Calculating the performance of 1-3 piezoelectric composites for hydrophone applications: An effective medium approach

摘要

A new method is presented for evaluating the performance of 1-3 polymer/piezoelectric ceramic composites for hydrophone applications. The Poisson's ratio effect, i.e., the enhancement of the hydrostatic performance which can be achieved by mixing piezoelectric ceramics with polymers, is studied in detail. Using an "effective medium" approach, algebraic expressions are derived for the composite hydrostatic charge coefficient d_h, the hydrostatic figure of merit d_hg_h, and the hydrostatic electromechanical coupling coefficient k_h in terms of the properties of the constituent materials, the ceramic volume fraction, and a microstructural parameter p. The high contrast in stiffness and dielectric constants existing between the two phases can be exploited to derive simple, geometry-independent approximations which explain quantitatively the Poisson's ratio effect. It is demonstrated that the stiffness and the Poisson's ratio of the polymer matrix play a crucial role in enhancing hydrophone performance. Using a differential scheme to model the parameter p, we evaluate d_h, d_hg_h, and k_h for polymer/piezoelectric ceramic systems at varying compositions. Several examples involving Pb (Zr,Ti)O_3 and (Pb,Ca)TiO_3 piezoelectric ceramics are given to illustrate the theory.