A micro-machined piezoelectric hydrophone with hydrostatically balanced air backing

A micro-machined hydrophone with a unimorphic piezoelectric membrane was developed. To enhance its applicability to SONAR, air backing was adopted for improved sensitivity in the low frequency range, and a hydrostatic pressure balancer was added for increased resistance to ambient pressure. The sensing component is a unimorph composed of a silicon membrane and a thin piezoelectric layer. The design takes into account the advantages of air backing and the effects of size, and the hydrostatic pressure balancer was devised to permit the correct flow of ambient liquid into the air space while in the initial state, resulting in pressurized air at the backside of the membrane when the ambient pressure rises. The hydrophone was fabricated by micromachining and was tested for overall performance and integrity under high pressure. The results of the testing suggest that this device could be used to detect underwater sounds in various applications.