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Journal of the Acoustical Society of America

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Jul 2012

Volume 132, Issue 1, pp. EL1-580

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Low-frequency resonance of an oblate spheroidal cavity in a soft elastic medium

David C. Calvo, Abel L. Thangawng, and Christopher N. Layman

J. Acoust. Soc. Am. Volume 132, Issue 1, pp. EL1-EL7 (2012); (7 pages)

Online Publication Date: 15 Jun 2012

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Axisymmetric monopole resonances of an oblate spheroidal cavity in a soft elastic medium are computed using both separation of variables and finite-element approaches. The resonances are obtained for compression wavelengths much longer than the cavity size and thus have a low-frequency character. Resonant frequencies for high-aspect-ratio oblate spheroids (either air-filled or evacuated) are found to be significantly lower than their spherical counterparts with equivalent volume. This finding contrasts with the case of an air bubble in water which features weak shape dependence. The results are relevant to the design of locally-resonant acoustic media using soft-lithography techniques with elastomers.
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43.20.Ks Standing waves, resonance, normal modes
43.40.Fz Acoustic scattering by elastic structures
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How the cross-sectional discontinuity between ear canal and probe affects the ear canal length estimation

Makram Zebian, Johannes Hensel, and Thomas Fedtke

J. Acoust. Soc. Am. Volume 132, Issue 1, pp. EL8-EL14 (2012); (7 pages)

Online Publication Date: 15 Jun 2012

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Many ear canal probes both deliver and measure sound via narrow tubes. This study investigates the effect of the cross-sectional discontinuity at the interface between ear canal models and the connecting tubes of a commercially available otoacoustic emission probe on the “acoustically” estimated cavity lengths. Rigid cavities having the same length but different diameters were produced, and modeled by the finite element method. Cavities with a diameter larger than 8 mm had acoustic lengths that considerably overestimated the real geometry. A length correction was derived, which, in most applications, compensates for the measurement errors emerging from the discontinuity effects.
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43.20.Ks Standing waves, resonance, normal modes
43.30.Ma Acoustics of sediments; ice covers, viscoelastic media; seismic underwater acoustics
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A model for spatial coherence from directive ambient noise in attenuating, dispersive media

Shane C. Walker

J. Acoust. Soc. Am. Volume 132, Issue 1, pp. EL15-EL21 (2012); (7 pages) | Cited 1 time

Online Publication Date: 15 Jun 2012

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As a complement to experimental efforts in seismics and acoustics to infer geo-acoustic properties of the propagation environment from the second order statistics of ambient noise measurements, a set of exact, explicit, closed form expressions for the cross-spectral density and spatial coherence of diffuse random wave fields is presented. Taken together, the expressions are well suited for modeling broadband, diffuse wave coherence in realistic scenarios involving directive, ambient noise from local (i.e., volume) and distant (i.e., plane wave) source features in an open, dispersive, attenuating medium.
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43.60.Cg Statistical properties of signals and noise
43.60.Jn Source localization and parameter estimation
43.30.Pc Ocean parameter estimation by acoustical methods; remote sensing; imaging, inversion, acoustic tomography
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Dual mechanisms in the perceptual processing of click train temporal regularity

Dennis P. Phillips, Rachel N. Dingle, Susan E. Hall, and Moragh Jang

J. Acoust. Soc. Am. Volume 132, Issue 1, pp. EL22-EL28 (2012); (7 pages)

Online Publication Date: 15 Jun 2012

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Two experiments measured human sensitivity to temporal jitter in 25-click trains with inter-click intervals (ICIs) between 5 and 100 ms. In a naturalistic experiment using wideband clicks, jitter thresholds were a nonmonotonic function of ICI, peaking for ICIs near 40–60 ms. In a subsequent experiment, clicks were high-passed and presented against a low-frequency noise masker. Jitter threshold vs ICI functions lost the positive slope over short ICIs but retained the negative slope at long ICIs. The same behavior was seen in click rate discrimination tasks. Different processes mediate regularity analysis for click trains with ICIs above and below 40–60 ms.
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43.66.Ba Models and theories of auditory processes
43.66.Lj Perceptual effects of sound
43.66.Mk Temporal and sequential aspects of hearing; auditory grouping in relation to music
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Single-channel dereverberation using a non-causal minimum variance distortionless response filter

Myung-Suk Song and Hong-Goo Kang

J. Acoust. Soc. Am. Volume 132, Issue 1, pp. EL29-EL35 (2012); (7 pages)

Online Publication Date: 15 Jun 2012

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This letter presents a single-channel speech dereverberation approach using a non-causal minimum variance distortionless response (MVDR) filter. The non-causal filter is adopted to utilize the additional information of the desired signal that lies in subsequent frames. Note that the desired signal output has minimal distortion due to the introduction of the MVDR criterion. The proposed system further suppresses the late reverberation by employing a statistical reverberant model. Experimental results demonstrate the superiority of the proposed algorithm to conventional approaches.
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43.60.Fg Acoustic array systems and processing, beam-forming
43.60.Pt Signal processing techniques for acoustic inverse problems
43.60.Hj Time-frequency signal processing, wavelets
43.60.Dh Signal processing for communications: telephony and telemetry, sound pickup and reproduction, multimedia
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Vibro-acoustic response of an infinite, rib-stiffened, thick-plate assembly using finite-element analysis

Marcel C. Remillieux and Ricardo A. Burdisso

J. Acoust. Soc. Am. Volume 132, Issue 1, pp. EL36-EL42 (2012); (7 pages)

Online Publication Date: 15 Jun 2012

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The vibration of and sound radiation from an infinite, fluid-loaded, thick-plate assembly stiffened periodically with ribs are investigated numerically using finite-element analysis. First, numerical simulations are compared to the analytical solutions presented recently for this particular problem [Hull and Welch, J. Sound Vib. 329, 4192–4211 (2010)]. It is shown that the solutions reported in this reference are partially incorrect because the number of modes was not chosen correctly. Subsequently, the numerical model is used to study the effect of repeated and equally spaced void inclusions on the vibro-acoustic response of the system.
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43.40.Fz Acoustic scattering by elastic structures
43.30.Jx Radiation from objects vibrating under water, acoustic and mechanical impedance
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Stress-dependent changes in the diffuse ultrasonic backscatter coefficient in steel: Experimental results

Christopher M. Kube, Hualong Du, Goutam Ghoshal, and Joseph A. Turner

J. Acoust. Soc. Am. Volume 132, Issue 1, pp. EL43-EL48 (2012); (6 pages)

Online Publication Date: 18 Jun 2012

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In this article, the effects of uniaxial compressive loading on the ultrasonic scattering from polycrystalline grains are shown for 10 MHz ultrasound in annealed, 1018 steel. The results show a decreasing value of the stress-dependent backscatter coefficient for normal incident ultrasound when the compression loading is perpendicular to the scattering direction. The change due to scattering is about 2 orders of magnitude greater than changes observed by others using ultrasonic wavespeed measurements. It is anticipated that this research can serve as the basis for many methods associated with nondestructive determination of stress in structural materials.
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43.35.Cg Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in solids; elastic constants
43.25.Ed Effect of nonlinearity on velocity and attenuation
43.35.Zc Use of ultrasonics in nondestructive testing, industrial processes, and industrial products
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Long-range time reversal communication in deep water: Experimental results

T. Shimura, Y. Watanabe, H. Ochi, and H. C. Song

J. Acoust. Soc. Am. Volume 132, Issue 1, pp. EL49-EL53 (2012); (5 pages)

Online Publication Date: 19 Jun 2012

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In December 2011 a long-range acoustic communication experiment was conducted in deep water, west of Izu-Ogasawara Islands, Japan. The experiment involved a stationary source (450–550 Hz) and an 18-element vertical array (102-m aperture), both deployed at around the sound channel axis. Initial analysis of data demonstrates that a data rate of 400 bits/s can be achieved over ∼600-km range in deep water using 16 quadrature amplitude modulation and passive time reversal equalization.
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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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Comparative investigation of elastic properties in a trabecula using micro-Brillouin scattering and scanning acoustic microscopy

Masahiko Kawabe, Kenji Fukui, Mami Matsukawa, Mathilde Granke, Amena Saïed, Quentin Grimal, and Pascal Laugier

J. Acoust. Soc. Am. Volume 132, Issue 1, pp. EL54-EL60 (2012); (7 pages)

Online Publication Date: 21 Jun 2012

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Micro-Brillouin scattering (μ-BR) and a 200 MHz scanning acoustic microscope (SAM) with similar spatial resolutions were applied to evaluate tissue elastic properties in two directions in a trabecula. Acoustic impedance measured by SAM was in the range of 5–9 Mrayl. Wave velocities determined by μ-BR were in the range of (4.75–5.11) × 103 m/s. Both exhibited a similar trend of variation across the trabecula and were significantly correlated (R2 = 0.63–0.67, p < 0.01). μ-BR is useful for the evaluation of tissue stiffness within a trabecula. Combined with SAM or nanoindentation, it can provide additional information to assess elastic anisotropy at the micro-scale.
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43.80.Cs Acoustical characteristics of biological media: molecular species, cellular level tissues
43.80.Ev Acoustical measurement methods in biological systems and media
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Detection of simultaneous modulation of interaural time and level differences: Effects of modulation rate and relative phase (L)

Shigeto Furukawa

J. Acoust. Soc. Am. Volume 132, Issue 1, pp. 1-4 (2012); (4 pages)

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The binaural system is known to be sluggish, i.e., unable to track modulations in interaural parameters even at a relatively slow rate. The present study evaluated the binaural system’s sensitivity to modulation phase rather than to modulation magnitude. The detectability of simultaneous modulations in interaural time and level differences with various relative phases were measured. It was found that for modulation rates up to 10–20 Hz, the detectability varied with the relative phase. This indicates that information about higher rates is lost at or below the level of cue integration.
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43.66.Pn Binaural hearing

Asynchronous multiuser underwater acoustic communications (L)

S. E. Cho, H. C. Song, and W. S. Hodgkiss

J. Acoust. Soc. Am. Volume 132, Issue 1, pp. 5-8 (2012); (4 pages) | Cited 1 time

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An asynchronous multiuser system is proposed to support multiple-access underwater communications without the use of code-division multiple-access or a feedback channel. The rich multipath channels experienced by spatially separated users will be sufficient to ensure separation of collided packets at the base station. The iterative receiver will employ a combination of adaptive time-reversal processing, matching pursuit, and successive interference cancellation in a block-wise fashion to achieve multiuser separability. Data collected during the KAM11 experiment are used to illustrate the system’s capability in a dynamic, time-varying environment.
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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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The impact of early reflections on binaural cues

Boris Gourévitch and Romain Brette

J. Acoust. Soc. Am. Volume 132, Issue 1, pp. 9-27 (2012); (19 pages)

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Animals live in cluttered auditory environments, where sounds arrive at the two ears through several paths. Reflections make sound localization difficult, and it is thought that the auditory system deals with this issue by isolating the first wavefront and suppressing later signals. However, in many situations, reflections arrive too early to be suppressed, for example, reflections from the ground in small animals. This paper examines the implications of these early reflections on binaural cues to sound localization, using realistic models of reflecting surfaces and a spherical model of diffraction by the head. The fusion of direct and reflected signals at each ear results in interference patterns in binaural cues as a function of frequency. These cues are maximally modified at frequencies related to the delay between direct and reflected signals, and therefore to the spatial location of the sound source. Thus, natural binaural cues differ from anechoic cues. In particular, the range of interaural time differences is substantially larger than in anechoic environments. Reflections may potentially contribute binaural cues to distance and polar angle when the properties of the reflecting surface are known and stable, for example, for reflections on the ground.
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43.20.El Reflection, refraction, diffraction of acoustic waves
43.66.Pn Binaural hearing
43.66.Qp Localization of sound sources
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Amplitude-dependent internal friction, hysteretic nonlinearity, and nonlinear oscillations in a magnesite resonator

V. E. Nazarov, A. B. Kolpakov, and A. V. Radostin

J. Acoust. Soc. Am. Volume 132, Issue 1, pp. 28-36 (2012); (9 pages)

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The results of experimental and theoretical studies of low-frequency nonlinear acoustics phenomena (amplitude-dependent loss, resonance frequency shifts, and a generation of second and third harmonics) in a magnesite rod resonator are presented. Acceleration and velocity oscillograms of vibrations of the free boundary of the resonator caused by harmonic excitations were measured and analyzed. A theoretical description of the observed amplitude dependences was carried out within the framework of the phenomenological state equations that contain either of the two types of hysteretic nonlinearity (elastic and inelastic). The type of hysteresis and parameters of acoustic nonlinearity of magnesite were established from comparing the experimental measurements with the theoretical dependences. The values of the parameters were anomalously high even when compared to those of other strongly nonlinear polycrystalline materials such as granite, marble, limestone, sandstone, etc.
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43.25.Ba Parameters of nonlinearity of the medium
43.25.Dc Nonlinear acoustics of solids
43.25.Ed Effect of nonlinearity on velocity and attenuation
43.25.Gf Standing waves; resonance

Collective bubble dynamics near a surface in a weak acoustic standing wave field

Xiaoyu Xi, Frederic Cegla, Robert Mettin, Frank Holsteyns, and Alexander Lippert

J. Acoust. Soc. Am. Volume 132, Issue 1, pp. 37-47 (2012); (11 pages)

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The transport of bubbles to a neighboring surface is very important in surface chemistry, bioengineering, and ultrasonic cleaning, etc. This paper proposes a multi-bubble transport method by using an acoustic standing wave field and establishes a model that explains the multi-bubble translation by expressing the balance between Bjerknes forces and hydrodynamic forces on a bubble in a liquid medium. Results indicated that the influence of primary Bjerknes force, secondary Bjerknes force, and buoyancy force on the bubble translation depends on the position of the target bubble in the acoustic field. Moreover, it was found that increasing the size of a bubble or pressure amplitude can accelerate the bubble motion and enhance the bubble-bubble interaction. The secondary Bjerknes force between two bubbles can switch from an attractive one when they oscillate in phase to a repulsive one when the bubble oscillations are out of phase. These findings provide an insight into the multi-bubble translation near a surface and can be applied to future bubble motion control studies, especially in drug delivery, sonoporation, and ultrasonic cleaning.
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43.25.Yw Nonlinear acoustics of bubbly liquids
43.20.Ks Standing waves, resonance, normal modes
43.35.Yb Ultrasonic instrumentation and measurement techniques
43.25.Qp Radiation pressure
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A relation between multipath group velocity, mode number, and ray cycle distance

Chris H. Harrison

J. Acoust. Soc. Am. Volume 132, Issue 1, pp. 48-55 (2012); (8 pages) | Cited 1 time

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Weston’s ray invariant or “characteristic time” in a range-dependent environment is exactly equivalent to the Wentzel–Kramers–Brillouin phase integral for ducted normal modes. By considering a ray element it is shown that the ray invariant can also be written in terms of ray cycle distance and cycle time. This leads to a useful formula for group velocity in terms of cycle distance and mode number. Drawing a distinction between the ray and wave interpretation, the Airy phase (i.e., the existence of a group velocity minimum) can be included in this approach. Favorable comparisons are made with group velocities derived from a normal mode model. The relationship is valid for variable sound speed and variable bathymetry, and this is demonstrated numerically. The formula is applicable to active sonar, multipath pulse shape, target signatures, reverberation, tomography, and underwater communications.
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43.30.Bp Normal mode propagation of sound in water
43.30.Cq Ray propagation of sound in water
43.30.Es Velocity, attenuation, refraction, and diffraction in water, Doppler effect
43.30.Vh Active sonar systems

Acoustic field and array response uncertainties in stratified ocean media

Thomas J. Hayward and Sagar Dhakal

J. Acoust. Soc. Am. Volume 132, Issue 1, pp. 56-68 (2012); (13 pages)

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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.
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43.30.Bp Normal mode propagation of sound in water
43.60.Fg Acoustic array systems and processing, beam-forming

Analysis of absorption performances of anechoic layers with steel plate backing

Hao Meng, Jihong Wen, Honggang Zhao, Linmei Lv, and Xisen Wen

J. Acoust. Soc. Am. Volume 132, Issue 1, pp. 69-75 (2012); (7 pages) | Cited 1 time

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Rubber layers with air-filled cavities or local resonance scatters can be used as anechoic coatings. A lot of researches have focused on the absorption mechanism of the anechoic coatings. As the anechoic coatings are bonded to the hull of submarine, the vibration of the hull should not be neglected when the analysis of the absorption characters is carried out. Therefore, it is more reasonable to treat the anechoic coating and the backing as a whole when the acoustic performance is analyzed. Considering the effects of the steel plate backing, the sound absorption performances on different models of anechoic coatings are investigated in this paper. The Finite Element Method is used to illustrate the vibrational behaviors of the anechoic coatings under the steel backings by which the displacement contours is obtained for analysis. The theoretical results show that an absorption peak is induced by the resonance of the steel slab and rubber layer. At the frequency of this absorption peak, the steel plate and the coating vibrates longitudinally like a mass-spring system in which the steel slab serves for mass and the coating layer is the spring. To illuminate the effects of the steel slab backing on the acoustic absorption, the thicknesses of the steel slab and the anechoic layer are discussed. Finally, an experiment is performed and the results show a good agreement with the theoretical analysis.
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43.30.Ky Structures and materials for absorbing sound in water; propagation in fluid-filled permeable material
43.20.Fn Scattering of acoustic waves

Shipping noise in whale habitat: Characteristics, sources, budget, and impact on belugas in Saguenay–St. Lawrence Marine Park hub

Cédric Gervaise, Yvan Simard, Nathalie Roy, Bazile Kinda, and Nadia Ménard

J. Acoust. Soc. Am. Volume 132, Issue 1, pp. 76-89 (2012); (14 pages) | Cited 1 time

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A continuous car ferry line crossing the Saguenay Fjord mouth and traffic from the local whale-watching fleet introduce high levels of shipping noise in the heart of the Saguenay–St. Lawrence Marine Park. To characterize this noise and examine its potential impact on belugas, a 4-hydrophone array was deployed in the area and continuously recorded for five weeks in May–June 2009. The source levels of the different vessel types showed little dependence on vessel size or speed increase. Their spectral range covered 33 dB. Lowest noise levels occurred at night, when ferry crossing pace was reduced, and daytime noise peaked during whale-watching tour departures and arrivals. Natural ambient noise prevailed 9.4% of the time. Ferry traffic added 30–35 dB to ambient levels above 1 kHz during crossings, which contributed 8 to 14 dB to hourly averages. The whale-watching fleet added up to 5.6 dB during peak hours. Assuming no behavioral or auditory compensation, half of the time, beluga potential communication range was reduced to less than ∼30% of its expected value under natural noise conditions, and to less than ∼15% for one quarter of the time, with little dependence on call frequency. The echolocation band for this population of belugas was also affected by the shipping noise.
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43.30.Nb Noise in water; generation mechanisms and characteristics of the field
43.50.Rq Environmental noise, measurement, analysis, statistical characteristics
43.80.Pe Agroacoustics

Compressive matched-field processing

William Mantzel, Justin Romberg, and Karim Sabra

J. Acoust. Soc. Am. Volume 132, Issue 1, pp. 90-102 (2012); (13 pages)

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Source localization by matched-field processing (MFP) generally involves solving a number of computationally intensive partial differential equations. This paper introduces a technique that mitigates this computational workload by “compressing” these computations. Drawing on key concepts from the recently developed field of compressed sensing, it shows how a low-dimensional proxy for the Green’s function can be constructed by backpropagating a small set of random receiver vectors. Then the source can be located by performing a number of “short” correlations between this proxy and the projection of the recorded acoustic data in the compressed space. Numerical experiments in a Pekeris ocean waveguide are presented that demonstrate that this compressed version of MFP is as effective as traditional MFP even when the compression is significant. The results are particularly promising in the broadband regime where using as few as two random backpropagations per frequency performs almost as well as the traditional broadband MFP but with the added benefit of generic applicability. That is, the computationally intensive backpropagations may be computed offline independently from the received signals, and may be reused to locate any source within the search grid area.
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43.30.Wi Passive sonar systems and algorithms, matched field processing in underwater acoustics
43.60.Jn Source localization and parameter estimation
43.60.Ek Acoustic signal coding, morphology, and transformation
43.60.Kx Matched field processing

Fiber-optic, cantilever-type acoustic motion velocity hydrophone

G. A. Cranch, G. A. Miller, and C. K. Kirkendall

J. Acoust. Soc. Am. Volume 132, Issue 1, pp. 103-114 (2012); (12 pages) | Cited 1 time

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The interaction between fluid loaded fiber-optic cantilevers and a low frequency acoustic wave is investigated as the basis for an acoustic vector sensor. The displacements of the prototype cantilevers are measured with an integrated fiber laser strain sensor. A theoretical model predicting the frequency dependent shape of acoustically driven planar and cylindrical fiber-optic cantilevers incorporating effects of fluid viscosity is presented. The model demonstrates good agreement with the measured response of two prototype cantilevers, characterized with a vibrating water column, in the regime of Re ≥ 1. The performance of each cantilever geometry is also analyzed. Factors affecting the sensor performance such as fluid viscosity, laser mode profile, and support motion are considered. The planar cantilever is shown to experience the largest acoustically induced force and hence the highest acoustic responsivity. However, the cylindrical cantilever exhibits the smoothest response in water, due to the influence of viscous fluid damping, and is capable of two axis particle velocity measurement. These cantilevers are shown to be capable of achieving acoustic resolutions approaching the lowest sea-state ocean noise.
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43.30.Yj Transducers and transducer arrays for underwater sound; transducer calibration
43.38.Ar Transducing principles, materials, and structures: general
43.38.Zp Acoustooptic and photoacoustic transducers
43.58.Wc Electrical and mechanical oscillators
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Scattering characteristics of Lamb waves from debondings at structural features in composite laminates

Ching-Tai Ng and Martin Veidt

J. Acoust. Soc. Am. Volume 132, Issue 1, pp. 115-123 (2012); (9 pages) | Cited 1 time

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This article investigates the scattering characteristics of Lamb waves from a debonding at a structural feature in a composite laminate. This study specifically focuses on the use of the low frequency fundamental antisymmetric (A0) Lamb wave as the incident wave for debonding detection. Three-dimensional finite element (FE) simulations and experimental measurements are used to investigate the scattering phenomena. Good agreement is obtained between the FE simulations and experimental results. Detailed parameter studies are carried out to further investigate the relationship between the scattering amplitudes and debonding sizes. The results show that the amplitude of the scattered A0 Lamb wave is sensitive to the debonding size, which indicates the potential of using the low frequency A0 Lamb wave as the interrogating wave for debonding detection and monitoring. The findings of the study provide improved physical insights into the scattering phenomena, which are important to further advance damage detection techniques and optimize transducer networks.
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43.35.Cg Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in solids; elastic constants
43.35.Zc Use of ultrasonics in nondestructive testing, industrial processes, and industrial products

Model for bubble pulsation in liquid between parallel viscoelastic layers

Todd A. Hay, Yurii A. Ilinskii, Evgenia A. Zabolotskaya, and Mark F. Hamilton

J. Acoust. Soc. Am. Volume 132, Issue 1, pp. 124-137 (2012); (14 pages) | Cited 1 time

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A model is presented for a pulsating spherical bubble positioned at a fixed location in a viscous, compressible liquid between parallel viscoelastic layers of finite thickness. The Green’s function for particle displacement is found and utilized to derive an expression for the radiation load imposed on the bubble by the layers. Although the radiation load is derived for linear harmonic motion it may be incorporated into an equation for the nonlinear radial dynamics of the bubble. This expression is valid if the strain magnitudes in the viscoelastic layer remain small. Dependence of bubble pulsation on the viscoelastic and geometric parameters of the layers is demonstrated through numerical simulations.
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43.35.Ei Acoustic cavitation in liquids
43.35.Mr Acoustics of viscoelastic materials

Radial and translational oscillations of an acoustically levitated bubble in aqueous ethanol solutions

Weicheng Cui, Weizhong Chen, Shuibao Qi, Chao Zhou, and Juan Tu

J. Acoust. Soc. Am. Volume 132, Issue 1, pp. 138-143 (2012); (6 pages)

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The radial and translational oscillations of a single cavitation bubble in a standing ultrasound wave were investigated experimentally at various driving acoustic pressures for aqueous ethanol solutions with different bulk molar fractions of ethanol range of 0–1.3×10−3. The results show that both the lower and upper stability thresholds of the acoustic driving pressure decreased as the concentration of ethanol was increased. At a given driving pressure the ambient and maximum bubble sizes increased with increasing ethanol concentration. In addition, as the ethanol was increased, the sonoluminescence intensity decreased while the bubble dynamics remained largely unchanged. The translational oscillation of the levitated bubble, however, became increasingly violent with increasing ethanol concentration. The displacement of the bubble reached 0.7 mm at the highest concentration studied (1.3×10−3) and the maximum bubble size was found to change as the bubble jumped up and down. This bubble translation may be responsible for the decrease of the acoustic driving pressure threshold and suggests that repetitive injection of ethanol molecules into the bubble takes place. These results may account for the different sensitivities of single bubble and multi-bubble sonoluminescence to the presence of volatile additives.
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43.35.Hl Sonoluminescence
43.35.Ei Acoustic cavitation in liquids

An acousto-optic beamformer

Antoni Torras-Rosell, Salvador Barrera-Figueroa, and Finn Jacobsen

J. Acoust. Soc. Am. Volume 132, Issue 1, pp. 144-149 (2012); (6 pages)

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There is a great variety of beamforming techniques that can be used for localization of sound sources. The differences among them usually lie in the array layout or in the specific signal processing algorithm used to compute the beamforming output. Any beamforming system consists of a finite number of transducers, which makes beamforming methods vulnerable to spatial aliasing above a certain frequency. The present work uses the acousto-optic effect, i.e., the interaction between sound and light, to localize sound sources in a plane. The use of a beam of light as the sensing element is equivalent to a continuous line aperture with an infinite number of microphones. This makes the proposed acousto-optic beamformer immune to spatial aliasing. This unique feature is illustrated by means of simulations and experimental results within the entire audible frequency range. For ease of comparison, the study is supplemented with measurements carried out with a line array of microphones.
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43.35.Sx Acoustooptical effects, optoacoustics, acoustical visualization, acoustical microscopy, and acoustical holography
43.60.Fg Acoustic array systems and processing, beam-forming

Frequency-radial duality based photoacoustic image reconstruction

S. M. Akramus Salehin and Thushara D. Abhayapala

J. Acoust. Soc. Am. Volume 132, Issue 1, pp. 150-161 (2012); (12 pages) | Cited 1 time

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Photoacoustic image reconstruction algorithms are usually slow due to the large sizes of data that are processed. This paper proposes a method for exact photoacoustic reconstruction for the spherical geometry in the limiting case of a continuous aperture and infinite measurement bandwidth that is faster than existing methods namely (1) backprojection method and (2) the Norton-Linzer method [S. J. Norton and M. Linzer, “Ultrasonic reflectivity imaging in three dimensions: Exact inverse scattering solution for plane, cylindrical and spherical apertures,” Biomedical Engineering, IEEE Trans. BME 28, 202–220 (1981)]. The initial pressure distribution is expanded using a spherical Fourier Bessel series. The proposed method estimates the Fourier Bessel coefficients and subsequently recovers the pressure distribution. A concept of frequency-radial duality is introduced that separates the information from the different radial basis functions by using frequencies corresponding to the Bessel zeros. This approach provides a means to analyze the information obtained given a measurement bandwidth. Using order analysis and numerical experiments, the proposed method is shown to be faster than both the backprojection and the Norton-Linzer methods. Further, the reconstructed images using the proposed methodology were of similar quality to the Norton-Linzer method and were better than the approximate backprojection method.
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43.35.Ud Thermoacoustics, high temperature acoustics, photoacoustic effect
43.60.Pt Signal processing techniques for acoustic inverse problems
43.60.Rw Remote sensing methods, acoustic tomography
43.60.Lq Acoustic imaging, displays, pattern recognition, feature extraction
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