bluuebunny/crossref_metadata_2025 huggingface dataset:
The significance of spectral synchrony in broadband signal detection
Authors: Houtgast T.
Published: October 2005

The masked threshold of a brief and broadband signal was determined for various patterns of temporal delays among the individual 1/3-octave-band contributions. The signal consisted of the sum of nine individual Gaussian-shaped tone pulses, such that (1) the effective bandwidth of each tone pulse was 1/3 octave, (2) the center frequencies were located at 1/3-octave intervals (from 500 up to 3170 Hz), and (3) the intensity ratios were such that all nine individual tone pulses had the same masked threshold (in pink noise) when presented individually. The masked threshold of the total stimulus was determined as a function of the temporal interrelation among the nine tone pulses. For the condition of perfect spectral synchrony (i.e., temporal coincidence of the peaks of the nine Gaussian-shaped envelopes), detection threshold was found to be about 6 dB better than in the case of a desynchronized stimulus for which the nine individual tone pulses were distributed randomly within a 100-ms interval (which is well within the traditional integration window for signal detection.) This phenomenon of synchrony-facilitated broadband detection has interesting implications, both for signal-detection theory and from a functional point of view.
Effect of peripheral and central auditory lesions on auditory pattern perception
Authors: Musick Frank E. , Pinheiro Marilyn
Published: October 2005

Auditory patterns composed of three successive tone bursts of either 880(Low) or 1122(High) Hz were arranged to yield six types of patterns (i.e., LLH, LHL, HLL, HHL, HLH, LHH). The tones in the patterns had a 150-ms duration, 10-ms rise-fall and 200 ms interstimulus interval. A normal performance criteria for these monaurally presented patterns was established on 31 normal subjects. Pattern data were then collected on groups of subjects with documented lesions of the cochlea, brain stem, or auditory areas of the cerebrum. Results indicated that almost 90% of subjects with cochlear lesions (N = 29) performed within the normal criteria, while over 80% of the 29 subjects with cerebral lesions yielded abnormal results. Approximately one half of the 22 subjects with brain stem involvement demonstrated normal performance on the pattern task. An additional analysis revealed that a high percentage of subjects with lesions limited to one hemisphere demonstrated bilateral ear deficits for pattern identification.
Behavioral and physiological measures of temporary threshold shift
Authors: Gans Donald P.
Published: October 2005

Physiological studies of temporary threshold shift (TTS) have produced conflicting evidence regarding the contribution of peripheral and neural components to the hearing loss. Under appropriate recording and analysis techniques, it was found that the cochlear microphonic and summating potential exhibit similar amounts of TTS as the whole nerve action potential (AP). An important assumption is that the AP is an accurate measure of hearing loss. Two independent studies have produced evidence that central auditory pathways are strongly affected during TTS which would invalidate the AP as an accurate measure. To examine this possibility, behavioral thresholds were determined in 14 gerbils prior to and following exposure to an 8000-Hz pure tone. Each gerbil was subsequently anesthetized, the middle ear surgically exposed, and an electrode inserted in the cochlea. AP post-exposure thresholds were compared to normative data for calculation of AP TTS. It was found that behavioral and AP TTS were not statistically different at any of the four test frequencies. These data are consistent with traditional theories of a cochlear origin for TTS. [Work supported by NSF.]
Measurements of in vitro outer hair cell motility in the mammalian cochlea
Authors: Evans B. Niles , Warner R. , Yonovitz A.
Published: October 2005

The sensory receptors of albino guinea pigs were dissociated and maintained in high sodium culture media. Outer hair cells were examined in response to current stimulation and cholinomimetic compounds. Two types (I and II) of movement have been detected. Small type I responses were seen when stimulated by electrodes placed in the medium along the long axis of the cell similar to those observed by Brownell (SEM/III, 1984). Large type I responses at higher current densities were seen by the suction electrode technique. These motile events appear to be graded in response and restricted to the supranuclear region. A video camera and phototransister were utilized with an inverted microscope. A signal averaging system allowed the recording of the displacement function of the cell. Frequency responses of the cells were derived and the input-output function modeling the movement was determined. Type II acetylcholine or carbachol-induced movements were seen in a proportion of the cells examined. These movements were slow sustained contractions which appear to be reversible when the compound is washed out of the medium. We found the outer hair cell to be exquisitely sensitive to osmotic fluctuation. Further evidence confirming efferent stimulation is presently being sought.
Levitation using intense acoustic fields at high temperatures
Authors: Whymark Roy R. , Rey Charles A. , Danley Thomas J. , Hammarlund Gregory , Merkley Dennis R.
Published: October 2005

Intense acoustic fields can be used to position objects without mechanical contact. This phenomenon finds application in high-temperature materials research by enabling a specimen to be heated, melted, reacted, cooled, and solidified in a containerless state. The acoustic force vectors capable of levitating an object are given by the gradient of the acoustic potential energy density. By suitable shaping of the acoustic field, a closed energy well can be created and a small specimen captured therein. Some recent experiments were carried out in microgravity aboard the Space Shuttle in order to reduce the requirements for intense acoustic fields, typically from 145 to 165 dB, at 15 kHz. Preliminary results are presented showing successful containerless processing of glass specimens of density 5 g/cm3 at 1550 °C. Ground-based experiments have levitated densities of 20 g/cm3 at STP and densities up to 4 g/cm3 at 1000 °C. Various results from these experiments will be presented along with a discussion of the effects of acoustic cooling, thermal perturbations of the acoustic field, and the presence of harmonics. [Work supported by NASA.]
Application of acoustic levitation to the investigation of melting and freezing phenomena
Authors: Trinh Eugene H.
Published: October 2005

Ultrasonic levitators have been used in ground-based laboratories to observe melting and freezing phenomena characteristic of organic materials and metals. The behavior of freely suspended substances undergoing a first-order phase transition and the influence of a high-intensity acoustic field have been of primary interest. The undercooling ability of the materials and the acoustic field-melt interaction are related subjects, and some experimental observations have been obtained in order to elucidate this relationship. The size of the levitated samples is on the order of 1 mm and the temperature range studied is between − 25° and 400 °C. [Work supported by NASA.]
Discrete-element acoustic analysis of submerged structures using doubly asymptotic approximations
Authors: DeRuntz John A.
Published: October 2005

Doubly asymptotic approximations have been found to offer significant advantages for the treatment of steady-state fluid-structure interaction in vibration, acoustic-radiation, and acoustic-scattering problems for complex submerged structures. This paper describes the theoretical foundations, development, and verification of two boundary-element/finite-element processors that implement this approach. The first processor is SWEEPS, which determines the structural response of and surface pressure on a vibrating submerged body using an iterative, incremental frequency technique for computational efficiency. The second is TARGET, which embodies a discretized form of the Helmholtz integral equation to obtain fluid pressures away from the body. To test these processors, two problems involving a spherical shell in an infinite fluid have been solved. The first problem is one of modal internal forcing; while the second is concerned with forcing by incident plane waves. The computational results exhibit excellent agreement with closed form solutions.
Application of finite element methods for scattering and vibration problems
Authors: Vataden Vasundara V.
Published: October 2005

The scattering of waves by an inclusion of arbitrary shape is a problem of interest in several fields of engineering. Several of the analytical/numerical techniques that have been developed in recent years, although easy to implement and of wide applicability, are not satisfactory for truly arbitrary geometries, materials that are inhomogeneous and/or anisotropic and when nearby boundaries are involved. For such problems, we have found it convenient to develop a hybrid method using the finite element approximation in a bounded region enclosing the inclusion and the fields in the infinite exterior domain are expanded in wavefunctions that satisfy radiation conditions. Fields and appropriate derivatives are matched at physical and mathematical boundaries leading to a solution of the fields in the entire region. A slightly different approach has been developed for thin elastic shells of arbitrary shape immersed in water. For this problem the modal impedance of the shell is found using shell theory and a finite element technique. The impedance is then used in the integral representations for the exterior problem and solved by the usual T-matrix approach. Some of the examples that will be discussed are (1) scattering of elastic waves by voids and solid inclusions embedded in a solid, (2) scattering of elastic waves by a transversely isotropic piezoelectric inclusion, (3) scattering of acoustic waves by thin elastic shells, laminated composite shells, and stiffened shells in water, and (4) natural vibration frequencies and mode shapes of objects of arbitrary shape.
Response of axisymmetric shells in an acoustic medium
Authors: Bronowicki A. J. , Nelson R. B.
Published: October 2005

The frequency domain response of arbitrary closed shells of revolution immersed in an infinite acoustic medium is considered. A reduction in dimensionality of the problem is achieved through a decomposition of motion into circumferential harmonics. The acoustic relation is thus represented as an integral equation defined along the shell meridian. This relation, derived on the basis of a Green's function technique featuring toroidal wavefunctions, is applicable to surfaces having arbitrary meridianal shape, including corners. In order to assure uniqueness of solution, interior equations are appended to the set of surface integral equations. The concept of an acoustic element is introduced with meridianal pressure variation determined by the response at a number of surface pressure nodes. The structure is represented in terms of an assemblage of conical frustum shell elements having either two or three nodal rings. The fluid-structure interaction relation is consistently developed on the basis of modal degrees of freedom. The final product is an accurate, efficient scheme to predict structural response, and surface and exterior pressure fields. Examples considered include: spherical and toroidal substitute problems, a truncated cylinder having specified radial motion, and response of a spherical elastic shell excited by a harmonic point load.
An approximation finite element surface impedance representation for energy absorbing layers
Authors: Kalinowski Anthony J.
Published: October 2005

A procedure for determining the scattered pressure field due to a monochromatic harmonic wave that is normally incident upon an energy absorbing submerged structure is treated. The case where the structure is modeled with finite elements and the surrounding fluid is represented with either acoustic finite elements or a boundary integral approach is considered. Finite element modeling problems arise when the details of the submerged structure in the neighborhood of the fluid-structure interface are not macroscopically homogeneous and in particular when the inhomogeneities are small relative to the acoustic wavelength. An approximate procedure is presented for replacing the detailed microscopic representation of the layered surface configuration with an equivalent simple surface impedance finite element which is specially designed to work at the frequencies of interest.
Fractal finite element mesh generation for vibration problems
Authors: Jeng J.-H. , Varadan V. V. , Varadan V. K.
Published: October 2005

A new approach for solving plate vibration problems has been formulated by using the elastic Sierpinski gaskets and finite element methods. The Sierpinski gaskets are geometric fractals which are self-similar under scale transformation. Modeling a finite plate element with the basic Sierpinski gasket unit, the equations of motion of the basic unit are derived. A build up process is formed by linking three identical units together. Finally, systematic recurrence relations are generated. The advantage of this approach is that the dynamic matrix of the system has the same dimension at each build up step. The basic vibration properties, computation time, and memory requirements are discussed and critically compared with traditional finite element methods by discussing a specific example. In general, finite element mesh generation based on geometric fractals offers much promise in reducing storage requirements and computation times significantly.
Infants' discrimination of cooperating and conflicting voicing cues
Authors: Eilers Rebecca E. , Moroff Debra , Oiler D. Kimbrough , Urbano Richard
Published: October 2005

The perceptual interaction of voicing cues that differentiate between final position /d/ and /t/ was investigated in 6–8-month-old infants. Fifty-two infants were divided into four groups; half received three contrastive pairs of two-syllable stimuli [ma + syllable] and the other half received analogous three-syllable stimuli [masa + syllable]. Infants' discrimination was tested using the visually reinforced infant speech discrimination paradigm. Half the infants in each syllable condition received cooperating cues for final voicing; the other half received conflicting cues. The cooperating stimuli were (1) [masamad]-[masamat] (voicing only), (2) [masamad]-[masama:d] (vowel duration only), and (3) [masama:d]-[masamat] (voicing + vowel duration). The competing group received (1) [masamad]-[masamat], (2) [masamat-masama:t], and (3) [masamad]-[masama:t]. Analysis of variance yielded a significant stimulus-pair effect but did not yield a significant syllable effect or a cue-group by stimulus-pair interaction. However, post hoc analysis indicated that vowel duration was a more potent cue than voicing and multiple cues were significantly better discriminated than single cues (pairs 1 and 2). No decrement in performance resulted from competing cues. Implications for development are discussed.
Infant speech-discrimination testing: Effect of stimulus intensity and methodological model on estimates of performance
Authors: Nozza Robert J.
Published: October 2005

Infant speech-sound discrimination data have typically been obtained at only a single stimulus intensity level, with no consideration given to the bias in outcome that can result when full performance—intensity (P-I) functions are not determined. Another potential for bias lies in the assumption made about the underlying methodological model. Data from infant head-turn discrimination studies are treated as if from a single-interval psychophysical procedure, but the infant is operating with high temporal uncertainty. The task is better described as vigilance. This investigation was done to measure performance versus intensity (50 to 70 dB SPL) in a phoneme discrimination task (/ba/versus/da/) by infants and to determine if the choice of underlying methodological model influences results. Results indicate that performance varies with intensity and suggest caution in interpreting results obtained at a single stimulus intensity level. The P-I functions have similar form under both models, but the finding of a response decrement, typical of vigilance rather than fixed-interval tasks, supports the appropriateness of the vigilance model. Analysis of response density over time, as suggested by Watson and Nichols [J. Acoust. Soc. Am. 59, 655–668 (1976)] for vigilance-type data, provides limited support for the use of the single-interval model with the VRISD (undefined trials) procedure. [Supported by Pennsylvania Lions Hearing Research Foundation.]
Acquisition of pitch contours by infants
Authors: Stark Rachel E. , Bond Jennifer L. , Heinz John M.
Published: October 2005

It has been suggested that infants may acquire control of pitch contour in their vocal productions according to an invariant schedule. The present study was designed to examine pitch contours in the vocalizations of infants in the first eighteen months of life. Eight to ten infants were recorded on a limited longitudinal basis, i.e., across each of the following are ranges: 2–10, 12–23, 26–36, 40–55, and 72–88 weeks (45 infants in all). Forty to fifty vocalizations were selected randomly from each infant's output at the first and the last of these recordings. These vocalizations were analyzed acoustically by means of computer-assisted spectral analyses and pitch extraction program. Pitch contours were categorized according to the range in which they occurred, as well as their falling/rising characteristics. Developmental differences were documented with respect to pitch contour types across age levels. However, significant differences among infants within age levels were also found. The results suggest that, while there may be an invariant developmental schedule for pitch contour production, this schedule is not highly correlated with chronologic age. [Work supplied by Bureau of Community Health Services, Maternal and Child Health.]
Vowel intrinsic pitch in 1-year-olds?
Authors: Bauer Harold R.
Published: October 2005

Intrinsic pitch is distinctive of human vowels in older children and adults. Because of the ontogenetic reconfiguration of the human vocal tract, the relationship between tongue height and the fundamental frequency of infant vowels remains in question. In this paper, the instrinsic pitch of high- versus low- front and back vowels was measured from 13-month-old infants. Six infants were recorded interacting with their mothers at home. High-quality wireless microphone, time-coded, 1-h recordings were narrowly transcribed by two investigators with the aid of frequency and amplitude displays. The subsample of high and low vowels was drawn from a computerized database for acoustic analysis. Vowels were analyzed for F0 with narrow-band spectrographs. Measurements were made from the center of each vowel and the results subjected to statistical analysis. Results were related to individual variability in infant F0 and the reconfiguration of the human infant vocal tract.
Acoustic consequences of fricative-vowel anticipatory coarticulation in young children
Authors: Nittrouer Susan
Published: October 2005

The acoustic consequences of various forms of anticipatory coarticulation have been studied in adult speech, but only a few studies have investigated these effects in young children. One hypothesis is that young children coarticulate less, producing speech in a more segmental manner than adults. According to this idea, coarticulation develops gradually, possibly to improve articulatory efficiency. In the present experiment, 40 subjects (eight children at each of the ages 3, 4, 5, and 7 years and eight adults) were recorded saying the syllables /∫i/,/si/,/∫u/, and /su/ eight times each. The center of gravity of the fricative spectrum and second formant values, both in the fricative and at the onset of voicing, were measured. Effects of vowel context were more strongly evident in measurements made within the fricative portion of the signal for children than for adults, but children's vocalic formant transitions were reduced relative to adult transitions. These results suggest that, in fricative-vowel sequences, children tend to coarticulate (or coproduce) the two segments more strongly than adults do. This finding may indicate that, in fact, children produce speech in a less segmental manner than adults. [Work supported by NICHD Grant HD-01994.]
Plasticity in adult and child speech production
Authors: Flege James Emil
Published: October 2005

This study examined the ability of nine adult and nine children (aged 6–9 years) to speak with thin (0.5 mm) experimental prostheses in the mouth. One prosthesis conformed closely to the upper teeth and hard palate; the other substantially altered oral cavity geometry by reducing by one-half the volume under the palatal vault. Degree of adaptation was estimated by having listeners rate the adequacy of words (pea, tea, sea, she) produced in two lists read before insertion of the prostheses (baseline), immediately after insertion, 4 and 12 min after insertion, and twice after removal. The children were less able than adults to adapt to modest vocal tract changes, but more able to adapt to changes requiring reparameterization that went beyond the normal bounds of articulatory variation. Ratings of the children's but not the adults' production of sea decreased significantly compared to baseline immediately after insertion of the conforming prosthesis. However, the children showed somewhat greater success in adapting to the cavity-altering prosthesis, the presence of which caused a sharp drop in listeners' ratings. Their sea, but not the adults', received significantly higher ratings when produced 12 min than immediately after insertion. These findings suggest that the developing coordinative structures of children are less flexible but more plastic than those of adults. [Work supported by NIH grant NS20572.]
Spectral broadening by ocean microstructure
Authors: Goodman Lou , Jilling Adam
Published: October 2005

In the past decade there has been a great deal of interest in the use of a sonar to infer physical properties of the ocean. Acoustic Tomography and FLIP high-frequency active sonar system are examples of successful efforts. Recently there has been interest in whether high-frequency sonar can be used to measure the smallest scale of ocean fluctuations, microstructure, typically of order meters and smaller in the open ocean. A critical problem which arises in attempting such measurements is that the scattering volume is typically of order of the scale of the variability resulting in Doppler spread as well as Doppler shift. In this work the nature of this spread is examined using a realistic form of microstructure field—one which takes into account both space and time variability. A Brownian motion type of model for the scatterers, which is often employed, will be shown in general to be inappropriate. It will be shown that the temporal correlation of the returned signal is not ergodic. This result is related to the nature of the fourth-order moment, which unlike the second-order moment contains information on the spatial correlation of the scatterer motion.
Measurements of the source levels of shallow explosive charges
Authors: Chapman N. Ross
Published: October 2005

Experiments have been carried out to measure the source levels of standard 0.82 kg SUS (Signal Underwater Sound) charges at nominal depths of 18, 91, and 180 m. The source levels are reported in this paper for 1/3 octave bands from 5 to 500 Hz. Approximately 30 charges for each depth were included in the analysis, and the standard deviation was less than 1 dB for each frequency band. The source levels estimated from these data were compared to the previous results of Gaspin and Shuler which were based on hand drawn pressure waveforms. Their values are generally within 2 or 3 dB of the measured source levels but there are some greater differences. Reasons for the disagreement between the two sets of values are suggested. In addition to the measured source levels, source levels for 0.82 kg SUS at 244 and 610 m, and for 22.7 kg (50 lb) charges at 100 and 200 m have been estimated using a scaling technique [R. Hughes, in Underwater Acoustics and Signal Processing (Reidel, New York, 1981), pp. 87–91]. The spectra of standard SUS measured at 91 and 180 m were scaled, and the source levels obtained in this way are accurate for frequencies up to three or four times as large as the bubble frequency. These results are also presented in 1/3 octave bands, and are compared to previously published values.
Source parameter estimation in correlated spatial noise
Authors: Baggeroer A. B. , Kuperman W. A. , Schmidt H.
Published: October 2005

Several authors have proposed estimating the location parameters of a source using coherent predictions of the acoustic field. The signal processing is the spatial equivalent to matched filtering which is optimum only for white noise, i.e., uncorrelated from sensor to sensor. Alternatively, others have introduced the maximum likelihood method which can be shown to be a simple mapping to the matched filter if the noise is white. For closely spaced sensors white noise is not a good model; moreover, the signal and noise propagate in the same medium and must have similar characteristics. (For example, in the ocean waveguide model both the signal and noise are functions of the shape and composition of the boundaries as well as the sound-speed profile.) This paper introduces the Kuperman-Ingenito correlated noise model [J. Acoust. Soc. Am. 67, 1988 (1980)] to obtain predictions of source location parameter estimation performance. These are compared with the appropriate Cramer-Rao bounds.
Inferring the sound-speed profile from shots recorded on vertical arrays
Authors: Frazer L. Neil
Published: October 2005

Let φ (x,z,ω) be the pressure data recorded on a vertical array from a shot at range x. Suppose there are N such shots, all at the same depth but with a range increment Δx. The resulting pressure data are used to form the data matrices A and B in each of which the row index is depth and the column index is range. The first (last) column of A is the data from the second (last) range whereas the first (last) column of B is the data from the first (next to last) range. Therefore, A = exp (iΔxH)B, where H is the matrix of the operator [ω2/c2(z) + ρ(z)∂zρ−1(z)∂z]1/2 in the PE equation (i∂x + H)φ = 0 governing pressure propagation in a stratified ocean. To get the sound-speed profile first form H = (1/iΔx)ln(AB−), where B− is a generalized inverse of B; then multiply H by itself to get H2; then compute the “standard symbol matrix” Hs2 (p,z) = ∫dz′ exp(ipz′) ×H2(z′,z′ − z); then fit a quadratic in p to each column of the symbol matrix in order to recover the coefficients of p0 and p in the expression Hs2(p,z) = ω2/c2(z) − p2 − ipρ′(z)/ρ(z). [Work supported by ONR.]
Implementation of the Wigner distribution function for representing the dynamics of acoustic signal spectra
Authors: Yen N.
Published: October 2005

The Wigner distribution function, originally defined in quantum mechanics for the probability function expressed in terms of the simultaneous value of coordinates and momenta, is used to represent the time-varying signal cojointly in time and frequency domains. Although its formulation resembles the Fourier transform of the time-dependent correlation function, direct application of the transformation technique to its discrete version for a finite duration signal generally encounters problems of aliasing and nonpositive value during computation. To alleviate those shortcomings, a numerical process based on the FFT algorithm has been developed by reformating the given signal and the computed result. This modified Wigner distribution function provides the dynamic interpretation for the signal's frequency component change with time. Examples of its implementation with several types of acoustic signals are illustrated wth such time-frequency representation.
Effects of ocean environment on the operation of a synthetic aperture sonar
Authors: Tarng Jean-Hwan , Yang C. C.
Published: October 2005

The application of a synthetic aperture radar has made the resolution increase tremendously in microwave imaging on the ground. The same principle can be applied to acoustic imaging for targets in an ocean. However, the scenario of acoustic wave propagation in the ocean environment is much more complicated than that of microwave propagation in the atmosphere. In this paper, effects of ocean environment on the operation of a synthetic aperture sonar are discussed. The sound-speed profile is the first factor whose effects need to be investigated. Also, random fluctuations of the sound speed due to fine structures and internal waves in the ocean produce other effects. Among the parameters of a synthetic aperture sonar, the sizes of the resolution cell in the azimuthal and range directions, azimuth ambiguity, and range ambiguity are of great concern. Cases with various sonar carrier velocities are considered. [Work supported by ARL, The Pennsylvania State University.]
Peak sidelobe estimator for randomized arrays
Authors: Lockwood James C. , Law David
Published: October 2005

A randomized line array is formed by randomly perturbing an equally spaced, deterministic array. For small perturbations, it has been shown that the variance of the sidelobe amplitude is less, over a significant portion of the beam pattern, than for larger perturbations. The present paper quantifies the effect of this variance dependency on the magnitude of the peak sidelobe. The analysis follows that presented by Steinberg [Principles of Aperture and Array System Design (Wiley, New York, 1976), pp. 147–166], in which for a given confidence level the upper bound on the peak sidelobe is derived. Steinberg's work is based on a totally random array, and makes use of the fact that all the sidelobes are statistically the same to obtain a closed-form expression for the peak sidelobe level as a function of confidence level. In the present work the mean and variance associated with each independent sidelobe position are computed and combined to give results that depend on the original array configuration and on the size of the perturbation. It is shown that a randomized array with a moderately small perturbation may have a significantly lower peak sidelobe than the corresponding totally random array.
Low-frequency transmission losses and effective flexural rigidity of cracked ice cover
Authors: Chamuel Jacques R. , Brooke Gary H.
Published: October 2005

Upward refraction in the artic causes substantial interactions of underwater acoustic waves with the ice cover. Although several research papers focused on the effects of ice cover roughness on transmission losses, apparently no studies have been reported on the effects of cracks in the ice cover on reducing the flexural rigidity of the ice plate in relation to leaky Lamb waves and energy exchange between the water and the ice. Coupling between the acoustic waves in the water and the elastic waves in the ice plate depends on the relative densities and phase velocities of the waves. Depending on the number, size, and spatial distribution of the cracks, the flexural wave velocity of a low-frequency component may be higher or lower than the water compressional velocity. The steep sloped region of the flexural wave dispersion curve makes the low-frequency transmission characteristics very sensitive to the presence of cracks which reduce the flexural rigidity. Laboratory ultrasonic models are used to provide physical insights into a potentially important low-frequency transmission loss mechanism caused by the effective reduced flexural rigidity of the cracked ice cover. Thin plates with machined multiple shallow cracks are utilized. The crack spacing is about half a wavelength and the crack depth is less than 1/6 the plate thickness. [Work supported by DREP.]
The use of acoustic versus optic range sensors in manufacturing systems
Authors: Prinz F. B.
Published: October 2005

Range information is very important for automatic control of manufacturing systems. Part location, edge detection, and motion guidance are just a few examples of problems in which range information is required. Through simple time-of-flight measurements acoustic systems can conveniently and reliably provide the distance between the sensor and the workpiece. Scanning with the acoustic transducer furthermore allows one to reconstruct the nearfield 3-D environment. Difficulties arise primarily from the need that the workpiece surface should be reasonably parallel to the surface of the acoustic transducer. Iterative search strategies allow one to overcome this problem. Alternatively, optical range-finding systems typically use triangulation strategies to measure the sensor/workpiece distance. Their depth resolution is comparable to that of acoustic transducers. The lateral resolution is better in optical systems. Furthermore, the orientation dependence of the workpiece/sensor surface is less critical than it is for acoustic transducers. Acoustic systems are less expensive than their optical counterparts. They also can survive in the sometimes harsh manufacturing environment. The advantages and disadvantages of optical and acoustical range finding sensors are discussed in the context of applied manufacturing problems.
Precision in ultrasonic gauging
Authors: Hickling Robert , Marin Samuel P.
Published: October 2005

In ultrasonic gauging it is important to realize that only the perpendicular distance to a surface can be measured unambiguously using a single emitting-receiving transducer. Factors that affect the accuracy of the measurement are, signal-to-noise ratio, spot size, depth of field, alignment of the transducer axis perpendicular to the reflecting surface, dimensional accuracy in the construction of the transducer, and compensation for change in the speed of sound in air due to temperature changes and other effects. Experimental results are presented which show that distances up to 200 mm can be measured with an accuracy of ±0.1 mm, provided there is adequate compensation for change in temperature of the air. Spot size, or lateral resolution, is dependent on the frequency of the ultrasound which has an upper limit of about 1 MHz because of attenuation due to absorption. The smallest spot size that can be attained, therefore, is about 1 mm, between the 6-dB points. However, a deviation of 1 deg from the perpendicular can produce a lateral error of about ±2 mm at a distance of 100 mm. Factors affecting accuracy in ultrasonic gauging are reviewed in the paper.
Ultrasonic background noise in industrial environment
Authors: Bass Henry E. , Bolen Lee N.
Published: October 2005

Special high-frequency microphone systems were developed, and ultrasonic noise associated with various manufacturing operations was measured in the frequency range 0–1 MHz in order to evaluate typical noise environments for ultrasonically controlled robots. Industrial operations studied include impact, bending, grinding and drilling, laser etching, and high-velocity fluid or air sprays. The first three operations provide little ultrasonic energy above 100 kHz. For these processes, ultrasonic sensors operating above 100 kHz should have an advantage since signal and noise will both fall off with increasing frequency. Ultrasonic emission from laser etching was found to be quite broadband, making such processes less suitable for ultrasonic control. High-velocity fluid or air sprays are most prevalent sources of ultrasonic noise. The noise from these sources rolls off slowly with frequency, and no frequency bands without noise exist for ultrasonic sensing below several hundred kHz. For applications requiring ultrasonic sensing, aerodynamic noise should be reduced.
Individual differences in auditory-evoked responses: Second report
Authors: Lauter Judith L. , Loomis Robert L.
Published: October 2005

Last spring we reported to this meeting findings from a series of auditory-evoked response (AER) tests designed for studying individual differences in AER's by comparing between-subject (BS) variability with within-subject (WS) variability. The series involved a repeated-measures design, where seven young adult subjects were tested weekly for eight sessions; in each session, AER's were collected for right monaural, left monaural, and binaural click stimulation. Continuing analysis of the brain stem data, focusing on comparisons of binaural versus monaural responses, shows further examples of: (1) clear differences between the two types of variability; (2) distinct patterns, or “profiles,” of individual performance that are articulated both in terms of differences according to ear of stimulation and peak of the response; (3) striking degree of replicability of individual patterns of performance; (4) deviations from replicability that most often take one of two forms—(a) increases in stability with continued testing, and/or (b) “emergence” of response patterns that may result in the response profile of one subject coming to resemble that shown by other individuals. [Work supported, in part, by AFOSR 84-0335 and 85-0379.]
The complex event-related potential (CERP): Perturbations in the high-rates auditory steady-state response following an omitted stimulus
Authors: Makeig Scott , Galambos Robert
Published: October 2005

When a train of brief or impulsive sound stimuli is delivered to the adult auditory system at repetition rates near 40/s, a near-sinusoidal so-called high-rates steady-state evoked response (HRR) is recorded from the scalp [Galambos et al., Proc. Natl. Acad. Sci. 78, 2643–2647 (1981)]. Amplitude and phase perturbation in this ongoing response following another experimental event can be observed by averaging responses time locked to the event and narrow-band filtering at the stimulus rate. A complex event-related potential (CERP) is the result. The CERP is a two-dimensional frequency-domain analog of the usual one-dimensional time-domain event-related potential (ERP). We report here a demonstration that the HRR may be perturbed for several hundred milliseconds after a single click has been dropped out of the stimulus train. The high-rates CERP provides another window on event-related brain dynamics parallel to the auditory slow-wave sequence. [Work supported by the NIH.]
Effects of airborne upper sonic and ultrasonic acoustic radiation and proposed threshold limit values for human exposure
Authors: Michael Paul L. , Kerlin Roger L.
Published: October 2005

In 1974, a literature search and a field study by these authors and co-workers at the Environmental Acoustics Laboratory were completed and sought to evaluate industrial exposure to airborne acoustic radiation above 10 kHz. The reported effects of exposure to such radiation and the three existing sets of human exposure limits for airborne upper sonic and ultrasonic acoustic radiation proposed by investigators from three different countries (the USA, England, and Russia) were documented and discussed as part of a final report prepared for the sponsor [P. L. Michael, R. L. Kerlin, G. R. Bienvenue, and J. H. Prout, An Evaluation of Industrial Acoustic Radiation Above 10 KHz, Environmental Acoustics Laboratory, The Pennsylvania State University, University Park, PA, Final Report, Contract No. HSM-99-72-125, Physical Agents Branch, NIOSH, Cincinnati, OH, p. 210 (February 1974)]. These results will be presented and discussed, and, in particular, their role as part of the documentation for the threshold limit values for airborne upper sonic and ultrasonic acoustic radiation in the work environment proposed by the American Conference of Governmental Industrial Hygienists. [Work supported by NIOSH.]
High-frequency acoustic systems for robotic applications
Authors: Smith R. W. , Walters Rex , Carlson John , Harris Robert
Published: October 2005

High-frequency ultrasonic systems, operating in the 200-kHz to 1-MHz frequency range and using air as the acoustic coupling medium are an effective complement to optical systems for robotic and industrial measurement applications. An air-coupled ultrasonic system was developed which produces well damped and focussed ultrasonic beams with good spatial resolution. Tests show that distance measurements with a resolution of 0.001 in. can be made through several inches of air at a rate of several hundred Hz. Focused transducers can reduce the effective area of measurement to below 0.05 in. at the focal point. The system was employed in several applications, including parts profiling, thickness testing, and the detection of missing parts. The apparent advantages that acoustic devices have over optical systems include lower cost by a factor of 5 or 10, and a higher speed of operation by perhaps 2 orders of magnitude.
Distance measurement using airborne sound
Authors: Meyer Paul A.
Published: October 2005

Inspection of manufactured material and components often involves characterization of size or shape. If large quantities of components must be inspected, as is usually the case on a production line, a rapid automated inspection process is desirable. This presentation reviews the use of airborne ultrasound as the basis for such a system. Time-of-flight measurements of acoustic pulses through air can be used for distance measurement with range resolution of 0.01 mm (0.0004 in.). Coupling this instrumentation to a data acquisition system permits high-speed, automated dimensional checks. But a more important feature of an airborne sound system is that contacting the part is not required enabling rapid characterization of components difficult to measure by other means. These include runout on abrasive surfaces such as grinding wheels or discontinuous surfaces, such as tire treads. Finally, since ultrasonic distance measurements can be updated at several hundred hertz noncontact time motion studies are possible. No loading is applied to the structure under investigation so that characterization of “delicate” vibrating components is possible.
Ultrasonic study of an emulsion of toluene in water
Authors: Gultepe M. A. Barrett , Gultepe M. E. , McCarthy J. L. , Yeager E.
Published: October 2005

Previously reported ultrasonic attenuation results in the frequency range 4 to 50 MHz and theoretical predictions [J. R. Allegra and S. A. Hawley, J. Acoust. Soc. Am. 51, 1545 (1971)] for an emulsion of toluene in water have indicated that the observed excess attenuation in the measured frequency range was largely due to heat conduction losses. In the present paper, ultrasonic absorption measurements on a 20% emulsion of toluene in water in the frequency range 1 to 135 MHz at 25 °C are described. The excess attenuation due to the emulsion globules as a function of frequency was compared with explicit expressions for heat conduction, viscous drag losses, and scattering of sound by emulsion globules. Unlike the previous work, the agreement between theoretically predicted excess attenuation and that observed can only be obtained if a wide distribution of globule sizes was assumed. The assumption of a globule size distribution spanning from 600 to 6000 Å in diameter produced a theoretical curve in good agreement with the observed excess absorption over the entire frequency range. [Work supported by ONR.]
Re-examination of boric acid relaxation with high-precision spherical resonator
Authors: Gultepe M. A. Barrett , Gultepe M. E. , Yeager E. , Mellen R. H.
Published: October 2005

The dependence of low-frequency sound absorption on pH as a function of B(OH)3 concentration in 0.725M NaCl was studied with a computer-controlled high-precision spherical resonator. For these measurements, a 100-liter titanium spherical resonator was mode mapped in the frequency range of 2 to 100 kHz when containing distilled water, then 0.1M, and finally 0.725M NaCl solutions. Frequency shifts and decay rates of the radial modes were studied with the NaCl concentrations. Using a solution of boric acid equal in concentration to sea water (4.2 × 10−4 M) at pH 8.2, in 0.725M NaCl, reliable absorption measurements have been made at frequencies as low as 6 kHz. [Work partially supported by ONR.]
Factors affecting the ultrasonic measurement of porosity in cast aluminum
Authors: Rypien David V. , Adler Laszlo
Published: October 2005

An ultrasonic method was developed to measure the average pore radius and volume fraction of porosity in cast aluminum [L. Adler, J. Acoust. Soc. Am. Suppl. 1 76, S83 (1984)]. This study was limited to samples having smooth parallel surfaces, containing average pore radii ranging from 50 to 200μm, and volume fractions less than 6%. In order to increase the practical applications of this method, samples were analyzed with: (1) the as-cast (rough) surface intact, (2) with increased volume fractions, and (3) increasing the length of the cast samples. By using the original method, it was found that the calculated volume fraction for the above cases were significantly underestimated. Analyses of these factors and methods for determining possible corrections to improve this method are suggested. The results obtained from this investigation are also compared to the previous measurements. [This work was supported by the Center of NDE operated by Ames Laboratory for the Air Force Wright Aeronautical Materials Laboratory.]
Wideband acoustic response of fluid-saturated porous rocks
Authors: Schmidt Ehud I. , Nur Amos M.
Published: October 2005

The complex compressional and shear frequency-dependent elastic constants of nonporous solids and porous rocks are measured in the frequency range 5 kHz to 1 MHz. The measurements are performed in a continuous wave acoustic transmission bridge using cylindrical samples. Use of waveguided samples prevents problems of diffraction and wavefront spreading, which are difficult to correct over broad frequency ranges. The theory of waveguided elastic wave propagation in media with complex elastic constants (generalization of the Pochammer-Cree solution) is presented. This theory is utilized in the interpretation of the experimental results from nonporous solids with real and complex frequency-independent elastic constants, solids with complex frequency-dependent elastic constants, and rocks with effective complex frequency-dependent elastic constants. For solids with frequency-independent complex elastic constants (constant Q) the results reveal the appearance of specific dissipation peaks associated with waveguide geometry. Results for fluid-saturated porous rocks are discussed in the context of the cumulative effects of fluid viscosity, solid-fluid interfacial energy, and grain scattering.
Rigid, acoustically transparent plastic based on fluoroepoxy
Authors: Thompson Corley M. , Griffith James R.
Published: October 2005

The performance of many underwater acoustical systems would be greatly improved by the use of a structurally rigid material that is nearly transparent acoustically. This means that the material possesses sound speed and density each equal to that of the water medium. The best available commercial materials show a sound speed that is 40% higher than water, and thus are not quite nontransparent acoustically. In earlier work [C. M. Thompson and J. R. Griffith, J. Acoust. Soc. Am. Suppl. 1 70, S74 (1981)] it was shown that a new material based on a partially fluorinated epoxy has much promise. This presentation reports the optimization of the fluoroepoxy by compounding with two different microballoon fillers. The density and sound speed are reported with this choice and are shown to be independently adjustable. Thus a precise match of each with the medium is possible. Samples were fabricated and measured for acoustic transparency by use of panel tests. Results at frequencies down to 10 kHz are presented. The nonacoustic properties are described, and the identity of a commerical source of the material are presented.