ASA 126th Meeting Denver 1993 October 4-8

5aSA4. Impulse response for backscattering by a thin spherical shell: Measurement and wave interpretation.

Gregory Kaduchak Christopher S. Kwiatkowski Philip L. Marston

Dept. of Phys., Washington State Univ., Pullman, WA 99164-2814

A broadband sheet source was developed to produce a pressure impulse with a planar wave front containing a wide range of frequency components [C. S. Kwiatkowski et al., to be presented at this meeting]. This source is nearly acoustically transparent and was used for backscattering from an empty stainless steel spherical shell where prominent features in the shell's calculated impulse response are observed over a wide frequency interval. A wideband hydrophone was placed in the far field of the scatterer on the opposite side of the source. Time records reveal a gaussian wave packet associated with the excitation of the subsonic a[sub 0-] wave responsible for a large backscattering enhancement near the coincidence frequency. Superposed on the same records are large contributions from the low frequency excitation of the breathing mode [G. Kaduchak and P. L. Marston, J. Acoust. Soc. Am. 93, 2700--2706 (1993)]. The shell used in the experiment has a thickness to radius ratio of 2% for which the above scattering phenomena occur for frequencies less than 450 kHz. [Work supported by ONR.]