The dynamic bending piezoelectric properties of polyvinylidene fluoride cantilevers in the millimeter size range is reported. These devices are being investigated with the intention of developing a piezoelectric device based inner ear cochlear implant. The size restrictions and fluid environment of the inner ear place special requirements on a piezoelectric device, and it is essential to perform basic studies on sensor materials, deformation modes and device configurations to develop a successful implant. Results from both basic vibration tests and underwater acoustic measurements are presented. Experimental modal analysis reveals that millimeter length cantilevers exhibit three bending resonances under 1 kHz. The modal frequencies are sensitive functions of the length and thickness of the film, and are also affected substantially by the width of the cantilever and the nature of the electrode material. Further, all bending piezoelectric modes display high piezoelectric coupling
coefficients in the range 0.2 - 0.35, and damping of < 2%.
Experimental results are compared with a theoretical model of unimorph piezoelectric cantilever beams. Underwater acoustic measurements also reveal that single-cantilever devices in the millimeter length display acoustic sensitivities in the -195 to -210 dB range, in the 2 - 10 kHz regime. These sensitivities are comparable to commercial devices of larger size and more complex
design. The viability of use of the conducting polymer polypyrrole
as the electrode material in polymer piezoelectric sensors is also
investigated. Results show that devices with polypyrrole electrodes are at least as sensitive as devices with metal electrodes, and these type all-polymer devices thus have great promise. The results presented in this paper can be used to design an appropriate sensory implant, as well as in other audio frequency applications.