摘要:

Most transducer devices used in present day sonar arrays are usefully approximated as single degree of freedom devices. The type of device that dominates the present systems are Tonpilz transducers. As system requirements move to lower frequency regimes, devices such as these become too large to be handled manageably. New types of devices, typically having more than one important vibrational mode and significantly smaller dimensions, are being investigated for future applications. Most of the analysis techniques presently used have been developed to support single degree of freedom devices. New tools are needed to analyze devices that rely on more than one vibrational mode to perform their mission. The technique described here combines finite‐element analysis (FEA) methods with tools that have already been developed, providing a bridge to previous analysis techniques. This allows the considerable investment made in the development of previous techniques to be applied to devices where they may not otherwise have been considered sufficiently accurate.

ISSN:0001-4966    

DOI:10.1121/1.399943

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

A unidirectional magnetostrictive/piezoelectric hybrid transducer was constructed that produced enhanced motion at one end and canceled motion at the other end. In the simplest form the transducer consists of a quarter wavelength section of piezoelectric material joined to a quarter wavelength section of Terfenol‐D rare earth magnetostrictive material. A 3‐kHz experimental hybrid transducer with a total length of approximately 18 in. (0.46 m) was constructed with a small central mass and two small identical end piston masses. Measurements and calculations on this device showed an average front‐to‐back ratio of approximately 17 dB.

ISSN:0001-4966    

DOI:10.1121/1.399847

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

Transients in piezoelectric transducers using spatial impulse responses and a finite‐element method have been studied. The developed calculation procedure makes it possible to obtain two‐dimensional nonstationary electroacoustic fields inside a transducer as well as spatial distributions on its surfaces under various driving conditions. Numerical simulations of plane and concave transducers have been carried out. The edges of the piezoelectric elements in both cases are sources of strong spurious impulsive waves propagating to the center of a transducer. Some methods to improve the uniformity of the spatial distributions and reduce the amplitude of spurious waves have been proposed. The results obtained may be of particular interest for calculating more accurately pulsed ultrasonic fields radiated by piezoelectric transducers of finite dimensions.

ISSN:0001-4966    

DOI:10.1121/1.399959

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

A new method of measuring the impedance of locally reacting material placed in an acoustic field distributed over higher‐order modes is presented. By a Fourier–Lommel’s transform of the acoustic pressure measured in a duct of a cylindrical cross section lined with this material, duct eigenvalues are determined. Impedance is then deduced from the boundary limit relationship taken at the liner face. Experiments have been conducted and show that this method is reliable in determining impedance if care is taken to localize precisely the radial position of the microphone. Also, among previous methods where impedance is deduced from nonlocal measurements, the technique presented has the advantage that it can be experimentally set up in a short‐lined duct and not be perturbed by edge effects at boundary cross sections located at the beginning and the end of the liner.

ISSN:0001-4966    

DOI:10.1121/1.399942

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

Longitudinal acoustic wave measurements performed on isotropic aluminum buffer rods with uniform, notched, and tapered peripheries are presented. The buffer rods considered have diameters between a few and several tens of acoustic wavelengths, and lengths of more than a hundred acoustic wavelengths. The buffer rod with a tapered shape was found to be the most effective for eliminating trailing echoes associated with mode conversion on the outer walls of the rods.

ISSN:0001-4966    

DOI:10.1121/1.399946

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

The heating of tissues by the absorption of ultrasound is an important safety consideration in the use of diagnostic ultrasound. This paper shows that models of ultrasonic heating for this situation need to take account of nonlinear propagation. Measurements were made of the temperature rise in a sample of tissue‐mimicking gel, caused by the application of 3.6‐MHz focused ultrasonic beams for 3 min. The propagation path to the focus was in water, to mimic the situation where the fetus is scanned through the full bladder. The effect of nonlinear propagation was seen by changing the pressure amplitude of the pulse, while altering the pulsing regime to preserve a constant spatial‐peak temporal‐average intensity of 1 W cm−2. When nonlinear distortion was present, an enhancement in the temperature rise was observed, which correlated with the value of the shock parameter. The enhancement ratio was typically up to a factor of 3, and the maximum temperature rise observed was 2 °C. This enhanced heating was seen both at the surface of the tissue‐mimicking gel and after propagation through 23 mm of the material. Under conditions of nonlinear propagation, the maximum heating usually occurs in the prefocal region, rather than at the focus.

ISSN:0001-4966    

DOI:10.1121/1.399950

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

Woodwind air column models can be used to analyze the acoustical properties of existing instruments, in designing new air columns or modifying historical or contemporary instruments, and in constructing time‐domain simulations of woodwinds either for testing theories of woodwind acoustics or as a method of music synthesis. Two types of models and their applications are described, both using a highly accurate representation of each tonehole. The first model generalizes the Benade lattice model, which admits of an analytical solution, and experimental data confirming important features of the model are described. The second model is a computational model based upon a transfer‐matrix formulation. It is well suited to generating a number of important air column response functions and is simple to alter for a variety of air column configurations. An example illustrating the use of this transfer‐matrix model is presented for a cylindrical bore flute air column. The Hilbert transform applied to the reflection function assists in the interpretation of the response of the air column, when viewed in the time domain.

ISSN:0001-4966    

DOI:10.1121/1.399911

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

This article describes an experimental study of the timing in the grand piano action. The function of the action is described by timetables for the motions of the moving parts. Important timing properties included are the relation between key bottom contact and hammer–string contact, the interval of free hammer motion before the impact on the string, and the hammer–string contact duration. The influence of the regulation and dynamic level on these timing properties is analyzed. The results of the measurements are discussed, with a focus on the implications for piano playing, regulation, and design.

ISSN:0001-4966    

DOI:10.1121/1.399933

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

Using the phenomenon of duplex perception, previous researchers have shown that certain manipulations affect the perception of formant transitions as speech but not their perception as nonspeech ‘‘chirps,’’ a dissociation that is consistent with the hypothesized distinction between speech and nonspeech modes of perception [Libermanetal., Percept. Psychophys.30, 133–143 (1981); Mann and Liberman, Cognition14, 211–235 (1983)]. The present study supports this interpretation of duplex perception by showing the existence of a ‘‘double dissociation’’ between the speech and chirp percepts. Five experiments compared the effects of stimulus onset asynchrony, backward masking, and transition intensity on the two sides of duplex percepts. It was found that certain manipulations penalize the chirp side but not the speech side, whereas other manipulations had the opposite effect of penalizing the speech side but not the chirp side. In addition, although effects on the speech side of duplex percepts have appeared to be much the same as in the case of normal (electronically fused) speech stimuli, the present study discovered that manipulations that impaired the chirp side of duplex percepts had considerably less effect on the perception of isolated chirps. Thus it would seem that duplex perception makes chirp perception more vulnerable to the effects of stimulus degradation. Several explanations of the data are discussed, among them, the view that speech perception may take precedence over other forms of auditory perception [Mattingly and Liberman, inSignalsandSense:LocalandGlobalOrderinPerceptualMaps, edited by G. M. Edelman, W. E. Gall, and W. M. Cowan (Wiley, New York, in press); Whalen and Liberman, Science237, 169–171 (1987)].

ISSN:0001-4966    

DOI:10.1121/1.399845

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

In a series of experiments, a variant of duplex perception was investigated. In its original form, duplex perception is created by presenting an isolated transition to one ear and the remainder of the syllable, the standard base, to the other ear. Listeners hear a chirp at the ear receiving the isolated transition, and a full syllable at the ear receiving the base. The new version of duplex perception was created by presenting a third‐formant transition in isolation to one ear and the same transition electronically mixed with the base to the other ear; the modified base now has all the information necessary for syllabic perception. With the new procedure, listeners reported hearing a chirp centered in the middle of their head and a syllable in the ear presented the modified base that was clearer than that produced by the isolated transition and standard base. They could also reliably choose the patterns that contained the additional transition in the base when attending to either the phonetic or nonphonetic sides of the duplex percept. In addition, when the fundamental frequency, onset time, and intensity of the isolated third‐formant transition were varied relative to the base, the phonetic and nonphonetic (lateralization) percepts were differentially affected, although not always reliably. In general, nonphonetic fusion was more affected by large differences in these variables than was phonetic fusion. However, when two isolated third‐formant transitions were presented dichotically, fusion and the resulting central location of the chirp failed markedly with relatively small differences in each variable. The results were discussed in terms of the role of fusion in the new version of duplex perception and the nature of the information that undergoes both phonetic and nonphonetic fusion.

ISSN:0001-4966    

DOI:10.1121/1.399846

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP