ASA 127th Meeting M.I.T. 1994 June 6-10

1pAO12. Design and development of a low-frequency torsional shear wave transducer for ocean sediment applications.

Alan K. Walden

Thomas R. Howarth

James A. Tims

Naval Res. Lab., Underwater Sound Reference Detachment, P.O. Box 568337, Orlando, FL 32856-8337

A new low-frequency torsional shear wave transducer for ocean sediment applications has been developed. The transducer design includes a combination of a lightweight radiating structure and piezoelectric material. The ``spool-shaped'' structure is composed of solid lexan machined in the form of a cylinder centered between two radiating disks. The piezoelectric material, in the form of ceramic ring segments, is electrically configured for the ``1--5'' drive mode and rigidly attached circumferentially along each end of the cylinder. Operation of the transducer as a shear wave transmitter is based on a high torque being applied to the structure by the electromechanical action of the electrically driven piezoelectric ceramics. As the ceramics are excited, a resulting torque is coupled through the structure's disks and radiated into the surrounding medium. The transducer structure is designed to exhibit a torsional resonance at 2 kHz. Based on the reciprocal nature of the piezoelectric ceramic, the transducer can also be employed as a shear wave receiver. Experimental results demonstrate that the transducer is an effective means of transmitting and receiving low-frequency shear waves in sediment. Good control over the acoustic waveform is obtained. Performance is investigated as a function of transmitter--receiver distance.