Electric power generation using a vibration of a polyurea piezoelectric thin film

An electric energy harvesting using a polyurea piezoelectric thin film is discussed. In this energy harvesting system, the mechanical energy is converted to the electric energy through the piezoelectric effect of the polyurea film on the device. The electric energy harvesting methods using the piezoelectric elements have been reported by several groups, and in most of these reports, piezoelectric zirconate titanate (PZT) was employed as the piezoelectric material. We propose the energy harvesting device with a polyurea thin film, which is formed through the vapor deposition polymerization with 4,4′-diphenylmethane diisocyanete (MDI) and 4,4′-diamino diphesyl ether (ODA). The conversion efficiency from the mechanical energy to the electric energy was calculated by using the finite elemental analysis (FEA) on the cantilever configuration. It was found that the higher conversion efficiency could be obtained with the thinner and shorter configuration of the cantilever while the resonance frequency of the device increased. The experiments were carried out with the electric power generation device having the polyurea thin film with the thickness of 3 μm attached to the beryllium copper cantilever with the thickness of 0.1 mm. The vibration in the vertical direction, which induces the bending vibration on the cantilever, was applied to the device and the output voltage was measured by connecting the load resistances. The output power was measured with changing the load resistance value from 10 kΩ to 10 MΩ, and the value of the load resistance had the optimum value of 1 MΩ, which corresponds to the calculated value by the FEA. The conversion efficiency was improved by changing the cantilever length and the efficiency of 0.233% could be obtained with the 4-mm-length cantilever.