Clamping effect on the piezoelectric properties of poly(vinylidene fluoride-trifluoroethylene) copolymer

Abstract

In hydrophone applications, PVDF and its copolymers provide high sensitivity because of high piezoelectric voltage coefficient gh and large figure of merit dhgh. PVDF samples can be mechanically clamped in the plane perpendicular to the polar direction by cementing metal plates to their surface as electrodes. By this means, the transverse piezoelectric responses can be almost eliminated. The hydrostatic coefficient dhc and ghc of clamped samples can be increased significantly over the coefficients dh and gh of free samples. In this paper, the temperature and pressure dependence of dh, gh, dhc, and ghc, and dielectric constant ε33 and ε33c of free and clamped P(VDF-TrFE) (75/25) copolymer samples were investigated. The effects of the sample dimensions and other parameters on the clamping were also studied. Based on the constitutive equations, the expressions for effective piezoelectric strain coefficient d3ic (i = 1, 2, and 3) of a clamped sample have been derived, and the hydrostatic strain coefficient dhc derived from the direct and the converse piezoelectric effects are compared. The experimental results are in good agreement with the calculations.