ASA 127th Meeting M.I.T. 1994 June 6-10

5aUW10. Influence of the incidence angle on the scattering by a circular cylindrical shell.

Gerard Maze

Fernand Leon

Naum Veksler

Jean Ripoche

Lab. d'Acoust. Ultrason. et d'Electron. LAUE) URA CNRS 1373, Univ. du Havre, Place R. Schuman, 76610 Le Havre, France

The resonance scattering theory (RST) developed by Flax et al. [J. Acoust. Soc. Am. 63, 723--731 (1978)] allows one to explain the structure of the spectra at scattering by a cylindrical shell at normal incidence. The resonances are related to the circumferential waves propagating around the shell. In this presentation, the problem of scattering of an obliquely incident plane acoustic wave by a circular cylindrical shell is considered. The resonance spectra obtained by the MIIR ``in propagation'' show resonance peaks related to the A, S[sub 0], T[sub 0], and T[sub 1] waves. The wide deep dips observed on the reflection spectra are particularly analyzed using the calculation of modal resonance components. These dips are attributed to a wave with modal resonance components having a small Q factor and situated sufficiently near each other with an important overlap. The position of dips depends on the incidence angle. With incidence angles larger than the second critical angle, resonance peaks are clearly observed on the reflection spectra that are related to the A wave and wide dips related to modal resonance components of the second type of the A[sub 0] wave; when the incidence angle increases the central frequency of these dips decreases.