Volume 116, Issue 4, October 2004
Index of content:
- GENERAL LINEAR ACOUSTICS 
116(2004); http://dx.doi.org/10.1121/1.1786293View Description Hide Description
Reciprocity, energy conservation, and time-reversal invariance are three general properties of the wave fields that imply algebraic scattering matrix properties. In this paper, these scattering matrix properties are established for waveguides when evanescent modes are taken into account. The situations correspond to guided acoustic pressurewaves in fluids and Lamb waves in solids treated with the same formalism. The relations between the three properties verified by the scattering matrix are then discussed, and it is found that, as soon as two properties are verified, the third is also verified.
116(2004); http://dx.doi.org/10.1121/1.1788733View Description Hide Description
In the present paper we are concerned with sound propagation and attenuation in two- or three-dimensional lined bends. First it is shown that the effect of locally reacting absorbing materials at the walls of a waveguide can easily be taken into account in the multimodal formulation proposed in earlier papers by the authors, and, for bends, algebraic solutions are carried out for the acoustic field and scatteringproperties. Then a study of the soundattenuation in lined bends is given using the multimodal formulation and the properties of such waveguides are shown and discussed, in particular, the presence of a plateau of attenuation at high frequencies and a whispering gallery effect that occurs in bends.
116(2004); http://dx.doi.org/10.1121/1.1778840View Description Hide Description
The directivity of acoustic radiation from a rectangular piston arbitrarily located on a rigid prolate spheroidal baffle is formulated. The piston is assumed to vibrate with uniform normal velocity and the solution is expressed in terms of a modal series representation in spheroidal eigenfunctions. The prolate spheroidal wave functions are obtained using computer programs that have been recently developed to provide accurate values of the wave functions at high frequencies. Results are presented in the form of far-field polar directivity patterns for various piston/spheroid acoustic sizes, piston locations on the spheroid, and spheroidal shapes.