Piezoelectricity in polyurethane films induced by electrostriction and bias electric field

Transverse piezoelectricity was observed in isotropic polyurethane films, which was caused by electrostriction and a bias electric field. The non-diagonal component of the electrostrictive constant tensor R₃₁ was determined from the piezoelectric constant d₃₁ , which was measured by applying the sinusoidal stress T₁ and detecting the sinusoidal electric displacement D₃ in polyurethane films with different bias dc fields. The 1-axis was the direction of the length of the film and the 3-axis was normal to the film. The higher electrostrictive constant R31 was obtained for the films with the lower elastic constant c₁ and the higher dielectric constant ε₃. The largest value of R₃₁ was 7.5×10^-18 m²/V² and the piezoelectric constant d₃₁ at a dc bias field of 5 MV/m was 38 pC/N, which was about twice that of poled PVDF films