Resonance features in the backscattering cross-sections (BSCS) of an air-filled steel spherical shell submerged in water and insonified by a plane CW (continuous wave) sound wave are analyzed. The concepts of Rayleigh (R), whispering gallery (WG), and Lamb waves in half spaces and plates in vacuo are generalized to curved solid and hollow bodies immersed in fluids. The authors study how each shell-wave manifests itself in the various frequency band of the body's BSCS. They display dispersion plots for the phase velocities of the various waves in widebands, and compare Lamb and R/WG waves as the shell becomes a solid sphere, in order to extract their similarities. It is demonstrated that the fluid-loadings, the shell thickness, and the curvatures of the body generate novel waves in the shell and its BSCS that could not have come from earlier models that ignored these effects.
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