Research On Vibration Energy Harvester Based On Piezoelectric Cantilever

With the development of wireless sensor network technology and portable devices, the power supply via the battery becomes one of the bottlenecks. In order to achieve finite lifetime of self-powered systems, the desiderating thing is to provide electric energy for such devices and networks by utilizing the vibration energy from the ambient environment. Converting vibration energy into electric energy by piezoelectric materials attracts more and more attention and becomes the hot point in micropower field. However, the problems are that the modeling theory needs to be further investgated, the structures of the piezoelectric energy harvester are ought to be improved because of the small output voltage and optimizing the harvesting circuits and storage devices are much in demand.According to the above problems, this dissertation first investgated the development trend of the piezoelectric vibration energy harvesting at home and abroad, and then anylized the types of the piezoelectric materials, the structures of the devices, the vibration mode and harvesting circuits and strorage devices and compared the merits and shortcoming of the different parts of structures and harvesting circuits, finally, proposed the research content of piezoelectric vibration energy harvester.Based on Hamilton's principle, this dissertation studied the vibration equations and electric traits of the piezoelectric unimorph cantilever, and then made a quantitative analysis on the output energy and load power of the piezoelectric unimorph cantilever.According the above study results, the static and dynamic analysis of the piezoelectric unimorph cantilever through ANSYS finite element software are presented. In static analysis, the geometric parameters of piezoelectric ceramic and substrate influcing the output voltage are investigated in detail which establishes a solid theory foundation for optimizing the devices, while in dynamic analysis the resonant frequencies and eigemodes of the piezoelectric unimorph cantilever and its harmonic analysis are also presented, which provides an efficient instruction for the after testing and analysis.This dissertation built a testing system for piezoelectric energy harvesting based on the above research, and tested and compared through simulation the size structure of piezoelectric unimorph catilever influcing the output voltage and achieved indentical results,the energy generator with a beam dimension about 50 mm×20 mm×0.5mm and the piezoelectric unimorph dimension about 10 mm×10 mm×0.4mm produced 11V pp, 34uW with the optimal resistive load of 470KΩfrom 1g (1g = 9.81m / s2) at its resonant frequency of 34Hz , and then made a comparison on conventional capacitor, supercapacitor and rechargeable battery. In addition, the structures of the devices were improved and the piezoelectric bimorph cantilever and muiltlayer structures were desighed, respectively. The energy generator with a beam dimension about 50 mm×20 mm×0.5mm and the piezoelectric bimorph in parallel dimension about 10 mm×10 mm×0.4mm produced 16.97V pp, 76.5uW with the optimal resistive load of 470KΩfrom 1g at its resonant frequency of 33Hz , this result showed that, compared with the piezoelectric unimorph cantilever, the piezoelectric bimorph cantilever could improve the output voltage and power, while the muiltilayer structures could increase the output current and energy. This provides an application prospect of power supply for wireless sensor networks and portable devices.In the end, the works of this dissertation are sunnarized briefly, and the next work is figured out, including the novel reseach ideas.