bluuebunny/crossref_metadata_2025 huggingface dataset:
A composite model of the auditory periphery for the processing of speech based on the filter response functions of single auditory-nerve fibers
Authors: Jenison Rick L. , Greenberg Steven , Kluender Keith R. , Rhode William S.
Published: October 2005

A composite model of the auditory periphery, based upon a unique analysis technique for deriving filter response characteristics from cat auditory-nerve fibers, is presented. The model is distinctive in its ability to capture a significant broadening of auditory-nerve fiber frequency selectivity as a function of increasing sound-pressure level within a computationally tractable time-invariant structure. The output of the model shows the tonotopic distribution of synchrony activity of single fibers in response to the steady-state vowel [q] presented over a 40-dB range of sound-pressure levels and is compared with the population-response data of Young and Sachs (1979). The model, while limited by its time invariance, accurately captures most of the place-synchrony response patterns reported by the Johns Hopkins group. In both the physiology and in the model, auditory-nerve fibers spanning a broad tonotopic range synchronize to the first formant (F1), with the proportion of units phase-locked to F1 increasing appreciably at moderate to high sound-pressure levels. A smaller proportion of fibers maintain phase locking to the second and third formants across the same intensity range. At sound-pressure levels of 60 dB and above, the vast majority of fibers with characteristic frequencies greater than 3 kHz synchronize to F1 (512 Hz), rather than to frequencies in the most sensitive portion of their response range. On the basis of these response patterns it is suggested that neural synchrony is the dominant auditory-nerve representation of formant information under ‘‘normal’’ listening conditions in which speech signals occur across a wide range of intensities and against a background of unpredictable and frequently intense acoustic interference.
A comparison of steady-state evoked potentials to modulated tones in awake and sleeping humans
Authors: Cohen Lawrence T. , Rickards Field W. , Clark Graeme M.
Published: October 2005

Steady-state evoked potential responses were measured to binaural amplitude-modulated (AM) and combined amplitude- and frequency-modulated (AM/FM) tones. For awake subjects, AM/FM tones produced larger amplitude responses than did AM tones. Awake and sleeping responses to 30-dB HL AM/FM tones were compared. Response amplitudes were lower during sleep and the extent to which they differed from awake amplitudes was dependent on both carrier and modulation frequencies. Background EEG noise at the stimulus modulation frequency was also reduced during sleep and varied with modulation frequency. A detection efficiency function was used to indicate the modulation frequencies likely to be most suitable for electrical estimation of behavioral threshold. In awake subjects, for all carrier frequencies tested, detection efficiency was highest at a modulation frequency of 45 Hz. In sleeping subjects, the modulation frequency regions of highest efficiency varied with carrier frequency. For carrier frequencies of 250 Hz, 500 Hz, and 1 kHz, the highest efficiencies were found in two modulation frequency regions centered on 45 and 90 Hz. For 2 and 4 kHz, the highest efficiencies were at modulation frequencies above 70 Hz. Sleep stage affected both response amplitude and background EEG noise in a manner that depended on modulation frequency. The results of this study suggest that, for sleeping subjects, modulation frequencies above 70 Hz may be best when using steady-state potentials for hearing threshold estimation.
A class of sequential robust partition detectors with dependent sampling
Authors: Voudouri Evriclea , Kurz Ludwik
Published: October 2005

In this paper, the problem of signal detection in severe and/or changing noise environments, often encountered in underwater acoustics and communications, is considered. The detectors operate in sequential, i.e., variable sample size, mode at near optimum levels for a particular noise environment and are robust by maintaining high efficiency in other than the nominal noise environments by adapting their optimum nonlinearity using an m-interval polynomial approximation (MIPA) of it. Furthermore, the assumption of independent samples is relaxed, allowing higher transmission rates for lower error rates. The proposed sequential detectors work well for coherent and noncoherent detection, are asymptotically optimum and, for small signal-to-noise ratios (SNR), increase their transmission rate up to four times as compared to their fixed-sample size counterparts. The performance of the detectors is evaluated in typical underwater noise fields. It is demonstrated that their efficiency with respect to sequential MIPA detectors with independent sampling is improved, in some cases up to the order of the dependence of the samples Q. It is emphasized that the MIPA detectors are easy to implement. The estimation and updating of the detector parameters may be accomplished using parallel processors operating in a recursive mode without disturbing the decision process.
Perth–Bermuda sound propagation (1960): Adiabatic mode interpretation
Authors: Heaney K. D. , Kuperman W. A. , McDonald B. E.
Published: October 2005

A 1960 experiment is examined in which sound from three underwater explosions near Perth, Australia, was detected near Bermuda. A recent attempt [Munk et al., J. Phys. Ocean. 18, 1876 (1988)] to calculate propagation paths for this event included rotational flattening of the Earth and horizontal refraction determined from the vertical sound speed minimum. That calculation left Bermuda in a shadow zone. The current work invokes adiabatic mode theory to include refraction due to horizontal variations in the vertical mode structure. These results include separate horizontal rays for each of the first few vertical modes, using an archival data set of 230 ocean sound profiles to generate the modes numerically. Where appropriate, interaction with bathymetry is included. This solution possesses two eigenray groups: Group A passes just south of the Cape of Good Hope, at which point group B is almost 1000 km to the south. Intermediate rays are blocked by islands. Group A proceeds unimpeded to Bermuda for a total time of flight of 13 354±5 s, while group B interacts slightly with bathymetry off Brazil, arriving at 13 403±9 s, and suffering roughly 7–12 dB more bottom attenuation. The spread in these arrivals overlaps satisfactorily with experimental data (main arrival at 13 364±5 s; pulse train half-width 15 s; second arrival 30±5 s later roughly 10 dB below the first arrival).
Utilizing the acoustical Doppler effect to localize aircraft.
Authors: Ferguson Brian G.
Published: October 2005

The acoustical Doppler effect deals with cases of relative motion between a listener and a sound source, and includes the effects of motion of the medium itself relative to both the source and the listener. The acoustic source of interest here is a propeller-driven aircraft whose acoustic emissions are received by a microphone located at ground level. This paper shows that the altitude and speed of the aircraft can be estimated by processing the acoustic data from the microphone. In the present experiment, the aircraft flies at a constant altitude and speed over the microphone’s position and the Doppler frequency of the spectral line corresponding to the propeller blade rate is estimated at short time intervals during the aircraft’s transit overhead. Using the altitude and speed of the acoustic source as the variable parameters, a simple model is fitted to the observed variation of the blade rate with time; estimates of the aircraft’s altitude and speed correspond to a least-mean-squares curve fit of the model to the observations. These estimates are then compared with the actual altitude and speed recorded by the aircraft.
Fine structure variability of acoustic signals propagating to two convergence zones.
Authors: Council O. P. , Keaton V. N.
Published: October 2005

The influence of propagation to two convergence zones on active sonar signals was investigated by transmitting a wavetrain consisting of a 100-ms, 400-Hz-wide LFM and a 10-s binary phase code. The center frequency of both signals was 1-kHz. The wavetrain was received and recorded over a period of 14 h on a surface vessel two convergence zones removed from the transmitting vessel. The received signals were examined by matched filtering of the LFM and binary phase code and by spectral analysis of the LFM and the carrier frequency of the phase code. Statistically significant variation over time in the signal was observed both in which of the four predicted multipaths were actually detected and in the delay structure within particular arrivals. The spectrum of deep refracted LFM signals showed the expected fading at selected frequencies but which frequencies were attenuated varied dramatically from ping to ping. Corresponding variability in the matched filter output was also observed. Variability in the total multipath structure of the received signal ranged from clear presence of all four predicted arrivals to clear presence of only one, which was interpreted as the deep refracted arrival.
Scattering by an open sphere: Exact solution and comparison with a boundary integral method.
Authors: Elias G. , Malbéqui P.
Published: October 2005

The objective of the paper is to extend the variety of exact solutions in acoustic scattering configurations that may be used to validate numerical methods. The radiation of an acoustic point source located at the center of a hard sphere with a circular aperture is analyzed. In comparison with standard scattering problems, as the diffraction of a plane wave by a closed sphere, this problem adds a sharp edge. The exact solution is derived from an expansion of the pressure field on spherical Bessel functions and Legendre polynomials, and solving the linear system obtained for the coefficients. In terms of the reduced wave number ka, the truncation of the system to only 4ka coefficients insures a stable and accurate solution. A boundary integral method originally developed by Handi [Doctoral thesis, Université de Technologie de Compiègne (1982)] is used as a numerical method. Comparisons between the two sets of solutions for various wave number and aperture size show a quite good agreement, with relative differences in the far field of about 1%.
The generalized Stoneley and Rayleigh waves on cylindrical shells.
Authors: Talmant M. , Conoir J. M. , Rousselot J.-L. , Quentin G.
Published: October 2005

This paper dealt with acoustical scattering resulting from a plane harmonic wave normally incident upon an infinite elastic circular cylindrical shell immersed in water and filled with air. Various circumferential surface modes have been experimentally and numerically observed. The so called l=0 and l=1 circumferential waves are considered. A numerical study of their behavior at high frequency, when the relative thickness of the shell remains constant, is achieved in the complex wave-number plane. The results are presented in the form of trajectories in the complex wave-number plane and of curves of phase velocity and attenuation by reradiation in water plotted as function of reduced frequency. At low frequency, the trajectory of the circumferential waves on shells depends strongly on the value of the relative thickness of the shell. Nevertheless, it is shown that, at high frequency, the effect of the internal interface becomes negligible and, for all values of the relative thickness considered, the l=0 wave (respectively, l=1 wave) on cylindrical shells tends toward the Stoneley wave (respectively, Rayleigh wave) on solid cylinder and, in the limit of very high frequency, when the curvature becomes negligible, their common limit is their flat-surface counterparts.
More on high-frequency scattering from spherical shells and internal reflection resonances.
Authors: Gaunaurd G. C.
Published: October 2005

It is shown that it is possible to excite very large return signals at frequencies corresponding to values at which the half-integral wave lengths (due to the dilatational wave of the material) are equal to the shell thickness. At those values the longitudinal waves are transparent to the shell and reflect from the inner surface. The reflected signals add coherently with the specularly scattered signal yielding a large return. The width of the resonance is related to the fact that at oblique incident angles the shell appears thicker and thus gives rise to lower frequency components of the resonance. The upper limit of the resonance may be found by the flat plane limit for the shell thickness. A partial wave study shows that this prediction and interpretation of these events is valid.
A stochastic approach to plane wave reflection from a randomly layered porous seabed.
Authors: Badiey M. , Cheng A. , Jaya I. , Schulkin M.
Published: October 2005

Based on Biot theory, the seabed of the shallow ocean is considered as an inhomogeneous, poroelastic medium in order to calculate the complex reflection coefficient of plane waves. In addition to the inhomogeneities, the physical properties of the seabed are considered to vary randomly with depth as a one dimensional stochastic sequence. Using the statistical distribution of these fluctuations in depth many numerical realizations of a finely layered medium are generated. The Monte Carlo algorithm is used to obtain the probability distribution for the reflection coefficient versus frequency and grazing angle through a large number of simulations. The sensitivity of the deterministic system response to the degree of randomness in the seabed physical properties is analyzed. It is found that the complex reflection is sensitive to the random structure of seabed shear modulus, porosity, and permeability. A unique scatter relation exists in phase and amplitude of the reflection coefficient which is related to the relaxation frequency of the porous seabed at the low-grazing angles.
High-resolution 3-D measurements of subbottom geoacoustic properties using a laterally towed multichannel hydrophone array.
Authors: Yamamoto Tokuo
Published: October 2005

Accurate measurements of high-resolution three-dimensional geo- acoustics properties of the subbottom are badly needed for modeling of scattering and reverberation of acoustic waves. A new seismic reflection system called ‘‘Kite,’’ consisting of a programmable source at 1–20 kHz and a laterally towed 24-channel hydrophone array, has been tested off the coast of Miami Beach in June 1991. Single pulse at 3.5 and 10 kHz, as well as pseudorandom binary sequences, are used as source excitations. The experimental setup of the Kite as well as the preliminary results of the 3-D subbottom geoacoustic structures are reported in this paper. The results show that this method provides a swift and accurate way to measure 3-D subbottom structures. [Work supported by ONR, Code 1125OA.]
Hybrid ray-mode parametrization of pulsed radiation from a submerged acoustic source in the presence of a plane or cylindrical layer.
Authors: Felsen Leopold B. , Niu Feng
Published: October 2005

Pulsed excitation of submerged plates and shells is of current interest for various applications in structural acoustics. The interpretation of numerically or experimentally generated reference data is strongly dependent on the processing strategy in the (space-time)-(wave-number-frequency) phase space. To explore various analysis and synthesis options, point-source-excited prototype problems are considered in which infinite flat plates or cylindrical shells are approximated by fluid layers. Formal solutions are obtained by spectral decomposition into the temporal (ω) and transverse spatial (kt) wave-number domains. Signal-processing alternatives with different wave-physical content result from the sequence (kt before or after ω) chosen for the spectral inversion. For each option, one may develop a rigorous observable-based parametrization (OBP) in terms of self-consistent hybrid (wave front)–(pulsed mode) combinations that extend the frequency domain ray-mode OPB into the time domain. Asymptotics valid in the mid- and high-frequency ranges permits developing of a physically incisive description that tracks the acoustic wave field between arbitrarily located source and observer along wave front and phase-matched modal ray paths, which adjust themselves in accord with the self-consistently coupled space-time-dependent ω(r, t)−kt (r, t) spectra. The spectral self-consistency condition and its projections corresponding to various phase space processing options can be interpreted graphically by recourse to the modal dispersion surface for the layers. Some numerical examples illustrate these considerations for a plane layer. [Work supported by ONR.]
Dynamics of a baseball bat.
Authors: Van Zandt L. L. , Hansen Uwe J.
Published: October 2005

A theory of the elastic behavior of an irregularly shaped, cylindrically symmetric object is developed and applied to the study of the familiar baseball bat. The normal mode, standing wave patterns of elastic vibrations are obtained and displayed graphically. Geometric parameters and elastic constants are verified using the resonance frequencies below 5 kHz obtained experimentally from impact excited transfer functions. The lowest 20 normal modes, extending in frequency up to about 10 kHz, are used to study and display the elastic response of the bat in the first few milliseconds after striking a ball. The contribution of the normal mode elastic vibrations to the hit ball speed is also developed, and the consequences for the batter are explored.
Effects of auditory streaming on voicing judgment of Japanese intervocalic stop consonants.
Authors: Kashino Makio
Published: October 2005

An intervocalic voiceless stop consonant is perceived as voiced when the silence duration of its closure is reduced. The present study tries to clarify effects of auditory streaming of the sounds before and after the silence on this phenomenon. Phonetic identification tests are conducted for natural VCV (C=/p,t,k/) sequences (1) and those with three different types of preclosure portion of reduced streaming while varying silence duration. The degraded preclosure portions are those pronounced by the same talker but in isolation (2), one pronounced by a different talker (3), and noise burst with spectrum and amplitude envelopes resembling the original. The result with natural sequences indicates that perception of the consonant is shifted to voiced as silence duration is reduced. For stimuli whose preclosure portion is replaced, stream segregation (overlapping illusion) is observed and silence duration shows no effect on consonant perception at all. The present results indicate that silence duration can be a voicing cue only when sounds before and after the silence are interpreted as one speech event. Since masking ability of the sound before the silence is almost the same for all types of stimuli, the present result cannot be explained by the masking hypothesis.
Perception of coarticulated tones.
Authors: Xu Yi
Published: October 2005

Tones, like segments, coarticulate with one another in speech. Tonal coarticulation reduces the F0 excursion of a dynamic tone when it is in a mismatched context, that is, when the two ends of that tone do not have the same underlying pitch register as the adjacent parts of the surrounding tones, e.g., in case a rising tone is surrounded by two rising tones. To examine the perceptual effect of tonal coarticulation, trisyllabic Mandarin words were altered by changing one of their initial consonants so that they became nonsense words. These triplets were used as stimuli for identification of the tones on their middle syllables. Overall identification was well above chance, indicating listeners’ use of the information provided by the tonal context. However, with mismatched contexts, identification was slightly poorer than with matched contexts, indicating that actual F0 contour is also important for tonal identification for connected speech. To further test the perceptual effect of tonal coarticulation, the first syllable and the last syllable within each triplets were swapped, and the resulting nonsense triplets were again used as stimuli for identification of the tones in the middle. When the first and the last syllables had the same tone, identification was unaffected. When the two differed, however, a rising tone was mostly heard as a falling one and vice versa when the swapping had changed a previously mismatched context into a matched one, whereas identification was not much affected if the swapping changed a matched context into a mismatched one. This indicates that listeners factor out, or compensate for, variations due to the tonal context when trying to identify a target tone. [Work supported by NIH Grant HD-01994.]
Age-related changes in articulation of /b/ and /w/.
Authors: Slawinski Elzbieta B.
Published: October 2005

The present study has examined the effect of the age of the speaker on the duration of prevoicing, release, and transition in the articulated phonemes /b/ and /w/. Thirty normal subjects, belonging to three age groups: 20–30, 50–60, and 70–80 years old, were asked to pronounce the syllables /wa/ and /ba/. It was found that prevoicing in both phonemes becomes significantly longer with age; however, duration of the release segment is not influenced by age. Results demonstrated that speakers in the three age groups differed significantly in the duration of the articulated /w/ transition (the elderly produced a significantly shorter transition than the younger subjects). Moreover, analyses demonstrated a relationship between the duration and the difference between offset and onset frequencies of F2 transition of the /w/ phoneme. This is probably due to age-related changes in tongue and jaw movements during /w/articulation. Moreover, the perceptual results indicated that the boundary of phonemic contrast /b–w/ was shifted significantly toward shorter transition durations as a function of age.
Characterizing the change from casual to careful style in spontaneous speech.
Authors: Eskénazi Maxine , Isard Amy
Published: October 2005

An examination has been carried out to determine which elements speakers use when changing style from casual to careful speech in a dialog situation. If automatic characterization of what an individual chooses to use to be more clearly understood can be achieved, benefits for speech synthesizers would include clearer and more natural speech. The present study uses data collected in a ‘‘spontaneous’’ situation, where 12 subjects each had two scenarios to act out with a ‘‘Wizard’’ partner guiding the course of the dialog. At two crucial points, the Wizard pretended not to be able to hear the subject, saying ‘‘comment?’’ (‘‘what?’’). The subject’s exchanges just before and after the Wizard’s interjection were compared. Acoustic (voicing and formants, for example), phonological (number of segments and reduction phenomena), and prosodic (especially intensity and duration) elements have been examined. Results show which of these are modified when the change of style occurs. The study underlines the fact that the choice of elements is not the same for all speakers; individuals and groups of individuals use different strategies to arrive at their own versions of careful speech.
Inhibition: Islands in a stream.
Authors: Daly D. M. , Wada J. A.
Published: October 2005

In patients with seizures, reversible perceptual aberrations can accompany changing inhibitory balance. We report three cases with complex partial seizures (CPS) and reversible unilaterally prolonged transitions on synthetic consonant/vowel (Ge/Ye) sets [Daly etal., J. Neurophysiol. 44, 200–222 (1980)]. A 34-year-old patient with eight anterior temporal slow and spike foci during testing had intervals with marked pallor and lip smacking but reported no seizure. Left ear boundary shifted ∼30 ms over 20 min, then resolved; right ear was unaffected. A 32-year-old patient with left temporal arteriol venal malformation (AVM) during testing had intervals with pallor, dilated pupils, and brief arrest, ending with transient apraxia. Patient denied aura or seizure, but reported that proportion of ge had differed between ears: right ear boundary shifted ∼40 ms over 10 min. A 33-year-old patient with left (primary) and right anterior temporal sharp wave foci during testing had an ∼8-min interval when left ear boundary shifted ∼50 ms. Following brief arrest, chewing motions, pulsatile pupils, and fast blinks, the patient spoke to respond: left ear continued extended; right ear ge were reported as la/le but boundary was unshifted. The distribution of transition shifts is consistent with increased GABA-ergic inhibition, and with temporal sequence may reflect differing mesial and lateral temporal involvement. A parsimonious explanation must allow inhomogeneities of inhibition both between and within cortical areas.
Three-dimensional source localization in a range-dependent environment: Comparison of matched-mode and matched-field processing.
Authors: Bogart Christopher W. , Yang T. C.
Published: October 2005

Matched-mode localization of a simulated acoustic source in range, depth, and bearing is demonstrated for multiple vertical arrays. Specific examples shown use twin vertical arrays in a sloping bottom environment, with sound speed increasing with depth. The environment is modeled with adiabatic normal modes. Results of matched-mode source localization are compared with matched-field localization results. It is found for the cases studied that matched-mode processing is an order of magnitude faster than matched-field processing. Matched-mode processing consistently gives equal or lower sidelobe levels than matched-field processing. Comparison of several array configurations (differing in number of phones, vertical aperture, and location) indicates better performance for the arrays that resolve more normal modes.
Time delay estimation for deterministic transients using second- and higher-order correlations.
Authors: Pflug Lisa A. , Ioup George E. , Ioup Juliette W. , Field Robert L. , Leclere James H.
Published: October 2005

Computer simulations are used to evaluate the performance of cross correlations, bicorrelations, and tricorrelations for time delay estimation of bandlimited deterministic transients in the presence of Gaussian noise for both known and unknown sources. Signals with and without multipath distortion are analyzed. Comparisons of performance are based on probabilities of correct correlation peak location as well as means, standard deviations, and maximum error values of incorrect correlation peak locations for a sequence of signal-to-noise ratios. The effects of rectification on these measures are investigated. For an unknown source, the higher-order correlations (with and without rectification) give higher probabilities of correct peak location than second order for some signals. For most signals with an unknown source, the standard deviations of incorrect peak locations are significantly lowered using rectification. Rectification does not produce this result when using a known source. For known source cases, the cross correlation usually shows higher probability of correct peak location than the higher-order correlations. [Work supported by NOARL.]
Scattering of acoustic waves by a scatterer in a layered medium.
Authors: Kuo M. K.
Published: October 2005

In this paper, the scattering of acoustic waves by a scatterer in a layered medium is considered. The crucial steps of the analyses are the application of direct boundary element formulation together with a suitable Green’s function solution. The needed Green’s function is constructed by a global matrix technique. The essence of the method is the use of pressure at each interface (including the outer surface) as basic unknowns. The continuity of pressure along the interfaces of the multilayered medium is then ensured automatically. These as yet undetermined interface pressures are finally determined from the boundary conditions at the outer surface of multilayered medium and the continuities of normal velocities along interfaces. The resulting linear system of equations is straightforward assembled and manifested in a global form. The sizes of the matrices are only N×N, which is only 1/4 of storage of the original global matrix formulation proposed by Schmidt. The complete scattering is then computed by boundary element and compared against the results obtained by PE. In the cases of acoustic scatterer, PE is presumed to work quite well, at least in the forward propagation portion. The effects of elastic scatterer are then discussed.
The bending wave transfer function on a disordered plate.
Authors: Norris Andrew
Published: October 2005

The transfer of acoustic energy in a flat plate with periodic and nonperiodic disorder is studied. The motivation comes from the experimental observations of Ye etal. that strongly localized modes occur over a relatively broad ‘‘band gap’’ on a 1-in.-thick steel plate supporting lucite blocks arranged in a square lattice. The frequency range is such that flexural wave effects dominate in the steel plate, suggesting a simple model for the system. Only flexural waves are considered and the blocks are replaced by point scatterers. In this picture, the experimentally observed localization corresponds to the first band gap of the periodic system. The model also leads to considerable analytical simplicity in the corresponding 1-D system. The transfer function is computed by considering a large but finite periodic 2-D system with multiple scattering between all blocks. The results show good quantitative agreement with the experimental measurements. Numerical results will also be presented for disordered arrays of blocks on a flat plate.
Observation of acoustic wave localization.
Authors: Ye Ling , Cody George , Zhou Minyao , Sheng Ping , Norris Andrew
Published: October 2005

Acoustic wave propagation has been studied in a composite elastic plate consisting of a periodic square array (horizontal period=7 in.) of 190 lucite blocks (3.5×3.5×3 in.) glued to a 1-in.-thick, 6×6-ft steel plate. Elastic wave propagation is excited using a 0.2-ms force transducer and the vertical response is measured by an accelometer (0–25.6 kHz). The significant feature of the data is a 20- to 30-dB gap in the amplitude of the frequency response of the transfer function in the band between 2000 and 3800 Hz, which roughly corresponds to wavelengths coherently scattered by horizontal and diagonal arrays of lucite blocks, as well as to the first Brillouin zone of the square array. The decay length of the strongly localized bending wave mode is of the order of one unit cell ≊10 in. The decay length of the localized mode exponentially increases at the high-frequency side of the gap with an inverse logarithmic derivative of 120 Hz. It is believed that the interaction between the propagating bending mode of the plate and the coherent shear vibrations of the fixed lucite blocks is responsible for the observed elastic wave localization. Comparison is made to exact calculations of the transfer function for a uniform composite plate and calculations of the propagating bending and shear modes of an infinite periodic array of lucite blocks on a steel plate.
Pulse distortion in nondiffracting beam pulse echo systems.
Authors: Fatemi Mostafa , Ahanessians R.
Published: October 2005

Ultrasonic nondiffracting beams, generated by J0 radial weighing sources, have recently been introduced and suggested for medical imaging and nondestructive testing. Due to inherent dispersion, a pulse generated by such an aperture exhibits distortion as it propagates away from the source. Performance of a pulse echo system depends, in part, on pulse shape. A model for the point response of a pulse echo system with J0 aperture, derived by a short bandpass pulse, is presented here. The point response is defined as the received pulse by the aperture when the transmitted pulse is reflected back by a point target. The model describes the envelope of the point response by three terms: amplitude, delay, and spread. Oscillatory component of the point response is described by instantaneous frequency and a constant phase term. Computer simulation for the special case of a Gaussian pulse will be presented. The model provides computationally simple expressions for evaluating parameters of nondiffracting pulse echo systems, such as axial resolution, intensity, and echo displacement, in terms of aperture beamwidth, center frequency, and target-to-aperture distance.
Sound pressure waveforms generated by an optimized photoacoustic source.
Authors: Oksanen Markku , Wu Junru
Published: October 2005

A sound pulse is generated when a laser pulse is absorbed in an interface of a transparent and nontransparent solid. The displacement amplitude of the thermoelastically generated pulse can be theoretically predicted, but the theory gives the solution as a product of the Hankel and Laplace transformed source term and a weight function [F. A. McDonald, Appl. Phys. Lett. 54 (16), 1504–1506 (1989)]. The inversion problem is solved numerically with nontrivial spatial and temporal laser light properties. The calculated displacement amplitude is used to numerically predict the pressure waveform radiated into a fluid that is in contact with the solid. Material properties of the solid are chosen to maximize the sound pressure in the fluid for use with a low-power diode pumped Nd:YAG-laser. [This work is supported by BF Goodrich Simmonds Precision Aircraft Systems.]
Thermo-acoustic efficiency of a pulse-heating, electrical discharge source.
Authors: Olson Allen H.
Published: October 2005

Electrical energy stored in a high-voltage capacitor bank is rapidly switched across a pair of electrodes immersed in a conductive fluid, such as seawater. As electrical current passes between the transducer electrodes, the fluid is rapidly heated and expands, producing acoustic waves. The current density defines the spatial distribution of the heating as well as the electrical resistance of the transducer. Computed and measured resistance agrees within experimental accuracy (a few percent). Using the wave equation, with an appropriate source heating term, the acoustic efficiency (acoustic energy/heat energy) of the pulse-heating mechanism is shown to increase linearly in proportion to the heat-energy density and to decrease inversely in proportion to the square of the heating time. The validity of this scaling relationship is confirmed experimentally for energy densities below 200 J/cc. Extrapolation of this relationship predicts 10% efficiency at 1000 J/cc, although this has not yet been confirmed experimentally.
Reconstruction of transducer surface velocity distributions from a limited number of acoustic pressure field measurements.
Authors: Blakey J. R.
Published: October 2005

The accurate prediction of the acoustic field of a transducer requires a detailed knowledge of its surface velocity distribution. The normal surface velocity distribution of pistonlike plane transducers can be deduced from a suitable spatial transformation of the acoustic pressure distribution measured over a plane parallel to the transducer surface. This method normally requires a large number of time-consuming precision measurements and a corresponding computational effort. Less intense methods of transducer characterization, which can predict radiation fields to an acceptable accuracy, are therefore of some interest. The ‘‘effective radius’’ method is a well-known example of such an approach. This contribution discusses a method of reconstructing approximate surface velocity distributions from the inversion of the axial pressure distribution and presents some typical results obtained from this approach.
Pulse phase-locked loop technology-based methods for measurement of ultrasonic velocity.
Authors: Cantrell John H. , Yost William T.
Published: October 2005

A new instrument based on a constant frequency pulse phase-locked loop concept has been developed to accurately measure the ultrasonic phase velocity in condensed matter. Measurements of the sound velocity in ultrapure water are reported in which both damped and undamped transducers are used with the instrument together with reflectors of various thicknesses placed in the sound propagation path. An analysis of measurements made with the new instrument and similar measurements, taken under identical experimental conditions, using a popular variable frequency pulsed-phase-locked loop instrument is reported. Uncertainties in both measurement systems are analyzed and discussed. A method for measuring inherent phase shifts, not addressed by previous investigators, within the variable frequency pulsed phase-locked loop system and a derivation of the equations that govern its use as a bolt-tension measuring device are presented. The effects of a finite pulse length on the measurements of phase velocity in dispersive media are addressed.
The effects of ultrasound on membrane-bound ATPase activity.
Authors: Dinno Mumtaz A. , Fisher Robert J. , Matthews John C. , Crum Lawrence A. , Kennedy Wendy
Published: October 2005

Ultrasound frequencies ranging from 26 kHz–10 MHz are used in a number of applications varying from cell disruptions to therapeutic and diagnostic procedures. Previous results from our laboratory have demonstrated that 1-MHz ultrasound at therapeutic intensities causes significant changes in the electrophysiological properties of epithelial tissues. The nature of these alterations indicated that, among other effects, the Na/K-dependent ATPase activity of the tissue was reduced. In this study, the effects of ultrasonic irradiation (30 kHz) on enzyme activities in two model systems have been examined: one membrane incorporated (Na/K-dependent ATPase in inverted erythrocyte ghosts from rat blood) and the other in ‘‘free’’ solution (ATP-dependent firefly luciferin/luciferase reaction). Ultrasonic irradiation produced irreversible decreases in the activity of the enzyme in each system. At present, the analysis leads one to conclude that sono-chemical (including free radical) and not thermal effects on the enzyme molecules are responsible for the activity decreases. These results support the hypothesis that the effects of ultrasonic irradiation were, in part, due to effects on the activity of Na/K-dependent ATPase. Furthermore, the results of this study demonstrate that sono-chemical-induced enzyme activity changes may represent a much more common and pervasive effect than is commonly realized. [Work supported by the NIH under Grant No. 5-RO1-CA-39374-05.]
Simulated capillary blood flow measurement using a nonlinear ultrasonic contrast agent.
Authors: Schrope Beth , Newhouse Vernon , Uhlendorf Volkmar
Published: October 2005

A system is proposed for measuring slow, small volume blood flow, such as that found in the capillary beds. The method relies on the injection of a strongly nonlinear echocardiographic contrast agent, whose echoes are then analyzed by a modified Doppler process. The contrast agent is necessary to increase the signal-to-clutter ratio from the small blood volume, and to distinguish the blood movement from other moving structures, such as vessel walls or surrounding tissue. The nonlinear properties of this saccharide-based contrast agent are described, as evidenced by experimental evaluation. The contrast agent and signal-processing modality were then tested in a blood flow simulator, at velocities as low as 1.5 mm/s, with good results. In addition, an analysis for applying this technique invivo was conducted, accounting for the dynamic and acoustic parameters of the physiological environment. Finally, some specific applications for this method are discussed, including its limitations. [Work supported by NSF and Schering AG.]
Ultrasonic attenuation spectroscopy research for food dispersion measurement.
Authors: Yinguan Wang , Jingsheng Wei
Published: October 2005

Theoretical research work has been done for understanding the principle of the ultrasonic absorption in food dispersion. Four ultrasonic attenuation measurement methods have been developed. These are the through transmission method, through transmission substitution method, pulse echo substitution method, and pulse echo method. The first three methods compare echoes collected from a reference material of known ultrasonic properties with that of the sample. The last method compares reflected echoes collected from measurements on the sample only. An ultrasonic attenuation spectroscopy system for the study of ultrasonic properties of food dispersion has been developed. The results of tests on castor oil are in good agreement with the literature values. Experiments on skimmed milk, semi-skimmed milk, full fat milk, and homogenized milk’s ultrasonic attenuation spectra have been performed. The results demonstrate the effects of both fat content and fat globule particle size on the ultrasonic attenuation characteristics of milk.
Numerical integration of acoustic field data using the exterior Helmholtz integral equation.
Authors: Clark Joseph A.
Published: October 2005

Experimental measurements of acoustic pressures and normal pressure gradients over a closed surface surrounding an acoustic source can determine the acoustic field throughout the entire volume of a homogeneous region outside the measurement surface. One means for determining the extended field is to numerically integrate the exterior Helmholtz integral equation over the measurement surface. An implementation of this approach utilizing a finite-difference approximation to the exact Helmholtz equation integrated over a generalized cylindrical measurement surface has been developed to study acoustic fields radiating from large, immersed structures. In this talk the numerical algorithm will be described, and examples based on both simulated and actual measurement data will be presented. The results show pressure, velocity, and intensity distributions in the evanescent wave region immediately adjacent to localized and distributed acoustic sources, in the geometric near field and in the acoustic far field. Effects of errors due to finite spacing of measurement points over the measurement surface will be illustrated and evaluated.
Dispersion and repopulation of the Heard–Ascension modes.
Authors: Shang E. C. , Wang Y. Y. , Georges T. M.
Published: October 2005

The modal spectrum of the PE field (MOSPEF) along the horizontally refracted ray path to model the Heard–Ascension Island propagation is used. First, the travel-time error imposed by the PE approximation is discussed, and an analytic formula for travel-time error is given to clarify the validity of the PE application. Second, the modal repopulation caused by mode coupling at the transition from the surface duct to the deep SOFAR duct is estimated. Finally, modal dispersion effects, including modal arrival time spreading and the modal pulse elongation within the transmitted bandwidth, are calculated based upon a second-order Taylor expansion of the MOSPEF phase. By using a finite-difference technique instead of Fourier decomposition of the transmitted spectrum, only three frequencies (56.99, 57.00, and 57.01 Hz) are needed to characterize the dispersion. [This work was supported by ONR and NOAA.]
Using acoustic phase to estimate change in acoustic travel time.
Authors: Spiesberger John L. , Bushong Paul J. , Metzger Kurt , Birdsall Theodore G.
Published: October 2005

A signal processing technique is described that provides precise estimates of the change in travel time of acoustic pulses using an optimal combination of multipath phase and amplitude [J. L. Spiesberger etal., J. Oceanogr. Eng. 14, 108–119 (1989)]. Limits to the precision of the estimator for basin-scale transmissions (0.135 ms at 2-min interval) are imposed by internal waves rather than acoustic noise. The technique does not require any understanding of the spatial coordinates of acoustic paths between the source and receiver and is thus easy to use. The technique was used in the Heard Island feasibility experiment. Applications of this signal processing technique to new observations of mode 1 internal waves in the north Pacific Basin are also discussed.
A borehole electrodeless arc discharge source.
Authors: Mahrer Kenneth D.
Published: October 2005

Southwest Research Institute has built and is testing a new, impulsive, deep-borehole, high-temperature, electrodeless arc discharge acoustic source or ‘‘sparker.’’ Upon completion, it will be capable of operating at 10 000 ft and 125 °C on a standard seven-conductor wireline using 220 VAC, 60-cycle power. The tool is about 25 ft long by 4.5 in. in diameter. The source signal is generated by the transient discharge of a capacitor bank through two electrically insulated bodies of electrolyte connected by a narrow, orifice-shaped, aperture channel in a very high-resistivity ceramic disk. Each firing releases approximately 1.2 kJ of energy. The source is virtually erosion-free. Hence the source waveform is highly repeatable. It generates signals in a passband of 200–2000 Hz with a sustained firing rate faster than 1 firing per 5 s. At present, the tool has been tested at the Texaco’s Humble, Texas test site and BP’s Devine, Texas test site. During the Humble tests, data were recorded simultaneously by a three-channel hydrophone string in a borehole 270 ft from the source borehole, by a 32-channel hydrophone streamer 557 ft from the source borehole, and by a 30 three-component cemented geophone string 361 ft from the source borehole. At the Devine, test data were recorded by a single-channel hydrophone in a well 330 ft from the source well. [Work supported by a specific consortium of oil, gas, oil and gas service, and equipment companies.]
Frequency control of blast-induced ground vibrations.
Authors: Crenwelge Otto E.
Published: October 2005

A site-specific approach is presented for controlling the amplitude, frequency, and duration of ground vibrations induced by blasting operations. Using measured single-charge response functions, and proper frequency control of the pulse train excitation applied to the overburden, significant reductions in vibration amplitude and duration may be achieved for multiple-charge production blasts. A case study is used to illustrate these effects, even though the charge weight per delay was increased multifold.
A fiber-optic interferometric accelerometer/geophone system.
Authors: Gardner D. L. , Brown D. A. , Garrett S. L.
Published: October 2005

A variety of transducers presently exists for geophysical exploration, ranging from suites of land-based geophones, seismometers, and accelerometers to towed hydrophone arrays for off-shore surveying. Miles of electrical cabling are required to implement these systems. To exploit the advantages of long-distance fiber-optic communication technology and to avoid temperature sensitive electronics in warm down-hole applications, several intrinsically optical fiber-optic acoustic and acceleration/geophone transducers have been developed within the NPS Physics Dept. Recent advances at NPS in the development of low-cost interferometric signal demodulators permit the implementation of an economical measurement system, whereby the fiber-optic transducer output may be made indistinguishable from a similar electrical transducer. Push–pull fiber-optic accelerometer/geophone designs employing an all-fiber Mach–Zehnder interferometer, a 3×3 coupler, and a demodulator system will be described. [Work supported by the Naval Postgraduate School Direct Funded Research Program and the Naval Sea Systems Command.]
Wave equation solution by a coupled-mode, multiple-reflection series method.
Authors: Pai D. M.
Published: October 2005

In inhomogeneous media, wave equations are nonseparable and numerical techniques are usually employed. This paper presents an efficient and stable eigenmode solution method. In the method, the medium is divided to thin layers; eigenmodes are found for each layer and then coupled to form the final solution. The method differs from the usual eigenmode methods in that mode couplings are achieved through an iterative, one-way-wave, multiple reflection series, which requires only matrix–vector multiplications. The solution is computationally simple, has physical interpretation, and remains stable with respect to evanescent waves.