Tensile and bending piezoelectricity of single-film PVDF monomorphs and bimorphs

Films of 22 μm thick polyvinylidenefluoride (PVDF) are poled with partially penetrating monoenergetic electron beams, resulting in monomorph polarizations (zero polarization over part of the sample thickness and large polarization over the remaining part) or bimorph polarizations (polarization changing its sign within the sample) with corresponding distributions of piezoelectricity. Experimental data for the tensile piezoelectric strain constant d₃₁ and the bending piezoelectric stress constant β₃₁ with values as high as 13 pC/N and 110 nC/m, respectively, are reported. Both constants decrease with increasing energy of the electron beam. Upon annealing, d₃₁ drops initially more rapidly than β₃₁, whereas the opposite is true at later times. The mechanical resonance frequencies and the mechanical deflection under DC bias are discussed