Design And Dynamic Analysis Of Wideband Multi-stable Frequency Up-converting Energy Harvester For Low Frequency Operation

In the last few years,harvesting vibration energy from environment via piezoelectric materials has being a promising technology to power small sensors and MEMS.Around us,most of the ambient vibrations are characterized by low-frequency,low acceleration and broadband.As one of the potential energy harvesting structure,multi-stable system can generate significantly amplitude under low-frequency broadband excitation,which makes it become a research hot spot in piezoelectric vibration energy harvesting.At present,the research on multi-stable energy harvesting primarily focuses on bi-stability and tri-stability.However,enlarging the interwell motion and shallowing the potential barrier are two contradictory effects in a multi-stable system.Under low intensity excitation,creating more stable equilibrium positions is necessary to increase the amplitude of interwell motion in multi-stable oscillator.In addition,frequency-up conversion technology is widely used to improve the power density of energy harvester.However,the bandwidth of the traditional frequency-up conversion technology is narrow,which against harvesting energy from environmental vibration with broadband in nature.To this end,this paper proposes a quin-stable piezoelectric vibration energy harvesting methods,and then introduces such multi-stable nonlinearity to frequency-up conversion technology.In this study,theoretical modeling,numerical simulation and experimental research are applied to investigate the bifurcation characteristics and complex responses of the system.The relationship between system parameters,excitation conditions,vibration response and output power are also investigated.The main results are as follows.This work proposes a wideband quintuple-well potential piezoelectric-based vibration energy harvester using a combined nonlinearity:the magnetic nonlinearity induced by magnetic force and the piecewise-linearity produced by mechanical impact.The parameter region,in which the configuration of magnets could satisfy the forming condition of quin-stability,is obtained through magnetic dipole model.Numerical and experimental techniques are used to analyze and compare the efficiencies between the quin-stable and the conventional tri-stable energy harvester.The results show that the quin-stable energy harvester has a lower threshold of high-energy interwell motions and can be more efficient in harvesting energy over a wider bandwidth when compared with the tri-stable one.In addition,the distance between the permanent magnets and magnetic pole direction will affect the multi-stability of harvester.Multi-stable characteristics of harvester can be performed by four combinations of permanent magnet polarity,which correspond to different distance between magnets.To improve the bandwidth and expand the working band to low frequencies,the quin-stable nonlinearity is introduced in the conventional frequency-up conversion technology.The design,theoretical analysis and experimental verification of a low frequency driven,frequency up-converted broadband quin-stable energy harvester are performed.Results show that,introducing quin-stable nonlinearity in frequency-up conversion technology can improve the output power of harvester.The soften effect induced by magnetic force in harvester could broaden its operating bandwidth to lower frequencies.This indicates the potentiality of the proposed IQEH for low frequency applications such as human motions.Combined with the former work,a new multi-stable wideband harvester is presented.The proposed harvester can possess arbitrary multiple stability induced by the combined nonlinearities of cantilever-stopper engagement and magnetoelasticity.The dynamic characteristics of four typical configurations at different levels of harmonic excitation are explored by numerical methods and verified by experiments.The coupling between the cantilever beam,stopper and magnetic field can create an arbitrary number of stable states,while the stability of the zero equilibrium position can be controlled by the initial stiffness of the cantilever and the distance between magnets.In addition,the cantilever-stopper impact could hinder the global large-amplitude motion but maintain the local one.Then,this paper proposes models and experiments of a wideband piezoelectric vibration energy harvester with a quadruple-well potential induced by the combined nonlinearity of cantilever-surfaces contact and magnetoelasticity.The influence of design parameters on the cantilever curvature and static equilibrium position is analyzed through the mathematical model.The dynamic responses of the present energy harvester with a quadruple-well potential are explored by numerical simulations and validated by experiments.The above works extend the existing multi-stable system and combine the multi-stable nonlinearity with frequency-up conversion technology.A new architecture of energy harvesting is formed and the corresponding nonlinear dynamic characteristics is investigated.Considering the major nonlinear factors,the bifurcation and complex response of the system are analyzed,especially their influence on the electrical output performance.The conclusions can provide some theoretical foundations for designing and optimizing multi-stable energy harvester.