ASA 126th Meeting Denver 1993 October 4-8

4aEA3. Broadband impulse transducer for measurement of backscattering by objects in water.

Christopher S. Kwiatkowski Gregory Kaduchak Philip L. Marston

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

A broadband impulse pressure transducer was developed using a 15x15 cm sheet of PVDF in water. Both sides of the sheet were in contact with the water and subsequently larger sheets were used. A planar transient wavefront was achieved by applying a step voltage across the sheet. Prior to the arrival of waves from the edge of the sheet, the radiated wave was nearly unipolar and impulsive for frequencies up to 1 MHz. The transducer is useful for measuring the backscattering or reflected impulse response of objects in water because the backscattered or reflected wave is nearly completely transmitted through the sheet. Thus a small broadband receiver can be placed behind the sheet transducer. The transmission was demonstrated by measuring the impulse reflected by a plate and the transducer was used to measure the short-term impulse response by an elastic shell. After a sufficiently long time, the received impulse response is contaminated by edge contributions. [Work supported by ONR.]