摘要:

A theoretical model of transverse waves propagating on piezoelectric plates of finite thickness under metal strip gratings is proposed. Different mechanical and electrical boundary conditions are considered and their influence on the propagation characteristics of the waves is emphasized. In all the cases, the dispersion curve relating the angular frequency to the wave number exhibits more than only one stopband as found in the usual analysis of surface transverse waves on semi-infinite substrates. This model has been used to calculate the resonance frequencies of synchronous devices on AT-cut and Z-cut quartz plates. These theoretical predictions are compared to experimental results obtained using synchronous devices built on 128-μm-thick Z-cut plate of quartz and AT-cut plate of quartz and operating at frequency range 80–150 MHz.

ISSN:0001-4966    

DOI:10.1121/1.420096

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

Integral expressions are derived for the displacement response tensor of a semi-infinite anisotropic elastic continuum of unrestricted symmetry to a concentrated force suddenly applied to its surface. The surface response is reduced to a one-dimensional integral for numerical evaluation, while the interior response is left as a two-dimensional integral. Calculated surface response functions for Cu(001) are presented. These display multiple Rayleigh wave arrival singularities as well as bulk wave arrivals. Calculated interior response functions for Zn(0001) are presented. These display bulk and head wave arrivals. In followup papers these methods will be used in the interpretation of capillary fracture generated waveforms measured in a number of different materials.

ISSN:0001-4966    

DOI:10.1121/1.420053

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

Energy vortices in time-averaged energy flows of time-harmonic fields are considered. The purpose of the paper is to verify the supposition that the energy flux along an elastic waveguide with an obstacle is blocked completely at the stop frequencies by the vortices. It is hoped that this work will draw attention to the analogy between energy and fluid flows which is potentially fruitful for understanding various wave phenomena. The normal-mode diffraction by a surface punch on an elastic layer is taken as an example. For tracing energy streamlines in the near field up to the obstacle, a special efficient semianalytical approach has been developed. To illustrate the stated supposition, plots of transmission coefficients versus frequency and figures of the near-field streamline structures are given.

ISSN:0001-4966    

DOI:10.1121/1.420054

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

A doubly asymptotic approximation (DAA) is an approximate temporal impedance relation at the boundary of a continuous medium. Here, first- and second-order DAAs are formulated for an infinite external poroelastic medium described by Biot’s equations. As with their acoustic, elastodynamic, and electromagnetic predecessors, the poroelastodynamic DAAs approach exactness in both the early-time (high-frequency) and late-time (low-frequency) limits, effecting a smooth transition between. They also lend themselves to straightforward boundary-element discretization, producing matrix ordinary differential equations in time that are readily solved by numerical integration. An initial examination of poroelastodynamic DAA accuracy is presented for two problems with spherical symmetry.

ISSN:0001-4966    

DOI:10.1121/1.420097

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

The phenomenon of leaky free waves in the modal response of a uniform shell is manifest if (1) in the absence of fluid loading the locus of the free waves as a function of frequency crosses from the subsonic region to the supersonic region across the sonic locus and (2) in the presence of fluid loading the fluid surface impedance at and in the vicinity of the sonic locus is high and the introduction of this fluid loading does not, in itself, prevent the free waves of concern from reaching the sonic locus. In this consideration the sonic locus remains fixed relative to the properties of the shell and, therefore, changes in the fluid loading, on a given shell, are induced by changes in the fluid density only. The phenomenon of leaky free waves in the modal response of a uniform cylinder is investigated. It is found that two distinct examples of leaky free waves are manifested. The first is associated with the flexural free waves that reside in a frequency range that lies above the critical frequency with respect to the speed of sound in the fluid, and the second is associated with the curvature free waves that reside in a frequency range that lies below the ring frequency. The phenomenon of leaky free waves in these two examples is computed, displayed, and discussed.

ISSN:0001-4966    

DOI:10.1121/1.420055

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

A schlieren technique is used to visualize the fluid cavity resonances of an insonified fluid-filled (brass) cylindrical shell in the high-frequency overlapping resonance regime,kb>30,wherebis the inner radius of the shell. Hybridization of modes occurs at frequencies where resonances interfere and the resulting dissymetrization of the wave fields are evident in the experimental images. Similar behavior is seen in theoretical predictions obtained using the normal mode series solution for a shell excited by a plane wave. At very high frequencies(kb>100)the field in the cavity has characteristics that can be associated with a ray description of acoustic propagation; in these cases caustics are observed in the acoustic field.

ISSN:0001-4966    

DOI:10.1121/1.420056

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

The longitudinal–torsional composite vibration of a sectional exponential horn was studied theoretically and experimentally. The horn consists of an exponential horn with an untapered rod at its large end. Based on the plane-wave approximation, the resonance frequency equations and other characteristics for the longitudinal and torsional vibrations of the horn were derived and some theoretical curves were given. Since the sound speeds of the longitudinal and torsional vibrations are different in the same material, the longitudinal and torsional vibrations in a horn are generally difficult to resonate at the same resonance frequency. In this paper, to overcome this problem, the cross-sectional radius decay coefficient of the exponential part in the sectional horn, which determines the sound speeds and other performance parameters of the horn, is selected to make the longitudinal and torsional vibrations resonate at the same frequency. By means of this method, the simultaneous resonance of the longitudinal and torsional vibrations in the horn is achieved by choosing the proper value of the radius decay coefficient. Some sectional exponential horns were designed and made, their resonance frequencies were measured, and the vibrational characteristics of the horn under large excitation were observed qualitatively. Experimental results show that the measured resonance frequencies of the horns are in good agreement with the theoretical results, and the measured resonance frequencies of the longitudinal and torsional vibrations are also in good agreement with each other. Therefore the simultaneous resonance of the longitudinal and torsional vibrations in the same horn are achieved both theoretically and experimentally. This kind of sectional exponential horn can be used in ultrasonic machining, ultrasonic drilling, ultrasonic fatigue testing, and other applications which need very large mechanical displacement amplitudes.

ISSN:0001-4966    

DOI:10.1121/1.420098

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

Effective use of the Fourier series boundary element method (FBEM) for everyday applications is hindered by the significant numerical problems that have to be overcome for its implementation. In the FBEM formulation for acoustics, some integrals over the angle of revolution arise, which need to be calculated for every Fourier term. These integrals were formerly treated for each Fourier term separately. In this paper a new method is proposed to calculate these integrals using fast Fourier transform techniques. The advantage of this integration method is that the integrals are simultaneously computed for all Fourier terms in the boundary element formulation. The improved efficiency of the method compared to a Gaussian quadrature based integration algorithm is illustrated by some example calculations. The proposed method is not only usable for acoustic problems in particular, but for Fourier BEM in general.

ISSN:0001-4966    

DOI:10.1121/1.420099

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

The spectral theory developed by Zabolotskaya [J. Acoust. Soc. Am.91, 2569–2575 (1992)] for nonlinear Rayleigh waves in isotropic solids is generalized to include fields with nonperiodic waveforms and nonplanar spatial dependencies. Model equations for cylindrical waves and diffracting beams that have been used in previous work, and which were obtained in anad hocmanner, are derived here rigorously from first principles. The present theory for plane waves, which is derived using Hamiltonian formalism, is shown to be equivalent to the theory obtained by Parker [Int. J. Eng. Sci.26, 59–75 (1988)], whose derivation is based on a different approach.

ISSN:0001-4966    

DOI:10.1121/1.420057

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

The localized concentration of energy during a single bubble collapse is manifested in two forms, which are the emission of an acoustic pulse, and the emission of a light pulse. Through precise control of experimental parameters, one can levitate a single bubble in a standing wave field and measure the magnitude of the acoustic and light pulses resulting from the violent collapse of the cavity. The information acquired from such measurements provides better understanding of the mechanisms that are responsible for the emissions, which may lead to the practical application of controlled bubble implosions. An experimental apparatus was developed to measure the acoustic and light emissions from a single, stable sonoluminescing bubble. Two surfactant additives were studied to determine the effects on the bubble emissions. Triton X-100, which has previously been shown to provide free interfacial motion, reduced the magnitude of both the acoustic and light pulses from the bubble. The protein bovine serum albumin (BSA) which has been shown to hinder interfacial motion, allowed the bubble to be driven to higher acoustic pressures, and resulted in an increase in the magnitude of the light pulses from the bubble. Images of the sonoluminescing bubble indicate that the collapse remains spherical in the cases presented, and that bubble translation can be correlated with weak acoustic and light emissions.

ISSN:0001-4966    

DOI:10.1121/1.420100

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP