Determination of the piezoelectric coefficient d(33) at high frequency by laser interferometry

The charge coefficient d(33) of a piezoelectric material is usually measured at low frequency (50 - 100 Hz) using devices such as the Berlincourt meter and this d(33) is then assumed to be a constant at all other frequencies. To test the validity of this assumption, a high frequency optical heterodyne interferometer was used to measure d(33) as a function of frequency up to the megahertz region where the piezoelectric materials are used in transducer applications. The coefficient was obtained by measuring the strain induced by an applied electric field. The materials studied included z-cut lithium niobate (LiNbO3) and vinylidene fluoride/trifluoroethylene (VF2/VF3) copolymer. The results are reported.