Acoustically transparent hydrophone probe

• US 4,517,665 A
• Filed: 11/17/1983
• Issued: 05/14/1985
• Est. Priority Date: 11/24/1980
• Status: Expired due to Fees

• Current Assignee: United Jewish Appeal of Greater New York
• Original Assignee: United States Department Of Health And Human Services
• Inventors: Harris, Gerald R., DeReggi, Aime S.
• Primary Examiner(s): TUDOR, HAROLD JAY
• Application Number:
  US06/553,387
• Time in Patent Office: 544 Days
• Field of Search: 367/140, 367/141, 367/155, 367/153, 367/160, 367/161, 367/163, 367/164, 367/165, 367/170, 310/365, 310/330, 310/366, 310/331, 310/800, 310/332, 179/110 A, 179/111 E, 307/400
• US Class Current: 367/163
• CPC Class Codes: B06B 1/0688 with foil-type piezoelectric elements, e.g. PVDF
• CPC Class Codes: Y10S 310/80 Piezoelectric polymers, e.g. PVDF

Abstract

An acoustically transparent hydrophone probe consisting of a rigid hoop structure in which is secured an assembly of very thin piezoelectric polymer sheet material, such as polyvinylidene fluoride, with one or more very small central sensitive portions. In its simplest form it consists of a single sheet with a small central poled piezoelectric area and with very thin metallic electrodes deposited on the sheet on opposite sides of the piezoelectric area and having fine conductive leads extending from the electrodes and adapted to be connected to a suitable amplifier or transmission line. The sheet is of biaxially stretched material, and is held taut in the hoop structure. Other embodiments may employ multiple sheets. With two sheets, the outermost surfaces are metallized and are at common ground potential, and the inner surfaces have superimposed deposited metallic electrodes with poled piezoelectric areas adjacent thereto. The electrodes have superimposed deposited metallic leads which have a common electrical connection to a transmission line or to an amplifier. With four sheets, the two innermost sheets form a bilaminate subassembly similar to the 2-sheet embodiment. The outer sheets have metallized outer surfaces which are grounded. Between said outer sheets and the bilaminate subassembly, guard rings coaxial with the piezoelectric active areas are provided. The guard rings can be driven electrically in a manner to eliminate the effects of the capacitance of the electrical leads.

Claims

1. A hydrophone device comprising supporting hoop means of a selected area, sheet means of biaxially oriented polymer material secured in said hoop means and held thereby in a taut condition, said polymer sheet means having a poled piezoelectric area of predetermined size, the selected area of said sheet means defined by said hoop means being larger than the size of said poled piezoelectric area, and said poled piezoelectric area being located in said sheet means in spaced relation to said hoop means such that said hoop means during use remains outside the region of the medium subjected to the acoustic energy and the point being probed by said hydrophone device, said sheet means having electrode means of deposited metal on one side of said poled piezoelectric area, and guard ring means of deposited metal on the other side of said piezoelectric area, said guard ring means being substantially coaxial with said electrode means, said sheet means having a thickness selected such that it is substantially acoustically transparent in liquid, and respective electrical leads of deposited metal on said sheet means, connected to said electrode means and guard ring means and extending toward the periphery of said sheet means, said deposited electrode means, guard ring means, and electrical leads comprising metal films having thicknesses selected such that the electrode means, guard ring means, and electrical leads do not affect the acoustical transparency of said sheet means, wherein said sheet means comprises two identical polymer membranes bonded together defining respective piezoelectric laminae and being provided with abutting deposited electrodes smaller than about 1 mm in diameter, the two membranes each having a poled piezoelectric area adjacent said abutting deposited electrodes, and said piezoelectric area being oppositely poled, whereby the piezoelectric laminae are electrically connected in parallel, wherein said electrical leads connected to said abutting deposited electrodes include respective superimposed strips of deposited metal between the two membranes, having a common center connection junction near the perimeters of the membranes, and wherein said electrical leads connected to said guard rings include strips of deposited metal on the outer surfaces of the two membranes adjacent said superimposed strips in electricaly shielding relation thereto, having a common guard connection junction near the perimeters of the membranes, and wherein said sheet means also comprises two additional polymer membranes bonded to the outer surfaces of said two identical polymer membranes and having outer metallized surfaces defining ground electrodes, a triaxial transmission line secured to said hoop means, said transmission line having an outer conductor sleeve, a guard sleeve and a center conductor, means connecting said common connection junction to said center conductor, means connecting said common guard connection junction to said guard sleeve, and means connecting said ground electrodes to said outer conductor sleeve.

2. The hydrophone device of claim 1 and wherein said deposited electrode means and electrical leads comprise metal film which are approximately 0.2 micrometers in thickness.

3. The hydrophone device of claim 1 and wherein said poled piezoelectric areas are each approximately 0.5 mm in diameter.

4. The hydrophone device of claim 1 and wherein said sheet means comprises semicrystalline polymer sheet material of the group comprising polyvinylidene fluoride and copolymers of vinylidene flouride with tetrafluoroethylene or trifluoroethylene.

5. The hydrophone device of claim 1 and wherein said poled piezoelectrid areas are located substantially centrally of said sheet means.

6. The hydrophone device of claim 5 and wherein each said sheet means is approximately 25 micrometers in thickness.

7. The hydrophone device of claim 1 further including means to drive said guard sleeve electrically.

8. The hydrophone device of claim 1 and wherein said hoop means comprises inner and outer relatively rigid hoop rings clampingly securing said sheet means therebetween.

9. A hydrophone device according to claim 1, having an array of multiple piezoelectric areas.