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Journal of the Acoustical Society of America

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Dec 2010

Volume 128, Issue 6, pp. EL355-3830

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Sex-related differences in vocal responses to pitch feedback perturbations during sustained vocalization

Zhaocong Chen, Peng Liu, Jeffery A. Jones, Dongfeng Huang, and Hanjun Liu

J. Acoust. Soc. Am. Volume 128, Issue 6, pp. EL355-EL360 (2010); (6 pages)

Online Publication Date: 06 Dec 2010

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The present study assessed the effect of sex on voice fundamental frequency (F0) responses to pitch feedback perturbations during sustained vocalization. Sixty-four native-Mandarin speakers heard their voice pitch feedback shifted at ±50, ±100, or ±200 cents for 200 ms, five times during each vocalization. The results showed that, as compared to female speakers, male speakers produced significantly larger but slower vocal responses to the pitch-shifted stimuli. These findings reveal a modulation of vocal response as a function of sex, and suggest that there may be a differential processing of vocal pitch feedback perturbations between men and women.
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43.70.Bk Models and theories of speech production
43.72.Ar Speech analysis and analysis techniques; parametric representation of speech

Improved space time prewhitener for linear frequency modulation reverberation using fractional Fourier transform

Ruhang Wang, Jianguo Huang, Tian Ma, and Qunfei Zhang

J. Acoust. Soc. Am. Volume 128, Issue 6, pp. EL361-EL365 (2010); (5 pages)

Online Publication Date: 06 Dec 2010

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This letter presents an improved space time prewhitening method for linear frequency modulation (LFM) reverberation. The proposed method transforms the reverberation to fractional Fourier domain to whiten using fractional Fourier transform. The linear varying frequency in LFM reverberation is focused on a stationary frequency, and the adjacent block signal is used as the reference signal of prewhitening. Finally, experiment results with real reverberation data verify that the proposed method improves the detection performance of active sonar in shallow sea significantly.
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43.30.Vh Active sonar systems
43.60.Gk Space-time signal processing, other than matched field processing
43.60.Hj Time-frequency signal processing, wavelets

A representation for Green’s function retrieval by multidimensional deconvolution

Kees Wapenaar and Joost van der Neut

J. Acoust. Soc. Am. Volume 128, Issue 6, pp. EL366-EL371 (2010); (6 pages) | Cited 6 times

Online Publication Date: 06 Dec 2010

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Green’s function retrieval by crosscorrelation may suffer from irregularities in the source distribution, asymmetric illumination, intrinsic losses, etc. Multidimensional deconvolution (MDD) may overcome these limitations. A unified representation for Green’s function retrieval by MDD is proposed. From this representation, it follows that the traditional crosscorrelation method gives a Green’s function of which the source is smeared in space and time. This smearing is quantified by a space–time point-spread function (PSF), which can be retrieved from measurements at an array of receivers. MDD removes this PSF and thus deblurs and deghosts the source of the Green’s function obtained by correlation.
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43.60.Ac Theory of acoustic signal processing
43.60.Tj Wave front reconstruction, acoustic time-reversal, and phase conjugation

Long-range multi-carrier acoustic communications in shallow water based on iterative sparse channel estimation

Taehyuk Kang, H. C. Song, W. S. Hodgkiss, and Jea Soo Kim

J. Acoust. Soc. Am. Volume 128, Issue 6, pp. EL372-EL377 (2010); (6 pages)

Online Publication Date: 06 Dec 2010

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Long-range orthogonal frequency division multiplexing (OFDM) acoustic communications is demonstrated using data from the Kauai Acomms MURI 2008 (KAM08) experiment carried out in about 106 m deep shallow water west of Kauai, HI, in June 2008. The source bandwidth was 8 kHz (12–20 kHz), and the data were received by a 16-element vertical array at a distance of 8 km. Iterative sparse channel estimation is applied in conjunction with low-density parity-check decoding. In addition, the impact of diversity combining in a highly inhomogeneous underwater environment is investigated. Error-free transmission using 16-quadtrative amplitude modulation is achieved at a data rate of 10 kb/s.
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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

On the acoustical relevance of supraglottal flow structures to low-frequency voice production

Zhaoyan Zhang and Juergen Neubauer

J. Acoust. Soc. Am. Volume 128, Issue 6, pp. EL378-EL383 (2010); (6 pages)

Online Publication Date: 06 Dec 2010

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The supraglottal flow exhibits many complex phenomena such as recirculation, jet instabilities, jet attachment to one vocal fold wall, jet flapping, and transition to turbulence. The acoustical relevance of these flow structures to low-frequency voice production was evaluated by disturbing the supraglottal flow field using a cylinder and observing the consequence on the resulting sound pressure field. Despite a significantly altered supraglottal flow field due to the presence of the cylinder, only small changes in sound pressure amplitude and spectral shape were observed. The implications of the results on our understanding of phonation physics and modeling of phonation are discussed.
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43.70.Bk Models and theories of speech production
43.72.Ar Speech analysis and analysis techniques; parametric representation of speech

The use of frequency resolution in echolocation for modeling three dimensional environments

Benjamin D. Huebschman

J. Acoust. Soc. Am. Volume 128, Issue 6, pp. EL384-EL389 (2010); (6 pages)

Online Publication Date: 10 Dec 2010

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Bats use echolocation to navigate three dimensional obstacles while locating, identifying, and engaging targets. A theory is offered of image processing during the search and navigation phase of echolocation that uses Doppler frequency shifts. The information in frequency changes across the angle of elevation can be used to generate a three dimensional model of the environment when combined with the timing and the relative amplitude of the returned signals. The mathematics of frequency shifts for an emitter traveling at a large fraction of the velocity of propagation (c) is presented. Reported behavior that can be explained by this phenomenon is discussed.
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43.60.Lq Acoustic imaging, displays, pattern recognition, feature extraction
43.28.Py Interaction of fluid motion and sound, Doppler effect, and sound in flow ducts
43.60.Vx Acoustic sensing and acquisition
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A binaural beat constructed from a noise (L)

Michael A. Akeroyd

J. Acoust. Soc. Am. Volume 128, Issue 6, pp. 3301-3304 (2010); (4 pages)

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The binaural beat has been used for over 100 years as a stimulus for generating the percept of motion. Classically the beat consists of a pure tone at one ear (e.g., 500 Hz) and the same pure tone at the other ear but shifted upward or downward in frequency (e.g., 501 Hz). An experiment and binaural computational analysis are reported which demonstrate that a more powerful motion percept can be obtained by applying the concept of the frequency shift to a noise, via an upward or downward shift in the frequency of the Fourier components of its spectrum.
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43.66.Pn Binaural hearing
43.66.Qp Localization of sound sources
43.66.Nm Phase effects

Ultrasonic airborne insertion loss measurements at normal incidence (L)

Jayrin Farley and Brian E. Anderson

J. Acoust. Soc. Am. Volume 128, Issue 6, pp. 3305-3307 (2010); (3 pages) | Cited 1 time

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Transmission loss and insertion loss measurements of building materials at audible frequencies are commonly made using plane wave tubes or as a panel between reverberant rooms. These measurements provide information for noise isolation control in architectural acoustics and in product development. Airborne ultrasonic sound transmission through common building materials has not been fully explored. Technologies and products that utilize ultrasonic frequencies are becoming increasingly more common, hence the need to conduct such measurements. This letter presents preliminary measurements of the ultrasonic insertion loss levels for common building materials over a frequency range of 28–90 kHz using continuous-wave excitation.
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43.55.Rg Sound transmission through walls and through ducts: theory and measurement
43.35.Zc Use of ultrasonics in nondestructive testing, industrial processes, and industrial products
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A mode matching method for modeling dissipative silencers lined with poroelastic materials and containing mean flow

Benoit Nennig, Emmanuel Perrey-Debain, and Mabrouk Ben Tahar

J. Acoust. Soc. Am. Volume 128, Issue 6, pp. 3308-3320 (2010); (13 pages) | Cited 3 times

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A mode matching method for predicting the transmission loss of a cylindrical shaped dissipative silencer partially filled with a poroelastic foam is developed. The model takes into account the solid phase elasticity of the sound-absorbing material, the mounting conditions of the foam, and the presence of a uniform mean flow in the central airway. The novelty of the proposed approach lies in the fact that guided modes of the silencer have a composite nature containing both compressional and shear waves as opposed to classical mode matching methods in which only acoustic pressure waves are present. Results presented demonstrate good agreement with finite element calculations provided a sufficient number of modes are retained. In practice, it is found that the time for computing the transmission loss over a large frequency range takes a few minutes on a personal computer. This makes the present method a reliable tool for tackling dissipative silencers lined with poroelastic materials.
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43.20.Mv Waveguides, wave propagation in tubes and ducts
43.28.Py Interaction of fluid motion and sound, Doppler effect, and sound in flow ducts
43.50.Gf Noise control at source: redesign, application of absorptive materials and reactive elements, mufflers, noise silencers, noise barriers, and attenuators, etc.
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Nonlinear propagation of spark-generated N-waves in air: Modeling and measurements using acoustical and optical methods

Petr Yuldashev, Sébastien Ollivier, Mikhail Averiyanov, Oleg Sapozhnikov, Vera Khokhlova, and Philippe Blanc-Benon

J. Acoust. Soc. Am. Volume 128, Issue 6, pp. 3321-3333 (2010); (13 pages) | Cited 1 time

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The propagation of nonlinear spherically diverging N-waves in homogeneous air is studied experimentally and theoretically. A spark source is used to generate high amplitude (1.4 kPa) short duration (40 μs) N-waves; acoustic measurements are performed using microphones (3 mm diameter, 150 kHz bandwidth). Numerical modeling with the generalized Burgers equation is used to reveal the relative effects of acoustic nonlinearity, thermoviscous absorption, and oxygen and nitrogen relaxation on the wave propagation. The results of modeling are in a good agreement with the measurements in respect to the wave amplitude and duration. However, the measured rise time of the front shock is ten times longer than the calculated one, which is attributed to the limited bandwidth of the microphone. To better resolve the shock thickness, a focused shadowgraphy technique is used. The recorded optical shadowgrams are compared with shadow patterns predicted by geometrical optics and scalar diffraction model of light propagation. It is shown that the geometrical optics approximation results in overestimation of the shock rise time, while the diffraction model allows to correctly resolve the shock width. A combination of microphone measurements and focused optical shadowgraphy is therefore a reliable way of studying evolution of spark-generated shock waves in air.
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43.25.Cb Macrosonic propagation, finite amplitude sound; shock waves
43.25.Zx Measurement methods and instrumentation for nonlinear acoustics
43.28.Mw Shock and blast waves, sonic boom
43.28.Js Numerical models for outdoor propagation

On the third- and fourth-order constants of incompressible isotropic elasticity

Michel Destrade and Raymond W. Ogden

J. Acoust. Soc. Am. Volume 128, Issue 6, pp. 3334-3343 (2010); (10 pages)

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Consider the constitutive law for an isotropic elastic solid with the strain-energy function expanded up to the fourth order in the strain and the stress up to the third order in the strain. The stress–strain relation can then be inverted to give the strain in terms of the stress with a view to considering the incompressible limit. For this purpose, use of the logarithmic strain tensor is of particular value. It enables the limiting values of all nine fourth-order elastic constants in the incompressible limit to be evaluated precisely and rigorously. In particular, it is explained why the three constants of fourth-order incompressible elasticity μ, math, and math are of the same order of magnitude. Several examples of application of the results follow, including determination of the acoustoelastic coefficients in incompressible solids and the limiting values of the coefficients of nonlinearity for elastic wave propagation.
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43.25.Dc Nonlinear acoustics of solids
43.25.Ed Effect of nonlinearity on velocity and attenuation
43.25.Fe Effect of nonlinearity on acoustic surface waves
43.25.Ba Parameters of nonlinearity of the medium

Dynamic acoustoelastic testing of weakly pre-loaded unconsolidated water-saturated glass beads

Guillaume Renaud, Samuel Callé, and Marielle Defontaine

J. Acoust. Soc. Am. Volume 128, Issue 6, pp. 3344-3354 (2010); (11 pages)

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Dynamic acoustoelastic testing is applied to weakly pre-loaded unconsolidated water-saturated glass beads. The gravitational acceleration produces, on the probed beads, a static stress of order 130 Pa, thus the granular medium is close to the jamming transition. A low-frequency (LF) acoustic wave gently disturbs the medium, inducing successively slight expansion and compaction of the granular packing expected to modulate the number of contacts between beads. Ultrasound (US) pulses are emitted simultaneously to dynamically detect the induced modification of the granular skeleton. US propagation velocity and attenuation both increase when the LF pressure increases. The quadratic nonlinear elastic parameter β, related to the pressure dependence of US propagation velocity, was measured in the range 60–530 if water-saturated glass beads are considered as an effective medium. A dynamic modification of US scattering induced by beads is proposed to modulate US attenuation. Complex hysteretic behaviors and tension-compression asymmetry are also observed and analyzed by time-domain and spectral analyses. Furthermore acoustic nonlinearities are measured in cases of quasi-static and dynamic variations of the LF wave amplitude, providing quantitatively similar acoustic nonlinearities but qualitatively different.
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43.25.Ed Effect of nonlinearity on velocity and attenuation
43.25.Zx Measurement methods and instrumentation for nonlinear acoustics
43.20.Hq Velocity and attenuation of acoustic waves
43.25.Ba Parameters of nonlinearity of the medium

Minimum radiation force target size for power measurements in focused ultrasonic fields with circular symmetry

K. Beissner

J. Acoust. Soc. Am. Volume 128, Issue 6, pp. 3355-3362 (2010); (8 pages)

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The time-averaged ultrasonic power emitted by medical ultrasonic equipment is mostly measured using a radiation force balance, and the question of the necessary target size is of practical importance. The question is answered here by calculations based on a Rayleigh integral algorithm for fields from circular, focusing transducers. This case occurs particularly in the field of high-intensity therapeutic ultrasound. The calculation yields the necessary size of an absorbing target so that the radiation force is 98% of that exerted on an absorber of infinite lateral size, and this as a function of the transducer-to-target distance, of the transducer radius in comparison with the wavelength and of the focus (half-)angle. Several distributions of the transducer vibration amplitude are considered. The Rayleigh integral strictly applies only to planar transducers, but among the amplitude distributions there is also one that allows the simulation of the spherically curved transducer type often found in practice.
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43.25.Qp Radiation pressure
43.80.Vj Acoustical medical instrumentation and measurement techniques
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Series expansions of rotating two and three dimensional sound fields

M. A. Poletti

J. Acoust. Soc. Am. Volume 128, Issue 6, pp. 3363-3374 (2010); (12 pages)

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The cylindrical and spherical harmonic expansions of oscillating sound fields rotating at a constant rate are derived. These expansions are a generalized form of the stationary sound field expansions. The derivations are based on the representation of interior and exterior sound fields using the simple source approach and determination of the simple source solutions with uniform rotation. Numerical simulations of rotating sound fields are presented to verify the theory.
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43.28.Py Interaction of fluid motion and sound, Doppler effect, and sound in flow ducts
43.25.Cb Macrosonic propagation, finite amplitude sound; shock waves
43.28.Mw Shock and blast waves, sonic boom
43.20.Bi Mathematical theory of wave propagation

Series expansion for the sound field of a ring source

Michael J. Carley

J. Acoust. Soc. Am. Volume 128, Issue 6, pp. 3375-3380 (2010); (6 pages)

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An exact series expansion for the field radiated by a monopole ring source with angular variation in source strength is derived from a previously developed expression for the field from a finite disk. The derived series can be used throughout the field, via the use of a reciprocity relation, and can be readily integrated to find the field radiated by arbitrary circular sources of finite extent, and differentiated to find the field due to higher order sources such as dipoles and quadrupoles.
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43.28.Ra Generation of sound by fluid flow, aerodynamic sound and turbulence
43.40.Yq Instrumentation and techniques for tests and measurement relating to shock and vibration, including vibration pickups, indicators, and generators, mechanical impedance
43.20.Rz Steady-state radiation from sources, impedance, radiation patterns, boundary element methods
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The effects of external acoustic pressure fields on a free-running supercavitating projectile

Peter J. K. Cameron, Peter H. Rogers, and John W. Doane

J. Acoust. Soc. Am. Volume 128, Issue 6, pp. 3381-3392 (2010); (12 pages) | Cited 1 time

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Proliferation of supercavitating torpedoes has motivated research on countermeasures against them as well as on the fluid phenomenon which makes them possible. The goal of this research was to investigate an envisaged countermeasure, an acoustic field capable of slowing or diverting the weapon by disrupting the cavitation envelope. The research focused on the interactions between high pressure amplitude sound waves and a supercavity produced by a small free-flying projectile. The flight dynamics and cavity geometry measurements were compared to control experiments and theoretical considerations were made for evaluating the effects. Corrugations on the cavity/water interface caused by the pressure signal have been observed and characterized. Results also show that the accuracy of a supercavitating projectile can be adversely affected by the sound signal. This research concludes with results that indicate that it is acoustic cavitation in the medium surrounding the supercavity, caused by the high pressure amplitude sound, that is responsible for the reduced accuracy. A hypothesis has been presented addressing the means by which the acoustic cavitation could cause this effect.
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43.30.Lz Underwater applications of nonlinear acoustics; explosions
43.35.Ty Other physical effects of sound
43.35.Ei Acoustic cavitation in liquids
43.25.Yw Nonlinear acoustics of bubbly liquids

Trans-dimensional geoacoustic inversion

Jan Dettmer, Stan E. Dosso, and Charles W. Holland

J. Acoust. Soc. Am. Volume 128, Issue 6, pp. 3393-3405 (2010); (13 pages) | Cited 1 time

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This paper develops a general trans-dimensional Bayesian methodology for geoacoustic inversion. Trans-dimensional inverse problems are a generalization of fixed-dimensional inversion that includes the number and type of model parameters as unknowns in the problem. By extending the inversion state space to multiple subspaces of different dimensions, the posterior probability density quantifies the state of knowledge regarding inversion parameters, including effects due to limited knowledge about appropriate parametrization of the environment and error processes. The inversion is implemented here using a reversible-jump Markov chain Monte Carlo algorithm and the seabed is parametrized using a partition model. Unknown data errors are addressed by including a data-error model. Jumps between dimensions are implemented with a birth–death methodology that allows transitions between dimensions by adding or removing interfaces while maintaining detailed balance in the Markov chain. Trans-dimensional inversion results in an inherently parsimonious solution while partition modeling provides a naturally self-regularizing algorithm based on data information content, not on subjective regularization functions. Together, this results in environmental estimates that quantify appropriate seabed structure as supported by the data, allowing sharp discontinuities while approximating smooth transitions where needed. This approach applies generally to geoacoustic inversion and is illustrated here with seabed reflection-coefficient data.
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43.30.Pc Ocean parameter estimation by acoustical methods; remote sensing; imaging, inversion, acoustic tomography
43.30.Ma Acoustics of sediments; ice covers, viscoelastic media; seismic underwater acoustics
43.60.Pt Signal processing techniques for acoustic inverse problems

Bayesian evidence computation for model selection in non-linear geoacoustic inference problems

Jan Dettmer, Stan E. Dosso, and John C. Osler

J. Acoust. Soc. Am. Volume 128, Issue 6, pp. 3406-3415 (2010); (10 pages)

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This paper applies a general Bayesian inference approach, based on Bayesian evidence computation, to geoacoustic inversion of interface-wave dispersion data. Quantitative model selection is carried out by computing the evidence (normalizing constants) for several model parameterizations using annealed importance sampling. The resulting posterior probability density estimate is compared to estimates obtained from Metropolis–Hastings sampling to ensure consistent results. The approach is applied to invert interface-wave dispersion data collected on the Scotian Shelf, off the east coast of Canada for the sediment shear-wave velocity profile. Results are consistent with previous work on these data but extend the analysis to a rigorous approach including model selection and uncertainty analysis. The results are also consistent with core samples and seismic reflection measurements carried out in the area.
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43.30.Pc Ocean parameter estimation by acoustical methods; remote sensing; imaging, inversion, acoustic tomography
43.60.Pt Signal processing techniques for acoustic inverse problems
43.30.Ma Acoustics of sediments; ice covers, viscoelastic media; seismic underwater acoustics

Source motion detection, estimation, and compensation for underwater acoustics inversion by wideband ambiguity lag-Doppler filtering

Nicolas F. Josso, Cornel Ioana, Jérôme I. Mars, and Cédric Gervaise

J. Acoust. Soc. Am. Volume 128, Issue 6, pp. 3416-3425 (2010); (10 pages)

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Acoustic channel properties in a shallow water environment with moving source and receiver are difficult to investigate. In fact, when the source-receiver relative position changes, the underwater environment causes multipath and Doppler scale changes on the transmitted signal over low-to-medium frequencies (300 Hz–20 kHz). This is the result of a combination of multiple paths propagation, source and receiver motions, as well as sea surface motion or water column fast changes. This paper investigates underwater acoustic channel properties in a shallow water (up to 150 m depth) and moving source-receiver conditions using extracted time-scale features of the propagation channel model for low-to-medium frequencies. An average impulse response of one transmission is estimated using the physical characteristics of propagation and the wideband ambiguity plane. Since a different Doppler scale should be considered for each propagating signal, a time-warping filtering method is proposed to estimate the channel time delay and Doppler scale attributes for each propagating path. The proposed method enables the estimation of motion-compensated impulse responses, where different Doppler scaling factors are considered for the different time delays. It was validated for channel profiles using real data from the BASE’07 experiment conducted by the North Atlantic Treaty Organization Undersea Research Center in the shallow water environment of the Malta Plateau, South Sicily. This paper provides a contribution to many field applications including passive ocean tomography with unknown natural sources position and movement. Another example is active ocean tomography where sources motion enables to rapidly cover one operational area for rapid environmental assessment and hydrophones may be drifting in order to avoid additional flow noise.
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43.30.Pc Ocean parameter estimation by acoustical methods; remote sensing; imaging, inversion, acoustic tomography
43.60.Mn Adaptive processing
43.60.Pt Signal processing techniques for acoustic inverse problems
43.30.Cq Ray propagation of sound in water
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Linearized forward and inverse problems of the resonant ultrasound spectroscopy for the evaluation of thin surface layers

Michal Růžek, Petr Sedlák, Hanuš Seiner, Alena Kruisová, and Michal Landa

J. Acoust. Soc. Am. Volume 128, Issue 6, pp. 3426-3437 (2010); (12 pages) | Cited 1 time

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In this paper, linearized approximations of both the forward and the inverse problems of resonant ultrasound spectroscopy for the determination of mechanical properties of thin surface layers are presented. The linear relations between the frequency shifts induced by the deposition of the layer and the in-plane elastic coefficients of the layer are derived and inverted, the applicability range of the obtained linear model is discussed by a comparison with nonlinear models and finite element method (FEM), and an algorithm for the estimation of experimental errors in the inversely determined elastic coefficients is described. In the final part of the paper, the linearized inverse procedure is applied to evaluate elastic coefficients of a 310 nm thick diamond-like carbon layer deposited on a silicon substrate.
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43.35.Cg Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in solids; elastic constants
43.35.Ns Acoustical properties of thin films
43.40.At Experimental and theoretical studies of vibrating systems

Low Mach number analysis of idealized thermoacoustic engines with numerical solution

Omar Hireche, Catherine Weisman, Diana Baltean-Carlès, Patrick Le Quéré, and Luc Bauwens

J. Acoust. Soc. Am. Volume 128, Issue 6, pp. 3438-3448 (2010); (11 pages)

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A model of an idealized thermoacoustic engine is formulated, coupling nonlinear flow and heat exchange in the heat exchangers and stack with a simple linear acoustic model of the resonator and load. Correct coupling results in an asymptotically consistent global model, in the small Mach number approximation. A well-resolved numerical solution is obtained for two-dimensional heat exchangers and stack. The model assumes that the heat exchangers and stack are shorter than the overall length by a factor of the order of a representative Mach number. The model is well-suited for simulation of the entire startup process, whereby as a result of some excitation, an initially specified temperature profile in the stack evolves toward a near-steady profile, eventually reaching stationary operation. A validation analysis is presented, together with results showing the early amplitude growth and approach of a stationary regime. Two types of initial excitation are used: Random noise and a small periodic wave. The set of assumptions made leads to a heat-exchanger section that acts as a source of volume but is transparent to pressure and to a local heat-exchanger model characterized by a dynamically incompressible flow to which a locally spatially uniform acoustic pressure fluctuation is superimposed.
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43.35.Ud Thermoacoustics, high temperature acoustics, photoacoustic effect

Diffuse ultrasonic backscatter at normal incidence through a curved interface

Goutam Ghoshal and Joseph A. Turner

J. Acoust. Soc. Am. Volume 128, Issue 6, pp. 3449-3458 (2010); (10 pages)

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Diffuse ultrasonic backscatter techniques are useful for probing heterogeneous materials to extract microstructural parameters and detect flaws which cannot be detected by conventional ultrasonic techniques. Such experiments, usually done using a modified pulse-echo technique, utilize the spatial variance of the signals as a primary measure of microstructure. Quantitative ultrasonic scattering models include components of both transducer beams as well as microstructural scattering information. Of particular interest for interpretation of many experiments is the propagation through a liquid–solid interface. Here, a recent single-scattering model is expanded to include components needed for comparison with experiments. In particular, the Wigner distribution of the displacement profile is derived to model the beam pattern of an ultrasonic transducer through a curved liquid-solid interface. A simple Gaussian beam is used to model the transducer beam pattern. This expression is then used in conjunction with an appropriate scattering operator to complete the derivation. The theory developed is then compared with experimental results for a fine-grained steel using both a planar and a cylindrical interface. These results are anticipated to impact ultrasonic nondestructive evaluation and characterization of heterogeneous media with arbitrary curvatures.
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43.35.Yb Ultrasonic instrumentation and measurement techniques
43.20.Bi Mathematical theory of wave propagation
43.20.Gp Reflection, refraction, diffraction, interference, and scattering of elastic and poroelastic waves
43.35.Cg Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in solids; elastic constants
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Dynamic behavior of the circular membrane of an electrostatic microphone: Effect of holes in the backing electrode

Thomas Lavergne, Stéphane Durand, Michel Bruneau, Nicolas Joly, and Dominique Rodrigues

J. Acoust. Soc. Am. Volume 128, Issue 6, pp. 3459-3477 (2010); (19 pages) | Cited 1 time

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Today, several applications require using electrostatic microphones in environments and/or in frequency ranges, which are significantly different from those they were designed for. When low uncertainties on the behavior of acoustic fields, generated or measured by these transducers, are required, the displacement field of the diaphragm of the transducers (which can be highly nonuniform in the highest frequency range) must be characterized with an appropriate accuracy. An analytical approach, which leads to results depending on the location of the holes in the backing electrode (i.e., depending on the azimuthal coordinate) not available until now (regarding the displacement field of the membrane in the highest frequency range, up to 100 kHz), is presented here. The holes and the slit surrounding the electrode are considered as localized sources described by their volume velocity in the propagation equation governing the pressure field in the air gap (not by nonuniform boundary conditions on the surface of the backing electrode as usual). Experimental results, obtained from measurements of the displacement field of the membrane using a laser scanning vibrometer, are presented and compared to the theoretical results.
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43.38.Bs Electrostatic transducers
43.38.Kb Microphones and their calibration

Theoretical and experimental analysis of the electromechanical behavior of a compact spherical loudspeaker array for directivity control

Alexander Mattioli Pasqual, Philippe Herzog, and José Roberto de França Arruda

J. Acoust. Soc. Am. Volume 128, Issue 6, pp. 3478-3488 (2010); (11 pages) | Cited 1 time

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Sound directivity control is made possible by a compact array of independent loudspeakers operating at the same frequency range. The drivers are usually distributed over a sphere-like frame according to a Platonic solid geometry to obtain a highly symmetrical configuration. The radiation pattern of spherical loudspeaker arrays has been predicted from the surface velocity pattern by approximating the drivers membranes as rigid vibrating spherical caps, although a rigorous assessment of this model has not been provided so far. Many aspects concerning compact array electromechanics remain unclear, such as the effects on the acoustical performance of the drivers interaction inside the array cavity, or the fact that voltages rather than velocities are controlled in practice. This work presents a detailed investigation of the electromechanical behavior of spherical loudspeaker arrays. Simulation results are shown to agree with laser vibrometer measurements and experimental sound power data obtained for a 12-driver spherical array prototype at low frequencies, whereas the non-rigid body motion and the first cavity eigenfrequency yield a discrepancy between theoretical and experimental results at high frequencies. Finally, although the internal acoustic coupling affects the drivers vibration in the low-frequency range, it does not play an important role on the radiated sound power.
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43.38.Hz Transducer arrays, acoustic interaction effects in arrays
43.38.Dv Electromagnetic and electrodynamic transducers
43.60.Fg Acoustic array systems and processing, beam-forming

Pulse mode of operation of a spherical piezoceramic transducer filled with liquid and having a correcting electric circuit

S. I. Konovalov and A. G. Kuz’menko

J. Acoust. Soc. Am. Volume 128, Issue 6, pp. 3489-3495 (2010); (7 pages)

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By means of a computational method, the possibility of radiating a short acoustic pulse by a transducer in the form of a piezoceramic sphere internally filled with liquid is investigated. An electric inductive–resistive circuit is connected to the electric input of the transducer. Solution is obtained based on scheme-analogs theory for piezoceramic transducers, and spectral Fourier transform theory. The values of parameters of the system, providing minimal durations of radiated signals, are determined. Computation was carried out for different values of relative thicknesses of the transducer wall. The estimates of durations and amplitudes of the acoustic signals radiated into the external medium are obtained.
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43.38.Yn Impulse transducers
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