1pSA5. High-frequency backscattering enhancements for thick truncated cylindrical shells in water at oblique incidence.

Session: Monday Afternoon, June 16

Author: Scot F. Morse
Location: Phys. Dept., Washington State Univ., Pullman, WA 99164-2814
Author: Philip L. Marston
Location: Phys. Dept., Washington State Univ., Pullman, WA 99164-2814
Author: Gregory Kaduchak
Location: Univ. of Texas, Austin, TX 78713-8029


Various authors have shown that the backscattering by a finite thin cylindrical shell at oblique incidence is enhanced when resonance conditions are met for the propagation of a leaky wave on the shell [see, e.g., M. L. Rumerman, J. Acoust. Soc. Am. 93, 55--65 (1993)]. To explore the backscattering enhancements relevant to high-frequency detection, impulse response measurements were carried out for slender thick cylindrical shells using a broad bandwidth PVDF sheet source, for tilt angles ranging from broadside to end-on incidence. These measurements reveal large backscattering enhancements beyond the shear wave cutoff angle, which extend to near end-on incidence in the coincidence frequency region. A simple approximation for the phase velocities of several surface waves is used to identify the underlying mechanisms. A broad enhancement feature is shown to result from the axial propagation of the supersonic a[inf 0] leaky Lamb wave. The associated meridional ray radiates a backward directed wavefront having a vanishing Gaussian curvature. Also observable are what appear to be resonance loci associated with the helical propagation of the subsonic a[inf 0-]. [Work sponsored in part by the Office of Naval Research and by the ARL:UT Independent Research and Development Program.]

ASA 133rd meeting - Penn State, June 1997