Publications (173)230.53 Total impact
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ABSTRACT: The theory for acoustic radiation force on a viscoelastic sphere of arbitrary size in tissue was extended at the spring 2013 ASA meeting to account for nonaxisymmetric fields incident on the scatterer [Ilinskii et al., POMA 19, 045004 (2013)]. The results were presented in a form that permits inclusion of as many spherical harmonics as needed to describe the field structure. At the fall 2013 ASA meeting, it was shown that for spheres having sizes up to about one wavelength, only four or five spherical harmonics are required for convergence of the solution when plane waves are incident on the scatterer. At the present meeting, the model is applied to diffracting sound beams incident on the scatterer. The analysis is based on angular spectrum decomposition of the incident field, expansion of the resulting plane waves in spherical waves, then a Wigner transformation of the latter back into spherical coordinates with polar axis coinciding with the beam axis, and finally integration over solid angle to obtain the spherical wave amplitudes used in the theory. Results are presented for different radiation patterns illustrating dependence of the radiation force both on beamwidth and on wavelength relative to the size of the scatterer.The Journal of the Acoustical Society of America 04/2014; 135(4):2210. · 1.65 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: Surface acoustic waves (SAW) are used frequently in microfluidic devices. Normally SAWs are generated on the surface of a piezoelectric material. Commonly used PZT is not appropriate for biomedical applications because of its high lead content, over 60% by weight. In this talk, a study of nonlinear SAW propagation in a piezoelectric substrate is presented. Model equations describing nonlinear SAW propagation in a piezoelectric crystal are derived from first principles. Elastic, piezoelectric, dielectric, and electrostrictive properties of a crystal with arbitrary symmetry are taken into account. The derived evolution equations are integrated numerically to illustrate nonlinear distortion of an initially sinusoidal wave of finite amplitude. As an example, SAW propagation along the X axis on single crystal 127.680 YXcut lithium niobate (LiNbO3), referred to as 128YXLN, is considered. This LiNbO3 cut is typically used in microfluidic devices because it provides large mechanical displacements in the substrate. Analysis of the nonlinearity matrix permits quantification of the relative contributions to surface wave distortion from each physical phenomenon. [Work supported by the IR&D program at ARL:UT.].The Journal of the Acoustical Society of America 04/2014; 135(4):2218. · 1.65 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: William M. Carey is well known for his interest in sound propagation through bubbly liquids. He was also a champion of reattributing the low frequency effective medium model widely known as Wood's law to its original author Arnulph Mallock, who published a paper titled "The Damping of Sound by Frothy Liquids" in 1910. In the same spirit, this presentation will discuss the evolution of theories involving sound propagation through bubbly liquids over time from Mallock to modern day. Since bubble pulsations can exhibit strong nonlinearity, the presentation will conclude by reintroducing another oftenoverlooked modeling advance, at least in the western literature, that of Zabolotskya and Soluyan [Sov. Phys. Acoust. 13, 254256 (1967)] describing the nonlinear propagation of sound in bubbly liquids. [Work supported by ONR.].The Journal of the Acoustical Society of America 04/2014; 135(4):2232. · 1.65 Impact Factor 
Article: Nonlinear behavior of heterogeneous materials containing snapping acoustic metamaterial inclusions.
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ABSTRACT: This work studies the forced dynamical behavior of a heterogeneous material containing metamaterial inclusions undergoing large deformations. The inclusions exhibit nonmonotonic stressstrain behavior, modeled with an expansion to third order in volume strain, where the coefficients of the expansion depend on the metamaterial structure. The resulting constitutive behavior of interest displays regimes of both positive and negative stiffness and the inclusion therefore exhibits hysteretic snapping when forced by an acoustic pressure. Two cases are explored using a generalized RayleighPlesset analysis to model the largedeformation dynamics of the metamaterial inclusion following an approach similar to Emelianov et al. [J. Acoust. Soc. Am., 115, 581 (2004)]. The first case focuses on the forced dynamics of a single inclusion embedded in a weakly compressible elastic medium. The second case broadens the model to analyze the behavior of a heterogeneous material comprised of a low volume fraction of noninteracting metamaterial inclusions embedded in a weakly compressible material. Finally, estimates of the effective bulk modulus and loss factor of the heterogeneous medium are presented for instances of the forcing pressure inducing either large or small inclusion deformation. [Work supported by the ARL:UT McKinney Fellowship in Acoustics and the Office of Naval Research.].The Journal of the Acoustical Society of America 04/2014; 135(4):2255. · 1.65 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: Highly directional light sources such as flashlights and lasers are well known to most people. In contrast, highly directional acoustic sources, or in other words, sources of sound that are audible in only a very narrow region of space, are far less common. Many people have never experienced such a source, and the phenomenon is not found in nature. A highly directional source of sound known as a parametric array is used underwater for sonar applications, but the frequency (pitch) of the sound is often above the human hearing range. Similarly, highly directional, focused sound sources are regularly used in medical applications, but again, the frequency is too high to be heard. The narrowness of the acoustic beam cannot be experienced by human listeners. Recently, parametric array technology has been commercialized for use in air at frequencies in the human auditory range. These devices produce extremely narrow (on the order of 2 degrees) beams of audible sound. When pointed directly at one listener, the sound is virtually inaudible to another listener only a few feet away. Such a device will be demonstrated and the basic physics behind its operation will be explained.The Journal of the Acoustical Society of America 04/2014; 135(4):2249. · 1.65 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: A parabolic equation describing the propagation of collimated shear wave beams in isotropic elastic solids was derived by Zabolotskaya [Sov. Phys. Acoust. 32, 296299 (1986)], and was seen to contain both cubic and quadratic nonlinear terms at leading order. While secondorder nonlinear effects vanish for the quasiplanar case of linearlypolarized shear wave beams, the importance of quadratic nonlinearity for more complicated polarizations is not yet well understood. The current work investigates the significance of quadratic nonlinearity by considering secondharmonic generation in shear wave beams generated by a certain class of source polarizations that includes such cases as radial and torsional polarization, among others. Corresponding to such beams with Gaussian amplitude shading, analytic solutions are derived for the propagated beam at the source frequency and the second harmonic. Diffraction characteristics are discussed, and special attention is paid to the relationship between the source polarization of the beam and the polarization of the subsequently generated second harmonic. Finally, suggestions are made for possible experiments that could be performed in tissue phantoms, exploiting the theoretical results of this work. [Work supported by the ARL:UT McKinney Fellowship in Acoustics.].The Journal of the Acoustical Society of America 11/2013; 134(5):3997. · 1.65 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: Underwater noise due to both marine pile driving and offshore wind farm operation is not only radiated directly from the pile into the water, but also from the seabed surrounding the pile. While there is much interest in mitigating the noise from these activities, a better understanding of the source mechanisms and propagation is needed to determine optimal strategies for noise abatement. A recent analytical model of the acoustic field radiated by submerged piles includes radiation from the pile directly into the water and into a stratified viscoelastic sediment as well as propagation into a shallow water waveguide from both the direct and sediment radiation paths [Hay et al., Proceedings of Meetings on Acoustics 19, 070038 (2013)]. As a step towards validating this model, scalemodel experiments were conducted in the high kilohertz frequency range with a model pile consisting of a mechanically excited metallic tube inserted into a laboratory tank filled with two stratified layers to simulate the water/sediment interface. Measurements of the acoustic field in the experiment are compared with the model predictions, and the relevance of these results to implementing noise abatement strategies will be discussed. [Work supported by ARL:UT IR&D.].The Journal of the Acoustical Society of America 11/2013; 134(5):4060. · 1.65 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: Interest in characterizing nonlinearity in jet noise has motivated consideration of an effective Gol'dberg number for diverging waves [Baars and Tinney, Bull. Am. Phys. Soc. 57, 17 (2012)]. Fenlon [J. Acoust. Soc. Am. 50, 1299 (1971)] developed expressions for the minimum value of Γ, the Gol'dberg number as defined for plane waves, for which shock formation occurs in diverging spherical and cylindrical waves. The conditions were deduced from a generalized Khokhlov solution and depend on the ratio xsh/r0, where r0 is source radius, and xsh the planewave shock formation distance for Γ=∞. Alternatively, by taking the ratio of the nonlinear and thermoviscous terms in Fenlon's Eq. (2), it is proposed here that effective Gol'dberg numbers may be identified for spherical and cylindrical waves: Λ=Γexp(πxsh/2r0) and Λ=Γ/(1 + πxsh/4r0), respectively. For a given value of Λ, the diverging waves achieve approximately the same degree of nonlinear distortion as a plane wave for which the value of Γ is the same. Conversely, to achieve the same degree of nonlinear distortion as a plane wave with a given value of Γ, the value of Γ for, e.g., a spherical wave must be larger by a factor of exp(πxsh/2r0). Extensions to other spreading laws are presented.The Journal of the Acoustical Society of America 11/2013; 134(5):4099. · 1.65 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: Most common methods to include the effects of liquid compressibility in models for singlebubble dynamics rely on series expansions to some order in the inverse of the sound speed in the liquid. It has been shown that the KellerMiksis model for singlebubble dynamics can be obtained from a series expansion of a delay differential equation related to the RayleighPlesset equation for a single bubble. The iterative approach used to obtain the series expansion of the delaybased model becomes unworkable for more complicated models of bubble dynamics. Therefore, to provide an alternative, simpler method to model the effects of liquid compressibility, the delay differential equation model proposed by Ilinskii and Zabolotskaya [J. Acoust. Soc. Am. 92, 2837 (1992)] is analyzed directly. The results of the delaybased formulations are compared to those produced by models based on common series expansions. Alternative formulations of the delay differential equation are also considered and compared.The Journal of the Acoustical Society of America 11/2013; 134(5):3991. · 1.65 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: Acoustic radiation force on a scatterer in tissue depends on the compressibility and shear modulus of both the tissue and the scatterer. This force is related to the monopole and dipole scattering coefficients. The finite shear modulus of the tissue decreases the radiation force in comparison with the force exerted on the same scatterer surrounded by liquid. Shear moduli for soft tissue range from several kilopascals (breast, liver) to tens of kilopascals and higher for cornea, cartilage, and cancerous tissue. As reported previously, the radiation force on a bubble in tissue having 100 kPa shear modulus is 50% less than if the bubble is in water. This difference decreases for scatterers with finite shear moduli, examples of which are reported here. Additionally, displacement of a scatterer due to radiation force is inversely proportional to the shear modulus of the tissue, which permits measurement of the latter. Experiments demonstrating this technique are reviewed. In these experiments, the radiation force is applied to a gas microbubble produced by laserinduced optical breakdown, while displacement of the microbubble is measured by highfrequency ultrasound as a function of time. Results are reported for tissuemimicking phantoms and animal crystalline lenses in vitro.The Journal of the Acoustical Society of America 11/2013; 134(5):4009. · 1.65 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: This work considers nonlinear propagation in a medium consisting of a low volume fraction of metamaterial inclusions dispersed in a fluidlike material. The metamaterial inclusions of interest are assumed to possess nonmonotonic stressstrain constitutive relations, which results in regimes of negative stiffness. For modeling purposes, the constitutive relation for these inclusions is approximated with an expansion to third order in volume strain with coefficients that can be tuned with the geometry of the metamaterial structure and ambient pressure. A farreaching goal of this research is to model the hysteretic response of the heterogeneous medium resulting from metamaterial inclusion snapping events and the associated effect on acoustic disturbances that cycle through regimes of both positive and negative stiffness. As an initial step, results are presented here for small but finiteamplitude disturbances limited to local regions of the constitutive relation. For this case, the quadratic and cubic nonlinearity parameters B/A and C/A, respectively, as traditionally defined for fluids are obtained. An evolution equation with both quadratic and cubic nonlinearity is also obtained. Numerical solutions of the evolution equation illustrate nonlinear waveform distortion as a function of the volume fraction and constitutive behavior of the inclusions. [Work supported by ARL:UT McKinney Fellowship in Acoustics.].The Journal of the Acoustical Society of America 11/2013; 134(5):4027. · 1.65 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: In a previous presentation [J. Acoust. Soc. Am. 133, 3327 (2013)], an experimental model study of a pneumatic infrasound source that utilizes the pulsation of compressed air was discussed. The present paper discusses new measurements and theoretical modeling efforts that are currently underway. Measurements of the source level, directivity patterns, propagation loss, and frequency response are presented and analyzed. Acoustic and aerodynamic models are presented and discussed with a focus on modeling and predicting nearfield system performance using multipole (monopole, dipole, and quadrupole) representations of the sound source. Measurement techniques and engineering considerations are addressed, as are physical interpretations of the process. [Work supported by ARL:UT Austin.].The Journal of the Acoustical Society of America 11/2013; 134(5):4192. · 1.65 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: There is concern that underwater noise generated by marine construction activities and radiated by towers supporting offshore wind turbines may disturb marine mammals, or interfere with passive sensors and communication equipment. In order to understand these effects a semianalytic frequencydomain model was developed previously for the sound radiated in the water column by a pulsating cylindrical structure embedded in horizontally stratified layers of viscoelastic sediment. This model was in turn coupled to a parabolic equation code for longrange propagation over rangedependent environments [Hay et al., J. Acoust. Soc. Am. 133, 3396 (2013)]. A timedomain version of this model is now presented which enables simulation of impulsive sound sources such as those due to underwater pile driving, and pulsed tonal sources appropriate for use in a finitesized laboratory tank. In order to validate the model a scaled physical model, consisting of a laboratory tank and metallic cylindrical tube driven in the high kilohertz frequency range, was constructed. Simulations will be presented for a variety of sound sources, and preliminary comparisons with measurements from the scaled model experiments will be made.The Journal of the Acoustical Society of America 11/2013; 134(5):4023. · 1.65 Impact Factor 
Article: Measurement and modeling of pulsed bifrequency, nonlinear acoustic excitation of buried landmines.
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ABSTRACT: To help resolve certain practical issues with acoustical methods for humanitarian landmine detection, we have researched using a pulsed, standoff source method for acoustical excitation of the buried mine [J. Acoust. Soc. Am. 130, 2541 (2011); J. Acoust. Soc. Am. 133, 3457 (2013)]. Pulses consisting of two primary frequencies are used in order to search for induced nonlinear vibrations at interaction frequencies such as the sum frequency, which arise due to nonlinear interaction at the mine/soil interface. To model the pulsed excitation, we employ a fully nonlinear timedomain implementation of the lumpedelement model of nonlinear soil/mine interaction introduced by Donskoy et al. [J. Acoust. Soc. Am. 117, 690 (2005)]. Modeling is compared with experimental results, which are obtained with bifrequency pulses exciting a soil with a buried landmine replica, instrumented with a geophone and a nearby microphone. Cases investigated include: (1) target only, (2) buried target under disturbed soil, (3) disturbed soil only, and (4) undisturbed soil. Excitation both on and off the resonance of the buried mine is also investigated, as is burial in different soil types at various depths. [Work supported by the ARL:UT McKinney Fellowship in Acoustics.].The Journal of the Acoustical Society of America 11/2013; 134(5):4129. · 1.65 Impact Factor 
Article: Delay differential equation models for single and coupled bubble dynamics in a compressible liquid
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ABSTRACT: Various models for interacting spherical bubbles in a compressible liquid based on delay differential equations are considered. It is shown that most previously proposed models for interacting spherical bubbles in a compressible liquid based on the KellerMiksis and GilmoreAkulichev models are unstable for closely spaced bubbles. A new model for a single spherical bubble in a compressible liquid is proposed and used to derive a stable model for interacting bubbles. A qualitative comparison to the results of direct numerical integration of the fluid equations of motion suggests that the new model provides more accurate results than the standard KellerMiksis or GilmoreAkulichev models for single bubble dynamics.10/2013; 
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ABSTRACT: A model is developed for a pulsating and translating gas bubble immersed in liquid in a channel formed by two soft, thin elastic parallel layers having densities equal to that of the surrounding liquid and small, but finite, shear moduli. The bubble is nominally spherical but free to undergo small shape deformations. Shear strain in the elastic layers is estimated in a way which is valid for short, transient excitations of the system. Coupled nonlinear secondorder differential equations are obtained for the shape and position of the bubble, and numerical integration of an expression for the liquid velocity at the layer interfaces yields an estimate of the elastic layer displacement. Numerical integration of the dynamical equations reveals behavior consistent with laboratory observations of acoustically excited bubbles in ex vivo vessels reported by Chen et al. [Phys. Rev. Lett. 106, 034301 (2011) and Ultrasound Med. Biol. 37, 21392148 (2011)].The Journal of the Acoustical Society of America 08/2013; 134(2):145462. · 1.65 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: The analysis presented at the previous ASA meeting related to investigation of the acoustic radiation force on a sphere embedded in a soft elastic medium with shear modulus that is several orders of magnitude smaller than its bulk modulus. The acoustic field was assumed to be axisymmetric and the spherical scatterer to be located on the axis of the acoustic beam. When one of these conditions is violated, the problem loses its symmetry. In this talk, the acoustic radiation force is considered in the more general case of nonaxisymmetric fields. The calculation is performed in Lagrangian coordinates. All acoustic fields, incident as well as scattered, depend on all three spherical coordinates. The incident and scattered waves, which include both potential and solenoidal parts, are expanded with respect to spherical harmonics. An analytical expression for the acoustic radiation force derived in this investigation may contain as many spherical harmonics as needed. In limiting cases when the scatterer is in liquid and only two modes, monopole and dipole, remain in the scattered fields, the solution for the acoustic radiation force recovers the results reported by Gor'kov [Sov. Phys. Doklady 6, 773 (1962)]. [Work supported by NIH DK070618 and EB011603.].The Journal of the Acoustical Society of America 05/2013; 133(5):3237. · 1.65 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: Sustained tonal noise radiated by towers supporting offshore wind turbines contains energy in frequency bands that may disturb marine mammals, or interfere with passive sonar and seismic sensors and underwater communication equipment. Understanding the generation and propagation of underwater noise due to the operation of wind farms is important for determining strategies for mitigating the environmental impact of these noise sources. An analytic model based on a Green's function approach was previously developed for the sound radiated in the water column by a pulsating cylindrical structure embedded in horizontally stratified layers of viscoelastic sediment [Hay et al., J. Acoust. Soc. Am. 130, 2558 (2011)]. This model has since been adapted to include relaxation and viscous losses in seawater and empirical loss factors for the sedimentary layers. In order to validate the model simulations were compared with reported measurements collected near an operating wind turbine that include radial acceleration of the tower, taken to be the source condition, and sound pressure levels in the water column. For longrange propagation over rangedependent environments, the analytic model has been coupled to a parabolic equation code. Simulations are presented for several bathymetries, sediment types, and tower array configurations. [Work supported by Department of Energy DEEE0005380.].The Journal of the Acoustical Society of America 05/2013; 133(5):3396. · 1.65 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: Previous models and experiments have shown that direction of bubble translation near a viscoelastic layer depends on both the standoff distance of the bubble and the elastic properties of the layer. Here the individual forces due to the incident sound field and the field reflected from the viscoelastic layer are shown to compete with one another and ultimately determine the direction of bubble translation. In addition, many other factors pertinent to the direction of bubble translation such as the incident acoustic waveform, the phase and propagation direction of the incident field, and the radial bubble dynamics are considered. The force due to the viscoelastic layer is calculated using a Green's function, which takes into account elastic waves and viscosity in the layer and the viscous boundary layer at the solidliquid interface. [Work supported by the ARL:UT McKinney Fellowship in Acoustics and NIH DK070618.].The Journal of the Acoustical Society of America 05/2013; 133(5):3409. · 1.65 Impact Factor
Publication Stats
656  Citations  
230.53  Total Impact Points  
Top Journals
Institutions

1989–2014

University of Texas at Austin
 Department of Mechanical Engineering
Austin, Texas, United States


2013

Dynaflow, Inc.
Jessup, Maryland, United States


2012–2013

Brigham Young University  Provo Main Campus
 Department of Physics and Astronomy
Provo, Utah, United States


2009

Universiteit Twente
Enschede, Overijssel, Netherlands


2007

Stanford University
 E. L. Ginzton Laboratory
Palo Alto, CA, United States


2003

National Institute of Standards and Technology
Maryland, United States


1998

Acoustical Society of America
Norfolk, Virginia, United States
