bluuebunny/crossref_metadata_2025 huggingface dataset:
Ultrasonic modeling of acoustic scattering from striated surfaces depicting the Arctic Ocean ice cover
Authors: McClanahan Ted , Diachok Orest
Published: October 2005

Sea ice may be described as plates (on the order of 100 m wide, 3 m thick) interspersed with randomly spaced, randomly oriented, and randomly distributed in depth (on the order of 5 m) ridges. To determine the dominant factors affecting reflectivity from this medium, experiments have been designed using ultrasonic methods and plastic models that simulate particular features of sea ice. Initial tests were conducted with “infinitely” thick samples striated with parallel, equally and randomly spaced half-cylinders and compared with a theory due to Twersky; this theory appears to account for first order effects of sea ice on propagation loss. Results of the preliminary ultrasonic measurements will be presented and inferences discussed. Follow-on experiments, which will consider effects of preferred and ramdom ridge orientation and plate thickness, are expected to provide a baseline and a stimulus for refined theories of under-ice reflectivity and scattering.
Enhanced near-grazing forward scatter from a low roughness rigid surface
Authors: D'Spain Gerald L. , Novarini Jorge C. , Medwin Herman
Published: October 2005

During low-frequency near-grazing incidence and forward scatter from a low-roughness rigid surface, the received sound field comprises both volume and boundary wave components. The former is, to first order, equal to the mirror reflected signal from the surface. The usually ignored boundary wave component, on the other hand, responding to its cylindrical divergence and its catastrophic attenuation at higher frequencies and ranges, reaches amplitudes several times larger than that of a spherically diverging direct wave reflecting from a smooth surface. The consequent kr window of this enhanced forward propagating field, which has greater than unity reflection cooefficient, has been explored by scale model experiments. [Research supported by ONR.]
Swimbladder-depth relationships of fish causing volume reverberation in the Cariaco Trench
Authors: Love Richard H. , Fisher Robert A. , Wilson Marcia A.
Published: October 2005

Oceanic volume reverberation in the frequency range of 1 to 20 kHz is caused primarily by scattering from swimbladders of small midwater fish. As these fish undergo daily vertical migrations, the scattering characteristics of their swimbladders change, due to changes in ambient pressure. Two simple swimbladder-depth relationships have been postulated. The first is that fish work to keep their swimbladders at constant volume in order to remain neutrally buoyant at all times. The second is that fish conserve energy by passively allowing their swimbladders to remain at constant mass, or PV = constant. In order to investigate swimbladder-depth relationships, we have collected acoustic and biological volume reverberation data in the Cariaco Trench, where only two species of midwater fish were found. Acoustic results were reported previously [J. Acoust. Soc. Am. Suppl. 1 73, S97 (1983)]. Measured scattering strengths were compared to values obtained by applying a swimbladder scattering model to fish caught in discrete-depth biological trawls. Results of this comparison show that swimbladder-depth relationships in the Cariaco Trench are more complex than the constant volume or constant mass postulates. [Work supported by NORDA.]
High-frequency surface forward-scattering measurements
Authors: Thorsos Eric I.
Published: October 2005

Results from low-grazing-angle surface forward-scattering measurements made in the open ocean at 15–40 kHz will be presented. The data were obtained with broad beam transducers using 1.0-and 0.3-ms pulses. The data have been analyzed to obtain energy losses and pulse elongations associated with the surface interaction at several wind speeds. The implications of the measured losses in terms of near-surface bubble populations will be discussed. [Work supported by NAVSEA.]
Sound waves in roonm lined with anisotropic bulk-reaction porous layers
Authors: Burke Shawn
Published: October 2005

The steady-state response of a rectangular room to a monopole point source is studied. The room is lined over some portion of its surface with an anisotropic bulk reacting porous absorber. The boundary condition describing the porous liner is an anisotropic analogue of Bliss' bulk reaction boundary condition [D. Bliss, J. Acoust. Soc. Am. 71, 533–545 (1982)], which is valid when the acoustic wavelength is larger than the material thickness. The solution for the pressure response is given as a sum of eigenmodes, with a damping term due to the absorptive walls. This damping factor includes a component expressed in terms of the transverse wavenumber in the porous layer, demonstrating that bulk reacting liners augment sound absorption. The effect of the anisotropy on the attenuation is also seen to be important at these low frequencies, since the low modal density does not permit describing the absorptive liner in terms of a random incidence sound absorption coefficient. Numerical calculations for a “typical” room will be presented.
Low-cost qualification of a small (170 m3) reverberation room dedicated to fan sound power measurements
Authors: Champoux Y.
Published: October 2005

The qualification of a reverberation room for measurement of sources of discrete frequency sound is not an easy task. Especially if the room is small (the room has to handle 25 000 CFM) and when in an industrial content, the budget is very limited. Many articles have been written on the advantages of using a rotating diffuser in a reverberation room. [J. Tichy and P. K. Bade, J. Acoust. Soc. Am. 56, 137–143 (1974); D. Lubman, J. Acoust. Soc. Am. 56, 523–533 (1974)]. However, the majority of the proposed diffuser designs does not offer the possibility of changing easily the panel's orientation and consequently the shape of the diffuser. An original low-cost design that was used to qualify the room will be presented and special attention will be devoted to the panel attachment device. The figure of merit of the diffuser will be reported and the influence of the panel's orientation on the variance will be discussed. Some instruments required in the qualification procedure [ANSI S1.32-1980 (ASA 12-1980)] are very specialized and their purchase is sometimes difficult to justify. To get round this problem, new approaches have been developed, expecially with respect to the sine wave signal generator. Furthermore, the important effects of the analyzer filter's shape on the loudspeaker's qualification will be discussed. During the qualification process variations in the measured variance between two close locations of loudspeaker have been noticed. Experimental data, sustaining this, tend to indicate that the qualification criteria may be too lax on this point.
Number theory in music, speech, and acoustics
Authors: Schroeder Manfred R.
Published: October 2005

Number theory has been considered since time immemorial to be the very paradigm of pure (some would say useless) mathematics. Yet the theory of integers can provide totally unexpected answers to real-world problems. In acoustics, these range from the distribution of normal modes in rooms (a problem the author encountered in his thesis) and the construction of new musical scales to the optimum diffusion of sound (to improve acoustic quality in concert halls or to boost noise abatement). Even the making of precision measurements in physical acoustics and the design of low peak-factor waveforms (for farther-reaching sonar and better-sounding speech synthesizers) can profit from number theoretic relationships. These as well as a few applications to other fields will be discussed.
Significance of electrode configuration in EMG studies of speech production
Authors: Cooper Donald S.
Published: October 2005

EMG studies of speech production have most commonly used either a configuration in which the electrodes were inserted with the interelectrode axis parallel to that of the muscle fibers, or the Basmajian and Stecko configuration [J. Appl. Physiol. 17, 849 (1962)] in which the electrodes are offset across the cross section of the muscle. In a differential recording configuration the first procedure results in analog differencing of a single longitudinally propagating signal at a time lag determined by the interelectrode distance and the mean propagation velocity of the action potentials. The second procedure results in differencing of two different signals. Assuming again that the electrode insertions are parallel, in the Basmajian and Stecko procedure the relation between the two signals differenced depends both on the longitudinal separation of the electrodes and on their separation in two dimensions across the muscle cross section. The resulting waveform and spectral characteristics of the signals from the two types of insertions necessarily differ. Detailed effects depend on the size of the motor units and distribution of their fibers, interelectrode distance, and patterns of motor unit recruitment.
Glottal Imaging by Processing External Signals (GLIMPES)
Authors: Titze Ingo R.
Published: October 2005

An analysis-by-synthesis procedure for estimating the glottal configuration from acoustic and glottographic signals is described. Combinations of airflow, electroglottograph, photoglottograph, accelerometer, and microphone signals are used as inputs. Amplitude and frequency are first extracted from each cycle. The waveforms in each cycle are then parametrized by least-squares fitting of model waveforms [I. R. Titze, J. Acoust. Soc. Am. 75, 570–580 (1984)] that are based on an abduction quotient, a shape quotient, and a phase quotient, in addition to vibrational amplitude and period. Comparison is made here between configurations obtained from single waveforms and multiple waveforms. [Work supported by NINCDS.]
Electroglottographic, aerodynamic, and acoustic study of normal and breathy phonation
Authors: Hasegawa Akira , Mahshie James , Herbert Eugene , Pickett James M.
Published: October 2005

A series of experiments were conducted to delineate relationships between voice fundamental frequency (f0), vocal duty cycle (closure/f0 period), amount of unmodulated air flow (air leakage), and acoustic intensity during normal and breathy phonation of the vowel /ɑ/. The f0 and duty cycle parameters were extracted from the electroglottographic signal; the air flow was measured with a Rothenberg-type pneumotachograph. In order to control the parameters they were displayed graphically during data collection from five normal adult speakers. The results revealed: (1) a positive relationship between vocal duty cycle and acoustic intensity, and between air leakage and acoustic intensity, (2) an inverse relationship between vocal duty cycle and air leakage, (3) a reduction of the maximum duty cycle in the periphery of the speaker's f0 range, (4) speaker-specific phonatory control. Findings support the notion that the vocal tract is more weakly and less efficiently excited during breathy than normal phonation. [Work supported by the National Institute of Handicapped Research and the Gallaudet Research Institute.]
Pitch and amplitude perturbation analysis using electroglottography during sustained phonation
Authors: Haji Tomoyuki , Horiguchi Satoshi , Baer Thomas , Gould Wilbur J.
Published: October 2005

Elcetroglottography (EGG), an electrical impedance technique for the direct examination of vocal-fold closure, does not interfere with phonation and is noninvasive. In order to evaluate the regularity of vocal-fold vibration in normal subjects and patients with various laryngeal disorders, pitch and amplitude perturbation of EGG waves during sustained phonation were measured through a laboratory computer. These data were compared to the degree of hoarseness evaluated perceptually and by sound spectrographic analysis. Subjects produced /a/ in natural speaking voice. EGG signals were recorded by means of a Fourcin laryngograph. Fifth consecutive cycles of EGG waves during steady phonation were used for analysis. Three experts in voice pathology rated the degree of hoarseness of each voice sample. The results showed close relation between perturbation analysis of EGG waves and degree of hoarseness evaluated perceptually and by sound spectrographic analysis. There was some overlap between normal and pathological groups. It was found that amplitude perturbation was a more sensitive measure of the irregularity of vocal-fold vibration than pitch perturbation. Usefulness and limitation of this method are discussed. [Work partly supported by NIH Grant NS-13870.]
Invariance of transitional movements under changes in lexical stress
Authors: Beckman M. E. , Fujimura O. , Spencer W. R.
Published: October 2005

Comparisons of articulator movements from one occurrence to another of a word or sentence often show that a CV or VC transition has an invariant movement pattern over some fixed positional range. An earlier experiment showed that token-to-token variation within this “iceberg” portion is very small even when differences in constituent phrase structure or placement of focal stress cause considerable variability at the positional extremum for the adjacent consonant constriction or vowel target [Fujimura and Spencer, J. Acoust. Soc. Am. Suppl. 1 74, S117 (1983)]. The present experiment extends the search for such invariant movement patterns to utterances contrasting in lexical stress. Using the same database obtained by the x-ray microbeam system at the University of Tokyo [Kiritani et al., J. Acoust. Soc. Am. 57, 1516–1520 (1975)] and a similar search procedure, we examined tongue blade and lower lip movements in tokens of minimal pairs such as insight versus incite. Invariant portions were found for virtually all relevant transitions other than those from syllables in which lack of stress might be said to involve substantial vowel reduction.
Effects of bite-block speech on intrinsic segment duration and fundamental frequency
Authors: Smith Bruce L.
Published: October 2005

Various intrinsic durational and fundamental frequency effects commonly occur in vowel and consonant productions. For example, low vowels tend to be longer in duration than high vowels, alveolar stops tend to have shorter closure durations than labials and velars, and high vowels generally have higher fundamental frequencies than low vowels. While the fundamental frequency effect for vowels has been studied quite extensively, less is known about the basis of the intrinsic vowel and consonant duration differences. In order to study these durational effects, six adults each produced 72 [hVC] stimuli, representing six repetitions of all possible combinations of the vowels [i, u, æ, a] and the consonants [p, t, k]. Each was produced (1) as a “normal” syllable, (2) with a bite-block held between the molars, and (3) with clenched teeth. It was hypothesized that if the duration differences which are often seen involve mechanical effects of the mandible, stabilizing the jaw with a bite-block or by clenching the teeth would affect these intrinsic duration differences. Although the fixed-jaw conditions did affect the subjects' speech, intrinsic durational and fundamental frequency differences tended to be preserved.
Respiratory volume expenditures in the speech of the hearing impaired
Authors: Whitehead Robert L.
Published: October 2005

The purpose of the present study was to investigate the volumes of air expended on initial vowels and intervocalic fricatives produced in VCV syllables by normal hearing females and two groups of hearing-impaired females, one with intelligible speech and the other with semi-intelligible speech. Air volume was calculated by means of an integration of the volume velocity obtained via a pneumotachograph during production of the VCVs. The results indicated that the normally hearing and intelligible hearing-impaired speakers demonstrated similar air volumes on the initial vowels and similar air volumes on the fricatives. The semi-intelligible hearing-impaired speakers, however, produced the initial vowels with significantly greater volumes and the fricatives with less volumes than the other two groups. In addition, the total air volumes expended on the vowel/consonant combinations were significantly greater for the semi-intelligible hearing-impaired speakers. The results are discussed in relation to previously reported data on the aerodynamic and respiratory characteristics of the speech of the hearing impaired. [Work supported by U.S. Department of Education.]
Models of intensity discrimination
Authors: Colburn H. Steven
Published: October 2005

Models of intensity discrimination are reviewed. The rationale and mathematical structure of types of models are discussed in relation to both psychophysical and physiological data. Particular attention is paid to models that incorporate ideas or data from peripheral physiological studies. Models are distinguished on the basis of the structure of the information on single channels and on the basis of the comparison rules for combining channels. In particular, the question of time structure versus rate structure of information on individual channels and optimum versus nonoptimum channel combination rules will be addressed. In addition to a review of available models for discrimination performance, attention is given to estimating the performance that could be achieved by optimum use of specific aspects of the auditory-nerve patterns (e.g., average-rate, time-synchrony, and spread-of-excitation information). In general, our analysis demonstrates the sensitivity of model predictions to details of the auditory-nerve data that are difficult to estimate from available data. Based on available data, average-rate information appears adequate to achieve observed performance, although it seems more likely that the various types of information are combined differently in different experimental circumstances. [Work supported by U.S. Public Health Service (NINCDS).]
Human exposure to vibration and its measurement
Authors: Rasmussen Gunnar
Published: October 2005

Human response to noise and vibration has attracted substantial attention with the growing industrialization of our society. Measurement of annoyance, fatigue, and hazard related to subjective response is important if we look for protective limits and improvements. The established regulations for noise exposure and noise measuring techniques are widely used and discussed. However, we can all hear and share the acoustic experience. Vibration is much more difficult to share with the exposed person and has maybe therefore received less attention from the regulators as well as the environmentalists. The agreement on obtaining homogeneous data through standardized instrumentation is especially important in this case. The important characteristics involve frequency weighting and time weighting. Important descriptors within whole-body vibration and handarm vibration are standardized. Especially, measurement of transient vibration will be discussed. Different proposals are under evaluation: use of crest factor (peak over final, quad vibration dose (fourth root mean of fourth power acceleration), impulse extended dose, and vibration response method. Finally, one may propose the use of intensity, measuring force times velocity times cos φ using the intensity as an objective descriptor.
Speech adaptation to prosthodontically created palatal asymmetries
Authors: Hamlet Sandra L.
Published: October 2005

Speakers frequently show left-right asymmetries in palatographic patterns for /s/ and /l/. A suggestion has been made that anatomical asymmetries of the alveolar area and palate may be responsible. Five subjects were recorded speaking with three configurations of palatography prosthesis—natural, 4 mm of thickness on the right side, and 4 mm of thickness on the left side. For each of the deliberately asymmetrical configurations, one week of practice was provided with a dummy appliance, so that data represent adapted speech. For /l/ subjects did not appear to alter the symmetry of articulation to compensate for these changes. That is, the tongue merely encountered the extra thickness more fully and sooner. For /s/ there apparently was compensation to the extent that the anterior location of the air channel remained the same. Timing of contact for the lateral seal was affected for /s/ by the altered palatal contours, however. [Work supported by NIDR.]
Clinical screening of laryngeal pathology by voice
Authors: Kasuya Hideki , Ebihara Satoshi , Yoshida Hajime
Published: October 2005

A system for the clinical screening of laryngeal pathology by voice has been developed on a computer. In designing the system special attention has been paid to an early detection of cancer of the vocal folds. The system employs multiple acoustic parameters which are derived from both vibration signals of the skin in front of the trachea and speech signals. The parameters are associated with (1) perturbations in pitch period and amplitude sequences, (2) noise energy included in the glottal sound source, and (3) spectral variations of the waveform from period to period. Since clinical screening experiments started in November 1982, the system has been tested so far with samples uttered by more than 1500 subjects, showing reasonable performance as compared with the results of perceptual evaluation that was carried out in parallel with the acoustic analysis by a specially trained laryngologist. [Work supported by Scientific Research Grant-In-Aid from the Ministry of Education, Science and Culture, Japan.]
Computer-aided speech onset analysis in stuttering therapy
Authors: Agnello Joseph G. , Weiler Ernest M. , Hornsby James
Published: October 2005

The previous hard-wired speech onset comparator (Agnello, 1976) has been replaced by a series of programming options using a TRS-80 and condenser microphone assembly. Options allow for six methods of acoustic analysis and feedback to focus on common stuttering characteristics. Choices of word list difficulty, rapid feedback, and individualized analysis have resulted in improved motivation while rehearsing and identifying onset control strategies in the first two groups of patients. Details will be presented.
Modulation thresholds for Meniere's and neuroma patients
Authors: Formby C.
Published: October 2005

Detection thresholds for sinusoidally amplitude modulated noise were measured across modulation frequency for listeners suffering (1) chronic Meniere's disease and (2) acoustic neuroma. The average Meniere's thresholds were similar to normal thresholds through 60 Hz, at higher modulation frequencies sensitivity declined at approximately twice the normal rate [(—)6 dB/oct vs (—)3 dB/oct]. The Meniere's data can be described well by the mathematical representation for a low-pass filter with a cutoff frequency of 60 Hz. The neuroma patients exhibited a general reduction in sensitivity to modulation and also a lower cutoff frequency, approximately half the normal value. Meniere's thresholds may be explained by poor frequency selectivity due to hydrops. The neuroma thresholds reflect: (1) hearing loss at higher audiometric frequencies, those frequencies most important for optimum modulation detection and (2) secondarily, the direct effect of the tumor, which disrupts low-frequency modulation detection. One may presumably account for these findings by: (1) broadening of the predetection filter (in Meniere's disease) and (2) lowering the cutoff frequency of the low-pass filter (in acoustic neuroma) in Viemeister's [J. Acoust. Soc. Am. 66, 1364–1380 (1979)] envelope detector scheme. Paradoxical SISI phenomena will be discussed in terms of these findings and Viemeister's model. [Work supported by NIH and ASHF/Psi Iota Xi.]
The perception of plosive consonants by hearing-impaired listeners
Authors: de Laat J. A. P. M. , Plomp R.
Published: October 2005

The reduced speech perception by hearing-impaired subjects has often been studied. In order to investigate the role of coarticulation we did some experiments on a group of 20 hearing-impaired and 10 normal-hearing subjects. From 45 embedded CVCVC words we deleted either the plosive bursts, or the vocalic CV or VC transitions, or the stationary vowel portions, or any combination of these four. The listeners were asked to identify the three plosive consonants in the resulting stimuli. The results for the normal-hearing subjects agree with results of Schouten and Pols [Proc. 10th ICPS, Utrecht (1983), p. 464]: identification is affected more by deletion of plosive bursts than of vocalic transitions, and in medial consonants the CV transition contains more information about the consonant than does the VC transition. For the hearing-impaired listeners the vocalic transitions play a more important role: identification with the plosive bursts only results in guessing; in contrast with the results for the normal-hearing subjects more errors occur for the final consonant than for the initial or the medial consonant. We also found some relations with other auditory functions measured. [Work supported by ZWO.]
Perception of spectral information by normal-hearing and hearing-impaired listeners
Authors: Dubno Judy R. , Dirks Donald D. , Schaefer Amy B.
Published: October 2005

Recent investigations have emphasized the importance of short-term onset spectra for consonant recognition. While examination of this acoustic cue, which emphasizes the multidimensional nature of the speech perception process, appears promising, the results have not yet led to a clear understanding of the speech recognition deficit encountered by hearing-impaired individuals. In a series of experiments, minimum syllable duration required for recognition of consonant-vowel syllables and the ability to categorize consonants by place of articulation was determined for normal-hearing and hearing-impaired listeners. Performance by normal-hearing listeners was excellent for stimuli > 20 ms, while results for hearing-impaired subjects varied widely, a finding which appears to be systematically related to differences in audibility of the speech signal. To measure syllable audibility, we examined the spectral information in the consonant-onset time period by measuring the onset spectrum (averaged over a 25.6-ms window) at the output of the test earphone. Acoustic spectra, rather than conventional electrical measurements, more accurately represent the spectral cues available in these short stimuli, and may provide insight into performance differences among hearing-impaired subjects. [Work supported by NINCDS.]
Infinite peak clipping as a means of amplitude compression
Authors: Zurek P. M. , Silletto K. A. , Hildebrant E. M.
Published: October 2005

Infinite peak clipping is a simple and effective technique for transmitting speech over an analog channel with limited dynamic range. However, the technique has yet to be applied seriously to the problem of limited auditory dynamic range accompanying sensorineural hearing loss. In this project we have begun assessing infinite clipping as a means of amplitude compression by determining: (1) the compression of the range of speech levels when clipping is followed by post-filtering (as is presumed to occur when clipped speech is analyzed by the ear); and (2) the spectral distortions due to clipping and how these can be minimized by prefiltering. We have found that the (10%–90%) widths of level distributions of clipped-and-filtered speech are about 10–15 dB and relatively independent of the characteristics of the post-filter. Detrimental distortions of speech spectra can be reduced by isolating the formant regions with filters before and after the clippers. Intelligibility results with preliminary clipping-based systems will be described. [Work supported by NIH.]
Some alternative methods for the measurement or determination of the human eardrum impedance
Authors: Kuhn George F.
Published: October 2005

The uncertainties in the measurement of the eardrum impedance at low frequencies due to the microphone placement and/or due to the transfer function of the source can be avoided through the use of a velocity-controlled source, combined with a single pressure measurement at the source. Due to the reciprocal spreading between the source size and the number of higher order acoustic wave components, the source should be of as large a diameter as possible. At high frequencies, the eardrum impedance can be determined via pressure measurements with a half-wavelength long microphone, of arbitrary cross-sectional area, which distorts neither the measured (plane wave) pressure nor the eardrum pressure. Schemes for the absolute calibration for such a measuring system will be described also.
System for automatically tracking changes in interfacial tension
Authors: Hsu Chaur-Jian , Apfel Robert E.
Published: October 2005

A technique is presented for automatically monitoring changes of the interfacial tension between two liquids when a surfactant is added to one of them. A drop of one liquid is acoustically levitated in the other liquid and also is acoustically driven into quadrupole shape oscillations. The frequencies associated with several phase angles (between the drop's oscillation and the drying force) near the quadrupole resonance are measured, allowing the interfacial tension to be calculated given the drop's diameter and the densities of the two liquids. A feedback scheme is used to control the driving frequency, such that the phase is locked at a selected angle as the surface-active molecules pack into the interface and the resonance frequency changes. Therefore, the history of the interfacial tension after the drop is injected can be obtained. Some data for the interfaces between water-surfactant solutions and some common hydrocarbon liquids will be presented. The final equilibrium interfacial tensions will be compared with existing data from the literature. [Work supported by ONR.]
Sound radiation from the evaporating droplet and the growing and collapsing bubble formed from the fully evaporated droplet
Authors: Kwak Ho-Young
Published: October 2005

It is well known that one may heat a liquid held at 1 atm to a temperature far above its boiling point without the occurrence of boiling. The maximum temperature limit at which the liquid boils explosively is called the superheat limit of the liquid. Usually this limit is determined by heating the test droplet in a host liquid—droplet explosion technique [M. Blander and J. L. Katz, AICh. E J. 21, 833 (1975)]. Sound radiation from the rapidly evaporating butane droplet at this limit and the growing and collapsing bubble formed from the fully evaporated droplet in a host liquid (ethylene glycol) is studied quantitatively. The experimental observation [J. E. Shepherd and B. Sturtevant, J. Fluid Mech. 121, 379 (1982)] of the time dependence of the farfield pressure signal from the compact point source—the evaporating droplet and the growing and collapsing bubble—is consistent with calculated values.
Thermal behavior of bubbles in large-amplitude motion
Authors: Prosperetti A. , Crum L. A.
Published: October 2005

A simple model incorporating thermal effects in large-amplitude radial bubble motion is formulated and compared with available linear theories. Its application to the acoustic levitation of bubbles is discussed and compared with experimental data. [Work supported by ONR and NSF.]
Cavitation from short acoustic pulses
Authors: Fowlkes J. B. , Crum L. A.
Published: October 2005

We wish to present some preliminary results of a study of the generation of cavitation by short pulses of 1-MHz ultrasound. In order to avoid the problems associated with acoustic detection, we have developed a photometric cavitation detection mechanism that utilizes a photomultiplier and chemical additives that enhance the light output due to sonoluminescence and chemiluminescence. Light outputs that suggest the presence of cavitation have been observed for pulse lengths as short as 10 μs at moderate acoustic intensities (actual values are awaiting the arrival of a calibrated probe). A description of the apparatus as well as a report on our latest results will be given. [Work supported in part by the National Science Foundation and the Food and Drug Administration.]
Ultrasonic wave propagation in temperature gradients
Authors: Johnson John A. , Lott Layman A.
Published: October 2005

Ultrasonic methods are being developed for sensing and control of high temperature material processes such as welding and solidification. One of the problems in these methods is distortion of the sound field caused by the change in material properties due to temperature gradients. This paper describes two methods for calculating the effects of temperature on ultrasonic propagation in such systems. The first is a ray-tracing method in which the material is conceptually divided into a number of plane layers. The refraction at each layer boundary is calculated from Snell's law using the sound speeds determined from the temperatures of the adjacent layers. The time required for an ultrasonic pulse to traverse each layer is also calculated, allowing the determination of the total time through a particular part. The method has been successfully applied to calculating the time of arrival of echoes from various interfaces around a molten weld pool. The second method numerically solves the partial differential equations which describe sound propagation. A previously described computer program [J. A. Johnson, J. Nondest. Eval. 3, 27–37 (1982)] has been modified to account for temperature gradients and used to calculate the sound field as it propagates to a molten weld pool. [Work supported by the U.S. Department of Energy under DOE Contract No. DE-AC07-76ID01570.]
Scattering of an acoustic Gaussian beam from a fluid-solid interface
Authors: Pott John , Harris John G.
Published: October 2005

The reflection and refraction of a three-dimensional acoustic beam, whose amplitude is Gaussian in cross section, at a fluid-solid interface is studied. The acoustic Gaussian beam is constructed by assigning complex values to the source coordinates of an acoustic monopole, a technique used in optics to model coherent light beams. The incident beam is specularly reflected except at certain critical angles of incidence of which the Rayleigh angle is the most important. Near this angle the incident beam excites both a leaky Rayleigh wave and a reflected beam, and the interference between these two disturbances produces a shifted and distorted reflected wavefield. The incident beam, near normal incidence, is refracted into a compressional beam and a shear beam, both of whose amplitudes are Gaussian in cross section. Whereas the incident beam has a circularly shaped cross section, both transmitted beams have elliptically shaped cross sections. [Work supported by NSF.]
Attenuation measurements of fast and slow waves in alternating solid fluid layered systems
Authors: Plona T. J. , Winkler K. W.
Published: October 2005

The problem of wave propagation in a periodically stratified medium consisting of alternating solid and ideal fluid layers has been solved and the calculations indicate two distinct slowness surfaces which give two plane-wave speeds for all directions of propagation except normal to the layering. Previous comparisons of theory and experiments focused on the phase velocities of these two plane-wave modes (i.e., the fast wave and the slow wave) in water/Plexiglas or water/metal layered systems. In this paper we address the measured attenuation of these two modes. Specifically, we have made broadband ultrasonic propagation experiments centered at 500 kHz on models composed of Plexiglas plates (or brass plates) immersed in water where the volume concentration (porosity) of water was 0.11, 0.20, 0.33, and 0.5. In these models the water layer was held constant at 0.79 mm and the solid layer thickness varied. The one wave normal to the layering and the two waves that can propagate parallel to the layering are observed and their phase speeds agree with the exact theory. The frequency dependence of the measured attenuation of both waves agree with the results of Biot's theory of long wavelength propagation in a fluid filled porous elastic medium.
Low-frequency vibrational modes of fluid-loaded thin spherical shells. II.L.H
Authors: Green Roger , Hackman H. , Trivett D. H. , Flax L.
Published: October 2005

Previously, we presented [L. H. Green et al., J. Acoust. Soc. Am. Suppl. 1 75, S77 (1984)] an analysis of the low-frequency high-Q resonances of thin spherical shells. The previous investigation centered on providing a physical explanation for the strong coupling of the lowest frequency resonances to the fluid medium. We extend the analysis to more completely explore the effects of fluid loading on the high-Q resonances. In particular, as the phase velocity of the low speed (first mode) wave on a thin spherical shell approaches the speed of sound in the fluid, the dispersion curve for the elastic wave appears to merge with that of the “creeping wave.” A physical explanation of this effect will be provided along with numerical results based on the linear theory of elasticity.
Sound transmission into arbitrarily loaded, resonating shells
Authors: Gaunaurd G. , Barlow J.
Published: October 2005

We develop the exact analytical model required to computationally study the transmission of incident acoustic energy into submerged elastic cylindrical shells subjected to arbitrary loads on their outer surface. This basic model uses the exact formulation of linear elastodynamics to describe the shell motions, and that of general linear acoustics to describe the wave motion in the inner and outer fluids. Hence, for this linear problem the superposition principle permits the separation of the contribution to the internally transmitted field caused by the incident wave, from those caused by the surface load. We compute and display isobaric contours of the internally transmitted pressure field exhibiting its caustics and their progressive development as the frequency is increased within the bad 0 ⩽ k3 ⩽ 10. The contour plots are generated for all possible combinations of loading and insonification conditions, and in all cases we compute an advantage ratio PR. This ratio measures the gain that would result from sensing the internally transmitted field, rather than the field external to the shell. In all cases PR > 1 and in many instances (to be discussed) PR > 1. For moderate surface loads, the shell acts as a very effective sound concentrator, particularly near the resonances of its monopole mode. The study clearly demonstrates the shell's filtering behavior in the frequency domain, and its focusing action in space. [Work supported by ONR.]
The inadequacy of thin cylindrical shell theories based on Kirchhoff's assumptions
Authors: Trivett D. H.
Published: October 2005

In a previous paper [D. H. Trivett, J. Acoust. Soc. Am. Suppl. 1 75, S77 (1984)] the existence of a low-frequency, low phase velocity axisymmetric mode in a thin cylindrical shell was demonstrated. This mode is not obtained as a solution to the equations of present thin shell theories, a result which can be traced to the invalidity of the assumptions of Kirchhoff's theory of plates when applied to a cylindrical shell (the application of Kirchhoff's assumptions to cylindrical shells is due to Love and most subsequent researchers, not Kirchhoff. In this paper the thin shell assumptions are discussed and numerical solutions to the exact linear elastic equations are presented demonstrating their invalidity at low frequency.
Ray-mode equivalent and hybrid formulation for source-excited vibrational motion in an elastic plate
Authors: Lu I. T. , Felsen L. B.
Published: October 2005

Impact excited vibrations in a multiwave layer can be represented in terms of ray fields or of normal mode fields. At early observation times, multiply reflected ray fields can be distinguished by their different arrivals where at later times, their collective effect is best expressed by the normal modes. Instead of utilizing rays or modes separately, as has been customary, a recently developed hybrid theory for multiwave layered media permits both to be combined self-consistently, and in convenient proportions [I. T. Lu, L. B. Felsen, and A. Kamel, Wave Motion (to appear)]. The hybrid formulation is based on a ray-mode equivalent whereby a given slowness spectral interval can be filled either with rays or with modes subject to a spectral remainder. Moreover, the ray proliferation due to wave coupling at each encounter with a boundary avoided by introduction of “eigenrays,” which are composed of self-similar combinations of the various wave fields. The general theory is here applied to the dilational and shear waves in an elastic plate. High-frequency motion at given range is calculated in terms of ray fields, normal mode fields, eigenrays, and hybrid combinations, using exact generating spectral integrals and also simplified asymptotic approximations. The numerical results confirm the validity of the ray-mode equivalent and establish conditions where the hybrid scheme offers an attractive option. [Work supported by NSF and ONR.]
High-frequency vibration generation by a moment drive
Authors: Brown Richard N.
Published: October 2005

A scheme for generating vibration by using two closely spaced piezoelectric transducers to create a moment rather than a force drive is described. The advantage of the moment drive is the reduced acoustic emission from the nearfield vibration of the drive. This can be important in situations where the radiation from other regions of a structure [for example frames, stringers, etc.) is being studied. The two transducers are spaced at less than a structural 1/2 wavelength. The amplitude and phase of the electrical driving signals are adjusted to produce out-of-phase accelerations at each transducer's drive point. Measurements on a flat plate in a reverberant test room verified theoretical estimates of the lesser radiated sound power. Over a frequency range of 0.2 to 2 kHz, the moment drive produced 15-0 dB less sound power than a force drive, for the same average level of vibration on the plate. A benefit is that the most reduction occurs at the lowest frequency where other means of suppression are less effective. [Work supported by ONR.]
Lamb waves in laminated composite plates
Authors: Chimenti D. E. , Nayfeh Adnan H.
Published: October 2005

Measurements of ultrasonic reflectance from laminated composite plates of glass-epoxy immersed in a fluid have been carried out in order to study the behavior of Lamb waves in these materials. Initial experiments have been performed on unidirectional composites of varying plate thickness with the projection of the incident acoustic wave vector oriented parallel to the fiber direction. By varying the incident ultrasound frequency, we observe the existence of several Lamb wave modes at incident angles from 10 to 45 degrees. These data have been compared to the results of a model calculation using a mixture theory to derive the elastic properties of the plate and an approximate analytical method to calculate the modes of a fluid-loaded, anisotropic plate. In many cases the agreement is quite good, but under some conditions we are not able to observe all the modes predicted by our model. We also present measurements of the reflected beam profiles showing the presence of leaky Lamb waves.
Power flow measurements in beams with small localized damping
Authors: Carroll G. P. , Clark J. A.
Published: October 2005

In an effort to establish the limitations of structural vibration intensity measurements for determining power flow in reverberant fields, classical power flow measurements were made on a free-field beam with point force excitation at one end and small local damping at the other. These classical methods were based on standing wave ratio measurements, measurements using force gauge/accelerometer combinations, and reverberation decay measurements. An investigation into the factors influencing the accuracy of these measurements was conducted. The force gauge/accelerometer measurements were found to be extremely sensitive to sensor phase inaccuracies if large reactive power components were present. These problems were avoided by conducting the experiment at frequencies where this reactive component was negligible (resonance) and by choosing damping materials which were mostly dissipative at these frequencies. Having established error bounds for these classical measurements it was possible to experimentally study the accuracy of intensity measurements by measuring known power flow in the presence of known reverberation. The results of this experiment will be discussed along with theoretical predictions of errors associated with intensity measurements in reverberant fields. [Research supported by David Taylor Naval Ship Research and Development Center, Washington, DC.]
Transfer function determination in structures and enclosures using adaptive linear prediction techniques
Authors: Swanson David , Tichy Jiri
Published: October 2005

Given a structure or enclosure with a finite number of bandlimited sources radiating energy into it, the transfer functions between any two points are found using adaptive pole-zero digital filters with a leasts-squared-error criterion when the signals at the points in the structure or enclosure are known. The number of poles and zeros in the adaptive filter is chosen higher than the assumed number of resonances and antiresonances between the points of interest to insure that all the dominant features of the transfer function are matched by the adaptive filters. The mathematical basis for deriving the filter parameters directly from the observed input/output time series can be found from using a lattice method solution to the multichannel Yule-Walker equations [B. Friedlander, Proc. IEEE 70 (8), 841–852 (1982)]. The computed poles and zeros of the adaptive filter provide more information than traditional Fourier cross spectra or statistical energy analysis methods.
The need for supercomputers in ocean acoustics
Authors: Dozier Lewis B.
Published: October 2005

Recent work by the author has included two computation-intensive models that suffer severe practical limitations if forced to run on commonly available computers such as a DEC VAX 11/780. Results of one of the models PERUSE were recently published [J. Acoust. Soc. Am. 75, 1415 (1984)]. The second model is a state-of-the-art coupled mode model described by C. A. Boyles [J. Acoust. Soc. Am. 73, 800 (1983)] and implemented numerically by the author [J. Acoust. Soc. Am. Suppl. 1 73, S96 (1983)]. Results of both models will be presented and discussed in light of how computation time relates to the complexity of the particular problem being solved. Citing also earlier work by the author and F. D. Tappert [J. Acoust. Soc. Am. 63, 353 and 533 (1978)] involving expensive Monte Carlo calculations required to verify a theory of stochastic wave propagation, a forceful argument will be made that solutions to some of the most pressing problems on the frontier of ocean acoustics today require the use of supercomputers or dedicated array processors.