Composite piezoelectric transducers

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, ceramic-plastic composites have been fabricated with 3-3 phase connectivity by the replication of natural template structures such as coral. Composites prepared in this way have piezo-electric g and g_h coefficients more than an order of magnitude higher than the coefficients of the homogeneously poled ferroelectric ceramic. A simplified fabrication technique has been developed by mixing volatilizable plastic spheres and PZT powder. When sintered and backfilled with epoxy, and poled, these composites give excellent piezoelectric voltage coefficients. Large voltage coefficients were also obtained from 3-1 piezoelectric composites made by embedding PZT fiber arrays in epoxy cement. A continuous poling method has been developed for these fibers which makes it possible to assemble complex composites from pre-poled PZT fibers in epoxy matrices. Multilayer composites with 2-2 connectivity have been produced for filters and other high-frequency applications. Processing methods for producing 3-1 and 2-2 connected composites are described.