Response of a spherical shell to incident sound in water at high frequency.

Continuum-theory computations show that, for high-frequency continuous-wave excitation, the elastic waves in the shell structure separate into surface waves at the inner and outer surfaces of the shell, particularly at the back of the shell away from the incident sound. The computations also show how the elastic waves depart from consistency with thin-shell theory, at low to intermediate frequencies, as frequency increases. At high frequencies, the principal reaction occurs at the front of the shell closest to the sound source. Further exploration of high-frequency behavior is needed, particularly as it relates to ray theory. It is necessary also to relate the elastic waves in the structure to the scattered sound field, especially through use of resonance scattering theory.