The Study On Nonlinear Electrostatic Energy Harvester Based On MEMS Technology

With the development of MEMS(microelectromechanical system) technology and reduced power consumption of WSN(wireless sensor network), it is possible to obtain indefinitely life-time of system operation by MEMS-based vibration energy harvesters. There are three basic mechanisms by which vibration can be converted to electrical energy:piezoelectric, electro-magnetic and electrostatic. On the basis of comprehensive comparison of the merits of each conversion mechanism, electrostatic mechanism is chosen as the research topic.In present, most of the researches are focused on linear resonant vibration energy harvesters which have a narrow operating bandwidth and operate efficiently only when the excitation frequency is very close to the resonant frequency of the harvester. This thesis described two different energy harvesters:linear motion energy harvester with nonlinear spring and two-stage transduction, rotation energy harvester with two-stage transduction. In order to gain the resonant frequency, bandwidth and output power of the linear motion structure, detailed simulation and experiment test were performed.The main chapters of this thesis are as follows:In chapter 1, the converted principles of three basic mechanisms were introduced. The current researches on vibration energy harvesters were presented. The main research contents and methods were discussed.In chapter 2, three basic topologies for electrostatic energy conversion and simple charge pump circuit were studied. The theories of the design were stated thoroughly in three aspects. First, the characteristics and the research methods of nonlinear theory were discussed. So as to clearly understand the nonlinear stiffness, Duffing spring equation was studied. Second, the characteristics and analysis methods of the impact structure were expounded. Third, the design theories of rotation structure were studied which included two sides:the stability condition and serpentine spring.In chapter 3, three kinds of nonlinear spring, one serpentine spring, two types of impact structure and comb capacitor were designed. The whole structures of linear motion energy harvester and rotation energy harvester were designed too. For the purpose of getting the resonant frequency, ANSYS was utilized to simulate these two devices. The second stage of linear motion device was also carried out static analysis by ANSYS to determine the position of impacted point. Lumped element model of the first stage of linear motion energy harvester including both the mechanical and electrical subsystems was established to simulate the device performance.In chapter 4, machining process of the MEMS device was introduced briefly. Three times processing were conducted to obtain complete and good devices for experimental test.In chapter 5, design of PCB board and establishment of test bench were discussed in brief. Experiment of the first stage of linear motion energy harvester was conducted to get the resonant frequency, optimal load, capacitance, etc. The reasons of the distinction between simulation and experiment were discussed in detail.In chapter 6, the main work of this thesis was summarized and experimental conclusions were drawn. The problems and shortages of this thesis were analyzed and future research proposals were suggested.