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Feb 2010

Volume 127, Issue 2, pp. EL19-1180

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Crosstalk mitigation using adaptive time reversal

H. C. Song, J. S. Kim, W. S. Hodgkiss, and J. H. Joo

J. Acoust. Soc. Am. Volume 127, Issue 2, pp. EL19-EL22 (2010); (4 pages) | Cited 2 times

Online Publication Date: 08 Jan 2010

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Although the spatial focusing property of the conventional time reversal approach facilitates multiuser communications, there always is residual crosstalk between users. A recent paper [ Kim and Shin, J. Acoust. Soc. Am. 115, 600–606 (2004) ] proposed an adaptive active time reversal approach for simultaneous multiple focusing with minimal interference. This letter applies the adaptive approach to passive time reversal, multiuser communications for additional suppression of crosstalk among users. Experimental data at 3.5 kHz with a 1-kHz bandwidth demonstrate as much as 6.5-dB improvement per user in terms of output signal-to-noise ratio for three-user communications over a 20-km range in 120-m deep shallow water.
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43.60.Dh Signal processing for communications: telephony and telemetry, sound pickup and reproduction, multimedia
43.60.Gk Space-time signal processing, other than matched field processing
43.60.Fg Acoustic array systems and processing, beam-forming
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Effects of stimulus duration on amplitude modulation processing with cochlear implants

Xin Luo, John J. Galvin, III, and Qian-Jie Fu

J. Acoust. Soc. Am. Volume 127, Issue 2, pp. EL23-EL29 (2010); (7 pages) | Cited 5 times

Online Publication Date: 11 Jan 2010

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This study investigated temporal integration processes underlying cochlear implant (CI) users’ amplitude modulation processing. Thresholds for modulation detection (AMDTs) and modulation frequency discrimination (AMFDTs) were measured for 50-, 100-, and 200-Hz modulation frequencies with stimulus durations from 50 to 400 ms in eight adult CI users. The results showed significant interactions between modulation frequency and stimulus duration for AMDTs and AMFDTs. The data suggest that temporal integration limits CI users’ sensitivity to low temporal pitch over short durations, and that temporal integration over longer durations may not enhance CI users’ sensitivity to high temporal pitch.
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43.66.Ts Auditory prostheses, hearing aids
43.66.Fe Discrimination: intensity and frequency
43.66.Hg Pitch
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A simple method to account for size effects in the transfer matrix method

Dilal Rhazi and Noureddine Atalla

J. Acoust. Soc. Am. Volume 127, Issue 2, pp. EL30-EL36 (2010); (7 pages) | Cited 2 times

Online Publication Date: 12 Jan 2010

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The transfer matrix method based is extensively used and well-validated for predicting the transmission loss of multilayer structures. However, this method leads to poor results at low frequencies due to the infinite extent assumption it is based on. This paper presents an efficient implementation of a Rayleigh-integral based method to account for the finite size effects. The accuracy of the method is illustrated by various examples.
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43.40.Yq Instrumentation and techniques for tests and measurement relating to shock and vibration, including vibration pickups, indicators, and generators, mechanical impedance
43.25.Qp Radiation pressure
43.50.Cb Noise spectra, determination of sound power
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Recognition of interrupted sentences under conditions of spectral degradation

Monita Chatterjee, Fabiola Peredo, Desirae Nelson, and Deniz Başkent

J. Acoust. Soc. Am. Volume 127, Issue 2, pp. EL37-EL41 (2010); (5 pages) | Cited 7 times

Online Publication Date: 13 Jan 2010

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Cochlear implant (CI) and normally hearing (NH) listeners’ recognition of periodically interrupted sentences was investigated. CI listeners’ scores declined drastically when the sentences were interrupted. The NH listeners showed a significant decline in performance with increasing spectral degradation using CI-simulated, noise-band-vocoded speech. It is inferred that the success of top-down processes necessary for the perceptual reconstruction of interrupted speech is limited by even mild degradations of the bottom-up information stream (16 and 24 band processing). A hypothesis that the natural voice-pitch variations in speech would help in the perceptual reconstruction of the sentences was not supported by experimental results.
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43.66.Ts Auditory prostheses, hearing aids
43.71.Es Vowel and consonant perception; perception of words, sentences, and fluent speech
43.71.Ky Speech perception by the hearing impaired
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Ray-based blind deconvolution in ocean sound channels

Karim G. Sabra, Hee-Chun Song, and David R. Dowling

J. Acoust. Soc. Am. Volume 127, Issue 2, pp. EL42-EL47 (2010); (6 pages) | Cited 3 times

Online Publication Date: 13 Jan 2010

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This letter describes a ray-based blind deconvolution technique for ocean sound channels that produces broadband estimates of the source-to-array impulse response and the original source waveform from array-measured signals corrupted by (unknown) multipath propagation. The technique merely requires elementary knowledge of array geometry and sound speed at the array location. It is based on identifying a ray arrival direction to separate source waveform and acoustic-propagation phase contributions to the received signals. This technique successfully decoded underwater telecommunication sequences in the bandwidth 3–4 kHz that were broadcast 4 km in a 120-m-deep ocean sound channel without a-priori knowledge of sound channel characteristics.
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43.30.Wi Passive sonar systems and algorithms, matched field processing in underwater acoustics
43.60.Pt Signal processing techniques for acoustic inverse problems
43.30.Cq Ray propagation of sound in water
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Structural damage identification in plates via nonlinear structural intensity maps

Fabio Semperlotti and Stephen C. Conlon

J. Acoust. Soc. Am. Volume 127, Issue 2, pp. EL48-EL53 (2010); (6 pages) | Cited 4 times

Online Publication Date: 14 Jan 2010

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A nonlinear structural intensity concept is presented as an approach for the identification of defects displaying nonlinear vibration behavior. The nonlinear structural dynamic response exhibited by a riveted joint with loosened fasteners connecting a stiffener with a flat panel is investigated. The excitation, generating elastic waves with dominant bending components, triggers the nonlinear contact between the plate and the stiffener inducing a dynamic response rich with nonlinear harmonics. Experimental structural intensity maps are evaluated at the super-harmonic frequencies. This technique provides an experimental approach for the characterization and two dimensional visualization of nonlinear types of defects.
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43.40.Le Techniques for nondestructive evaluation and monitoring, acoustic emission
43.40.Ga Nonlinear vibration
43.40.At Experimental and theoretical studies of vibrating systems
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Orienting attention during phonetic training facilitates learning

Eric Pederson and Susan Guion-Anderson

J. Acoust. Soc. Am. Volume 127, Issue 2, pp. EL54-EL59 (2010); (6 pages) | Cited 2 times

Online Publication Date: 14 Jan 2010

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The role of consciously directed attention toward speech input in learning has not yet been determined. Previous phonetic learning studies have manipulated acoustic signals and response feedback, but not conscious control over attentional orienting. This study tests whether directed attention facilitates learning of phonetic information. Two monolingual English-speaking groups were trained with feedback on the same auditory stimuli: Hindi words. One group was instructed to attend to the consonants and the other to the vowels. The consonant-oriented group, but not the vowel-oriented group, demonstrated post-training improvement in consonant perception, confirming a role for consciously directed attentional mechanisms during phonetic learning.
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43.71.Hw Cross-language perception of speech
43.71.Ft Development of speech perception
43.71.Es Vowel and consonant perception; perception of words, sentences, and fluent speech
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The neural code for interaural time difference in human auditory cortex

Nelli H. Salminen, Hannu Tiitinen, Santeri Yrttiaho, and Patrick J. C. May

J. Acoust. Soc. Am. Volume 127, Issue 2, pp. EL60-EL65 (2010); (6 pages) | Cited 4 times

Online Publication Date: 19 Jan 2010

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A magnetoencephalography study was conducted to reveal the neural code of interaural time difference (ITD) in the human cortex. Widely used crosscorrelator models predict that the code consists of narrow receptive fields distributed to all ITDs. The present findings are, however, more in line with a neural code formed by two opponent neural populations: one tuned to the left and the other to the right hemifield. The results are consistent with models of ITD extraction in the auditory brainstem of small mammals and, therefore, suggest that similar computational principles underlie human sound source localization.
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43.64.Ri Evoked responses to sounds
43.66.Pn Binaural hearing
43.64.Bt Models and theories of the auditory system
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Verification of a near-field error sensor placement method in active control of compact noise sources

Benjamin M. Shafer, Kent L. Gee, and Scott D. Sommerfeldt

J. Acoust. Soc. Am. Volume 127, Issue 2, pp. EL66-EL72 (2010); (7 pages)

Online Publication Date: 22 Jan 2010

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Recent experiments in active noise control (ANC) have used near-field error sensors whose locations are determined according to the minimization of sound power. Sensors should be placed in regions where the sound pressure reductions are the greatest during sound power minimization of the ANC system. Near-field pressure measurements of noise sources with and without ANC were made. With the error sensors in theoretically ideal locations, the measured near-field pressure map approximates the theoretical map created under the condition of minimized radiated power. Moving the error sensors to theoretically nonideal locations greatly reduces the attenuation of radiated sound power.
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43.28.Ra Generation of sound by fluid flow, aerodynamic sound and turbulence
43.50.Ki Active noise control
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Auditory-model based robust feature selection for speech recognition

Christos Koniaris, Marcin Kuropatwinski, and W. Bastiaan Kleijn

J. Acoust. Soc. Am. Volume 127, Issue 2, pp. EL73-EL79 (2010); (7 pages) | Cited 2 times

Online Publication Date: 25 Jan 2010

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It is shown that robust dimension-reduction of a feature set for speech recognition can be based on a model of the human auditory system. Whereas conventional methods optimize classification performance, the proposed method exploits knowledge implicit in the auditory periphery, inheriting its robustness. Features are selected to maximize the similarity of the Euclidean geometry of the feature domain and the perceptual domain. Recognition experiments using mel-frequency cepstral coefficients (MFCCs) confirm the effectiveness of the approach, which does not require labeled training data. For noisy data the method outperforms commonly used discriminant-analysis based dimension-reduction methods that rely on labeling. The results indicate that selecting MFCCs in their natural order results in subsets with good performance.
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43.71.-k Speech perception
43.72.Qr Auditory synthesis and recognition
43.72.Ne Automatic speech recognition systems
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A non-linear three-dimensional model for quantifying microbubble dynamics

Abhay V. Patil, Paul Reynolds, and John A. Hossack

J. Acoust. Soc. Am. Volume 127, Issue 2, pp. EL80-EL86 (2010); (7 pages) | Cited 3 times

Online Publication Date: 25 Jan 2010

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A three-dimensional non-linear model for simulating microbubble response to acoustic insonation is presented. A 1 μm radius microbubble stimulated using positive and inverted 2.4 MHz pulses produced radius-time curves that matched (error <10%) with the experimental observation. A bound 2.3 μm radius microbubble insonated using 2.25 MHz 6 cycle pulse was observed to oscillate with max/min oscillations 45% lower than that of the free microbubble, this correlated ( ∼ 10% error) with the observations of Garbin et al. [ Appl. Phys. Lett. 90, 114103 (2007) ]. The adherent microbubble oscillated asymmetrically in the plan view and symmetrically in the elevation view, consistent with the previous experimental results.
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43.80.Qf Medical diagnosis with acoustics
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Scattering by an arrangement of eccentric cylinders embedded on a coated cylinder with applications to tomographic density imaging

Roberto J. Lavarello and Michael L. Oelze

J. Acoust. Soc. Am. Volume 127, Issue 2, pp. 645-648 (2010); (4 pages)

Online Publication Date: 05 Feb 2010

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The solution to the scattering of an incident pressure wave by an arrangement of eccentric cylinders embedded inside a pair of concentric cylinders is derived here using a combination of T-matrix and mode-matching approaches. This method allows the generation of synthetic data from relatively complex structures to be used for the validation of acoustic tomography methods. An application of the solution derived here is illustrated by reconstructing sound speed and density profiles from a complex phantom using inverse scattering.
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43.20.Fn Scattering of acoustic waves
43.35.Wa Biological effects of ultrasound, ultrasonic tomography

Theoretical model for the threshold onset of contrast microbubble oscillations

Alexander A. Doinikov and Ayache Bouakaz

J. Acoust. Soc. Am. Volume 127, Issue 2, pp. 649-651 (2010); (3 pages)

Online Publication Date: 05 Feb 2010

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It has been reported recently through high speed optical observations of phospholipid-coated contrast microbubbles that there is a threshold value for the acoustic pressure amplitude below which the radial oscillation of the microbubbles does not occur. In this Letter, it is suggested that this threshold behavior results from the fact that a phospholipid layer, as a physical material, has a certain value of the limiting shear stress so that its deformation does not start until this limiting value is exceeded. A theoretical model is proposed for the description of this phenomenon. The model explains the experimentally observed dependence of the threshold onset of microbubble oscillation on the initial bubble radius.
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43.25.Yw Nonlinear acoustics of bubbly liquids
43.35.Ei Acoustic cavitation in liquids
43.80.Qf Medical diagnosis with acoustics

The influence on predicted harmonic and distortion product generation of the position of the nonlinearity within cochlear micromechanical models

Jacqueline A. How, Stephen J. Elliott, and Ben Lineton

J. Acoust. Soc. Am. Volume 127, Issue 2, pp. 652-655 (2010); (4 pages) | Cited 2 times

Online Publication Date: 05 Feb 2010

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Numerical techniques are used to explore the influence on the predicted basilar membrane (BM) response of the position of the nonlinearity within the micromechanical feedback loop of an active nonlinear cochlear model. This position is found to influence both the harmonic and distortion product spectra of the predicted BM response. The BM motion at the fundamental or primary frequencies is not significantly altered by the position of the nonlinearity, however, provided that the gain is appropriately adjusted. The observed effects are explained in terms of the frequency responses of the elements within the micromechanical feedback loop.
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43.64.Kc Cochlear mechanics
43.64.Bt Models and theories of the auditory system
43.64.Jb Otoacoustic emissions

Modulation rate discrimination using half-wave rectified and sinusoidally amplitude modulated stimuli in cochlear-implant users

Heather A. Kreft, Andrew J. Oxenham, and David A. Nelson

J. Acoust. Soc. Am. Volume 127, Issue 2, pp. 656-659 (2010); (4 pages) | Cited 1 time

Online Publication Date: 05 Feb 2010

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Detection and modulation rate discrimination were measured in cochlear-implant users for pulse-trains that were either sinusoidally amplitude modulated or were modulated with half-wave rectified sinusoids, which in acoustic hearing have been used to simulate the response to low-frequency temporal fine structure. In contrast to comparable results from acoustic hearing, modulation rate discrimination was not statistically different for the two stimulus types. The results suggest that, in contrast to binaural perception, pitch perception in cochlear-implant users does not benefit from using stimuli designed to more closely simulate the cochlear response to low-frequency pure tones.
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43.66.Ts Auditory prostheses, hearing aids
43.66.Fe Discrimination: intensity and frequency
43.66.Hg Pitch

Psychophysical tuning curves and recognition of highpass and lowpass filtered speech for a person with an inverted V-shaped audiogram

Vinay and Brian C. J. Moore

J. Acoust. Soc. Am. Volume 127, Issue 2, pp. 660-663 (2010); (4 pages)

Online Publication Date: 05 Feb 2010

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A single subject whose audiogram resembled an inverted V shape (good hearing at 4000 Hz, and poorer hearing at other frequencies) was tested. Results of the threshold-equalizing noise test suggested that a dead region (DR) in the cochlea was present at all test frequencies from 500 to 3000 Hz, but no DR was present at 4000 Hz. Psychophysical tuning curves (PTCs) obtained using signal frequencies of 2000, 3000, 4000, and 6000 Hz showed upward shifted tips for the lowest two signal frequencies, and a downward shifted tip for the highest frequency. The results of the PTCs suggested a functioning region extending from 3900 to 5100 Hz, with DRs outside that range. The identification of nonsense syllables, amplified according to the “Cambridge formula,” was measured as a function of lowpass or highpass filter cutoff frequency. The results suggested that useful speech information could only be extracted from a limited frequency range around 4000 Hz.
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43.71.Ky Speech perception by the hearing impaired
43.66.Ts Auditory prostheses, hearing aids
43.71.Gv Measures of speech perception (intelligibility and quality)
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The scattering of sound by a long cylinder above an impedance boundary

Wai Keung Lui and Kai Ming Li

J. Acoust. Soc. Am. Volume 127, Issue 2, pp. 664-674 (2010); (11 pages) | Cited 2 times

Online Publication Date: 05 Feb 2010

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The classical problem of sound scattering by an acoustically hard cylinder due to a point monopole and a line airborne source is extended in the present study. The solution to the homogeneous Helmholtz equation is expressed in a cylindrical coordinate system and represented by an expansion of Fourier integrals. Incorporating the image source method and the Bessel function addition theorem, the analytical solution is derived for the prediction of multiple scattering of sound by a hard cylinder placed above a ground surface of finite impedance. The total sound field can be expressed as a sum of four components: the incident field, the reflected wave, and the scattered fields from the cylinder and its image. The total far-field scattered potential was evaluated asymptotically by the method of stationary phase. Experimental measurements by using a point source were conducted in an anechoic chamber to validate the theoretical formulations. The numerical predictions of using a point source model give good agreements with all the experimental data but there are obvious discrepancies in the spectral magnitudes between the calculation and experimental results when a line source model is used to simulate the scattering problem due to a point source excitation.
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43.20.Bi Mathematical theory of wave propagation
43.20.El Reflection, refraction, diffraction of acoustic waves
43.20.Fn Scattering of acoustic waves
43.28.Js Numerical models for outdoor propagation

A residual-potential boundary for time-dependent, infinite-domain problems in computational acoustics

Thomas L. Geers and Michael A. Sprague

J. Acoust. Soc. Am. Volume 127, Issue 2, pp. 675-682 (2010); (8 pages)

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A theoretically exact computational boundary is introduced that is based on modal residual potentials for the spherical geometry. The boundary produces a set of first-order, uncoupled ordinary differential equations for nodal boundary responses, and a set of uncoupled time-stepping equations for modal boundary responses. The two sets are coupled through nodal-modal transformation based on the orthogonal surface functions for the spherical boundary. Numerical results generated with the boundary are presented for a step-wave-excited, elastic, spherical shell submerged in an infinite acoustic medium. Extension of the method to other separable geometries for partial differential equations defined in unbounded domains is mentioned.
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43.20.Px Transient radiation and scattering
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Nonlinear reflection of shock shear waves in soft elastic media

Gianmarco Pinton, François Coulouvrat, Jean-Luc Gennisson, and Mickaël Tanter

J. Acoust. Soc. Am. Volume 127, Issue 2, pp. 683-691 (2010); (9 pages) | Cited 2 times

Online Publication Date: 05 Feb 2010

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For fluids, the theoretical investigation of shock wave reflection has a good agreement with experiments when the incident shock Mach number is large. But when it is small, theory predicts that Mach reflections are physically unrealistic, which contradicts experimental evidence. This von Neumann paradox is investigated for shear shock waves in soft elastic solids with theory and simulations. The nonlinear elastic wave equation is approximated by a paraxial wave equation with a cubic nonlinear term. This equation is solved numerically with finite differences and the Godunov scheme. Three reflection regimes are observed. Theory is developed for shock propagation by applying the Rankine–Hugoniot relations and entropic constraints. A characteristic parameter relating diffraction and non-linearity is introduced and its theoretical values are shown to match numerical observations. The numerical solution is then applied to von Neumann reflection, where curved reflected and Mach shocks are observed. Finally, the case of weak von Neumann reflection, where there is no reflected shock, is examined. The smooth but non-monotonic transition between these three reflection regimes, from linear Snell–Descartes to perfect grazing case, provides a solution to the acoustical von Neumann paradox for the shear wave equation. This transition is similar to the quadratic non-linearity in fluids.
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43.25.Cb Macrosonic propagation, finite amplitude sound; shock waves
43.25.Dc Nonlinear acoustics of solids
43.25.Jh Reflection, refraction, interference, scattering, and diffraction of intense sound waves

Nonlinear Biot waves in porous media with application to unconsolidated granular media

Olivier Dazel and Vincent Tournat

J. Acoust. Soc. Am. Volume 127, Issue 2, pp. 692-702 (2010); (11 pages) | Cited 4 times

Online Publication Date: 05 Feb 2010

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The nonlinear propagation through porous media is investigated in the framework of Biot theory. For illustration, and considering the current interest for the determination of the elastic properties of granular media, the case of nonlinear propagation in “model” granular media (disordered packings of noncohesive elastic beads of the same size embedded in a visco-thermal fluid) is considered. The solutions of linear Biot waves are first obtained, considering the appropriate geometrical and physical parameters of the medium. Then, making use of the method of successive approximations of nonlinear acoustics, the solutions for the second harmonic Biot waves are derived by considering a quadratic nonlinearity in the solid frame constitutive law (which takes its origin from the high nonlinearity of contacts between grains). The propagation in a semi-infinite medium with velocity dispersion, frequency dependent dissipation, and nonlinearity is first analyzed. The case of a granular medium slab with rigid boundaries, often considered in experiments, is then presented. Finally, the importance of mode coupling between solid and fluid waves is evaluated, depending on the actual fluid, the bead diameter, or the applied static stress on the beads. The application of these results to other media supporting Biot waves (porous ceramics, polymer foams, etc.) is straightforward.
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43.25.Dc Nonlinear acoustics of solids
43.20.Jr Velocity and attenuation of elastic and poroelastic waves
43.20.Gp Reflection, refraction, diffraction, interference, and scattering of elastic and poroelastic waves
43.20.Bi Mathematical theory of wave propagation

Acoustic microstreaming around a gas bubble

Alexander A. Doinikov and Ayache Bouakaz

J. Acoust. Soc. Am. Volume 127, Issue 2, pp. 703-709 (2010); (7 pages) | Cited 7 times

Online Publication Date: 05 Feb 2010

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The problem of acoustic microstreaming that develops around a gas bubble in an ultrasound field is considered. It is shown that the solutions obtained previously by Wu and Du [ (1997). J. Acoust. Soc. Am. 101, 1899–1907 ], which are based on the assumption that viscous effects are essential only within a thin boundary layer while beyond the boundary layer the liquid can be considered to be inviscid, lead to a severe underestimation of the power of acoustic streaming. An improved theory is suggested that corrects the errors of the previous theory and extends its limits. The proposed theory treats the entire bulk of the liquid outside the bubble and the gas inside the bubble as viscous heat-conducting fluids. No restrictions are imposed on the size of the bubble relative to the viscous, thermal, and sound wavelengths in the ambient liquid and those in the internal gas medium. All modes of the bubble’s motion (volume pulsation, translation, and shape oscillations) are taken into account. Expressions for the radial and tangential stresses produced by the acoustic streaming are also derived. Numerical examples for parameters of interest are presented.
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43.25.Nm Acoustic streaming
43.25.Yw Nonlinear acoustics of bubbly liquids
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A frequency domain linearized Navier–Stokes equations approach to acoustic propagation in flow ducts with sharp edges

Axel Kierkegaard, Susann Boij, and Gunilla Efraimsson

J. Acoust. Soc. Am. Volume 127, Issue 2, pp. 710-719 (2010); (10 pages) | Cited 3 times

Online Publication Date: 05 Feb 2010

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Acoustic wave propagation in flow ducts is commonly modeled with time-domain non-linear Navier–Stokes equation methodologies. To reduce computational effort, investigations of a linearized approach in frequency domain are carried out. Calculations of sound wave propagation in a straight duct are presented with an orifice plate and a mean flow present. Results of transmission and reflections at the orifice are presented on a two-port scattering matrix form and are compared to measurements with good agreement. The wave propagation is modeled with a frequency domain linearized Navier–Stokes equation methodology. This methodology is found to be efficient for cases where the acoustic field does not alter the mean flow field, i.e., when whistling does not occur.
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43.28.Py Interaction of fluid motion and sound, Doppler effect, and sound in flow ducts
43.20.Fn Scattering of acoustic waves
43.20.Mv Waveguides, wave propagation in tubes and ducts
43.28.Ra Generation of sound by fluid flow, aerodynamic sound and turbulence
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Inverse problem in anisotropic poroelasticity: Drained constants from undrained ultrasound measurements

James G. Berryman and Seiji Nakagawa

J. Acoust. Soc. Am. Volume 127, Issue 2, pp. 720-729 (2010); (10 pages) | Cited 4 times

Online Publication Date: 05 Feb 2010

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Poroelastic analysis has traditionally focused on the relationship between dry and drained constants, which are assumed known, and the saturated or undrained constants, which are assumed unknown. However, there are many applications in this field of study for which the main measurements can only be made on the saturated/undrained system, and then it is uncertain what the effects of the fluids were on the system, since the drained constants remain a mystery. The work presented here shows how to deduce drained constants from undrained constants for anisotropic systems having symmetries ranging from isotropic to orthotropic. Laboratory ultrasound data are then inverted for the drained constants in three granular packings: one of glass beads, and two others for distinct types of more or less angular sand grain packings. Experiments were performed under uniaxial stress, which resulted in hexagonal (transversely isotropic) symmetry of the poroelastic response. One important conclusion from the general analysis is that the drained constants are uniquely related to the undrained constants, assuming that porosity, grain bulk modulus, and pore fluid bulk modulus are already known. Since the resulting system of equations for all the drained constants is linear, measurement error in undrained constants also propagates linearly into the computed drained constants.
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43.30.Ma Acoustics of sediments; ice covers, viscoelastic media; seismic underwater acoustics
43.30.Pc Ocean parameter estimation by acoustical methods; remote sensing; imaging, inversion, acoustic tomography
43.20.Jr Velocity and attenuation of elastic and poroelastic waves
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Scattering of the fundamental torsional mode at an axial crack in a pipe

M. Ratassepp, S. Fletcher, and M. J. S. Lowe

J. Acoust. Soc. Am. Volume 127, Issue 2, pp. 730-740 (2010); (11 pages) | Cited 6 times

Online Publication Date: 05 Feb 2010

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A quantitative study of the interaction of the T(0,1) torsional mode with an axial defect in a pipe is presented. The results are obtained from finite element simulations and experiments. The influence of the crack axial extent, depth, excitation frequency, and pipe circumference on the scattering is examined. It is found that the reflection from a defect consists of a series of the wave pulses with gradually decaying amplitudes. Such behavior is caused by the shear waves diffracting from the crack and then repeatedly interacting with the crack due to circumferential propagation. Time-domain reflection coefficient analysis demonstrates that the trend of the reflection strength for different crack lengths, pipe diameters, and frequencies from a through-thickness crack satisfies a simple normalization. The results show that the reflection coefficient initially increases with the crack length at all frequencies but finally reaches an oscillating regime. Also, at a given frequency and crack length the reflection decreases with the increase in pipe circumference. An additional scattering study of the shear wave SH0 mode at a part-thickness notch in a plate shows that the reflection coefficient, when plotted against depth of the notch, increases with both frequency and notch depth.
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43.35.Cg Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in solids; elastic constants
43.20.Fn Scattering of acoustic waves
43.20.Mv Waveguides, wave propagation in tubes and ducts
43.35.Zc Use of ultrasonics in nondestructive testing, industrial processes, and industrial products

Polycrystalline gamma-plutonium’s elastic moduli versus temperature

I. Stroe, J. B. Betts, A. Trugman, C. H. Mielke, J. N. Mitchell, M. Ramos, F. J. Freibert, H. Ledbetter, and A. Migliori

J. Acoust. Soc. Am. Volume 127, Issue 2, pp. 741-745 (2010); (5 pages) | Cited 2 times

Online Publication Date: 05 Feb 2010

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Resonant ultrasound spectroscopy was used to measure the elastic properties of pure polycrystalline 239Pu in the γ-phase. Shear and longitudinal elastic moduli were measured simultaneously and the bulk modulus was computed from them. A smooth, linear, and large decrease in all elastic moduli with increasing temperature was observed. The Poisson ratio was calculated and an increase from 0.242 at 519 K to 0.252 at 571 K was found. These measurements on extremely well-characterized pure Pu are in agreement with other reported results where overlap occurs. We calculated an approximate Debye temperature ΘD = 144 K. Determined from the temperature variation in the bulk modulus, γ-Pu shows the same Grüneisen parameter as copper.
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43.35.Cg Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in solids; elastic constants
43.20.Ye Measurement methods and instrumentation
43.25.Gf Standing waves; resonance
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