bluuebunny/crossref_metadata_2025 huggingface dataset:
Elastic guided waves and the Floquet concept in periodically layered plates
Authors: Chimenti D. E. , Shull P. J. , Datta S. K.
Published: October 2005

This paper describes the results of experiments and calculations on the interaction of ultrasound with aluminum/aramid-epoxy composites (ARALLTM), a planar laminate of alternating constituent layers. The plates have been investigated experimentally using fluid-coupled leaky wave techniques, and theoretically using both a partial wave analysis and also a stiffness-based numerical approach. Frequency zones of wave transmission and reflection, similar to those predicted for periodic media have been observed and modeled in the bilayered plates. The onset of this behavior has been simulated numerically by incrementally varying lamina properties starting from a homogeneous average value. It is demonstrated that the transmission zones arise from a consolidation or clustering of the uniform-plate minima into frequency zones or bands, similar to Floquet wave behavior. Moreover, these bands, and the associated dispersion curves, are approximately constant in frequency, entirely unlike the behavior expected for a homogeneous plate. It is suggested that the large phase shifts induced in a layered medium composed of elastically contrasting media are responsible for this observation. This mechanism also leads to a correspondence between the number of reflection minima and layer unit cells. The effect of structural symmetry on the reflection function has also been studied. The theoretical predictions compare very well, in nearly every case, to the experimental results.
A model for assessing the impact of vessel noise on odontocete communication
Authors: Cosens Susan E.
Published: October 2005

Offshore industrial noise sources ensonify marine mammal habitat and may mask detection of social signals and important environmental sounds. A probabilistic model of sound detection was developed for assessing the impact of underwater icebreaker noise on signal detection by beluga whales and narwhals. The probability of detecting sample signals, in the absence of vessel noise, was compared to that of detecting the same signals in ship noise, using the MV arctic, as a sample noise source. Analysis of signal detection probabilities showed that loud signals centered on the 5-kHz critical band were more severely masked by ship noise than were quiet 5-kHz signals or loud 2-kHz signals. Thus long-range calls seem to be more susceptible to masking by ship noise than are short-range calls. The model could also be applied to other critical bands of interest. Changes in the probability of detecting vessel noise, as estimated by the model, were also correlated with changes in beluga and narwhal behavior, observed in response to the vessel in operation.
The effects of noise on dolphin echolocation
Authors: Au Whitlow W. L. , Nachtigall Paul E.
Published: October 2005

The echolocation capabilities of dolphins can be seriously affected by natural ambient and man-made noise. Many echolocation experiments have been conducted at our facility to study the effects of noise on the echolocation behavior and capabilities of dolphins. When a beluga was transported from San Diego Bay, California to Kaneohe Bay, Hawaii, the whale adjusted its sonar emissions to compensate for the louder ambient noise environment in Kaneohe Bay. It emitted higher intensity signals which had peak frequencies that were approximately one octave higher than in San Diego. Experiments with echo-locating dolphins have shown that their target detection and discrimination capabilities can be severely degraded by the introduction of masking noise. In most situations, the dolphins compensated for the presence of masking noise by emitting more clicks per scan and by increasing their signal intensity. The response latency defined as the time between the cessation of the last click in a click train and the touching of a response paddle also increased as the masking noise level increased. However, the effects of noise emanating from a specific location can be minimized by a dolphin utilizing the directional property of its auditory system.
Interaural time discrimination in the bottlenose dolphin
Authors: Moore P. W. B. , Pawloski Deborah A.
Published: October 2005

Binaural hearing is the advantage of two ears over one. Localization studies with marine mammals have shown that acoustic localization underwater is mediated by the same binaural mechanisms used by other mammals in air. Dolphin echolocation abilities are enhanced by the use of two separate receivers. Au and Moore [J. Acoust. Soc. Am. 75, 255–262 (1984)] modeled the animal’s hearing system as a two-element array using receiving beam pattern measurements. The present study sought to measure the interaural phenomena of interaural time difference discrimination (ITD) and interaural intensity difference discrimination (IID). A dolphin was trained to accept contact hydrophones, attached by suction cups, to the outer surface of the lower jaw in the area of the pan-bone and to perform detection threshold experiments. Audiometric data at several frequencies indicate that the dolphin minimum threshold for pure tones may be 20 dB different when measured with jaw phones. The first behavioral measures of ITD and IID discrimination and for a cetacean have been obtained. ITD and IID for clicks trains of various frequencies, presented with interclick intervals simulating various echolocation target ranges were collected. This method of collecting audiometric data represents a new approach for assessing bearing capabilities in cetaceans.
Bioacoustics of baleen whales: From infrasonics to complex songs
Authors: Clark Christopher W. , Ellison William T.
Published: October 2005

One reason for concern over potential effects of man-made sounds on marine mammals stems from the fact that most baleen whales produce intense, low-frequency sounds. Complete descriptions of vocal repertoires are still lacking for many of the 11 species, and our understanding of how whales use sounds is poor. The application of passive array techniques has provided unique and exciting insights into the biological significance of whale sounds. Acoustic studies on bowhead whales migrating off Point Barrow, Alaska and recent work on pelagic species (including blue, finback, and minke whales) clearly demonstrate that whales are vocally active and produce a variety of signals. Whales counter-call, adopt distinctive call types when traveling in acoustic herds, sing complex songs using two simultaneous, nonharmonically related voices, and produce extremely long, patterned sequences of infrasonic calls. These results support the conclusion that sounds serve a variety of important communicative functions. There is also reason to believe that some whales actively use surface reverberation as a navigational cue. Thus the concern over the potential impact of man-made noise on the whales’ acoustic behaviors is legitimate and this issue requires continued attention. [Work supported by ARPA, ONR, and the Department of Wildlife Management, Barrow, AK.]
Standard reversible transducer (USRD type E37) for high frequencies to 2.0 MHz at hydrostatic pressures to 20.7 kPa (3000 psi)
Authors: Tims James A. , Ivey Larry E.
Published: October 2005

A new pressure-stable reversible standard transducer, USRD E37, has been developed at the Naval Research Laboratory, Underwater Sound Reference Detachment for the frequency range 100 kHz to 2.0 MHz at hydrostatic pressure to 20.7 MPa (3000 psi) with operating temperatures from 5 to 35 °C within this frequency range. This USRD E37 maintains a smooth response over the broad frequency spectrum previously covered by both the USRD E27 and E8 standard transducers, which were not stable with temperature and static pressure. The E37 has been calibrated to 6894 kPa (1000 psi) at 3 °C. Its unique sensor configuration design uses a lead titanate disc sensor supported by a butyl rubber ring. The faces of the sensor are covered with PRC PR-1538 polyurethane and are held in place in the frame assembly by thin wire. The receiver preamplifier assembly is specially designed for high-frequency operation, with a built-in bypass relay to allow signals to be transmitted. The cylindrically designed outer housing is made of polycarbonate and has been statically pressure tested to 31.026 MPa (4500 psi).
Variational principle modeling of class IV flextensional transducers
Authors: Robinson Harold C.
Published: October 2005

The variational principle is an approximation method that allows one to obtain accurate estimates of certain quantities using relatively crude trial functions for the physical behavior. This principle is applied to transducer analysis by coupling a variational principle developed for the driving element (including piezoelectric effects) to one for the shell. The motion of the transducer is, in turn, coupled to a variational principle for the surface pressure in a fluid medium. The modeling of a class IV flextensional transducer will be presented in detail. The invacuo resonance frequencies for the piezoelectric driving stack and elliptical shell, as well as the invacuo mode shapes for the driver-shell combination will be compared with existing theoretical and finite-element analyses. Variationally determined surface pressures for a single transducer will be presented and compared to finite-element results. Admittance plots and beam patterns for the single element will be shown. [This work was sponsored by the Office of Naval Research.]
Linearizing the output of nonlinear transducers by preprocessing their input signals
Authors: Forsythe S. E.
Published: October 2005

A technique has been developed at USRD to drive transducers to amplitudes at which nonlinearities in the output normally become evident while maintaining the output signal as a faithful copy of the drive signal. This is done by preprocessing the desired signal using a transducer model that includes the transducer’s nonlinearity. The model is stated as a system of coupled ordinary differential equations (ODEs) which define the dynamic variables of the system (positions, velocities, accelerations) as well as the parameters of the system (masses, stiffnesses, viscosities, etc.). Instead of integrating the ODEs using the known drive, as would be done to predict the system’s output, the ODEs are explicitly solved ‘‘backwards’’ given the desired output. This solution typically requires the accurate numerical calculation of derivatives as well as the point-by-point solution of simultaneous nonlinear equations. Techniques for the efficient solution of the equations as well as solubility issues are discussed. [Work support by Space & Naval Warfare Systems Command.]
Two complex effective lengths for air columns
Authors: Ayers R. Dean
Published: October 2005

In the context of a plane-wave approximation for acoustic waves in an air column, the pressure reflection coefficient R is related to the relative input impedance Z/Zc by a simple bilinear transformation. At any location along the air column, the complex effective length to an open, downstream end of an equivalent cylinder is defined as Lo ≡(j/2k0)ln(−R), where k0 is the undamped propagation number, and that to a closed end is defined as Lc≡(j/2k0)ln(R). The real parts of these quantities are just the conventional effective lengths to the corresponding ends, which have been used in the study of musical wind instruments. The imaginary parts incorporate the effects of damping within the air column and at its downstream termination. The common theme here is a simple extrapolation of interfering, damped plane waves, with k0 serving as an artificially large attenuation constant. Lc turns out to be more useful than L0 for analyzing the brass instruments [R. D. Ayers, J. Acoust. Soc. Am. Suppl. 1 88, S163 (1990)], and an earlier treatment of undamped horns made implicit use of a real Lc [R. W. Pyle, Jr., J. Acoust. Soc. Am. 57, 1309–1317 (1975)]. This new treatment is more realistic, computationally simpler, and conceptually more straightforward.
Input response of cylindrical and conical bores with a single tone hole: Measurements and predictions
Authors: Wilson Teresa , Keefe Douglas
Published: October 2005

There exist few measurements on the acoustical response of tone holes in conical-bore air columns. For practical application to woodwind design, the accuracy of predictive models is said to be insufficient [McCann and Mathews, J. Acoust. Soc. Am. 91, 2449 (A) (1992)]. Experiments performed test the transmission line model of air columns and tone holes. The input impedance was measured over the range 150–10 000 Hz for a single tone hole in a cylindrical bore and in a conical bore. The cylindrical bore had length 920 mm and radius 7.2 mm, and the conical bore had length 630 mm, entry radius 6.5 mm, and exit radius 12.5 mm. In woodwinds, the low-frequency resonances control the playing frequencies. Hence, the resonance frequencies under 1 kHz were predicted from a model of the air column and tone hole. The measured and predicted resonance frequencies for the cylindrical bore agreed to within 6±6 cents and for the conical bore agreed to within 23±18 cents. The errors in the conical-bore theory are largest at low frequencies. Work is underway to refine the theory of tone holes in conical bores.
Experiments with an acoustic harassment system to limit seal movements
Authors: Mate Bruce
Published: October 2005

To control the distribution of seals around salmon hatcheries, pond tests were conducted using swept frequencies between 2 and 20 kHz. This did not affect salmonid movements or reproduction. Aperiodic 12- or 17-kHz pulses of varying duration were effective at levels of 187 dB re: 1 μPa in reducing seal abundance near several hatcheries and pen aquaculture facilities. A few larger (possibly older) seals habituated or were less sensitive, and foraged with modified techniques. For sea lions, the same system produced a dramatic initial startle response but was otherwise totally ineffective. Many marine mammals react to moving sound sources even if loud stationary sources are tolerated. Early in this experimentation, swept frequencies were eliminated for simplicity. However, the illusion of motion as simulated by Doppler-like sweeps may have been lost in the process. Operant conditioning research suggests that an aversive stimulus is best maintained when used aperiodically. If several stimuli have a deterrent effect, this effect can be sustained longer by intermixing the stimuli to avoid or delay habituation. These principles may also be applicable to intentional harassment and industrial effects.
Model eigenfunction perturbations and group speed tomography
Authors: McDonald B. Edward , Baggeroer Arthur B.
Published: October 2005

Certain problems in acoustic thermometry of ocean climate (ATOC) require evaluating the response of modal group speeds to perturbations in the ocean sound-speed profile. Two different approaches have been taken recently by researchers, resulting in two perturbation expressions whose equivalence is not immediately evident. The first approach, used by Lynch etal. [J. Acoust. Soc. Am. 89, 648 (1991)], results in an integral equation involving the frequency derivative of the eigenfunctions. The second approach, under current investigation, yields an integral equation involving the response of the eigenfunctions to sound-speed perturbations. The two expressions are shown to be equivalent by means of their projections onto the set of modal eigenfunctions. These results are discussed in relation to group travel-time tomography.
Rectified diffusion and single-bubble sonoluminescence
Authors: Lofstedt Ritva , Barber Bradley P. , Putterman Seth
Published: October 2005

The remarkably low solubility of air in water may be essential to the observation of stable single-bubble sonoluminescence (SL) in this system. In other liquids, the mass exchange during a single cycle appears to be sufficient to quench single-bubble SL. To gain insight into this issue, (1) a theory is developed that unifies mass diffusion and the Rayleigh–Plesset equation, and (2) laser scattering is used as a probe of the time change of bubble parameters due to mass diffusion. [Work supported by the U.S. DOE Division of Advanced Energy Projects and Division of Engineering and Geophysics (Theory); R. L. is an AT&T fellow.]
Effect of microbubbles on self-similar waterborne shocks
Authors: McDonald B. Edward
Published: October 2005

Similarity solutions developed from the equations of nonlinear acoustics [P. H. Rogers, J. Acoust. Soc. Am. 62, 1412–1419 (1977); B. E. McDonald and J. Ambrosiano, J. Acoust. Soc. Am. 84, 1497–1503 (1988)] have adequately accounted for the range dependence of overpressures in the propagation of underwater spherical shocks, while giving only fair to poor predictions for relaxation time constants at large ranges from the source. The relaxation time discrepancy seems to suggest an anomalously large nonlinearity coefficient at great distances from the source. The effect of minute quantities of entrained air on the shock similarity solution for water is investigated. It is well known that microbubbles can greatly increase the nonlinearity coefficient of water at ambient conditions. At high pressures, however, bubbles may collapse to the point of being dynamically unimportant. The equation of state for water is modified to account for ambient microbubble populations, and the resulting equations solved for self-similar shock profiles. Using air void fraction as a fit parameter, observed relaxation time data are analyzed to yield the levels of entrained air that may have been present in various underwater explosive experiments.
Hot topics in noise: Sound quality of products
Authors: Cann Richard G.
Published: October 2005

The quality of a sound that a product makes is used by the listener in many ways. Broadly, the listener judges from the sound quality the identification of the type of the source. Once identified, the information contained in the sound may be used further. It may be used for practical diagnostic purposes, such as identifying an unanticipated fault or a mode of operation. It may also be used on an aesthetic level to qualify the acceptance of the product. So, in many ways what one hears is used similarly to what one smells or even tastes. Over the years, researchers in psychoacoustics have developed many metrics for sound quality. However, the primary focus has been toward one end of the sound-quality acceptance spectrum—those sounds that annoy or irritate rather than those sounds that gain acceptance or please. The application of sound-quality techniques implies that well-defined specifications for the sound quality must be written so that a manufacturer is clearly able to accept or reject a product. This requirement will be even more acute in the future when many more products will be designed on one continent, built on another, and used on a third.
Underwater testing of a thermoacoustic sound projector
Authors: Black Steven C.
Published: October 2005

For about the last 10 yr, there has been a growing interest in the thermoacoustic method of transduction. Recently, research has been conducted at Los Alamos National Laboratory on the development of a high-power, low-frequency underwater sound projector based on the concept of a thermoacoustic engine [G. W. Swift, J. Acoust. Soc. Am. 84, 1145 (1988)]. The design of this new transducer consists of a long straight tube deployed vertically. The upper portion of the tube is gas filled and contains the heat engine driver. The lower portion is water filled and acts as an impedance matching section. A small-scale demonstration device has been built and was tested both in air and in water. The demonstration device is approximately 9 m in length and operates in the frequency range of 100 to 200 Hz. In conjunction with experimental testing, modeling of the in-water behavior of this demonstration device was also performed. Results from the modeling and the in-water testing will be presented. [Work sponsored by SPAWAR.]
Electromechanical properties of new electrostrictive materials for underwater acoustical applications
Authors: Rittenmyer Kurt M. , Ting Robert Y.
Published: October 2005

Electrostrictive ceramics are known to be capable of generating strains that far exceed those of conventional piezoelectric lead–zirconate–titanate (PZT) ceramics. Several lead–magnesium–niobate (PMN) compositions developed earlier were useful only at higher temperatures than those of interest to the sonar community. A new barium-modified PMN–PT ceramic is described. This material can operate at lower temperatures and has very low losses, making it a prime candidate for high-power sonar transducer applications. Another family of electrostrictive materials capable of generating large strains is lanthanum-modified PZT (or PLZT). These materials exhibit strains up to 0.1% along with extremely high dielectric strength, but their hysteresis losses are higher than those of PMN or PMN–PT ceramics. Since the maximum possible strain output is usually the important parameter in actuator applications, the PLZT family may have potential for new actuator designs. Strain measurements for these new electrostrictive ceramics at high electric fields but different frequency ranges are presented. [Work supported by ONR.]
Hot topics in physical acoustics
Authors: Crum Lawrence A.
Published: October 2005

Because of the technical area of physical acoustics represents the center of Lindsay’s Wheel of Acoustics, this area is often the origin of many research topics that eventually find application in other committees, and even other disciplines. Thus, ‘‘hot’’ topics in physical acoustics can be defined as anything done by physical acousticians, especially if they involve bubbles! However, for the benefit of those from outside this area who want to learn something about this exciting committee, a number of topics that are currently of major interest will be discussed briefly and a few selected topics of particular interest to the presenter will be discussed in more detail. In particular, it will be shown how a few specific topics being developed by physical acousticians have direct relevance to problems of more general interest to our society. For example, advances in the important new area of sonochemistry await progress in the fundamental understanding of sonoluminescence; advances in the new ventures of medical ultrasound, such as extracorporeal shock wave lithotripsy and ultrasonic surgery, await a more complete understanding of acoustic cavitation and nonlinear acoustics; the utilization of containerless processing of exotic materials in space awaits developments in acoustic levitation and an understanding of the surface-oscillation characteristics of liquid drops. These and similar topics will be discussed in some detail.
Scattering by a layered poroelastic obstacle embedded in a poroelastic host
Authors: Lim Raymond
Published: October 2005

A transition-matrix formulation of the field scattered by a three-dimensional, multilayered, poroelastic obstacle embedded in a poroelastic host is obtained by extending Peterson and Ström formulation for scalar waves [B. Peterson and S. Ström, J. Acoust. Soc. Am. 57, 2–13 (1975)]. An exact solution of the vector Biot equations is obtained, obeying all boundary conditions prescribed on all boundaries of the layered obstacle. By numerically implementing the solution for general poroelastic media, scattering with hosts and obstacles made of loss general media is conveniently predicted by choosing material parameters in a limiting sense. Examples are presented to study the scattering dynamics of layered spheres and spherical shells embedded in fluid and poroelastic hosts.
Coupled wave equations for numerical calculation of acoustical propagation and scattering by atmospheric turbulence
Authors: De Antonio Michael , Goedecke George H. , Auvermann Harry J.
Published: October 2005

The usual approximate acoustic wave equations [e.g., A. D. Pierce, J. Acoust. Soc. Am. 87, 2292 (1990)] were developed for ambient conditions (turbulence) in which the scale length a of the spatial variation of temperature and flow velocity is much larger than the acoustical wavelength λ; this is not the case in many applications of interest. An alternative set of coupled acoustical wave equations, valid for any a/λ, is presented. These equations involve no approximations except the usual neglect of the viscosity terms in the Navier–Stokes equation for the acoustic flow. For quasistatic or ‘‘frozen’’ turbulence, the integral forms of these equations are presented, suitable for application of the digitized Green’s function method [G. H. Goedecke and Sean G. O’Brien, Appl. Opt. 27, 2431 (1988)].
First-order acoustical wave equations and scattering by atmospheric turbulence and turbules
Authors: Goedecke George H. , Pellegrino Paul M. , De Antonio Michael , Auvermann Harry J.
Published: October 2005

The first Born approximation has often been used to predict acoustical scattering by the quasistatic temperature fluctuations and velocities associated with atmospheric turbulence. For this approximation, only terms linear in these disturbances need be retained in the wave equation. Terms in this first-order wave equation involving spatial derivatives of the flow field have often been dropped. It is shown that retaining these terms yields a Born scattering amplitude equal to cos(θ) times that obtained when they are dropped, where θ is the scattering angle. It is also shown that this Born scattering amplitude is identically zero in the forward direction for any solenoidal flow velocity field that goes to zero faster than r−3 as r→∞. Analytic expressions and numerical results for the first Born differential and total cross sections are obtained for a model localized turbule. The model employs nonuniform rotation about an axis, as modulated by an axisymmetric Gaussian, plus commensurate temperature variation.
Prediction of masked detection thresholds for noise signals centered in a gated noise masker
Authors: Formby C. , Heinz M. G. , Luna C. E.
Published: October 2005

A new detection model can predict masked detection thresholds for a range of signal bandwidths (W=62–6000 Hz) and durations (T=10 to 500 ms) for noise signals centered at 2500 Hz in an uncorrelated 500-ms, 6000-Hz-wide masker (N0=53 dB SPL/Hz). The new model effectively takes into account relative cues resulting from temporal and spectral differences between the signal and masker to supplement energy detection. These relative cues are (1) greatest when the durations and spectra of the signal and masker are most disparate and (2) eliminated when the signal and masker are matched temporally and spectrally. The relative timing and spectral shape cues combine independently and equally to enhance detection by as much as 10–12 dB relative to energy detection alone. The derivation of the new detection model will be explained and predictions from the new model will be compared with experimentally measured masked detection thresholds. The overall agreement between predicted and measured thresholds is excellent (r=0.95). [Research supported by NIH.]
Effects of amplitude modulation on gap detection in wideband noisebursts
Authors: Snell Karen B. , Janardan Ajit
Published: October 2005

Recent studies suggest that fluctuations in the envelopes of narrow-band signals influence the detection of temporal gaps. In this study, the effects of amplitude modulation on gap detection using wideband noisebursts were measured by varying depth of modulation and phase angle. Gap detection thresholds were obtained for four subjects with normal hearing. The digitized noisebursts were 6 kHz in bandwidth and 150 ms in duration. The level of each noiseburst was jittered (70–75 dB SPL) and modulated with a 20-Hz sinusoid. Gaps were placed 100 ms after stimulus onset. Gap detection thresholds were estimated at six modulation depths (0 to 100%) and at one random and three fixed phase angles. A continuous white noise (45 dB SPL) was mixed with the signals. Thresholds were obtained in an adaptive, 2IFC procedure using 100 trial runs. Twenty-four conditions were completed in random order in 2 h. Several replications were completed by subjects. Mean gap detection thresholds increased with depth of modulation and varied with phase angle. Mean gap detection thresholds were smallest (2.5–4.0 ms) for the noisebursts which were least modulated (0–40%). Mean thresholds were largest (20 ms or more) for the noisebursts modulated 100% at a random phase. These results are consistent with recent findings using narrowband signals [B. R. Glasberg and B. C. J. Moore, Hear. Res. 64, 81–92 (1992)].
Which ear has the asynchronous signal?
Authors: Pollack Irwin
Published: October 2005

Small differences in the frequency of pure tones are heard as changes in loudness, either when the tones are presented within the same ear (monaural beats) or when presented to the separate ears (binaural beats). With complex tones, comparable differences in fundamental frequency (asynchrony) are heard as changes in roughness or musicality. With two fundamental frequencies presented to each ear, a wide combination of monaural and binaural roughness changes are produced. Under conditions where monaural and binaural roughness changes are clearly detected, the identification of which one of the two ears is asynchronous (one ear asynchronous, the other ear synchronous) is at chance. Substantial interaural differences in intensity are required for the successful uncoupling of the asynchronous ear.
Dynamics of a dual-driver acoustic resonator and control system used in a thermoacoustic refrigerator
Authors: Gaitan D. Felipe , Garrett Steven L.
Published: October 2005

Until the development of the Thermoacoustic life sciences refrigerator (TALSR) [S. L. Garrett etal., J. Acoust. Soc. Am. 93, 2364 (1993)], all previous thermoacoustic refrigerators employed only a single electrodynamic driver. Due to the acoustic power requirements for TALSR, a dual-driver, half-wavelength engine was designed. This introduces additional complications for the resonance frequency control and tracking circuitry since each driver constitutes a driven simple harmonic oscillator and the two drivers, both of which have an associated microphone and accelerometer, are coupled by an acoustically resonant system. A computer model of the three strongly interacting resonant systems will be described along with a series of experimental measurements that explored a variety of operating conditions. [Work supported by NASA—Life Sciences Division and the Naval Postgraduate School Direct Funded Research Program.]
Experimental heat exchanger performance in a thermoacoustic prime mover
Authors: Castro Nelson C. , Hofler Thomas J. , Atchley Anthony A. , Gardner David L.
Published: October 2005

The effectiveness of heat transfer between the thermoacoustic stack and a typical copper fin heat exchanger is determined by the detailed gas motion and thermal diffusion, and the fin geometry. This effectiveness depends strongly on acoustic amplitude and heat load, as does the ability of the copper to conduct the heat. These and other nonlinear effects contribute to limiting the amplitude of a prime mover. A modular prime mover experiment has been built so that the limiting amplitude can be measured with a variety of heat exchanger geometries, with the goal of finding the best geometry. The liquid nitrogen temperature experiment uses a heavier gas, such as neon, at a low pressure in order to minimize the heat load, and the temperature defects associated with copper conduction, while allowing large Mach numbers and gas particle displacements. In preliminary measurements, peak pressure amplitudes are in access of 20% of the mean pressure and the peak-to-peak acoustic displacements are comparable to the stack length. Such large displacements take the study of prime movers into a poorly explored region. [Work supported by the Naval Research Laboratory and the Office of Naval Research.]
The role of importance sampling in the establishment of normal ranges for speech characteristics
Authors: Lemke Jon H. , Samawi Hani
Published: October 2005

Most measurements of voice characteristics have inherently skewed distributions that have never been characterized for individuals without speech disorders, that is, individuals with ‘‘normal’’ voices. Any diagnostic value these measures might have requires that one studies the characteristics of these ‘‘normal’’ voice distributions, in particular the quantiles necessary to establish the normal range. The focus will be on perturbations measures, such as jitter and shimmer. To solve this problem a method of importance sampling has been developed for estimating quantiles of skewed distributions. Importance sampling is a modified bootstrap procedure with exponential tilting, that is, a resampling method where the probabilities of the original observations appearing in the new samples are no longer equally weighted but are weighted by their closeness as an order statistic to the quantile being estimated. To estimate the normal limits of jitter and shimmer without resampling procedures will require at least 800 subjects. However, to estimate the normal limits with the same efficiency using this modified importance sampling technique will require approximately 80 subjects. The assessment of voice is very expensive and time consuming. There will never be 800 normal voice assessments conducted under identical conditions by anyone. How modified importance sampling can be used to establish normal limits for jitter and shimmer will be demonstrated with data collected at the Denver Center for the Performing Arts, Denver, Colorado, and the Wendell Johnson Speech and Hearing Center, University of Iowa, Iowa City, Iowa.
MRI measurements and acoustic investigation of the nasal and paranasal cavities
Authors: Dang Jianwu , Honda Kiyoshi , Suzuki Hisayoshi
Published: October 2005

Morphological measurements of the nasal and paranasal cavities were performed to speculate on the acoustic properties of the human nasal tract. The magnetic resonance imaging (MRI) technique was used to measure the three-dimensional structure of the vocal tract. The area function of the nasal tract was calculated from seven subjects at rest. The whole vocal tract was measured from five subjects during sustained pronunciation of nasal consonants. A marked morphological difference was observed between these data and the previous data particularly in the middle portion of the nasal tract. The previous data measured from cadaver specimens have a wide cavity in the middle portion possibly due to absent or dehydrated mucous membrane, while these data show narrow passages caused by thick mucosa. It was confirmed by an experiment that the above difference was reproducible by applying an adrenaline-like agent onto the nose. The acoustic transfer function was calculated from these data, and the speech sound, recorded soon after MRI scan, was used to evaluate the transfer function. The results indicate that the asymmetry of two nostrils can cause an extra pole-zero pair, and suggest that the paranasal cavities can play an important role in shaping spectral characteristics of human nasal cavities.
Scattering from under-ice features and estimation of ice roughness parameters
Authors: Kapoor Tarun K. , Schmidt Henrik
Published: October 2005

Previous results by Kapoor and Schmidt [J. Acoust. Soc. Am. 93, 2419 (A) (1993)] have shown the possibility of isolating scattering hot spots under the ice sheet by matched-field processing of short-range returns assuming point scatterers. A natural extension of this approach is to model the scattered field, or replica field, assuming a more realistic model of the scatterers. Here, examination of the low-frequency scattering data from the CEAREX 89 field experiments conducted in the Central Arctic region with 1.8-lb SUS charges detonated at nominal depths of 800 ft is continued. The beamformer outputs from the crossed horizontal array and vertical line arrays are combined simulating a volumetric array, which provides much better resolution of the under-ice features. The scatterers are modeled as hemispherical and half-cylindrical protuberances. Importance of elastic properties of the ice and the protuberances will be addressed. Ice roughness parameters are estimated using the method of small perturbations. [Work supported by ONR.]
Retroreflective backscattering of sound in water due to Lamb waves on plates with corners: Observations
Authors: Dodd S. S. , Loeffler C. M. , Marston P. L.
Published: October 2005

A leaky Lamb wave is known to be launched on a flat elastic surface plate in water when the surface normal lies near a cone whose symmetry axis gives the k vector of the incident sound. These water tank experiments with a 600-kHz sonar demonstrate that when the plate has a corner with edges meeting at angles of 90° and 45°, the wave vector of the Lamb wave is reversed due to repeated reflections at the edges that form the corner. The resulting leaky radiation gives a pronounced enhancement of the backscattering that depends only weakly on the orientation of the corner. Reductions in amplitude with deviations of the corner angle from 90° and with tilts of the surface normal were observed and they generally support the approximate analysis of P. L. Marston etal. (Abstract 4pSA2 at this meeting). For a suitably cut randomly oriented plate, the retroreflective enhancement is more likely to be observed than the specular reflection since then the normal must lie on a narrow range of angles.
High-resolution beam spectra of forward surface scattered signals in shallow water
Authors: Lee Yung P. , Spofford Charles W.
Published: October 2005

A shallow water experiment was conducted to examine the directionality and spectral spread of cw signals after multiple interactions with the sea surface. Bottomed sources with frequencies between 200 and 300 Hz and two bottomed arrays with apertures up to 250 m were employed allowing source–receiver distances of 6–15 km under a variety of sea conditions and angles of paths with respect to the seas. High-resolution adaptive beamforming techniques were used to suppress grating lobes and compensate for array distortions from linear. Directional beam spectra of the signals were observed illustrating dependences on wind speed and direction with respect to the signal path. The results are interpreted in terms of Bragg scatter from the surface wave.
Comparison of UMPE/PEREV bistatic reverberation predictions with observations in the ARSRP Natural Lab
Authors: Smith Kevin B. , Tappert Frederick D. , Hodgkiss William S.
Published: October 2005

During the summer of 1993 acoustic experiment sponsored by the ONR Acoustic Reverberation Special Research Program, bistatic bottom reverberation measurements were made within the ARSRP Natural Laboratory near the mid-Atlantic ridge. Employing a version of the University of Miami Parabolic Equation (UMPE) model [MPL Tech. Memo, 432 (1993)] incorporating Tappert’s PE Reverberation (PEREV) model, calculations of monostatic and bistatic reverberation within the Natural Laboratory have been made. The UMPE/PEREV model predicts a strong correlation between areas of high reverberation and high bottom ensonification. Furthermore, the wave scattering strength predicted by the PEREV model is shown to depend on the bottom roughness spectrum evaluated at the Bragg wave number 2k0 sin(φs/2) where φs is the azimuthal scattering angle. Due to the typical power-law form of the roughness spectrum, this suggests that the wave scattering strength is enhanced in the direction of forward scatter. These predictions will be compared to the observations and the validity of hypotheses will be addressed. [Work supported by ONR, Code 1125OA.]
Ultrasonic modeling of sea ice seismoacoustic wave phenomena
Authors: Chamuel Jacques R.
Published: October 2005

A variety of broadband Arctic seismoacoustic wave phenomena are demonstrated using laboratory ultrasonic modeling techniques introduced by the author in the mid 1970s to study the generation, propagation, detection, and scattering of low-frequency underwater acoustic waves coupled to the heterogeneous ice cover. Data on frequency-dependent under-ice reflectivity, effective elastic properties, low-frequency transmission loss, horizontal refraction, wave conversion, and low grazing angle backscattering are discussed. Different guided leaky and trapped waves from range-dependent models are isolated and examined including flexural waves, shear horizontal waves, Rayleigh waves, Scholte waves, edge plate waves, and wedge waves. The laboratory models consisted of finite floating plates with cracks, ridges, low-velocity layers, boreholes, trapped air pockets, solid wedges, and suspensions. The results provide physical insight into realistic 3-D problems and lead to the development of comprehensive understanding of near-field and long-range seismoacoustic phenomena essential for interpreting and inverting Arctic acoustic data, planning field experiments, and predicting ice failure modes from acoustic emission. The generic findings are applicable to ocean bottom interacting acoustic waves, nondestructive testing, and ultrasonic imaging. [Work supported by DREP and ONR.]
Feasibility of acoustic thermometry of Arctic Ocean climate change
Authors: Mikhalevsky Peter N.
Published: October 2005

Inverting observations of changes in long-range acoustic travel time, phase, amplitude, and modal dispersion has been proposed for the Arctic Ocean. Initial calculations [Mikhalevsky etal., ‘‘Arctic Ocean Warming; Can We Measure it Acoustically?,’’ The Oceanographic Society, Second Scientific Meeting, St. Petersburg, FL (March 1991)] showed that it could be possible to monitor ocean volume warming, and changes is sea ice extent and thickness. New results will be presented using higher fidelity acoustic modeling and the results of other international collaborators, including the Russians, will be summarized. Plans for a feasibility test in the Arctic are underway for a spring 1994 experiment.
Stationary phase evaluation of the bottom interacting field in isovelocity water
Authors: Ainslie Michael A.
Published: October 2005

The near surface sound pressure field in an isovelocity ocean is calculated analytically using ray theory and then normal mode theory for two different bottom types: first, a simple reflecting bottom with constant density and sound speed for which the two methods give identical solutions; then, a refracting bottom with constant sound-speed gradient. In the latter case the two solutions differ only (a) by a cumulative π/2 phase difference in the transition through each caustic, and (b) in the vicinity of the caustics themselves where the ray theory is inapplicable. The normal mode sum is evaluated by means of a Poisson sum, each term of which is then integrated using the stationary phase approximation, giving closed form expressions for the contribution from each ray path (or group of ray paths) that are identical to the ray approximation (apart from the phase) away from caustics, and provide a uniformly valid solution through the caustics. The resulting formulas are used to simplify the interpretation of complicated interference effects often predicted by numerical models. Specifically, comparisons are made with numerical predictions using the fast field method at 25 and 250 Hz, showing close agreement through caustics as well as in shadows for a 1000-m water depth.
Anomalous parabolic equation results for propagation in leaky surface ducts
Authors: Porter Michael B. , Jensen Finn B.
Published: October 2005

Surface ducts are formed by wind mixing at the sea surface and are a common feature in many of the world’s oceans. These surface ducts have the effect of channeling acoustic energy for long ranges. This paper, however, focuses on the energy that leaks out of the surface duct—paths that are typically neglected by ray models. It is found that the leakage energy at lower frequencies can be surprisingly strong so that a receiver in a ray-theory shadow zone is actually well insonified. Furthermore, the leakage energy is refracted back into the duct where it may dominate the ducted paths. Inside the duct, these two arrivals add up constructively or destructively resulting in anomalously high or low acoustic levels in the surface duct relative to a prediction that neglects the leaky arrival. Thus, a full-wave model is needed; however, certain types of parabolic equations (PEs) fail for these problems because they scramble the phases of the two dominant arrivals. The same mechanism that causes the PEs to fail makes the problem very sensitive to environmental data. For instance, a change in the mean duct speed of 0.5 m/s can also produce large changes in the acoustic levels.
A transition-matrix formulation of scattering in homogeneous, saturated, porous media
Authors: Kargl Steven G. , Lim Raymond
Published: October 2005

Scattering by an obstacle embedded within a homogeneous host is analyzed in the context of Biot’s theory. Both host and scatterer are assumed to be fluid-saturated poroelastic media. A transition matrix that accounts for the additional slow longitudinal wave is constructed from a Betti’s identity generalized to poroelastic media. Extinction, scattering, and absorption cross sections are defined for objects embedded in nonattenuating hosts. When attenuation is significant in the host (as is typical in saturated porous media), appropriately scaled, far-field scattering amplitudes are used to investigate scattering dynamics. General results are presented and specialized to spherical objects where the elements of the transition matrix may be obtained in closed form. Using effective medium estimates of Biot parameters where needed, numerical calculations of cross sections and scattering amplitudes are presented for incident plane-wave fields. Several limiting cases are discussed.
A T matrix for scattering from a doubly infinite fluid–solid interface with doubly periodic surface roughness
Authors: Bishop Garner C. , Smith Judy
Published: October 2005

The T-matrix formalism is used to calculate scattering of a plane wave from a doubly infinite fluid–solid interface with doubly periodic surface roughness. The Helmholtz–Kirchhoff integral equations are used to represent the scattered pressure field in the fluid and the displacement field in the solid. The boundary conditions are applied and a system of four coupled integral equations is obtained. The incident and scattered pressure fields in the fluid, as well as the surface pressure field, are represented by infinite series of scalar Floquet plane waves, while the scattered displacement field in the solid and the surface displacement field are represented by infinite series of rectangular vector basis functions constructed from Floquet plane waves. This process discretizes the integral equations and transforms them into a system of four coupled doubly infinite linear equations. The extended boundary condition is applied and the T matrix that relates the spectral amplitudes of the incident field to the spectral amplitudes of the scattered fields is constructed. An exact analytic solution and numerical results are obtained for plane wave scattering from doubly periodic sinusoidal and triangular surface roughness.