Improved piezoelectrics for hydrophone applications based on calcium-modified lead titanate poly(vinylidene fluoride) composites

Piezoelectric composites comprising dispersions of free-flowing calcium-modified lead titanate powders in a poly(vinylidene fluoride) matrix have been developed and characterized as materials for hydrophone applications. We find that these composites provide highly desirable properties: (1) high figures of merit, g(h)d(h)=50(+/-5) X 10(-13) m(2) N-1, and a relatively low dielectric loss tangent, less than 0.018; (2) convenient melt processibility; (3) no significant sensitivity changes in going to high pressures (14 MPa or 2 kpsi); (4) thermal stability of the poled state for months at 100 degrees C; and (5) easy fabrication. This performance results from material choices and from special ceramic powder processing and composite preparation methods that optimize the achievable degree of ceramic poling, the remanent polarization, and the transfer of mechanical energy to the dispersed ceramic. Materials design concepts, composite processing, and device construction and evaluation are described. (C) 1998 Elsevier Science S.A.