ASA 129th Meeting - Washington, DC - 1995 May 30 .. Jun 06

1aPA6. Resonant behavior of two eclipsed shells: Quasiharmonic study.

P. Pareige

Elm. Kheddioui

J. M. Conoir

J. L. Izbicki

Lab. d'Acoust. Ultrason. et d'Electron., U.R.A. C.N.R.S. 1373, Univ. du Havre, place Robert Schuman, 76 610 Le Havre, France

The purpose of this paper is the presentation of temporal, frequential, and angular experimental studies of the acoustic scattering by two identical air-filled elastic shells immersed in water. They are insonified by a quasiharmonic wave at normal incidence. The distance between the shells is about 1 to 3 diameters of one shell. The frequency range investigated corresponds to the whispering gallery wave resonances (l=2). The configuration considered is the eclipsed one: Emitter and shells are on the same axis. The complex structure of the backscattered temporal signal is analyzed and theoretically justified. According to the part of the temporal signal considered, different backscattering spectra are obtained and analyzed. The results are discussed in term of acoustic rays involving internal and external acoustic waves. In addition, a phenomenon of acoustic interference is clearly shown. At the resonance frequencies of one shell, the angular diagram shapes are justified and compared to those provided by an analytic model. In all cases, the results are compared to the well-known results provided by the study of a single shell.