The design and construction of the terminal and source transducers, a reciprocal spherical piezoelectric ceramic transducer, and the probe hiydrophones that are part of a new USRD measuring facility are described. The facility is used for the calibration of underwater sound transducers in the frequency range 10 to 4000 Hz at hydrostatic pressure to 10,000 psig and controlled temperature from 3 to 45 0 C. It operates on the principle of active-impedance termination in a rigid-walled, water-filled tube. PROBLEM STATUSThis is an interim report on the problem. PROBLEM AUTHORIZATION

The USRD type G40 calibrator is a shipboard system for conveniently calibrating hydrophones and their associated measuring systems by the comparison method in the fr.equency range 25-1000 Hz.This system provides isolation from mechanical deck vibrations and ship roll or pitch, and it can generate sound pressure levels from 130 to 190 dB re 1 j•Pa from 0.22-to 22.3-V driving signals.Subject Classifications: 30.85.

Smooth response, omnidirectionality, and wide dynamic range are features of a new reference standard probe hydrophone for the frequency range 10 Hz-200 kHz at hydrostatic pressure to 1000 psig and temperature from 5 ø to 35øC. The nominal end-of-cable sensitivity is --116.9 dB re 1 V/t•bar from 10 Hz to 60 kHz.

A hydrophone calibrator has been developed by the Naval Research Laboratory to calibrate hydrophones as large as 12 cm in diameter by the comparison method in the frequency range 25–1000 Hz at sound pressure levels from 130 to 190 dB re 1 µPa. Thus, it is possible to calibrate a hydrophone immediately before deployment and immediately after recovery. The calibration can include the complete electronic measuring system as well as the hydrophone. Vertical stabilization of the calibrator for ship roll and pitch of 10° and isolation from ship's noise are provided.

The characteristics of lead metaniobate make it peculiarly suited to hydrophone applications where high hydrostatic pressures are encountered. Some hydrophone design parameters are discussed, properties of various materials are compared, and the measured performance of hydrophones containing lead metaniobate elements is presented.