DETERMINATION OF THE PIEZOELECTRIC COEFFICIENT D(33) AT HIGH-FREQUENCY BY LASER INTERFEROMETRY

The charge coefficient d(33) of a piezoelectric material is usually me asured at low frequency (50 - 100 Hz) using devices such as the Berlin court meter and this d(33) is then assumed to be a constant at all oth er frequencies. To test the validity of this assumption, a high freque ncy optical heterodyne interferometer was used to measure d(33) as a f unction of frequency up to the megahertz region where the piezoelectri c materials are used in transducer applications. The coefficient was o btained by measuring the strain induced by an applied electric field. The materials studied included z-cut lithium niobate (LiNbO3) and viny lidene fluoride/trifluoroethylene (VF2/VF3) copolymer. The results are reported.