Design And Research Of Low Frequency Multi-DOF Piezoelectric Energy Harvester

With the development of electronic technology,power supply for passive micro electronic devices has become a hot research topic.Due to the advantages of simple fabrication and high energy conversion efficiency,piezoelectric energy harvester has become the focus of scholars at home and abroad.Piezoelectric energy harvester can capture the vibration energy in the environment and convert it into electrical energy.However,because the frequency and direction of environmental vibration are usually unknown,the vast majority of vibration environments in natural environment are low-frequency vibration environments,and there are vibrations in all directions.Therefore,starting from the cantilever-type piezoelectric energy harvester,through the analysis of ANSYS finite element software and experimental verification,this paper proposes two kinds of stepped and field shape piezoelectric energy harvester which can collect energy in multiple vibration directions under low frequency vibration environment,so as to improve the output voltage and output power.Firstly,the simulation analysis and experimental study of the stepped piezoelectric energy harvester are carried out,and the effects of different beam lengths and different excitation directions on the output performance are studied respectively.Its resonant frequency is between 10-20 Hz,which meets the low-frequency vibration frequency range in the actual environment.At the resonant frequency,the structure has the maximum voltage and power output,and the half-power bandwidth is about 1.5Hz.The longer the middle beam,the larger the left beam length ratio,the lower the first resonance frequency and the larger the matched impedance.Select the left,center and right beam lengths as30 mm,30mm and 70 mm respectively,and apply a sinusoidal acceleration of 0.5g on the xoz plane.When the excitation direction is 15° along the Z-axis,the structure has the maximum output performance.The maximum output power of the three piezoelectric plates is 2.3m W,1.11 m W and 0.64 m W,respectively.In order to capture energy in multiple vibration directions better,another field shape piezoelectric energy harvester was proposed,and the effects of rod length,mass position and excitation directions on its output performance were analyzed.The measured open circuit voltage and output power have 1-2 peaks within 10-20 Hz,and the half-power bandwidth of a single peak is above 1.2Hz.The vibration modes along the x or y direction are greatly affected by changing the rod.The longer the rod length is,the lower the resonant frequency of the first and third order is.Compared with the structure with the mass block in the middle,the resonant frequency of the structure can be reduced by placing the mass block at four corners.When the length of the rod is 100 mm,the measured maximum output power of the four piezoelectric plates in parallel is 1.62 m W and 0.84 m W at the second and third modes frequencies,respectively.In xoz plane will encourage direction by along the z axis direction gradually become along the x axis,two order within 10-20 Hz modal in the corresponding peak gradually shifts,namely the second order modal frequency of the peak gradually decreases,and the third order peak increases gradually,modal frequencies within 0-90° is two peak,to make the structure not only can capture multiple direction vibration energy,at the same time also has a larger bandwidth.The alternating current generated by piezoelectric energy harvests needs to match an energy storage circuit to convert the alternating current into direct current.Therefore,an improved inductive energy harvesting circuit of self-powered series synchronous switch is proposed in this paper.Compared with the standard energy harvesting circuit and the traditional inductive energy harvesting circuit of series synchronous switch,the improved circuit has only one single envelope detection switch controlled by double capacitors,which greatly reduces the number of components in the circuit,and improves the maximum output power while ensuring a lower optimal load.The measured maximum output power of the stepped and field shape piezoelectric energy harvests is more than 4.7times that of the standard energy harvesting circuits.