MATERIAL APPLICATION STUDY FOR VERY LOW FREQUENCY HYDROPHONE

A REQUIREMENT EXISTS FOR THE DETECTION AND IDENTIFICATION OF UNDERWATER ACOUSTICS OF VERY LOW FREQUENCIES AT EXTREMELY LOW AMPLITUDES IN AMBIENT WATER PRESSURES OF 3000 TO 5000 PSI. THE GENERATED OUTPUT FROM THE BASIC SENSOR MUST PRODUCE A NOISE FREE SIGNAL LEVEL OF SUFFICIENT AMPLITUDE SUITABLE FOR SIGNAL CONDITIONING FOR TELEMETERING TO SHIP, SHORE OR SATELLITE. DEVELOPMENT BY OMUTEC, ODETICS HAS BEEN IN PROGRESS USING A PIEZOELECTRIC SENSOR AND A CHARGE AMPLIFIER; HOWEVER, DUE TO JOHNSON NOISE OR PYROELECTRIC EFFECTS IN PIEZOELECTRIC CRYSTALS, THERMAL ISOLATION IS REQUIRED TO ELIMINATE DRIFT DUE TO TEMPERATURE CHANGES. THE HYDROPHONIC TRANSDUCER IS CAPABLE OF OPERATING AT DEPTHS OF UP TO 10,000 FEET AND CAN DETECT PRESSURE VARIATIONS OF .00142 PSI AND HAS A BANDWIDTH RESPONSE FROM .03 HZ TO 10KHZ. AN ANALYSIS OF MAGNETOELASTIC MATERIAL INDICATES THAT IT WOULD HAVE DISTINCT ADVANTAGES OVER PIEZOELECTRIC CRYSTALS FOR LOW FREQUENCY SENSITIVITY AND TEMPERATURE STABILITY.