Observation of the midfrequency enhancement of tone bursts backscattered by a thin spherical shell in water near the coincidence frequency

Abstract

A prominent feature predicted for the backscattering of tone bursts by thin spherical shells is an enhancement of a guided wave contribution in the midfrequency range [L. G. Zhang et al., J. Acoust. Soc. Am. 91, 1862–1874 (1992)]. This feature may be useful for certain inverse problems and is associated with a strongly coupled slightly subsonic wave denoted by some authors as the a0− wave. The present research gives a comparison between a ray approximation and experiments in which tone bursts having carrier frequencies in the range 35