Abstract
Previous experiments and analysis have shown that the backscattering from thick-walled finite cylindrical shells can be significantly enhanced in and above the coincidence frequency region over a large range of angles of the incident sound [S. F. Morse et al., J. Acoust. Soc. Am. 103, 785–794 (1998)]. In this presentation, impulse backscattering measurements performed with a wide bandwidth PVDF sheet source are analyzed in terms of a simple joint time-frequency representation. When plotted for a sequence of specific tilt angles, it is possible to identify and then observe the progression of individual ray contributions as the coupling conditions to the shell are changed. In the frequency range investigated, where ka<45 and kh<3.4, several of the surface waves excited are highly dispersive and as a result are launched on the shell over a wide range of frequencies and tilt angles, including end-on incidence. The analysis described also confirms various features of the responsible scattering mechanisms predicted by ray theory. The results show the importance of time-frequency analysis to the identification of back scattering in a situation where no exact reference solution is available. [Work supported by the Office of Naval Research.] a)Currently with Naval Research Laboratory, Code 7136, 4555 Overlook Ave. SW, Washington, DC 20375.
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