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Journal of the Acoustical Society of America

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Mar 2009

Volume 125, Issue 3, pp. EL85-1845

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Steep and shallow phase gradient distortion product otoacoustic emissions arising basal to the primary tones

Glen K. Martin, Barden B. Stagner, Paul F. Fahey, and Brenda L. Lonsbury-Martin

J. Acoust. Soc. Am. Volume 125, Issue 3, pp. EL85-EL92 (2009); (8 pages) | Cited 8 times

Online Publication Date: 02 Feb 2009

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Distortion product otoacoustic emission (DPOAE) level/phase maps were collected in humans with and without an interference tone (IT) near the DPOAE frequency place (fdp) at primary-tone levels of 75 dB SPL. A DPOAE component with the expected steep phase gradient could be extracted at fdp, however, considerable vertical-phase banding, presumably indicative of reflection emissions, remained. An IT placed 0.33 oct above f2 removed most of this banding, revealing DPOAE components originating basal to the IT frequency place. These findings suggest that the commonly accepted two-source model of DPOAE generation may need to be qualified when higher primary-tone levels are utilized.
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43.64.Bt Models and theories of the auditory system
43.64.Jb Otoacoustic emissions
43.64.Kc Cochlear mechanics
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Adaptation to frozen babble in spoken word recognition

Robert Albert Felty, Adam Buchwald, and David B. Pisoni

J. Acoust. Soc. Am. Volume 125, Issue 3, pp. EL93-EL97 (2009); (5 pages) | Cited 1 time

Online Publication Date: 02 Feb 2009

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Previous research has shown that listeners can adapt to particular samples of noise, a phenomenon known as “frozen noise” [ Langhans and Kohlrausch, J. Acoust. Soc. Am. 91, 3456–3470 (1992) ]. However, no studies have reported a similar effect for multi-talker babble. The results of this study comparing open-set word recognition in multi-talker babble showed that listeners are significantly more accurate when the babble is fixed than when the babble is random. This documents the effect the authors refer to as “frozen babble.”
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43.71.Sy Spoken language processing by humans
43.72.Dv Speech-noise interaction
43.71.Gv Measures of speech perception (intelligibility and quality)
43.71.Es Vowel and consonant perception; perception of words, sentences, and fluent speech
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Effect of a competing instrument on melodic contour identification by cochlear implant users

John J. Galvin, III, Qian-Jie Fu, and Sandra I. Oba

J. Acoust. Soc. Am. Volume 125, Issue 3, pp. EL98-EL103 (2009); (6 pages) | Cited 5 times

Online Publication Date: 05 Feb 2009

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Cochlear implant (CI) users have limited access to fundamental frequency (F0) and timbre cues, which are needed to segregate competing voices and/or musical instruments. In the present study, CI users’ melodic contour identification was measured for three target instruments in the presence of a masker instrument; the F0 of the masker was varied relative to the target instruments. Mean CI performance significantly declined in the presence of the masker, while mean normal-hearing performance was largely unaffected. However, the most musically experienced CI users were able to make use of timbre and F0 differences between instruments.
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43.66.Ts Auditory prostheses, hearing aids
43.66.Jh Timbre, timbre in musical acoustics
43.66.Hg Pitch
43.75.Cd Music perception and cognition
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Investigation of four distinct glottal configurations in classical singing—A pilot study

Christian T. Herbst, Sten Ternström, and Jan G. Švec

J. Acoust. Soc. Am. Volume 125, Issue 3, pp. EL104-EL109 (2009); (6 pages) | Cited 6 times

Online Publication Date: 05 Feb 2009

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This study investigates four qualities of singing voice in a classically trained baritone: “naïve falsetto,” “countertenor falsetto,” “lyrical chest” and “full chest.” Laryngeal configuration and vocal fold behavior in these qualities were studied using laryngeal videostroboscopy, videokymography, electroglottography, and sound spectrography. The data suggest that the four voice qualities were produced by independently manipulating mainly two laryngeal parameters: (1) the adduction of the arytenoid cartilages and (2) the thickening of the vocal folds. An independent control of the posterior adductory muscles versus the vocalis muscle is considered to be the physiological basis for achieving these singing voice qualities.
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43.75.Rs Singing
43.72.Ar Speech analysis and analysis techniques; parametric representation of speech
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Contribution of very low amplitude-modulation rates to intelligibility in a competing-speech task

Christian Füllgrabe, Michael A. Stone, and Brian C. J. Moore

J. Acoust. Soc. Am. Volume 125, Issue 3, pp. 1277-1280 (2009); (4 pages) | Cited 1 time

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It is generally agreed that the slow fluctuations in the envelope of speech in different spectral channels carry critical information for intelligibility. Previous studies in which amplitude modulation (AM) was selectively removed from the speech signal showed that modulation rates between 4 and 16 Hz are most important, and that rates falling outside this range contribute little or not at all to speech intelligibility. The present study investigated the role of very low (<4 Hz) AM rates in the ability to identify sentences in an interfering background talker. The mixture was processed through a noise vocoder. The depth of AM with rates below 4, 1.3, or 0.4 Hz was reduced using a multi-channel envelope compressor with a high compression ratio. Data obtained using nine normal-hearing listeners demonstrate that low-rate AM, in the range 0.4–4 Hz, contributes to the intelligibility of relatively long speech utterances, at least for adverse listening conditions in which background noise is present and listeners are forced to rely on envelope cues in a few spectral channels.
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43.66.Mk Temporal and sequential aspects of hearing; auditory grouping in relation to music
43.71.Sy Spoken language processing by humans
43.71.Es Vowel and consonant perception; perception of words, sentences, and fluent speech

A multi-rate decay model to predict energy-based acoustic parameters in churches

Francesco Martellotta

J. Acoust. Soc. Am. Volume 125, Issue 3, pp. 1281-1284 (2009); (4 pages) | Cited 7 times

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Multi-rate decays are sometimes observed in room acoustics, appearing when markedly different volumes are coupled together and resulting in nonlinear decay curves. Such behavior appears in several churches at the very beginning of the decay process, although in conditions which cannot be explicitly referred to as coupling phenomena. Consequently, multi-rate exponential decays may be suitable to model energy distribution in this group of buildings, providing a more elegant and easily applicable set of equations in place of a previously defined “linear” model, used to adapt Barron’s revised theory. The paper shows that the multi-rate approach ensures ease of calculation, without significant loss in accuracy in predicting energy-based acoustic parameters.
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43.55.Br Room acoustics: theory and experiment; reverberation, normal modes, diffusion, transient and steady-state response
43.55.Gx Studies of existing auditoria and enclosures
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An investigation of Rubens flame tube resonances

Michael D. Gardner, Kent L. Gee, and Gordon Dix

J. Acoust. Soc. Am. Volume 125, Issue 3, pp. 1285-1292 (2009); (8 pages) | Cited 2 times

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The Rubens flame tube is a century-old teaching demonstration that allows observers to visualize acoustic standing wave behavior [ H. Rubens and O. Krigar-Menzel, (1905). Ann. Phys. 17, 149–164 ]. Flammable gas inside the tube flows through holes drilled along the top, and flames are then lit above. The tube is closed at one end and driven with a loudspeaker at the other end. When the tube is driven at one of its resonance frequencies, flames form a visual standing wave pattern as they vary in height according to the pressure amplitude in the tube. Although the basic performance of the tube has been explained [ G. Ficken and C. Stephenson, (1979). Phys. Teach. 17, 306–310 ], this paper discusses a previously unreported characteristic of the tube: a shift of the tube’s resonance frequencies away from those predicted by simple introductory physics. Results from an equivalent circuit model of the tube and agreement between experiments and the model suggest that the shift is caused by the presence of the holes. For teachers and educators seeking to better understand and explain the tube to students, this article serves as a resource regarding the basic phenomena affecting the behavior of the tube.
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43.10.Sv Education in acoustics, tutorial papers of interest to acoustics educators
43.20.Ks Standing waves, resonance, normal modes
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Two-dimensional wave propagation in an elastic half-space with quadratic nonlinearity: A numerical study

Sebastian Küchler, Thomas Meurer, Laurence J. Jacobs, and Jianmin Qu

J. Acoust. Soc. Am. Volume 125, Issue 3, pp. 1293-1301 (2009); (9 pages) | Cited 3 times

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This study investigates two-dimensional wave propagation in an elastic half-space with quadratic nonlinearity. The problem is formulated as a hyperbolic system of conservation laws, which is solved numerically using a semi-discrete central scheme. These numerical results are then analyzed in the frequency domain to interpret the nonlinear effects, specifically the excitation of higher-order harmonics. To quantify and compare the nonlinearity of different materials, a new parameter is introduced, which is similar to the acoustic nonlinearity parameter β for one-dimensional longitudinal waves. By using this new parameter, it is found that the nonlinear effects of a material depend on the point of observation in the half-space, both the angle and the distance to the excitation source. Furthermore it is illustrated that the third-order elastic constants have a linear effect on the acoustic nonlinearity of a material.
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43.25.Dc Nonlinear acoustics of solids
43.25.Ba Parameters of nonlinearity of the medium
43.35.Cg Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in solids; elastic constants

Nonlinear nonclassical elasticity applied to the analysis of low frequency flexural vibrations: Theory and experiments

Ignacio Tinao Perez-Miravete, Cleofé Campos-Pozuelo, and Angel Perea

J. Acoust. Soc. Am. Volume 125, Issue 3, pp. 1302-1309 (2009); (8 pages) | Cited 2 times

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Motivated by the increasing interest on nonlinear nondestructive damage detection, a comparison of the nonlinear elastic behavior of damaged samples and their intact state is presented. Flexural vibration is induced in thin glass plates with laser thermal shock induced micro-cracks by means of two thin piezo-ceramic patches glued in a bimorph configuration. The cases of direct excitation of a resonance and excitation of an internal resonance cases are considered. The resulting nonlinear vibrations exhibit the main features of quadratic hysteresis: linear variation of the resonance frequency and quadratic production of the third harmonic. A theoretical model for nonlinear resonant flexural vibrations based on the Preisach–Mayergoyz constitutive relations is proposed for damage quantification. Experimental comparison between the intact and damaged sample indicates an increase in the relevant nonlinearity parameter, indicating a widening of the hysteresis loop due to damage.
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43.25.Dc Nonlinear acoustics of solids
43.25.Gf Standing waves; resonance
43.25.Ts Nonlinear acoustical and dynamical systems

Nonlinear frequency shifts in acoustical resonators with varying cross sections

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

J. Acoust. Soc. Am. Volume 125, Issue 3, pp. 1310-1318 (2009); (9 pages) | Cited 2 times

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The frequency response and nonlinear resonance frequency shift of an acoustical resonator with losses and having a varying cross section were investigated previously using Lagrangian mechanics and perturbation for resonator shapes that are close to cylindrical [ M. F. Hamilton, et al., J. Acoust. Soc. Am. 110, 109–119 (2001) ]. The same approach is extended here to include resonators having any shape for which the Webster horn equation is a valid model in the linear approximation. Admissible shapes include cones and bulbs proposed for acoustical compressors. The approach is appropriate for approximate but rapid parameter estimations for resonators with complicated shapes, requiring far less computation time than for direct numerical solution of the one-dimensional model equation frequently used for such resonators [ Ilinskii et al., J. Acoust. Soc. Am. 104, 2664–2674 (1998) ]. Results for cone and bulb shaped resonators with losses are compared with results from the direct numerical solution. The direction of the resonance frequency shift is determined by the efficiency of second-harmonic generation in modes having natural frequencies below versus above the frequency of the second harmonic, and how the net effect of this coupling compares with the frequency shifts due to cubic nonlinearity and static deformation.
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43.25.Gf Standing waves; resonance

Acoustic microstreaming around an isolated encapsulated microbubble

Xiaozhou Liu and Junru Wu

J. Acoust. Soc. Am. Volume 125, Issue 3, pp. 1319-1330 (2009); (12 pages) | Cited 4 times

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An analytical theory has been developed to calculate microstreaming velocity inside and outside an encapsulated microbubble (EMB) in a viscous liquid produced by its oscillations driven by an ultrasound field, taking account of two predominant modes of the EMB’s motion: a monopole (pulsation) and a dipole (translational harmonic vibrations). Analytical expressions of radial as well as tangential stresses are derived near the shell of the EMB. Numerical calculations in parameter regimes applicable to sonoporation are presented. For the calculation the following parameters unless specified otherwise are used: f = 1 MHz, r0 = 2 μm, κ = 1.4, ρL = 1000 kg/m3, ρs = 1100 kg/m3, P0 = 100 kPa, μs = 0.05 Pa s, μL = 0.001 Pa s, σ1 = 0.04 N/m, σ2 = 0.005 N/m, and Gs = 15 MPa. The calculated results show that the streaming velocity and stresses near an EMB are functions of the mechanical properties of shell and gas. Overall, the streaming velocity and stresses for an EMB are found to be greater than those for a similar size free bubble under the same ultrasound excitation. This finding is consistent with the existing theory of acoustic streaming of an oscillating bubble near a boundary given by Nyborg (1958) [J. Acoust. Soc. Am. 30, 329–339 ].
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43.25.Nm Acoustic streaming
43.25.Yw Nonlinear acoustics of bubbly liquids

Model of coupled pulsation and translation of a gas bubble and rigid particle

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

J. Acoust. Soc. Am. Volume 125, Issue 3, pp. 1331-1339 (2009); (9 pages) | Cited 5 times

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A model of the interaction of a spherical gas bubble and a rigid spherical particle is derived as a coupled system of second-order differential equations using Lagrangian mechanics. The model accounts for pulsation and translation of the bubble as well as translation of the particle in an infinite, incompressible liquid. The model derived here is accurate to order R5/d5, where R is a characteristic radius and d is the separation distance between the bubble and particle. This order is the minimum accuracy required to account for the interaction of the bubble and particle. Dependence on the size and density of the particle is demonstrated through numerical integration of the dynamical equations for both the free and forced response of the system. Numerical results are presented for models accurate to orders higher than R5/d5 to demonstrate the consequences of truncating the equations at order R5/d5.
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43.25.Yw Nonlinear acoustics of bubbly liquids
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An analytical model for turbulence scattered rays in the shadow zone for outdoor sound propagation calculation

Yiu Wai Lam

J. Acoust. Soc. Am. Volume 125, Issue 3, pp. 1340-1350 (2009); (11 pages) | Cited 1 time

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In outdoor sound propagation, an inherent problem of the ray tracing method is its inability to determine the sound pressure level in the shadow zone, where geometrical rays do not penetrate. This is a serious problem in a turbulent atmosphere where significant sound energy will be scattered into the shadow. Empirical corrections that are determined from measurements or numerical simulations are limited to situations within the bounds of the empirical corrections. This paper describes a different approach where the ray tracing model is modified analytically into a scattered ray model. Rays are first diffracted from the shadow boundary, which is determined by the geometrical ray paths. The diffracted rays are then scattered by turbulence in their way to the receiver. The amount of scatter is determined from turbulence statistics that are determined from a Gaussian turbulence model. Most of the statistics are determined analytically except one element, which is determined empirically from numerical simulations. This turbulence scattered ray model is shown to have good accuracy against calculations based on the parabolic equation, and against previously published measurement data. It was found that the agreement is good both with and without turbulence, at distance up to 2 km from the shadow boundary.
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43.28.Gq Outdoor sound propagation and scattering in a turbulent atmosphere, and in non-uniform flow fields
43.28.Js Numerical models for outdoor propagation
43.50.Vt Topographical and meteorological factors in noise propagation

Flow-structure-acoustic interaction in a human voice model

Stefan Becker, Stefan Kniesburges, Stefan Müller, Antonio Delgado, Gerhard Link, Manfred Kaltenbacher, and Michael Döllinger

J. Acoust. Soc. Am. Volume 125, Issue 3, pp. 1351-1361 (2009); (11 pages) | Cited 18 times

Online Publication Date: 04 Mar 2009

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For the investigation of the physical processes of human phonation, inhomogeneous synthetic vocal folds were developed to represent the full fluid-structure-acoustic coupling. They consisted of polyurethane rubber with a stiffness in the range of human vocal folds and were mounted in a channel, shaped like the vocal tract in the supraglottal region. This test facility permitted extensive observations of flow-induced vocal fold vibrations, the periodic flow field, and the acoustic signals in the far field of the channel. Detailed measurements were performed applying particle-image velocimetry, a laser-scanning vibrometer, a microphone, unsteady pressure sensors, and a hot-wire probe, with the aim of identifying the physical mechanisms in human phonation. The results support the existence of the Coanda effect during phonation, with the flow attaching to one vocal fold and separating from the other. This behavior is not linked to one vocal fold and changes stochastically from cycle to cycle. The oscillating flow field generates a tonal sound. The broadband noise is presumed to be caused by the interaction of the asymmetric flow with the downstream-facing surfaces of the vocal folds, analogous to trailing-edge noise.
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43.28.Ra Generation of sound by fluid flow, aerodynamic sound and turbulence
43.72.Ar Speech analysis and analysis techniques; parametric representation of speech
43.50.Nm Aerodynamic and jet noise
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Ray-based description of normal modes in a deep ocean acoustic waveguide

A. L. Virovlyansky, A. Yu. Kazarova, and L. Ya. Lyubavin

J. Acoust. Soc. Am. Volume 125, Issue 3, pp. 1362-1373 (2009); (12 pages) | Cited 3 times

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Modal structure of the wave field in a deep ocean environment with sound speed fluctuations induced by random internal waves is considered. An approximate analytical description of the modal structure at megameter ranges is derived by combining two known results: (i) relations expressing mode amplitudes through parameters of ray paths and (ii) stochastic ray theory. For a monochromatic wave field, a simple analytical estimate has been obtained for a coarse-grained distribution of acoustic energy between normal modes. Significant attention has been paid to the investigation of the mode pulses, that is, sound pulses carried by individual modes. Analytical estimates for the spread of mode pulse and bias of its mean travel time in the presence of internal waves are derived.
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43.30.Bp Normal mode propagation of sound in water

Prediction of acoustic radiation from axisymmetric surfaces with arbitrary boundary conditions using the boundary element method on a distributed computing system

Louise Wright, Stephen P. Robinson, and Victor F. Humphrey

J. Acoust. Soc. Am. Volume 125, Issue 3, pp. 1374-1383 (2009); (10 pages) | Cited 1 time

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This paper presents a computational technique using the boundary element method for prediction of radiated acoustic waves from axisymmetric surfaces with nonaxisymmetric boundary conditions. The aim is to predict the far-field behavior of underwater acoustic transducers based on their measured behavior in the near-field. The technique is valid for all wavenumbers and uses a volume integral method to calculate the singular integrals required by the boundary element formulation. The technique has been implemented on a distributed computing system to take advantage of its parallel nature, which has led to significant reductions in the time required to generate results. Measurement data generated by a pair of free-flooding underwater acoustic transducers encapsulated in a polyurethane polymer have been used to validate the technique against experiment. The dimensions of the outer surface of the transducers (including the polymer coating) were an outer diameter of 98 mm with an 18 mm wall thickness and a length of 92 mm. The transducers were mounted coaxially, giving an overall length of 185 mm. The cylinders had resonance frequencies at 13.9 and 27.5 kHz, and the data were gathered at these frequencies.
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43.30.Jx Radiation from objects vibrating under water, acoustic and mechanical impedance
43.58.Ta Computers and computer programs in acoustics
43.58.Vb Calibration of acoustical devices and systems
43.30.Xm Underwater measurement and calibration instrumentation and procedures

Use of acoustic navigation signals for simultaneous localization and sound-speed estimation

E. K. Skarsoulis and G. S. Piperakis

J. Acoust. Soc. Am. Volume 125, Issue 3, pp. 1384-1393 (2009); (10 pages) | Cited 1 time

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The possibility of exploiting low-resolution acoustic signals used for the navigation of Lagrangian floats to simultaneously estimate the speed of sound is studied. Acoustic navigation of Lagrangian floats is regularly carried out by measuring travel times from three fixed stations assuming a known value for the speed of sound. The sound speed is considered here as a variable of the problem to be estimated from the travel-time data simultaneously with the horizontal location of the float. The estimation problem is linearized and solved analytically, and closed-form expressions for the sound-speed estimation errors are derived. Typical acoustic navigation (RAFOS) signals are characterized by limited time resolution (0.2 s) challenging the accuracy of sound-speed estimation, depending on the location of the float with respect to the fixed stations. By exploiting travel-time data from multiple floats, the sound-speed estimation accuracy can be increased, which reflects in higher localization accuracy as well. In the case of a single float improved sound-speed estimates and localization results can be obtained by combining travel-time data from different float locations. Numerical results verify the theoretical error estimates and demonstrate the efficiency of the method.
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43.30.Pc Ocean parameter estimation by acoustical methods; remote sensing; imaging, inversion, acoustic tomography
43.60.Jn Source localization and parameter estimation

Measurements of three-dimensional propagation in a continental shelf environment

Kevin D. Heaney and James J. Murray

J. Acoust. Soc. Am. Volume 125, Issue 3, pp. 1394-1402 (2009); (9 pages) | Cited 6 times

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Although a significant amount of theoretical and numerical modeling effort has been put into the study of three-dimensional (3D) acoustic propagation on a coastal wedge, including the development of the ASA 3D benchmark problem set, there have been few observations of the predicted 3D propagation effects. Significant horizontal multipath arrivals were observed in a pair of acoustic transmission tests on the continental shelf off the east coast of Florida in September 2007 and February 2008. For many transmissions, arrivals were received coming from nearly the global positioning system (GPS) bearing of the ship, as well as up to 30 deg inshore of the true bearing. The inshore path was up to 25 dB stronger than the direct path in some cases. The experimental waveforms transmitted included continuous-wave transmissions ranging in frequency from 24 to 415 Hz as well as wideband linear frequency modulation pulses (20–420 Hz). Horizontal multipath arrivals were observed for source ranges from 10 to 80 km, source depths of 20 and 100 m, and along several different bearings (inshore and along the 250 m isobath). It is a conclusion of this paper that the bearing bias and multiple horizontal arrivals are the result of 3D propagation due to the local shoaling bathymetry.
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43.30.Xm Underwater measurement and calibration instrumentation and procedures
43.30.Bp Normal mode propagation of sound in water
43.30.Cq Ray propagation of sound in water

Array element localization using ship noise

Michael G. Morley, Stan E. Dosso, and N. Ross Chapman

J. Acoust. Soc. Am. Volume 125, Issue 3, pp. 1403-1409 (2009); (7 pages) | Cited 1 time

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This paper describes a method of estimating hydrophone positions in a receiver array using the noise from a passing ship. Relative arrival times of the ship-noise signal between pairs of hydrophones are obtained from several time windows of data (corresponding to different ship locations) by cross-correlating the band-pass filtered time series. The relative arrival times are used as data in an array element localization inversion to estimate both the hydrophone and ship locations based on iterated linearization of the acoustic ray equations. The inversion applies the method of regularization to include prior information such as approximate location estimates and uncertainties for the source and receivers and the expectation that the array shape and∕or source tracks are smooth functions of position. Linearized and nonlinear (Monte Carlo) estimates of the position errors are in good agreement and indicate a high degree of confidence in the receiver positions (relative uncertainties of approximately 0.2 m in the horizontal and 0.05–0.1 m in the vertical). The ability to improve upon the initial source position estimates depends on the geometry of the problem, as investigated with simulations.
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43.30.Xm Underwater measurement and calibration instrumentation and procedures
43.60.Pt Signal processing techniques for acoustic inverse problems
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Chirp excitation technique to enhance microbubble displacement induced by ultrasound radiation force

Yi Hu, Dong Zhang, Hairong Zheng, and Xiufen Gong

J. Acoust. Soc. Am. Volume 125, Issue 3, pp. 1410-1415 (2009); (6 pages) | Cited 2 times

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Ultrasound radiation force has been proposed to increase the targeting efficiency in ultrasonic molecular imaging and drug delivery. A chirp excitation technique is proposed to increase the radiation force induced microbubble displacement and might potentially be used for enhancing the targeting efficiency of microbubble clouds. In this study, a modified Rayleigh–Plesset equation is used to estimate the radius-time behavior of insonified microbubbles, and the translation of insonified microbubbles is calculated by using the particle trajectory equation. Simulations demonstrate that the chirp excitation is superior to the sinusoidal one in displacing microbubbles with a wide-size distribution, and that the performance is dependent on the parameters of the chirp signal such as the center frequency and frequency range. For Gaussian size distributed microbubble clouds with mean diameter of 3.5 μm and variance of 1, a 2.25 MHz chirp with frequency range of 1.5 MHz induces about 59.59% more microbubbles over a distance of 10 μm during 200 μs insonification, compared to a 2.25 MHz sinusoidal excitation with equal acoustic pressure.
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43.35.Mr Acoustics of viscoelastic materials
43.35.Wa Biological effects of ultrasound, ultrasonic tomography

Acoustic field in a quasi-spherical resonator: Unified perturbation model

Cécile Guianvarc’h, Laurent Pitre, Michel Bruneau, and Anne-Marie Bruneau

J. Acoust. Soc. Am. Volume 125, Issue 3, pp. 1416-1425 (2009); (10 pages) | Cited 3 times

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Gas-filled quasi-spherical resonators are excellent tools for the measurement of thermophysical properties of gas and have also been retained for the determination of the Boltzmann constant with a low uncertainty, which can be derived from measurements of both the speed of sound in a noble gas and the volume of the resonator. To achieve this, a detailed modeling of the acoustic field in quasi-spherical resonators is of importance. Several phenomena and perturbations must be taken into account, including, among inertia and compressibility, heat conduction, viscosity, the shape of the resonator, small irregularities on the wall, and so on. The aim of this paper is to provide improvements to the current models of the acoustic field in such resonator. Namely, the model given here takes into account all the different perturbing elements together in a unique formalism, including the coupling between the different perturbing elements and the resulting modal coupling in a consistent manner. The first results obtained from this analytical model on a simple configuration show that the effect of modal coupling is small but should not be neglected regarding the accuracy required here, even if several improvements could still be provided to this new unified model.
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43.35.Ud Thermoacoustics, high temperature acoustics, photoacoustic effect
43.20.Ks Standing waves, resonance, normal modes

Photoacoustic tomography with a single detector in a reverberant cavity

B. T. Cox and P. C. Beard

J. Acoust. Soc. Am. Volume 125, Issue 3, pp. 1426-1436 (2009); (11 pages) | Cited 2 times

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In conventional biomedical photoacoustic tomography (PAT), ultrasonic pulses generated through the absorption of nanosecond pulses of near-infrared light are recorded over an array of detectors and used to recover an image of the initial acoustic pressure distribution within soft tissue. This image is related to the tissue optical coefficients and therefore carries information about the tissue physiology. For high resolution imaging, a large-area detector array with a high density of small, sensitive elements is required. Such arrays can be expensive, so reverberant-field PAT has been suggested as a means of obtaining PAT images using arrays with a smaller number of detectors. By recording the reflections from an acoustically reverberant cavity surrounding the sample, in addition to the primary acoustic pulse, sufficient information may be captured to allow an image to be reconstructed without the need for a large-area array. An initial study using two-dimensional simulations was performed to assess the feasibility of using a single detector for PAT. It is shown that reverberant-field data recorded at a single detector are sufficient to reconstruct the initial pressure distribution accurately, so long as the shape of the reverberant cavity makes it ray-chaotic. The practicalities of such an approach to photoacoustic imaging are discussed.
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43.35.Ud Thermoacoustics, high temperature acoustics, photoacoustic effect
43.20.Ks Standing waves, resonance, normal modes
43.60.Pt Signal processing techniques for acoustic inverse problems
43.28.We Measurement methods and instrumentation for remote sensing and for inverse problems

Laser ultrasonic inspection of the microstructural state of thin metal foils

O. Balogun, R. Huber, D. Chinn, and J. B. Spicer

J. Acoust. Soc. Am. Volume 125, Issue 3, pp. 1437-1443 (2009); (7 pages) | Cited 1 time

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A laser-based ultrasonic technique suitable for characterization of the microstructural state of metal foils is presented. The technique relies on the measurement of the intrinsic attenuation of laser-generated longitudinal waves at frequencies reaching 1 GHz resulting from ultrasonic interaction with the sample microstructure. In order to facilitate accurate measurement of the attenuation, a theoretical model-based signal analysis approach is used. The signal analysis approach isolates aspects of the measured attenuation that depend strictly on the microstructure from geometrical effects. Experimental results obtained in commercially cold worked tungsten foils show excellent agreement with theoretical predictions. Furthermore, the experimental results show that the longitudinal wave attenuation at gigahertz frequencies is strongly influenced by the dislocation content of the foils and may find potential application in the characterization of the microstructure of micron thick metal foils.
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43.35.Zc Use of ultrasonics in nondestructive testing, industrial processes, and industrial products
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On-axis and far-field sound radiation from resilient flat and dome-shaped radiators

Ronald M. Aarts and Augustus J. E. M. Janssen

J. Acoust. Soc. Am. Volume 125, Issue 3, pp. 1444-1455 (2009); (12 pages) | Cited 5 times

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On-axis and far-field series expansions are developed for the sound pressure due to an arbitrary, circular symmetric velocity distribution on a flat radiator in an infinite baffle. These expansions are obtained by expanding the velocity distributions in terms of orthogonal polynomials R2n0(σ/a) = Pn(2(σ/a)2−1) with Pn the Legendre polynomials. The terms R2n0 give rise to a closed-form expression for the pressure on-axis as well as for the far-field pressure. Furthermore, for a large number of velocity profiles, including those associated with the rigid piston, the simply supported radiator, and the clamped radiators as well as Gaussian radiators, there are closed-form expressions for the required expansion coefficients. In particular, for the rigid, simply supported, and clamped radiators, this results in explicit finite-series expressions for both the on-axis and far-field pressures. In the reverse direction, a method of estimating velocity distributions from (measured) on-axis pressures by matching in terms of expansion coefficients is proposed. Together with the forward far-field computation scheme, this yields a method for far-field loudspeaker assessment from on-axis data (generalized Keele scheme). The forward computation scheme is extended to dome-shaped radiators with arbitrary velocity distributions.
Show PACS
43.38.Ar Transducing principles, materials, and structures: general
43.20.Bi Mathematical theory of wave propagation
43.40.At Experimental and theoretical studies of vibrating systems
43.20.Px Transient radiation and scattering

Effect of electrical circuits on duration of an acoustic pulse radiated by a piezoplate

S. I. Konovalov and A. G. Kuz’menko

J. Acoust. Soc. Am. Volume 125, Issue 3, pp. 1456-1460 (2009); (5 pages) | Cited 2 times

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By means of numerical computation, pulse mode of a piezoelectric radiator in the form of a plate, loaded with a liquid and connected to R-L circuits in various combinations, is investigated. The computations were carried out having taken into account the internal resistance of the electric generator. Numerical results, based on the theory, are provided for examples of parallel and series circuits connected to a piezoelectric plate. The optimal values of parameters are determined, providing minimal duration of radiated acoustic pulses.
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43.38.Yn Impulse transducers
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