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.