Research On A Mechanical Piezoelectric Energy Harvester With Spring Stoppers And Its Performance

As a device that can transform vibration energy into electrical energy and autonomous feed to wireless sensor,piezoelectric energy harvester has attracted extensive attention of researchers.Spring stopper is one of the techniques to improve the performance of nonlinear piezoelectric energy harvester.However,this technique has been aurally utilized in the harvesters in which the nonlinear force is generated by magnets.Whereas in some special occasions,the presence of magnets may affect the normal operation of other equipment.Therefore,the research on non-magnetic piezoelectric energy harvester with spring stoppers has certain theoretical and practical significance.A mechanical piezoelectric energy harvester with spring stoppers is proposed in this thesis.In this energy harvester,two linear springs are connected to the mass block at the end of the cantilever beam to introduce nonlinear force,and two linear springs are symmetrically placed at a certain distance on either sides of the mass block as spring stoppers.With the mathematical model the harvester,the effects of the spring stoppers on the elastic restoring force,the equilibrium points and their locations,and the potential energy function of the system are studied,further more,the dynamic response and the performance of the harvester under simple harmonic excitation and chaotic excitation are also studied with simulations.The results of the studies will provide reference for the design of the piezoelectric energy harvester with spring stoppers.The main research work and conclusions of this thesis are as follows:1.The dynamic model of mechanical piezoelectric energy harvester with spring stoppers is established.Based on the model,the equilibrium points and static bifurcation of the system are analyzed.The results show that the elastic restoring force and the potential energy function of the system are changed when the spring stopper works,so the number and locations of equilibrium points,bifurcation of the system are affected to differnt extents.2.The dynamic response and captive energy characteristics of energy harvester under simple harmonic excitation are studied as the system are in monostable,bistable and tristable states respectively.The effects of the stiffness and the clearance of the spring stopper on the dynamic response and captive energy characteristics of energy harvester are also studied.The results show that due to the action of spring stoppers,the motion amplitude of the cantilever beam will be reduced,and so does the the maximum capture voltage.On the other hand,since the frequency ratio of the energy harvester changes dynamically with the displacement of the cantilever beam and the external excitation frequency,it is possible to maintain the the frequency ratio approximately to the resonance frequency ratio of the system,then working bandwidth of the energy harvesteris is broadened.3.Taking Duffing vebitor as the excitation of the harvester,the dynamic response and captive energy characteristics of energy harvester system under chaotic excitation are studied.The results show that the captive energy characteristics of the system will increase with the increase of vibration intensity no matter in the monostable state,or in bistable and tristable states.The effect of spring stopper on the reducing the motion amplitude of cantilever beam is obvious,and as the a result,the maximum capture voltage is also reduced.