bluuebunny/crossref_metadata_2025 huggingface dataset:
A simple coupled wedge mode propagation method
Authors: Fawcett John A. , Westwood Evan K. , Tindle Chris T.
Published: October 2005

In this paper an efficient coupled-mode method is presented for modeling acoustic propagation in a multi-faceted oceanic waveguide. The method is based on the concept of ‘‘wedge modes,’’ which are identical to the usual normal modes of a range-invariant waveguide except that the mode functions are referenced to the arc of a circle rather than a vertical line. Within each wedge-like section of the waveguide, wedge modes are assumed to propagate adiabatically. At junctures of waveguide facets, the incident field from the previous wedge is coupled into the wedge modes of the following wedge, and the new set of wedge modes is again propagated adiabatically. ‘‘Leaky modes,’’ which account for energy that is only partially reflected at the basement interface and which are important only at short ranges in flat waveguides, are included because conversion between leaky and trapped modes is important in many range-variable waveguide geometries. Coupling of the two sets of wedge modes at facet interfaces is performed using a method that does not assume mode orthogonality in the water. Agreement in the field computed using the coupled wedge mode method and a parabolic equation method is found to be very good.
A practical application of the Galerkin method to the broadband calculation of normal modes for underwater acoustics
Authors: Koch Robert A. , Knobles D. P.
Published: October 2005

A new application of the Galerkin technique to the calculation of the normal modes that are used to describe underwater acoustic propagation is presented. This expansion approximation method (EAM) is especially relevant for broadband normal mode calculations in which normal mode eigenvalues, depth functions, and attenuations are needed. The EAM is used to construct approximate normal mode eigenvalues and depth functions for some frequency from eigenvalues and depth functions previously calculated at another, higher frequency. The EAM approach for broadband underwater acoustic propagation calculations is evaluated in comparison with an exact normal mode model calculation of impulse responses and other broadband results.
Ultrasonic four-wave mixing mediated by an aqueous suspension of microspheres: Theoretical steady-state properties
Authors: Simpson Harry J. , Marston Philip L.
Published: October 2005

A novel mechanism is analyzed for the interaction of sound with sound that relies on the slow response of the acoustic medium to the radiation pressure of a pump wave. The coupling mechanism is analogous to optical four-wave mixing in photorefractive materials. Counter propagating ultrasonic pump waves establish a standing wave in a dilute suspension of microspheres. In response, the spheres are attracted to pressure nodes and form spatially periodic bands. The Bragg reflection of a higher frequency probe wave from the concentrated layers of microspheres generates a fourth wave. Its amplitude is calculated by two methods that are found to give mutually consistent results for the dependence of the reflectivity on the pump wave amplitude. Both methods use a Born approximation that neglects the depletion of the probe wave propagating through the layered region. One of the calculations uses a symmetric Epstein layer to approximate the local refractive index variations. The other method is based on a Fourier decomposition of the spatial acoustic refractive index variations for layers of particles given by a Boltzmann distribution in a periodic energy well. The Bragg reflectivity is found to saturate with increasing pump pressure when the energy well becomes deep in comparison to the thermal energy kBT.
Finite amplitude flexural vibrations at ultrasonic frequencies in metallic bars
Authors: Campos-Pozuelo C. , Gallego-Juárez J. A.
Published: October 2005

This paper deals with a theoretical and experimental study about the nonlinear behavior of metals subjected to intense ultrasonic, flexural vibrations. In the theoretical analysis a one-dimensional, second-order wave equation is established and solved by means of the successive approximation method. The solution for standing, flexural waves is obtained by applying the superposition principle. Spatial distributions of force, momentum, and particle velocity are derived as well as the waveforms. The experimental study is carried out with resonant, prismatic bars driven at their central sections at frequencies in the range of 20–30 kHz. The samples are driven by means of a piezoelectric transducer. The vibration amplitudes and waveforms are monitored by using a laser vibrometer. Good agreement is found comparing the experimental and theoretical results.
Acousto-optic imaging of focused ultrasound pressure fields
Authors: Neighbors Thomas H. , Mayer Walter G. , Ruf Herbert J.
Published: October 2005

Focused sound field measurements typically involve needle- or membrane-type transducers stepped across the sound field. This process produces an apparent image of the sound field limited by probe linearity, effective aperture size, and experimental alignment. Historically, acousto-optic schlieren imaging has provided an effective, qualitative technique for examining a sound-pressure field. In this paper the schlieren technique is extended to provide quantitative measurements of the peak focused sound-pressure field without in situ disruptions. A numerical solution of the Khokhlov–Zabolotskaya–Kuznetsov parabolic equation is used to predict the sound-pressure field for a line focused transducer. Enhancements in the standard numerical solution include a floating boundary condition and an adaptive technique for adjusting the computation effectiveness consistent with nonlinearity induced harmonic growth. Key features of the experimental setup are outlined and theoretical predictions compared with experimental measurements made with the extended schlieren technique.
Sound field of a baffled piston source covered by a porous medium layer
Authors: Amédin Celse K. , Berry Alain , Champoux Yvan , Allard J.-F.
Published: October 2005

Two models for the prediction of sound transmission through a thick layer of material which lies on a horizontal baffle are presented. These models are a preliminary investigation of a method for the acoustical and physical characterizations of porous materials. The acoustic source is assumed to be a circular, baffled piston source mounted under a layer of porous material. The sound is transmitted through the porous layer to the semi-infinite half-space above the layer. The models are used to calculate the transfer function between the volume velocity of the source and the sound pressure above the porous material. The first model is based on the integral method in which appropriate Green’s functions are used to describe the sound field, and on a collocation procedure. The second model uses a method of decomposition of the sound field into cylindrical waves. The numerical results of the two models are in good agreement. A significant sensitivity of the transmitted sound field to the material’s physical characteristics is observed. The models’ predictions are in good agreement with those from the literature on the limiting case of a circular piston radiating in a semi-infinite medium. The cylindrical wave decomposition method is found to be much faster in terms of computation time, and more general than the integral method model.
Transient analysis of the transmitting properties of a focused acoustic transducer with an arbitrary rim
Authors: de Hoop Adrianus T. , Zeroug Smaine , Kostek Sergio
Published: October 2005

Closed-form analytic expressions are derived for the efficient calculation of the transient acoustic wave field emitted by a focused transducer with a spherical surface. The radiated transient acoustic wave field is evaluated by applying the Maggi–Rubinowicz transformation to the Kirchhoff–Huygens representation of the wave field. This transformation results in a line integral representation along the rim of the radiating aperture that holds for a rim of arbitrary shape, and for both planar and nonplanar radiators. The line integral is readily evaluated numerically and the results are used to study the shape of the beam emitted by the transducer in its dependence on the shape of the rim. This is shown through numerical results for a spherical-cap transducer and a spherically curved rectangular-strip transducer. The computation time needed to evaluate the (one-dimensional) integrals is in the order of seconds on a standard workstation.
Articulatory organization of mandibular, labial, and velar movements during speech
Authors: Kollia H. Betty , Gracco Vincent L. , Harris Katherine S.
Published: October 2005

It has been shown that articulator movements during speech are adjusted along a number of spatiotemporal dimensions. For example, variations in the extent of lip, jaw, or tongue motion are associated with proportional changes in the respective articulators’ peak velocity. Modifications in the timing of lip and jaw actions are apparently constrained, exhibiting relative timing covariation. Syllable prominence systematically affects some combination of the articulator motion parameters, i.e., extent, speed, and duration. The present investigation is an attempt to extend observations of the spatiotemporal properties of articulator movement to include the velum. Lip, jaw, and velar kinematics were recorded optoelectronically and simultaneously with the acoustic signal during productions of the utterance /mayebnayeb/. The spatial and temporal relations between the lips, the jaw, and the velum were examined and compared across articulators. For movements associated with each syllable, the velum displayed scaling patterns qualitatively similar to those of the lips and jaw. Moreover, velocity–displacement relations were more robust for the lowering than for the raising movements of the velum. There was evidence of interarticulator coupling between the velum and the jaw, and between the velum and the upper lip, although this coupling was not as strong as that observed among the oral articulators. Articulator specific differences in velocity–displacement correlations and degree of interarticulator cohesion for the various movement phases may be related to a combination of aerodynamic and phonetic factors, such as the phonologically noncontrastive nature of nasalization in English.
An articulatory study of fricative consonants using magnetic resonance imaging
Authors: Narayanan Shrikanth S. , Alwan Abeer A. , Haker Katherine
Published: October 2005

Magnetic resonance images of the vocal tract during sustained production of the fricatives /s, sh, f, θ, z, yog, v, edh/ by four subjects are analyzed. Measurements of vocal-tract lengths and area functions, and morphological analyses of the vocal tract and tongue shapes for these sounds are presented. Interspeaker differences in area functions are found to be greater in the pharyngeal cavity than in the buccal cavity with the nonstrident fricatives exhibiting greater differences than the strident ones. The anterior tongue body of the alveolar stridents exhibit concave cross-sectional shapes while that of the postalveolars show a relatively raised tongue body with flat or slightly convex cross-sectional shapes. The concave tongue shapes of the alveolars result in a more abrupt area function behind the constriction when compared to that of the postalveolars. Laminality or apicality of articulation is found to be speaker dependent. Moreover, a greater degree of anterior medial grooving and lateral lingua-palatal contact is found in apical alveolar fricatives than in laminal ones. The posterior tongue body of all fricatives shows concave cross-sectional shapes. Voiced fricatives are characterized by larger pharyngeal volumes than the unvoiced fricatives due to tongue-root advancement. Tongue-shape asymmetries are found to be subject and, in some cases, sound dependent.
Differences in frequency modulation detection and fundamental frequency discrimination between complex tones consisting of resolved and unresolved harmonics
Authors: Plack Christopher J. , Carlyon Robert P.
Published: October 2005

Three experiments investigated the finding [Shackleton and Carlyon, J. Acoust. Soc. Am. 95, 3529–3540 (1994)] that listeners are very poor at detecting frequency modulation (FM) imposed on complex-tone carriers consisting of harmonics unresolved by the peripheral auditory system. In the first experiment, stimuli consisted of the harmonics of a 62.5- or 250-Hz fundamental (f0) passed through a bandpass filter with cutoff frequencies of 1375 and 1875 Hz. This produced two complexes, one with resolved and one with unresolved harmonics. Threshold measurements confirmed that listeners were very poor at detecting 5-Hz FM imposed on a 200-ms unresolved group, but that performance was relatively good for the resolved group. In addition, the results revealed that, for the unresolved group, thresholds for detecting FM were similar to thresholds for detecting an f0 difference between two static 50-ms complex-tone bursts presented 50 ms apart. The second experiment added a third complex consisting of the harmonics of a 250-Hz f0 passed through a bandpass filter with cutoff frequencies of 5500 and 7500 Hz. These harmonics were also unresolved. Both groups of unresolved harmonics produced similar results, indicating that f0 per se did not determine the results from the first experiment.

The second experiment confirmed the results of the first experiment and in addition showed that, for unresolved harmonics only, there was a large increase in the frequency difference limen (FDL) for changes in f0 as the duration of the tone was decreased from 200 to 50 ms. A final experiment was conducted to examine this duration effect. A fourth complex was added which included various harmonics of a 250-Hz f0 chosen so that no two harmonics were the same between the two observation intervals. This complex was low-pass filtered at 1875 Hz. For this second group of resolved harmonics, listeners could not perform the FDL task by comparing the frequencies of individual harmonics: some computation of f0 was required. FDLs for the two resolved groups showed little variation with duration whereas the FDLs for the unresolved groups increased dramatically as the duration was decreased below 100 ms. Measurement of psychometric functions showed that this result reflected a differential effect of duration on detectability itself, as characterized by d′. It is argued that the poor performance on FM detection for groups of unresolved harmonics reflects a poor performance on f0 extraction over short durations. Furthermore, it is suggested that the differential effects of duration for the resolved and unresolved harmonics may reflect the operation of two distinct pitch mechanisms.
Infants’ pitch perception: Inharmonic tonal complexes
Authors: Clarkson Marsha G. , Clifton Rachel K.
Published: October 2005

Two experiments assessed the effects of inharmonicity on 7- to 8-month-old infants’ perception of the pitch of tonal complexes. A number of harmonic and inharmonic complexes were presented in a visually reinforced operant head turn procedure. In both experiments, infants demonstrated the ability to discriminate two harmonic complexes based on missing fundamental frequencies of 160 and 200 Hz. After learning this basic task, infants learned to discriminate inharmonic complexes, which were created by shifting the partials of the harmonic complexes upward by 30 Hz (experiment 1) or 20 Hz (experiment 2). Finally, three spectrally different inharmonic complexes represented each pitch, and infants attempted to categorize those complexes according to their pitches. In both experiments, infants successfully discriminated the pitches of the spectrally varying tonal complexes, but their performance deteriorated for the more strongly inharmonic complexes of experiment 1. These results suggest that, as for adults, the salience of pitch for inharmonic sounds decreases with increasing inharmonicity.
Effect of signal component phase on asynchrony discrimination
Authors: Zera Jan , Green David M.
Published: October 2005

The ability of listeners to detect the temporal asynchrony of a single harmonic in complex sounds was measured. The listeners discriminated an asynchronous complex from one in which all harmonics were synchronous (standard). The asynchrony was created either at the onset or offset of the complex. In the asynchronous complex, one component either began or ended after all other components in the complex, or it began or ended prior to all other components in the complex. The phase of the signal component was systematically varied in the range from 0° to 180°. All nonsignal components had the same sine phase. The results show that detecting the asynchrony at the onset is superior when all components are in sine phase. Altering the phase of the signal component increased thresholds by as much as a factor of 50, with the largest thresholds obtained when the signal component was inverted in phase. For offset conditions, the phase of the signal component had a much smaller and less consistent effect. Some of the observed effects of phase on the asynchrony thresholds can be understood by considering the response of the Roex filter [Patterson et al., J. Acoust. Soc. Am. 72, 1788–1803 (1982)] centered at the signal frequency.
Reliability of pure-tone thresholds at high frequencies
Authors: Zhou Bin , Green David M.
Published: October 2005

Standing waves in the ear canal are created by the interference of two plane waves of the same frequency traveling in opposite directions. One manifestation of this phenomena is that any lateral motion of the transducer produces a change in the length of the canal and therefore, in general, a change in the sound level at the eardrum. Because of the smaller wavelength at the higher frequencies, the changes produced by movement of the transducer will be larger for the higher frequencies than for the lower frequencies. Thus, when the transducer is removed and replaced between successive threshold estimates, it is expected, from physical principles alone, that the intrasubject reliability of the estimates should be better at the lower frequencies. Previous studies, however, have shown that the intrasubject reliability of threshold estimates is nearly the same at both the low (0–8 kHz) and the high (8–16 kHz) frequency regions. A possible explanation for these anomalous results is proposed. While it is found that transducer placement increases the variability of threshold estimates more at the higher frequencies, it has also been found that conventional headphones reduce the size of the standing wave ratios compared with a hard wall termination. An additional factor is the steeper slope of the psychometric function at the higher frequencies. The combination of these factors produces a standard deviation for threshold estimates that is only about 1 dB larger at the high than at the low frequency region.
A spectral network model of pitch perception
Authors: Cohen Michael A. , Grossberg Stephen , Wyse Lonce L.
Published: October 2005

A model of pitch perception, called the spatial pitch network or SPINET model, is developed and analyzed. The model neurally instantiates ideas from the spectral pitch modeling literature and joins them to basic neural network signal processing designs to simulate a broader range of perceptual pitch data than previous spectral models. The components of the model are interpreted as peripheral mechanical and neural processing stages, which are capable of being incorporated into a larger network architecture for separating multiple sound sources in the environment. The core of the new model transforms a spectral representation of an acoustic source into a spatial distribution of pitch strengths. The SPINET model uses a weighted ‘‘harmonic sieve’’ whereby the strength of activation of a given pitch depends upon a weighted sum of narrow regions around the harmonics of the nominal pitch value, and higher harmonics contribute less to a pitch than lower ones. Suitably chosen harmonic weighting functions enable computer simulations of pitch perception data involving mistuned components, shifted harmonics, and various types of continuous spectra including rippled noise. It is shown how the weighting functions produce the dominance region, how they lead to octave shifts of pitch in response to ambiguous stimuli, and how they lead to a pitch region in response to the octave-spaced Shepard tone complexes and Deutsch tritones without the use of attentional mechanisms to limit pitch choices. An on-center off-surround network in the model helps to produce noise suppression, partial masking, and edge pitch. Finally, it is shown how peripheral filtering and short-term energy measurements produce a model pitch estimate that is sensitive to certain component phase relationships.
Grouping in pitch perception: Evidence for sequential constraints
Authors: Darwin C. J. , Hukin R. W. , Al-Khatib Batul Y.
Published: October 2005

Evidence is presented that sequential auditory grouping constraints apply to the perception of pitch. Experiment 1 shows that the pitch changes produced by mistuning the fourth harmonic of a 90-ms 12-harmonic 155-Hz fundamental complex tone are substantially reduced when the complex is preceded by four 90-ms tones at the same frequency as the mistuned component. Both the pitch changes and their reduction by the tonal sequence precursor remain when the mistuned component and the precursor are presented contralateral to the remaining components. Experiment 2 shows that reducing the level of the same mistuned component reduces the size of the pitch change, but only if the mistuned component is presented ipsilaterally. To the extent that adaptation can be equated with a physical reduction in level, this result provides further evidence against peripheral adaptation playing a significant role in the auditory grouping of harmonics in pitch perception.
The ‘‘inverse problem’’ solved for a three-dimensional model of the cochlea. I. Analysis
Authors: de Boer Egbert
Published: October 2005

With nonactive cochlear models of the ‘‘classical’’ type, it is impossible to simulate the characteristic type of frequency selectivity that is revealed by modern mechanical measurements of the motion of the basilar membrane (BM). Locally active models of the cochlea have been proposed to alleviate this problem but it remains uncertain whether the real cochlea is active in this sense. The present study was undertaken to investigate this subject in a more general and systematic way than has hitherto been done. The ‘‘inverse’’ problem is solved for a three-dimensional (3-D) model and a procedure is developed for recovering the BM impedance needed to simulate the given BM response function. In the present paper the theoretical basis of the procedure is presented, and an analysis is given of the validity of the method and the errors involved. It is shown why the inverse problem is ‘‘ill-posed’’ and why the results of our procedure are more accurate in the region of the response peak than in the more basal region of the model. The latter finding serves to delimit the domain within which results of an inverse procedure (for instance, in the short- or long-wave approximation) are to be judged. In a subsequent paper the technique developed will be applied to actual data sets from the literature on mechanical BM measurements.
Fractal characterization of ultrasonic backscattered signals from single crystal and polycrystalline materials
Authors: Dutta Debashree , Barat P.
Published: October 2005

For the first time the concept of fractal geometry is introduced to characterize discrete ultrasonic time domain signals from a single crystal, a polycrystalline metal, and an alloy. These signals possess unique fractal dimensions and remain invariant with the change in sampling rate of signal capturing. The fractal dimension of these signals were evaluated by both the box counting method and the power spectrum method. The similarity and difference in the fractal dimension of these signals obtained from the above two methods have been discussed.
Matched-signal (‘‘MESS’’) processing by the ocean
Authors: Parvulescu Antares
Published: October 2005

This paper was originally written in 1967 and then delivered at the University of Hawaii in 1969 in a series of three lectures. Minor modifications of the original paper have been made, in the form of deletions of now well-known subjects. Scientific advances since 1969 are not discussed. The author’s matched-signal (‘‘MESS’’) technique and his detailed 1965–67 environmental measurements have so far been made known only to a limited audience. A patent [A. Parvulescu, U.S. Patent No. 3, 939, 461 (19 November 1962)] was granted to the author in 1962 and declassified in 1976. The paper is being published now, because the MESS technique continues to be significant in its own right, and because it is useful for making environmental and operational measurements. Certain comments, for example, those addressing the practical limitations in performing correlations, while no longer true, were previously driving forces and are mentioned as such. Similarly, it may be noted that the agreement between models and measurements has improved over the years.
Reduced-complexity spatial and temporal processing of underwater acoustic communication signals
Authors: Stojanovic M. , Catipovic J. A. , Proakis J. G.
Published: October 2005

Multichannel processing of high-speed underwater acoustic communication signals requires computationally intensive receiver algorithms. The size of adaptive filters, determined by the extent of ocean multipath, increases with signaling rate and limits system performance through large noise enhancement and increased sensitivity of computationally efficient algorithms to numerical errors. To overcome these limitations, reduction in receiver complexity is achieved by exploiting the relationship between optimal diversity combining and beamforming. Under relatively simple conditions, two adaptive receivers, one based on diversity combining which does not rely on any spatial signal distribution, and the other based on optimal beamforming, are shown to achieve the same performance. The beamforming approach, however, leads to a receiver of lower complexity. Carrying these observations over to a general case of broadband transmission through an unknown channel, a fully adaptive receiver is developed which incorporates a multi-input multi-output, many-to-few combiner, and a reduced-complexity multichannel equalizer. Receiver operations are optimized jointly to ensure minimum mean-squared error performance of data detection. Results of processing experimental shallow water data demonstrate the capability to fully exploit spatial diversity of underwater multipath while keeping the complexity at an acceptable level.
Objective analysis versus subjective assessment of vowels pronounced by deaf and normal-hearing children
Authors: Bakkum Mark J. , Plomp Reinier , Pols Louis C. W.
Published: October 2005

Objective whole-spectrum and formant analyses have been performed on all 15 Dutch vowels pronounced in /C1VC2/ words by 24 deaf and 24 normal-hearing children, in order to develop a model of pronunciation quality for evaluating (deaf) speech; the results as obtained for adult males by Bakkum et al. [J. Acoust. Soc. Am. 94, 1989–2004 (1993)] have been verified and extended. Spectral representations of the vowels were created by determining the output levels of a bank of 16 filters (90–7200 Hz), with 1/3-oct bandwidths and logarithmic spacing of their center frequencies. Spectral differences agree well with subjective differences in pronunciation quality obtained from magnitude estimation and identification experiments. Spectral differences not related to pronunciation quality judgments arise as a consequence of physiological interspeaker differences and variation in fundamental frequency, but these differences can be compensated for by speaker-normalization and F0-compensation procedures. Using principal components analysis (PCA), the vowel spectra can be described by a limited number of dimensions, without losing much information; a description in a two-dimensional PCA subspace still agrees well with the subjective judgments and it also agrees with a description by the first two formants. The whole-spectrum approach provides a determinate, readily interpretable model of pronunciation quality for evaluating vowels. As a practical advantage, its computational requirements are modest and, in conjunction with PCA, the vowel dynamics can be visualized, which makes the approach suitable for vowel training and diagnostics.
Effects of bandwidth on glottal airflow waveforms estimated by inverse filtering
Authors: Alku Paavo , Vilkman Erkki
Published: October 2005

The aim of this research was to examine the effect of the bandwidth on parameters that are used to quantify glottal airflow waveforms that have been obtained by inverse filtering the acoustic signals. Three bandwidths (1, 2, and 4 kHz) were compared using /a/ vowels of different phonation types. Glottal waveforms were characterized using three ratios computed from the flow (open quotient, speed quotient, and closing quotient) and two parameters extracted from the differentiated flow (the amplitude of the negative peak and the return time from the negative peak to zero level). The results show that especially in pressed phonation the bandwidth should be at least 4 kHz. Distortion caused by an insufficient frequency range was most severe in the parameters extracted from the flow derivatives. Among the parameters computed from the flow signals, the closing quotient was affected most when the bandwidth was reduced.
Detecting signals of unexpected or uncertain durations
Authors: Dai Huanping , Wright Beverly A.
Published: October 2005

Expectation of signal duration influences the signal detectability. This is demonstrated in two experiments in which percent correct was measured for both tonal and noise signals whose durations were either unexpected or uncertain. In both experiments, the signal at each duration was set to have a d′ of about 1.5 when that duration was presented alone and expected. When the six subjects were led to expect a short- or a long-duration signal using the probe-signal method, the detectability of signals decreased to near chance as the signal duration deviated from the expected value (experiment 1). When the subjects were led to expect a range of durations, the detectability was only slightly worse than when each signal was presented alone (experiment 2). Those results suggest that listeners adjust their temporal-integration intervals according to the demand of the specific task. Finally, the results obtained with the noise signal were analyzed using the multiple-look model and a modified energy-detector model. Assuming that the integration interval is matched to the expected signal duration, both models predict the detection of signals having unexpected durations reasonably well. Both models, however, fail to predict the small effect of duration uncertainty.
Padé approximants for the acoustical characteristics of rigid frame porous media
Authors: Chandler-Wilde S. N. , Horoshenkov K. V.
Published: October 2005

In this paper it is shown that a number of theoretical models of the acoustical properties of rigid frame porous media, especially those involving ratios of Bessel functions of complex argument, can be accurately approximated and greatly simplified by the use of Padé approximation techniques. In the case of the model of Attenborough [J. Acoust. Soc. Am. 81, 93–102 (1987)] rational approximations are produced for the characteristic impedance, propagation constant, dynamic compressibility, and dynamic density, as a function of frequency and the material parameters. The model proposed by Stinson and Champoux [J. Acoust. Soc. Am. 91, 685–695 (1992)] is approximated via rational approximation for the viscosity correction function.
Nonlinear poroelasticity for a layered medium
Authors: Norris Andrew N. , Grinfeld Michael A.
Published: October 2005

The equations of motion and the nonlinear constitutive theory of fluid-filled poroelastic media are derived from the fundamental equations of elasticity and fluid mechanics for the constituents. A two-scale spatial expansion and the method of homogenization are employed. Explicit equations are obtained for the special case of a medium consisting of alternating solid and fluid layers. The linearized theory is examined in depth for the particular case of isotropic solid layers. The governing effective poroelastic medium is transversely isotropic, and wave solutions are discussed and compared with previous studies.
Focusing in transmit–receive mode through inhomogeneous media: The time reversal matched filter approach
Authors: Dorme Christian , Fink Mathias
Published: October 2005

For a few years, adaptive time delay focusing techniques have been extensively studied in order to focus through inhomogeneous media. However, these techniques can only correct the effects of a thin aberrator located near the array. Time reversal of ultrasonic fields allows another approach to focus in the transmit mode through inhomogeneous media. Compared to the adaptive time delay focusing technique, time reversal requires the transmission of different waveforms from each individual element of an array. Focusing via time reversal is shown to be optimal in comparison with time delay focusing since it realizes the spatio-temporally matched filter to the inhomogeneous propagation transfer function between the array and the focal point. In previous papers [Fink et al., Proc. IEEE Ultrasonics Symposium, Montreal (1989)], focusing by time reversal has been described in the transmit mode only. A complete focusing in inhomogeneous medium requires the extension of this technique in the receive mode. This paper describes the extension of the matched filter approach in the receive mode and it is shown that optimal focusing in this mode can be achieved using adaptive convolution beamforming techniques instead of simple time delay lines. Theoretical and experimental results are presented to show the efficiency of this technique compared to adaptive delay line focusing.
Multichannel impulse responses for outdoor sound propagation
Authors: Berkhout A. J. , Boone M. M. , Valks P. J. M.
Published: October 2005

A new visualization method is introduced to present simulated and measured impulse responses for outdoor sound propagation. The method stems from seismic imaging technology and provides significantly improved insight in the complexity of outdoor sound. The proposed transmission images are multichannel and unambiguously show the characteristic multiarrival effect in outdoor sound measurements. Caustics and ground reflections are clearly visible and the related wavefront directions can be easily estimated. The new visualization method is explained and illustrated with a number of practical examples. In addition, it is shown that the method is very effective for comparing different numerical simulation techniques. The examples demonstrate that the images reveal the strong and weak points of different algorithms in a transparent and detailed way. Transmission images should thus play an important role in the refinement of numerical simulation methods for outdoor sound propagation.
Scattering from collective modes of air bubbles in water and the physical mechanism of superresonances
Authors: Feuillade C.
Published: October 2005

A coupled oscillator method is used to describe collective acoustic resonances and scattering from multiple air bubbles in water. By recombining equations, the problem is decomposed into that of scattering from individual normal modes of the ensemble. Each mode has specific resonant properties. ‘‘Symmetric’’ modes, where the bubbles oscillate in phase with each other, typically show downward frequency shifts and increased damping. ‘‘Antisymmetric’’ modes, where some or all of the bubbles oscillate in antiphase, generally show upward frequency shifts and reduced damping. For two bubbles the method predicts frequency shifts which agree with experimental results. The resonance response functions predict that a two bubble system may become superresonant provided (a) the mode is antisymmetric, (b) the individual bubbles are primarily radiation damped, and (c) the bubbles are spaced such that the modal damping is small. Superresonant scattering is dipolar and propagates little energy in the far field, making the phenomenon difficult to observe experimentally. Scattering from a bubble reflected in a pressure release surface may show the phenomenon strongly. The antisymmetric modes of a triangular arrangement of three bubbles are degenerate and may also become superresonant. The damping of line ensembles of bubbles varies strongly with the bubble spacing.
Ultrasonic diffraction from a transducer with arbitrary geometry and strength distribution
Authors: Ogi Hirotsugu , Hirao Masahiko , Honda Takashi , Fukuoka Hidekazu
Published: October 2005

The exact solution to the Helmholtz equation with a Dirichlet boundary condition is obtained to study three-dimensional ultrasonic diffraction phenomena and derive the numerical data of amplitude loss and the phase shift for correcting induced errors. Calculation is made for near-field diffraction, for the rectangular transducers, and for the transducers with strength distribution on the radiating area. In the near field, where the wavelength and the propagation distance are comparable with each other, the longitudinal and shear waves undergo different diffraction. For transducers having a noncircular shape and a strength distribution on the area, both the amplitude loss and the phase shift experience different tendencies from the classical work on the circular piston source. Use of diffraction data specific to each measurement condition is then necessary to correct the errors. The calculated results are verified for pulse-echo measurements using a shear-wave electromagnetic acoustic transducer.
Bi-orthogonality relationships involving porous media
Authors: Scandrett C. L. , Frenzen C. L.
Published: October 2005

Bi-orthogonality relationships are established for a vertically heterogeneous porous media in contact with a fluid, a solid, a second porous medium, and a free surface. Fraser’s bi-orthogonality relation for propagation of Rayleigh–Lamb modes in a plate with traction-free surfaces is shown to be a special case of the bi-orthogonality relations derived herein in which the medium can be thought of as a porous slab with zero porosity.
X-ray film database for speech research
Authors: Munhall K. G. , Vatikiotis-Bateson E. , Tohkura Y.
Published: October 2005

X-ray films have been the basis of much of our knowledge of speech production. Unfortunately, as these films age they deteriorate and they may be lost as a research resource. In this paper a database of x-ray films is described. A set of 25, high-quality x-ray films have been transferred to videodisk. The 1-h videodisk contains films provided by C. Rochette (Université Laval) and K. Stevens and J. Perkell (M.I.T.). The subjects were native speakers of Canadian English or French. The images were transferred to video frame-by-frame and the accompanying audio recordings have been synchronized with the images. The videodisk is being distributed to the speech research community.
Cross-spectral matrix estimation effects on adaptive beamforming
Authors: Grant David E. , Gross Jonathan H. , Zebrick Lawrence Mimi
Published: October 2005

Adaptive beamforming algorithms that use cross-spectral matrix (CSM) data to calculate optimum weights are sensitive to the number of unsmoothed CSM samples used in the CSM estimate. Assuming that the samples used in the CSM estimate are independent identically Gaussian distributed with zero mean, it is shown that the output power of a minimum variance distortionless response (MVDR) beamformer using the estimated CSM is biased low relative to the output power of a MVDR beamformer using the true CSM. Using data from a horizontal line array deployed in a shallow water, high noise environment, the MVDR beamformer output power has been measured with various numbers of samples used in the CSM estimate. The number of CSM samples was varied by changing the time-bandwidth product. The measured median beam noise levels are compared with the theory. Conclusions are drawn about the number of samples that should be used to obtain a reliable CSM estimate, and about how stationary the data are within the time-bandwidth integration used in the CSM estimates.
Echolocation signals and transmission beam pattern of a false killer whale (Pseudorca crassidens)
Authors: Au Whitlow W. L. , Pawloski Jeffrey L. , Nachtigall Paul E. , Blonz Michèle , Gisner Robert C.
Published: October 2005

The echolocation transmission beam pattern of a false killer whale (Pseudorca crassidens) was measured in the vertical and horizontal planes. A vertical array of seven broadband miniature hydrophones was used to measure the beam pattern in the vertical plane and a horizontal array of the same hydrophones was used in the horizontal plane. The measurements were performed in the open waters of Kaneohe Bay, Oahu, Hawaii, while the whale performed a target discrimination task. Four types of signals, characterized by their frequency spectra, were measured. Type-1 signals had a single low-frequency peak at 40±9 kHz and a low-amplitude shoulder at high frequencies. Type-2 signals had a bimodal frequency characteristic with a primary peak at 46±7 kHz and a secondary peak at 88±13 kHz. Type-3 signals were also bimodal but with a primary peak at 100±7 kHz and a secondary peak at 49±9 kHz. Type-4 signals had a single high-frequency peak at 104±7 kHz. The center frequency of the signals were found to be linearly correlated to the peak-to-peak source level, increasing with increasing source level. The major axis of the vertical beam was directed slightly downward between 0 and −5°, in contrast to the +5 to 10° for Tursiops and Delphinapterus. The beam in the horizontal plane was directed forward between 0° and −5°. In both planes, the type-1 signals had the broadest beam pattern, followed by the type-2 and type-3 signals, with the narrowest beam pattern being exhibited by the type-4 signals. The beam pattern in the horizontal plane was much narrower than the beam pattern in the vertical plane.
A model for acoustic backscatter from muddy sediments
Authors: Boyle Frank A. , Chotiros Nicholas P.
Published: October 2005

It is well known that muddy sediments often contain significant amounts of gas of biological origin. Since the scattering cross section of a gas bubble in water is typically 1000 times its geometric cross section, it is reasonable that an acoustic backscatter model intended to work over muddy sediment should contain a bubble resonance scattering component. In this paper a heuristic model is presented, based on scattering from a distribution of suspended bubbles in mud. For acoustic propagation purposes, the mud is treated as a viscous fluid. Since estimates of bubble size distributions in mud are currently unavailable, a bubble distribution similar in shape to that observed in the water column is assumed. The model’s only free parameter is the gas fraction, which can be varied to fit the model to observed data. Small amounts of gas appear to be sufficient to produce observed levels of backscatter. For a homogeneous bubble distribution, the model can be inverted to give an estimate of the gas bubble size distribution from measured backscatter data. A discussion of depth dependent bubble distributions is included. The simplest case is that of a homogeneous bubble half-space buried underneath a finite gasless layer. The thickness of the layer appears to affect the grazing angle dependence of the backscatter significantly.
Lake-bottom recognition using a wideband sonar system and time-frequency analysis
Authors: Andrieux Nicolas , Delachartre Philippe , Vray Didier , Gimenez Gérard , Dziedzic Albin
Published: October 2005

The work presented in this paper deals with the response of underwater bottom insonified with wideband ultrasonic signals. The aim of the study is to investigate the feasibility of the recognition of the nature of sediment layer using a wideband sonar system and time-frequency representations of backscattered echoes from the bottoms. The experiments have been performed in a natural environment, in Lake Geneva. Time-frequency representations of backscattered echoes based on the pseudo-Wigner distribution are realized. A method of feature extraction using the energy distribution of the time-frequency images associated with the echoes is presented. Two classification techniques have been applied to recognize the nature of the lake bottom: a classical discriminant analysis and a neural network approach using multilayer perceptron architecture. The average recognition rates for five different types of lake bottom and for both techniques are presented and compared.
Outdoor sound propagation in the presence of atmospheric turbulence: Experiments and theoretical analysis with the fast field program algorithm
Authors: L’Espérance André , Gabillet Yannick , Daigle Gilles A.
Published: October 2005

Results of experimental measurements of sound propagating over the range from 16 to 250 m at frequencies between 160 and 2000 Hz in a refracting atmosphere are described. Wind velocity and temperature are also measured simultaneously with the acoustical measurements at different heights. The meteorological measurements provide the sound-speed profile as well as the strength of turbulence up to an elevation of 32 m. The measurements are sampled every 0.25 s, thus providing a continuous record of sound-speed profiles and sound-pressure levels over time. The individual sound-speed profile is used to generate predicted sound levels that are compared with the measured sound levels.
Nonspecular reflection of two- and three-dimensional acoustic beams from fluid-immersed cylindrically layered elastic structures
Authors: Zeroug Smaine , Felsen Leopold B.
Published: October 2005

This paper extends the complex ray analysis developed for nonspecular reflection of quasi-Gaussian acoustic beams from fluid-loaded plane elastic structures [S. Zeroug and L. B. Felsen, ‘‘Nonspecular reflection of two- and three-dimensional acoustic beams from fluid-immersed plane layered elastic structures,’’ J. Acoust. Soc. Am. 95, 3075–3089 (1994)] to cylindrically layered configurations. Except for the adaptation to cylindrical geometry, the rigorous spectral and subsequent asymptotic techniques employed for the plane layered case remain intact. Thus the quasi-Gaussian beams with arbitrary collimation and arbitrary incidence angles are again modeled by the complex source point (CSP) method and the formal complex wave-number spectral integrals for the total scattered field are reduced asymptotically to yield numerically efficient algorithms parametrized in terms of self-consistently interacting specularly reflected and leaky wave fields, which model the proper wave physics. Results are obtained for reflection of two-dimensional (2-D) and three-dimensional (3-D) CSP beams from an aluminum solid cylinder in water, and for 2-D CSP beams from a fluid-loaded cylindrical shell whose modes are assumed, in the high-frequency regime, to be derivable approximately from those for the fluid-loaded plate. The data reveal a strong dependence on the cylindrical surface curvature which manifests itself in the resulting reflectivity pattern through multiple beam splitting for diverging as well as collimated incident beams. These observations pertain not only when the incident beam is phase matched to a leaky wave but also for incidence angles far from the phase-matched condition. Physical explanations are given for these phenomena which are compared with, and related to, those encountered for the planar configurations. As for the planar case, the outcome is a versatile algorithm for predicting interaction of arbitrarily collimated 2-D and rotationally symmetric 3-D acoustic beams with cylindrically curved elastic media, at arbitrary angles of incidence.