Bending piezoelectricity of FEP-Teflon electrets

Bending piezoelectricity of unpoled and/or poled films of FEP Teflon was investigated. Commercial films whose thickness ranged from 25 to 500 μm were used. The bending piezoelectric coefficient, β ₃₃₁, for unpoled or poled films, obtained by applying an electric field E_p=1×10⁷ V/m at 130°C, were estimated as (0.14-1.0)×;10^-9 C/m. The polarity of β₃₃₁ changed when E _p was larger than 5×10⁷ V/m. Both surfaces of the unpoled film were negatively charged, while the surface charge of the poled film consisted of homocharges. Based on these results, mechanisms for the generation of bending piezoelectricity in the films are discussed