摘要:

Otoacoustic emissions measured in the external ear canal describe responses that the cochlea generates in the form of acoustic energy. For the convenience of discussing their principal features, emitted responses can be classified into several categories according to the type of stimulation used to evoke them. On this basis, four distinct but interrelated classes can be distinguished including spontaneous, transiently evoked, stimulus-frequency, and distortion-product otoacoustic emissions. The present review details the findings that have been described for each emission type according to this classification schema. Additionally, the known features of emitted responses are discussed for both normally hearing and hearing-impaired humans and experimental animals, and with respect to their potential clinical applications. The findings reviewed here clearly indicate that future studies of otoacoustic emissions will significantly increase our understanding of the basic mechanisms of cochlear function while, at the same time, provide a new and important clinical tool.

ISSN:0001-4966    

DOI:10.1121/1.400897

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

Using the chirpztransform, a numerically efficient adaptive integration algorithm for fast-field programs has been developed. The fast-field program (FFP) is a numerically efficient algorithm for computation of the sound pressure due to a time harmonic point source above a general boundary in a layered medium. The new algorithm allows the user to specify the precise location of the range sample points, or “detectors,” independent of the horizontal wave-number sampling grid. This feature makes the algorithm particularly attractive for use in applications where sampling on a predetermined spatial is required. An example of such an application is the computation of the acoustic frequency response as a function of range. In this case the complex sound pressure must be computed at many frequencies while maintaining a constant range sampling interval. In addition, the algorithm can be used to recompute the sound pressure field with different range resolutions without recomputing the horizontal wave-number spectrum samples. It is also shown that the algorithm can be used to adaptively increase the number of integration points required to evaluate the Sommerfeld integral that results from the FFP type of formulation.

ISSN:0001-4966    

DOI:10.1121/1.400896

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

Magnetoacoustic waves are considered as a system. Bose–Einstein statistics are applied to find the equation of state and thermodynamic quantities of the system. It is found that energy and pressure of the system are directly proportional to the cube of absolute temperature. Adiabatic changes of the system are also discussed.

ISSN:0001-4966    

DOI:10.1121/1.400898

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

Acoustic diffraction from a line impulse by an absorbing half plane in the presence of a moving fluid is considered. The field is calculated using spatial and temporal Fourier transforms. The results for a finite pulse are also presented. The physical interpretation of the results is then discussed.

ISSN:0001-4966    

DOI:10.1121/1.400899

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

A technique is presented which has been developed for calculating fields in two-phase mixtures when the material properties of the two phases are very dissimilar. A pair of coupled integral equations are derived and then solved together using an alternating recursion. This gives rise to a pair of coupled perturbation series (corresponding to the field point being in one or the other of the two phases). Truncations of the series then lead to descriptions of the solution fields which are valid in the regime of very small (but not necessarily zero) material property ratios. The specific problem of acoustic-wave fields due to a point source in a two-fluid mixture is treated in full and serves to illustrate the procedure. The results are applied to the case of plane-wave interaction with a flat plane interface, where it is shown that the perturbation series do indeed produce expansions of the exact solutions.

ISSN:0001-4966    

DOI:10.1121/1.400900

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

This paper highlights the radically different wavelength dependences of the ratio of scattering to geometric cross section for stiffness-, resistance-, and mass-controlled scatterers characterized by their bulk modulus and structural damping. The relation between solutions formulated by various authors, notably between Rayleigh’s and Lamb’s mutually exclusive results, is explored. Finally, the generalized Rayleigh scattering solution is illustrated for a cavity in a viscoelastic matrix.

ISSN:0001-4966    

DOI:10.1121/1.400901

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

This article presents a fundamentally oriented analysis of the complex-kaplane pole structure of theSmatrix for spherical shells in the thickness range0.02a⩽h⩽0.10a(ais the outer radius of the sphere) for the high-frequency region (100

ISSN:0001-4966    

DOI:10.1121/1.400902

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

A modification of the physical optics surface source density based on the Lynch variational approach is proposed for the case of scattering by one-dimensional pressure-release Gaussian random rough surfaces. Rather than the local radius of curvature, it involves the surface correlation length and introduces new criteria validating the physical optics evaluation of the coherent and incoherent scattering intensities. Closed expressions for the coherent reflection coefficient and the incoherent scattering cross section are derived without resorting to high-frequency approximation techniques. Numerical data based on these expressions and conventional geometrical optics shadowing theory are presented and shown to be in very good agreement with recently published exact Monte Carlo simulation results.

ISSN:0001-4966    

DOI:10.1121/1.400903

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

Lateral-wave representation of forced acoustic oscillations in a homogeneous gas contained within a perfectly rigid cavity are compared for two cases that differ only by the presence in one case of a rigid inner core in addition to the rigid outer shell of the cavity. The two representations exhibit increasingly similar laterally propagating modes as the core of the one case is made smaller relative to the wavelength of the oscillation, although significant differences persits near the mode cutoffs. When the core is present, the propagating modes are accompanied by a discrete spectrum of evanescent lateral modes. The evanescent modes become increasingly dense as the size of the core is reduced, to be replaced entirely by a continuous evanescent spectrum in the absence of the core. This continuous spectrum, which is shown in the present instance not always to be negligible, arises mathematically in a manner similar to the “background” continuum found in lateral-wave decompositions of the scatter of acoustic waves from penetrable cylinders and spheres.

ISSN:0001-4966    

DOI:10.1121/1.400904

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

This paper describes a method used to analyze and synthesize acoustsic plane-wave matching structures between a transducer and a medium of arbitrary characteristic impedance. The analysis is applicable to multilayer structures with periodic discontinuities in characteristic impedance. It is shown that the frequency response of such structures is approximately equal to the discrete Fourier transform of the individual layer reflection coefficients. The synthesis procedure uses the inverse discrete time Fourier transform to generate a sequence of layer reflection coefficients, and applies a boundary condition to calculate the characteristic impedances. Using this method, wide bandwidth matching structures can be obtained using finite impulse response (FIR) filter topologies as a model. A numerical example is presented to show how the procedure is implemented, and a linear analysis is performed which models the layers of the synthesized structure as ideal transmission lines. The results of the analysis are in good agreement with the response predicted by the Fourier method.

ISSN:0001-4966    

DOI:10.1121/1.400905

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP