摘要:

The radiated pressure fields of axisymmetric ultrasonic transducers have been measured experimentally at a single frequency to a high resolution. Results in both the nearfield and farfield have been compared to the prediction of theory in three dimensions, developed to examine transducers vibrating with an arbitrary amplitude and phase distribution across their front face. Good correlation was obtained for polyvinylidene fluoride (PVDF) radiators, assuming plane‐piston‐type behavior. For lead zirconate titanate (PZT) transducers, marked amplitude variations with radius across the disk face were encountered, and these needed to be modeled theoretically to obtain good agreement with experiment. Other predictions of theory which are of interest to applications involving acoustical imaging are presented.

ISSN:0001-4966    

DOI:10.1121/1.394164

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

A mathematical model for the transmitting response and electrical impedance of a free‐flooded, thickness‐polarized piezoelectric cylinder transducer has been developed. The elasticity of the cylinder is described using membrane equations which have been modified to account for piezoelectric effects. An additional consequence of the piezoelectricity of the shell is a significant alteration in the boundary conditions for the ends of the cylinder. A particular solution to the membrane equations which satisfies these modified boundary conditions is obtained. The complete solution for the vibration of the cylinder is then found in the form of a sum of the particular solution and the normal modes appropriate to a nonpiezoelectric cylinder with free ends. The acoustic field loads the solution, couples the normal modes, further couples the particular solution and the normal modes, and changes the boundary conditions. The acoustic influence coefficients needed to incorporate these effects are calculated using theshipcomputer program. The water‐loaded normal surface velocities are determined and the surface pressures and farfield radiation characteristics are calculated usingship. The model fully accounts for such effects as the cavity resonance, the velocity of the ends of the cylinder, distribution of velocity along the length of the cylinder, and the difference between the velocity on the inner and outer surfaces of the cylinder. Comparisons between theoretical and experimental results are presented.

ISSN:0001-4966    

DOI:10.1121/1.394174

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

A theorem is presented that permits analytical reduction of the disturbing influence of the edge‐diffracted wave arising in reflection measurements made on thin acoustical panels. This theorem permits a better estimate to be made of the infinite‐plane reflection coefficient than is possible by directly using experimental data obtained from a finite sample panel (since such data are contaminated by edge diffraction). It is analytically demonstrated that the theorem is exact for the case of a perfectly rigid sample panel and for the case of a perfectly soft sample panel. This means that, for these two limiting cases, the theorem entirely eliminates the disturbing influence of the edge‐diffracted wave. (For the exact form of the theorem the source is required to be a Dirac delta‐function point source, and the sample must be of infinitesimal thickness. The cross‐sectional shape of the sample, however, is arbitrary.) An approximate form of the theorem is presented for the case of a penetrable panel. In this case the panel may have nonzero thickness, but the theorem is no longer exact. The penetrable case was investigated experimentally using underwater measurements made on a polymethylmethacrylate sample panel of 2.54‐cm thickness. The sample was square with a side length of 76 cm. The data demonstrate that the technique is capable of achieving a significant reduction of the edge‐diffracted wave arising in thin‐panel reflection measurements.

ISSN:0001-4966    

DOI:10.1121/1.394163

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

The theoretical basis of a new method for obtaining both reflection and transmission mode images of the nonlinear parameterB/Ais given. An expression for the instantaneous (not cumulative) phase shift in a sinusoidal probe waveform due to nonlinear interaction with an arbitrary pump waveform propagating in the opposite direction is derived. This instantaneous phase shift is proportional to the convolution of the pump waveform with the spatial distribution of the nonlinear parameterB/Aalong the propagation path of the pump and interacting probe. The instantaneous phase of the probe can be obtained in real time giving a measure of the variation ofB/Aalong an image line.

ISSN:0001-4966    

DOI:10.1121/1.394186

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

The ultrasonic behavior of glass‐filled xanthan solutions was studied in the frequency range 5–105 MHz as a function of filler particle size and filler concentration. The glass beads were characterized by measuring the particle size distributions. Unfilled xanthan solution exhibited one relaxation process in this frequency range. The frequency dependence of excess attenuation exhibited two peaks. One of these peaks was in the same frequency range as the relaxation for the unfilled solution and has been interpreted as being due to a modification of the background molecular relaxation. The other process was a complex combination of thermal, viscous, and scattering effects, with multiple scattering being the dominant mechanism at higher concentrations. Although the system studied here was different from an emulsion or suspension in that the continuous phase was viscoelastic, the ultrasonic behavior could be qualitatively explained using existing theories for emulsions and suspensions.

ISSN:0001-4966    

DOI:10.1121/1.394152

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

The validity of wave equations employed as system models in acoustical diffraction tomography is investigated using simulations and measurements of the scattering of plane ultrasound waves by cylinders. It is demonstrated by simulation and experiment that it can be appropriate to neglect density fluctuations and shear waves, implying that the commonly used form of the wave equation suitably describes scattering by fluctuations of acoustic speed and absorption. Diffraction tomographic reconstructions of simulated data reveal the importance of absorption, the behavior of the real and imaginary parts of the reconstructed refractive index, and the relative advantages and limitations of the Born and Rytov approximate transformations.

ISSN:0001-4966    

DOI:10.1121/1.394081

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

An articulation index calculation procedure developed for use with individual normal‐hearing listeners [C. Pavlovic and G. Studebaker, J. Acoust. Soc. Am.75, 1606–1612 (1984)] was modified to account for thedeterioration in suprathreshold speech processing produced by sensorineural hearing impairment. Data from four normal‐hearing and four hearing‐impaired subjects were used to relate the loss inhearing sensitivity to the deterioration in speech processing in quiet and in noise. The new procedureonly requires hearing threshold measurements and consists of the following two modifications of the original AI procedure of Pavlovic and Studebaker (1984): (1) Thespeech and noise spectrumdensities are integrated over bandwidths which are, when expressed in decibels, larger than the critical bandwidths by 10% of the hearing loss. This is in contrast to the unmodified procedure whereintegration is performed over critical bandwidths. (2) The contribution of each frequency to the AI is the product of its contribution in the unmodified AI procedure and a ‘‘speechdesensitization factor.’’ The desensitization factor is specified as a function of the hearing loss.The predictive accuracies of both the unmodified and the modified calculation procedures were assessed by comparing the expected and observed speech recognition scores offour hearing‐impaired subjects under various conditions of speech filtering and noise masking. The modified procedure appears accurate for general applications. In contrast,the unmodified procedure appears accurate only for applications where results obtained under various conditions on a single listener are compared to each other.

ISSN:0001-4966    

DOI:10.1121/1.394082

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

Electroglottography (EGG) was used to monitor vocal fold vibration patterns in normal subjects and patients with various laryngeal disorders. In order to evaluate the regularity of vocal fold vibration, frequency and amplitude perturbation of EGG waves during sustained phonation were measured with a laboratory computer. The data were compared to the degree of hoarseness evaluated by auditory perception and by sound spectrographic analysis. Frequency and amplitude perturbation measures showed some overlap between normal and pathological groups. However, there was a close relation between perturbation analysis of EGG waves and degree of hoarseness (Spearman’s rank correlation coefficientrs=0.73,p<0.0005). Amplitude perturbation was found to be a more sensitive measure of the irregularity of vocal fold vibration than frequency perturbation.

ISSN:0001-4966    

DOI:10.1121/1.394083

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

The conventional model for broadband discrimination assumes that resolution is limited by peripheral internal noise that is statistically independent across channels. In this paper, we extend this model in a number of directions. In particular, we compute, compare, and discuss the effects of interchannel correlation and central noise on the sensitivity indexd’, for discrimination of overall level and discrimination of spectral shape.

ISSN:0001-4966    

DOI:10.1121/1.394084

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

An intermittent tone in one ear may induce a large decline in the loudness of a continuous tone in the contralateral ear [Botteetal., J. Acoust. Soc. Am.72, 727–739 (1982)]. To uncover the basis for this induced loudness adaptation, the method of successive magnitude estimations was used to measure the loudness of a test tone in one ear during and after a single presentation of a briefinducertone in the contralateral ear. Duration and frequency of the inducer were varied. The frequency of the test tone was set at 500, 1000, or 3000 Hz. Both inducer and test tones were at 60 dB SPL. When the inducer lasted 5 s or more and was at the same frequency as the test tone, the loudness of the test tone was reduced by 80% to 100% while the inducer was on. As the inducer frequency moved away from the test tone, the loudness reduction declined gradually except for a more marked drop at the point where the frequency separation exceeded the critical bandwidth. Loudness remained depressed after the inducer went off. Additional measurements showed that the amount of loudness reduction corresponded closely to the measured movement of the inducer’s sound image away from the center of the listener’s head (decentralization).

ISSN:0001-4966    

DOI:10.1121/1.394085

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP