Patent GB-1348401-A (GB)
Title: Pressure sensitive hydrophone
IPC: G01V1/20
Filed: 1971-06-04
Abstract: 1348401 Hydrophones WHITEHALL ELECTRONICS CORP 4 June 1971 [29 June 1970] 18939/71 Headings H4J and H4D An electroacoustic transducer comprises a radially polarized piezoelectric cylinder with electrodes on its inner and outer surfaces and inwardly dished circular diaphragms covering the opposite ends of the cylinder. A marine hydrophone unit 35<SP>1</SP> (Fig. 7) comprises an annular radially polarized piezoelectric element 37 of lead zirconate titanate, silver coated on its outer and inner surfaces 36, 38. Conductors 41, 42 are connected to these surfaces by solder or conductive cement 40. Conductor 41 passes through a radial hole in the element 37 and is insulated from electrode 36 by an insulating sleeve 45. Two diaphragms 39<SP>1</SP> are secured to the element 37 by cement 44. Annular lips 39a<SP>1</SP> may be provided to facilitate location of the diaphragms 39<SP>1</SP> on the element 37. The diaphragms 39<SP>1</SP> are of plastics with or without reinforcing filaments, or of metal. Their concavity may be formed prior to assembly, but preferably flat diaphragms 39<SP>1</SP> are secured to the ends of the element 37 and the conductors 41, 42 are secured to provide a leakproof volume. Hydrostatic pressure is then applied to the exterior sufficient to provide the concavity. A hydrophone assembly for use in a streamer comprises two hydrophone units 35 (Fig. 5A) electrically connected in parallel to leads 32, 33. An outer steel tube 28 has perforated end caps 29. A cylindrical spacer 30 is of rigid material and has a rib 30A secured by screws to the inner surface of the tube 28. A partition 30B is provided and openings 34 in the spacer and in the end caps 29 permit neutral buoyancy liquid in the streamer to pass freely. Resilient rings 31 are bonded by epoxy adhesive to the spacer 30 and units 35. The hydrophone assembly 25 extends between a pair of rigid plastics spacers 21a, 21b (Fig. 3), and is held in a flexible vinyl tube 24. Cut-outs at the ends of the tube 24 leave fingers 24a which fit on to three strain cables 22. Three signal conductors 26 pass through cut-outs between the fingers 24a and through the spacers 21a, 21b. An outer vinyl jacket 23 has the pair of spacers 21a, 21b located about 6 inches apart, and the next spacers about 6 feet further along. An active streamer section (Fig. 2, not shown) has a plurality of hydrophone assemblies 25 connected in parallel to an impedance matching transformer (20A). The streamer is towed by a boat having a lead-in cable (12), Fig. 1 (not shown), which may have fairings and contain signal wires and strain cable. The streamer may have elastic sections (13), active sections (14), inactive sections (15), depth control elements (16) and a trailing element (17). If desired, an active streamer section has a matching transformer (20a), Fig. 8 (not shown), and transducer assemblies 20b, 20c, 20d ... &c. of different sensitivities disposed to produce a tapered non-uniform array, e.g. for providing a directional characteristic. The sensitivity may be varied by varying the dishing of the diaphragms 39<SP>1</SP> and/or diaphragm thickness or material. Instead of a streamer, a single hydrophone unit 35<SP>1</SP> or an assembly 25 may be housed in a container (47), Fig. 9 (not shown), and held up by a buoy or float (48). The container is secured by an anchor (51) and a cable (49) leads to an amplifier or a transmitter for transmitting output to a remote location.