ON THE USE OF HOMOGENIZATION THEORY TO DESIGN OPTIMAL PIEZOCOMPOSITESFOR HYDROPHONE APPLICATIONS

We consider an optimal design of composite hydrophones consisting of p arallel piezoelectric PZT rods that are embedded in a porous polymer m atrix. Given the material properties of the polymer and PZT ceramic, w e have optimally designed the piezocomposite to maximize the hydrostat ic coupling factor, hydrophone figure of merit, or electromechanical c oupling factor, using the methods of homogenization theory. The optima l composite is obtained by using a two-step procedure: (i) first we fi nd the ideal structure of the matrix material by weakening the polymer by an optimal arrangement of pores, and (ii) then we embed the PZT ro ds in this matrix. The design parameters are the shape, volume fractio n, and spatial arrangement of the piezoceramic rods, and the structure of the matrix material. It turns out that the optimal matrix is highl y anisotropic and is characterized by negative Poisson's ratios in cer tain directions. The optimal composites possess performance characteri stics that are significantly higher than those of a piezocomposite wit h an isotropic polymer matrix. The results can be viewed as theoretica l upper bounds on the hydrophone performance. (C) 1997 Elsevier Scienc e Ltd.