NETWORK ANALYSIS OF SCATTERING FROM AN INTERNALLY LOADED SPHERICAL-SHELL - RESONANCE IDENTIFICATION AND FREQUENCY-BY-FREQUENCY LIMITS ON THE SCATTERED FIELD

A generalized network model is used to interpret the scattering from a submerged spherical shell with a two-spring/two-mass internal structu re. In this model, generally available results are used for the fluid/ shell transmission paths, and lumped element methods are used for the internal structure's admittance. This formulation emphasizes the field quantities at the submerged-shell/intenal-structure interface. Of cou rse, the network model has several forms; admittance, impedance, and n etwork scattering are possible (among others). Impedance comparison at the fluid/nominal-shell interface has been previously shown to determ ine high-Q resonances in the scattered response associated with the lo wer-branch spherical-harmonic modes. Admittance comparison at the subm erged-shell/intenal-structure interface shows that the internal struct ure shifts these lower-branch resonances and broadens their peaks. The sawtooth pattern generated by these shifted and broadened resonances distinguishes the form function with internal structure from the form function without. Finally, network scattering variables and a power-fl ow constraint are used to determine frequency-by-frequency bounds on t he possible acoustic scattering for any passive internal point loading . The scattering with the given lossless, two-spring/two-mass internal structure oscillates between the maximum and minimum possible. (C) 19 95 Acoustical Society of America.