Design And Implementation Of Piezoelectric Energy Harvester For Low-frequency Vibration Environment

Piezoelectric energy harvester can directly convert the ambient vibration energy into electricity to supply low-power electronic devices,has become a research focus in energy technologies.As one of the most common structural,piezoelectric cantilever beams are being widely studied with relatively low resonant frequencies and high conversion efficiencies.However,the piezoelectric cantilever beams can produce high energy density only near the resonant frequencies.In natural environment,most of the vibration are in infrasound frequencies(such as wave fluctuation,human motion and so on),at the same time,its magnitude and direction are fluctuant.Therefore,the random nature of ambient vibration makes it difficult for piezoelectric cantilever beams to work at resonant frequencies,which results in a very low generation performance.This article mainly aims at the piezoelectric cantilever beams and make investigation on pendulum ball impactexcited piezoelectric energy harvester in low frequency vibration through finite element analysis and experimental verification.The influence of material properties and structural parameters on the output characteristics of piezoelectric cantilevers have been analyzed by finite element method and verified by experiments.In addition,the relationships among output voltage,output power,optimal load and internal impedance of single piezoelectric cantilevers,parallel bipiezoelectric cantilevers and series bi-piezoelectric cantilevers have been discussed.Through the analysis,when the excitation frequency slightly shifts away the resonance frequency of the harvester,the power generation is drastically reduced,which results in a narrow operating frequency bandwith of piezoeletric cantilever beam.The output power characteristics of piezoelectric cantilever beam under impact force are demonstrated by finite element simulation analysis.Based on the cantilever beam structure,a single pendulum ball impact-excited piezoelectric energy harvesting device has been designed.According to the finite element simulation analysis and actual testing results,it is confirmed that the device can effectively convert the vibration energy of the low-frequency environment into the high-frequency collision between the pendulum and the cantilevers,so as to generate a high output voltage and power.When the ambient frequency of vibration is 2Hz,the collision frequency between the pendulum and the cantilevers reaches 10 Hz.The peak output voltage generated by the collision of two piezoelectric cantilevers are respectively 30.2V and 26.1V.Under the parallel connection of two piezoelectric cantilevers,a maximum average power of 10.53?W can be achieve across a 130k? external load resistance.The impact between the pendulum ball and the cantilevers can be caused by the external vibration frequency range from 1Hz to 8Hz.According to the practical application,such as collecting vibration energy from wave fluctuation or human motion,a bi-pendulum ball impact-excited piezoelectric energy harvester has been proposed.Compared with the single pendulum ball structure,the bipendulum ball structure can interact with two cantilever beams in one collision.By this structure,not only the output power of the piezoelectric energy absorbing device is increased,but also the optimal load of the piezoelectric energy absorbing device can be effectively reduced.A maximum average power of 43?W can be achieve across a 47k? external load resistance and 2Hz jitter vibration.By using a bridge rectifier circuit,the AC can be converted into DC output with an open-circuit voltage of 5.07 V,which is sufficient for the MEMS power requirements.