bluuebunny/crossref_metadata_2025 huggingface dataset:
Array detection of random signals in spherically invariant noise
Authors: Izzo Luciano , Tanda Mario
Published: October 2005

The locally optimum array detector for a random signal embedded in spherically invariant noise is synthesized. In this observation model, the signal of interest is common to each array element and the noise samples are assumed to be spatially independent across the array, but temporally correlated. Moreover, the noise at each sensor is modeled as a spherically invariant random process, which is completely characterized by the univariate probability density function, the mean, and the covariance function. The performance is assessed via computer simulations and is compared with those of two suboptimum detectors. The first one is the locally optimum detector for Gaussian correlated noise; the second one is the locally optimum detector for temporally independent non-Gaussian noise samples.
A computational model of echo processing and acoustic imaging in frequency- modulated echolocating bats: The spectrogram correlation and transformation receiver
Authors: Saillant Prestor A. , Simmons James A. , Dear Steven P. , McMullen Teresa A.
Published: October 2005

The spectrogram correlation and transformation (SCAT) model of the sonar receiver in the big brown bat (Eptesicus fuscus) consists of a cochlear component for encoding the bat’s FM sonar transmissions and multiple FM echoes in a spectrogram format, followed by two parallel pathways for processing temporal and spectral information in sonar echoes to reconstruct the absolute range and fine range structure of multiple targets from echo spectrograms. The outputs of computations taking place along these parallel pathways converge to be displayed along a computed image dimension of echo delay or target range. The resulting image depicts the location of various reflecting sources in different targets along the range axis. This series of transforms is equivalent to simultaneous, parallel forward and inverse transforms on sonar echoes, yielding the impulse responses of targets by deconvolution of the spectrograms. The performance of the model accurately reproduces the images perceived by Eptesicus in a variety of behavioral experiments on two-glint resolution in range, echo phase sensitivity, amplitude-latency trading of range estimates, dissociation of time- and frequency-domain image components, and ranging accuracy in noise.
Measurements of elastic constants of very thin anisotropic plates
Authors: Rokhlin S. I. , Wang W.
Published: October 2005

This paper describes an ultrasonic technique for the determination of elastic constants of anisotropic plates with thickness less than the ultrasonic wavelength. The technique is based on measuring transmission zeros and maxima for an ultrasonic wave obliquely incident upon a plate immersed in water. The transmission zeros result from interaction between longitudinal (symmetric) and flexural (antisymmetric) guided waves in a thin plate. It is shown that the angle positions of the transmission zeros are strongly dependent on the plate’s longitudinal stiffness. The technique is demonstrated for the determination of elastic constants of porous aluminum oxide membranes with parallel through-thickness pores. Such membranes are transversely isotropic with the isotropy plane parallel to the median plane. A nonlinear least-squares algorithm, which takes the elastic constants as free parameters and minimizes the deviation between the measured and calculated angles of the transmission zeros and maxima, was used to determine the plate stiffness and shear modulus. In addition, the shear modulus in the plane of the plate is measured from wave resonances of the fluid-filled pores. A comparison with theoretical predictions using different micromechanical models to estimate the elastic constants of the porous Al2O3 layer is given.
Ray chaos in underwater acoustics in view of local instability
Authors: Yan Jianguo
Published: October 2005

It has previously been shown that acoustic ray paths in range-dependent ocean models exhibit chaotic behavior. The objective of this paper is to investigate the influence of sound-speed profile and perturbation on the ray chaos. Considering that chaos results from the instability of nonlinear equations, the instability of Hamilton’s ray equations is analyzed by using linear stability analysis. An instability criterion is derived as follows: [C02/C(z0)4]{C(z0)[∂2C(z0)/∂z2] −3[∂C(z0)/∂z]2}+∂2g(z0,r0)/∂z2<0, where C0 is the reference sound speed, C is the sound speed, g is the range-dependent perturbation in potential function, z is the depth, z0 is the reference depth, and r0 is the reference range. By analyzing instability, it is inferred that (1) the instability criterion is a necessary condition for ray chaos; (2) ray chaos may be induced if the derivative ∂2g/∂z2 is negative and ‖∂2g/∂z2‖ is large; and (3) double-channel propagation is more likely to exhibit chaotic behavior. These ideas are then illustrated numerically by using two simple models: Munk’s canonical sound-speed profile and a double-channel North Atlantic profile, with a periodically range-dependent perturbation.
Sound scattering by rough elongated elastic objects. III. Experiment
Authors: Gurley J. V. , Stanton T. K.
Published: October 2005

Measurements of the acoustical backscattering from a long randomly rough stainless steel cylinder immersed in water are presented to quantitatively illustrate the effects of small scale surface roughness. The cylinder radius varies along its lengthwise axis creating one-dimensional rotationally symmetric roughness (rms variations ∼1% of mean radius). Using recently published rough cylinder formulations [T. K. Stanton, J. Acoust. Soc. Am. 92, 1641–1664 (1992) and T. K. Stanton and D. Chu, J. Acoust. Soc. Am. 92, 1665–1678 (1992)], explicit approximate expressions are derived for the backscattered field for the laboratory pulse-echo environment: spherically spreading directional source and receiver with arbitrary beam patterns. The actual target surface profile is well described and used as input in the numerical simulations. Agreement is found between measurements and simulation predictions both in the mean field levels and the field fluctuations over a wide range of (geometric scattering) frequencies. Roughness-induced effects such as decreases in the overall levels and pulse spreading of echoes from the front interface and circumferential waves are illustrated.
Spherical wave backscatter from straight cylinders: Thin-wire standard targets
Authors: Sheng Jinyu , Hay Alex E.
Published: October 2005

Analytical results are obtained for the amplitude of a spherical wave backscattered from a solid cylinder immersed in water. The effects of transducer directivity and transmitted pulse duration are included. Backscatter measurements for comparison with theory are made using straight stainless steel wires ranging from 0.13 to 0.26 mm diameter, and acoustic transceivers operating at 1, 2.25, and 5 MHz. The results are used to evaluate the use of thin wires as standard targets.
Target strength estimation from echo ensembles
Authors: Palumbo Dominic , Penrose John D. , White Brian A.
Published: October 2005

A Monte Carlo computer model of echo formation has been used to evaluate techniques for estimating acoustic target strength. The process is applied to echo ensembles associated with the use of a monostatic sounder with a single beam of simple shape. Simulated data are fitted to theoretical probability density or cumulative probability functions for a variety of conditions representing scattering regimes encountered at sea. The results indicate that target strength estimates within 1–1.5 dB of correct values may be obtained by processing ensembles of echoes for a variety of nonidealized regimes. These include target groupings with variable length, some multiple target content in signal statistics, and departure from Rayleigh statistics as a descriptor of scattering length variation and hence backscattered pressure amplitude due to fluctuating target attitude in the sound beam.
Estimation of seafloor microtopographic roughness through modeling of acoustic backscatter data recorded by multibeam sonar systems
Authors: Matsumoto Haruyoshi , Dziak Robert P. , Fox Christopher G.
Published: October 2005

A method is described for estimating parameters related to the power-law frequency spectrum of seafloor interface roughness from acoustic backscatter strength measured from hull-mounted multibeam sonar arrays. Scattering parameters for a sediment-free seafloor are inversely derived from backscatter data using a Kirchhoff-based interface scattering model developed by Jackson et al. [J. Acoust. Soc. Am. 79, 1410–1422 (1986)]. A variety of data reduction routines are employed, including slope correction, beam-pattern and pulse-width corrections [de Moustier et al., J. Acoust. Soc. Am. 90, 522–531 (1991)], ping cross correlation, and an indirect method to account for the lack of system calibration. The method is applied to well-studied areas of the Juan de Fuca Ridge and the results compared to geological ground truth. Preliminary results indicate that the method may be valuable as a survey tool for routine mapping of seafloor acoustic properties.
An acoustic metric for assessing change in vowel production by profoundly hearing-impaired children
Authors: Fourakis M. , Geers A. , Tobey E.
Published: October 2005

The purpose of this study was to investigate the feasibility of developing an acoustic metric to assess vowel production in profoundly hearing-impaired children. The approach taken was to develop a metric from acoustic analysis of vowel productions and then compare it with the perceptual ratings of the same productions by listeners. Speech samples were collected from three profoundly hearing-impaired children participating in a longitudinal study that investigated the effectiveness of assistive listening devices upon speech development. The metric used the extracted fundamental and first, second, and third formant frequencies to represent the tokens as points in a three-dimensional auditory-perceptual space modeled after earlier work by Miller [J. Acoust. Soc. Am. 85, 2114–2134 (1989)]. Euclidean distances were determined between each point and the intended vowel, which was represented by coordinates taken from the Peterson and Barney [J. Acoust. Soc. Am. 24, 175–184 (1952)] data for children. The data suggest that the three-dimensional metric provides significant correlations between production and perception.
Two experiments on the temporal boundaries for the nonlinear additivity of masking
Authors: Cokely Carol Geltman , Humes Larry E.
Published: October 2005

The present paper describes the results from two experiments which explored the temporal boundary between overlapping and nonoverlapping maskers and its effects on the additivity of masking. In the first experiment, detection thresholds for a short-duration 1000-Hz signal were measured in the presence of two equal-duration broadband maskers which varied in degree of temporal overlap. Following complete overlap of maskers, the temporal separation of masker onsets was systematically varied to create conditions ranging from partially overlapping simultaneous masking to combined forward and backward masking. The signal was always temporally centered between the onset of the first masker and the offset of the second masker. Nonlinear additivity of masking occurred for the majority of subjects when maskers and signal did not overlap, whereas linear additivity resulted for all subjects when the maskers and signal overlapped. In the second experiment, two separate forward maskers were used so that masker/masker overlap could be manipulated independent from masker/signal overlap. Maskers were changed gradually from temporally overlapping, or concurrent, forward maskers to sequential forward maskers. Results for all subjects showed nonlinear additivity for all combined-masker conditions. Together, these two experiments indicated that nonlinear masking additivity is observed when the signal does not overlap temporally with the maskers. However, when maskers and signal overlap temporally (and spectrally), linear additivity is observed.
The incorporation of level and level-invariant cues for the detection of a tone added to noise
Authors: Richards Virginia M. , Nekrich Robert D.
Published: October 2005

The potential contribution of level-dependent and level-invariant cues for the detection of a tone added to narrow bands of noise was assessed in two experiments. In the first experiment, three masker bandwidths, 40, 120, and 360 Hz, and three center frequencies, 600, 1800, and 5400 Hz were tested. For the tone-in-noise detection task, the signal to be detected was a tone with a frequency equal to the center frequency of the noise masker. The level of the added tone was adjusted so as to generate d′ scores of approximately 2 in a two-alternative, forced-choice procedure. Then, the distributions of across-interval changes in level were measured. The distribution of differences in level was applied to either the noise-alone or the tone-plus-noise stimuli, allowing the measurement of sensitivity to changes in level for a two-interval, forced-choice intensity discrimination task. For one of the four observers, there was a good correspondence between the d′ values obtained in the tone-in-noise task and the d′ values obtained in the intensity discrimination task. For the other three observers, the discriminability of changes in intensity could not account for the detection of a tone added to noise. In order to estimate sensitivity to level-invariant cues, the noise-alone and tone-plus-noise waveforms were scaled so as to present no reliable differences in level, and observers again detected which stimulus contained the added tone.

Normalization led to d′ scores smaller than those obtained in the initial tone-in-noise discrimination task, but performance levels did not fall to chance. For three of the four observers, the detection of a tone added to noise appeared to depend on both level and level-invariant cues. In a second experiment, psychometric functions were obtained for the detection of a tone added to noise, for the detection of changes in level associated with the noise-alone and the tone-plus-noise stimuli, and for the detection of a tone added to noise using noise-alone and tone-plus-noise waveforms with no reliable differences in level. The maskers were centered at 1800 Hz, and bandwidths of 40 and 100 Hz were tested. Individual differences in detection strategy were obtained. Two observers appeared to rely on changes in level, one observer appeared to rely on level-invariant cues, and the remaining four observers appeared to adopt a decision strategy that integrated level and level-invariant cues. The results suggest that (a) both level-dependent and level-invariant cues are available to the observer for the detection of a tone added to noise, and (b) different observers employ the cues in different ways.
Isolating the dynamic attributes of musical timbrea)
Authors: Iverson Paul , Krumhansl Carol L.
Published: October 2005

Three experiments examined the dynamic attributes of timbre by evaluating the role of onsets in similarity judgments. In separate experiments, subjects heard complete orchestral instrument tones, the onsets of those tones, and tones with the onsets removed (‘‘remainders’’). Ratings for complete tones corresponded to those for onsets, indicating that the salient acoustic attributes for complete tones are present at the onset. Ratings for complete tones also corresponded to those for remainders, indicating that the salient attributes for complete tones are present also in the absence of onsets. Subsequent acoustic analyses demonstrated that this pattern of similarity was due to the centroid frequencies and amplitude envelopes of the tones. The results indicate that the dynamic attributes of timbre are not only present at the onset, but also throughout, and that multiple acoustic attributes may contribute to the same perceptual dimensions.
Perturbation analysis of nonlinear effects in moving coil transducers
Authors: Sherman Charles H. , Butler John L.
Published: October 2005

A perturbation expansion model is presented for the evaluation of the second and third harmonic distortion in moving coil transducers. The model is applied to a particular underwater sound piston transducer resulting in a favorable comparison with measurements. The model should be useful for analyzing transducer data to determine the cause of nonlinear effects. The model can also provide information regarding different nonlinear mechanisms and different driving conditions. It was found that constant current drive gives higher harmonic distortion at certain frequencies near and below resonance while constant voltage drive gives higher harmonic distortion above resonance.
The method of the local parabolic approximation for rough surface scattering
Authors: Ivanova Kristinka , Broschat Shira L.
Published: October 2005

A method for evaluation of scattering from rough surfaces which is similar to the Kirchhoff approximation is considered. However, it is based on a local parabolic approximation of the surface irregularities rather than a tangent plane approximation and two iterations of the surface field integral equation. The method, first proposed by Belobrov and Fuks [Izv. VUZ Radiofiz. 29, 1083–1089 (1986); Sov. Phys. Acoust. 31, 442–445 (1985)], accounts for local diffraction effects. Important modifications to the original method are introduced and extensive numerical results for Gaussian, one-dimensional randomly rough surfaces for both the Dirichlet and Neumann problems are provided. The validity of the local parabolic approximation is assessed by comparison with results from Monte Carlo simulations. It is demonstrated that the local parabolic approximation improves the Kirchhoff approximation for large and intermediate values of the surface correlation length especially in the backscattering region.
Focusing with plane time-reversal mirrors: An efficient alternative to closed cavities
Authors: Cassereau Didier , Fink Mathias
Published: October 2005

In this paper, a theoretical foundation is proposed and numerical results are provided for focusing by plane, time-reversal mirrors of finite dimensions in a homogeneous fluid. The basic ideas are the same as those used in the closed time-reversal cavity (CTRC) system [Cassereau et al., Proc. IEEE Ultrason. Symp., 1613–1618 (1990); D. Cassereau and M. Fink, IEEE Trans. Ultrason. Ferroelec. Freq. Control 39, 579–592 (1992)], except that the most unrealistic assumptions made in this theoretical approach are dropped. Plane mirrors are considered that do not surround the object source, and different kinds of radiation conditions are introduced on the surface of these mirrors, in order to obtain more realistic situations from an experimental point of view. The results are compared with those of the CTRC system and it is shown how the focal pattern is changed in comparison with the pattern of the theoretical (and ideal) model. The differences between several radiation conditions on the surface of the mirror are also analyzed. The theory is based on a time domain formulation of diffraction, but a frequency analysis provides closed form solutions in some particular cases. Numerical results show that plane time-reversal mirrors of finite dimensions represent an efficient and realistic alternative to the CTRC system.
Coda spectral power and apparent attenuation factor of acoustic waves in 3-D random media
Authors: Tran Quang Huy , Jannaud Lionel , Adler Pierre
Published: October 2005

The propagation of acoustic waves in three-dimensional random media is studied by means of synthetic seismograms produced by extensive finite-difference simulations. Gaussian or exponential stationary media, probed by a Ricker pulse, are considered. Coda spectral power, as well as frequency dependence of the apparent attenuation factor, are studied. When the relative velocity fluctuations are smaller than 5%, the numerical results are in good agreement with theoretical predictions, at least as far as the coda spectral power is concerned. These results are discussed and recommendations are made for future investigation.
Numerically stable global matrix approach to radiation and scattering from spherically stratified shells
Authors: Schmidt Henrik
Published: October 2005

Although the theoretical formulation in terms of spherical harmonics for seismoacoustic propagation in spherically stratified, fluid/elastic media has been known for many decades, its numerical implementation is nontrivial. Thus, the limited machine precision is incapable of directly representing the dynamic range of the spherical harmonics throughout the stratification. The numerical solution for the expansion coefficients is therefore inherently unstable. However, this problem is equivalent to the numerical stability issue facing numerical implementation of the depth-separated wave equation for plane-stratified media. There, numerical stability has been obtained by properly factorizing the depth exponentials, and a number of stable algorithms are available. Here, an equivalent factorization of the spherical harmonics is described. The formulation is directly compatible with the global matrix approach used in the SAFARI plane-stratified model, and this code has therefore been straightforwardly modified to provide unconditionally stable solutions for arbitrary fluid/elastic, spherical stratifications. The performance of the model is illustrated by a few numerical examples of relevance to structural acoustics.
Acoustic radiation due to surface wave breaking
Authors: Kennedy Robert M.
Published: October 2005

The results of a recent paper [R. M. Kennedy, J. Acoust. Soc. Am. 91, 1974–1982 (1992)] are corrected and extended to quantitatively relate parameters of the spectrum of sea-surface-generated acoustic radiation to parameters of surface gravity wave breaking. Specifically the frequency of the maximum acoustic energy spectrum scales with the characteristic length of the wave-breaking process and the acoustic energy scales directly with wave energy dissipated by wave breaking. Furthermore, it is shown that the measured fraction of the wave energy dissipated by wave breaking that is radiated as acoustic energy agrees closely with similar laboratory measurements [M. R. Loewen and W. K. Melville, J. Fluid Mech. 224, 601–623 (1991)]. This latter result requires a correction be made to parameters found in the original paper. These conclusions have important implications to acoustical oceanography objectives.
Simulated annealing as a method of deconvolution for acoustic transients measured on a vertical array
Authors: Smith James F. , Finette Steven
Published: October 2005

The temporal signature of an acoustic pulse propagating in an ocean waveguide is estimated from passively sensed multichannel data. A general formalism is provided for source signature extraction using a parallel deconvolution algorithm based on simulated annealing. The approach is tested on two sets of experimental data using a broadband signal (25–110 Hz) recorded on a vertical array located at distances of one and two convergence zones from the source. As a demonstration of the computational feasibility of this method, the algorithm is shown to be capable of reproducing the signature using a random initial estimate of the source time series in conjunction with a good estimate of the Green’s function. Normalized cross correlation between the known transmitted signature and its deconvolved estimate are calculated for the two experimental cases and indicate that both magnitude and phase spectra are faithfully reconstructed. Additional constraints on the optimization process are easily incorporated, providing an extremely general procedure for optimization quite independent of calculus-based approaches (i.e., derivative-based methods).
Auditory spectral discrimination and the localization of clicks in the sagittal plane
Authors: Hartmann William Morris , Rakerd Brad
Published: October 2005

Experiments show that the ability of human listeners to localize an impulsive sound in the medial sagittal plane (front, overhead, rear) deteriorates as the level of the sound increases. This negative level effect is strong for clicks but does not appear for broadband noise. It is conjectured that the negative level effect arises because the tonotopic excitation pattern is broadened for intense impulsive sounds. As a result, the spectral peaks and valleys, which are caused by anatomical filtering and which normally code for localization in the sagittal plane, are less recognizable. Filtered click discrimination experiments using headphones also show a negative level effect for clicks, but not for noise, and support this conjecture.
Vulnerability and adaptation of distortion product otoacoustic emissions to endocochlear potential variation
Authors: Mills David M. , Norton Susan J. , Rubel Edwin W
Published: October 2005

The endocochlear potential (EP) was reversibly decreased in adult gerbils by the intraperitoneal injection of furosemide, while cochlear functioning was monitored by measurement of distortion production otoacoustic emissions (DPE) at a range of stimulus intensities. Stimulus frequencies for DPEs were f1=6.8 and f2=8 kHz (f2/f1=1.18). Emissions monitored in the ear canal and scala media were 2 f1−f2, 3f1−2 f2, 2 f2−f1, and f2−f1. Typically, the EP decreased smoothly, reached a minimum one-half hour after injection, then recovered slowly over several hours. Emissions at 2 f1−f2 and 3f1−2 f2 at low stimulus levels were particularly vulnerable to the change in EP. These vulnerable emissions showed characteristic trajectories in which the amplitudes changed little with the initial EP decrease, then dropped sharply as the EP continued to decrease. However, the amplitudes, then began to recover even before the EP reached minimum, and recovered completely while the EP remained subnormal. The trajectories of the other odd order emissions were similar, but lacked the abrupt decrease. The variation of the even order (f2−f1) component was completely different, but appeared related to the odd order trajectories in a complex fashion. During the initial decrease for the vulnerable components, the decrease in emission amplitude (in dB) was found to be proportional to the square of the change in EP (in mV). The recovery with a subnormal EP was interpreted as an adaptive effect with a time constant of about 15 min.
Sampling requirements and aliasing for higher-order correlations
Authors: Pflug Lisa A. , Ioup George E. , Ioup Juliette W.
Published: October 2005

While sampling at a Nyquist frequency equal to the highest frequency present in the data (critical sampling) is sufficient to prevent aliasing in both the data and the autocorrelation of a bandlimited energy signal, the sampling requirements for the avoidance of aliasing in higher-order correlations and spectra are not the same. Also, there is a difference in aliasing effects depending on whether one samples the original continuous-time signal and calculates the autocorrelation or one samples the continuous-time autocorrelation. This distinction between sampling procedures must be made for correlations of higher order, as well, for which not only the type of aliasing but also the sampling requirements to prevent aliasing differ. In particular, if one samples the continuous-time autobicorrelation or autotricorrelation, critical sampling is sufficient to prevent aliasing. In practice, however, it is not usually the continuous-time autobicorrelation or autotricorrelation that is sampled. Generally, it is the original continuous-time signal that is sampled and used to calculate the discrete-time autobicorrelation or autotricorrelation. In this case, to prevent aliasing, the sampling interval for the autobicorrelation must be no greater than two-thirds the interval associated with critical sampling, and no greater than one-half for the autotricorrelation.

Numerical calculations of autocorrelation, autobicorrelation, and autotricorrelation zero-lag values corresponding to spectral area and volume as well as bispectral contour plots for two model bandlimited energy signals are presented as demonstrations of these conclusions. Sampling requirements for higher-order correlations of rectified signals are also discussed. If the signal is to be rectified for use in a correlation detector or time delay estimator, then the sampling rate must increase to accommodate the higher frequencies that usually result from the process of rectification. Spectral masking filters, which remove aliasing in higher-order correlations, are defined and a bispectral filter is applied to some representative energy signals. Lag domain convolution filters for the removal of aliasing in the bicorrelation and tricorrelation are also given. These filters assume critical sampling or finer for the original signal to remove aliasing effects totally.
A study of an actively controlled noise barrier
Authors: Omoto A. , Fujiwara K.
Published: October 2005

This paper describes an application of active control of sound diffracted by a barrier. The basis of this application is the cancellation of the sound pressure at the diffraction edge, which behaves like a virtual source to the diffracted field. Several points on the edge were canceled simultaneously by several secondary sources to get a large attenuation over a wide area. While many factors appear to influence the effectiveness of active control, the points of cancellation on the diffraction edge and the arrangement of the secondary sources were studied. The optimum conditions for control were investigated using numerical simulation. These conditions were then confirmed experimentally using multichannel adaptive signal processing. It was found that control is stable and effective when the intervals of the points of cancellation on the edge are shorter than half of the wavelength, and that attenuation is greatest when the secondary sources are nearest the primary source.
On feedforward active control of sound and vibration using vibration error signals
Authors: Snyder Scott D. , Tanaka Nobuo
Published: October 2005

The problem of sensing structural vibration to provide an error signal for vibration source-based adaptive feedforward control systems implemented to attenuate globally both structural and acoustic disturbances is considered. It is shown that designing a control system that simply aims to minimize structural vibration is not necessarily the best approach, particularly in structural/acoustic problems. Rather, by considering the governing equation of the global error criterion of interest it is possible to derive orthogonal groups of structural modes that contribute to the error criterion as a set. It is these orthogonal groupings that should be sensed as an error signal by an adaptive feedforward control system (and minimized in amplitude), a task that could be accomplished using shaped piezoelectric polymer film sensors or discrete measurement/modal filtering techniques. Specific examples relating to the minimization of radiated acoustic power and acoustic potential energy in a coupled enclosure are given, showing that in the former case the use of a vibration-based error signal is a practical alternative to the use of an acoustic signal, while in the latter case practicality is more system-dependent.
Modal impedances for two spheres in a thermoviscous fluid
Authors: Hasheminejad Mohamad , Geers Thomas L.
Published: October 2005

A modal impedance matrix is formulated for two spheres undergoing axisymmetric oscillations in a thermoviscous acoustic medium. The formulation utilizes the governing equations of Epstein and Carhart [J. Acoust. Soc. Am. 25, 553–565 (1953)] and the analysis method of Guz and Golovchan [Diffraction of Elastic Waves in Multiply Connected Bodies (U.S. Department of Commerce, Washington, DC, 1973)]. The impedance matrix is used to generate dilatational and translational surface-force curves for dilatational and translational surface motion. Three models of the acoustic medium are examined: full thermoviscous, thin boundary layer, and ideal acoustic. Numerical results for water and air display the limitations of the last two models.
Sound dispersion and attenuation in the thickness direction of paper materials
Authors: Brodeur Pierre H. , Hall Maclin S. , Esworthy Chris
Published: October 2005

A through-transmission, dry-contact ultrasonic technique aimed at investigating sound propagation in the thickness direction of paper materials is presented. The method uses piezoelectric ceramic transducers immersed in fluid-filled rubber wheels. Thickness and longitudinal velocity are determined from time domain measurements for several commercial paper specimens between 40 and 1750 μm. Dispersion and attenuation are reported at frequencies up to 1.5 MHz. Dispersion is less than 10% between 0.25 and 1.25 MHz. Amplitude calculations are used to evaluate the attenuation coefficient versus the frequency. Using a nearly local form of the Kramers–Kronig relationships, the attenuation coefficient is also obtained from the phase information. By comparing the amplitude- and phase-determined attenuation coefficients, an apparent reflection coefficient is predicted. It is shown that the Kramers–Kronig relationships can be applied to papers thicker than 200 μm under dry coupling conditions. The attenuation coefficient is inversely related to the elastic stiffness for homogeneous specimens. A linear relationship is observed between the attenuation loss and the thickness. The apparent reflection coefficient correlates to the apparent surface roughness of paper.
The physical mechanisms leading to electrical breakdown in underwater arc sound sources
Authors: Olson Allen H. , Sutton Stephen P.
Published: October 2005

Underwater electrical arcs have long been used as an impulsive sound source, although efforts to improve efficiency and control acoustic output have been limited by inadequate understanding of the arc initiation process. An experimental study of electrical breakdown in seawater is presented and a model for arc initiation is proposed. It is shown that breakdown is not driven by the achievement of a critical electric field strength, but is an energy-dependent process. Provided the field is applied for a sufficiently long time, breakdown is demonstrated to occur at very low field strength. The breakdown time is shown to be linearly correlated with the time at which a threshold vaporization energy is dissipated in the fluid. This threshold energy is determined acoustically, by measuring the minimum electrical pulse energy required to observe steam bubble formation and collapse. These observations are used to support a model for breakdown in seawater based on vaporization as the initiating mechanism. The model is shown to be consistent with experiments up to field strengths of 50 kV/cm.
Thermoacoustics of traveling waves: Theoretical analysis for an inviscid ideal gas
Authors: Raspet Richard , Bass Henry E. , Kordomenos John
Published: October 2005

Standard thermoacoustic sources and refrigerators have the stack placed near one end in a standing wave tube. This selection of the stack position optimizes the thermoacoustic effect. For certain applications, however, the effect of a thermoacoustic stack on a traveling wave is of primary interest. Equations governing wave propagation through a stack analogous to the short stack approximation of standing wave thermoacoustics have been derived for an ideal gas. When the wave propagates in the direction of increasing temperature, the wave is amplified by an amount dependent upon the temperature gradient. Waves propagating in the opposite direction are attenuated. Counterpropagating waves in a standing wave tube encounter both. In this case, the results reduce to those developed earlier by Swift [J. Acoust. Soc. Am. 84, 1145–1180 (1988)] and others.
The interaction of Lamb waves with delaminations in composite laminates
Authors: Guo N. , Cawley P.
Published: October 2005

The S0 Lamb mode can propagate over distances of the order of 1 m in composite laminates and so has the potential to be used in long-range nondestructive inspection. This paper discusses the interaction of the S0 Lamb mode with delaminations. The dispersion curves and the corresponding stress and displacement mode shapes of the lower order Lamb modes are obtained analytically and the interaction of the S0 mode with delaminations at different interfaces in a composite laminate is then studied both by finite element analysis and by experiment. It is shown that the amplitude of the reflection of the S0 mode from a delamination is strongly dependent on the position of the delamination through the thickness of the laminate and that the delamination locations corresponding to the maximum and minimum reflectivity correspond to the locations of maximum and minimum shear stress across the interface in the S0 mode.
Broadband measurements of the acoustic backscatter cross section of sand particles in suspension
Authors: He Cheng , Hay Alex E.
Published: October 2005

A method using a broadband transducer to measure the acoustic backscatter cross section of suspended sand particles is investigated. The frequencies used range from 1.3 to 2.8 MHz, and the sand sizes from 100- to 350-μm diameter. The measurements are made in the transducer near field. The measured form factor is compared with the theoretical result for the movable rigid sphere model, and with previous narrow-band measurements.
Objective analysis versus subjective assessment of vowels pronounced by native, non-native, and deaf male speakers of Dutch
Authors: Bakkum Mark J. , Plomp Reinier , Pols Louis C. W.
Published: October 2005

An objective analysis has been performed on all 15 Dutch vowels pronounced in /hVt/ words by nine native Dutch, nine non-native, and six deaf males. Spectral representations of the vowel segments were created by determining the mean output levels of a bank of 16 filters (90–7200 Hz), with 1/3-oct bandwidths and logarithmic spacing of their center frequencies. The adequacy of the objective analysis is determined by the extent to which spectral information provides an accurate description of pronunciation quality. Spectral distances between the 24 utterances of each monophthong agree rather well with subjective distances obtained by listeners in an elaborate paired-comparisons experiment. For the various monophthongs, the correlation coefficients are within the range 0.63 to 0.88; averaging across all 12 monophthongs of each speaker results in a coefficient of 0.94. Furthermore, it appeared that the objective spectral analysis is as reliable as a subjective assessment by magnitude estimation by two to three listeners. Using principal components analysis (PCA), the number of dimensions by which the vowel spectra are described can be reduced. For the various monophthongs the range of the correlation coefficients between subjective distances and objective distances in a two-dimensional PCA subspace is 0.30–0.93. The three groups of speakers can still be distinguished in this subspace. In the extreme case of the deaf speakers all vowels are strongly ‘‘neutralized,’’ whereas the different vowels of the native speakers are well separated, especially after speaker normalization; results are less clear for the non-natives.
High-frequency bistatic ocean surface scattering
Authors: Culver Richard Lee , Neuman Peter
Published: October 2005

Understanding and being able to predict high-frequency (10- to 100-kHz) acoustic scattering in the ocean for bistatic geometries (transmitter and receiver not collocated) has become increasingly important in recent years. For example, bistatic surface and bottom scattering must be understood in order to predict the angular dependence or spatial coherence of acoustic signals which have propagated through a shallow water channel. A high-frequency ocean surface scattering experiment conducted by Dahl and Jessup in 1992 using FLIP utilized an omnidirectional source and a line array receiver to measurement out-of-plane scattering at wind speeds up to 7 m/s. Estimates of low grazing angle bistatic scattering strength have been derived from these measurements, and are shown to compare favorably to theory developed by S. T. McDaniel. The McDaniel model utilizes composite-roughness theory to predict surface shape effects and includes attenuation and isotropic scatter by subsurface resonant bubbles. Bubble scattering is predicted to be the dominant mechanism at medium to high wind speeds and low grazing angles, and the FLIP experiment data offer evidence that this is the case.
High-frequency forward scattering from Gaussian spectrum, pressure release, corrugated surfaces: Catastrophe theory modeling
Authors: Williams K. L. , Stroud J. S. , Marston P. L.
Published: October 2005

Exact integral equations for the acoustical pressure scattered from a rough pressure release surface can be written down and solved numerically. However, analytical head way into the problem, gained at the expense of various approximations, can lend physical insight not easily obtained numerically. This, in part, motivated the work to be discussed. In particular, a high-frequency approximation will be presented for forward scattering from Gaussian spectrum, pressure release, corrugated surfaces. The analysis is most directly applicable to forward scattering from an ocean surface dominated by swell. The presentation uses ideas and results from catastrophe theory [M. V. Berry, ‘‘Waves and Thom’s Theorem,’’ Advan. Phys. 25, 1–26 (1976); P. L. Marston, PhysicalAcoustics (Academic, New York, 1992), Vol. 21, pp. 1–234] to include diffraction. Catastrophe theory allows one to write down the scattered pressure in terms of a finite set of diffraction catastrophes and stationary phase contributions. The catastrophe theory results will be compared to numerical integration results for an individual rough surface to demonstrate their validity and the insight they supply. Both steady state and pulse comparisons will be made. Evidence will be presented that this ‘‘high-frequency’’ approximation is usable down to frequencies where the wavelength is twice the rms roughness of the surface. [Work supported by Office of Naval Research.]
High-frequency forward scattering from Gaussian spectrum, pressure release, corrugated surfaces: Experiment and comparison with catastrophe theory
Authors: Stroud J. S. , Marston P. L. , Williams K. L.
Published: October 2005

A single realization of a Gaussian spectrum surface, rms roughness 1.5 cm, correlation length 10 cm was manufactured out of styrofoam. This surface provided a pressure release, corrugated surface for an underwater, forward scattering investigation. Omni-directional source and receiver were used in the frequency range of 100 to 300 kHz. Short pulses were used to allow isolation of individual contributions to the scattered field. These individual contributions were then classified using catastrophe theory [M. V. Berry, ‘‘Waves and Thom’s Theorem,’’ Advan. Phys. 25, 1–26 (1976); P. L. Marston, PhysicalAcoustics (Academic, New York, 1992), Vol. 21, pp. 1–234]. Scans at a constant distance from the mean of the rough surface were used to determine the peak forward scattered pressure. Composites of these types of scans are shown and discussed using catastrophe theory. The catastrophe theory simulation is shown to be a valid approximation to the wavefield for a wide range of frequencies. [Work supported by Office of Naval Research.]
High-frequency propagation in a turbulent shallow water environment
Authors: DiIorio Daniela , Farmer David M.
Published: October 2005

A high-frequency (67-kHz) acoustic propagation experiment conducted in a shallow tidal channel provides an opportunity for comparison of observed acoustical scintillations with available theory. The tidal current ensures that the acoustic path runs through a turbulent boundary layer at all times. Analysis of log-amplitude, phase, and phase-difference signals shows close agreement with the weak scattering theory of Tatarski using the Kolmogorov turbulence model together with the Taylor hypothesis of ‘‘frozen’’ advected turbulence. By combining acoustic data with direct measurement of temperature and salinity fluctuations using insitu sensors, the contribution of turbulent velocity fluctuations to the scintillation signal is evaluated. The results show that turbulent velocity fluctuations rather than temperature and salinity variability are the dominant source of observed acoustic fluctuations, leading to estimates of turbulent energy dissipation in the range ε≊10−5 m2 s−3.
Sea surface reverberation: A review
Authors: McDaniel Suzanne T.
Published: October 2005

Measurements of reverberation from the sea surface and the accompanying development of theories to explain the experimental results are reviewed from a historical perspective. Because of the relative ease of measurement, significant amounts of sea surface reverberation data have been amassed that yield a clear picture of the dependence of measured reverberation levels on acoustic frequency, grazing angle, and wind speed. The evolution of theoretical treatments of rough surface scattering and scattering from the layer of wind-generated microbubbles that exist below the surface is also reviewed, as are the empirical models that describe ocean surface roughness and subsurface bubble distributions. For acoustic frequencies of 3–60 kHz, the data are consistent with the view that the reverberation is due to rough surface scattering at moderate to high grazing angles, and at low grazing angles to scattering from resonant subsurface microbubbles. At frequencies below 1 kHz, measured reverberation levels at low grazing angles exceed those expected from rough surface scatter alone. However, the source of the anomalous reverberation is in this case not clear. For both of the frequency ranges considered, disparities of an order of magnitude exist between measurements performed under similar environmental conditions. At high frequencies, disparately high reverberation levels are observed in coastal areas; at low frequencies the source of such disparities is unknown.
Mutual dependence of octave-band contributions to speech intelligibility
Authors: Steeneken Herman J. M.
Published: October 2005

Current objective measures for predicting the intelligibility of speech assume that this can be modeled as a simple addition of the contributions from individual frequency bands. The articulation index (Al) and speech transmission index (STI) are based on this assumption. There is evidence that the underlying assumption of mutually independent contributions is not valid and may lead to erroneous prediction for conditions with a limited frequency transfer, with spectral gaps or with spectrally localized masking. An experiment was performed focused on the contributions from individual frequency bands. For this purpose the speech signal was subdivided into 7 octave bands with center frequencies ranging from 125 Hz to 8 kHz. For 26 different combinations of 3 or more octave bands the CVC-word score (consonant–vowel–consonant, nonsense words) was obtained at three signal-to-noise ratio. For an improved prediction of the observed intelligibility, a revised model was designed that accounts for mutual dependency between adjacent octave bands by the introduction of a redundancy correction (second order cross-product terms). A similar model was found for male and female speech. The data also provided a verification of the relation between signal-to-noise ratio and the contribution to the STI.