Patrick J. Evans
AT&T Bell Lab., Rm 15G-322, 67 Whippany Rd., P.O. Box 903, Whippany, NJ 07981-0903
J. Hal Jerman
IC Sensors, Inc.
A packaged hydrophone based on silicon micromachining technology has been developed. The device is a pressure-balanced, variable-gap capacitor that features a corrugated, bossed, movable diaphragm and a novel, vented backplate design with a pattern of channels to limit viscous resistance. The device is designed for better-than-ambient-limited signal-to-noise performance well down into the infrasonic band (5 Hz) and for reasonably flat frequency response to 1 kHz. The device can be packaged in 3 cm[sup 3], including a reservoir for the compliant, pressure-balancing fluid and preamplifier electronics. Due to the pressure-balancing feature, the device survives and retains sensitivity, within several dB, down to the deepest ocean depths. Design criteria include low-cost manufacturability. This paper discuses the theory of device operation, design rationale, and techniques used in piece-part fabrication. Comparisons between design predictions and laboratory measurements of several performance parameters are made. Last, opportunities for design improvements based both upon these measurements and upon theoretical considerations are discussed, for example ac biasing for super-sensitive transducers, useful in short dipoles and other applications. [The research reported here was sponsored by the Naval Air Warfare Center, (NAWC), Aircraft Division, Warminister, PA, under Contract No. 62269-90-C-0526.]