Controlling the piezoelectric activity distribution in poly(vinylidene fluoride) transducers

The depth dependence of piezoelectric activity of poly(vinylidene fluoride) (PVF2) films was determined under a variety of conditions. When films of PVF2 were poled in stacks without central conductive layers present, the resulting piezoelectric activity profile was strongly field dependent. Lower poling fields favored anode activity, whereas at higher poling fields cathode activity increased. When central conductive layers were present during poling, the cathode side was more active than the anode side if the samples were cooled with the poling field applied. When the field was removed before cooling, the center of the stack was most active. In samples poled in temperature gradients, the cool side, whether anode or cathode, was most active. A technique for determining the overall asymmetry in a single sheet is described, and use of asymmetric films as flexure devices is discussed.