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

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(h)g(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(h)g(h), and k(h) for polymer/piezoelectric ceramic systems at varying compositions. Several examples involving Pb (Zr, Ti)O-3 and (Pb, Ca)TiO3 piezoelectric ceramics are given to illustrate the theory. (C) 1998 Acoustical Society of America. [S0001-4966(97)00506-7].