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Journal of the Acoustical Society of America

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Sep 2011

Volume 130, Issue 3, pp. 1091-1781

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Quasi-Gaussian beam analytical basis and comparison with an alternative approach (L)

Philip L. Marston

J. Acoust. Soc. Am. Volume 130, Issue 3, pp. 1091-1094 (2011); (4 pages)

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A superposition of propagating Bessel beams was recently numerically demonstrated to approximate a Gaussian beam and was used to evaluate the scattering by a sphere centered on the focal point of the beam. An analytical beam synthesis used in optics by Agrawal and Pattanayak [J. Opt. Soc. Am. 69, 575–578 (1979)] is found here to be recovered as the weak focusing limit of the quasi-Gaussian beam when evanescent contributions are omitted from the analytical synthesis. The propagating-wave part of the analytical synthesis has similarities to, and differences from, the recent quasi-Gaussian approximation.
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43.35.Bf Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in liquids, liquid crystals, suspensions, and emulsions
43.20.Bi Mathematical theory of wave propagation
43.30.Gv Backscattering, echoes, and reverberation in water due to combinations of boundaries
43.20.Fn Scattering of acoustic waves

Beamforming with a circular array of microphones mounted on a rigid sphere (L)

Elisabet Tiana-Roig, Finn Jacobsen, and Efren Fernandez-Grande

J. Acoust. Soc. Am. Volume 130, Issue 3, pp. 1095-1098 (2011); (4 pages)

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Beamforming with uniform circular microphone arrays can be used for localizing sound sources over 360∘. Typically, the array microphones are suspended in free space or they are mounted on a solid cylinder. However, the cylinder is often considered to be infinitely long because the scattering problem has no exact solution for a finite cylinder. Alternatively one can use a solid sphere. This investigation compares the performance of a circular array mounded on a rigid sphere with that of such an array in free space and mounted on an infinite cylinder, using computer simulations. The examined techniques are delay-and-sum and circular harmonics beamforming, and the results are validated experimentally.
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43.60.Fg Acoustic array systems and processing, beam-forming

The impact of reverberant self-masking and overlap-masking effects on speech intelligibility by cochlear implant listeners (L)

Kostas Kokkinakis and Philipos C. Loizou

J. Acoust. Soc. Am. Volume 130, Issue 3, pp. 1099-1102 (2011); (4 pages) | Cited 2 times

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The purpose of this study is to determine the relative impact of reverberant self-masking and overlap-masking effects on speech intelligibility by cochlear implant listeners. Sentences were presented in two conditions wherein reverberant consonant segments were replaced with clean consonants, and in another condition wherein reverberant vowel segments were replaced with clean vowels. The underlying assumption is that self-masking effects would dominate in the first condition, whereas overlap-masking effects would dominate in the second condition. Results indicated that the degradation of speech intelligibility in reverberant conditions is caused primarily by self-masking effects that give rise to flattened formant transitions.
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43.71.Ky Speech perception by the hearing impaired
43.66.Ts Auditory prostheses, hearing aids
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Fast asymptotic solutions for sound fields above and below a rigid porous ground

Kai Ming Li and Sheng Liu

J. Acoust. Soc. Am. Volume 130, Issue 3, pp. 1103-1114 (2011); (12 pages)

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The current study simultaneously addresses the problem of reflection and refraction of sound from a rigid porous ground surface. A more rigorous approach is used to derive more accurate asymptotic solutions that can be cast in a convenient form for ease of numerical implementations. The solutions provide means for rapid computations of the sound fields above and below the rigid porous ground. The improved asymptotic formulas for both situations agree well with numerical results obtained by other numerical schemes, which are more accurate but computationally more intensive. More importantly, the asymptotic solutions can be written in the well-known form of the Weyl–van der Pol formula, which provides a direct correlation between the reflected wave term for the sound field above the porous ground and the transmitted (refracted) wave term for the sound field below.
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43.20.El Reflection, refraction, diffraction of acoustic waves
43.28.En Interaction of sound with ground surfaces, ground cover and topography, acoustic impedance of outdoor surfaces
43.28.Hr Outdoor sound sources
43.28.Fp Outdoor sound propagation through a stationary atmosphere, meteorological factors
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On the use of Gegenbauer reconstructions for shock wave propagation modeling

Yun Jing and Greg T. Clement

J. Acoust. Soc. Am. Volume 130, Issue 3, pp. 1115-1124 (2011); (10 pages)

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In therapeutic ultrasound, the presence of shock waves can be significant due to the use of high intensity beams, as well as due to shock formation during inertial cavitation. Although modeling of such strongly nonlinear waves can be carried out using spectral methods, such calculations are typically considered impractical, since accurate calculations often require hundreds or even thousands of harmonics to be considered, leading to prohibitive computational times. Instead, time-domain algorithms which generally utilize Godunov-type finite-difference schemes are commonly used. Although these time domain methods can accurately model steep shock wave fronts, unlike spectral methods they are inherently unsuitable for modeling realistic tissue dispersion relations. Motivated by the need for a more general model, the use of Gegenbauer reconstructions as a postprocess tool to resolve the band-limitations of the spectral methods are investigated. The present work focuses on eliminating the Gibbs phenomenon when representing a steep wave front using a limited number of harmonics. Both plane wave and axisymmetric 2D transducer problems will be presented to characterize the proposed method.
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43.25.Cb Macrosonic propagation, finite amplitude sound; shock waves
43.25.Jh Reflection, refraction, interference, scattering, and diffraction of intense sound waves

Nonlinear acoustic wave equations with fractional loss operators

Fabrice Prieur and Sverre Holm

J. Acoust. Soc. Am. Volume 130, Issue 3, pp. 1125-1132 (2011); (8 pages) | Cited 2 times

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Fractional derivatives are well suited to describe wave propagation in complex media. When introduced in classical wave equations, they allow a modeling of attenuation and dispersion that better describes sound propagation in biological tissues. Traditional constitutive equations from solid mechanics and heat conduction are modified using fractional derivatives. They are used to derive a nonlinear wave equation which describes attenuation and dispersion laws that match observations. This wave equation is a generalization of the Westervelt equation, and also leads to a fractional version of the Khokhlov–Zabolotskaya–Kuznetsov and Burgers’ equations.
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43.25.Dc Nonlinear acoustics of solids
43.20.Bi Mathematical theory of wave propagation
43.35.Cg Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in solids; elastic constants
43.35.Mr Acoustics of viscoelastic materials

Generalized response of a sphere embedded in a viscoelastic medium excited by an ultrasonic radiation force

Matthew W. Urban, Ivan Z. Nenadic, Scott A. Mitchell, Shigao Chen, and James F. Greenleaf

J. Acoust. Soc. Am. Volume 130, Issue 3, pp. 1133-1141 (2011); (9 pages)

Online Publication Date: 02 Sep 2011

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The response of an embedded sphere in a viscoelastic medium excited by acoustic radiation force has been studied in both the time- and frequency-domains. This model is important because it can be used to characterize the viscoelastic properties of the medium by fitting the response to the theoretical model. The Kelvin–Voigt model has been used exclusively in these models. An extension to the previously reported models is described so that any viscoelastic rheological model can be used. This theoretical development describes the generalized embedded sphere response both in the time and frequency domains. Comparing the results from derivations in both domains showed very good agreement with a median absolute error (MAE) ranging from 0.0044 to 0.0072. Good agreement is demonstrated with finite element model simulations and the theory with a MAE of 0.006. Lastly, results for characterization of gelatin and rubber materials with the new theory are shown where the MAE values were used to determine which rheological model best describes the measured responses.
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43.25.Qp Radiation pressure
43.35.Mr Acoustics of viscoelastic materials
43.35.Yb Ultrasonic instrumentation and measurement techniques
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Sound, infrasound, and sonic boom absorption by atmospheric clouds

Michaël Baudoin, François Coulouvrat, and Jean-Louis Thomas

J. Acoust. Soc. Am. Volume 130, Issue 3, pp. 1142-1153 (2011); (12 pages)

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This study quantifies the influence of atmospheric clouds on propagation of sound and infrasound, based on an existing model [Gubaidulin and Nigmatulin, Int. J. Multiphase Flow 26, 207–228 (2000)]. Clouds are considered as a dilute and polydisperse suspension of liquid water droplets within a mixture of dry air and water vapor, both considered as perfect gases. The model is limited to low and medium altitude clouds, with a small ice content. Four physical mechanisms are taken into account: viscoinertial effects, heat transfer, water phase changes (evaporation and condensation), and vapor diffusion. Physical properties of atmospheric clouds (altitude, thickness, water content and droplet size distribution) are collected, along with values of the thermodynamical coefficients. Different types of clouds have been selected. Quantitative evaluation shows that, for low audible and infrasound frequencies, absorption within clouds is several orders of magnitude larger than classical absorption. The importance of phase changes and vapor diffusion is outlined. Finally, numerical simulations for nonlinear propagation of sonic booms indicate that, for thick clouds, attenuation can lead to a very large decay of the boom at the ground level.
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43.28.Bj Mechanisms affecting sound propagation in air, sound speed in the air
43.28.Dm Infrasound and acoustic-gravity waves
43.20.Hq Velocity and attenuation of acoustic waves
43.28.Mw Shock and blast waves, sonic boom

In situ calibration of atmospheric-infrasound sensors including the effects of wind-noise-reduction pipe systems

Thomas B. Gabrielson

J. Acoust. Soc. Am. Volume 130, Issue 3, pp. 1154-1163 (2011); (10 pages)

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A worldwide network of more than 40 infrasound monitoring stations has been established as part of the effort to ensure compliance with the Comprehensive Nuclear Test Ban Treaty. Each station has four to eight individual infrasound elements in a kilometer-scale array for detection and bearing determination of acoustic events. The frequency range of interest covers a three-decade range—roughly from 0.01 to 10 Hz. A typical infrasound array element consists of a receiving transducer connected to a multiple-inlet pipe network to average spatially over the short-wavelength turbulence-associated “wind noise.” Although the frequency response of the transducer itself may be known, the wind-noise reduction system modifies that response. In order to understand the system’s impact on detection and identification of acoustical events, the overall frequency response must be determined. This paper describes a technique for measuring the absolute magnitude and phase of the frequency response of an infrasound element including the wind-noise-reduction piping by comparison calibration using ambient noise and a reference-microphone system. Measured coherence between the reference and the infrasound element and the consistency between the magnitude and the phase provide quality checks on the process.
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43.28.Dm Infrasound and acoustic-gravity waves
43.58.Vb Calibration of acoustical devices and systems

Aeroacoustic sources of motorcycle helmet noise

J. Kennedy, O. Adetifa, M. Carley, N. Holt, and I. Walker

J. Acoust. Soc. Am. Volume 130, Issue 3, pp. 1164-1172 (2011); (9 pages)

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The prevalence of noise in the riding of motorcycles has been a source of concern to both riders and researchers in recent times. Detailed flow field information will allow insight into the flow mechanisms responsible for the production of sound within motorcycle helmets. Flow field surveys of this nature are not found in the available literature which has tended to focus on sound pressure levels at ear as these are of interest for noise exposure legislation. A detailed flow survey of a commercial motorcycle helmet has been carried out in combination with surface pressure measurements and at ear acoustics. Three potential noise source regions are investigated, namely, the helmet wake, the surface boundary layer and the cavity under the helmet at the chin bar. Extensive information is provided on the structure of the helmet wake including its frequency content. While the wake and boundary layer flows showed negligible contributions to at-ear sound the cavity region around the chin bar was identified as a key noise source. The contribution of the cavity region was investigated as a function of flow speed and helmet angle both of which are shown to be key factors governing the sound produced by this region.
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43.28.Ra Generation of sound by fluid flow, aerodynamic sound and turbulence
43.50.Nm Aerodynamic and jet noise
43.50.Lj Transportation noise sources: air, road, rail, and marine vehicles
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Observationally constrained modeling of sound in curved ocean internal waves: Examination of deep ducting and surface ducting at short range

Timothy F. Duda, Ying-Tsong Lin, and D. Benjamin Reeder

J. Acoust. Soc. Am. Volume 130, Issue 3, pp. 1173-1187 (2011); (15 pages) | Cited 1 time

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A study of 400 Hz sound focusing and ducting effects in a packet of curved nonlinear internal waves in shallow water is presented. Sound propagation roughly along the crests of the waves is simulated with a three-dimensional parabolic equation computational code, and the results are compared to measured propagation along fixed 3 and 6 km source/receiver paths. The measurements were made on the shelf of the South China Sea northeast of Tung-Sha Island. Construction of the time-varying three-dimensional sound-speed fields used in the modeling simulations was guided by environmental data collected concurrently with the acoustic data. Computed three-dimensional propagation results compare well with field observations. The simulations allow identification of time-dependent sound forward scattering and ducting processes within the curved internal gravity waves. Strong acoustic intensity enhancement was observed during passage of high-amplitude nonlinear waves over the source/receiver paths, and is replicated in the model. The waves were typical of the region (35 m vertical displacement). Two types of ducting are found in the model, which occur asynchronously. One type is three-dimensional modal trapping in deep ducts within the wave crests (shallow thermocline zones). The second type is surface ducting within the wave troughs (deep thermocline zones).
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43.30.Bp Normal mode propagation of sound in water
43.30.Re Signal coherence or fluctuation due to sound propagation/scattering in the ocean
43.30.Dr Hybrid and asymptotic propagation theories, related experiments
43.20.El Reflection, refraction, diffraction of acoustic waves

Acoustic inversions for measuring boundary layer suspended sediment processes

Peter D. Thorne, David Hurther, and Benjamin D. Moate

J. Acoust. Soc. Am. Volume 130, Issue 3, pp. 1188-1200 (2011); (13 pages) | Cited 1 time

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Although sound has been applied to the study of sediment transport processes for a number of years, it is acknowledged that there are still problems in using the backscattered signal to measure suspended sediment parameters. In particular, when the attenuation due to the suspension becomes significant, the uncertainty associated with the variability in the scattering characteristics of the sediments in suspension can lead to inversion errors which accumulate as the sound propagates through the suspension. To study this attenuation propagation problem, numerical simulations and laboratory experiments have been used to assess the impact unpredictability in the scattering properties of the suspension has on the acoustically derived suspended sediments parameters. The results clearly show the commonly applied iterative implicit inversion can lead to calculated sediment parameters, which become increasingly erroneous with range, as the sound propagates through the suspension. To address this problem an alternative approach to the iterative implicit formulation is investigated using a recently described dual frequency inversion. This approach is not subject to the accumulation of errors and has an explicit solution. Here the dual frequency inversion is assessed and calculated suspended sediment parameters are compared with those obtained from the iterative implicit inversion.
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43.30.Ft Volume scattering
43.30.Gv Backscattering, echoes, and reverberation in water due to combinations of boundaries
43.30.Pc Ocean parameter estimation by acoustical methods; remote sensing; imaging, inversion, acoustic tomography
43.20.Fn Scattering of acoustic waves

Effects of locally resonant modes on underwater sound absorption in viscoelastic materials

Jihong Wen, Honggang Zhao, Linmei Lv, Bo Yuan, Gang Wang, and Xisen Wen

J. Acoust. Soc. Am. Volume 130, Issue 3, pp. 1201-1208 (2011); (8 pages) | Cited 1 time

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Recently, by introducing locally resonant scatterers with spherical shape proposed in phononic crystals into design of underwater sound absorption materials, the low-frequency underwater sound absorption phenomenon induced by the localized resonances is observed. To reveal this absorption mechanism, the effect of the locally resonant mode on underwater sound absorption should be studied. In this paper, the finite element method, which is testified efficiently by comparing the calculation results with those of the layer multiple scattering method, is introduced to investigate the dynamic modes and the corresponding sound absorption of localized resonance. The relationship between the resonance modes described with the displacement contours of one unit cell and the corresponding absorption spectra is discussed in detail, which shows that the localized resonance leads to the absorption peak, and the mode conversion from longitudinal to transverse waves at the second absorption peak is more efficient than that at the first one. Finally, to show the modeling capability of FEM and investigate shape effects of locally resonant scatterers on underwater sound absorption, the absorption properties of viscoelastic materials containing locally resonant scatterers with ellipsoidal shape are discussed.
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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
43.20.Bi Mathematical theory of wave propagation

Underwater Mach wave radiation from impact pile driving: Theory and observation

Per G. Reinhall and Peter H. Dahl

J. Acoust. Soc. Am. Volume 130, Issue 3, pp. 1209-1216 (2011); (8 pages)

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The underwater noise from impact pile driving is studied using a finite element model for the sound generation and parabolic equation model for propagation. Results are compared with measurements using a vertical line array deployed at a marine construction site in Puget Sound. It is shown that the dominant underwater noise from impact driving is from the Mach wave associated with the radial expansion of the pile that propagates down the pile after impact at supersonic speed. The predictions of vertical arrival angle associated with the Mach cone, peak pressure level as function of depth, and dominant features of the pressure timeseries compare well with corresponding field observations.
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43.30.Nb Noise in water; generation mechanisms and characteristics of the field
43.30.Jx Radiation from objects vibrating under water, acoustic and mechanical impedance

Experimental testing of the noise-canceling processor

Michael D. Collins, Ralph N. Baer, and Harry J. Simpson

J. Acoust. Soc. Am. Volume 130, Issue 3, pp. 1217-1221 (2011); (5 pages)

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Signal-processing techniques for localizing an acoustic source buried in noise are tested in a tank experiment. Noise is generated using a discrete source, a bubble generator, and a sprinkler. The experiment has essential elements of a realistic scenario in matched-field processing, including complex source and noise time series in a waveguide with water, sediment, and multipath propagation. The noise-canceling processor is found to outperform the Bartlett processor and provide the correct source range for signal-to-noise ratios below − 10 dB. The multivalued Bartlett processor is found to outperform the Bartlett processor but not the noise-canceling processor.
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43.30.Nb Noise in water; generation mechanisms and characteristics of the field
43.30.Wi Passive sonar systems and algorithms, matched field processing in underwater acoustics

Resolving Lambertian surface orientation from fluctuating radiance

Nicholas C. Makris and Ioannis Bertsatos

J. Acoust. Soc. Am. Volume 130, Issue 3, pp. 1222-1231 (2011); (10 pages)

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A maximum likelihood method for estimating remote surface orientation from multi-static acoustic, optical, radar, or laser images is presented. It is assumed that the images are corrupted by signal-dependent noise, known as speckle, arising from complex Gaussian field fluctuations, and that the surface properties are effectively Lambertian. Surface orientation estimates for a single sample are shown to have biases and errors that vary dramatically depending on illumination direction. This is due to the signal-dependent nature of speckle noise and the nonlinear relationship between surface orientation, illumination direction, and fluctuating radiance. The minimum number of independent samples necessary for maximum likelihood estimates to become asymptotically unbiased and to attain the lower bound on resolution of classical estimation theory are derived, as are practical design thresholds.
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43.30.Pc Ocean parameter estimation by acoustical methods; remote sensing; imaging, inversion, acoustic tomography
43.30.Re Signal coherence or fluctuation due to sound propagation/scattering in the ocean

Travel-time tomography in shallow water: Experimental demonstration at an ultrasonic scale

Philippe Roux, Ion Iturbe, Barbara Nicolas, Jean Virieux, and Jérôme I. Mars

J. Acoust. Soc. Am. Volume 130, Issue 3, pp. 1232-1241 (2011); (10 pages) | Cited 1 time

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Acoustic tomography in a shallow ultrasonic waveguide is demonstrated at the laboratory scale between two source–receiver arrays. At a 1/1 000 scale, the waveguide represents a 1.1-km-long, 52-m-deep ocean acoustic channel in the kilohertz frequency range. Two coplanar arrays record the transfer matrix in the time domain of the waveguide between each pair of source–receiver transducers. A time-domain, double-beamforming algorithm is simultaneously performed on the source and receiver arrays that projects the multi-reflected acoustic echoes into an equivalent set of eigenrays, which are characterized by their travel times and their launch and arrival angles. Travel-time differences are measured for each eigenray every 0.1 s when a thermal plume is generated at a given location in the waveguide. Travel-time tomography inversion is then performed using two forward models based either on ray theory or on the diffraction-based sensitivity kernel. The spatially resolved range and depth inversion data confirm the feasibility of acoustic tomography in shallow water. Comparisons are made between inversion results at 1 and 3 MHz with the inversion procedure using ray theory or the finite-frequency approach. The influence of surface fluctuations at the air–water interface is shown and discussed in the framework of shallow-water ocean tomography.
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43.30.Pc Ocean parameter estimation by acoustical methods; remote sensing; imaging, inversion, acoustic tomography
43.60.Fg Acoustic array systems and processing, beam-forming
43.60.Pt Signal processing techniques for acoustic inverse problems

Information and linearity of time-domain complex demodulated amplitude and phase data in shallow water

Jit Sarkar, Bruce D. Cornuelle, and W. A. Kuperman

J. Acoust. Soc. Am. Volume 130, Issue 3, pp. 1242-1252 (2011); (11 pages) | Cited 2 times

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Wave-theoretic ocean acoustic propagation modeling is used to derive the sensitivity of pressure, and complex demodulated amplitude and phase, at a receiver to the sound speed of the medium using the Born–Fréchet derivative. Although the procedure can be applied for pressure as a function of frequency instead of time, the time domain has advantages in practical problems, as linearity and signal-to-noise are more easily assigned in the time domain. The linearity and information content of these sensitivity kernels is explored for an example of a 3–4 kHz broadband pulse transmission in a 1 km shallow water Pekeris waveguide. Full-wave observations (pressure as a function of time) are seen to be too nonlinear for use in most practical cases, whereas envelope and phase data have a wider range of validity and provide complementary information. These results are used in simulated inversions with a more realistic sound speed profile, comparing the performance of amplitude and phase observations.
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43.30.Pc Ocean parameter estimation by acoustical methods; remote sensing; imaging, inversion, acoustic tomography
43.60.Rw Remote sensing methods, acoustic tomography

Effects of multiple scattering, attenuation and dispersion in waveguide sensing of fish

Mark Andrews, Zheng Gong, and Purnima Ratilal

J. Acoust. Soc. Am. Volume 130, Issue 3, pp. 1253-1271 (2011); (19 pages)

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An ocean acoustic waveguide remote sensing system can instantaneously image and continuously monitor fish populations distributed over continental shelf-scale regions. Here it is shown theoretically that the areal population density of fish groups can be estimated from their incoherently averaged broadband matched filtered scattered intensities measured using a waveguide remote sensing system with less than 10% error. A numerical Monte-Carlo model is developed to determine the statistical moments of the scattered returns from a fish group. It uses the parabolic equation to simulate acoustic field propagation in a random range-dependent ocean waveguide. The effects of (1) multiple scattering, (2) attenuation due to scattering, and (3) modal dispersion on fish population density imaging are examined. The model is applied to investigate population density imaging of shoaling Atlantic herring during the 2006 Gulf of Maine Experiment. Multiple scattering, attenuation and dispersion are found to be negligible at the imaging frequencies employed and for the herring densities observed. Coherent multiple scattering effects, such as resonance shifts, which can be significant for small highly dense fish groups on the order of the acoustic wavelength, are found to be negligible for the much larger groups typically imaged with a waveguide remote sensing system.
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43.30.Sf Acoustical detection of marine life; passive and active
43.30.Vh Active sonar systems
43.30.Gv Backscattering, echoes, and reverberation in water due to combinations of boundaries
43.20.Fn Scattering of acoustic waves

Trading detection for resolution in active sonar receivers

Nabin S. Sharma, John R. Buck, and James A. Simmons

J. Acoust. Soc. Am. Volume 130, Issue 3, pp. 1272-1281 (2011); (10 pages)

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This paper proposes an active sonar receivers that offers a smooth trade-off between detection and resolution. A matched filter is the optimal detector of known signals in white Gaussian noise but may fail to resolve the targets if the time separation of targets is less than the mainlobe width of the autocorrelation function of the transmitted signal. An inverse filter achieves optimal resolution performance for multiple targets in the absence of noise, but amplifies the noise outside the signal bandwidth in a manner that makes it impractical in many realistic scenarios. The proposed active sonar receiver, the variable resolution and detection receiver (VRDR) combines the matched and inverse filter properties to achieve a smooth trade-off between detection and resolution. Simulated receiver operating characteristics demonstrate that for a range of dipole sonar targets, the performance of the VRDR is superior to the matched and inverse filter, as well as another previously proposed bandlimited inverse filter.
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43.30.Vh Active sonar systems

Target time smearing with short transmissions and multipath propagation

Chris H. Harrison

J. Acoust. Soc. Am. Volume 130, Issue 3, pp. 1282-1286 (2011); (5 pages)

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In active sonar the target echo level is often estimated with a propagation model that adds all multipath arrivals. If the (post-correlator) transmitted pulse is short compared to the multipath time spread then there is effectively an extra loss (which may be substantial) since only a few of the paths contribute to the target echo at any one instant. This well known “time-smearing” loss is treated in a self-consistent manner with previous calculations of reverberation [Harrison, J. Acoust. Soc. Am. 114, 2744–2756 (2003)] to estimate the target response and the signal-to-reverberation-ratio. Again isovelocity water, Lambert’s law, and reflection loss proportional to angle are assumed. In this important short pulse regime the target response becomes independent of boundary reflection properties but proportional to transmitted pulse length. Thus the signal-to-reverberation-ratio becomes independent of pulse length. The effect on signal-to-ambient-noise is also investigated and the resulting formulas presented in a table.
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43.30.Vh Active sonar systems
43.30.Cq Ray propagation of sound in water

Performances of human listeners and an automatic aural classifier in discriminating between sonar target echoes and clutter

Nancy Allen, Paul C. Hines, and Victor W. Young

J. Acoust. Soc. Am. Volume 130, Issue 3, pp. 1287-1298 (2011); (12 pages)

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Human listening tests were conducted to investigate if participants could distinguish between samples of target echoes and clutter obtained from a broadband active sonar experiment. For each echo, the listeners assigned a rating based on how confident they were that it was a target echo or clutter. The measure of performance was the area under the binormal receiver-operating-characteristic (ROC) curve, Az. The mean performance was Az = 0.95 ± 0.04 when signals were presented with their full available acoustic bandwidth of approximately 0–2 kHz. It was Az = 0.77 ± 0.08 when the bandwidth was reduced to 0.5–2 kHz. The error bounds are stated as 95% confidence intervals. These results show that the listeners could definitely hear differences, but their performance was significantly degraded when the low-frequency signal information was removed. The performance of an automatic aural classifier was compared against this human-performance baseline. Results of statistical tests showed that it outperformed 2 of 13 listeners and 5 of 9 human listeners in the full-bandwidth and reduced-bandwidth tests, respectively, and performed similarly to the other listeners. Given its performance, the automatic aural classifier may prove beneficial to Navy sonar systems.
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43.30.Vh Active sonar systems
43.60.Bf Acoustic signal detection and classification, applications to control systems
43.66.Gf Detection and discrimination of sound by animals
43.66.Jh Timbre, timbre in musical acoustics
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Medium characterization from interface-wave impedance and ellipticity using simultaneous displacement and pressure measurements

K. N. van Dalen, G. G. Drijkoningen, D. M. J. Smeulders, H. K. J. Heller, C. Glorieux, B. Sarens, and B. Verstraeten

J. Acoust. Soc. Am. Volume 130, Issue 3, pp. 1299-1312 (2011); (14 pages)

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The interface-wave impedance and ellipticity are wave attributes that interrelate the full waveforms as observed in different components. For each of the fluid/elastic-solid interface waves, i.e., the pseudo-Rayleigh (pR) and Stoneley (St) waves, the impedance and ellipticity are found to have different functional dependencies on Young’s modulus and Poisson’s ratio. By combining the attributes in a cost function, unique and stable estimates of these parameters can be obtained, particularly when using the St wave. In a validation experiment, the impedance of the laser-excited pR wave is successfully extracted from simultaneous measurements of the normal particle displacement and the fluid pressure at a water/aluminum interface. The displacement is measured using a laser Doppler vibrometer (LDV) and the pressure with a needle hydrophone. Any LDV measurement is perturbed by refractive-index changes along the LDV beam once acoustic waves interfere with the beam. Using a model that accounts for these perturbations, an impedance decrease of 28% with respect to the plane wave impedance of the pR wave is predicted for the water/aluminum configuration. Although this deviation is different for the experimentally extracted impedance, there is excellent agreement between the observed and predicted pR waveforms in both the particle displacement and fluid pressure.
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43.35.Pt Surface waves in solids and liquids
43.35.Ud Thermoacoustics, high temperature acoustics, photoacoustic effect
43.58.Bh Acoustic impedance measurement
43.40.Sk Inverse problems in structural acoustics and vibration

Linear frequency modulation photoacoustic radar: Optimal bandwidth and signal-to-noise ratio for frequency-domain imaging of turbid media

Bahman Lashkari and Andreas Mandelis

J. Acoust. Soc. Am. Volume 130, Issue 3, pp. 1313-1324 (2011); (12 pages) | Cited 1 time

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The development of the pulse compression photoacoustic (PA) radar using linear frequency modulation (LFM) demonstrated experimentally that spectral matching of the signal to the ultrasonic transducer bandwidth does not necessarily produce the best PA signal-to-noise ratio, and it was shown that the optical and acoustic properties of the absorber will modify the optimal bandwidth. The effects of these factors are investigated in frequency-domain (FD) PA imaging by employing one-dimensional and axisymmetric models of the PA effect, and a Krimholtz–Leedom–Matthaei model for the employed transducers. LFM chirps with various bandwidths were utilized and transducer sensitivity was measured to ensure the accuracy of the model. The theory was compared with experimental results and it was shown that the PA effect can act as a low-pass filter in the signal generation. Furthermore, with the PA radar, the low-frequency behavior of two-dimensional wave generation can appear as a false peak in the cross correlation signal trace. These effects are important in optimizing controllable features of the FD-PA method to improve image quality.
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43.35.Ud Thermoacoustics, high temperature acoustics, photoacoustic effect
43.35.Sx Acoustooptical effects, optoacoustics, acoustical visualization, acoustical microscopy, and acoustical holography
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On the acoustic radiation modes of compact regular polyhedral arrays of independent loudspeakers

Alexander Mattioli Pasqual and Vincent Martin

J. Acoust. Soc. Am. Volume 130, Issue 3, pp. 1325-1336 (2011); (12 pages) | Cited 1 time

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Compact spherical loudspeaker arrays can be used to provide control over their directivity pattern. Usually, this is made by adjusting the gains of preprogrammed spatial filters corresponding to a finite set of spherical harmonics, or to the acoustic radiation modes of the loudspeaker array. Unlike the former, the latter are closely related to the radiation efficiency of the source and span the subspace of the directivities it can produce. However, the radiation modes depend on frequency for arbitrary distributions of transducers on the sphere, which yields complex directivity filters. This work focuses on the most common loudspeaker array configurations, those following the regular shape of the Platonic solids. It is shown that the radiation modes of these sources are frequency independent, and simple algebraic expressions are derived for their radiation efficiencies. In addition, since such modes are vibration patterns driven by electrical signals, the transduction mechanism of compact multichannel sources is also investigated, which is an important issue, especially if the transducers interact inside a shared cabinet. For Platonic solid loudspeakers, it is shown that the common enclosure does not lead to directivity filters that depend on frequency.
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43.38.Hz Transducer arrays, acoustic interaction effects in arrays
43.60.Fg Acoustic array systems and processing, beam-forming
43.20.Rz Steady-state radiation from sources, impedance, radiation patterns, boundary element methods
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