Pressure compensated hydrophone with constant stiffness

Claim 1

A HYDROPHONE COMPRISING A HOUSING, A PICKUP SYSTEM WITHIN SAID HOUSING COMPRISING FIXED AND MOVABLE ELEMENTS PROVIDING ELECTRICAL OUTPUT SIGNALS AS THE RESULT OF MOVEMENTS OF THE MOVABLE ELEMENT UNDER THE ACTION OF PRESSURE VARIATIONS IN LIQUID SURROUNDING THE HYDROPHONE, MEANS PROVIDING A FLEXIBLE BOUNDARY SEPARATING THE PICKUP SYSTEM FROM SURROUNDING LIQUID, MEANS PROVIDING AN AIR CHAMBER SURROUNDING SAID PICKUP SYSTEM AND BOUNDED, IN PART, BY SAID MEANS PROVIDING A FLEXIBLE BOUNDARY, MEANS FOR APPLYING TO THE AIR IN SAID CHAMBER A PRESSURE SUBSTANTIALLY EQUAL TO THE STATIC PRESSURE OF LIQUID SURROUNDING THE HYDROPHONE, AND MOVABLE MEANS FORMING A PART OF THE BOUNDARY OF SAID AIR CHAMBER AND MAINTAINING A SUBSTANTIALLY CONSTANT RATIO OF THE PRESSURE WITHIN SAID AIR CHAMBER TO ITS VOLUME, THEREBY TO MAINTAIN SUBSTANTIALLY CONSTANT THE STIFFNESS OF THE AIR WITHIN SAID CHAMBER IRRESPECTIVE OF VARIATIONS OF PRESSURE OF SAID AIR.