Perforated Pzt-Polymer Composites with 3-1 and 3-2 Connectivity for Hydrophone Applications.

Considerations of the influence of crystal symmetry, macrosymmetry, and interphase connectivity have been used to explore possible macrostructures of interest as piezoelectric composites. Based on these design considerations and the earlier work on composites with different connectivities, new composites with different connectivity patterns were fabricated, and their performance was evaluated for hydrophone applications. Most of the work was concentrated on composites with 3-1 and 3-2 connectivity. These composites were prepared by drilling either circular or square holes in prepoled PZT blocks, in a direction perpendicular to the poled axis and by filling the drilled holes with Spurrs epoxy. Initial theoretical modeling of the piezoelectric properties of these composites had shown a significant reduction in dielectric constants and a large enhancement in the piezoelectric (')d(,h) and g(,h) coefficients. The above model predicted large variations in both the dielectric and piezoelectric properties of composites on the geometry of composites (hole size, width and thickness). The model also predicted higher figures of merit for 3-2 composites. Experimentally, the effects of several variables, such as poling of the composites during different stages of sample preparation, geometry and size of the composite and use of coupling agents, etc. on dielectric and piezoelectric properties of 3-1 composites, were investigated. On samples optimized for hydrophone performance, the g(,h) and (')d(,h)g(,h) coefficients of composites were about 4 and 40 times greater for 3-1 composites and 25 and 150 times greater for 3-2 composites than those of solid PZT, respectively. For 3-1 composites, there was practically no variation of g(,h) with pressure up to 8.4 MPa. In the case of 3-2 composites, there was a slight variation of g(,h) with pressure. Experimentally observed trends in the variation of dielectric and piezoelectric properties of both 3-1 and 3-2 composites were similar to those predicted by the model, and, as predicted by the model, 3-2 composites showed higher piezoelectric figures of merit than 3-1 composites.