AN ADAPTIVE COMPENSATION SYSTEM FOR PERFORMANCE IMPROVEMENT OF PIEZOELECTRIC HYDROPHONES

HYDROPHONE OUTPUT LEVEL IS, IN GENERAL, INVERSELY PROPORTIONAL TO THE AMOUNT OF CABLE CAPACITANCE BETWEEN THE CRYSTAL ELEMENT AND THE FIRST IIAPEDANCE BUFFERING PREAMPLIFIER. INDUCTIVE TUNING CAN CANCEL THIS CAPACITIVE LOADING, BUT ONLY IN A VERY NARROW FREQUENCY BAND. THE SYSTEM PROPOSED HERE IS TO BE BASED ON THE ACTIVE CIRCUIT SYNTHESIS OF A NEGATIVE CAPACITANCE, WHICH WILL COMPENSATE FOR THE CABLE CAPACITANCE, AS WELL AS FOR THE CRYGTAL'S BLOCKED CAPACITANCE, WITHOUT THE FREQUENCY DEPENDENCE OF INDUCTIVE TUNING. THE SYETEM IS 'ADAPTIVE' IN THAT IT WILL BE DESIGNED TO AUTOMATICALLY SENSE THE AMOUNT OF POSITIVE CAPACITANCE PRESENT IN THE HYDROPHONE PLUS CABLE, AND PROVIDE A SUITABLE AMOUNT OF SYNTHETIC NEGATIVE CAPACITANCE TO SIGNIFICANTLY IMPROVE HYDROPHONE OUTPUT LEVEL AND EXTEND HIGH FREQUENCY BAND WIDTH, WITHOUT CAUSING SYSTEM INSTABILITY. THEORETICAL SIGNAL TO NOISE PERFORMANCE WILL BE DETERMINED AND AN AMPLIFIER WITH VERY LOW NOISE-FIGURE WILL BE DEVELOPED FOR USE AS THE COMPENSATION CIRCUIT NEGATIVE CAPACITANCE SYNTHESIZER AND PREAMPLIFIER. A BREADBOARD SYSTEM WILL BE FABRICATED, AND TESTED USING A WIDE BAND DUMMY HYDROPHONE CIRCUIT. IF AVAILABLE FROM THE GOVERNMENT, AN ACTUAL HYDROPHONE CAN BE TESTED IN AN ACOUSTIC TEST FACILITY SUITABLE FOR HIGH FREQUENCY MEASUREMENTS. A SURVEY OF AVAILABLE SPECIAL PURPOSE HIGH FREQUENCY PROBE HYDROPHONES WILL BE PERFORMED TO ASSESS TYPICAL LIMITATIONS IN HIGH FREQUENCY RESPONSE AND OUTPUT LEVEL. EXPECTED IMPROVEMENTS IN PERFORMANCE USING THE COMPENSATION SYSTEM WILL BE CALCULATED. HYDROPHONE SIZE CAN BE SIGNIFICANTLY REDUCED.