Capped ceramic hydrophones

Attaching specially shaped thin metal caps, each containing a shallow inner cavity, to the electroded surfaces of a piezoelectric ceramic will significantly enhance its hydrostatic sensitivity. The presence of the cavities allows the metal caps to convert a portion of the incident axial-direction stress into radial and tangential stresses of opposite sign, thus allowing the amplified d/sub 31/ and d/sub 33/ coefficients of the poled ceramic to now add together as opposed to subtracting from one another, thus magnifying the d/sub h/. By capping a PZT-552 disk, the d/sub h/ can be amplified by a factor of nearly 100 and the g/sub h/ by a factor of almost 50. These particular hydrophones show the most promise for use in shallow water applications.