Underwater flat-panel transducer arrays

Abstract

Flat-panel arrays less than 3 mm thick have been constructed from miniature flextensional transducers (cymbals) and from small hollow sphere transducers (BBs) embedded in polymer matrices. Both are intended for large area, volume restricted applications. Transmit voltage response (TVR) and free field voltage sensitivity (FFVS) measurements are reported on these structures along with some design variants. The basic cymbal transducer is a small class V flextensional transducer consisting of a PZT disk and two shaped metal caps which act as motion amplifiers. Originally designed as actuators and hydrophones, they are now being developed as shallow water sound projectors and receivers. Their low cost and thin profile allow the cymbal transducers to be assembled into large flexible flat-panel arrays. We have modeled and tested a number of modified cymbals and cymbal arrays. Mini-cymbals and maxi-cymbals ranging in diameter from 3 to 30 mm have extended the frequency range to 1-100 kHz. Cymbal arrays incorporating 10 to 100 transducers have given excellent results as underwater projectors and receivers in the 10-40 kHz range. BB hollow sphere arrays work best at higher frequencies near the breathing mode resonance, generally above 100 kHz. Millimeter size hollow spheres are produced using a coaxial nozzle slurry process and by a sacrificial core coating process in sizes ranging from 1-10 mm in diameter and 10-200 /spl mu/m in wall thickness. Two poling configurations have been studied: radial poling with inside and outside electrodes, and tangential poling with top and bottom outside electrodes. The principal modes of vibration are the breathing mode (100-800 kHz) and the wall thickness vibration (10-100 MHz). BBs are now used as miniature hydrophones and are being developed as high frequency biomedical transducers and as multi-element arrays.