LOW FREQUENCY UNDERWATER SOUND CALIBRATION SOURCE

A NEW AND PROPRIETARY LOW-FREQUENCY CERAMIC SONAR PROJECTOR ELEMENT HAS BEEN DEVELOPED, BASED ON A MODIFIED FLEXURE BAR, AND TERMED A FITZGERALD FLEXBAR. A REPRESENTATIVE DESIGN IS SHOWN FOR A FLEXDUCER CONSISTING OF 4 FLEXBARS ENCAPSULATED INTO A HOUSING 3-1/2"D X 18"H WITH A NOMINAL RESONANT FREQUENCY OF \210 HZ WHEN LOADED IN WATER. BASED ON EQUIVALENT CIRCUIT CALCULATIONS, IT IS SHOWN THAT QM\25 AND THAT THE MAXIMUM (STRESS LIMITED) OUTPUT IS OF THE ORDER OF \3 ACOUSTIC WATTS. WITH AN APPROPRIATE EQUALIZING NETWORK, THE FLEXDUCER WOULD BE CAPABLE OF 1 ACOUSTIC WATT OUTPUT OVER A FREQUENCY BAND OF \165 HZ TO \265 HZ. MECHANO-ACOUSTIC EFFICIENCIES OF \75% ARE EXPECTED. FOR DEEP-WATER OPERATIONS (\500 FT.) PRESSURE EQUALIZATION WOULD BE ACHIEVED BY MEANS OF A DOUBLE-STAGE REGULATOR AND A PRESSURIZED AIR TANK.