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A pressure-sensitive reference hydrophone for the frequency range 0.3 Hz to 20 kHz at hydrostatic pressure to 10 000 psig and temperature from 5° to 35°C has been developed at the Naval Research Laboratory, Underwater Sound Reference Division. The nominal open-circuit crystal sensitivity of the hydrophone is −85.5±0.5 dB re 1 V/μbar from 1 Hz to 15 kHz; the output of the lithium sulfate sensitive element is increased by a transistorized 10-dB-gain (nominal) preamplifier. A novel cable gland improves the high-pressure reliability of the hydrophone.

This paper presents the design and development of a truly omnidirectional, low-frequency, high-power, underwater sound projector standard. The transducer is operational within the frequency range from 1 Hz to 10 kHz, with a transmitting response which is stable with hydrostatic pressures up to 1524 kPa (152-m depth) and temperatures from 5 to 35°C, and can be used as a hydrophone or a projector. The sensitive element is a 22.9-cm (9.0 in.) o.d. piezoelectric lead zirconate–lead titanate (MIL-STD 1376, Type 1) hollow sphere encapsulated in polyurethane. This transducer, designated the USRD type F80, produces an undistorted omnidirectional source level that is linear with driving voltages up to 1000 V rms, and can also be electrically tuned for a higher response at predetermined, discrete frequencies. This paper includes an electroacoustic equivalent circuit model of the transducer, compares the predicted to the measured transmitting response, and discusses the mechanical and electrical design.

Air bubbles on the surface of a sonar transducer cause disturbances in the calibration response. Several materials have been used at various facilities to cause the air bubbles to release more easily from the transducer surface. This report explains the mechanism of these surface active materials and compares them in terms of surface tension in solution, persistence on a rubber surface, and compatibility with other materials. Also reported are the results of field tests of each of the surface active materials on ten soiled transducers. The best materials proved to be Aerosol OT-100R,a combination of OT-100 and JoyR detergent, and JoyR detergent alone.