A cantilever-type vibration energy harvester (VEH) made of polyvinylidene difluoride (PVDF) was fabricated and characterized. PVDF is one of the polymer piezoelectric materials, which is more flexible than ceramic-based piezoelectric materials such as lead zirconate titanate (PZT). The fabrication process of VEH is as follows: a PVDF film was coated on a phosphor bronze plate by bar-coating method, followed by polarization by corona discharge method. Aluminum top electrode was deposited on the PVDF film by sputtering. One end of the plate was clamped by a fixture to form a cantilever, the length of which is 25 mm. Output power P at the resonance frequency (=55 Hz) was measured as a function of load resistance R with the acceleration set at 17 m/s2. Maximum output reached 4.3 μW at R = 2.1 MΩ. This result is not inferior compared with other reported VEHs using ceramic piezoelectric material. Spray coating was carried out to form PVDF film on a 3D surface. This method is suitable for fabricating a uniform thin film on a three-dimensional (3D) surface, even if it is complicatedly curved. In this study, PVDF film was formed on a 3D helical compressing spring, and the deposition on it was successfully achieved.
Part of the book: Piezoelectricity