bluuebunny/crossref_metadata_2025 huggingface dataset:
Dynamic permeability and borehole Stoneley waves: A simplified Biot–Rosenbaum model
Authors: Tang X. M. , Cheng C. H. , Toksöz M. N.
Published: October 2005

Stoneley waves in permeable boreholes are diagnostic of formation permeability because their propagation is affected by the dynamic fluid flow at the borehole wall. This flow using the concept of dynamic permeability is characterized. The applicability of the dynamic permeability to porous media was examined by applying it to a single fracture case and was found to agree excellently with the fracture conductivity derived from an exact solution. In dealing with the interaction of a Stoneley wave with a porous formation, the problem is decomposed into two parts. The first is the interaction of the Stoneley with an equivalent elastic formation without fluid flow. The second is the interaction with the flow that is governed by the dynamic permeability. In this manner, a simple model for the Stoneley propagation in permeable boreholes was obtained. The Stoneley-wave attenuation and dispersion characteristics from this model were compared with those from the complete model of the Biot–Rosenbaum theory in the case of a hard and a soft formation, respectively. The results from both models were found to agree very well for a hard formation, although they differ at higher frequencies for a soft formation because of the increased solid compressibility. The theoretical predictions from this simple model were also compared with recently published laboratory data of Stoneley-wave measurements, performed at both low- and high-frequency regions of Biot theory. The simple model and experiment are in excellent agreement. Because of the simplicity of the model, it can be easily applied to problems concerning Stoneley propagation in permeable boreholes, especially to an inverse problem to extract formation permeability from Stoneley-wave measurements.
Time-domain analysis of the energy exchange between structural vibrations and acoustic radiation using near-field acoustical holography measurements
Authors: Mann J. Adin , Williams Earl , Washburn Karl , Grosh Karl
Published: October 2005

The vibrational energy in a structure and the radiated acoustic energy are analyzed in the time domain using data from near-field acoustical holography measurements. A signal processing method is described that uses data from a single broadband acoustical holography measurement to determine the structural and acoustic responses for synthetic forces different from the original measurement force. The processing is based on the assumption that the measured acoustic pressure and particle velocity are related to the drive force by a linear shift invariant transfer function. Finite time length synthetic forces are examined for measurements from a fluid-loaded, point-driven, finite cylindrical shell. Comparisons of the amount of energy input to the structure by the driver, the energy injected into the fluid near field, and the energy radiated to the fluid far field show large amounts of energy that enter the fluid near field while the drive force is on, but then re-enter the structure where it is damped once the drive force is turned off. We are also able to see the rate that energy radiates to the acoustic far field and the areas of the structure which contribute most significantly to the far-field radiation. Results show that approximately 50% of the far-field energy is radiated during the active time of a transient driving force.
Layered piezoelectric resonators with an arbitrary number of electrodes (general one-dimensional treatment)
Authors: Nowotny Helmut , Benes Ewald , Schmid Michael
Published: October 2005

A general transfer matrix description for one-dimensional layered structures consisting of piezoelectric and nonpiezoelectric anisotropic layers of arbitrary number is used to calculate the electrical admittance matrix for such resonators with N electrodes. The calculation is done in detail for linearly stacked resonators with two free surfaces as well as for ring resonators with a closed acoustical path. Experimental and theoretical results are given and compared for a ring resonator with two piezoelectric layers excited by four electrodes. Such a configuration can be used to generate unidirectional resonant waves.
Discrimination of formant transition onset frequency: Psychoacoustic cues at short, moderate, and long durations
Authors: Porter Robert J. , Cullen John K. , Collins M. Jane , Jackson Dena F.
Published: October 2005

Two experiments determined the just noticeable difference (jnd) in onset frequency for speech formant transitions followed by a 1800-Hz steady state. Influences of transition duration (30, 45, 60, and 120 ms), transition-onset region (above or below 1800 Hz), and rate of transition were examined. An overall improvement in discrimination with duration was observed suggesting better frequency resolution and, consequently, better use of pitch/timbre cues with longer transitions. In addition, falling transitions (with onsets above 1800 Hz) were better discriminated than rising, and changing onset to produce increments in transition rate-of-change in frequency yielded smaller jnd’s than changing onset to produce decrements. The shortest transitions displayed additional rate-related effects. This last observation may be due to differences in the degree of dispersion of activity in the cochlea when high-rate transitions are effectively treated as non-time-varying, wideband events. The other results may reflect mechanisms that extract the temporal envelopes of signals: Envelope slope and magnitude differences are proposed to provide discriminative cues that supplement or supplant weaker spectrally based pitch/timbre cues for transitions in the short-to-moderate duration range. It is speculated that these cues may also support some speech perceptual decisions.
Psychometric functions for level discrimination
Authors: Buus So/ren , Florentine Mary
Published: October 2005

To determine the form of psychometric functions for 2I,2AFC level discrimination (commonly called intensity discrimination), ten increment levels were presented in random order within blocks of 100 trials. Stimuli were chosen to encompass a wide range of conditions and difference limens: eight 10-ms tones had frequencies of 0.25, 1, 8, or 14 kHz and levels of 30, 60, or 90 dB SPL; two 500-ms stimuli also were tested: a 1-kHz tone at 90 dB SPL and broadband noise at 63 dB SPL. For each condition, at least 20 blocks were presented in mixed order. Results for five normal listeners show that the sensitivity, d′, is nearly proportional to ΔL{=20 log[(p+Δp)/p], where p is sound pressure} over the entire range of difference limens. When d′ is plotted against Weber fractions for sound pressure, Δp/p, or intensity, ΔI/I, exponents of the best-fitting power functions decrease with increasing difference limens and are less than unity for large difference limens. The approximately proportional relation between d′ and ΔL agrees with modern multichannel models of level discrimination and with psychometric functions derived for single auditory-nerve fibers. The results also support the notion that the difference limen, expressed as ΔLDL and plotted on a logarithmic scale, is an appropriate representation of performance in level-discrimination experiments.
Comodulation masking release over a three octave range
Authors: Cohen Marion F.
Published: October 2005

Comodulation masking release (CMR) for a variable frequency 50-ms tone-burst signal was measured in the usual manner, except that the overall level of the 100-Hz-wide masker band was varied from 18 to 78 dB SPL in 20-dB steps. The 100-Hz-wide cue band, which remained centered at 1000 Hz, was presented at an overall level of 78 dB SPL. Presentation was either monotic or dichotic, with the cue band presented to the nonsignal ear only. Averaged results show monotic CMR values as high as 7 dB when the masker band/signal was centered at 8000 Hz, or 3 oct away from the cue band, and 11 dB when it was 2 oct away. CMR for all frequency separations was reduced when the two noise bands were equal in level. The dichotic presentation resulted in a CMR that was somewhat smaller, and less dependent on, the relative levels of the two noise bands.
An interleaved tracking procedure to monitor unstable psychometric functions
Authors: Leek Marjorie R. , Hanna Thomas E. , Marshall Lynne
Published: October 2005

In some experimental situations, the psychometric function underlying performance may not be stable, but instead may shift along the stimulus axis in response to changes in attention, learning, or task difficulty. When this occurs, the measured threshold may be influenced and the slope of the measured function will be inaccurately shallow. With commonly used experimental procedures, it is difficult to know whether a shallow psychometric function slope is a true reflection of the sensory process, or is a result of ‘‘averaging’’ a highly variable underlying function. Here, a new method is described of estimating psychometric function slope from the variability in two interleaved adaptive tracks, consulted on alternate trials, that is resistant to the effects of shifting performance levels. Further, a mechanism is described for assessing the likelihood that a threshold was, in fact, stable over the course of its measurement. Computer simulations are reported as well as verification of the method in measurements of human performance on a psychophysical task. Several conditions of externally imposed variability were simulated to establish the ability of these procedures to identify unstable functions and produce accurate slope estimates. The procedures worked well for thresholds shifting by as little as 4 dB if the variation did not occur too rapidly. The procedure and associated analyses are recommended as a relatively ‘‘free’’ means of calculating slope and quantifying threshold reliability with little extra experimental effort.
Focalization: Environmental focusing and source localization
Authors: Collins Michael D. , Kuperman W. A.
Published: October 2005

Conventional matched-field processing (MFP) requires accurate knowledge of the ocean-acoustic environment. Focalization, which simultaneously focuses and localizes, eliminates this stringent requirement by including the environment in the parameter search space. This generalization of MFP involves defining an appropriate high-resolution cost function, parametrizing the search space of the environment and source, constructing solutions of the wave equation, and utilizing a nonlinear optimization method to search the parameter landscape for the global minimum of the cost function. Focalization is implemented using cost functions based on ray theory and wave theory, empirical orthogonal functions for the environmental description, and simulated annealing for optimization. Numerical simulations are presented to demonstrate the feasibility of focalization.
Loudspeaker frequency response and perceived sound quality
Authors: Gabrielsson Alf , Lindström Björn , Till Ove
Published: October 2005

The psychophysical relations between loudspeakers’ frequency response and their perceptual properties were investigated. The frequency response of 18 high-fidelity loudspeakers was measured in three different conditions: in free field, in reverberation room, and in the listening room itself. The perceptual data consisted of experienced listeners’ ratings of the same loudspeakers in seven scales: clarity, fullness, spaciousness, brightness, softness, absence of extraneous sounds, and fidelity (Gabrielsson and Lindström, 1985). Hypotheses concerning the psychophysical relations were stated on the basis of results from earlier listening tests. The relations obtained with measurements in the listening room showed better agreement with the hypotheses than those obtained by measurements in free field or in reverberation room.
Experimental evidence for a proposed surface soliton mechanism in wind–wave generation and scattering
Authors: Middleton David , Mellen Robert H.
Published: October 2005

Sonar and radar measurements both indicate that there are fundamental problems with the present wind–wave models of the sea surface at higher wave numbers: Backscattering strengths at high frequencies and small grazing angles are much greater than predicted 0(10–20 dB). In addition, the Doppler spectra show no evidence of the dispersion expected in gravity-capillary régimes. The usual quasilinear wave theories do not account for such effects. Accordingly, a new qualitative four-stage model for wave growth is proposed: (1) initiation of high-frequency surface ripples (catspaws) by the wind; (2) nonlinear formation of steep wave fronts; (3) generation of low-frequency waves by surface instability and wave–wind interaction; and (4) continued generation of unstable surface-disturbances which chaotically degenerate into ensembles of solitons, undergoing continuous creation and absorption, with the incoming energy balanced by dissipation. A preliminary theory of the resulting soliton-surface layer is discussed by D. Middleton [Computational Acoustics (North Holland, New York, 1988)]. Here, a broad range of experimental evidence is presented, in support of the proposed surface mechanism developed by Middleton. Thus, with assumptions not contrary to any of the known properties of the sea surface, quantitative scattering predictions of the model are seen to agree well with experiment, in particular with respect to backscattering strength, Doppler shift, and (point intensity) spectral levels, produced in known ‘‘bubble-free’’ régimes. These results provide extensive inferential support for the sea-surface and scattering models proposed here. However, further research is needed for explicit verification by direct observation and testing against more refined measurements of wave statistics and hydrodynamic theory.
Accuracy of audiometric test room simulations of three real-world listening environments
Authors: Cox Robyn M. , Alexander Genevieve C. , Rivera Izel M.
Published: October 2005

Hearing aid benefit depends primarily on the extent to which amplification facilitates speech understanding in typical everyday listening environments. In the hearing aid fitting process, improved speech understanding is often measured in an audiometric test room. However, because audiometric test rooms are smaller, quieter, and less reverberant than typical rooms, these data may not accurately predict speech understanding in daily life. This study was undertaken to evaluate the validity of three simulated real-world listening environments created in an audiometric test room. The three environments represented a typical living room, cocktail party, and classroom, respectively. Twenty normal-hearing subjects, listening monaurally, provided intelligibility scores for four phonetic contrasts produced by each of three normal talkers. Intelligibility obtained in the real environment was compared with that measured in the corresponding simulated environment. Results indicated that the relative intelligibility of talkers and phonetic contrasts remained essentially constant across each real-simulated environment pair, and that significant talker × contrast interactions seen in the real environments were usually reproduced in the simulated environments. However, there were somewhat fewer significant intelligibility differences in the simulated environments than in the real environments. Also, the intelligibility of one talker deteriorated more than expected in the simulated reverberant environment. Overall, the outcome suggested that these typical listening environments were rather accurately simulated (for monaural listening) in an audiometric test room using appropriate adjustments of presentation level, signal-to-babble ratio, and synthetic reverberation effects.
Spectral cues to perception of /d, n, l/ by normal- and impaired-hearing listeners
Authors: Revoile Sally G. , Pickett James M. , Kozma-Spytek Linda
Published: October 2005

The alveolar consonants /d, n, l/ occur frequently in intervocalic position in conversational speech but have received little study for differences in their acoustic cues. Impaired- and normal-hearing listeners were investigated for use of consonant-segment versus transition-segment cues to recognition of /d, n, l/ in /1C1/ tokens extracted from sentences. To examine the cues’ contribution to /d, n, l/ recognition, the segments were degraded singly or in combinations in the tokens as follows: [1C] or [C1] transitions were replaced by adjacent pitch periods from the respective vowels; the consonant segments were replaced by silence or by a synthetic consonant approximating the summed low-frequency spectra of the /d, n, l/ murmurs. The results with normal-hearing listeners showed that the presence of any one of the three segments, [1C] transition, [C1] transition, or natural consonant segment, supported a moderate to high level of /d, n, l/ recognition, depending on the phoneme. In contrast, the severely hearing-impaired listeners’ consonant recognition was poor on the basis of transition information, but better in the presence of the natural consonants. The /1C1/’s with the synthetic consonant yielded chance level performance for the hearing-impaired listeners but good consonant recognition for the normal-hearing listeners—a further indication that cues in the transitions were quite useful for the normal-hearing group but not for the hearing-impaired group.
Analysis of vocal tract shape and dimensions using magnetic resonance imaging: Vowels
Authors: Baer T. , Gore J. C. , Gracco L. C. , Nye P. W.
Published: October 2005

Magnetic resonance imaging (MRI) techniques were used to gather basic data to apply in computational models of speech articulation. Two experiments were performed. In experiment 1, voice recordings from two male subjects were obtained simultaneously with axial, coronal, or midsagittal MR images of their vocal tracts while they produced the four point vowels. Area functions describing the individual tract shapes were obtained by measurements performed on the MR images. Digital filters derived from these functions were then used to resynthesize the vowel sounds which were compared, both perceptually and acoustically, with the subjects’ original recordings. In experiment 2, axial images of the pharyngeal cavity were collected during the production of an ensemble of nine vowels. Plots of cross-sectional area versus the midsagittal width of the tract at different locations within the pharynx and for different vowel productions were used to derive a functional relationship between the two variables. Data from experiment 1 relating midsagittal width to cross-sectional area within the oral cavity were also examined.
Comodulation masking release as a function of level
Authors: Moore Brian C. J. , Shailer Michael J.
Published: October 2005

These experiments examine the effects of masker level on the magnitude of comodulation masking release (CMR). In experiment 1, threshold was measured for detecting a 2000-Hz signal in noise bands 100- or 3200 Hz wide, centered at the signal frequency. The noise was either amplitude modulated by a low-pass-filtered noise, or was unmodulated. At noise spectrum levels of 30 and 50 dB, thresholds were lower in the 3200-Hz-wide modulated noise than in the 100-Hz-wide modulated noise or the 3200-Hz-wide unmodulated noise, indicating a CMR. The magnitude of this CMR decreased at a noise spectrum level of 10 dB, and was very small at a spectrum level of −10 dB. In experiment 2, threshold was measured for a 700-Hz signal centered in a 20-Hz wide band of noise (the on-frequency band, OFB), both in the presence and absence of eight flanking bands (FBs) whose envelopes were either identical with that of the OFB (correlated condition) or were uncorrelated. Thresholds were lower in the correlated than in the uncorrelated condition, indicating a CMR. When the OFB and the FBs were presented to the same ear, the CMR decreased when the spectrum level of all bands was below 30 dB, or when the spectrum level of the FBs was decreased below 40 dB keeping the level of the OFB constant at 40 dB. When the OFB and the FBs were presented to opposite ears, the CMR decreased when the spectrum level of all bands was decreased below 30 dB or when the spectrum level of the FBs was decreased below 40 dB, keeping the level of the OFB fixed at 40 or 60 dB. However, the CMR was almost independent of the spectrum level of the OFB (over the range 10–70 dB) when the spectrum level of the FBs was held constant at 60 dB. The results are interpreted in terms of perceptual grouping mechanisms. Implications for the measurement of CMR in hearing-impaired subjects are also discussed.
Effect of amplitude modulation on profile detection
Authors: Dai Huanping , Green David M.
Published: October 2005

The effect of amplitude modulation on profile detection was examined in three experiments. The observer’s task was to determine in which observation interval an increment was added to the 1000-Hz target component of a multitone complex in which the components were equally spaced on a logarithmic frequency scale from 200 to 5000 Hz. The target was unmodulated throughout the study. In some conditions, all nontarget components of the standard were modulated in phase; in other conditions, they were modulated with random phase. In experiment 1, the threshold was measured as a function of the modulation rate. The results show that, at low modulation rates, 5 Hz for example, modulation elevates threshold by about 13 dB. The threshold decreases as the modulation rate increases, with the threshold elevation being only 3 dB at 80 Hz. In experiment 2, threshold was measured as a function of modulation depth for both 21- and 5-component complexes. The results show that for a 5-Hz modulation rate the threshold decreases as the modulation depth decreases, and that the rate of decrease is greater for the 21-component complex than for the 5-component complex. In experiment 3, the effects of random-phase modulation were explored; the phase of the modulation waveform was randomly chosen for each component. The results show that there is no difference between in-phase and random-phase modulation when each component occupies a different critical band. If, however, two or more components occupy the same critical band, then randomizing the phase of modulation reduces the effective depth of modulation within that critical band, and the effect of modulation is thereby lessened.
On the transmission of sound generated by an electromagnetic device from the mastoid process to the petrous bone
Authors: Buchman E. , Rosenhouse G. , Shupak A. , Shimoni U.
Published: October 2005

An electromagnetic device (EMD) for sound transmission from the mastoid process to the petrous part of the temporal bone was designed, built, and analyzed. A theoretical model was developed in order to predict the EMD acoustical performance and the distortion caused by skull bones. This model enabled the investigation of various technical improvements and calibration options. The EMD was miniaturized by using rare earth magnets in the construction of both external transmitter and internal receiver. In vitro implantation of the internal receiver into the mastoid process was carried out by simple mastoidectomy techniques. The input and output powers of the system, including the EMD and skull bones components, were measured and the power transfer function was calculated. The sound, which was generated by the EMD and transmitted through the dry as well as simulated cadaver skull, had high fidelity in spite of some vibratory distortion at the lower sonic frequencies. Results suggest that further development of hearing aids based on electromechanical sound transmission should take into account the specific acoustic response pattern of the skull bones.
An evaluation of eight computer models of mammalian inner hair-cell function
Authors: Hewitt Michael J. , Meddis Ray
Published: October 2005

Eight computer models of auditory inner hair cells have been evaluated. From an extensive literature on mammalian species, a subset of well-reported auditory-nerve properties in response to tone-burst stimuli were selected and tested for in the models. This subset included tests for: (a) rate-level functions for onset and steady-state responses; (b) two-component adaptation; (c) recovery of spontaneous activity; (d) physiological forward masking; (e) additivity; and (f) frequency-limited phase locking. As models of hair-cell functioning are increasingly used as the front end of speech-recognition devices, the computational efficiency of each model was also considered. The evaluation shows that no single model completely replicates the subset of tests. Reasons are given for our favoring the Meddis model [R. Meddis, J. Acoust. Soc. Am. 83, 1056–1063 (1988)] both in terms of its good agreement with physiological data and its computational efficiency. It is concluded that this model is well suited to provide the primary input to speech recognition devices and models of central auditory processing.
Sound transmission between rooms: A comparative analysis of calculation methods
Authors: Mahdavi Ardeshir
Published: October 2005

The quantity of sound transmission between adjacent rooms depends not only on the sound insulation characteristics of the partition element (wall or ceiling) but also on the construction and geometry of the flanking building elements. A number of models have been introduced recently in order to enable the designer to calculate the sound transmission between rooms on the basis of geometry and construction data. These models consider the direct sound transmission as well as the flanking transmission paths. The study presented here pertains to a comparative analysis of four models for computation of the sound-level difference between adjacent rooms (in massive building constructions). The comparison was based on data derived from ‘‘virtual’’ constructions as well as measurements. A statistical analysis of the relative deviations of the results and the correlation between calculation and measurement data are presented.
Time domain analysis of normal mode, parabolic, and ray solutions of the wave equation
Authors: Boden Linda , Bowlin James B. , Spiesberger John L.
Published: October 2005

Estimation of sound speed and temperature fields from tomographic data requires knowledge of the accuracy of the forward model. For this reason, time domain results using three models derived from the acoustic wave equation are compared here. The models chosen for the analysis are normal modes (NM) and the parabolic equation (PE) and ray approximations. (The NM and PE time series are obtained via Fourier synthesis). The analysis is done using a depth-dependent sound-speed profile where only refracted and surface-reflected/refracted energy is allowed to propagate. Because the NM representation is theoretically exact in this environment, it is used as the comparative base. Travel-time sequences generated using the PE and ray approximations are compared to those generated using NM. For the angular aperature analyzed (±9 to ±16.5 deg), phase errors in the PE models investigated limit reliable predictions of travel time to distances of about 1000 km. However, the ray approximation is found to be adequate for estimating arrival times at ranges out to 4000 km for frequencies of 100 Hz and above.
Acoustic sampling volume
Authors: Foote Kenneth G.
Published: October 2005

Knowledge of the acoustic sampling volume is necessary in many quantitative applications of acoustics. In general, the sampling volume is not merely a characteristic of the transmitting and receiving transducers, but also depends on the concentration and scattering properties of the target, the kind of signal processing performed on the echo, and the detection threshold. These dependences are stated explicitly in formulas for the sampling volume and a differential measure, the effective equivalent beam angle. Numerical examples are given for dispersed or dense concentrations of both point scatterers and directional fish scatterers. Application of theory to optical and other remote sensing techniques is mentioned.
Acoustic reflections from arctic ice at 15–300 kHz
Authors: Garrison G. R. , Francois R. E. , Wen T.
Published: October 2005

Underwater acoustic systems operating in the Arctic are generally used to detect ice or objects in an ice background. In either case, knowledge of the reflections from ice, both undisturbed and ridged, is necessary. For the past few years, the authors have been measuring monostatic reflections near normal incidence from arctic ice to advance this knowledge. In 1988, reflections at 20–80 kHz were measured from the ends of four cylindrical blocks of flat arctic ice with diameters of 27–84 cm. The blocks were individually depressed below the surface so that their reflections were separable from those off the underside of the ice canopy. The transducer was moved horizontally beneath the block to measure the angular response pattern. Examination of the bottom of the block after it was removed showed that the surface was flat except for some roughness with a standard deviation less than 3 mm. Compared with solid ice, the skeletal layer reduced normal-incidence reflection by 8–11 dB. The results were consistent for all four blocks, confirming that the results were valid. Measurements of reflection from the underside of the ice canopy at 15–300 kHz gave similar results and extended the frequency range. Measurements of the physical properties of the ice were helpful in analyzing the nature of the reflection.
Slowly varying method for high-frequency scalar scattering problems
Authors: Zhu Han
Published: October 2005

A new formulation called the slowly varying method (SVM) is proposed in this paper to solve high-frequency scalar scattering problems. It is well known in linear acoustics that, excited by a plane harmonic incident wave U0(x) impinging on a scatterer, the scattered field U(x) for a Neumann boundary value problem or ∂U(x)/∂n for a Dirichlet boundary value problem is quickly varying on a scatterer when ka≫1, where k is the wave number and a is a typical scatterer dimension. The paper shows that for the same ka the function V(x)=U*0(x)U(x) for the Neumann boundary condition and Vn(x)=U*0(x)∂U(x)/∂n for the Dirichlet boundary condition exhibit much slower variations on the scatterer compared with those of U(x) and ∂U(x)/∂n for some cases. Here, U*0(x) is the complex conjugate of U0(x). The relations among V(x), Vn(x) and the acoustic energy densities have been analyzed. A new boundary integral equation in terms of the unknown function V(x) or Vn(x) on the scatterer may be derived. This boundary integral equation can be either solved by the BEM or asymptotically simplified by the stationary phase method and other approximations. For the former case, the requirement that the boundary element dimension should be proportional to 1/(ka) may be waived for obtaining satisfactory numerical results. For the latter case, a non-element numerical solution of V(x) or Vn(x) then may be obtained by an algebraic arithmetic without solving large-dimensional linear-algebraic equations. A few numerical results obtained by the SVM are presented in the paper as well as their comparison with the conventional BEM solutions.
Experimental investigations of Lamb waves on pulsed piezoelectric transducers and their ultrasonic radiation into liquids
Authors: Jia Xiaoping , Berger Jacques , Quentin Gérard
Published: October 2005

In addition to the classical fundamental thickness mode, multiple echoes of Lamb waves have been observed on pulsed circular piezoelectric transducers, by using an optical heterodyne interferometer. With an efficient resonance spectrum technique, the group velocities of the Lamb waves are deduced quantitatively. The radiation of these waves into liquids (usually water), which create so called ‘‘head waves’’ and are not predicted by the piston model, were detected by a hydrophone. Comparison between the optical and hydrophone probe measurements demonstrates a good agreement.
Comparison of Terfenol-D and PZT-4 power limitations
Authors: Moffett Mark B. , Powers James M. , Clark Arthur E.
Published: October 2005

A previous article [Moffett et al., J. Acoust. Soc. Am. 89, 1448–1455 (1991)], comparing the radiated-power limitations of Terfenol-D and PZT-4, is revisited. When the power at resonance is stress-limited (as is the case for high mechanical quality factor Q), the maximum allowable stress amplitude Tmax is the compressive prestress value, so that tension in the Terfenol-D is avoided. When this value is chosen for Tmax, rather than the smaller Tmax’s of the previous article, Terfenol-D is shown to be superior to PZT-4 in power capability at all values of the quality factor Q.
Time-domain observation of otoacoustic emissions during constant tone stimulation
Authors: Brass David , Kemp D. T.
Published: October 2005

Observations of the otoacoustic emissions (OAEs) evoked during a continuous single stimulus tone have been made on humans using a nonlinear residual time domain technique. The technique, described in this paper, involved the digital summation of responses to contiguous stimulation intervals, some of which included short bursts of a suppressor, or probe, tone. Stimulus intervals are constructed so that both the stimulus and probe tones summed to zero cyclically, leaving a residual response. This residual is attributable to the nonlinearity of the whole acoustic response, as measured in the ear canal, to the stimulus and probe tone complex. A theoretical treatment of this paradigm is presented examining the relation of this residual to the OAE evoked by the stimulus tone. It is shown experimentally that the residual, found at the stimulus tone frequency, has a latency and a saturating input–output growth functions indicative of an OAE. The detailed OAE amplitude-versus-frequency variations, and the general latencies of the OAEs in two human ears were measured using both the constant tone evoked residual method described and the click evoked delayed emission method. The results from both methods are in agreement. The frequency-dependent properties of the suppression of the OAE were investigated using various stimuli to probe frequency ratios. The continuous tone time domain residual method has advantages for the observation of stimulus frequency OAEs and for relating these to any distortion product simultaneously generated.
Neural correlates of nonmonotonic temporal acuity for voice onset time
Authors: Sinex Donal G. , McDonald Lynn P. , Mott John B.
Published: October 2005

Human and chinchilla listeners exhibit nonmonotonic temporal acuity for speech sounds differing in voice onset time (VOT). Characteristics of the neural discharge pattern or of the stimuli themselves that might account for the pattern of temporal acuity have not been described. Responses of chinchilla auditory-nerve fibers to syllables from an alveolar VOT continuum were measured. Peak discharge rates and peak response latencies elicited by the syllables with the shortest and longest VOTs were highly variable across groups of neurons with similar characteristic frequencies. For VOTs from the middle of the continuum, peak responses were larger, and response latencies were nearly constant across the same group of neurons. Overall, the magnitude and temporal variability of the responses of populations of primary auditory neurons varied nonmonotonically with VOT, consistent with the pattern of psychophysical temporal acuity for these syllables exhibited by humans and chinchillas. Spectral analyses suggested by the pattern of neural responses indicated that synchronous or correlated spectral cues were available over a wider bandwidth for those syllables from the middle of the continuum for which the neural representation was least variable.
Temporal representation of rippled noise in the anteroventral cochlear nucleus of the chinchilla
Authors: Shofner William P.
Published: October 2005

This paper describes the temporal responses of anteroventral cochlear nucleus (AVCN) units in the chinchilla to rippled noises. Rippled noise is generated when a wideband noise is delayed and added (cos+ noise) or subtracted (cos− noise) to the undelayed noise. Renewal densities were constructed to evaluate synchronous discharges at the delay. In response to rippled noise, AVCN units which show phase locking to best frequency (BF) tones gave renewal densities having major peaks at the delay for cos+ noise, but nulls at the delay for cos− noise. Most AVCN units which did not show BF phase locking gave renewal densities that did not contain features related to the rippled noise delay; a few of these nonphase-locked units did show peaks in renewal densities for both cos+ and cos− noises. Synchrony at the rippled noise delay was also demonstrated with evoked potential recording. Autocorrelation functions of the neurophonic potential showed peaks at the rippled noise delay for both cos+ and cos− noises. In addition, peaks could be observed in the autocorrelation functions of neurophonic potentials for rippled noises with delays as short as 1 ms; peaks were never observed in renewal densities of single units for ripple delays as short as 1 ms. The results show that a temporal representation of rippled noise delay does exist in the AVCN and are consistent with current hypotheses regarding functions of AVCN subsystems. The temporal representation of the delay is a presumptive neural code for the pitches of rippled noises.
The focus measurement technique for estimation of arbitrary time delays in multichannel, multievent systems
Authors: Jan Ben-Chung , Henriquez Juan A. , Riemer Terry E. , Trahan Russell E.
Published: October 2005

The estimation of arbitrary time delays in multichannel, multievent systems is studied using a new method called the focus measurement technique (FMT). The method introduced uses the window concept to isolate segments of the data record. However, instead of calculating the generalized cross correlation to estimate delays between data segments, the FMT (based on the assumption of normal distribution) combines windowed-segment points of every two channels to obtain the focal length of an ellipse which contains a certain amount of these distributed points. Based on simple geometric analysis, the FMT utilizes a windowed-segment distribution in order to estimate the event delays in the system. Simulation results show that this technique can find delays very accurately down to a signal-to-noise ratio (SNR=mean-square value of signal/mean-square value of noise) of 0 dB while reducing the amount of computation involved.
On subspace method for source localization
Authors: Naidu Prabhakar S.
Published: October 2005

A method of source localization in shallow water, based on subspace concept, is described. It is shown that a vector representing the source in the image space spanned by the direction vectors of the source images is orthogonal to the noise eigenspace of the covariance matrix. Computer simulation has shown that a horizontal array of eight sensors can accurately localize one or more uncorrelated sources in shallow water dominated by multipath propagation.
Temperature-rate-dependent thermoelastic waves in a homogeneous plate due to a suddenly punched hole
Authors: Chand Dayal , Sharma J. N.
Published: October 2005

The distribution of deformation, temperature, and stress in a homogeneous isotropic, thermally conducting, infinitely extended, stretched elastic plate due to a flat nose cylindrical projectile has been studied in the context of the Green–Lindsay theory of thermoelasticity. As the ‘‘second sound’’ effects are short lived, the discussion is confined to small-time approximations. The short-time solutions have been obtained by using the Laplace transforms technique. The deformation is found to be continuous but the temperature and stress are found to be discontinuous. The jumps obtained have been computed numerically and are represented graphically for carbon-steel material.
Invariance of the Doppler bandwidth with flow displacement in the illuminating field
Authors: Newhouse V. L. , Reid J.
Published: October 2005

It is known that if single frequency continuously transmitted ultrasound or electromagnetic energy is reflected from ‘‘straight line flow,’’ defined here as one or more scatterers moving with constant velocity along an infinite straight line, the Doppler effect will shift the echo spectrum center frequency from the transmitted value, and broaden its bandwidth. It is proved that if such straight line flow is shifted laterally or in range anywhere in the field, i.e. without change of orientation, its Doppler bandwidth remains unchanged. (The ‘‘Doppler bandwidth’’ is here defined as the frequency difference between the extrema of the echo power spectrum.) The theorem holds true even though the time domain echo changes dramatically with motion of the flow path, and is believed to be valid for electromagnetic as well as ultrasound waves. Its implications with respect to flow measurement, as well as preliminary experimental and computational confirmation, will be discussed.
Acoustic scattering in a three-dimensional oceanic waveguide using boundary integral equation methods
Authors: Dawson Trevor W.
Published: October 2005

This paper develops in more detail the theory for a fully three-dimensional version of an earlier boundary integral equation method (BIEM) formulation, for the computation of the scattering of underwater sound from compact deformations of an oceanic waveguide’s surfaces. The method allows for three-dimensional sources and boundary deformations in an otherwise uniform waveguide. The technique involves only integrations over the compact surface of the waveguide deformation. The implementation is illustrated for a seamountlike deformation in an oceanic waveguide.
Comparison of the Rayleigh–Fourier and extinction theorem methods applied to acoustic scattering in a waveguide
Authors: Kazandjian Luc
Published: October 2005

The Rayleigh–Fourier and extinction theorem method mathematical formalisms are established and compared in the case of acoustic scattering in a waveguide with impedance boundary conditions and one nonplanar surface. It is shown that the two methods are theoretically equivalent by using the properties of the solution given by the extinction theorem method. This result, which is confirmed by a perturbation approach, may be of practical importance in view of the better computational efficiency of the Rayleigh–Fourier method.
An acoustic scattering model for forests.
Authors: Rogers James C. , Chen Pu , Mueller Arnold
Published: October 2005

An acoustic scattering experiment was conducted in a mature deciduous forest using an impulse source with a useful frequency range from about 200 to 600 Hz. Measurements were made in several positions along a line starting from the edge of the forest to a depth of 200 m into the forest. A preliminary model was proposed to calculate the normalized scattered energy. This model assumes: (1) single scattering dominates, (2) the scattering patterns of scatterers (trees) are omnidirectional, (3) 1/r spreading loss, (4) no atmospheric absorption, and (5) the entire tree acts as a scattering center. A more complex model, which includes forest statistics, has also been developed. The modeling results are compared with the experimental data. They are quite similar especially for those cases where the source and receiver both are located in the deep forest. [Work supported by NASA.]
Hamilton’s principle and the derivation of shell theories to approximate vibrations of bounded elastic shells.
Authors: Dean Cleon E. , Werby Michael F.
Published: October 2005

The exact elastodynamic calculations for the motions of bounded elastic shells can be quite consumptive of both computer time and resources. As an alternative, the so-called shell theories simplify and speed up these calculations by making various dynamic assumptions about the motion of the shell surface when subjected to disturbances. This is typically done using variational considerations in which energy is minimized when various constraints are imposed. Exploitation of the technique using various assumptions gives rise to several shell theories. The resulting expressions are then used to calculate resonances over a frequency range and compared with the exact results. The various approximations are then ranked in order of their agreement to the exact results. Limitations of each of the methods are then outlined as well as those of shell methods in general. [Work supported by ONR/NOARL and by ONT Postdoctoral Fellowship Program.]
Water-borne waves at the interface of evacuated elastic spherical shells and pseudo-Stoneley resonances.
Authors: Werby M. F.
Published: October 2005

Monochromatic plane waves are known to excite resonances on submerged elastic spherical evacuated shells. The resonances are related to symmetric and antisymmetric Lamb modes found in free vibrations and can be observed by examining the backscattered echo’s (form functions) that lead to characteristic ‘‘tell-tale’’ resonance signatures. A partial wave analysis of the individual modes can reveal the nature of the resonances, provided one is able to subtract the correct acoustical background from the shell. The recent development of the correct acoustical background is taken advantage of to analyze the partial wave components of shell resonances. It is easy to distinguish between the Lamb modes that are also apparent in the form functions. However, an additional resonance is observed at high frequencies that correspond to waves which are broad in partial wave space and which propagate in the fluid at the fluid–shell interface at about the speed of sound of the ambient fluid. It may be assumed that they are related to Stoneley waves observed at the interface of a flat plate evacuated on one side and with a fluid on the other and may therefore be referred to as pseudo-Stoneley resonances. The significance of these waves at coincidence frequency will be discussed.
A systematic study of calculations for scattering of plane waves from submerged elastic solid cylinders with hemispherical caps.
Authors: Werby M. F. , Dean C. E.
Published: October 2005

It is possible to employ the extended boundary condition equations (EBC) method due to Waterman to describe scattering from axially symmetric submerged elastic targets over a broad frequency range. The problem of scattering from cylinders with hemispherical end caps offers one a useful target to analyze. Resonance phenomena predicted by the EBC calculations are analyzed and a systematic study of results is presented. In addition, bending resonances are predicted by the theoretical calculations and compared with predictions from bar theory. A series of predictions are made for various materials and aspect ratios to aid future experimental work.
On the attenuation of slow waves in air-saturated porous materials.
Authors: Nagy Peter B.
Published: October 2005

Certain important properties of porous materials, such as porosity, tortuosity, permeability, and internal damping, are not directly accessible from conventional acoustic measurements made on the frame itself. These quantities can be better assessed from measuring the slow-wave velocity and attenuation, at least whenever this elusive mode is detectable at all. Recently, a novel experimental technique was introduced based on the transmission of airborne ultrasound through air-filled porous samples, which lends itself quite readily to such measurements, even in highly attenuating natural rocks [P. B. Nagy and L. Adler, J. Acoust. Soc. Am. Suppl. 1 87, S145 (1990)]. Depending on the average grain size and the inspection frequency, the attenuation coefficient is dominated by viscous and thermal losses or scattering. Experimental results show that, rather surprisingly, the scattering induced attenuation is linearly proportional to frequency and it does not depend on the grain size. Different physical explanations for this unusual behavior are considered and checked against experimental observations. [Work supported by U.S. Department of Energy, Basic Energy Sciences Grant No. DE-FG-02-87ER1374.9A000.]