Passive sonic buoy incorporating sealed hydrophone - contains watertight membrane with piezoelectric transducer and amplifier between two lead spheres

摘要

A passive sonic buoy, for launching from an aeroplane or helicopter, comprises a cylindrical container for a parachute, a transmitter with a deployable aerial and comprising a transmitter module, a hydrophone (22) a power supply unit and a cable (7) which automatically unrolls on freeing of the hydrophone from the container. The hydrophone comprises a watertight elastic membrane (48) containing two substantially hemispherical lead spheres (42,43) gripping a hollow ceramic cylinder (44) containing a piezo-electric transducer (40) and a preamplifier circuit on a printed circuit board (45). The upper sphere (42) is covered with an aerodynamic cap (46) in elastomeric material with an axial passage for the cable (7). The spheres provide isolation of the transducer from marine parasitic noise.