摘要:

An analysis is presented for the design of piezoelectric transducers in a sandwich configuration using a stepped horn as a particle velocity amplifier. The condition for maximum power delivery to the load impedance is established in terms of the parameters of the horn and the piezoelectric material. As an example, the method of false position is used to find solutions numerically for the dimensions of a horn suitable for radiating into steam.

ISSN:0001-4966    

DOI:10.1121/1.401914

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

The use of single and double layers of piezoelectric material to form acoustically active surfaces for the elimination of reflected and transmitted waves is first discussed from a theoretical standpoint. Experiments are then described in which the piezoelectric compositepiezorubberis used as the transducing material in single and double layer active surfaces. It is demonstrated that with the single layer, either reflection or transmission can be eliminated, while both reflection and transmission can practically be eliminated with the double layer. The electrical driving signals applied to the active surfaces in order to accomplish this are shown to agree well with theoretical models using material parameters for piezorubber determined from impedance measurements.

ISSN:0001-4966    

DOI:10.1121/1.402384

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

A general transfer matrix description for one‐dimensional layered structures consisting of piezoelectric and nonpiezoelectric anisotropic layers of arbitrary number is used to calculate the electrical admittance matrix for such resonators withNelectrodes. The calculation is done in detail for linearly stacked resonators with two free surfaces as well as for ring resonators with a closed acoustical path. Experimental and theoretical results are given and compared for a ring resonator with two piezoelectric layers excited by four electrodes. Such a configuration can be used to generate unidirectional resonant waves.

ISSN:0001-4966    

DOI:10.1121/1.401915

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

The optimum design of a piezoelectric diaphragm consisting of a piezoelectric plate and a base plate and used in telephone transducers is described. First, the relationship between the microphone and earphone sensitivities and the dimension ratios (a thickness ratio and a radius ratio) of the piezoelectric plate to the base plate is determined. Then the relationships between the maximum sensitivities, the optimum dimension ratios where the maximum sensitivities are obtained, and the material constant ratios (Young’s modulus ratio and a density ratio) are examined. The base plate material should be harder and lighter than that for the piezoelectric plate to achieve high sensitivities. A diaphragm designed for an earphone or sounder can be used in a microphone as well. Experimental results agree well with the calculated values.

ISSN:0001-4966    

DOI:10.1121/1.401916

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

This paper describes a precision method for phase match of microphones. The coupler method consists of an acoustical driver that excites two test microphones simultaneously in a small cavity. The phase response contribution of the associated preamplifiers and amplifiers is eliminated with an interchange procedure, which enables the relative phase of a pair of microphones to be assessed accurately. The uncertainty of the method is dependent upon the uncertainty of the phase meter or phase measuring system. Over a frequency range from 63 Hz to 2 kHz and with a commercial phase meter that has an uncertainty of ±0.02 deg, the uncertainty of this coupler method for phase comparison is approximately ±0.05 deg. The coupler is useful over a frequency range from 10 Hz to 6.3 kHz.

ISSN:0001-4966    

DOI:10.1121/1.401917

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

This study had a twofold purpose: to determine if music recorded or processed digitally retains a sampling frequency artifact on vinyl records, and to find whether the playing of such records has an effect on the turntable speed. A sharp peak in the record’s acoustic power spectrum was noted on some recordings at 44.1 kHz, an agreed upon standard sampling frequency for digital recordings. No unexplainable differences in the rotational speed between the test ‘‘digital’’ records and the control ‘‘analog’’ records were observed during the study.

ISSN:0001-4966    

DOI:10.1121/1.401918

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

A single‐probe heterodyne laser interferometer has been modified to a dual‐probe modality by utilizing the reference beam as a second probe. It is shown that the two probing beams display the same sensitivity, independent of the difference in reflectivities at the two points of detection on the specimen. The dual‐probe interferometer allows measurements of the same surface wave signal at two points. The instrument is particularly suited for the measurement of the speed and attenuation of surface waves. The interferometer has been employed to determine phase velocities and attenuation coefficients for surface wave propagation over an aluminum plate with increasing degrees of surface roughness.

ISSN:0001-4966    

DOI:10.1121/1.401919

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

A differential laser Doppler velocimeter (LDV) has been assembled and tested to provide noninvasive absolute measurements of acoustic particle displacements of standing waves generated in a water‐filled tube. The principle of the technique [see K. J. Taylor, J. Acoust. Soc. Am.59, 691–694 (1976)] is to measure the Doppler shift of laser light scattered from colloidal microparticles oscillating under the action of an acoustic field. The system tested is capable of detecting particle displacements of the order of a few nanometers with a bandwidth of several kilohertz. The performances and limitations of the system are discussed. In particular, the effect of Brownian motion is shown to produce only negligible broadening of the spectral density of the signal of interest. The sensitivity of the present LDV system is estimated to be very close to the shot noise limit of the photomultiplier tube used to detect the Doppler shift of the scattered light. Experimental results are obtained under controlled laboratory situations with calibrated microparticles of radii 10, 1, 0.1, and 0.01 μm in suspension in very pure (reverse osmosis) water.

ISSN:0001-4966    

DOI:10.1121/1.401920

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

Using cylindrical quartz crystal torsional resonators operating at 39 and 75 kHz to generate shear waves in aqueous solutions of the proteins bovine serum albumin and hemoglobin and the polypeptide polyl‐glutamic acid, it has been possible to determine the complex dynamic shear viscosities of the solutions. The effects of concentration,pH, and denaturation using various agents have been studied. It is possible to relate the viscosity and configurational elasticity of the solutions, to the intramolecular and intermolecular forces associated with the proteins. Various effects that had been found earlier in compressional wave absorption studies of the proteins at frequencies between 60 and 400 kHz and attributed to conformational changes of bovine serum albumin and the quaternary doublet interactions of hemoglobin have been confirmed and emphasized by the use of shear waves.

ISSN:0001-4966    

DOI:10.1121/1.401921

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

Two experiments determined the just noticeable difference (jnd) in onset frequency for speech formant transitions followed by a 1800‐Hz steady state. Influences of transition duration (30, 45, 60, and 120 ms), transition‐onset region (above or below 1800 Hz), and rate of transition were examined. An overall improvement in discrimination with duration was observed suggesting better frequency resolution and, consequently, better use of pitch/timbre cues with longer transitions. In addition, falling transitions (with onsets above 1800 Hz) were better discriminated than rising, and changing onset to produce increments in transition rate‐of‐change in frequency yielded smaller jnd’s than changing onset to produce decrements. The shortest transitions displayed additional rate‐related effects. This last observation may be due to differences in the degree of dispersion of activity in the cochlea when high‐rate transitions are effectively treated as non‐time‐varying, wideband events. The other results may reflect mechanisms that extract the temporal envelopes of signals: Envelope slope and magnitude differences are proposed to provide discriminative cues that supplement or supplant weaker spectrally based pitch/timbre cues for transitions in the short‐to‐moderate duration range. It is speculated that these cues may also support some speech perceptual decisions.

ISSN:0001-4966    

DOI:10.1121/1.401922

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP