Abstract
A prominent feature predicted for the backscattering of tone bursts by thin spherical shells is an enhancement of a guided wave contribution near the first longitudinal resonance. This has been explained with a backward ray model of a leaky Lamb wave where energy is leaked off without having circumnavigated the back side of the shell [P. L. Marston et al., J. Acoust. Soc. Am. 90, 2341 (1991); D. H. Hughes, Ph.D. thesis, Washington State University (1992)]. The relevant s2b Lamb wave has opposing group and phase velocities giving rise to prompt radiation following the direct specular echo. The present research gives a comparison between a ray theory approximation and experiments in which tone bursts having carrier frequencies in the range 595<ka<640 were incident on an empty stainless steel spherical shell in water of radius a=12.7 cm. The sphere’s thickness to radius ratio is 2%. The response generally follows the predicted amplitude which can be close to 4.5 times the specular amplitude. [Work supported by ONR.]
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