RECIPROCITY CALIBRATION OF A SONAR TRANSDUCER FROM ELECTRICAL IMPEDANCE MEASUREMENTS IN WATER AND IN AIR : THE DELTA-Z RECIPROCITY CALIBRATION METHOD

Abstract
A method is described by which the free-field, open-circuit voltage sensitivity of a reversible underwater acoustic transducer may be obtained from measurements of its input electrical impedance in water and in air. This method, which we have termed the Delta-Z reciprocity calibration method, is being developed for the in-service calibration of sonar transducers installed in domes which can be flooded and purged. The application of the Delta-Z method to the calibration of a single tonpilz-type piezoelectric sonar transducer is described. The resulting sensitivity obtained using the Delta-Z method agrees within approximately one decibel with that obtained by a standard comparison calibration procedure over a two-octave frequency band about the nominal operating frequency of the transducer.