Research On Miniature Vibration Energy Harvester Of Low Frequency,Broadband And High Performance

In recent years,wireless sensor networks,field intelligent sensing systems,environment monitoring systems,individual-soldier wearable systems and ammunition intelligent systems have been developing quite rapidly,but they usually work in wild places,without power supply and wires,or work in movable environment,so the energy supply for these devices has become a big challenge to us.The chemical battery,as the existing main energy supply of these devices,has some disadvantages,like short storage time,large size,and needing frequent replacement.Thus,as an energy alternative to chemical batteries,the piezoelectric energy harvester,which can harvest energy from vibrating environment,has become a hot research topic.This kind of energy harvester has many advantages,such as long use life,simple structure,easy to miniaturize,no heating,no electromagnetic interference and no pollution etc.Particularly,the piezoelectric-electromagnetic composite energy harvester,considering the characteristics of both high voltage?piezoelectric energy harvesting?and high current?electromagnetic energy harvesting?,has become a research hotspot in energy collection.In this paper,aiming at the key problems of the vibration energy harvester,such as the frequency,bandwidth and power etc.,we have combined theoretical analysis with numerical simulation and experimental tests,thoroughly studying the low frequency band,wide frequency band and high performance of the self-designed piezoelectric energy harvester/the piezoelectric-electromagnetic composite energy harvester.The main work and innovative research results are as follows:?1?Aiming at the dynamic characteristics of the mass block-continuous beam structure,we established a general dynamic model of electro-mechanical coupling,systematically analyzed the static,quasi-static and dynamic forms of motion.Through analysis,we obtained the structural mechanics parameters and electrical parameters and worked out the calculation method of multi-order modes and the corresponding application range of the three models based on the vibration mode function.Then,we used the prototype of the cantilever-beam piezoelectric energy harvester to do experimental tests,verifying the correctness of the theoretical model and the simulation results.?2?Based on the cantilever-beam piezoelectric energy harvesting structure,three methods were proposed to improve the piezoelectric performance:1)to change the shape of the cantilever beam,namely changing the rectangular beam where the strain is concentrated on the root into the trapezoidal beam or triangular beam where the strain is more uniform on the surface;2)to change the original cantilever-beam structure into the double-end fixed beam structure,improving the utilization level of the piezoelectric material and increasing the output power.3)to change the piezoelectric mode,namely changing the d₃₁ working mode whose piezoelectric coefficient is lower into the d₃₃ working mode that has a higher piezoelectric coefficient,enhancing the output performance of the harvester;?3?Considering that there exists a torsional mode in the low frequency vibration mode,according to the characteristics of torsional vibration,we established a theoretical model of the torsional vibration energy harvester that uses the piezoelectric material d₃₆ mode to work and designed a prototype of the torsional vibration energy harvester.Through simulation analysis and experiments,we proved the correctness of the theoretical model,providing theoretical basis and practical experience for further researching and utilizing torsional mode to harvest energy.?4?We put forward a method of designing a miniature piezoelectric-electromagnetic composite energy harvester based on an“?”shape magnet,which vastly improves the electromagnetic energy harvesting efficiency.The piezoelectric state equation was established based on the lumped parameter method;the corresponding theoretical derivation was also done on the output performance.We developed a composite energy harvester prototype and studied the influence of the factors on the output performance of the energy harvester,like whether there is an“?”shape magnet or not,the number of coils,the distance between the magnet and the coils etc.The results show that this miniature piezoelectric-electromagnetic composite energy harvester with an“?”shape magnet can enhance the output power of the previous generation composite energy harvester by an order of magnitude.?5?A MEMS piezoelectric-electromagnetic composite energy harvester of high efficiency and broadband was creatively presented;and the systematic research was done in the aspects of designing,producing,packaging and testing etc.With large deformation nonlinearity introduced,the energy harvesting frequency band of the MEMS structure was enormously broadened;and by using the planar multi-layer micro-coils,the electromagnetic energy harvesting characteristics were highlighted.After analysis,the results show that,compared with the single piezoelectric energy harvester,the nonlinear effect of the composite energy harvester is prominently enhanced,the frequency band is greatly broadened and the output performance is also obviously improved.In addition,from the experiments,we also find that the output power of the piezoelectric-electromagnetic composite energy harvester with double-end fixed four-beam structure is significantly increased;and the trapezoidal design of the double-end fixed beam can reduce the natural frequency and effectively increase the output voltage.