A small, standard, lithium sulfate hydrophone has been calibrated by a reciprocity-coupler method in the frequency range 20 cps-3 kc/sec and at hydrostatic pressures from 0–16 000 psi. The sensitivity of the hydrophone is stable to within ±0.3 dB in this pressure range.
A new calibration standard hydrophone for use in the frequency range 5 cps to 150 kc is described. The active element is a lithium sulfate crystal on a tungsten backing plate. The free-field voltage sensitivity (end-of-cable) is −90±3 db re 1 v per μbar throughout most of the frequency range. The sensitivity is little affected by temperature changes in the range 1° to 25°C, and is not affected by hydrostatic pressure changes in the range 0 to 1000 psig. Directivity patterns are very nearly those to be expected from a 1-in. piston.
A piston-type resonant element for use in underwater sound-transducer arrays is described. The acoustic loading on the piston is varied by the use of a shallow cavity. The element is stable under high hydrostatic pressure, and its efficiency is higher than 90% over a broad bandwidth. An equivalent circuit that successfully reproduces the measured characteristics of the transducer is developed.
The bubble transducer consists of a conventional low-impedance electrodynamic driver with an air-filled rubber membrane, or "bubble," of adjustable volume over the diaphragm. The system at resonance produces large volume displacement of the water with small linear diaphragm displacement at frequencies below 200 cps. For constant diaphragm volume velocity, the addition of the resonating bubble increases the power output by a factor of approximately 1000.
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