Eric Smith
Preston S. Wilson
John A. Behrens
Thomas G. Muir
Appl. Res. Labs., Univ. of Texas, Austin, TX 78713-8029
Use of seismic interface waves in applications such as buried object detection and echo ranging introduce special transduction needs. Because the spectrum of interface wave excitations can be very complicated, involving modes of different polarizations and speeds, a transducer is required that can select isolated modes as well as isolated frequencies. For applications in unconsolidated sediments, problems of consistency and stability must also be overcome. Experiments with such a transducer have been carried out on a natural hard-sand beach of the Gulf of Mexico. The device is an independently amplitude- and phase-controlled bidirectional oscillator coupled to the sediment. Preliminary results indicate that mode isolation is indeed possible, and also that high degrees of mechanical efficiency and consistency can be achieved in coupling to sediments. [Work supported by the Office of Naval Research.]