Effective Medium Theories and Effective Electromechanical Coupling Factors for Piezoelectric Composites

Two examples of piezoelectricity in composite materials are studied. The first con sists of a laminate of a homogeneous piezoelectric reinforced with a non-piezoelectric material, e.g., a metal. The effective piezoelectric response tensor is computed, as well as the effective elec tromechanical coupling factors, which measure the efficiency in converting electricity into mechanical work and vice versa. The second example consists of an isotropic polycrystalline material. Here, we study the influence of the piezoelectric coupling at the grain level on the effective permittivities via an effective medium approximation. The results are compared with experimental data and with predictions of other effective medium theories. We also give a theorem which provides an absolute upper bound on the effective electromechanical coupling factor for arbitrary piezoelec tric composites.