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 polyme r/piezoelectric ceramic composites for hydrophone applications. The Po isson's ratio effect, i.e., the enhancement of the hydrostatic perform ance which can be achieved by mixing piezoelectric ceramics with polym ers, is studied in detail. Using an ''effective medium'' approach, alg ebraic expressions are derived for the composite hydrostatic charge co efficient d(h), the hydrostatic figure of merit d(h)g(h), and the hydr ostatic electromechanical coupling coefficient k(h) in terms of the pr operties of the constituent materials, the ceramic volume fraction, an d a microstructural parameter p. The high contrast in stiffness and di electric constants existing between the two phases can be exploited to derive simple, geometry-independent approximations which explain quan titatively the Poisson's ratio effect. It is demonstrated that the sti ffness and the Poisson's ratio of the polymer matrix play a crucial ro le 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 polym er/piezoelectric ceramic systems at varying compositions. Several exam ples involving Pb (Zr, Ti)O-3 and (Pb, Ca)TiO3 piezoelectric ceramics are given to illustrate the theory. (C) 1998 Acoustical Society of Ame rica. [S0001-4966(97)00506-7].