Acoustically transparent hydrophone probe

Claim 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.