A resonant scattering formalism for a fluid loaded elastic spherical near a planar boundary

Abstract

Free field scattering from stationary fluid loaded elastic targets is well known and understood in terms of free field resonant scattering theory (RST), that it is given by the superposition of resonant and background components, and that the resonant components can be isolated by subtraction of an appropriate background. Backgrounds for isolating free field resonance spectra are well known. However, RST for scattering from a fluid loaded elastic target near a planar boundary where target scattering is accompanied by target-boundary scattering is less well known. A T-matrix formalism for plane wave scattering from rigid and soft spheres near a planar penetrable boundary is generalized to include a fluid loaded elastic spherical shell and RST is used to replace the free field T-matrix for the elastic shell that occurs within the formalism. It is shown that target-boundary scattering couples resonant and background components, couples modal resonances, and produces super-resonances. A background is introduced and it is shown that while background scattering is suppressed, coupled background and resonant scattering is not. Numerical results demonstrate some of the effects of target boundary scattering on the free field resonant spectrum of the shell as well as the dependence of target-boundary scattering on target.