摘要:

Abstract not available.

ISSN:0001-4966    

DOI:10.1121/1.421140

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

Abstract not available.

ISSN:0001-4966    

DOI:10.1121/1.421144

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.421147

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

The purpose of these acoustical patent reviews is to provide enough information for a Journal reader to decide whether to seek more information from the patent itself. Any opinions expressed here are those of the reviewers as individuals and are not legal opinions. Printed copies of United States Patents may be ordered at $3.00 each from the Commissioner of Patents and Trademarks, Washington, DC 20231. Patents are available via the Internet athttp://www.uspto.gov.

ISSN:0001-4966    

DOI:10.1121/1.423117

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

Ultrasonic waves reflected from the front and back surfaces of a thin layer are often not separated in the time domain, and interfere. The spectrum of the resulting interference signal depends on (a) the thickness of the layer and the elastic moduli and density of the layer and the surrounding material (substrates), and (b) properties of the layer/substrate interface which can be described in terms of the interfacial stiffness. In this paper the effect of interfacial stiffness is isolated by considering the ultrasonic wave interaction with a solid layer compressed between two substrates of the same material. Since the layer and the substrate have identical properties the effect of impedance difference on the layer reflection vanishes. An aluminum system is selected for the experiment; the contacting surfaces are roughened and varying pressure is applied to model imperfect interface changes. It is shown both theoretically and experimentally that the contact pressure increase results in increase of the interfacial stiffness and spectral minima shift to higher frequency. A simple analytical expression relating the reflection minimum position to the interfacial stiffness is derived and shows good agreement with experimental results. It is shown that in the high-interfacial-stiffness limit the resonance minima positions are given by the conditionh=λ/4+nλ/2,n=0,1,2,… .In the limit of low interfacial stiffness the first minimum shifts to zero and higher order resonances are given byh=nλ/2.Since the resonance minima measurements can be done with high precision it is proposed to use the frequency minimum shift for determination of interfacial stiffness and, consequently, the quality of the interfacial contact.

ISSN:0001-4966    

DOI:10.1121/1.423235

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

The mandate of ASA Working Group S12/WG11 has been to develop “laboratory and/or field procedure(s) that yield useful estimates of field performance” of hearing protection devices (HPDs). A real-ear attenuation at threshold procedure was selected, devised, tested via an interlaboratory study, and incorporated into a draft standard that was approved in 1997 [J. D. Royster et al., “Development of a new standard laboratory protocol for estimating the field attenuation of hearing protection devices. Part I. Research of Working Group 11, Accredited Standards Committee S12, Noise,” J. Acoust. Soc. Am.99, 1506–1526 (1996); ANSI S12.6-1997, “American National Standard Methods for Measuring Real-Ear Attenuation of Hearing Protectors” (American National Standards Institute, New York, 1997)]. The real-world estimation procedure utilizes a subject-fit methodology with listeners who are audiometrically proficient, but inexperienced in the use of HPDs. A key factor in the decision to utilize the subject-fit method was an evaluation of the representativeness of the laboratory datavis-à-visattenuation values achieved by workers in practice. Twenty-two field studies were reviewed to develop a data base for comparison purposes. Results indicated that laboratory subject-fit attenuation values were typically equivalent to or greater than the field attenuation values, and yielded a better estimate of those values than did experimenter-fit or experimenter-supervised fit types of results. Recent data which are discussed in the paper, but which were not available at the time of the original analyses, confirm the findings.

ISSN:0001-4966    

DOI:10.1121/1.423236

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

It is shown that the known solution of the acoustic scattering problem on a supported elastic plate, described by the Timoshenko model, should be corrected. The general formulation of the contact conditions that imply the reciprocity principle is given. Sommerfeld’s formula and the “optical” theorem for the model are formulated. They lead to the uniqueness of the solution. The numerical comparison of the effective cross section of scattering from supported elastic plate described by the Kirchhoff and by the Timoshenko models is presented.

ISSN:0001-4966    

DOI:10.1121/1.421195

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

It was shown by Purcell [J. Acoust. Soc. Am.100, 2919–2936 (1996)] that the Rayleigh equations in the Fourier domain for the reflection coefficients for scattering of a plane wave from a pressure-release sinusoid are valid if the maximum slope of the sinusoidKd<0.6627.This current work finds the corresponding constraint sufficient for the validity of Rayleigh’s equations for a more general periodic surface consisting of a finite sum of sinusoids. The mathematical basis of the derivation of the Rayleigh equations from the Helmholtz integral formula is a Fourier series given by Oberhettinger. Unlike the single sinusoid case developed by Purcell (referenced above), the analysis of the general periodic surface given here requires an analytic continuation argument. In addition, a set of (infinite linear) equations of the “second kind” is derived for the reflection coefficients for the general periodic surface. This guarantees that the truncation solutions for the reflection coefficients converge and are unique. The matrix elements involved in these equations of the second kind require the numerical evaluation of a finite integral (a generalization of Bessel’s integral for the integer index Bessel functions) and all calculations required can be performed by desktop computing.

ISSN:0001-4966    

DOI:10.1121/1.421237

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

The dispersion equation for Love wave propagation in a layer lying over a half-space is derived. Both media are assumed to be transversely isotropic fluid-saturated poroelastic solids with principal axes perpendicular to the surface. The analysis is based on the Biot’s theory. The dissipation due to fluid viscosity is considered and therefore the dispersion equation is complex and intractable analytically. An iterative procedure is developed to solve this equation. Two situations are discussed in detail: (i) an elastic layer overlying a poroelastic half-space and (ii) a poroelastic layer lying over an elastic half-space. Dispersion curves and attenuation curves of Love waves are plotted for these two cases. In addition, the upper and lower bounds of Love wave speeds are also explored.

ISSN:0001-4966    

DOI:10.1121/1.421196

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

This paper presents a numerical program for the simulation of elastic wave propagation and scattering in three-dimensional (3-D) cylindrical coordinates based on the first-order velocity-stress finite-difference scheme on staggered grids. Both Liao’s and Lindman’s absorbing boundary conditions are implemented for the exterior boundaries to efficiently truncate the computation domain for elongated 3-D well logging problems. Symmetric and anti-symmetric boundaries in azimuthal and axial directions are also implemented in the code to further reduce the size of the problem. Included for the first time with this code are very large and complex geometrical structures such as the whole slotted sleeve housing of a sonic well-logging tool which typically involves hundreds of millions of unknowns. The calculation for such a large problem only takes a couple of days on a four-processor SGI Power Challenge machine. Different types of slotted sleeve models are studied for sonic logging tools. Simulation results show that different slotted sleeves vary widely in delaying and attenuating the pipe waves which travel along the tool housing. A new slotted sleeve structure with three horizontal slot sections for every vertical slot period is proposed for better performance. A dipole source is found to produce much cleaner waveforms than a monopole source.

ISSN:0001-4966    

DOI:10.1121/1.421230

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP