Research On Performance Optimization Of Self-adaptive Piezoelectric Energy Harvester With Resonance Frequency Tuning By Magnetic Force

In the past two decades,energy harvesting technology has received more and more attention from scholars in the fields of mechanics,electronics,physics,and aviation.Using the positive piezoelectric effect of piezoelectric materials for energy harvesting,on the one hand,can reduce the cost of using batteries,on the other hand,it also implements the concept of green development.As a piezoelectric cantilever beam is the most common and simple energy harvester,considering how to optimize its energy harvesting performance has a high reference value for studying more complex and efficient energy harvesting structures.The traditional piezoelectric cantilever beam only relies on the large deformation at the resonance frequency,and the efficiency is low.Therefore,in order to improve the environmental applicability of the piezoelectric energy harvester and expand the frequency range,this paper takes the piezoelectric cantilever beam as the research object.Under different excitation levels,magnetic force is introduced to optimize the performance of the energy harvester;at the same time,it is proposed an adaptive tuning scheme.The main research contents of the thesis are as follows:(1)The working principle of the cantilever piezoelectric energy harvester is analyzed in detail,and the distributed parameter model of the segmented piezoelectric cantilever beam is established;then,the finite element model is established for comparison and verification with the distributed parameter model;finally,the tip displacement response of the cantilever piezoelectric energy harvester,the output voltage and power are analyzed.(2)A piezoelectric energy harvester with adjustable frequency is designed.First,using the magnetic attraction between two permanent magnets as the axial tension applied to the cantilever beam,a linear dynamic model of the cantilever beam piezoelectric energy harvester is established;then,a finite element cantilever beam piezoelectric coupling model and a magnetic force model are established;Subsequently,a piezoelectric energy harvester experimental test device under the axial magnetic force was built,and the natural frequency of the structure was changed by adjusting the axial distance between the two magnets;finally,the influence of axial force on the natural frequency,voltage response,the tip displacement and optimal load resistance is discussed.(3)A self-adaptive piezoelectric energy harvesting scheme with resonance frequency tuning by magnetic force is proposed.This scheme finds the maximum voltage response to match the natural frequency with the excitation frequency.The idea of gradually reducing the tuning step size is used to improve the tuning accuracy.First,the basic structural design and theoretical basis of the self-adaptive system are introduced;then,the entire process of the self-adaptive tuning scheme is described in detail and apply the scheme to a specific experimental system;the experiment result shows that self-adaptive piezoelectric energy harvesting method has good applicability and effectiveness.(4)The self-adaptive tuing scheme is introduced into the nonlinear system to improve the output performance of the piezoelectric energy harvester.First,the Lagrangian equation is used to establish the nonlinear dynamic equation of the cantilever beam piezoelectric energy harvester,and the nonlinear vibration response analysis is performed;then,an adaptive nonlinear piezoelectric energy harvesting experimental platform is built to verify the theoretical model;finally,the adaptive tuning of the nonlinear system is completed and improving the energy capture efficiency.