Resonant acoustic scattering from elastic cylindrical shells

Abstract

The normal mode solution of the scattered pressure due to a normally incident plane acoustic wave on an infinitely long, air-filled aluminum cylindrical shell in water is analyzed. Our study yields a physical interpretation of normal mode contributions to the backscattering function. The modes in the near-soft (thin-shell) region are compared to theoretical predictions and empirical observations. Transitions from Rayleigh-type surface waves to Lamb-type waves are found to take place for thin shells. A smooth transition of the first transverse wave on a thick shell to that of the first symmetric Lamb wave on a thin shell is shown to occur, and the inception of these thin-wall modes is investigated as a function of shell thickness. Also, the antisymmetric Lamb mode is shown to exist and its intermittent nature is examined.