Design And Research Of Vibration Energy Harvesters For Fatigue Resistance Improvement

Environmental energy harvesting technology can effectively promote the development of civil engineering materials and related components toward self-awareness and self-powering,and therefore has broad application prospects in the field of intelligent structural health monitoring.However,most of the research now focuses on how to improve the power generation efficiency of energy harvesters,while less research has been conducted on the whole life cycle cost performance of harvesters,especially the fatigue resistance performance.In fact,many existing technologies to enhance the power generation efficiency of harvesters are achieved at the expense of their own fatigue resistance performance.At present,cantilever beam type structure is widely used in the design of energy harvesters,which has the advantages of simple structure and high energy conversion efficiency,but the concentration of stress and strain at the fixed end under the effect of long-term vibration easily triggers fatigue damage,which affects the service life of the harvester.In order to delay the fatigue damage of the harvester and improve the working life,this work systematically investigates the vibration energy harvester through numerical simulation and shaker experiments.Firstly,mechanical structures such as levers and gears are introduced into the harvester to realize the vibration from low frequency to high frequency through the reasonable design of transmission ratio and force arm,so that the energy of pedestrian vibration can be collected efficiently.Different from the traditional harvester that puts the piezoelectric material close to the surface of the harvester,this harvester separates the piezoelectric material from the structure itself and collects the vibration energy by striking the piezoelectric material,and is able to ensure the normal use of the harvester by replacing the piezoelectric material.For the curved energy harvester,the design incorporates the nonlinear theory that the surface will exhibit a bistable phenomenon.Simulation software is used to simulate the stress-strain of the curved surface,and then the piezoelectric material is attached to the area with high stress variation to improve the power generation efficiency.The curved energy harvester is able to reduce the stress-strain concentration in a region and delay the fatigue damage by changing the stress of its surface in real time during the vibration process.The results show that the output voltage of the harvester is significantly better than that of the cantilever beam structure and other curved structures,and it is experimentally verified that the increase of the surface thickness will help the output voltage to be uniform and stable;the maximum effective voltage of a single piezoelectric thin film PVDF reaches 7.28 V and the maximum peak-to-peak voltage reaches 30.8 V under the best working condition of the harvester.The best matched load resistance values of the harvester under various operating conditions are mainly distributed in the range of 600 KΩ to 900 KΩ;the maximum power output under vertical vibration excitation reaches 129.44 μW.The related research results will promote the progress of energy harvester research in fatigue damage.Then,we designed a harvester that can capture the energy of horizontal and vertical vibration by making the curvature of the curved surface change under the effect of vibration while playing a supporting role through a reasonable design.The results of the numerical simulation show that the stress-strain distribution of the harvester changes while the curvature changes during the motion;the larger stress values of the harvester surface are distributed in different regions under different motion directions,so that the harvester reduces the concentration of stress-strain in a certain region for a long time and weakens the fatigue damage caused by the concentration of stress-strain.The effect of different parameters on the output performance was investigated through laboratory parametric experiments to optimize the performance of the harvester.The surface energy harvester can retard the risk of fatigue damage to a certain extent,but it cannot completely avoid fatigue damage.To further reduce the risk of fatigue damage,the idea of magnetic levitation is introduced.First,numerical simulations of two conventional electromagnetic type harvesters show that fatigue damage near the fixed end of the cantilever beam will affect the service life of the structure.For the proposed electromagnetic vibration energy harvester,the magnet can provide mutual repulsive force to balance with gravity while changing the magnetic field,so that one end of the harvester is suspended,which reduces the stress concentration phenomenon in the harvester structure itself and can improve the fatigue life of the harvester.Experimental results show that the harvester’s displacement and output voltage are significantly higher at resonant frequencies.If further optimization makes the harvester completely in suspension,fatigue damage will be eliminated in principle,and this study provides a reference for the fatigue life study of electromagnetic vibration energy harvesters.The above research contents and related results promote the research on fatigue life of vibration energy harvester to a certain extent,and provide reference for the research on durability and stability of the harvester,which will promote the healthy development of vibration energy harvester.