Study On Converse Piezoelectric Effect And Harvesting Characteristics Of The Series Nonlinear Piezoelectric Energy Harvesting System

Nonlinear piezoelectric energy harvester has attracted much more attention due to its high efficiency under the low frequency and broadband circumstance.In order to enhance the the efficiency of the harvester,several harvesters are wired in series or parallel to form an array of harvesting.In the case of wired in series,the motion of each harvester might be quite different as its different location,but has influence on the motion of other harvestes since the piezoelectric material possess converse piezoelectric effect which transform the electric energy into mechanical energy.Such coupling of motion surly affects the efficiency of the system.In this regard,this thesis focuses on the dynamics and performance of series nonlinear piezoelectric energy harvester aiming at providing some useful reference for its design,and further,new idea for analysis of nonlinear dynamical system and chaos.The main work and conclusions of this thesis are as follows:1.Based on the piezoelectric effect of piezoelectric materials,an electromechanical coupling equation of the series nonlinear piezoelectric energy harvesting system is established by applying Lagrange's equation and Kirchhoff's law,by the magnitude of the magnetic force,the dynamic characteristics of the system under small magnetic force are analyzed,and the dynamic behavior of the system with different combinations of excitation amplitude and combinations of excitation frequency under large magnetic force is studied as well.The results show that a piezoelectric harvester,either for periodic or chaotic motion,it will cause vibration propagation or chaotic propagation due to the converse piezoelectric effect,and it will make the other harvester behave the same movement even without input excitation.2.For vibration propagation of series system when the magnetic force is samll,the relationship between the displacement response and the excitation amplitude is derived using the multi-scale method.With the formula obtained,the influence of system parameters of converse piezoelectric effect on vibration propagation is analyzed.The results show the index of vibration propagation will increase as the equivalent load or equivalent electromechanical coupling coefficient increase.3.Refer to chaos propagation,a kind of vibration propagation when the magnetic force is large,the index is the ratio of k₁-step chaos intensity riginated from uniform theory.The results from simulations show that the index of chaos propagation will increase as the equivalent load or equivalent electromechanical coupling coefficient increase4.The characteristics of the series energy harvesting system are studied.The influences of many factors,such as the exciting amplitude,exciting frequency,equivalent load,the equivalent electromechanical coupling coefficient and the number of energy harvesters,on the efficiency of the system are discussed respectively.The efficiency of the series nonlinear piezoelectric harvesting system will be the best when each piezoelectric harvester has a large period of motion,there is a positive correlation between the excitation frequency and the excitation amplitude of extremum point,and the optimal load electrical resistance of the system is not the same at different excitation amplitude and excitation frequency.5.The results show that the chaotic motion can enhance the efficiency of the series energy harvesting system under weak exciting,the edge of chaos of the piezoelectric energy harvester is studied by combining the Melnikov theory with numerical simulation,and the impact of the system parameters on the edge of chaos are discussed.The study reveals that the edge of chaos obtained by the Melnikov method is more conservative and larger than the edge obtained by the simulation solution in general.