Pressure Vessel for Farfield Sonar Transducer Calibration

The calibration of sonar transducers under pressure has been a difficult and lengthy task. A pressure vessel has been designed and constructed specifically for such calibration, with walls as acoustically transparent as possible and yet physically strong enough to withstand reasonable internal pressures. The transducer to be calibrated is placed within the vessel and the whole assembly mounted for calibration. The second transducer used in the measurement is located outside the vessel and at the regular calibration distance. The acoustical path from one unit to the other is through the walls of the vessel. A surface-mounted water pump controls the internal pressure. This system subjects the test transducer to high static water pressure while the calibration is actually carried out in shallow water. The present vessel will accept transducers as large as 20 in. across and 36 in. long and will hold pressures up to 800 psi. The vessel has been successfully used over the range from 1000 cps to 250 kcps without interference from mechanical resonances, pattern distortion, or high attenuation.