Calculating the hydrophone response of piezoceramic-rod/piezopolymer-matrix composites

A simple physical model of rod composite piezoelectrics is extended to the case where both the polymer matrix and the ceramic rods are piezoelectric. This model incorporates the physical picture that strains and electric field are equal in both materials along the direction of the rods, while the stresses are equal in the plane perpendicular to the rods. If one switches to a coordinate system in which strain and electric field along the rods and the stresses in the perpendicular plane are the independent coordinates, the material properties of the composite are a simple volume fraction weighted average over the constituents´ properties. The hydrophone figure of merit is presented for a PZT5-rod/PVDF-matrix composite. The bulk of the piezoelectric response is provided by the piezoceramic; the anisotropic elastic properties of PVDF make it particularly suitable for the composite; and the fact that the piezoelectric constants of PZT and PVDF differ in sign would cause the two phases to act against each other if they were poled by the same bias field