摘要:

Analytical expressions are derived for the acoustic resonance frequency shifts in a hard‐walled spherical cavity, caused by the introduction of an eccentric small inner sphere. A straight‐forward and simple approach is employed to obtain a first‐order perturbation of the cavity wave function and the corresponding resonant frequency shift. The results are useful in a variety of problems connected with acoustic levitation and with excitation or probing of resonant cavities. Graphical results for some of the lower‐order resonant frequencies are given for various values of the parameters.

ISSN:0001-4966    

DOI:10.1121/1.402018

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

In the application of acoustic intensity method to study the acoustical field of a source, the interference due to a secondary source or a reflecting boundary becomes important. This study deals with the formulations of interference of acoustical pressure and intensity fields of two simple sources. The intensity interference is investigated in terms of both radial and transverse components. The predicted pressure‐intensity interference by the formulations agrees well with measurements carried out in an anechoic chamber.

ISSN:0001-4966    

DOI:10.1121/1.402019

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

The translational addition theorems for spherical wave functions are used to develop solutions for nonaxisymmetric acoustic field problems involving nonconcentric spherical boundaries. The forms of the addition theorems are discussed along with their use for translating modal expansions of spherical wave functions centered on one origin to another. In a typical problem involving a number of arbitrarily positioned spherical sources within a spherical‐shaped region, an infinite set of equations for the modal expansion coefficients is developed. This set must be truncated and then solved numerically. Assuming lossless media, comparison of the near‐field and far‐field‐radiated acoustic power provides a test of the accuracy of the numerical results. Other quantities of interest such as the radiation impedance of each source, including the mutual effects of all the other sources, and directivity patterns can be readily computed once a sufficient number of modal coefficients have been computed. In a companion paper [S. A. Lease and W. Thompson, Jr., J. Acoust. Soc. Am.90, xxx–xxx (1991)] numerical results are presented for the specific case of two identical monopole sources within a fluid sphere that is embedded in another infinite fluid medium.

ISSN:0001-4966    

DOI:10.1121/1.402020

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

The general analysis of nonaxisymmetric acoustic radiation in a spherical coordinate system, contained in a companion paper [S. A. Lease and W. Thompson, Jr., J. Acoust. Soc. Am.90, xxx–xxx (1991)], is specialized to the case of two, identical, in‐phase monopole sources similarly positioned within a fluid sphere. This special case allows the truncated system of equations to be reduced to a set involving (N+1)2unknowns. Special considerations in the development of afortranprogram to solve the system of equations are discussed. Numerical results for the radiated acoustic power, directivity patterns, and source radiation impedance for this specific case can be calculated by the program. Some numerical results are presented for a few specific choices of the many physical parameters that characterize the problem. The performance of the program for the various choices of physical parameters is discussed.

ISSN:0001-4966    

DOI:10.1121/1.402021

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

A regular integral equation based on the surface source distribution method is developed to solve the exterior acoustic radiation and scattering problems. This integral equation, formed by seeking the equivalent mixed‐layer potential distributed over an auxiliary surface retracted from the actual boundary, is uniquely solvable and has nonsingular kernel function. Hence, it is more amenable to numerical implementation and can circumvent the difficulties of singularity, nonuniqueness, and slope discontinuity of the conventional integral equation formulations. In contrast to the behavior of Fredholm integral equations of the second kind, the discretization of a regular integral equation will not result in a diagonally dominant coefficient matrix. To overcome the undesirable numerical instability, the optimal selection of the interior source surface is investigated through error estimate of the numerical integration. The versatility and accuracy of the proposed formulation are demonstrated by numerical examples involving spheres, prolate spheroids, and finite cylinders.

ISSN:0001-4966    

DOI:10.1121/1.402022

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

In addition to the classical fundamental thickness mode, multiple echoes of Lamb waves have been observed on pulsed circular piezoelectric transducers, by using an optical heterodyne interferometer. With an efficient resonance spectrum technique, the group velocities of the Lamb waves are deduced quantitatively. The radiation of these waves into liquids (usually water), which create so called ‘‘head waves’’ and are not predicted by the piston model, were detected by a hydrophone. Comparison between the optical and hydrophone probe measurements demonstrates a good agreement.

ISSN:0001-4966    

DOI:10.1121/1.402023

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

A previous article [Moffettetal., J. Acoust. Soc. Am.89, 1448–1455 (1991)], comparing the radiated‐power limitations of Terfenol‐D and PZT‐4, is revisited. When the power at resonance is stress‐limited (as is the case for high mechanical quality factorQ), the maximum allowable stress amplitudeTmaxis the compressive prestress value, so that tension in the Terfenol‐D is avoided. When this value is chosen forTmax, rather than the smallerTmax’s of the previous article, Terfenol‐D is shown to be superior to PZT‐4 in power capability at all values of the quality factorQ.

ISSN:0001-4966    

DOI:10.1121/1.402024

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

A previous discussion [J. Acoust. Soc. Am.85, 1560–1568 (1989)] on the energy band structure of target materials, suitable for generation of ultrashort optoacoustic pulses by photostriction, is extended and formalized. Details of the band structure necessary to suppress thermalization by holes are included. It is pointed out that the material should exhibit suitable gaps between valence bandsinadditiontohaving suitable gaps between conduction bands. The conditions that must be satisfied in order to prevent thermalization by electronsaswellasholes, a key feature necessary in the production of ultrashort pulses, are formalized. Some examples of materials approaching an ‘‘ideal’’ band structure are given.

ISSN:0001-4966    

DOI:10.1121/1.402025

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

The effect of compliant walls on the properties of a Helmholtz resonator is examined. The effective stiffness of the resonator is decreased by the wall compliance, while the effective mass is unchanged to leading order. The radiation resistance is also decreased due to a cancellation between the radiation from the cavity opening and the radiation from the cavity walls. This leads to a reduction in the cross section at resonance by the factor [Zs/(Zs+Z0f)]4, whereZsis the wall impedance andZ0fis the total fluid loading on the breathing mode of the cavity.

ISSN:0001-4966    

DOI:10.1121/1.402026

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.402388

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP