A GENERALIZED NETWORK FORMULATION FOR ACOUSTIC SCATTERING

The discretized Helmholtz and equivalence integral equations yield the impedance representation of a generalized network formulation for aco ustic scattering. Trans- and self-impedances relate the ensonification , the scattered field, and the pressure and velocity on the scatterer' s surface, S; the scatterer's dry impedance loads S. This formulation suggests applying analysis tools from electrical circuit theory: netwo rk element abstraction and change of field-variable basis. The scatter er's wet admittance (impedance) corresponds to the augmented driving p oint admittance (impedance) from electrical network theory. The lower- branch modes of the scattering from a submerged spherical shell occur when the reactance looking into the fluid from S negates that looking into the shell. Change of basis on S transforms the impedance represen tation into the admittance, arbitrary-reference, and network-scatterin g representations. The impedance, admittance, and arbitrary-reference representations naturally separate hard, soft, and intermediate backgr ound scattering, respectively. Scattering from passive objects with li mited vibrational degrees of freedom is bounded: the lower-branch mode s of the submerged spherical shell approach this bound. No bound exist s when the vibrational degrees of freedom are unlimited. (C) 1997 Acou stical Society of America.