Lab. d'Acoust. Ultrason. et d'Electron. LAUE) URA CNRS 1373, Univ. du Havre, Place R. Schuman, 76610 Le Havre, France
The observation of the guided waves p=1 and p=2 from an isotropic elastic hollow cylindrical shell of infinite length excited by an obliquely incident plane acoustic wave is investigated. The use of ``classic'' MIIR (method of isolation and identification of resonances) is limited because of the refraction effect of the surface wave: The state of stationarity generated at a resonance frequency occurs out of the insonified area of the cylindrical shell. This problem has been solved by a new method called MIIR ``in propagation.'' Then, an isolation and an identification are possible in a large range of incidence, contrary to the configuration of transducers according to Snell--Descartes' law (``classic'' MIIR). The resonances of the guided wave p=1 can be detected in a broad range of incidence angle. Contrary to the guided wave p=1, the experimental results achieved with incidence angles varying between 0(degrees) and the second critical angle show a particular evolution of the resonance frequencies of the guided wave p=2. The analysis of the theoretical width (Gamma) justifies the presence or the absence of resonances generated at an incident angle.