Ultra-wide bandwidth backscattering measurements using a transparent flat PVDF sheet source

Abstract

A thin extended flat PVDF film surrounded by water is demonstrated to be suitable for exploring scattering responses of complicated targets over a range of frequencies from below 2 kHz to 1000 kHz. The target lies close to the source, and in the configuration normally used, the scattering passes through the source to a distant hydrophone. While initial experiments [Kaduchak et al., J. Acoust. Soc. Am. 97, 2644–2708 (1995)] explored the resonances of spherical shells for which analytical solutions are known, recent experiments have explored novel features in the responses of truncated tilted cylinders that are either hollow [Morse et al., J. Acoust. Soc. Am. 103, 785–794 (1998)] or solid [K. Gipson, Ph.D. thesis, Washington State Univ. (1998)]. The spectrum radiated by the sheet can be altered by using voltage-step, voltage-pulse, or weighted chirp excitations. An equivalent circuit model is useful for describing the radiated spectrum. Crisp tone bursts have also been produced and used to study the low-frequency resonances of a steel shell in Lake Union (Seattle). [Work supported in part by the Office of Naval Research and by APL.]