The acoustic scattering by a submerged, elastic spherical shell: The transition from thin to thick shells

Abstract

A fundamentally oriented analysis of the pole structure of the acoustic scattering matrix in the low‐ to high‐frequency region (0⩽ka⩽1000) as a function of mode number, density, and sound speed for several shell thicknesses has been previously presented [J. Acoust. Soc. Am. Suppl. 1 83, S94 (1988); Suppl. 1 84, S185 (1988); Suppl. 1 85, S95 (1989)]. The three most interesting results of this analysis were: (1) Due to fluid loading, the vacuum antisymmetric Lamb mode a0 and the rigid Franz modes “switch tails” to produce a subsonic a0_ mode that resembles the vacuum antisymmetric Lamb mode at low ka and an a0+ mode that resembles a0 at high ka; (2) the mid‐frequency enhancement of a thin shell is associated with this bifurcation of the antisymmetric Lamb wave [J. Acoust. Soc. Am. 85, 114–124 (1989)]; and (3) the existence of strong thickness resonances associated with the existence of regions of negative group velocity for the third antisymmetric Lamb wave on a thin spherical shell. In this presentation, t...