Electroelastic waves in dielectrics modeled as polarizable continua

On the basis of a dielectric microcontinuum model, we investigate the problem of bulk wave propagation in a dielectric crystal with hexagonal material symmetry. The present linear micropolar model allows to express electric polarization via mechanical macro and micro-strain measures so that the coupling between acoustic and polarization modes can be described in terms of intrinsic dipole and quadrupole densities. The governing differential systems for different coupled modes are equivalent to some previous results of the classical phenomenological approach to ferroelectrics but also hold for piezoelectric solids with null intrinsic polarization. Resonance couplings between polaritons and acoustic waves arise from the dispersion equations depending on suitable relations among the micropolar constitutive parameters. Exploiting the dynamical representation of polarization for the admitted modes, we obtain piezoelectric coefficients and electromechanical coupling factors as functions of the wavelength (or frequency). As an application, a numerical example is given for the hexagonal phase of zinc sulfide.