Investigation On Dynamic Behavior Of L-shaped Piezoelectric Vibration Energy Harvester Under Multi-direction Excitation

With the development of micro electro mechanical systems(MEMS)and the growing demand of energy and the enhancement of environmental awareness,energy harvesting from ambient environment becomes one of ways to sustain energy supply.Among,piezoelectric energy harvester(PEH)has became the focus of researchers because of its advantages,such as simple structure,easy integration,high efficiency of energy harvesting and environmental friendliness and so forth.Researchers had taken more attention on PEHs to improve harvesting efficiency and broaden its bandwidth.However,proposed harvesters in the literatures have also some drawbacks like structural complexity and narrow frequency bandwidth.The L-shaped harvester is considered in this thesis.With different methods of theory,experiment and simulation,the dynamic responses and performance of L-shaped harvester are analyzed to investigate advantages and disadvantages of L-shaped harvester in multi-direction excitation,nonlinearity and broaden bandwidth.Results are helpful for design and apply of broadband,high-efficiency harvester.The main contents and the conclusions of this thesis are as follows.1.The performance of in-plane bending vibration and out-of-plane torsion vibration of the L-shaped piezoelectric vibration energy harvester is investigated.Based on Euler-Bernoulli beam theory,the decoupling mechanical models of bending vibration and torsion vibration are established and the theoretical solution of dynamic response and power output are also given that further the model is validated to be feasible with compared to experiements.Moreover,simulation models of four different types of harvesters including bending-torsional vibration L-shaped PEH are established and studied that compared on power output and harvesting efficiency.Results show that the bending-torsional coupling vibration L-shaped harvester has the merits of lower resonance frequencies and multi-peak responses and more average power outputs and higher energy density Which has became a potential structure of broadband and high-efficiency energy harvesting.2.Investigation on the influence of geometric nonlinearity and material nonlinearity to the L-shaped harvester.Based on extended Hamilton principle,the nonlinear mechanical model of L-shaped harvester is established and the numerical solution is also calculated by Runge-Kutta method.Besides,the reliability of the nonlinear model is verified with the experiments under the large-amplitude excitation.Based on the theoretical mechanical model,influence of geometric nonlinearity and material nonlinearity and both to the unimorph/bimorph L-shaped harvester are analyzed.It can be concluded that under large-amplitude excitation,dynamic responses of the L-shaped harvester become obvious softening or hardening because of its geometric nonlinearity while material nonlinearity have different effects on dynamic responses of the L-shaped harvester that maybe result in enhancement of softening and hardening or increasing of power outputs or almost no impact.Besides,comparison of the results of linear model and nonlinear model is given.Results can be helpful to the design and optimization of the harvester under large-amplitude excitation or high electric field.3.Investigation on the performance of the liquid-structure coupling piezoelectric energy harvester in which the tunning mass block is substituted for the liquid-filled container.A novel harvester that based on the liquid-structure coupling mechanism is proposed that makes use of the characteristics of liquid sloshing,such as multi-frequencies,low-frequency and so forth,and liquid-structure coupling effect.Based on the lumped-parameter model of the cantilever harvester and the liquid-sloshing model of the tunning container,the theoretical model of the liquid-structure coupling cantilever harvester is established amd solved by Runge-kutta method that compared with results of tests.Besides,experiments on the performance of the cantilever harvester and the L-shaped harvester under different types of the tunning container are conduced.It can be found from the experimental results that for the cantilever harvester and the L-shaped harvester,the tunning effect of the liquid-filled container results in that the single-peak voltage outputs near the first/second resonance frequency become multi-peak voltage outputs that is helpful to broaden its bandwidth and improve harvesting efficiency from ambient environment.