On the use of homogenization theory to design optimal piezocomposites for hydrophone applications

We consider an optimal design of composite hydrophones consisting of parallel piezoelectric PZT rods that are embedded in a porous polymer matrix. Given the material properties of the polymer and PZT ceramic, we have optimally designed the piezocomposite to maximize the hydrostatic coupling factor, hydrophone figure of merit, or electromechanical coupling factor, using the methods of homogenization theory. The optimal composite is obtained by using a two-step procedure: (i) first we find the ideal structure of the matrix material by weakening the polymer by an optimal arrangement of pores, and (ii) then we embed the PZT rods in this matrix. The design parameters are the shape, volume fraction, and spatial arrangement of the piezoceramic rods, and the structure of the matrix material. It turns out that the optimal matrix is highly anisotropic and is characterized by negative Poisson's ratios in certain directions. The optimal composites possess performance characteristics that are significantly higher than those of a piezocomposite with an isotropic polymer matrix. The results can be viewed as theoretical upper bounds on the hydrophone performance. (C) 1997 Elsevier Science Ltd.