bluuebunny/crossref_metadata_2025 huggingface dataset:
Broadband matched-field processing of transient signals in shallow water
Authors: Jesus S. M.
Published: October 2005

Range and depth source localization in shallow water amounts to the estimation of the normal-mode structure of the acoustic field. As ‘‘seen’’ by a vertical array, and from a modeling point of view, the normal-mode structure appears as a set of nonplane coherent waves closely spaced at a vertical angle. This paper presents a full-wave-field narrow-band high-resolution technique that uses the spectral decomposition of the sample covariance matrix to resolve the vertical arrival structure of the harmonic acoustic field. The broadband processor is obtained by weighted averaging of the narrow-band range-depth ambiguity estimates within the source signal frequency band. Results obtained on synthetic data show that its performance is always better than or equal to that of the generalized minimum variance processor, which itself largely outperforms the conventional matched-field processor. It is shown, using both simulated and experimental data, that the effect of the broadband processor is to increase the stability of the source location estimate. Results obtained with this processor on short transient pulses collected during the North Elba’89 experiment with a 62-m-aperture vertical array, showed stable and accurate localizations over long time intervals. It is also shown that the sound field, received over a given frequency band, is relatively stable over time and is in agreement with the predictions given by a standard normal-mode propagation model.
An experiment on matched-field acoustic tomography with continuous wave signals in the Norway Sea
Authors: Goncharov Valerii V. , Voronovich Alexander G.
Published: October 2005

An acoustic tomography experiment in the Norway Sea with continuous wave (cw) signals is described. Measurements were made using a point source and a vertical 560-m-long array 55 and 105 km apart. The tomography scheme was based on matched-field and matched-mode principles and consisted in ‘‘fitting’’ the media to the measured acoustic signal at the array. The sound-speed profiles were described at some points by empirical orthogonal functions and linear interpolation between these points was applied. Two- and six-parameter descriptions of the medium were in fact used. The results of tomography reconstruction of the sound-speed field agreed well with the spot measurements and demonstrated the feasibility of the tomography schemes applied.
Vibration and damping analysis of a scarf-jointed beam in flexure
Authors: Rao Mohan D. , Zhou Haiming
Published: October 2005

In this paper, an analysis for the determination of resonance frequencies, modal loss factors, and complex mode shapes of a simply supported beam with a scarf joint is presented. The system consists of a pair of isotropic or orthotropic beams that are scarf-jointed with a certain angle by a viscoelastic adhesive. The governing equations of motion of the system, for a general case of forced vibration under transverse distribution load, are first derived using the energy method and Hamilton’s principle. The adhesive material is modeled using the complex modulus approach. By using a finite-difference method, the numerical solutions of the governing equations for free vibration are obtained. A parametric study has been conducted to study the effects of various material and geometric parameters on the system’s dynamic stiffness and modal loss factors. It has been shown that there exists an optimum scarf angle for a given configuration that maximizes the system damping.
Sound scattering from cylindrical shells with internal elastic plates
Authors: Guo Y. P.
Published: October 2005

This paper examines sound scattering from cylindrical shells with internal structural loading. Here, the internal system is modeled by elastic plates, which support both longitudinal and flexural waves. It is shown that an internal plate may affect the scattering process in two ways: it may interact with shell waves at the attachment points and it may resonantly respond to the incidence excitation. For the former, the acoustic effects are the same as those caused by any other forms of internal loading, such as mass–spring systems, or by inhomogeneities of the shell itself, such as material imperfection. For the latter, it is shown that internal plate resonances may result in large amplitude coupling forces at the attachment points connecting the plate with the shell, which in turn affect the scattered field. It is shown that this resonance effect is clearly seen in the acoustic field only for light structural loading. Both pinned and clamped plates are examined, which only reveals small differences in the low- to mid-frequency domain. The effects of attachment locations are also examined. Three different regions on the shell surface are identified, in each of which the loading interacts with different kinds of shell waves, resulting in different scattering characteristics.
Cancellation of air-borne acoustic plane waves obliquely incident upon a planar phased array of active surface elements
Authors: Ruppel Timothy H. , Shields F. Douglas
Published: October 2005

The active reduction of sound reflected off an object is of much interest to researchers in acoustics. The approach often used is to control the sound in a given region (sensed by a series of point microphones) with destructive interference from a set of localized (point) sources whose strengths, phases, and locations can be adjusted. The work described herein involves extended surfaces which react to an incident wave in a prescribed manner. If this reaction is such that the surface radiates a wave 180° out of phase with and of the same amplitude as the reflected wave, the reflected wave is canceled. This paper reports on the construction and testing of a planar active surface capable of canceling the reflections of obliquely incident acoustic plane waves. Theoretical analysis is given, and the viscosity and thermal conductivity of the medium in which the surface operates are found to have negligible effect on the surface’s performance. Since the phase of an obliquely incident sound wave varies over an extended surface, an array of transducers is required to accomplish the desired control. The active surface described herein has the unique feature that the wave number and frequency of surface vibrations may be independently controlled. The surface was shown to perform well for 30- to 50-kHz sound. This technique also should be applicable to lower frequency sound, which is not easily controlled passively.
A unified approach to acoustical reflection imaging. II: The inverse problem
Authors: Berkhout A. J. , Wapenaar C. P. A.
Published: October 2005

Using the forward matrix model, as derived in part I [A. J. Berkhout, J. Acoust. Soc. Am. 93, xxx(1993)], it is shown that the first and main part of numerical acoustic imaging consists of a wave field extrapolation process by double matrix inversion. Physically, the wave field extrapolation process means that the downward propagation effects and the upward propagation effects are eliminated from the measurements. Next, the reflection information is extracted from the wave field extrapolation result. Optionally, the reflection information is translated to discipline-oriented material parameters by some data fitting process. Double focusing, i.e., focusing in emission and focusing in detection, is closely related to the above numerical imaging process. Finally, it is shown that imaging of zero-offset or puls-echo data can be formulated by single matrix inversion, involving phase shifts only.
Scattering by objects buried in underwater sediments: Theory and experiment
Authors: Lim Raymond , Lopes Joseph L. , Hackman Roger H. , Todoroff Douglas G.
Published: October 2005

The scattering of sound by objects buried in underwater sediments is studied in the context of an exactly soluble model. The model consists of two fluid half-spaces separated by a planar, fluid, transition layer of arbitrary thickness. Attenuation is included in any of these regions by using complex wave numbers. A directional source field, generated in the upper half-space by a continuous line array, insonifies an object placed in the lower half-space. The scattered field detected by another line array placed anywhere in the system may be calculated. The solution is determined from the T matrix for the bounded scattering system and is exact (in linear acoustics) to all orders of multiple scattering among the interfaces and object. Numerical results are presented to investigate the effect of the local acoustic environment on the free-field, in-water scattering resonances of thin spherical shells. The field scattered by a shallowly buried object is discussed with emphasis on the importance of evanescent wave scattering in detection from above the sediment over an extended range. An initial set of experiments meant to verify the model are described. Results are presented and discussed for the measured scattering response of buried, spherical, evacuated, steel shells, that are 2.25% and 11% of the outer radius in thickness.
Normal mode wave-number estimation using a towed array
Authors: Chouhan Harish M. , Anand G. V.
Published: October 2005

In the analysis of the null-steering technique of normal mode filtering presented by the authors previously [H. M. Chouhan and G. V. Anand, J. Acoust. Soc. Am. 89, 735–744 (1991)], it was assumed that the modal wave numbers km are known a priori. In practice, the waveguide parameters upon which the modal wave numbers depend are normally not known and are difficult to measure accurately. In order to use the null-steering technique of mode filtering, or in applications such as source localization and waveguide characterization, it is necessary to estimate the modal wave numbers. An estimation procedure using a towed horizontal line array is presented in this article. The method entails eigendecomposition of the range-averaged array signal correlation matrix. Range-averaging effectively decorrelates the normal mode signals and enables the use of high-resolution spectral estimation techniques such as MUSIC for estimating the modal wave numbers. Simulation results for the Pekeris model of the ocean are presented.
Eigenfrequencies of an acoustic rectangular cavity containing a rigid small sphere
Authors: Roumeliotis John A.
Published: October 2005

Analytical expressions are derived for the eigenfrequencies of any mode in a hard-walled acoustic rectangular cavity, containing an acoustically small rigid sphere. A straightforward and simple approach is employed to obtain a first-order perturbation of the cavity eigenfunctions and the corresponding eigenfrequency shifts. Rectangular wave functions, as well as their expansion in terms of cylindrical wave functions and finally in terms of spherical ones, are used. The results are useful in problems connected with acoustic levitation and with excitation or probing of resonant cavities. Some suggestions are made about the best positioning of the probe, for more exact measurement of the eigenfrequency of any mode in the unperturbed cavity. Graphical results for some of the lower-order modes are given, for various values of the parameters.
Effects of varying signal duration on pure-tone frequency discrimination in humans and monkeys
Authors: Sinnott Joan M. , Brown Charles H.
Published: October 2005

This study examined the effects of varying signal duration and pulse repetition rate on pure tone frequency difference limens (FDLs) at 500 Hz and 4 kHz in humans and monkeys. Two experiments examined FDLs as a function of tone duration from 12–400 ms, using stimuli presented either with a constant pulse rate, or with a constant interstimulus interval. In both cases, at 500 Hz, human FDLs increased more than monkey FDLs as duration decreased from 400 to 12 ms. This effect resulted in monkey FDLs that were about 14 times larger than human FDLs at 400 ms, but only about 4 times larger at 12 ms. At 4 kHz, human and monkey FDLs showed more similar rates of increase as duration decreased. A third experiment examined FDLs at 500 Hz for a 100-ms tone as a function of pulse rate (1 per 250–2000 ms). Here, FDLs for humans and monkeys varied in a similar fashion, indicating that both species’ sensitivity was similarly affected by manipulating temporal variables relating to memory load, rather than sensory coding. These data provide evidence that, at 500 Hz, humans have a qualitatively different pure tone frequency analyzing mechanism from monkeys, possibly based on better access to phase-locking mechanisms.
Production and perception of a novel, second-language phonetic contrast
Authors: Flege James Emil
Published: October 2005

Four experiments, all of which focused on vowel duration, assessed Chinese subjects’ production and perception of the contrast between /t/ and /d/ in the final position of English words. Vowel duration was measured in minimal pairs in the first experiment. The stimuli in natural-edited beat–bead and bat–bad continua in which vowel duration varied in 20-ms steps were then presented to native English and Chinese subjects in a forced-choice test, in an experiment using the method of adjustment, and in an imitation task. The non-natives who learned English in childhood closely resembled native speakers in all four experiments. Three groups of non-natives who had learned English as a second language in adulthood, on the other hand, differed from the native speakers. The late learners produced significantly longer vowels in words ending in /d/ than /t/. However, the late learners’ vowel duration differences were much smaller than the native speakers’, and were correlated significantly with degree of foreign accent in English. The late learners differed from the native speakers in several ways in the two perception experiments, and also in the imitation task. The pattern of significant and nonsignificant between-group differences, but not data for individual subjects, was consistent with the hypothesis that L2 (second language) production accuracy is limited by the adequacy of perceptual representations for sounds in the L2.
Digital time delay network for an active underwater acoustic coating
Authors: Howarth Thomas R. , Bao Xiaoqi , Moser Robert , Varadan Vijay K. , Varadan Vasundara V.
Published: October 2005

A digital time delay system has been developed for control of an active underwater coating. The coating contains piezoelectric polymer sensors and a piezocomposite actuator encapsulated within a host polymer. Its application is to be layered onto submerged objects that desire reduction of an underwater sound reflection. The control system featured considers a time delay network as opposed to an analog phase delay approach featured in past studies [Howarth et al., J. Wave Mat. Interact. 4, 83–88 (1989); Howarth et al., J. Acoust. Soc. Am. 91, 823–831 (1991)]. The concept of the active coating control is that of an open-loop velocity feedback between sensors and actuator. This scheme prevents feedback instability because the actuator output is acoustically decoupled from the sensors. The digital time delay controller has the added benefit of parallel multichannel processing to characterize both the incident acoustic pressure and the reflected pressure. The reflected pressure is monitored at the sensors for near-field determination of the effectiveness of the active coating system prior to far-field sound radiation. Experimental results were obtained for normal incidence in a water-filled acoustic pulse tube terminated at its boundary with an active coating and air backing. Echo reduction comparisons as functions of sound reduction and bandwidth are presented.
Design of sparse arrays in one, two, and three dimensions
Authors: Pumphrey Hugh C.
Published: October 2005

In order to detect the direction from which plane waves are arriving, it is common to use an array of microphones, or other sensors, which are uniformly spaced along a line, over a plane, or through a region of space. The outputs of the microphones are added together and averaged. Such an array is simple in concept but wasteful of microphones because a particular spacing between two microphones need only occur once if suitable processing is used. A uniform array in which some microphones have been removed is termed a sparse array; such an array requires longer averaging times if it is to achieve similar performance to the equivalent nonsparse array. This paper addresses the question of how to design such arrays when the original filled array consisted of microphones uniformly distributed along a line, over a square or throughout a cubic region of space. The line array has been studied extensively already, and it is found that the cubic array presents a similar, but more difficult problem. The most useful way, in general, of constructing a cubic array is as a product of sparse line arrays, but this does not always give the best answer. The square array is similar to the cubic one, but has an additional type of solution which is very simple and often the most efficient.
Adaptive acoustic echo cancellation microphone
Authors: Kuo Sen M. , Pan Zhibing
Published: October 2005

In teleconferencing, speaker-phone systems have an annoying acoustic echo problem. The acoustic echo canceller using an adaptive transversal filter is an effective solution. However, very-high-order adaptive filters have computational and convergence problems. Furthermore, acoustic echoes picked up by multiple microphones make the real-time application very difficult to implement. In this paper, a new approach to these problems is proposed. This new acoustic echo cancellation microphone system consists of two closely positioned directional microphones pointed in opposite directions and an adaptive filter. The adaptive filter converges to the transfer function difference between the two echo paths, which are similar since the two microphones are close to each other and far away from the loudspeaker. Therefore, a very-low-order adaptive filter is sufficient to reduce the echo. The steady-state analysis of this new system shows significant improvement over the traditional system. The system is tested using real speech data collected from a typical conference room. The experimental and simulation results show that more than 26 dB of cancellation can be achieved during the receive mode with the filter order equal to 64.
Acoustic radiation force on a bubble
Authors: Lee C. P. , Wang T. G.
Published: October 2005

For the radiation force acting on a small bubble in a liquid medium in the presence of a plane standing sound wave, there has been a longstanding discrepancy between the prediction of Yosioka and Kawasima [Acustica 5, 167–173 (1955)], and that of Eller [J. Acoust. Soc. Am. 43, 170–171 (1968)]. It is concluded that the two predictions are consistent if not for some algebraic mistake in the former work.
The three-dimensional vibration analysis of a cantilevered skewed helicoidal thick shell
Authors: McGee O. G.
Published: October 2005

The first known three-dimensional (3-D) vibration solutions for cantilevered skewed helicoidal thick shells are presented. The Ritz method is used to minimize the 3-D elasticity-based dynamical energies with displacements approximated by mathematically complete polynomials satisfying the clamped boundary conditions exactly. The accuracy of the method is established by convergence studies explicitly showing the effects of thickness ratio and twist angle in the presence of shell skewness. Results obtained using the present Ritz method are compared with those obtained in a detailed 3-D finite element analysis, where the correctness of various solid element discretizations are examined. This work offers some useful 3-D vibration results for the title problem with which future solutions drawn from higher-order thick shell theories may be compared.
New results for the elastic parabolic equation
Authors: Collins Michael D.
Published: October 2005

New results are presented for the elastic parabolic equation (PE). Galerkin’s method is applied to handle solid–solid interfaces efficiently. Rayleigh and Stoneley waves are handled with the elastic PE for the first time. Conversion formulas that are local in range are derived for obtaining quantities such as the horizontal displacement and the shear potential from the dependent variables of the nonstandard formulation of elasticity that is used with the elastic PE. The two-way elastic PE is implemented for problems involving realistic boundary and interface conditions and is applied to solve reverberation problems. The self-starter is generalized to problems involving a source in a solid layer. The energy-conserving PE is generalized to elastic media. The elastic PE is applied to problems involving the propagation of an interface wave up a sloping bottom and the cutoff of modes and coupling into shear-wave beams in the sediment. The latter problem is analogous to an acoustic problem that was solved by Jensen and Kuperman [‘‘Sound propagation in a wedge-shaped ocean with a penetrable bottom,’’ J. Acoust. Soc. Am. 67, 1564–1566 (1980)].
Space/time characteristics of localized transient fields from planar axisymmetric sources
Authors: Satyapal Shanti , Stepanishen Peter R.
Published: October 2005

Several approaches are presented to compute the acoustic transient field from planar axisymmetric circular sources vibrating with continuous space/time velocity distributions. These approaches include an impulse response approach for uniformly vibrating sources, and a generalized impulse response approach and a source discretization approach for nonuniformly vibrating sources. Also, two approximations for the far field will be overviewed. As a particular case of interest and importance, the acoustic field generated by a space/time modified power spectrum (MPS) driving pulse will be described using the various approaches. Numerical results are presented to illustrate the localized behavior of the space/time field. These results are compared to analogous results obtained from ordinary cw driving pulses. Methods to optimize the localization power of the MPS pulse are also discussed.
Interface reflection of spherical acoustic waves in the first- and second-order rational parabolic approximations and their artifacts
Authors: de Hoop Maarten V. , de Hoop Adrianus T.
Published: October 2005

The accuracy of the first- and second-order rational parabolic approximations of the ‘‘vertical’’ slowness and the nature of the artifacts associated with them in the space-time solutions to the acoustic wave equations in a fluid medium are investigated. In particular, the reflection of an impulsive, point-source generated, spherical wave against the boundary with a medium with a higher wave speed is analyzed. From the space-time Green’s functions in the relevant two-media configuration, evaluated with the aid of the modified Cagniard method, it is found that, instead of generating the real, physical head wave, the approximations generate artificial head-wavelike arrivals. The analysis makes explicit in which regions of space and in which time interval the artifacts show up and of what nature they are. Numerical results are presented.
Form factor of a cylindrical sonic source and application in borehole acoustics
Authors: Yu Shoumian , Liu Yinbin
Published: October 2005

By introducing the concept of a form factor for a cylindrical sonic source, a new method is constructed for solving boundary value problems of the wave field produced by such sources when the solutions for a simple source is known, provided the boundary conditions are axisymmetrical and are linear and homogeneous in the potentials. The form factor is defined in cylindrical coordinates as a function F(k) of the wave number k. The analytic properties of F(k) are described. It is proved that F(k) can be obtained from the far-field approximation and is related to the directional factor through a simple transformation. The form factors of several simple-shaped sources are derived. The theory is applied to the case of a borehole to show that the effect of the form factor on the profile of the full wavetrain is prominent in certain cases.
Exact reflection and transmission operator symbols in two-dimensional, invariant imbedding-based, propagation modeling
Authors: Fishman Louis
Published: October 2005

Recognizing that typical ocean propagation problems are essentially scattering problems in terms of a transition region and transversely inhomogeneous asymptotic half-spaces, wave-field splitting, invariant imbedding, and phase space methods have reformulated the problem in terms of an operator scattering matrix characteristic of the transition region. This approach solves the elliptic (fixed-frequency) scattering problem by well-posed marching (one-way) methods, and is centered on the reflection and transmission operator symbol equations. For several nontrivial, two-dimensional, refractive index profiles, these equations (and the wave-field equations) are solved exactly and analyzed. These results provide benchmark cases to test both the scattering operator and subsequent wave-field calculations, providing a severe test of the stiff nonlinear solvers employed in the numerical implementation of the method. The exactly solved models incorporate symmetric and asymmetric wells, trapped modes, and sharp-gradient features. Numerical results will be presented. [Work supported by NSF, AFOSR, ONR, ASEE, JEWC, and the S. N. Bose Centre for Basic Sciences.]
Critical propagation issues in shallow-water acoustics
Authors: Weston David E.
Published: October 2005

Several sets of propagation problems in shallow-water acoustics are discussed, covering overlapping frequency ranges. At VLF (say below 300 Hz) the bottom material is important, because energy travels in the bottom or because of attenuation associated with shear-wave coupling. At LF (say above 30 Hz) the presence of gas in surficial sediments can change boundary conditions and bottom losses, and even allow a new type of interface wave. At MF (300 Hz to several kHz) dispersed fish can raise the attenuation, typically by 1 dB/km. Fish have also been observed to dominate the echo structure or reverberation, out to 100 km. At HF (say above several 100 Hz) the sound-speed profile becomes important, partly because of channeling. At VHF (usually above several kHz) the propagation mechanisms tend to change from boundary reflection to boundary scattering. In addition all these effects are greatly influenced by distance and by water depth.
Autonomous vibration of simple pressure-controlled valves in gas flows
Authors: Fletcher N. H.
Published: October 2005

Pressure-controlled gas-flow valves are responsible for sound generation in woodwind and brass instruments, and in the vocalization of many animals. When only a single degree of freedom is allowed for the valve motion, four simple configurations are possible, depending upon the effect upon the valve opening of static overpressures applied at either inlet or outlet ports in the presence of the flow. It is shown that, depending upon the valve configuration, there exist particular ranges of acoustic impedance for the inlet and outlet ducts to the valve within which self-sustained valve oscillation is possible. The results are particularly simple when the lengths of these ducts are less than one-quarter of a wavelength at the resonant frequency of the valve, in which circumstance oscillation takes place close to that resonance frequency. The analysis treats only the initiation of oscillations of small amplitude, as a precursor to the maintenance of large-amplitude nonlinear oscillations.
A simple method for accurate prediction of finite barrier insertion loss
Authors: Lam Y. W. , Roberts S. C.
Published: October 2005

A simple model of diffraction is developed that can predict accurately the insertion loss of finite length barriers. The model is based on the geometric theory of minimum diffracted paths. Assumptions are made on the phase and amplitude of each diffracted wave to obtain a new and rather simple formulation of the solution. It provides a clear picture of the sound attenuation performance of a barrier as a function of barrier length. Extensive model experiments are used to verify the model. The model’s accuracy in predicting the overall pattern of the narrow-band insertion loss is found to be comparable to that of an integral equation method, although the latter method produces better prediction in the fine details of the sound field. The model is much simpler than and as accurate as other methods that apply the usual geometric solutions to each diffracted path, and represents a major improvement on Maekawa’s energy summation method for octave band finite barrier calculations.
Applications of the method for transducer transient suppression to various transducer types
Authors: Piquette Jean C.
Published: October 2005

Recently, a new method for suppressing the transient pressure radiation ordinarily produced by a projector in response to drive turnon and turnoff has been described [J. C. Piquette, ‘‘Method for transducer transient suppression I. Theory,’’ J. Acoust. Soc. Am. 92, 1203–1213 (1992) and ‘‘II. Experiment,’’ J. Acoust. Soc. Am. 92, 1214–1221 (1992)]. The experiments described in the earlier reports involved application of the method primarily to piezoelectric spherical transducers, although one preliminary application to an array of piezoelectric tubes was also considered. The present work involved the application of the method to a variety of transducer types to which the method had not been applied previously. These types are (i) flexural disk, (ii) Helmholtz resonator, (iii) moving coil, (iv) inductor-tuned Tonpilz, and (v) a dual transducer array of piezoelectric squares and disks. A high degree of transient suppression was observed in all units that were tested. Equivalent circuits useful for designing the transient-suppressing drive are also provided.
Internal stress wave measurements in solids subjected to lithotripter pulses
Authors: Gracewski S. M. , Dahake Girish , Ding Zhong , Burns S. J. , Everbach E. Carr
Published: October 2005

Semiconductor strain gauges were used to measure the internal strain along the axes of spherical and disk plaster specimens when subjected to lithotripter shock pulses. The pulses were produced by one of two lithotripters. The first source generates spherically diverging shock waves of peak pressure approximately 1 MPa at the surface of the specimen. For this source, the incident and first reflected pressure (P) waves in both sphere and disk specimens were identified. In addition, waves reflected by the disk circumference were found to contribute significantly to the strain fields along the disk axis. Experimental results compared favorably to a ray theory analysis of a spherically diverging shock wave striking either concretion. For the sphere, pressure contours for the incident P wave and caustic lines were determined theoretically for an incident spherical shock wave. These caustic lines indicate the location of the highest stresses within the sphere and therefore the areas where damage may occur. Results were also presented for a second source that uses an ellipsoidal reflector to generate a 30-MPa focused shock wave, more closely approximating the wave fields of a clinical extracorporeal lithotripter.
Intensity-weighted average of instantaneous frequency as a model for frequency discrimination
Authors: Anantharaman Jayanth N. , Krishnamurthy Ashok K. , Feth Lawrence L.
Published: October 2005

The intensity-weighted average of instantaneous frequency (IWAIF) is developed as a model to predict listener performance in tasks primarily requiring frequency discrimination. IWAIF is closely related to the envelope weighted average of instantaneous frequency (EWAIF) model proposed by Feth for similar tasks. The primary difference is that the IWAIF model uses intensity (envelope squared) as the weighting function instead of the envelope. The advantages of IWAIF over EWAIF are that (a) it has a convenient frequency domain interpretation; and (b) it is much simpler to compute than the EWAIF. The IWAIF is the ‘‘center of gravity’’ of the energy spectral density function of the signal.
On the pitch of two-tone complexes
Authors: Dai Huanping
Published: October 2005

The predictions of two models for the pitch of two-tone complexes were compared to pitch matching results obtained in a previous study [Feth, O’Malley, and Ramsey, J. Acoust. Soc. Am. 72, 1403–1412 (1982)] and the present study. In one model, the pitch value of a waveform was calculated from the envelope-weighted average of instantaneous frequency of the waveform (the EWAIF model). In the other model, the pitch value was calculated from the squared-envelope-weighted average of instantaneous frequency (the SEWAIF model). The SEWAIF model better predicts the data.
Spectral interference in a binaural detection task: Effects of masker bandwidth and temporal fringea)
Authors: Bernstein Leslie R. , Trahiotis Constantine
Published: October 2005

Recently, it was reported that the detectability of a 100-ms, 800-Hz tone (the target) presented antiphasically (Sπ) against a background of continuous, broadband, diotic noise could be degraded if a 400-Hz tone (the interferer) was gated simultaneously with the target [L. R. Bernstein, J. Acoust. Soc Am. 89, 1306–1313 (1991)]. This degradation, termed ‘‘interference,’’ was reduced by presenting the interferer continuously. In the present study, the amount of such interference was measured when the target was masked by either a broadband or a narrow-band (100-Hz-wide) noise. The narrow-band noise produced a relatively large masking-level difference, thereby allowing about 10 dB of interference to be observed. In other conditions, the interferer was turned on (temporally ‘‘fringed’’) prior to the target. The presence and duration of a forward fringe of the interferer did not reduce the interference, even for forward fringes of 320 ms. This result is consistent with those of Woods and Colburn [W. S. Woods and H. S. Colburn, J. Acoust Soc. Am. 91, 2894–2902 (1992)] who measured the detectability of interaural delay of low-frequency tones. The data from both studies indicate that binaural interference is observed even under conditions where interferers and targets are perceptually segregated in the sense that listeners hear more than one sound object.
Psychoacoustics of normal adult chickens: Thresholds and temporal integration
Authors: Saunders Samuel S. , Salvi Richard J.
Published: October 2005

Three adult female chickens were trained to detect pure tones using a positive reinforcement paradigm. A modified perometer estimation-through sequential testing (PEST) threshold determination procedure was used to measure the audiogram between 250 and 5500 Hz, at 0.1-octave steps over most of the range. For the mean audiogram, threshold increased rapidly below 400 Hz and above 4000 Hz. Between these extremes was a broad low threshold area where thresholds varied between 11 and 23 dB, with the lowest thresholds between 1000 and 2000 Hz. Audiograms were similar for all three subjects over the middle of the frequency range, but there was more variability across subjects at the extreme high and low frequencies. After determination of the audiogram, thresholds for 12 frequencies were measured as a function of stimulus duration (ranging from 16 to 750 ms) to determine a threshold-duration function. Average time constants varied from 148 to 348 ms, increasing with increasing stimulus frequency. Average slopes varied from 2.18 dB per doubling of duration to 2.61 dB per doubling of duration, increasing with increasing stimulus frequency. The increases in slope and time constant with stimulus frequency, while consistent, were small compared to the variability of these parameters across subjects.
Acoustic radiation pressure
Authors: Lee C. P. , Wang T. G.
Published: October 2005

Acoustic radiation pressure is an area in nonlinear acoustics that has been associated with a lot of confusion and controversy since the work by Lord Rayleigh. From the more recent works, it would appear that all the pieces necessary for a complete understanding of this topic exist. The purpose of this work is to put the pieces together and systematically present a coherent picture of the subject, starting from the first principles. The approach is based on the perturbation technique. Self-consistency will be emphasized. Therefore, although the Eulerian coordinates will mainly be used to formulate the problem, which will be shown to be very simple and straightforward, it will also be demonstrated how the same results can easily be obtained by using the more traditional Lagrangian coordinates, if the latter are applicable. It will also be argued that it is simpler to define Rayleigh and Langevin radiation pressures according to whether or not the system is subjected to a constraint.
Matched-field inversion for source localization with uncertain bathymetry
Authors: Dosso S. E.
Published: October 2005

A good knowledge of the bathymetry is required for reliable matched-field source localization in shallow-water environments. However, bathymetry can be difficult to measure in ice-covered Arctic waters. This letter describes a method for determining source location using simulated annealing to perform matched-field inversion with poor or little knowledge of the bathymetry. The inversion is carried out for source range and depth and a (range-dependent) model for bathymetry. Although the bathymetry cannot be determined uniquely in this manner, an effective model can be computed which allows accurate source localization. This method essentially applies the concepts of ‘‘focalization’’ [M. D. Collins and W. A. Kuperman, J. Acoust. Soc. Am. 90, 1410–1422 (1992)] to ocean bottom parameters.
Vertical array response to shipping noise: Model/measurement comparisons for range-dependent Mediterranean sites
Authors: Hamson Rachel M.
Published: October 2005

Modeling techniques for the prediction of vertical array response to shipping-dominated ambient noise in range-dependent environments are described, making use of the RANDI-2 noise model and the SUPERSNAP normal mode model. Detailed modeling for two sites in the central Mediterranean is carried out, which includes propagation of shipping noise via both upslope and downslope paths, together with small wind noise contributions. Results for frequencies of 300 and 600 Hz are compared with data taken on the SACLANT Centre vertical array in 1984–85, which showed, at one site, a dual-arrival structure with maximum noise at elevation angles of ±15° from the horizontal, and at a second site, a single broad lobe at the horizontal. The models successfully predict these two frequently observed structures. It is demonstrated that the noise from horizontal directions is due to downslope propagation from sources in shallow coastal water. Further model runs allow the prediction of vertical array response for different frequencies, array depths, and season. Results show that the dual-arrival structure of the first site for 300 Hz collapses to a single lobe structure at 50 Hz.
Harmonic generation in plane and cylindrical nonlinear Rayleigh waves
Authors: Shull D. J. , Hamilton M. F. , Il’insky Yu. A. , Zabolotskaya E. A.
Published: October 2005

Harmonic generation in plane and cylindrical nonlinear Rayleigh waves is investigated theoretically on the basis of spectral model equations for propagation in isotropic solids [E. A. Zabolotskaya, J. Acoust. Soc. Am. 91, 2569–2575 (1992)]. Approximate expressions are derived for second harmonic generation and for finite amplitude attenuation of the source frequency component. The expression for the source frequency component is in good agreement with numerical solutions of the model equations, even throughout the shock wave region. Acoustic saturation of both plane and cylindrical waves is predicted for sufficiently high source amplitudes, at which the amplitude of the Rayleigh wave at a given field point becomes independent of the source amplitude. Frequency spectra and time waveforms are calculated, and the spatial redistribution of the energy density due to harmonic generation is examined.
A radial solution of the Van der Pol–Rayleigh limit cycle oscillator for small ε
Authors: Raphael David T.
Published: October 2005

The Van der Pol equation limit cycle oscillator is known to be the same as that described by Rayleigh’s equation in acoustics. This paper presents a technique for obtaining a closed-form analytic form of the radial form of the Van der Pol equation and its limit cycle when the angular frequency is assumed to be constant-valued. When this condition of angular frequency is made, valid only in the range of small ε, the polar-coordinate form of the nonlinear differential equation is used in order to derive, using a variation-of-parameters approach, an exact solution involving modified Bessel functions and sinusoidal functions. The approximate solution to O(ε2) obtained by this method compares very well with known solutions, both analytically and graphically.
Investigation of fiber-matrix interface by guided waves: A perturbation analysis
Authors: Dai J. D. , Jen C. K.
Published: October 2005

A perturbation analysis of a cylindrical structure of a transversely isotropic (hexagonal) fiber in an infinite thick isotropic matrix with a thin isotropic interface (bonding) layer is presented. The perturbation formulation offers simplicity for numerical calculations and reveals the effects of density and stiffness constants (c11 and c44) of the bonding layer on the phase velocities and cutoffs of acoustic waves propagating along axial direction of the fiber. Numerical results for dispersion curves of pure guided flexural F11, F12, and F13 modes and torsional T01, T02, and T03 modes unperturbed and perturbed by the bonding layer are given as examples. It has been found that the reduction of density of the bonding layer increases the phase velocities while the reduction of stiffness constant c44 or c11 decreases the phase velocities of guided modes. However, the effect of c11 is negligible compared with that of density or c44. Effects of bonding layer material constants on the dispersion curves are larger for higher-order guided modes and when the operating frequencies are closer to the cutoffs, hence it is preferable to use higher-order modes and acoustic frequencies near cutoffs for the detection of the bonding quality.
Local temporal variance of Wigner’s distribution function as a spectroscopic observable: Lamb wave resonances of a spherical shell
Authors: Hughes D. H. , Marston P. L.
Published: October 2005

The time-frequency analysis of the transient response of elastic objects has been asserted to be useful for relating features of the scattering to physical parameters of the scatterer. [N. Yen, L. R. Dragonette, and S. K. Numrich, J. Acoust. Soc. Am. 87, 2359–2370 (1990)]. In this article, the Wigner distribution function is applied to the mean-square temporal spread (as a function of frequency) of the impulse response of a scatterer. The application is illustrated for a thin stainless steel shell in water. The emphasis is on resonance frequencies, where the temporal spread can be large, and locally the frequency response is taken to have a Breit–Wigner form. That approximation yields a simple relationship between the measure of the temporal spread, Q(ka), and the width of the resonance when evaluated at the resonance frequency. The frequency dependence is expressed in terms of the wave number–radius product ka for the shell. The analysis is supported by calculation of resonance widths from ray theory and by ray approximations of form function contributions that dominate Q(ka) near certain resonances.
Transient sound radiation from impulsively accelerated bodies
Authors: Wu Sean F.
Published: October 2005

This paper presents an integral formulation derived from the Kirchhoff integral theorem for predicting transient sound radiation from an impulsively accelerated body. The acoustic pressure is determined in an explicit form in the frequency domain, and subsequently converted to the time domain through Fourier transformations. This integral formulation can be extended to cases in which the body is subjected to an arbitrarily time-dependent excitation. The transient acoustic pressure is shown to be expressible as a convolution integral of the impulse response function to the time history of the surface velocity of the body. Since there is no relationship between the integral formulations for the exterior and interior regions, solutions for the radiated acoustic pressure in the exterior region are uniquem, even at frequencies corresponding to the eigenfrequencies of the related interior boundary value problem. Analytical results based on this integral formulation agree perfectly with those obtained using other methods for transient sound radiation from an explosively expanding sphere, impulsively accelerated rigid sphere, impulsively accelerated baffled, and unbaffled circular disks. Numerical implementations of the present integral formulation are expected to be more amenable to solution than directly solving the classical Kirchhoff integral formulation in which the frequency and time domains are fully coupled.
Air pressure regulation during speech productiona)
Authors: Moon Jerald B. , Folkins John W. , Smith Alice E. , Luschei Erich S.
Published: October 2005

Vocal tract pressures during speech tend to be maintained in the face of airway leaks that might be encountered by individuals with repaired palatal clefts. This study tested the hypothesis that such constant pressures can be explained as a consequence of constant pressure source characteristics of the respiratory system during speech production. This conceptualization differs from pressure regulation theories [e.g., D. Warren, Cleft Palate J. 23, 251–260 (1986)] which posit that active reflexive compensatory responses occur to regulate air pressure during speech. Four experiments were conducted to (a) confirm the distinction between constant flow versus constant pressure sources using a plastic vocal tract model, (b) compare air pressure and flow patterns associated with airway leaks in normal speakers to model data, (c) study the effects of gas density in the vocal tract model on air pressure and air flow patterns predicted by a nonreflexive constant pressure source hypothesis, and (d) compare air pressure and air flow patterns associated with airway leaks obtained from normal speakers using different gas densities to model data. Overall, observed flow and pressure patterns suggest the possible influence of constant pressure source characteristics of the respiratory system during speech on maintenance of intraoral air pressure.
The Brewster wave-number concept for elastodynamics
Authors: Ditri John J. , Lakhtakia Akhlesh
Published: October 2005

The existence of a Brewster wave number is demonstrated for the case of plane-wave reflection by a specularly smooth, planar interface joining two homogeneous, linearly elastic, isotropic solid half-spaces. Such a wave number is numerically shown to exist for two material combinations: steel–aluminum and steel–brass. The wave number can be such that plane waves are either propagating or evanescent. Since the calculated Brewster wave number is not dependent upon which of the two half-spaces contains the incident plane waves, it appears to be an intrinsic property of the bimaterial interface and hence may be useful in the characterization of such interfaces.
An exact solution for a reflection coefficient in a medium having an exponential impedance profile
Authors: Pendergraft Karen , Pieper Ronald
Published: October 2005

An exact analytical solution for the plane wave reflection coefficient in an isotropic, constant velocity medium exhibiting an exponential impedance space profile is derived. The analysis includes the effects of discontinuities at both boundaries of the impedance transformer. The derivation is based on an exact differential equation that describes the space evolution of the reflection coefficient along a nonuniform transmission line. Power transmission curves for various cases, including the exact quarterwave case, are presented.