Acoustic scattering by a submerged spherical shell: Thickness resonances revisited

In previous meetings [J. Acoust. Soc. Am. Suppl. 1 85, S95 (1989); 86, S4 (1989)], a fundamentally oriented analysis of the acoustic scattering from a spherical shell in the high-frequency region 0 < ka < 1000, based upon the analytic properties of the S matrix in the complex ka plane was presented. This analysis revealed the existence of an anomalously large thickness shear resonance as the single most dominant feature in the scattering from a thin spherical shell. This thickness resonance is associated with a region of negative group velocity near threshold for the plate-wave analog of the first symmetric Lamb wave on a thin spherical shell. In this presentation, results for higher-order modes and the effects of varying the material parameters of the shell on the thickness quasiresonance are presented. Results for a second thickness shear resonance associated with the opening of the fourth symmetric Lamb wave are also presented.