Analysis of piezoelectric thin film energy harvester for biomedical application

The effect of the thickness ratio variation of a unimorph piezoelectric energy harvester to the electric output under bending condition is studied. The harvester forms a blanket with PVDF-TrFE as an energy harvesting layer and Kapton film used as a substrate. The thickness of Kapton is fixed as 25um while the thickness of PVDF-TrFE is varied from 0.5 um to 20um. The voltage, charge and energy output are estimated by numerical and theoretical method under three different bending conditions with fair biomedical model. For all conditions, the Young's modulus ratio changes the optimal point of all outputs. The effect of surface patterning is studied with regard to the rib-base thickness ratio and the rib-spacing ratio. The voltage and electric energy output falls with the decrease of the base-rib thickness ratio. The charge output rises with the decrease of the base-rib thickness ratio. However, the charge increasing rate is smaller than the voltage decreasing rate. Hence, the electric energy decreasing rate is mostly affected by the voltage decreasing rate. By changing rib-spacing ratio, the electric energy output of the grated structure can be enhanced. If the piezo-substrate thickness ratio is larger than a specific value, the grated structure is more efficient than the planar structure. A recent study from Ran Liu group asserts that the piezoelectric effect becomes electrostatically stronger at the singularity point of the nano imprinted structure where the bending induced stress is also concentrated. Thereby, the grated structure would enhance the electric energy output of the energy harvester. Overall, this research will contribute to design optimal thin film energy harvester for biomedical application.