INHERENT BACKGROUND COEFFICIENTS FOR ACOUSTIC-RESONANCE SCATTERING FROM SUBMERGED, MULTILAYERED, CYLINDRICAL STRUCTURES

For the scattering of acoustic waves by an elastic shell, the acoustic al background coefficients are inherent in the scattering coefficients . The background coefficients for elastic empty shells, named the inhe rent background, can be obtained from the zero frequency limit of the modal accelerance in the scattering coefficients for analogous liquid shells, In this work, the concept of obtaining the inherent background is applied to multilayered elastic cylindrical structures. The inhere nt background manifests itself in the sound scattering by the liquid s tructures. The scattering S-function and the modal accelerance for the liquid system an determined by considering the incoming and outgoing waves, The accelerance of liquid layers is generalized so that the sca ttering function can be obtained by the recurrence relation for the ac celerances of the adjacent liquid layers. From the zero frequency limi t of the generalized accelerance of liquid structures, the constant mo dal accelerance is extracted and the general expression for the inhere nt background coefficients is obtained. The background coefficients de pend on the densities of the layers and ambient fluid medium, the rela tive thickness of each layer, and the normal mode number. The acoustic al background coefficients for solid cylinders, empty shells,fluid-fil led shells, and double-layered shells can be obtained by the appropria te limit of the density ratio and the relative thickness of layers in the generalized inherent background coefficients. The usefulness of th e proposed background is demonstrated for several examples of layered structures. (C) 1998 Acoustical Society of America. [S0001-4966(98)033 02-5].