A new method for the absolute measurement of piezoelectric coefficients on thin polymer films

A new quasistatic method to measure piezoelectric coefficients on thin polymer films is presented. This method is based on a combined experimental/analytical approach, where small polymer samples (6 mm x 3 mm x 110 microm) are encapsulated in a soft silicone rubber and an electric field is applied across their thickness (3-direction). Strains are measured optically along three perpendicular directions using a laser Doppler vibrometer, and the experimental measurements are used in a Rayleigh-Ritz energy minimization procedure implemented symbolically in MATHCAD, which yields the absolute piezoelectric coefficients d(3ii). These measured coefficients are material properties of the polymer and do not depend on the specific boundary conditions of the problem. The validity of the method is established using the ATILA finite element code. Experimental values of d(311), d(322), and d(333) obtained for polyvinylidene fluoride (PVDF) at room temperature, in the frequency range 500-2000 Hz, are presented and compared with existing data; excellent agreement is found. The extension of the method to the determination of electrostrictive coefficients on soft polyurethane materials is introduced.