Study On Low-frequency,Wideband Piezoelectric Vibration Energy Harvesting Technology

Wireless Sensor Network(WSN)plays an important role in army,aerospace,environmental monitoring,smart home,medical services,industry and so on.However,the power unit of WSN is supported by battery,which have the disadvantages of limited life,periodical replacement,and incompatible fabrication with COMS process.Clearly,the battery limits the further development of WSN.The energy harvesting technology,which can convert the micro-energy from environment into electricity,is an effective solution for powering WSN or other microelectronics.The micro-energy sources such as solar energy,vibration mechanical energy and thermal energy can be used for energy harvesting.Compared with the other micro-energy sources,vibration mechanical energy exists more widely in the environment,esecially in many places where people arrive difficultly.Thus,it will be more meaningful to investigate the vibration energy harvesting.And piezoelectric vibration energy harvester is highlighted as a new solution of WSN for the realization of passive power supply due to the advantages of easy integration with MEMS,no extra power supply and simple structure.However,the primary problem of how to develop a piezoelectric vibration energy harvester with low-frequency,wideband and high output performance has to be solved for the practical application.Therefore,it becomes very urgent to study the structure design,theoretical analysis,manufacturing process and performance characterization of low-frequency,wideband piezoelectric vibration energy harvester.In this project,a novel low-frequency,wideband piezoelectric vibration energy harvesting technology is proposed to achieve low-frequency and wideband energy harvesting through adopting a structure of multi beams driving single piezoelectric beam,using the nonlinear ropes-driven vibration mechanism.This thesis mainly focuses on the fundamental study of the proposed energy harvesting technology in unidirectional energy harvesting.Firstly,a rigid-flexible coupling nonlinear dynamic model is built up for this energy harvester,and its' working principle and energy harvesting performance of low frequency,wide bandwidth and output performance are investigated by using numerical simulation and experiments based on large scale prototype.Then,new optimization mechanisms are proposed to improve the output of the micro energy harvester,and MEMS process for the proposed energy harvester fabrication is designed and the output performance of the micro energy harvester is tested.Finally,the proposed low-frequency,wideband energy harvesting technology is used to achieve multi-directional energy harvesting,which shows superior performance in multi-directional energy harvesting.The main contents of this thesis are listed as follows:Firstly,the unidirectional ropes-driven piezoelectric vibration energy harvester based on the large-scale prototype is proposed.The working principle of the energy harvester is clarified,and the mass-stiffness-damping model and equivalent circuit model are built up.The low-frequency and wideband performance of the proposed energy harvester are investigated by numerical simulation and experiments.Simulation and experimental results show that the proposed energy harvester has superior performance of low frequency,wideband and unchanged output energy harvesting compared with the traditional wideband energy harvester.Furthermore,the parametric study on the rope-driven piezoelectric vibration energy harvester is carried out,which provides the theoretical foundation for the optimization design of the energy harvester in real application.The movement mechanism of the energy harvester is analyzed in detail.Then the effects of acceleration,rope margin and rope stiffness on the output are studied by numerical simulation and experiments.The experimental results agreed qualitatively with the simulation results.In order to improve the output performance of the micro ropes-driven piezoelectric vibration energy harvester further,two new optimization methods are proposed:?Structure optimization,a new mechanism—impact-and rope-driven hybrid mechanism is proposed.Both simulation and experimental results show that fewer low frequency driving beams can achieve wider bandwidth;the central working frequency can be changed easily by adjusting the rope-margin without any structure re-fabrication;the proposed device with one stopper can provide double protection for low frequency driving beam in the upward and downward directions by using the rope,thus,the reliability of the device is improved further.?Piezoelectric material optimization,using c-axis titled AlN film as the high frequency generated beam piezoelectric material,the influence of c-axis tilted angle and geometry parameters of AlN film on generated energy(E)and open circuit voltage(Vo)is analyzed under the fixed substrate.Results show that E and Vo can be improved by optimizing the c-axis tilted angle and geometry parameters.For a given structure size,E and Vo can be almost simultaneously improved by controlling c-axis tilted angle,E with optimal c-axis tilted angle can be amplified by more than 3 times,and the Vo is amplified by about 2 times;Under optimal c-axis tilted angle,the E and Vo could be further improved by geometry parameters.Optimizing the c-axis tilted angle is a direct and effective way to improve the output performance of MEMS piezoelectric vibration energy harvester.Based on the previous study on the large-scale ropes-driven piezoelectric vibration energy harvester,the micro energy harvester based on ropes-driven mechanism is fabricated to validate the superior performance.The MEMS fabrication process is designed and the output performance is tested.The experimental system for micro device is designed and set up,and results show that the micro device can also achieve low frequency and wideband energy harvesting.Finally,the proposed low-frequency,wideband energy harvesting technology is applied for multi-directional energy harvesting.A new multi-directional piezoelectric vibration energy harvester based on rope-driven mechanism is proposed.The experiment is carried out to study the effects of parameters and show how it harvests energy from human body.Results show that the output of the multi-directional energy harvester is almost not affected by the excitation direction,and it can realize lowfrequency and wideband energy harvesting in multi-directional excitation.The new multi-directional energy harvester can be used for human running and hand swing energy harvesting.It will be expected to open up more potential applications in complex environment.