Bending piezo-electricity of polymer electrets

Polypropylene (PP), polyvinylidene fluoride(PVDF) and copoly(vinylidene fluoride/tetrafluoroethylene) (copoly(VDF/TFE)) were polarized with various electric field (E) at room temperature, and the bending piezoelectric coefficients (β331)^P of these polymer electrets were measured. The value of β331 for PP electret under the bending deflection of 0.1 cm was estimated as 0.7 cgsesu for the poling field of EP =1×10⁵ V/cm, and increased monotonously with increasing Ep On the other hand, the values of β331 for both PVDF and copoly(VDF/TFE) increased with increasing E, reached a maximum, and then decreased until changing the polarity from negative to positive. Based on these experimental results, a mechanism for the generation of bending piezoelectricity in polymer electrets was proposed.