Vibration Energy Harvesting Based On Nonlinear Coupling And Coherence Resonance: Theory And Experiments

During the past few decades,low-power-consumption microelectronic devices like wireless sensors,data transmitter,medical implant and so on,have been increasingly developed and extensively applied in many areas of industry.The traditional chemical battery is incompetent for these micro devices due to the limited capacity.To provide a continuous necessary energy for these micro devices,explosive studies have been conducted on developing power generators that could directly scavenge energy from ambient sources in environment.Due to the high power in density and the advantage easy to be manufactured,the energy harvester based on piezoelectric effect have gained great attentions during the past few years.Piezoelectric vibration energy harvester(VEH)is such a power generator that harvest vibration energy from the environment by utilizing the piezoelectric polarization effect.Since nonlinear VEHs own a wider operational bandwidth and a higher output power than the traditional linear VEH,it was deeply investigated and became a cut-off technology recently.This paper aims at promoting the efficiency of piezoelectric energy harvesting,by developing some researches on innovative structure design,nonlinear dynamics analysis,stochastic vibration,nonlinear electromechanical coupling and vibration control.The main works and achieved outcomes are presented as follows:(1)Two alternatives have been proposed to enhance the performance of harvesting lowintensity random vibration energy.The first one focus on designing the potential shapes of a bistable VEH by utilizing an additional small magnet to decrease the potential barrier,so that the frequent snap-throughs of the bistable VEH can be easily induced by low-intensity random excitation.The feasibility of this method is proven by numerical simulations and experiments.The second one is introducing some stoppers into the bistable VEH.Results showed that our proposed bistable VEH with stoppers can transform the intra-well oscillation into inter-well oscillations,which results in large output voltages and an increase in energy harvesting efficiency.Moreover,it should be noted that only a proper distance of stopper could balance the frequency and amplitude of snap-through,thereby providing an increased power.(2)Experimental investigations on a vertical cantilever piezoelectric beam with a tip mass have been conducted.It is learned from the harmonic vibration experiments that,only when the amplitude of excitation falls in the region of unstability,can the parametric vibration take place and the piezoelectric beam generate large voltages.The parametric resonance can transform the vertical vibration energy into the horizontal one.Meanwhile,it should be noted that this strongly nonlinear VEH has a strong nonlinear mode interaction and internal resonance was observed.This can be exploited as a method to transform the high frequency vibration energy into lowfrequency vibration responses.(3)The dynamic responses and energy harvesting performances of a nonlinear coupled dual beam VEH working in quasilinear,monostable and bistable regions are evaluated.With the analytical model validated by numerical simulation,a comprehensive parametric analysis is conducted to evaluate the effects of base excitation,ratio of natural frequencies and electromechanical coupling,showing the benefits and limitations of the dual-beam VEH.The results show that the magnetic interaction produced nonlinearity and the two beams could achieve high-energy oscillations at the same time for power enhancement.However,the analysis also ascertains that the trade-off between the dual beams should be made according to the change of base excitation,ratio of natural frequencies and electromechanical coupling.The increased output of one beam is always accompanied by the decreased output of the other for the high-energy oscillations in both monostable and bistable configurations.The operational bandwidth is enlarged for both beams owing to the co-occurrence of high-energy oscillations of the dual beams,while the performance of the system as a whole is somewhat restricted by the trade-off.(4)To explore the critical influences of alternating current(AC)and direct current(DC)interface circuits on monostable VEH,the performance is evaluated in terms of generated power and useful operating bandwidth when it is connected to AC and DC interface circuits.Firstly,the harmonic balance analysis and equivalent circuit representation method are utilized to complete the modeling of nonlinear energy harvesters connected to AC and DC interface circuits.The performances of the monostable PEH connected to these interface circuits are then analyzed and compared,focusing on the influences of varying load,excitation and electromechanical coupling strength on the nonlinear dynamics,bandwidth and harvested power.Results indicate that both AC and DC interface circuits have a peculiar influence on the power peak shifting and operational bandwidth of the monostable PEH,which is quite different from that on the linear PEH.(5)For energy harvesting of vibration,maintaining a large-amplitude high-energy-orbit oscillation is highly desired.Hence,a voltage impulse perturbation approach based on negative resistance is proposed such as to trigger high-energy-orbit responses of a piezoelectric nonlinear energy harvester.Numerical simulations and experiments were conducted and the results demonstrated that the high-energy-orbit oscillations could be triggered by voltage impulse perturbation for both monostable and bistable configurations in the given various scenarios.It is revealed that the perturbation levels required to trigger and maintain high-energy-orbit oscillations are different for various excitation frequencies in the region where multiple solutions exist.The higher gain in voltage output for high-energy-orbit oscillation was captured,along with the demand of a higher voltage impulse perturbation level.