Dynamics and response of polymer-coated acoustic devices

The authors consider the dynamic behavior and the electrical response of a thickness-shear mode resonator with a polymer film coating one face. With glassy polymers this film tends to move synchronously with the oscillating resonator surface, while with rubbery polymers the upper portions of the film lag behind the driven resonator/film interface, causing shear deformation of the film. This dynamic behavior influences the electrical response of the resonator due to the coupling between shear displacement and electric field in the piezoelectric quartz. The film behavior trends were demonstrated by measuring the electrical characteristics of a polyisobutylene-coated resonator as a function of frequency and at several temperatures. It is shown how these changing film dynamics can he correlated with changes in the measured electrical response.<>