DIRECT MEASUREMENT OF THE TEMPERATURE-DEPENDENT PIEZOELECTRIC COEFFICIENTS OF COMPOSITE-MATERIALS BY LASER DOPPLER VIBROMETRY

The longitudinal (d33) and transverse (d31) piezoelectric coefficients of a piezoelectric composite material (NTK PR-306) are determined as functions of frequency and temperature by using laser Doppler vibrometry to measure the strain induced in the sample by an electric field. Measurements are performed over the temperature range from -50-degrees-C to 50-degrees-C and over a frequency range from 0.1-10 kHz. Some measurements were made at frequencies up to 100 kHz in order to demonstrate the ability of the technique at frequencies in the vicinity of an electromechanical resonance. The results show that the viscoelastic relaxation affects the piezoelectric response of the composite material primarily through the dielectric stiffness rather than the elastic stiffness. The d33 coefficient is observed to relax in a normal fashion near the glass transition of the polymer phase whereas the relaxation in the d31 coefficient varies over the entire measured range of temperature.