HIGH-FREQUENCY SCATTERING BY SHELLS

The scattering of a normally incident plane acoustic wave by a circula r cylindrical elastic shell is considered. In the complex wave number plane, the trajectories of the characteristic equation roots correspon ding to the circumferential waves l = 0 and l = 1 are studied as funct ions of frequency and relative shell thickness. Attention is focused o n the high frequency range, for which a transition from shell to solid cylinder occurs. The waves l = 0 and l = 1 reach asymptotically the c haracteristics of the Stoneley and the Rayleigh wave respectively on a solid cylinder. In addition, it is found that, for a constant and sma ll value of frequency and a very thin shell, the l = 1 wave properties tend towards those of the first Franz wave on a soft cylinder. The pe netration depths of both the Rayleigh and Stoneley waves inside the so lid cylinder are evaluated as functions of frequency.