Design And Experimental Study Of Nonlinear Preloaded Simply Supported Piezoelectric Beam Energy Harvester

Piezoelectric vibration energy harvester(PVEH)has shown wide application prospects in aerospace,biomedical,unmanned field monitoring,intelligent wearing equipment and other fields because of its simple structure,easy integration,high energy density and strong environmental adaptability.But,one of the bottlenecks is that the optimal energy capture frequency of piezoelectric arrays is so high and the frequency band is too narrow.So many nonlinear techniques have been used to solve this problem including prestressing induced frequency down and magnetically induced bistability.These two technologies have become the mainstream technologies and have been extensively studied by scholars at home and abroad.Based on the project of ‘NSFC' called ‘Research on Composite Thermal Power Generation Technology and Method of Piezoelectric and Shape Memory Alloy'(Project No.51707081),a kind of preloaded nonlinear simply supported piezoelectric beam(SSPB)energy harvester is proposed in this paper.Dynamic model is established for numerical analysis and experimental also carried out for verification.The specific research contents of this paper are as follows:Firstly,the structure and working principle of this preloaded nonlinear PVEH with elastic beam are introduced.The geometric non-linear relationship between the displacement of the end of SSPB and the deflection of the center of the SSPB is deduced,and the ABAQUS simulation and experimental verification are carried out.Then,the relationship between the total potential energy of SSPB and elastic beam is analyzed,and the appropriate pre-tightened stiffness and pre-tightened interval are selected to analyze the principle of energy conversion and the advantages of this structure in energy conversion.Secondly,the formulas of potential energy and kinetic energy of each part of the coupled-beam structure system are given.And then,the final electromechanical coupling equation model of this coupled-beam system is derived by using Lagrange Equation.The numerical experiments show that under different conditions of preloading,it can be achieved that the frequency reduction before buckling and the bandwidth of ideal energy capture increase;capturing energy at ultra-low frequency and get very wide bandwidth in critical buckling;the potential well transition is realized,the voltage output of piezoelectric oscillator is obviously improved,and the ideal bandwidth of energy capture is increased after buckling.Finally,a prototype of preloaded nonlinear SSPB energy harvester is made,and the experimental platform is set up to carry out the experiment.Firstly,the frequency-modulated effect of SSPB at constant excitation speed and constant acceleration is tested.In both cases,the optimal energy capture frequency of SSPB can be reduced from 20 Hz to 11 Hz,and the ideal energy capture bandwidth can be increased by 70.8%.When the excitation intensity is increased in the critical buckling state,the peak voltage can be increased and the ideal bandwidth of energy capture can be increased by 50%.Then,the experiments of increasing excitation acceleration of SSPB under pre-tightened,critical buckling and post-buckling states of three elastic beams with different stiffness were carried out respectively.It is found that the critical buckling and post-buckling output voltage of SSPB increase significantly with the increase of excitation acceleration,and the bandwidth increases obviously.For example,under the critical buckling condition of 1674N/m stiffness beam,the peak voltage increases from 48 V to 76V(up 58.3%)and the ideal bandwidth of energy capture increases from 4Hz to 6Hz(up 50%).The peak voltage of piezoelectric oscillator rises from 20 V to 55V(increased by 175%)and the bandwidth rises from 8Hz to 12Hz(increased by 50%)under the condition of post-buckling using elastic beam stiffness of 1674 N/m.Finally,we have done frequency modulation experiments with different pre-tightening quantities for SSPB under three conditions: no mass,4.2g mass and 8.4g mass.It is found that increasing the mass block is beneficial to increasing the ideal bandwidth of energy capture at low frequencies,but it can not continue to reduce the optimal frequency of energy capture significantly.