one or more registration fiducials, is insonified. Scattered acoustic information, including both transmitted and reflected waves, is received from the field. A representation of the field, including both the tissue and the registration fiducials, is then derived from the received acoustic radiation.
NASA Astrophysics Data System (ADS)
Meister, C.-V.; Mayer, B.; Hoffmann, D. H. H.
2012-04-01
The many-fluid magnetohydrodynamic theory is applied to describe the modification of the electromagnetic field of the ionospheric E-layer by acoustic-type waves. These waves originate from lower altitudes and may be caused by earthquake preparation processes. In comparison to former works, the different stratification of the positively and negatively charged ionospheric particles and of the neutral constituents is taken into account. There also the influence of the mean electric field on the different hight scales of the plasma parameters is discussed. Besides, the hight scales of the electric and magnetic wave fields are modeled. It is shown that at E-layer altitudes the acoustic waves may be converted into Alfvén waves. The dependence of these waves on the height scales of the plasma parameters of the particles and on the momentum transport between the charged and neutral particles is analysed. First estimates of the temperature variations within the E-layer because of the assumed acoustic-type waves of seismic origin are made.
Ahmed, Suzanne; Wang, Wei; Mair, Lamar O; Fraleigh, Robert D; Li, Sixing; Castro, Luz Angelica; Hoyos, Mauricio; Huang, Tony Jun; Mallouk, Thomas E
2013-12-31
The recent discovery of fuel-free propulsion of nanomotors using acoustic energy has provided a new avenue for using nanomotors in biocompatible media. Crucial to the application of nanomotors in biosensing and biomedical applications is the ability to remotely control and steer them toward targets of interest, such as specific cells and tissues. We demonstrate in vitro magnetic steering of acoustically powered nanorod motors in a biologically compatible environment. Steering was accomplished by incorporating (40 ± 5) nm thick nickel stripes into the electrochemically grown nanowires. An external magnetic field of 40-45 mT was used to orient the motors, which were acoustically propelled along their long axes. In the absence of a magnetic field, (300 ± 30) nm diameter, (4.3 ± 0.2) μm long nanowires with (40 ± 5) nm thick magnetic stripes exhibit the same self-acoustophoretic behavior, including pattern formation into concentric nanowire circles, aligned spinning chains, and autonomous axial motion, as their non-magnetic counterparts. In a magnetic field, these wires and their paths are oriented as evidenced by their relatively linear trajectories. Coordinated motion of multiple motors and targeting of individual motors toward HeLa cells with micrometer-level precision was demonstrated.
On the slow dynamics of near-field acoustically levitated objects under High excitation frequencies
NASA Astrophysics Data System (ADS)
Ilssar, Dotan; Bucher, Izhak
2015-10-01
This paper introduces a simplified analytical model describing the governing dynamics of near-field acoustically levitated objects. The simplification converts the equation of motion coupled with the partial differential equation of a compressible fluid, into a compact, second order ordinary differential equation, where the local stiffness and damping are transparent. The simplified model allows one to more easily analyse and design near-field acoustic levitation based systems, and it also helps to devise closed-loop controller algorithms for such systems. Near-field acoustic levitation employs fast ultrasonic vibrations of a driving surface and exploits the viscosity and the compressibility of a gaseous medium to achieve average, load carrying pressure. It is demonstrated that the slow dynamics dominates the transient behaviour, while the time-scale associated with the fast, ultrasonic excitation has a small presence in the oscillations of the levitated object. Indeed, the present paper formulates the slow dynamics under an ultrasonic excitation without the need to explicitly consider the latter. The simplified model is compared with a numerical scheme based on Reynolds equation and with experiments, both showing reasonably good results.
Coupled acoustic-gravity field for dynamic evaluation of ion exchange with a single resin bead.
Kanazaki, Takahiro; Hirawa, Shungo; Harada, Makoto; Okada, Tetsuo
2010-06-01
A coupled acoustic-gravity field is efficient for entrapping a particle at the position determined by its acoustic properties rather than its size. This field has been applied to the dynamic observation of ion-exchange reactions occurring in a single resin bead. The replacement of counterions in an ion-exchange resin induces changes in its acoustic properties, such as density and compressibility. Therefore, we can visually trace the advancement of an ion-exchange reaction as a time change in the levitation position of a resin bead entrapped in the field. Cation-exchange reactions occurring in resin beads with diameters of 40-120 microm are typically completed within 100-200 s. Ion-exchange equilibrium or kinetics is often evaluated with off-line chemical analyses, which require a batch amount of ion exchangers. Measurements with a single resin particle allow us to evaluate ion-exchange dynamics and kinetics of ions including those that are difficult to measure by usual off-line analyses. The diffusion properties of ions in resins have been successfully evaluated from the time change in the levitation positions of resin beads. PMID:20462180
Experimental Validation of FE/BEM Dynamic Strain Model Under Diffuse Acoustic Field Loading
NASA Technical Reports Server (NTRS)
Tsoi, W. Ben; Gardner, Bryce; Cotoni, Vincent
2010-01-01
Structural finite element (FE) models naturally output displacement or acceleration response data. However, they can also be used to compute stress, internal forces, and strain response. When coupled with a boundary element model (BEM) of the fluid surrounding the structure, a fully coupled analysis can be performed. Modeling a diffuse acoustic field in the BEM fluid provides an excitation like that found when the structure is placed in a reverberation chamber. Fully coupling the structural FE model to the acoustic BEM model provides a means to predict not only the acceleration response of the panel to diffuse field loading, but also the ability to predict the dynamic stress and strain response. This type of model has been available with current predictive tools, but experimental validation of the prediction of dynamic stress or strain is difficult to find. An aluminum panel was instrumented with accelerometers and strain gages and hung in a reverberation room and subjected to a diffuse acoustic field. This paper presents the comparison of the experimental and predicted results.
Acoustic Power Absorption and its Relation to Vector Magnetic Field of a Sunspot
NASA Astrophysics Data System (ADS)
Gosain, S.; Mathew, S. K.; Venkatakrishnan, P.
2011-02-01
The distribution of acoustic power over sunspots shows an enhanced absorption near the umbra - penumbra boundary. Previous studies revealed that the region of enhanced absorption coincides with the region of strongest transverse potential field. The aim of this paper is to i) utilize the high-resolution vector magnetograms derived using Hinode SOT/SP observations and study the relationship between the vector magnetic field and power absorption and ii) study the variation of power absorption in sunspot penumbrae due to the presence of spine-like radial structures. It is found that i) both potential and observed transverse fields peak at a similar radial distance from the center of the sunspot, and ii) the magnitude of the transverse field, derived from Hinode observations, is much larger than the potential transverse field derived from SOHO/MDI longitudinal-field observations. In the penumbra, the radial structures called spines (intra-spines) have stronger (weaker) field strength and are more vertical (horizontal). The absorption of acoustic power in the spine and intra-spine shows different behavior, with the absorption being larger in the spine as compared to the intra-spine.
NASA Astrophysics Data System (ADS)
Razaz, Mahdi; Kawanisi, Kiyosi; Kaneko, Arata; Nistor, Ioan
2015-12-01
A novel acoustic tomographic measurement system capable of resolving sound travel time in extremely shallow rivers is introduced and the results of an extensive field measurements campaign are presented and further discussed. Acoustic pulses were transmitted over a wide frequency band of 20-35 kHz between eight transducers for about a week in a meandering reach of theBāsen River, Hiroshima, Japan. The purpose of the field experiment was validating the concept of acoustic tomography in rivers for visualizing current fields. The particular novelty of the experiment resides in its unusual tomographic features: subbasin scale (100 m × 270 m) and shallowness (0.5-3.0 m) of the physical domain, frequency of the transmitted acoustic signals (central frequency of 30 kHz), and the use of small sampling intervals (105 s). Inverse techniques with no a priori statistical information were used to estimate the depth-average current velocity components from differential travel times. Zeroth-order Tikhonov regularization, in conjunction with L-curve method deployed to stabilize the solution and to determine the weighting factor appearing in the inverse analysis. Concurrent direct environmental measurements were provided in the form of ADCP readings close to the right and left bank. Very good agreement found between along-channel velocities larger than 0.2 m/s obtained from the two techniques. Inverted quantities were, however, underestimated, perhaps due to vicinity of the ADCPs to the banks and strong effect of river geometry on the readings. In general, comparing the visualized currents with direct nodal measurements illustrate the plausibility of the tomographically reconstructed flow structures.
NASA Astrophysics Data System (ADS)
Reinsch, Thomas; Jousset, Philippe; Henninges, Jan; Blanck, Hanna
2016-04-01
Seismic methods are particularly suited for investigating the Earth's subsurface. Compared to surface-measurements , wellbore measurements can be used to acquire more detailed information about rock properties and possible fluid pathways within a geothermal reservoir. For high temperature geothermal wells, however, ambient temperatures are often far above the operating temperature range of conventional geophones. One way to overcome this limitation is the application of fiber optic sensor systems, where only the passive optical fiber is subjected to downhole conditions. Their applicability is thus determined by the operating temperature range of the optical fiber. Choosing appropriate fibers, such sensor systems can be operated at temperatures far above 200°C. Along an optical fiber, the distributed acoustic sensing technology (DAS) can be used to acquire acoustic signals with a high spatial and temporal resolution. Previous experiments have shown that the DAS technology is well suited for active seismic measurements. Within the framework of the EC funded project IMAGE, a fiber optic cable was deployed in a newly drilled geothermal well (RN-34) within the Reykjanes geothermal field, Iceland. Additionally, a >15 km fiber optic cable, already available at the surface, was connected to a DAS read-out unit. Acoustic data was acquired continuously for 9 days. Hammer shots were performed at the wellhead as well as along the surface cable in order to locate individual acoustic traces and calibrate the spatial distribution of the acoustic information. During the monitoring period both signals from on- and offshore explosive sources and natural seismic events could be recorded. We compare the fiber optic data to conventional seismic records from a dense seismic network deployed on the Reykjanes in the course of the IMAGE project. Here, first results from the seismic survey will be presented.
Effects of static magnetic fields on light scattering in red chromatophore of goldfish scale
NASA Astrophysics Data System (ADS)
Iwasaka, M.
2010-05-01
Light scattering in a guanine crystal plate of goldfish scales was observed with and without static magnetic field exposure. Under a microscopic image with dark-field-illumination, the structural color of the scale by guanine plates was observed, and isolated chromatophores showed a twinkling which was the intermittent light scattering of the light from the side. The light scattering was quenched by static magnetic fields of more than 0.26 tesla (T). The quenching was reversibly occurred when the applied external magnetic fields were changed between ambient fields and 5 T. The quenched light scattering did not improve when the magnetic field was decreased from 5 to 0.3 T. It recovered to the original twinkling state about one minute after reaching an ambient geomagnetic field level. The mechanism of the quenched light scattering was speculated to be concerned with the possible magnetic orientation of guanine crystal plates, which were sustained by protein fibers in the red chromatophore. The diamagnetic complex of guanine crystal plates and protein fibers are the candidates for the nanosized light scattering controller based on the magnetic orientation mechanism.
A survey of the physical optics inverse scattering identity
NASA Astrophysics Data System (ADS)
Bojarski, N. N.
1982-09-01
An inverse scattering identity relating the characteristic function of a scatterer to the three-dimensional spatial Fourier transform of the augmented far field scattering amplitude is derived by applying the physical optics approximation to the acoustic and electromagnetic direct scattering integral representation. Because this identity requires full scattering data for all frequencies and aspect angles, an integral equation is developed for incomplete scattering data which solves for the unknown characteristic function of the scatterer in terms of the known incomplete scattering data. A regularized analytic closed form solution to this integral equation is obtained, and synthesized numerico-experimental results verifying the solution are presented.
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)
Dukeshire, Andrea
To efficiently model the effect of the airwave in the controlled-source electromagnetics (CSEM) method has historically been a problem of major interest. The methods proposed in this thesis provide a new method of simulating CSEM interactions in the finite-difference time-domain (FDTD) by using the total-field scattered-field (TFSF) formulation. TFSF provides an inherent separation of the total and scattered fields, which allows the proposed method to decompose the CSEM domain into separate simulation runs. By simulating the problem in stages, the process of extracting the response of the scatterer is streamlined. If the increased efficiency options within the proposed method are utilized, the efficiency of single forward simulations can be improved. This method shows potential for computational cost savings, especially in typical CSEM data analysis and reconstruction situations where numerous iterations of various scatterers are required.
NASA Astrophysics Data System (ADS)
Intonti, F.; Caselli, N.; Lawrence, N.; Trevino, J.; Wiersma, D. S.; Dal Negro, L.
2013-08-01
In this work, we employ scanning near-field optical microscopy, full-vector finite difference time domain numerical simulations and fractional Fourier transformation to investigate the near-field and propagation behavior of the electromagnetic energy scattered at 1.56 μm by dielectric arrays of silicon nitride nanopillars with chiral α1-Vogel spiral geometry. In particular, we experimentally study the spatial evolution of scattered radiation and demonstrate near-field coupling between adjacent nanopillars along the parastichies arms. Moreover, by measuring the spatial distribution of the scattered radiation at different heights from the array plane, we demonstrate a characteristic rotation of the scattered field pattern consistent with net transfer of orbital angular momentum in the Fresnel zone, within a few micrometers from the plane of the array. Our experimental results agree with the simulations we performed and may be of interest to nanophotonics applications.
Two Years of Industrial Experience in the Use of a Small, Direct Field Acoustic Chamber
NASA Astrophysics Data System (ADS)
Saggini, Nicola; Di Pietro, Vincenzo; Poulain, Nicolas; Herzog, Philippe
2012-07-01
Within Thales Alenia Space - Italy small satellite Assembly Integration and Test (AIT) plant, the need to develop a suitable facility for spacecraft acoustic noise test has arisen, with additional constraints posed by the necessity of a low impact on the existing building layout, low cost of procurement and operations, while maintaining a high reliability of the system for a theoretical maximum throughput of one test per week over an extended period of time, e.g. six months. The needs have been answered by developing a small (~40 m3 test volume), direct field (DF A T) acoustic test chamber, christened “Alpha Cabin”, where noise generation is achieved by means of commercial audio drivers equipped with custom enclosures. The paper starts with a brief presentation of the main characteristics of the system, but then concentrates on the lessons learnt and return of experience from the tests conducted in more than two years of continuous use. Starting from test article structural responses and their comparison with reverberant chambers, properties of the acoustic field and their implications on the former are analyzed.
Angular Spectrum Method for the Focused Acoustic Field of a Linear Transducer
NASA Astrophysics Data System (ADS)
Belgroune, D.; de Belleval, J. F.; Djelouah, H.
Applications involving non-destructive testing or acoustical imaging are more and more sophisticated. In this context, a model based on the angular spectrum approach is tackled in view to calculate the focused impulse field radiated by a linear transducer through a plane fluid-solid interface. It is well known that electronic focusing, based on a cylindrical delay law, like for the classical cases (lenses, curved transducer), leads to an inaccurate focusing in the solid due to geometric aberrations errors affecting refraction. Generally, there is a significant difference between the acoustic focal distance and the geometrical focal due to refraction. In our work, an optimized delay law, based on the Fermat's principle is established, particularly at an oblique incidence where the geometrical considerations, relatively simple in normal incidence, become quickly laborious. Numerical simulations of impulse field are judiciously carried out. Subsequently, the input parameters are optimally selected in order to achieve good computation accuracy and a high focusing. The overall results, involving compression and shear waves, have highlighted the focusing improvement in the solid when compared to the currently available approaches. Indeed, the acoustic focal distance is very close to geometrical focal distance and then, allows better control of the refracted angular beam profile (refraction angle, focusing depth and focal size).
Bai, Mingsian R; Wen, Jheng-Ciang; Hsu, Hoshen; Hua, Yi-Hsin; Hsieh, Yu-Hao
2014-10-01
A sound reconstruction system is proposed for audio reproduction with extended sweet spot and reduced reflections. An equivalent source method (ESM)-based sound field synthesis (SFS) approach, with the aid of dark zone minimization is adopted in the study. Conventional SFS that is based on the free-field assumption suffers from synthesis error due to boundary reflections. To tackle the problem, the proposed system utilizes convex optimization in designing array filters with both reproduction performance and acoustic contrast taken into consideration. Control points are deployed in the dark zone to minimize the reflections from the walls. Two approaches are employed to constrain the pressure and velocity in the dark zone. Pressure matching error (PME) and acoustic contrast (AC) are used as performance measures in simulations and experiments for a rectangular loudspeaker array. Perceptual Evaluation of Audio Quality (PEAQ) is also used to assess the audio reproduction quality. The results show that the pressure-constrained (PC) method yields better acoustic contrast, but poorer reproduction performance than the pressure-velocity constrained (PVC) method. A subjective listening test also indicates that the PVC method is the preferred method in a live room.
Surface contributions to scattered sound power using non-negative intensity.
Liu, Daipei; Peters, Herwig; Marburg, Steffen; Kessissoglou, Nicole
2016-08-01
Non-negative intensity is used to identify the surface areas of a structure that contributes to the scattered sound power. In the acoustic near field, the scattered sound power is predicted using non-negative intensity, as well as the scattered acoustic intensity integrated directly over the scatterer's surface area. In the acoustic far field, the scattered acoustic intensity and the scattered sound power are evaluated for three different receiver surface areas, corresponding to a sphere representing a far-field area that fully circumscribes the scatterer, and two hemispherical surfaces that correspond to partial far-field areas that do not fully circumscribe the scatterer. Back-calculated non-negative intensity that defines the sound scattered from the full or partial far-field receiver surface areas is also calculated and compared to the non-negative intensity obtained directly from the surface of the scatterer. To illustrate the numerical technique, the scattered acoustic intensity and scattered sound power of a rigid sphere, a rigid cylinder, and a rigid hemispherical shell are examined. PMID:27586749
Far-field acoustic data for the Texas ASE, Inc. hush house
NASA Astrophysics Data System (ADS)
Lee, R. A.
1982-04-01
This report supplements AFAMRL-TR-73-110, which describes the data base (NOISEFILE) used in the computer program (NOISEMAP) to predict the community noise exposure resulting from military aircraft operations. The results of field test measurements to define the single-event noise produced on the ground by military aircraft/engines operating in the Texas ASE Inc. hush-house are presented as a function of angle (0 deg to 180 deg from the front of the hush-house) and distance (200 ft to 2500 ft) in various acoustic metrics. All the data are normalized to standard acoustic reference conditions of 59 F temperature and 70% relative humidity. Refer to Volume I of the AFAMRL-TR-73-110 report for discussion of the scope, limitations, and definitions needed to understand and use the data in this report.
NASA Astrophysics Data System (ADS)
Tukmakov, A. L.
2015-01-01
A model of a multivelocity multitemperature polydisperse gas suspension has been constructed with account taken of coagulation. Calculations of the dynamics of an aerosol of a polydisperse composition in an acoustic resonator have been done and the derived regularities have been described. A system of Navier-Stokes equations for a compressible heat-conducting gas was used to describe the motion of a carrier medium. The dynamics of dispersed fractions is described by a system of equations including continuity, momentum, and internal-energy equations. The equations of motion of the carrier medium and dispersed fractions have been written with account of the interphase exchange of momentum and energy. The Lagrangian model has been used to describe the process of coagulation. The change in the dispersity of the gas suspension in the nonlinear field of an acoustic resonator has been analyzed.
On an acoustic field generated by subsonic jet at low Reynolds numbers
NASA Technical Reports Server (NTRS)
Yamamoto, K.; Arndt, R. E. A.
1978-01-01
An acoustic field generated by subsonic jets at low Reynolds numbers was investigated. This work is motivated by the need to increase the fundamental understanding of the jet noise generation mechanism which is essential to the development of further advanced techniques of noise suppression. The scope of this study consists of two major investigation. One is a study of large scale coherent structure in the jet turbulence, and the other is a study of the Reynolds number dependence of jet noise. With this in mind, extensive flow and acoustic measurements in low Reynolds number turbulent jets (8,930 less than or equal to M less than or equal to 220,000) were undertaken using miniature nozzles of the same configuration but different diameters at various exist Mach numbers (0.2 less than or equal to M less than or equal to 0.9).
Mapping the sound field of an erupting submarine volcano using an acoustic glider.
Matsumoto, Haru; Haxel, Joseph H; Dziak, Robert P; Bohnenstiehl, Delwayne R; Embley, Robert W
2011-03-01
An underwater glider with an acoustic data logger flew toward a recently discovered erupting submarine volcano in the northern Lau basin. With the volcano providing a wide-band sound source, recordings from the two-day survey produced a two-dimensional sound level map spanning 1 km (depth) × 40 km(distance). The observed sound field shows depth- and range-dependence, with the first-order spatial pattern being consistent with the predictions of a range-dependent propagation model. The results allow constraining the acoustic source level of the volcanic activity and suggest that the glider provides an effective platform for monitoring natural and anthropogenic ocean sounds. PMID:21428474
Computation of the pressure field generated by surface acoustic waves in microchannels.
Darinskii, A N; Weihnacht, M; Schmidt, H
2016-07-01
The high-frequency pressure induced by a surface acoustic wave in the fluid filling a microchannel is computed by solving the full scattering problem. The microchannel is fabricated inside a container attached to the top of a piezoelectric substrate where the surface wave propagates. The finite element method is used. The pressure found in this way is compared with the pressure obtained by solving boundary-value problems formulated on the basis of simplifications which have been introduced in earlier papers by other research studies. The considered example shows that the difference between the results can be significant, ranging from several tens of percent up to several times in different points inside the channel. PMID:27314212
Relativistic electron scattering from a freely movable proton in a strong laser field
NASA Astrophysics Data System (ADS)
Liu, Ai-Hua; Li, Shu-Min
2014-11-01
We study the electron scattering from the freely movable spin-1/2 proton in the presence of a linearly polarized laser field in the first Born approximation. The dressed state of the electron is described by a time-dependent wave function derived from a perturbation treatment (in a laser field). With the aid of numerical results we explore the dependencies of the differential cross section (DCS) on the electron-impact energy. Due to the mobility of the target, the DCS of this process is modified compared to the Mott scattering, especially in large scattering angles.
In-field stray light due to surface scattering effects in infrared imaging systems
NASA Astrophysics Data System (ADS)
Sun, Ke; Jiang, Hou-man; Cheng, Xiang-ai
2011-08-01
In-field stray light caused by surface scattering is a serious problem in many infrared imaging systems. Light that scattered from lenses in infrared imaging system produces a halo of stray light within the field of view and often degrades the performance of an optical system especially irradiated by intensive light such as laser. The experiments are performed by using infrared thermal imaging system, irradiated by CW DF infrared laser. The relationship between the diameter of saturated area on the detector and the incident laser irradiance is obtained, which can be well explained by the point spread function (PSF) of the optics including both diffraction and scattering components.
James, Kevin R; Dowling, David R
2011-02-01
Acoustic field calculations in underwater environments are often uncertain because the environmental parameters required for such calculations are uncertain. This letter compares the accuracy of direct simulations, the field shifting approximation, and polynomial chaos expansions for predicting acoustic amplitude uncertainty in 100-m-deep Pekeris waveguides having spatially uniform uncertain water-column sound speed. When this sound speed is Gaussian-distributed with a standard deviation of 1 m/s, direct simulations and polynomial chaos expansions, based on 21 field calculations, are more accurate than the field shifting approximation, based on two field calculations. This ranking reverses as the sound-speed standard deviation increases to 20 m/s.
Acoustic integrated extinction
Norris, Andrew N.
2015-01-01
The integrated extinction (IE) is defined as the integral of the scattering cross section as a function of wavelength. Sohl et al. (2007 J. Acoust. Soc. Am. 122, 3206–3210. (doi:10.1121/1.2801546)) derived an IE expression for acoustic scattering that is causal, i.e. the scattered wavefront in the forward direction arrives later than the incident plane wave in the background medium. The IE formula was based on electromagnetic results, for which scattering is causal by default. Here, we derive a formula for the acoustic IE that is valid for causal and non-causal scattering. The general result is expressed as an integral of the time-dependent forward scattering function. The IE reduces to a finite integral for scatterers with zero long-wavelength monopole and dipole amplitudes. Implications for acoustic cloaking are discussed and a new metric is proposed for broadband acoustic transparency. PMID:27547100
Mitigating stimulated scattering processes in gas-filled Hohlraums via external magnetic fields
Gong, Tao; Zheng, Jian; Li, Zhichao; Ding, Yongkun; Yang, Dong; Hu, Guangyue; Zhao, Bin
2015-09-15
A simple model, based on energy and pressure equilibrium, is proposed to deal with the effect of external magnetic fields on the plasma parameters inside the laser path, which shows that the electron temperature can be significantly enhanced as the intensity of the external magnetic fields increases. With the combination of this model and a 1D three-wave coupling code, the effect of external magnetic fields on the reflectivities of stimulated scattering processes is studied. The results indicate that a magnetic field with an intensity of tens of Tesla can decrease the reflectivities of stimulated scattering processes by several orders of magnitude.
Geints, Yu E; Zemlyanov, A A; Panina, E K
2014-01-31
The time dynamics of the optical field was theoretically considered in the near-field diffraction zone in the scattering of a femtosecond laser pulse by a transparent spherical microparticle. The spatial region of field focusing by the particle (the 'photonic jet' zone) was investigated; the evolution of the jet shape and the peak intensity in this region were analysed. For the first time it was determined that an extremely tight optical field localisation to a subdiffraction size is possible at a certain (resonance) temporal stage of photonic jet development. (radiation scattering)
Scattering measurements on natural and model trees
NASA Technical Reports Server (NTRS)
Rogers, James C.; Lee, Sung M.
1990-01-01
The acoustical back scattering from a simple scale model of a tree has been experimentally measured. The model consisted of a trunk and six limbs, each with 4 branches; no foliage or twigs were included. The data from the anechoic chamber measurements were then mathematically combined to construct the effective back scattering from groups of trees. Also, initial measurements have been conducted out-of-doors on a single tree in an open field in order to characterize its acoustic scattering as a function of azimuth angle. These measurements were performed in the spring, prior to leaf development. The data support a statistical model of forest scattering; the scattered signal spectrum is highly irregular but with a remarkable general resemblance to the incident signal spectrum. Also, the scattered signal's spectra showed little dependence upon scattering angle.
Solving outside-axial-field-of-view scatter correction problem in PET via digital experimentation
NASA Astrophysics Data System (ADS)
Andreyev, Andriy; Zhu, Yang-Ming; Ye, Jinghan; Song, Xiyun; Hu, Zhiqiang
2016-03-01
Unaccounted scatter impact from unknown outside-axial-field-of-view (outside-AFOV) activity in PET is an important degrading factor for image quality and quantitation. Resource consuming and unpopular way to account for the outside- AFOV activity is to perform an additional PET/CT scan of adjacent regions. In this work we investigate a solution to the outside-AFOV scatter problem without performing a PET/CT scan of the adjacent regions. The main motivation for the proposed method is that the measured random corrected prompt (RCP) sinogram in the background region surrounding the measured object contains only scattered events, originating from both inside- and outside-AFOV activity. In this method, the scatter correction simulation searches through many randomly-chosen outside-AFOV activity estimates along with known inside-AFOV activity, generating a plethora of scatter distribution sinograms. This digital experimentation iterates until a decent match is found between a simulated scatter sinogram (that include supposed outside-AFOV activity) and the measured RCP sinogram in the background region. The combined scatter impact from inside- and outside-AFOV activity can then be used for scatter correction during final image reconstruction phase. Preliminary results using measured phantom data indicate successful phantom length estimate with the method, and, therefore, accurate outside-AFOV scatter estimate.
The use of acoustic fields as a filtration and dewatering aid
Smythe; Wakeman
2000-03-01
An experimental rig has been developed to study the effects of electric and acoustic field combinations on the filtration rate of titanium dioxide suspensions. Ultrasound energy is applied tangentially to the filter medium. Electric field strengths, suspension characteristics and process parameters can all be varied independently. Results from an experimental programme demonstrate that the use of ultrasound across the cake surface can decrease the specific cake flow resistance and increase the filtration rates of low-concentration rutile suspensions (0.1% v/v). Changes in the conductivity induced by ultrasonic irradiation affect the suspension such that the application of an electrical field is enhanced, giving an equivalent electric field strength higher than that applied.
Acoustic anomalies in UPt{3} at high magnetic fields and low temperatures.
Feller, J. R.; Ketterson, J. B.; Hinks, D. G.; Dasgupta, D.; Sarma, B. K.; Materials Science Division; Northwestern Univ.; Univ. of Wisconsin at Milwaukee
2000-11-01
Ultrasound velocity and attenuation measurements were performed on single crystals of the heavy fermion compound UPt{sub 3} in magnetic fields up to 33 T and at temperatures ranging from 2.4 K to below 0.1 K. With longitudinal sound propagated in the crystallographic basal plane, parallel to the applied field, the familiar elastic softening is observed at the metamagnetic transition field H-20.2 T. More complicated structure emerges at low temperatures, including quantum acoustic oscillations and a second velocity minimum at -21.6 T. A weak frequency dependence (dispersion) is observed in the velocity. The ultrasonic data are analyzed using the Landau-Khalatnikov formalism, from which temperature- and field-dependent relaxation times are deduced.
NASA Astrophysics Data System (ADS)
Yu, Cong; Lai, Dong
2015-07-01
We study the effect of large-scale magnetic fields on the non-axisymmetric inertial-acoustic modes (also called p modes) trapped in the innermost regions of accretion discs around black holes (BHs). These global modes could provide an explanation for the high-frequency quasi-periodic oscillations (HFQPOs) observed in BH X-ray binaries. There may be observational evidence for the presence of such large-scale magnetic fields in the discs since episodic jets are observed in the same spectral state when HFQPOs are detected. We find that a large-scale poloidal magnetic field can enhance the corotational instability and increase the growth rate of the purely hydrodynamic overstable p modes. In addition, we show that the frequencies of these overstable p modes could be further reduced by such magnetic fields, making them agree better with observations.
Imaging of transient surface acoustic waves by full-field photorefractive interferometry.
Xiong, Jichuan; Xu, Xiaodong; Glorieux, Christ; Matsuda, Osamu; Cheng, Liping
2015-05-01
A stroboscopic full-field imaging technique based on photorefractive interferometry for the visualization of rapidly changing surface displacement fields by using of a standard charge-coupled device (CCD) camera is presented. The photorefractive buildup of the space charge field during and after probe laser pulses is simulated numerically. The resulting anisotropic diffraction upon the refractive index grating and the interference between the polarization-rotated diffracted reference beam and the transmitted signal beam are modeled theoretically. The method is experimentally demonstrated by full-field imaging of the propagation of photoacoustically generated surface acoustic waves with a temporal resolution of nanoseconds. The surface acoustic wave propagation in a 23 mm × 17 mm area on an aluminum plate was visualized with 520 × 696 pixels of the CCD sensor, yielding a spatial resolution of 33 μm. The short pulse duration (8 ns) of the probe laser yields the capability of imaging SAWs with frequencies up to 60 MHz. PMID:26026514
NASA Astrophysics Data System (ADS)
Raczkowska, A.; Gorska, N.
2012-12-01
Puck Bay is an area of high species biodiversity belonging to the Coastal Landscape Park of Baltic Sea Protected Areas (BSPA) and is also included in the list of the World Wide Fund for Nature (WWF) and covered by the protection program "Natura 2000". The underwater meadows of the Puck Bay are important for Europe's natural habitats due to their role in enhancing the productivity of marine ecosystems and providing shelter and optimal feeding conditions for many marine organisms. One of the dominant species comprising the underwater meadows of the Southern Baltic Sea is the seagrass Zostera marina. The spatial extent of underwater seagrass meadows is altered by pollution and eutrophication; therefore, to properly manage the area one must monitor its ecological state. Remote acoustic methods are useful tools for the monitoring of benthic habitats in many marine areas because they are non-invasive and allow researchers to obtain data from a large area in a short period of time. Currently there is a need to apply these methods in the Baltic Sea. Here we present an analysis of the mechanism of scattering of acoustic waves on seagrass in the Southern Baltic Sea based on the numerical modeling of acoustic wave scattering by the biological tissues of plants. The study was conducted by adapting a model developed on the basis of DWBA (Distorted Wave Born Approximation) developed by Stanton and Chu (2005) for fluid-like objects, including the characteristics of the Southern Baltic seagrass. Input data for the model, including the morphometry of seagrass leaves, their angle of inclination and the density plant cover, was obtained through the analysis of biological materials collected in the Puck Bay in the framework of a research project financed by the Polish Government (Development of hydroacoustic methods for studies of underwater meadows of Puck Bay, 6P04E 051 20). On the basis of the developed model, we have analyzed the dependence of the target strength of a single
Electron-nucleus scattering at small angles in the field of a pulsed laser wave
NASA Astrophysics Data System (ADS)
Lebed', A. A.
2016-04-01
We study scattering of an electron by a screened potential of a nucleus in the field of a pulsed laser wave at small scattering angles. The interaction of an electron with the field of a nucleus is considered in the first Born approximation. An external field of a pulsed laser is accounted accurately as a quasimonochromatic wave. Analytical expressions are obtained for the transition amplitude and the cross section of the considered process. Scattering kinematics is defined at the minimal value of a transferred momentum. In this case the cross section contains a peak near the preferred scattering direction. It is shown that the maximum value of the cross section is determined by both the initial-electron energy and the energy of an external-field photon. Thus, the cross section of electron-nucleus scattering in a pulsed laser field can exceed in two orders of magnitude the cross section in absence of an external field in the case of ultrarelativistic energies and external field of a free-electron laser with keV-order photon energy.
Wisniewska, Danuta M; Ratcliffe, John M; Beedholm, Kristian; Christensen, Christian B; Johnson, Mark; Koblitz, Jens C; Wahlberg, Magnus; Madsen, Peter T
2015-01-01
Toothed whales use sonar to detect, locate, and track prey. They adjust emitted sound intensity, auditory sensitivity and click rate to target range, and terminate prey pursuits with high-repetition-rate, low-intensity buzzes. However, their narrow acoustic field of view (FOV) is considered stable throughout target approach, which could facilitate prey escape at close-range. Here, we show that, like some bats, harbour porpoises can broaden their biosonar beam during the terminal phase of attack but, unlike bats, maintain the ability to change beamwidth within this phase. Based on video, MRI, and acoustic-tag recordings, we propose this flexibility is modulated by the melon and implemented to accommodate dynamic spatial relationships with prey and acoustic complexity of surroundings. Despite independent evolution and different means of sound generation and transmission, whales and bats adaptively change their FOV, suggesting that beamwidth flexibility has been an important driver in the evolution of echolocation for prey tracking. DOI: http://dx.doi.org/10.7554/eLife.05651.001 PMID:25793440
The effects of external acoustic pressure fields on a free-running supercavitating projectile.
Cameron, Peter J K; Rogers, Peter H; Doane, John W
2010-12-01
Proliferation of supercavitating torpedoes has motivated research on countermeasures against them as well as on the fluid phenomenon which makes them possible. The goal of this research was to investigate an envisaged countermeasure, an acoustic field capable of slowing or diverting the weapon by disrupting the cavitation envelope. The research focused on the interactions between high pressure amplitude sound waves and a supercavity produced by a small free-flying projectile. The flight dynamics and cavity geometry measurements were compared to control experiments and theoretical considerations were made for evaluating the effects. Corrugations on the cavity/water interface caused by the pressure signal have been observed and characterized. Results also show that the accuracy of a supercavitating projectile can be adversely affected by the sound signal. This research concludes with results that indicate that it is acoustic cavitation in the medium surrounding the supercavity, caused by the high pressure amplitude sound, that is responsible for the reduced accuracy. A hypothesis has been presented addressing the means by which the acoustic cavitation could cause this effect. PMID:21218872
Bulanov, Alexey V.; Nagorny, Ivan G.
2015-10-28
Researches of the acoustic effects accompanying optical breakdown in a water, generated by the focused laser radiation with power ultrasound have been carried out. Experiments were performed by using 532 nm pulses from Brilliant B Nd:YAG laser. Acoustic radiation was produced by acoustic focusing systems in the form hemisphere and ring by various resonance frequencies of 10.7 kHz and 60 kHz. The experimental results are obtained, that show the sharply strengthens effects of acoustic emission from a breakdown zone by the joint influence of a laser and ultrasonic irradiation. Essentially various thresholds of breakdown and character of acoustic emission in fresh and sea water are found out. The experimental result is established, testifying that acoustic emission of optical breakdown of sea water at presence and at absence of ultrasound essentially exceeds acoustic emission in fresh water. Atomic lines of some chemical elements like a Sodium, Magnesium and so on were investigated for laser breakdown of water with ultrasound field. The effect of magnification of this lines resolution for salt water in ultrasound field was obtained.
Dark matter effective field theory scattering in direct detection experiments
Schneck, K.; Cabrera, B.; Cerdeno, D. G.; Mandic, V.; Rogers, H. E.; Agnese, R.; Anderson, A. J.; Asai, M.; Balakishiyeva, D.; Barker, D.; Basu Thakur, R.; Bauer, D. A.; Billard, J.; Borgland, A.; Brandt, D.; Brink, P. L.; Bunker, R.; Caldwell, D. O.; Calkins, R.; Chagani, H.; Chen, Y.; Cooley, J.; Cornell, B.; Crewdson, C. H.; Cushman, Priscilla B.; Daal, M.; Di Stefano, P. C.; Doughty, T.; Esteban, L.; Fallows, S.; Figueroa-Feliciano, E.; Godfrey, G. L.; Golwala, S. R.; Hall, Jeter C.; Harris, H. R.; Hofer, T.; Holmgren, D.; Hsu, L.; Huber, M. E.; Jardin, D. M.; Jastram, A.; Kamaev, O.; Kara, B.; Kelsey, M. H.; Kennedy, A.; Leder, A.; Loer, B.; Lopez Asamar, E.; Lukens, W.; Mahapatra, R.; McCarthy, K. A.; Mirabolfathi, N.; Moffatt, R. A.; Morales Mendoza, J. D.; Oser, S. M.; Page, K.; Page, W. A.; Partridge, R.; Pepin, M.; Phipps, A.; Prasad, K.; Pyle, M.; Qiu, H.; Rau, W.; Redl, P.; Reisetter, A.; Ricci, Y.; Roberts, A.; Saab, T.; Sadoulet, B.; Sander, J.; Schnee, R. W.; Scorza, S.; Serfass, B.; Shank, B.; Speller, D.; Toback, D.; Upadhyayula, S.; Villano, A. N.; Welliver, B.; Wilson, J. S.; Wright, D. H.; Yang, X.; Yellin, S.; Yen, J. J.; Young, B. A.; Zhang, J.
2015-05-01
We examine the consequences of the effective eld theory (EFT) of dark matter-nucleon scattering or current and proposed direct detection experiments. Exclusion limits on EFT coupling constants computed using the optimum interval method are presented for SuperCDMS Soudan, CDMS II, and LUX, and the necessity of combining results from multiple experiments in order to determine dark matter parameters is discussed. We demonstrate that spectral di*erences between the standard dark matter model and a general EFT interaction can produce a bias when calculating exclusion limits and when developing signal models for likelihood and machine learning techniques. We also discuss the implications of the EFT for the next-generation (G2) direct detection experiments and point out regions of complementarity in the EFT parameter space.
Imaging of Passive Scalar Fields by Filtered Rayleigh Scattering
NASA Astrophysics Data System (ADS)
Kearney, Sean; Grasser, Thomas; Beresh, Steven; Schefer, Robert
2002-11-01
Filtered Rayleigh Scattering (FRS) is a molecular-filter-based, laser-diagnostic approach for multiparameter flowfield imaging that has been gaining popularity over the past 5-10 years [1]. Advantages of FRS for noninvasive gas-phase imaging include: (1) elimination of particle or chemical seeding requirements, (2) increased optical noise rejection allowing imaging close to walls and in "dirty" laboratory environments, (3) imaging of multiple flowfield parameters with a single diagnostic. In this work, the construction and performance of a FRS optical system for passive scalar imaging at Sandia National Laboratories is presented. Data were obtained in an open lab where no special precautions for the elimination of room particulate were made. Results from nonreacting jets and from a premixed flame are shown. Temperature imaging in a nonreacting, steady calibration jet reveals the precision of the time-averaged FRS thermometry results to be ±20 K, or 4of the characteristic temperature difference, while the single-laser-pulse precision is degraded to approximately ±40-50 K. These results are adequate for combustion thermometry purposes. Relative to the jet temperature measurements, species concentration imaging of a buoyant helium jet displays increased signal dynamic range and further improved precision. Reacting flow measurements from the combustion-product region of a methane-air Hencken-type premixed flame are also presented and a comparison of FRS and coherent anti-Stokes Raman scattering (CARS) experiments to calculated adiabatic-equilibrium product temperatures is made which validates the suitability of our FRS instrument for combustion temperature imaging. [1]G.S. Elliott, N. Glumac, and C.D. Carter, Meas. Sci. Tech., 12, 452, 2001.
NASA Technical Reports Server (NTRS)
Olsen, W. A.; Boldman, D.
1978-01-01
Fairly extensive measurements have been conducted of the turbulent flow around various surfaces as a basis for a study of the acoustic characteristics involved. In the experiments the flow from a nozzle was directed upon various two-dimensional surface configurations such as the three-flap model. A turbulent flow field description is given and an estimate of the acoustic characteristics is provided. The developed equations are based upon fundamental theories for simple configurations having simple flows. Qualitative estimates are obtained regarding the radiation pattern and the velocity power law. The effect of geometry and turbulent flow distribution on the acoustic emission from simple configurations are discussed.
Gulyaev, Yu V; Barabanenkov, Yu N; Barabanenkov, M Yu; Nikitov, S A
2005-08-01
We present an optical theorem for evanescent (near field) electromagnetic wave scattering by a dielectric structure. The derivation is based on the formalism of angular spectrum wave amplitudes and block scattering matrix. The optical theorem shows that an energy flux is emitted in the direction of the evanescent wave decay upon scattering. The energy emission effect from an evanescent wave is illustrated in two examples of evanescent wave scattering, first, by the electrical dipole and, second, one-dimensional grating with line-like rulings. Within the latter example, we show that an emitted energy flux upon evanescent wave scattering can travel through a dielectric structure even if the structure has a forbidden gap in the transmission spectrum of incident propagating waves.
NASA Astrophysics Data System (ADS)
Xu, Xiaodong; Agustin Flores Cuautle, Jose Jesus; Kouyate, Mansour; Bernardus Roozen, Nicolaas; Goossens, Jozefien; Menon, Preethy; Kuriakose Malayil, Maju; Salenbien, Robbe; Nair Rajesh, Ravindran; Glorieux, Christ; Griesmar, Pascal; Martinez, Loïc; Serfaty, Stéphane
2016-03-01
The evolution of the elastic and thermal properties of a tetramethylorthosilicate (TMOS)-based gel that exhibits an extraordinary ringing effect when enclosed in a bottle is investigated during the sol-gel transition. The results demonstrate the feasibility of three proposed experimental methods for monitoring of gels during their formation. The shear stiffening evolution during gelation is monitored by ringing bottle, resonant acoustic spectroscopy and by an ultrasonic technique using piezo electric excitation and detection. The evolution of the longitudinal modulus and the thermal diffusivity of the gel during stiffening are simultaneously determined by a combined photoacoustic and photothermal method based on heterodyne diffraction detection of impulsive stimulated scattering by, respectively, a propagating acoustic wave grating and a decaying thermal expansion grating that were both thermo elastically generated using a pulsed laser. Also, the feasibility of an inverse photopyroelectric method and a hot ball technique to monitor the thermal transport efficiency and thermal impedance of a forming gel by tracking the thermal conductivity, the thermal diffusivity, and the thermal effusivity is demonstrated. The network polymerization and stiffening during the sol-gel transition in TMOS-gel corresponds with substantial changes in the shear acoustic velocity and in all thermal properties, while the longitudinal acoustic velocity is only weakly affected.
Ranasinghesagara, Janaka C.; Hayakawa, Carole K.; Davis, Mitchell A.; Dunn, Andrew K.; Potma, Eric O.; Venugopalan, Vasan
2014-01-01
We develop an efficient method for accurately calculating the electric field of tightly focused laser beams in the presence of specific configurations of microscopic scatterers. This Huygens–Fresnel wave-based electric field superposition (HF-WEFS) method computes the amplitude and phase of the scattered electric field in excellent agreement with finite difference time-domain (FDTD) solutions of Maxwell’s equations. Our HF-WEFS implementation is 2–4 orders of magnitude faster than the FDTD method and enables systematic investigations of the effects of scatterer size and configuration on the focal field. We demonstrate the power of the new HF-WEFS approach by mapping several metrics of focal field distortion as a function of scatterer position. This analysis shows that the maximum focal field distortion occurs for single scatterers placed below the focal plane with an offset from the optical axis. The HF-WEFS method represents an important first step toward the development of a computational model of laser-scanning microscopy of thick cellular/tissue specimens. PMID:25121440
Far-field acoustic data for the Texas ASE, Inc. Hush-House, supplement
NASA Astrophysics Data System (ADS)
Lee, R. A.
1982-04-01
This report supplements AFAMRL-TR-73-110, which describes the data base (NOISEFILE) used in the computer program (NOISEMAP) to predict the community noise exposure resulting from military aircraft operations. The results of field test measurements to define the single-event noise produced on the ground by military aircraft/engines operating in the Texas ASE Inc. hush-house are presented as a function of angle (0 to 180 from the front of the hush-house) and distance (200 ft to 2500 ft) in various acoustic metrics.
Force on a heated sphere in a horizontal plane acoustic standing wave field
NASA Technical Reports Server (NTRS)
Leung, E. W.; Wang, T. G.
1985-01-01
The force on a heated sphere in a horizontal plane acoustic standing wave field is the subject of this investigation. The heated sphere produces a thermal gradient in the resonance chamber. The force on the sphere in a direction perpendicular to that of gravity is measured. This force is enhanced in the region near the pressure node, and is weakened in the region near the pressure antinode. Measurements of the force on a heated sphere with sound pressure levels between 148 and 156 dB are presented.
Study on the bubble transport mechanism in an acoustic standing wave field.
Xi, Xiaoyu; Cegla, Frederic B; Lowe, Michael; Thiemann, Andrea; Nowak, Till; Mettin, Robert; Holsteyns, Frank; Lippert, Alexander
2011-12-01
The use of bubbles in applications such as surface chemistry, drug delivery, and ultrasonic cleaning etc. has been enormously popular in the past two decades. It has been recognized that acoustically-driven bubbles can be used to disturb the flow field near a boundary in order to accelerate physical or chemical reactions on the surface. The interactions between bubbles and a surface have been studied experimentally and analytically. However, most of the investigations focused on violently oscillating bubbles (also known as cavitation bubble), less attention has been given to understand the interactions between moderately oscillating bubbles and a boundary. Moreover, cavitation bubbles were normally generated in situ by a high intensity laser beam, little experimental work has been carried out to study the translational trajectory of a moderately oscillating bubble in an acoustic field and subsequent interactions with the surface. This paper describes the design of an ultrasonic test cell and explores the mechanism of bubble manipulation within the test cell. The test cell consists of a transducer, a liquid medium and a glass backing plate. The acoustic field within the multi-layered stack was designed in such a way that it was effectively one dimensional. This was then successfully simulated by a one dimensional network model. The model can accurately predict the impedance of the test cell as well as the mode shape (distribution of particle velocity and stress/pressure field) within the whole assembly. The mode shape of the stack was designed so that bubbles can be pushed from their injection point onto a backing glass plate. Bubble radial oscillation was simulated by a modified Keller-Miksis equation and bubble translational motion was derived from an equation obtained by applying Newton's second law to a bubble in a liquid medium. Results indicated that the bubble trajectory depends on the acoustic pressure amplitude and initial bubble size: an increase of
2-D acoustic Laplace-domain waveform inversion of marine field data
NASA Astrophysics Data System (ADS)
Ha, Wansoo; Chung, Wookeen; Park, Eunjin; Shin, Changsoo
2012-07-01
The Laplace-domain full waveform inversion method can build a macroscale subsurface velocity model that can be used as an accurate initial model for a conventional full waveform inversion. The acoustic Laplace-domain inversion produced is promising for marine field data examples. Although applying an acoustic inversion method to the field data generally requires several pre-processing steps, pre-processing for the Laplace-domain inversion has not been explained in detail. We provide a detailed explanation of how to apply the Laplace-domain waveform inversion to field data through numerical tests with Gulf of Mexico data sets. The pre-processing includes bandpass filtering, muting of the noise before the first arrival, and extraction of the water depth. We choose the range and the interval between the Laplace damping constants empirically by applying a threshold value to the damped time traces and the Laplace-domain wavefields. The observed data are transformed to the Laplace domain using the selected damping; this method yielded a long-wavelength inversion result. The damping constant and the maximum offset affect the penetration depth of the inversion result. The maximum recording time is important for a stable Laplace-transformation and affects the inversion result; however, the latter effect is not significant.
Perez, Camilo; Chen, Hong; Matula, Thomas J; Karzova, Maria; Khokhlova, Vera A
2013-08-01
Extracorporeal shock wave therapy (ESWT) uses acoustic pulses to treat certain musculoskeletal disorders. In this paper the acoustic field of a clinical portable ESWT device (Duolith SD1) was characterized. Field mapping was performed in water for two different standoffs of the electromagnetic head (15 or 30 mm) using a fiber optic probe hydrophone. Peak positive pressures at the focus ranged from 2 to 45 MPa, while peak negative pressures ranged from -2 to -11 MPa. Pulse rise times ranged from 8 to 500 ns; shock formation did not occur for any machine settings. The maximum standard deviation in peak pressure at the focus was 1.2%, indicating that the Duolith SD1 generates stable pulses. The results compare qualitatively, but not quantitatively with manufacturer specifications. Simulations were carried out for the short standoff by matching a Khokhlov-Zabolotskaya-Kuznetzov equation to the measured field at a plane near the source, and then propagating the wave outward. The results of modeling agree well with experimental data. The model was used to analyze the spatial structure of the peak pressures. Predictions from the model suggest that a true shock wave could be obtained in water if the initial pressure output of the device were doubled.
Perez, Camilo; Chen, Hong; Matula, Thomas J.; Karzova, Maria; Khokhlova, Vera A.
2013-01-01
Extracorporeal shock wave therapy (ESWT) uses acoustic pulses to treat certain musculoskeletal disorders. In this paper the acoustic field of a clinical portable ESWT device (Duolith SD1) was characterized. Field mapping was performed in water for two different standoffs of the electromagnetic head (15 or 30 mm) using a fiber optic probe hydrophone. Peak positive pressures at the focus ranged from 2 to 45 MPa, while peak negative pressures ranged from −2 to −11 MPa. Pulse rise times ranged from 8 to 500 ns; shock formation did not occur for any machine settings. The maximum standard deviation in peak pressure at the focus was 1.2%, indicating that the Duolith SD1 generates stable pulses. The results compare qualitatively, but not quantitatively with manufacturer specifications. Simulations were carried out for the short standoff by matching a Khokhlov-Zabolotskaya-Kuznetzov equation to the measured field at a plane near the source, and then propagating the wave outward. The results of modeling agree well with experimental data. The model was used to analyze the spatial structure of the peak pressures. Predictions from the model suggest that a true shock wave could be obtained in water if the initial pressure output of the device were doubled. PMID:23927207
NASA Astrophysics Data System (ADS)
Kwon, Hyu-Sang; Kim, Yong-Joe; Bolton, J. Stuart
2003-01-01
Multireference, scan-based near-field acoustical holography is a useful measurement tool that can be applied when an insufficient number of microphones is available to make measurements on a complete hologram surface simultaneously. The scan-based procedure can be used to construct a complete hologram by joining together subholograms captured using a relatively small, roving scan array and a fixed reference array. For the procedure to be successful, the source levels must remain stationary for the time taken to record the complete hologram; that is unlikely to be the case in practice, however. Usually, the reference signal levels measured during each scan differ from each other with the result that spatial noise is added to the hologram. A procedure to suppress the effects of source level, and hence reference level, variations is proposed here. The procedure is based on a formulation that explicitly features the acoustical transfer functions between the sources and both the reference and scanning, field microphones. When it is assumed that source level changes do not affect the sources' directivity, a nonstationarity compensation procedure can be derived that is based on measured transfer functions between the reference and field microphones. It has been verified both experimentally and in numerical simulations that the proposed procedure can help suppress spatially distributed noise caused by the type of source level nonstationarity that is characteristic of realistic sources.
Dust acoustic shock wave in electronegative dusty plasma: Roles of weak magnetic field
Ghosh, Samiran; Ehsan, Z.; Murtaza, G.
2008-02-15
The effects of nonsteady dust charge variations and weak magnetic field on small but finite amplitude nonlinear dust acoustic wave in electronegative dusty plasma are investigated. The dynamics of the nonlinear wave are governed by a Korteweg-de Vries Burger equation that possesses dispersive shock wave. The weak magnetic field is responsible for the dispersive term, whereas nonsteady dust charge variation is responsible for dissipative term, i.e., the Burger term. The coefficient of dissipative term depends only on the obliqueness of the magnetic field. It is found that for parallel propagation the dynamics of the nonlinear wave are governed by the Burger equation that possesses monotonic shock wave. The relevances of the findings to cometary dusty plasma, e.g., Comet Halley are briefly discussed.
NASA Technical Reports Server (NTRS)
Slutsky, S.; Fischer, D.; Erdos, J. I.
1977-01-01
A small perturbation type analysis has been developed for the acoustic far field in an infinite duct extending upstream and downstream of an axial turbomachinery stage. The analysis is designed to interface with a numerical solution of the near field of the blade rows and, thereby, to provide the necessary closure condition to complete the statement of infinite duct boundary conditions for the subject problem. The present analysis differs from conventional inlet duct analyses in that a simple harmonic time dependence was not assumed, since a transient signal is generated by the numerical near-field solution and periodicity is attained only asymptotically. A description of the computer code developed to carry out the necessary convolutions numerically is included, as well as the results of a sample application using an impulsively initiated harmonic signal.
Dubnishchev, Yu N; Chugui, Yu V; Kompenhans, J
2009-10-31
The method of laser Doppler visualisation and measurement of the velocity field in gas and liquid flows by suppressing the influence of multiparticle scattering is discussed. The cross section of the flow under study is illuminated by a laser beam transformed by an anamorphic optical system into a laser sheet. The effect of multiparticle scattering is eliminated by obtaining differential combinations of frequency-demodulated images of the laser sheet in different regions of the angular spectrum of scattered light. (laser applications and other topics in quantum electronics)
A transform-pair relationship between incident and scattered fields from an arbitrary reflector
NASA Technical Reports Server (NTRS)
Ludwig, A. C.; Brunstein, S. A.
1978-01-01
It is shown that a transform-pair relationship exists between incident and scattered fields from an infinite, perfectly conducting reflector of arbitrary shape, when the physical optics approximation is applied. As an example of potential applications, this relationship is used to synthesize a reflector feed pattern required to produce a desired far-field pattern from a given paraboloidal reflector.
NASA Astrophysics Data System (ADS)
Jiang, Xue; Cheng, JianChun; Liang, Bin
2015-05-01
The field rotator is a fascinating device capable to rotate the wave front by a certain angle, which can be regarded as a special kind of illusion. We have theoretically designed and experimentally realized an acoustic field rotator by exploiting acoustic metamaterials with extremely anisotropic parameters. A nearly perfect agreement is observed between the numerical simulation and experimental results. We have also studied the acoustic property of the acoustic rotator, and investigated how various structural parameters affect the performances of such devices, including the operating frequency range and rotation angle, which are of particularly significance for the application. The inspection of the operating frequency range shows the device can work within a considerably broad band as long as the effective medium approximation is valid. The influence of the configuration of the metamaterial unit has also been investigated, illustrating the increase of anisotropy of metamaterial helps to enhance the rotator effect, which can be conveniently attained by elongating each rectangle inserted to the units. Furthermore, we have analyzed the underlying physics to gain a deep insight to the rotation mechanism, and discussed the application of such devices for non-plane wave and the potential of extending the scheme to three-dimensional cases. The realization of acoustic field rotator has opened up a new avenue for the versatile manipulations on acoustic waves and our findings are of significance to their design and characterization, which may pave the way for the practical application of such devices.
Scattering in an external electric field asymptotically constant in time
Adachi, Tadayoshi; Ishida, Atsuhide
2011-06-15
We show the asymptotic completeness for two-body quantum systems in an external electric field asymptotically non-zero constant in time. One of the main ingredients of this paper is to give some propagation estimates for physical propagators generated by time-dependent Hamiltonians which govern the systems under consideration.
Canonical Acoustics and Its Application to Surface Acoustic Wave on Acoustic Metamaterials
NASA Astrophysics Data System (ADS)
Shen, Jian Qi
2016-08-01
In a conventional formalism of acoustics, acoustic pressure p and velocity field u are used for characterizing acoustic waves propagating inside elastic/acoustic materials. We shall treat some fundamental problems relevant to acoustic wave propagation alternatively by using canonical acoustics (a more concise and compact formalism of acoustic dynamics), in which an acoustic scalar potential and an acoustic vector potential (Φ ,V), instead of the conventional acoustic field quantities such as acoustic pressure and velocity field (p,u) for characterizing acoustic waves, have been defined as the fundamental variables. The canonical formalism of the acoustic energy-momentum tensor is derived in terms of the acoustic potentials. Both the acoustic Hamiltonian density and the acoustic Lagrangian density have been defined, and based on this formulation, the acoustic wave quantization in a fluid is also developed. Such a formalism of acoustic potentials is employed to the problem of negative-mass-density assisted surface acoustic wave that is a highly localized surface bound state (an eigenstate of the acoustic wave equations). Since such a surface acoustic wave can be strongly confined to an interface between an acoustic metamaterial (e.g., fluid-solid composite structures with a negative dynamical mass density) and an ordinary material (with a positive mass density), it will give rise to an effect of acoustic field enhancement on the acoustic interface, and would have potential applications in acoustic device design for acoustic wave control.
Neutron Scattering at Highest Magnetic Fields at the Helmholtz Centre Berlin
NASA Astrophysics Data System (ADS)
Smeibidl, P.; Tennant, A.; Ehmler, H.; Bird, M.
2010-04-01
The Helmholtz Centre Berlin (HZB), formerly Hahn-Meitner Institute is a user facility for the study of structure and dynamics with neutrons and synchrotron radiation with special emphasis on experiments under extreme conditions. Neutron scattering is uniquely suited to study magnetic properties on a microscopic length scale, because neutrons have comparable wavelengths and, due to their magnetic moment, they interact with the atomic magnetic moments. At HZB a dedicated instrument for neutron scattering at extreme fields is under construction, the Extreme Environment Diffractometer ExED. It is projected according to the “time-of-flight” principle for elastic and inelastic neutron scattering and for the special geometric constraints of analysing samples in a high field magnet. The new magnet will not only allow for novel experiments, it will be at the forefront of development in magnet technology itself. The design of the magnet will follow the Series Connected Hybrid System Technology (SCH) developed at the National High Magnetic Field Laboratory (NHMFL) in Tallahassee, Florida. To compromise between the needs of the magnet design for highest fields and the concept of the neutron instrument, the magnetic field will be generated by means of a coned solenoid with horizontal field orientation. By using resistive insert coils, which are mounted in the room temperature bore of a superconducting cable-in-conduit (CIC) magnet, fields above 30 Tesla can be obtained in a geometry optimised for the demands of neutron scattering.
Nonlinear electron acoustic cyclotron waves in presence of uniform magnetic field
Dutta, Manjistha; Khan, Manoranjan; Ghosh, Samiran; Roychoudhury, Rajkumar; Chakrabarti, Nikhil
2013-04-15
Nonlinear electron acoustic cyclotron waves (EACW) are studied in a quasineutral plasma in presence of uniform magnetic field. The fluid model is used to describe the dynamics of two temperature electron species in a stationary charge neutral inhomogeneous background. In long wavelength limit, it is shown that the linear electron acoustic wave is modified by the uniform magnetic field similar to that of electrostatic ion cyclotron wave. Nonlinear equations for these waves are solved by using Lagrangian variables. Results show that the spatial solitary wave-like structures are formed due to nonlinearities and dispersions. These structures transiently grow to larger amplitude unless dispersive effect is actively operative and able to arrest this growth. We have found that the wave dispersion originated from the equilibrium inhomogeneity through collective effect and is responsible for spatiotemporal structures. Weak dispersion is not able to stop the wave collapse and singular structures of EACW are formed. Relevance of the results in the context of laboratory and space plasmas is discussed.
The acoustic field of singing humpback whales in the vertical plane
NASA Astrophysics Data System (ADS)
Au, Whitlow W. L.; Pack, Adam A.; Lammers, Marc O.; Herman, Louis; Andrews, Kimberly; Deakos, Mark
2003-04-01
A vertical array of five hydrophones was used to measure the acoustic field of singing humpback whales. Once a singer was located, two swimmers with snorkel gear were deployed to determine the orientation of the whale and to position the boat so that the array could be deployed in front of the whale at a minimum standoff distance of 10 m. The spacing of the hydrophones was 7 m with the deepest hydrophone deployed at depth of 35 m. An 8-channel TASCAM recorder having a bandwidth of 24 kHz was used to record the hydrophone signals. The location of the singer was determined by computing the time of arrival differences between the hydrophone signals. The maximum source level varied between individual units in a song, with values between 180 and 190 dB. The acoustic field determined by considering the relative intensity of higher frequency harmonics in the signals indicate that the sounds are projected in the horizontal direction with the singer's head canted downward 45 to 60°. High-frequency harmonics extended beyond 24 kHz, suggesting that humpback whales may have an upper frequency limit of hearing as high as 24 kHz.
Reconstruction of an acoustic pressure field in a resonance tube by particle image velocimetry.
Kuzuu, K; Hasegawa, S
2015-11-01
A technique for estimating an acoustic field in a resonance tube is suggested. The estimation of an acoustic field in a resonance tube is important for the development of the thermoacoustic engine, and can be conducted employing two sensors to measure pressure. While this measurement technique is known as the two-sensor method, care needs to be taken with the location of pressure sensors when conducting pressure measurements. In the present study, particle image velocimetry (PIV) is employed instead of a pressure measurement by a sensor, and two-dimensional velocity vector images are extracted as sequential data from only a one- time recording made by a video camera of PIV. The spatial velocity amplitude is obtained from those images, and a pressure distribution is calculated from velocity amplitudes at two points by extending the equations derived for the two-sensor method. By means of this method, problems relating to the locations and calibrations of multiple pressure sensors are avoided. Furthermore, to verify the accuracy of the present method, the experiments are conducted employing the conventional two-sensor method and laser Doppler velocimetry (LDV). Then, results by the proposed method are compared with those obtained with the two-sensor method and LDV.
Biswas, Tutul; Ghosh, Tarun Kanti
2013-01-23
We study the interaction between electron and acoustic phonons in a Rashba spin-orbit coupled two-dimensional electron gas using Boltzmann transport theory. Both the deformation potential and piezoelectric scattering mechanisms are considered in the Bloch-Grüneisen (BG) regime as well as in the equipartition (EP) regime. The effect of the Rashba spin-orbit interaction on the temperature dependence of the resistivity in the BG and EP regimes is discussed. We find that the effective exponent of the temperature dependence of the resistivity in the BG regime decreases due to spin-orbit coupling.
NASA Astrophysics Data System (ADS)
Oyama, Seiji; Yasuda, Jun; Hanayama, Hiroki; Yoshizawa, Shin; Umemura, Shin-ichiro
2016-07-01
A fast and accurate measurement of an ultrasound field with various exposure sequences is necessary to ensure the efficacy and safety of various ultrasound applications in medicine. The most common method used to measure an ultrasound pressure field, that is, hydrophone scanning, requires a long scanning time and potentially disturbs the field. This may limit the efficiency of developing applications of ultrasound. In this study, an optical phase contrast method enabling fast and noninterfering measurements is proposed. In this method, the modulated phase of light caused by the focused ultrasound pressure field is measured. Then, a computed tomography (CT) algorithm used to quantitatively reconstruct a three-dimensional (3D) pressure field is applied. For a high-intensity focused ultrasound field, a new approach that combines the optical phase contrast method and acoustic holography was attempted. First, the optical measurement of focused ultrasound was rapidly performed over the field near a transducer. Second, the nonlinear propagation of the measured ultrasound was simulated. The result of the new approach agreed well with that of the measurement using a hydrophone and was improved from that of the phase contrast method alone with phase unwrapping.
Light scattering from liquid crystal director fluctuations in steady magnetic fields up to 25 tesla
NASA Astrophysics Data System (ADS)
Challa, Pavan K.; Curtiss, O.; Williams, J. C.; Twieg, R.; Toth, J.; McGill, S.; Jákli, A.; Gleeson, J. T.; Sprunt, S. N.
2012-07-01
We report on homodyne dynamic light scattering measurements of orientational fluctuation modes in both calamitic and bent-core nematic liquid crystals, carried out in the new split-helix resistive magnet at the National High Magnetic Field Laboratory. The relaxation rate and inverse scattered intensity of director fluctuations exhibit a linear dependence on field-squared up to 25 tesla, which is consistent with strictly lowest order coupling of the tensor order parameter Q to field (QαβBαBβ) in the nematic free energy. However, we also observe evidence of field dependence of certain nematic material parameters, an effect which may be expected from the mean field scaling of these quantities with the magnitude of Q and the predicted variation of Q with field.
Light scattering from liquid crystal director fluctuations in steady magnetic fields up to 25 tesla.
Challa, Pavan K; Curtiss, O; Williams, J C; Twieg, R; Toth, J; McGill, S; Jákli, A; Gleeson, J T; Sprunt, S N
2012-07-01
We report on homodyne dynamic light scattering measurements of orientational fluctuation modes in both calamitic and bent-core nematic liquid crystals, carried out in the new split-helix resistive magnet at the National High Magnetic Field Laboratory. The relaxation rate and inverse scattered intensity of director fluctuations exhibit a linear dependence on field-squared up to 25 tesla, which is consistent with strictly lowest order coupling of the tensor order parameter Q to field (Q(αβ)B(α)B(β)) in the nematic free energy. However, we also observe evidence of field dependence of certain nematic material parameters, an effect which may be expected from the mean field scaling of these quantities with the magnitude of Q and the predicted variation of Q with field. PMID:23005438
NASA Astrophysics Data System (ADS)
Jiang, Jin-Chang; Jin, Hai-Qiang; Lin, Yun-Fang; Chen, Hao; Yang, Xin-Yu; Zeng, Xiao-Ping; Zhou, Xun
1998-07-01
The effect of magnetic field-free space (MFFS) on the acoustic behavior of budgerigar (Melopsittacus undulafus) is obvious. The daily frequency of their cries in uniform MFFS (UMFFS) and non-uniform MFFS (NMFFS) decreases by 44.7±10.0% as compared with that in the geomagnetic field (GMF) on the average. The occupation rate of protesting cries (R op) in NMFFS decreases by 8.5% 20.3% as compared with that in GMF on the average and shows an adaptability variation. In 75% of the observation days, the R op in UMFFS increases by 16.2% 23.3% as compared with that in GMF. As for the effect of MFFS on the rhythmic habits of budgerigars, only the ending time of crying is affected to certain extent, 67 minutes earlier than in GMF on the average.
Flow and acoustic field due to an inclined plate with a downstream splitter
NASA Technical Reports Server (NTRS)
Kim, C. M.; Conlisk, A. T.
1993-01-01
In the present work, the high Reynolds number flow past an inclined plate with a splitter plate placed in its wake is considered numerically. A numerical conformal mapping technique is employed to transform the two-plate system into the same number of cylinders: the flow field is assumed to be two-dimensional. The vortex shedding from the inclined plate is modelled using the discrete vortex method. It is shown that the splitter plate has a profound effect on the development of the flow over a range of values of a suitably defined offset parameter and for a range of positions of the leading edge of the splitter plate. The acoustic field is also calculated and the spectrum reflects the flow results.
Zhang, Yong-Bin; Jacobsen, Finn; Bi, Chuan-Xing; Chen, Xin-Zhao
2009-09-01
The advantage of using the normal component of the particle velocity rather than the sound pressure in the hologram plane as the input of conventional spatial Fourier transform based near field acoustic holography (NAH) and also as the input of the statistically optimized variant of NAH has recently been demonstrated. This paper examines whether there might be a similar advantage in using the particle velocity as the input of NAH based on the equivalent source method (ESM). Error sensitivity considerations indicate that ESM-based NAH is less sensitive to measurement errors when it is based on particle velocity input data than when it is based on measurements of sound pressure data, and this is confirmed by a simulation study and by experimental results. A method that combines pressure- and particle velocity-based reconstructions in order to distinguish between contributions to the sound field generated by sources on the two sides of the hologram plane is also examined.
Zhang, Yuning; Du, Xiaoze
2015-09-01
Predictions of the propagation of the acoustic waves in bubbly liquids is of great importance for bubble dynamics and related applications (e.g. sonochemistry, sonochemical reactor design, biomedical engineering). In the present paper, an approach for modeling the propagation of the acoustic waves in dilute bubbly liquids is proposed through considering the non-uniform pressure field outside the bubbles. This approach is validated through comparing with available experimental data in the literature. Comparing with the previous models, our approach mainly improves the predictions of the attenuation of acoustic waves in the regions with large kR0 (k is the wave number and R0 is the equilibrium bubble radius). Stability of the oscillating bubbles under acoustic excitation are also quantitatively discussed based on the analytical solution.
The measurement of geodesic acoustic mode magnetic field oscillations in J-TEXT tokamak
NASA Astrophysics Data System (ADS)
Lan, T.; Wu, J.; Shen, H. G.; Deng, T. J.; Liu, A. D.; Xie, J. L.; Li, H.; Liu, W. D.; Yu, C. X.; Sun, Y.; Liu, H.; Chen, Z. P.; Zhuang, G.
2014-10-01
Geodesic acoustic mode (GAM) magnetic field oscillations have been investigated using three-dimension magnetic probe and Langmuir probe arrays in the edge of J-TEXT tokamak. The probe arrays are placed on the two top windows of tokamak, separated toroidally. Inside the LCFS, GAM shows apparent oscillations in floating potential. In contrast, GAM magnetic field oscillations are not significant in raw magnetic fields signals. Using toroidal correlation technique, the GAM magnetic field oscillations are distinguished from ambient magnetic field. The amplitudes of three dimension GAM magnetic field fluctuations, as well as the dependence with local plasma parameters such as safety factor and plasma beta, are coincident with theoretical predictions. And its toroidal symmetry mode structure, i.e. n = 0, is identified. Furthermore, the GAM current sheet, in which GAM oscillates, is firstly verified with magnetic probes arrays in different radial positions, which may help us to understand the radial structure of GAM. Supported by NNSFC (Nos. 10990210, 10990211, 10335060, 10905057 and 11375188), CPSF (No. 20080440104), YIF (No. WK2030040019) and KIPCAS (No. kjcx-yw-n28).
NASA Astrophysics Data System (ADS)
Bi, ChuanXing; Jing, WenQian; Zhang, YongBin; Xu, Liang
2015-02-01
The conventional nearfield acoustic holography (NAH) is usually based on the assumption of free-field conditions, and it also requires that the measurement aperture should be larger than the actual source. This paper is to focus on the problem that neither of the above-mentioned requirements can be met, and to examine the feasibility of reconstructing the sound field radiated by partial source, based on double-layer pressure measurements made in a non-free field by using patch NAH combined with sound field separation technique. And also, the sensitivity of the reconstructed result to the measurement error is analyzed in detail. Two experiments involving two speakers in an exterior space and one speaker inside a car cabin are presented. The experimental results demonstrate that the patch NAH based on single-layer pressure measurement cannot obtain a satisfied result due to the influences of disturbing sources and reflections, while the patch NAH based on double-layer pressure measurements can successfully remove these influences and reconstruct the patch sound field effectively.
Electronic scattering of pseudo-magnetic field induced by local bump in graphene
NASA Astrophysics Data System (ADS)
Yang, Mou; Cui, Yan; Wang, Rui-Qiang; Zhao, Hong-Bo
2012-10-01
We investigated the electronic scattering properties of a local bump strain in graphene sheet in frame of Born approximation. The differential scattering cross section is a function of outgoing and incident angles and has the six-fold rotational symmetry with respect to both angles. The incident plane wave is scattered into two backward fan-waves in different directions in low energy limit and is split into two branches spanning the angle reversely proportional to the incident wavevector k in high energy limit. The total scattering cross section depends on incident wavevector by the form k5 in the former limit, while it is independent of k and sensitive to the incident orientation in the latter limit. We explained these features using the symmetry of the strain-induced pseudo-magnetic field.
Lee, Seungah; Park, Guenyoung; Chakkarapani, Suresh Kumar; Kang, Seong Ho
2015-01-15
Novel, fluorescence-free detection of biomolecules on nanobiochips was investigated based on plasmonic nanometal scattering in the evanescent field layer (EFL) using total internal reflection scattering (TIRS) microscopy. The plasmonic scattering of nanometals bonded to biomolecules was observed at different wavelengths by an electromagnetic field in the EFL. The changes in the scattering of nanometals on the gold-nanopatterned chip in response to the immunoreaction between silver nanoparticles and antibodies allowed fluorescence-free detection of biomolecules on the nanobiochips. Under optimized conditions, the TIRS immunoassay chip detected different amounts of immobilized antigen, i.e., human cardiac troponin I. The sandwich immuno-reaction was quantitatively analyzed in the dynamic range of 720 zM-167 fM. The limit of detection (S/N=4) was 600 zM, which was ~140 times lower than limits obtained by previous total internal reflection fluorescence and dark field methods. These results demonstrate the possibility for a fluorescence-free biochip nanoimmunoassay based on the scattering of nanometals in the EFL.
Lee, Seungah; Park, Guenyoung; Chakkarapani, Suresh Kumar; Kang, Seong Ho
2015-01-15
Novel, fluorescence-free detection of biomolecules on nanobiochips was investigated based on plasmonic nanometal scattering in the evanescent field layer (EFL) using total internal reflection scattering (TIRS) microscopy. The plasmonic scattering of nanometals bonded to biomolecules was observed at different wavelengths by an electromagnetic field in the EFL. The changes in the scattering of nanometals on the gold-nanopatterned chip in response to the immunoreaction between silver nanoparticles and antibodies allowed fluorescence-free detection of biomolecules on the nanobiochips. Under optimized conditions, the TIRS immunoassay chip detected different amounts of immobilized antigen, i.e., human cardiac troponin I. The sandwich immuno-reaction was quantitatively analyzed in the dynamic range of 720 zM-167 fM. The limit of detection (S/N=4) was 600 zM, which was ~140 times lower than limits obtained by previous total internal reflection fluorescence and dark field methods. These results demonstrate the possibility for a fluorescence-free biochip nanoimmunoassay based on the scattering of nanometals in the EFL. PMID:25128624
Elements of QED-NRQED effective field theory: NLO scattering at leading power
NASA Astrophysics Data System (ADS)
Dye, Steven P.; Gonderinger, Matthew; Paz, Gil
2016-07-01
The proton radius puzzle, i.e. the large discrepancy in the extraction of the proton charge radius between regular and muonic hydrogen, challenges our understanding of the structure of the proton. It can also be an indication of a new force that couples to muons, but not to electrons. An effective field theory analysis using nonrelativistic quantum electrodynamics (NRQED) indicates that the muonic hydrogen result can be interpreted as a large, compared to some model estimates, muon-proton spin-independent contact interaction. The muonic hydrogen result can be tested by a muon-proton scattering experiment, MUSE, that is planned at the Paul Scherrer Institute in Switzerland. The typical momenta of the muons in this experiment are of the order of the muon mass. In this energy regime the muons are relativistic but the protons are still nonrelativistic. The interaction between the muons and protons can be described by a hybrid QED-NRQED effective field theory. We present some elements of this effective field theory. In particular we consider O (Z α ) scattering up to power m2/M2 , where m (M ) is the muon (proton) mass and Z =1 for a proton, and O (Z2α2) scattering at leading power. We show how the former reproduces Rosenbluth scattering up to power m2/M2 and the latter the relativistic scattering off a static potential. Proton structure corrections at O (Z2α2) will be considered in a subsequent paper.
Near-field acoustic microbead trapping as remote anchor for single particle manipulation
NASA Astrophysics Data System (ADS)
Hwang, Jae Youn; Cheon, Dong Young; Shin, Hyunjune; Kim, Hyun Bin; Lee, Jungwoo
2015-05-01
We recently proposed an analytical model of a two-dimensional acoustic trapping of polystyrene beads in the ray acoustics regime, where a bead diameter is larger than the wavelength used. As its experimental validation, this paper demonstrates the transverse (or lateral) trapping of individual polystyrene beads in the near field of focused ultrasound. A 100 μm bead is immobilized on the central beam axis by a focused sound beam from a 30 MHz single element lithium niobate transducer, after being laterally displaced through hundreds of micrometers. Maximum displacement, a longest lateral distance at which a trapped bead can be directed towards the central axis, is thus measured over a discrete frequency range from 24 MHz to 36 MHz. The displacement data are found to be between 323.7 μm and 470.2 μm, depending on the transducer's driving frequency and input voltage amplitude. The experimental results are compared with their corresponding model values, and their relative errors lie between 0.9% and 3.9%. The results suggest that this remote maneuvering technique may be employed to manipulate individual cells through solid microbeads, provoking certain cellular reactions to localized mechanical disturbance without direct contact.
Near-field acoustic microbead trapping as remote anchor for single particle manipulation
Hwang, Jae Youn; Cheon, Dong Young; Shin, Hyunjune; Kim, Hyun Bin; Lee, Jungwoo
2015-05-04
We recently proposed an analytical model of a two-dimensional acoustic trapping of polystyrene beads in the ray acoustics regime, where a bead diameter is larger than the wavelength used. As its experimental validation, this paper demonstrates the transverse (or lateral) trapping of individual polystyrene beads in the near field of focused ultrasound. A 100 μm bead is immobilized on the central beam axis by a focused sound beam from a 30 MHz single element lithium niobate transducer, after being laterally displaced through hundreds of micrometers. Maximum displacement, a longest lateral distance at which a trapped bead can be directed towards the central axis, is thus measured over a discrete frequency range from 24 MHz to 36 MHz. The displacement data are found to be between 323.7 μm and 470.2 μm, depending on the transducer's driving frequency and input voltage amplitude. The experimental results are compared with their corresponding model values, and their relative errors lie between 0.9% and 3.9%. The results suggest that this remote maneuvering technique may be employed to manipulate individual cells through solid microbeads, provoking certain cellular reactions to localized mechanical disturbance without direct contact.
Klieber, Christoph; Hecksher, Tina; Pezeril, Thomas; Torchinsky, Darius H; Dyre, Jeppe C; Nelson, Keith A
2013-03-28
This paper presents and discusses the temperature and frequency dependence of the longitudinal and shear viscoelastic response at MHz and GHz frequencies of the intermediate glass former glycerol and the fragile glass former tetramethyl-tetraphenyl-trisiloxane (DC704). Measurements were performed using the recently developed time-domain Brillouin scattering technique, in which acoustic waves are generated optically, propagated through nm thin liquid layers of different thicknesses, and detected optically after transmission into a transparent detection substrate. This allows for a determination of the frequency dependence of the speed of sound and the sound-wave attenuation. When the data are converted into mechanical moduli, a linear relationship between longitudinal and shear acoustic moduli is revealed, which is consistent with the generalized Cauchy relation. In glycerol, the temperature dependence of the shear acoustic relaxation time agrees well with literature data for dielectric measurements. In DC704, combining the new data with data from measurements obtained previously by piezo-ceramic transducers yields figures showing the longitudinal and shear sound velocities at frequencies from mHz to GHz over an extended range of temperatures. The shoving model's prediction for the relaxation time's temperature dependence is fairly well obeyed for both liquids as demonstrated from a plot with no adjustable parameters. Finally, we show that for both liquids the instantaneous shear modulus follows an exponential temperature dependence to a good approximation, as predicted by Granato's interstitialcy model. PMID:23556795
Lee, Moohyung; Bolton, J Stuart; Mongeau, Luc
2003-08-01
The purpose of this study was to develop methods for visualizing the sound radiation from aeroacoustic sources in order to identify their source strength distribution, radiation patterns, and to quantify the performance of noise control solutions. Here, cylindrical Near-field Acoustical Holography was used for that purpose. In a practical holographic measurement of sources comprising either partially correlated or uncorrelated subsources, it is necessary to use a number of reference microphones so that the sound field on the hologram surface can be decomposed into mutually incoherent partial fields before holographic projection. In this article, procedures are described for determining the number of reference microphones required when visualizing partially correlated aeroacoustic sources; performing source nonstationarity compensation; and applying regularization. The procedures have been demonstrated by application to a ducted fan. Holographic tests were performed to visualize the sound radiation from that source in its original form. The system was then altered to investigate the effect of two modifications on the fan's sound radiation pattern: first, leaks were created in the fan and duct assembly, and second, sound absorbing material was used to line the downstream duct section. Results in all three cases are shown at the blade passing frequency and for a broadband noise component. In the absence of leakage, both components were found to exhibit a dipole-like radiation pattern. Leakage was found to have a strong influence on the directivity of the blade passing tone. The increase of the flow resistance caused by adding the acoustical lining resulted in a nearly symmetric reduction of sound radiation. PMID:12942967
NASA Astrophysics Data System (ADS)
Lee, Moohyung; Bolton, J. Stuart; Mongeau, Luc
2003-08-01
The purpose of this study was to develop methods for visualizing the sound radiation from aeroacoustic sources in order to identify their source strength distribution, radiation patterns, and to quantify the performance of noise control solutions. Here, cylindrical Near-field Acoustical Holography was used for that purpose. In a practical holographic measurement of sources comprising either partially correlated or uncorrelated subsources, it is necessary to use a number of reference microphones so that the sound field on the hologram surface can be decomposed into mutually incoherent partial fields before holographic projection. In this article, procedures are described for determining the number of reference microphones required when visualizing partially correlated aeroacoustic sources; performing source nonstationarity compensation; and applying regularization. The procedures have been demonstrated by application to a ducted fan. Holographic tests were performed to visualize the sound radiation from that source in its original form. The system was then altered to investigate the effect of two modifications on the fan's sound radiation pattern: first, leaks were created in the fan and duct assembly, and second, sound absorbing material was used to line the downstream duct section. Results in all three cases are shown at the blade passing frequency and for a broadband noise component. In the absence of leakage, both components were found to exhibit a dipole-like radiation pattern. Leakage was found to have a strong influence on the directivity of the blade passing tone. The increase of the flow resistance caused by adding the acoustical lining resulted in a nearly symmetric reduction of sound radiation.
Deformation of biological cells in the acoustic field of an oscillating bubble
Zinin, Pavel V.; Allen, John S.
2009-01-01
In this work we develop a theoretical framework of the interaction of microbubbles with bacteria in the ultrasound field using a shell model of the bacteria, following an approach developed previously [P. V. Zinin et al., Phys. Rev. E 72, 61907 (2005)]. Within the shell model, the motion of the cell in an ultrasonic field is determined by the motion of three components: the internal viscous fluid, a thin elastic shell, and the surrounding viscous fluid. Several conclusions can be drawn from the modeling of sound interaction with a biological cell: (a) the characteristics of a cell’s oscillations in an ultrasonic field are determined both by the elastic properties of the shell the viscosities of all components of the system, (b) for dipole quadrupole oscillations the cell’s shell deforms due to a change in the shell area this oscillation depends on the surface area modulus KA, (c) the relative change in the area has a maximum at frequency fK∼12πKA/(ρa3), where a is the cell’s radius and ρ is its density. It was predicted that deformation of the cell wall at the frequency fK is high enough to rupture small bacteria such as E. coli in which the quality factor of natural vibrations is less than 1 (Q < 1). For bacteria with high value quality factors (Q > 1), the area deformation has a strong peak near a resonance frequency fK; however, the value of the deformation near the resonance frequency is not high enough to produce sufficient mechanical effect. The theoretical framework developed in this work can be extended for describing the deformation of a biological cell under any arbitrary, external periodic force including radiation forces unduced by acoustical (acoustical levitation) or optical waves (optical tweezers). PMID:19391781
Deformation of biological cells in the acoustic field of an oscillating bubble.
Zinin, Pavel V; Allen, John S
2009-02-01
In this work we develop a theoretical framework of the interaction of microbubbles with bacteria in the ultrasound field using a shell model of the bacteria, following an approach developed previously [P. V. Zinin, Phys. Rev. E 72, 61907 (2005)]. Within the shell model, the motion of the cell in an ultrasonic field is determined by the motion of three components: the internal viscous fluid, a thin elastic shell, and the surrounding viscous fluid. Several conclusions can be drawn from the modeling of sound interaction with a biological cell: (a) the characteristics of a cell's oscillations in an ultrasonic field are determined both by the elastic properties of the shell the viscosities of all components of the system, (b) for dipole quadrupole oscillations the cell's shell deforms due to a change in the shell area this oscillation depends on the surface area modulus K{A} , (c) the relative change in the area has a maximum at frequency f{K} approximately 1/2pi square root[K{A}(rhoa;{3})] , where a is the cell's radius and rho is its density. It was predicted that deformation of the cell wall at the frequency f{K} is high enough to rupture small bacteria such as E . coli in which the quality factor of natural vibrations is less than 1 (Q<1). For bacteria with high value quality factors (Q>1) , the area deformation has a strong peak near a resonance frequency f{K} however, the value of the deformation near the resonance frequency is not high enough to produce sufficient mechanical effect. The theoretical framework developed in this work can be extended for describing the deformation of a biological cell under any arbitrary, external periodic force including radiation forces unduced by acoustical (acoustical levitation) or optical waves (optical tweezers). PMID:19391781
Effect of centerbody scattering on propeller noise
NASA Technical Reports Server (NTRS)
Glegg, Stewart A. L.
1991-01-01
This paper describes how the effect of acoustic scattering from the hub or centerbody of a propeller will affect the far-field noise levels. A simple correction to Gutin's formula for steady loading noise is given. This is a maximum for the lower harmonics but has a negligible effect on the higher frequency components that are important subjectively. The case of a blade vortex interaction is also considered, and centerbody scattering is shown to have a significant effect on the acoustic far field.
Chen, Tianrun; Ratilal, Purnima; Makris, Nicholas C
2008-11-01
An analytical expression is derived for the temporal coherence of an acoustic field after multiple forward scattering through random three-dimensional (3D) inhomogeneities in an ocean waveguide. This expression makes it possible to predict the coherence time scale of field fluctuations in ocean-acoustic measurements from knowledge of the oceanography. It is used to explain the time scale of acoustic field fluctuations observed at megameter ranges in various deep ocean-acoustic transmission experiments. It is shown that this time scale is nonlinearly related to the much longer coherence time scale of deep ocean internal waves through a multiple forward scattering process. It is also shown that 3D scattering effects become pronounced when the acoustic Fresnel width exceeds the cross-range coherence length of the deep ocean internal waves, which lead to frequency and range-dependent power losses in the forward field that may help to explain historic long range measurements.
NASA Astrophysics Data System (ADS)
Carlson, Arthur William
A measurement is reported which sets an upper bound on LHD-like density fluctuations in an FRC which is two orders of magnitude below the predicted levels. Particle loss from FRC's is known to occur anomalously fast, and this is usually attributed to effects of the LHD instability. If LHD waves are present, they can be measured using heterodyne detection of CO(,2) laser light scattered from the associated density fluctuations. In the present case, the usual scattering system was successfully modified to compensate for severe refraction of the beams by the plasma. This system was calibrated by detection of an electrooptically modulated CO(,2) laser beam, and by detection of light scattered from acoustic waves in salt. The plasma measurements made on the TRX-2 field-reversed theta-pinch covered all parameters at which LHD fluctuations might be expected to occur, namely wavenumbers from 30 to 240 cm('-1), frequencies from 10 to 300 MHz, and radii from one centimeter inside the separatrix to two centimeters outside. The lack of detectable scattered light under any of these conditions indicates ((delta)n/n) < 1 x 10('-4), compared to predictions of ((delta)n/n) ('(TURN)) 1 x 10('-2) based on mode coupling theory, ion -trapping theory, and observed transport rates. Several mechanisms are discussed which may stabilize LHD in these plasmas. Several alternate explanations of the observed anomalous transport rates in FRC's are also discussed.
NASA Astrophysics Data System (ADS)
Kurata, Tomohiro; Oda, Shigeto; Kawahira, Hiroshi; Haneishi, Hideaki
2016-10-01
We have previously proposed an estimation method of intravascular oxygen saturation (SO_2) from the images obtained by sidestream dark-field (SDF) imaging (we call it SDF oximetry) and we investigated its fundamental characteristics by Monte Carlo simulation. In this paper, we propose a correction method for scattering by the tissue and performed experiments with turbid phantoms as well as Monte Carlo simulation experiments to investigate the influence of the tissue scattering in the SDF imaging. In the estimation method, we used modified extinction coefficients of hemoglobin called average extinction coefficients (AECs) to correct the influence from the bandwidth of the illumination sources, the imaging camera characteristics, and the tissue scattering. We estimate the scattering coefficient of the tissue from the maximum slope of pixel value profile along a line perpendicular to the blood vessel running direction in an SDF image and correct AECs using the scattering coefficient. To evaluate the proposed method, we developed a trial SDF probe to obtain three-band images by switching multicolor light-emitting diodes and obtained the image of turbid phantoms comprised of agar powder, fat emulsion, and bovine blood-filled glass tubes. As a result, we found that the increase of scattering by the phantom body brought about the decrease of the AECs. The experimental results showed that the use of suitable values for AECs led to more accurate SO_2 estimation. We also confirmed the validity of the proposed correction method to improve the accuracy of the SO_2 estimation.
NASA Astrophysics Data System (ADS)
Yuan, Wuhan; Shan, Jerry; Liu, Liping
2015-11-01
The microstructure of suspensions of spheroidal ferromagnetic particles with subwavelength size can be controlled by an external field, making it possible to develop novel broadband acoustic materials with anisotropic and tunable acoustic properties. In this study we experimentally show that dilute suspensions of nickel microflakes exhibit a 20% to 30% change in attenuation coefficient at MHz frequencies upon changing the direction of an external magnetic field, at particle volume fractions of only 0.5%. Further investigations are conducted to study the mechanism behind this anisotropy. The effects of particle aligning and chaining are analyzed with the aid of optical transmission measurements. By making comparison to suspensions of spherical particles, we show that the ellipsoidal shape of the nickel microflakes plays an important role in tunable acoustic properties of these suspensions.
A high-field (30 Tesla) pulsed magnet instrument for single-crystal scattering studies
NASA Astrophysics Data System (ADS)
Islam, Zahirul; Nojiri, Hiroyuki; Narumi, Yasuo; Lang, Jonathan
2010-03-01
Pulsed magnets have emerged as a viable approach at synchrotron x-ray facilities for studying materials in high magnetic fields. We are developing a new high-field (30 Tesla) pulsed magnet system for single-crystal x-ray diffraction studies. It consists of a single 18mm-bore solenoid, designed and built at Tohoku University using high-tensile-strength and high conductivity CuAg wires. A dual-cryostat scheme has been developed at Advanced Photon Source in order to cool the coil using liquid nitrogen and the sample using a closed-cycle cryostat independently. Liquid nitrogen cooling allows repetition rate of a few minutes for peak fields near 30 Tesla. This scheme is unique in that it allows the applied magnetic field to be parallel to the scattering plane. Time-resolved scattering data are typically collected using a fast one-dimensional strip detector. Opportunities and challenges for experiments and instrumentation will be discussed.
Observation of Marine Animals Using Underwater Acoustic Camera
NASA Astrophysics Data System (ADS)
Iida, Kohji; Takahashi, Rika; Tang, Yong; Mukai, Tohru; Sato, Masanori
2006-05-01
An underwater acoustic camera enclosed in a pressure-resistant case was constructed to observe underwater marine animals. This enabled the measurement of the size, shape, and behavior of living marine animals in the detection range up to 240 cm. The transducer array of the acoustic camera was driven by 3.5 MHz ultrasonic signals, and B-mode acoustic images were obtained. Observations were conducted for captive animals in a water tank and for natural animals in a field. The captive animals, including fish, squid and jellyfish, were observed, and a three-dimensional internal structure of animals was reconstructed using multiple acoustical images. The most important contributors of acoustic scattering were the swimbladder and vertebra of bladdered fish, and the liver and reproductive organs of invertebrate animals. In a field experiment, the shape, size, and swimming behavior of wild animals were observed. The possibilities and limitations of the underwater acoustic camera for fishery applications were discussed.
Modeling and experimental study on near-field acoustic levitation by flexural mode.
Liu, Pinkuan; Li, Jin; Ding, Han; Cao, Wenwu
2009-12-01
Near-field acoustic levitation (NFAL) has been used in noncontact handling and transportation of small objects to avoid contamination. We have performed a theoretical analysis based on nonuniform vibrating surface to quantify the levitation force produced by the air film and also conducted experimental tests to verify our model. Modal analysis was performed using ANSYS on the flexural plate radiator to obtain its natural frequency of desired mode, which is used to design the measurement system. Then, the levitation force was calculated as a function of levitation distance based on squeeze gas film theory using measured amplitude and phase distributions on the vibrator surface. Compared with previous fluid-structural analyses using a uniform piston motion, our model based on the nonuniform radiating surface of the vibrator is more realistic and fits better with experimentally measured levitation force. PMID:20040404
On the horizontal wobbling of an object levitated by near-field acoustic levitation.
Kim, Cheol-Ho; Ih, Jeong-Guon
2007-11-01
A circular planar object can be levitated with several hundreds of microns by ultrasonic near-field acoustic levitation (NFAL). However, when both the sound source and the levitated object are circularly shaped and the center of the levitated object does not coincide with the source center, instability problem often occurs. When this happens, it becomes difficult to pick up or transport the object for the next process. In this study, when the center of the levitated object was offset from the source center, the moving direction of the levitated object was predicted by using the time averaged potential around the levitated object. The wobbling frequency of the levitated object was calculated by analyzing the nonlinear wobbling motion of the object. It was shown that the predicted wobbling frequencies agreed with measured ones well. Finally, a safe zone was suggested to avoid the unstable movement of an object. PMID:17590402
Near and Far Field Acoustic Pressure Skewness in a Heated Supersonic Jet
NASA Astrophysics Data System (ADS)
Gutmark, Ephraim; Mora, Pablo; Kastner, Jeff; Heeb, Nick; Kailasanath, Kailas; Liu, Junhui; University of Cincinnati Collaboration; Naval Research Laboratory Collaboration
2012-11-01
The dominant component of turbulent mixing noise in high speed jets is the Mach wave radiation generated by large turbulent structures in the shear layer The Over-All Sound Pressure Level (OASPL) in the far field peaks in a direction near the Mach wave angle. ``Crackle'' is another important component of high speed jet noise. Crackle cannot be recognized in the spectrum of the acoustic pressure signal, but it appears in the temporal waveform of the pressure as sharply rising peaks. Skewness levels of the pressure and dP/dt have been used as a measure of crackle in high specific thrust engines and rockets. In this paper, we focus on recognizing a technique that identifies the impact of different test conditions on the near-field and far-field statistics of the pressure and dP/dt signals of a supersonic jet with a design Mach number of Md=1.5 produced by a C-D conical nozzle. Cold and hot jets, T0=300K and 600K, are tested at over, design, and under-expanded conditions, with NPRs=2.5, 3.671, 4.5, respectively. Second, Third and Forth order statistics are examined in the near and far fields. Rms, skewness and kurtosis intensity levels and propagation are better identified in the dP/dt than in the pressure signal. Statistics of the dP/dt demonstrate to be a better measure for crackle. Project funded by ONR grant.