Study Of D₃₃ Mode Piezoelectric Energy Harvester Based On Flexible Substrate

With the merit of small volume, high integration density and high conversion efficiency, traditional piezoelectric energy harvester with silicon substrate has been embedded into micro mobile devices and provides energy for them. To overcome the problem of incomplete polarizaion, bending electric field exiting in conventional d33 mode piezoelectric energy harvester and the problem that silicon structures can be easily broken under impact or violent vibrations, a complete d33 mode piezoelectric energy harvester using flexible stainless steel substrate with interdigital electrode running through the piezoelectric layer rather than on the surface was proposed.Based on the established electromechnical model of complete d33 mode energy harvester, the mathematical expressions of output voltage and power of energy harvester were deduced. The resonance frequency of cantilever with 30μm thickness stainless steel was calculated and the influence of electrode size, material thickness and vibration acceleration on the output power was explored based on the electromechnical model. Analysis results showed that complete d33 mode piezoelectric energy harvester with silicon substrate generate more power than the surface d33 mode piezoelectric energy harvester with the same dimension when the gap is larger than 16μm. Analysis results showed that complete d33 mode piezoelectric energy harvester with stainless steel outputs nearly 3.38 times of the complete interdigital electrodes d33 mode piezoelectric energy harvester of the same size with silicon substrate under the same excitation conditions. When the thickness of the substrate is given, there always exits an optimal material thickness or an optimal thickness ratio which makes the piezoelectric energy harvester obtains the maximum output power.The fabrication process of complete d33 mode piezoelectric energy harvester was designed. The deposition of 200μm thickness SiO2 on stainless steel and preparation PZT films using electrohydrodynamic atomization method were carried out. The films were characterizated using XRD method and the result showed that the fabricated film had good perovskite structure. But the bottom electrode was short circuit because the SiO2 was too thin. In addition, the vibration testing system for piezoelectric energy harvester was set up and d31 mode piezoelectric energy based on PI substrate was tested using the system.