Effective surface permittivity of piezoelectric substrates coated with thin polymer films

In this work, an approach based on the effective permittivity concept is developed to model surface acoustic wave (SAW) propagation on a piezoelectric substrate coated with a thin viscoelastic film. In a first step, the effective permittivity is extended to include an elastic layer, taking into account the particle displacements in the film and using appropriate boundary conditions. In a second step, mechanical losses are introduced in the film by means of complex elastic constants. As a consequence, the positions of the zero and the pole of the effective permittivity function, which are related to SAW velocity under free or metallized surface, move from the real axis to the complex plane, allowing to determine attenuation and velocity of the lossy Rayleigh wave.