Piezoelectric behavior of different home made polyvinylidene fluoride films

Strain and stress piezoelectric coefficients of different home made blow extruded and monoaxially drawn films as well as a commercial biaxially drawn film of polyvinylidene fluoride, were measured after thermal poling. For instance, blow extruded films poled at 90°C, 1 MV cm−1 for one hour gave: d 31 = 9 pCN−1, whereas with the same poling parameters and with monoaxially drawn home made films d 31 = 25 pCN−1. Different behaviors of the piezoelectric coefficients with the poling field were observed for blow extruded and biaxially drawn films on one hand, and uniaxially stretched film on the other hand. Estimations of the permanent polarization for the poled films were tried by different methods using the piezoelectric coefficients measured. Frequency response curves of earphones with membranes of different films and designed for the telephone set were compared.