Nonlinear Dynamic Characteristics Of Multi-field Coupled Piezoelectric Energy Harvester

The output power and conversion efficiency of piezoelectric energy harvesters is a hotspot at home and abroad,the way which uses a magnetic field to shift the resonance peak to broaden the bandwidth of nonlinear piezoelectric energy harvesters is more efficient and more adaptive than that of linear piezoelectric energy harvesters.The response becomes more complex due to the nonlinear characteristics of the magnetic field in the system,so revealing the dynamic response characteristics of the force-magneto-electric multi-field coupled piezoelectric energy harvester system has become an essential part of system optimization.The response law of the system under harmonic and random excitation is revealed,and the relationship between the response characteristics of the system and the system parameters and excitation conditions is analyzed by combining theoretical modeling,analytical analysis,numerical calculation and experimental research.For the force-magneto-electric multi-field coupled piezoelectric energy harvester with external magnetic field,a nonlinear horizontal and longitudinal nonlinear magnon model is established under different magnetic force models by using different magnet action models as the object.A generalized Hamiltonian principle,Rayleigh-Ritz method,constant electric field assumption for piezoelectric elements and Euler-Bernoulli beam theory are used to establish a distributed electromechanical coupling model for multi-field coupled multi-directional piezoelectric energy harvester transverse and longitudinal vibrations,and the model is nondimensionalized.The incremental harmonic balance method was used to analyze the non-dimensional model,and the four-five-order Runge-Kutta method was used to verify the correctness of the analytical solution,and to obtain the response characteristics and performance output of the system under different structural parameters and conditions of different magnetic model systems.By using the Gaussian white noise as the excitation,the FPK equation of multi-field coupled piezoelectric energy harvester model under random vibration is used to obtain the response probability density function under different system parameters.The ignorance of high-order cumulant truncation method is utilized to obtain the system response smoothed mean square value and power spectral density function.The results show that,the magnetic attraction model system can effectively increase the longitudinal response amplitude of the system,increase the frequency band and the output voltage of system response,and make the system resonant frequency move to low frequency,while the magnetic repulsion force on the other hand,can shifte the resonance frequency of the system to high frequencies to meet the requirement that the resonance frequency can be adjustable within a certain range.Finally,an experimental platform is built to study the response characteristics of the piezoelectric energy harvester under different magnetic force models,different magnet spacing and different excitation conditions.The experimental results shows that,when the magnet spacing is 15mm and the excitation amplitude is lm/s2,the system output voltage is increased by about 6 times compared to the case without magnetic input,and the resonance frequency is reduced from 17.3Hz to 9.5Hz.When the system is added with the magnetic repulsion force,the response output of the system resonance is slightly reduced.As the magnetic spacing decreases,the system resonance frequency increases from 17.3 Hz to 20.5 Hz.When the distance between magnets decreases or the excitation amplitude increases,the system output increases.The addition of magnetic attraction not only increases the system output,but also reduces the system resonance frequency,broadens the response frequency band.