Study On Key Technologies Of Electret-based Electrostatic Energy Harvester

With the rapid development of MEMS and CMOS sensors and improvement of data processing capabilities we have entered the era of the internet of everything(Io E),and the ensuing problem of sensor power supply has attracted more and more people’s attention.Vibration energy harvester that can directly convert vibration energy into electrical energy from the environment have become hot topics in recent years because of the short life,large size,long-term storage and other shortcomings of traditional chemical batteries.The electrostatic energy harvester is one type of vibration energy harvester which has attractted more and more attention with the advantages of low cost and easy compatibility with MEMS technology.This article study the V-VEHs’characteristics in depth through theoretical analysis,numerical simulation and experimental tests,respectively.Giving effective solutions from three aspects of theoretical modeling,improving the vibration structural and optimizing key parameters to the problems that the V-VEHs currently face such as coupling mechanism is not clear,high environmental sensitive frequency,narrow half-power bandwidth and low efficiency,etc.The main research results of this thesis are as follows:(1)According to Hamilton Principle,the governing equation of the beam-type electrostatic energy harvester is established,and the dynamic law of the electrostatic energy harvester is revealed,which provides a theoretical basis for the research of the electrostatic energy harvester.For the out-of-plane V-VEHs based on doubly-clamped beams,the expression of the vibration response,output current and power of the V-VEHs in the case of small displacement are deduced.The coupling mechanism between the mechanical vibration unit and the electrostatic unit is revealed.The electrostatic unit affects its dynamic response by changing the equivalent damping and equivalent stiffness of the mechanical vibration unit,which in turn changes its electrical output.For the first time,a variable capacitance model for different electrets length of V-VEHs is established,the model’s accuracy is verified by finite element simulation software COMSOL.The effects of load resistance,initial air gap,electret surface potential,and electret length on the resonant frequency,half-power bandwidth,and output power of the V-VEHs are studied by theoretical analysis,numerical simulation,and experimental tests,respectively.In order to ensure the V-VEHs obtain higher output power and also obtain a greater half power bandwidth at the same time,the optimal design parameters for load resistance,initial air gap,electret surface potential and electret length are given according to the results of the study.(2)In order to reduce the environmental sensitive frequency of the V-VEHs,an up-conversion structure is first introduced in the V-VEHs.The frequency conversion mechanism of the up-conversion structure is studied by experimental testing,an completely inelastic impact electromechanical coupling model of the V-VEHs based on an up-conversion structure is established according to the experimental test results,and the expression of the vibration response and output voltage of the V-VEHs is also deduced.A prototype of the V-VEHs based on an up-conversion structure is fabricated,the effect of high frequency beam’s damping ratio and natural frequency on the output characteristics of the V-VEHs is experimentally tested.The results show that the smaller the high-frequency beam’s damping ratio is,the better the output performance of the V-VEHs is,and there exists an optimal high-frequency beam’s natural frequency that to maximize the output power of the V-VEHs.The V-VEHs can convert part of the vibration energy within the vibration frequency between 1Hz and 70 Hz into electrical energy under the action of the excitation load with the amplitude is8 m/s~2 after the introduction of the up-conversion structure.(3)A non-linear up-conversion based V-VEHs has been proposed for the first time in this thesis,and the dynamic model of the nonlinear up-conversion structure is established,and the mathematical expressions between the amplitude of the free end of the low-frequency beam and the excitation acceleration amplitude,excitation frequency and nonlinear factor are deduced.Numerical simulations and experimental results show that with the introduction of nonlinear repulsion,with the increase of nonlinear repulsive force,the environmental sensitive frequency of the V-VEHs decreases,the bandwidth increases,and the output voltage amplitude increases significantly also.After the introduction of nonlinear suction force,with the increase of nonlinear suction force,the environmental sensitive frequency of the V-VEHs increases,the bandwidth gradually increases and finally stabilizes,and the output voltage amplitude increases first and then decreases with the increase of the nonlinear suction force.(4)Aiming at the problem of low energy convert efficiency of the single V-VEHs,a electrostatic-piezoelectric-electromagnetic multimode hybrid up-conversion based vibration energy harvester is proposed on the basis of an up-conversion V-VEHs without increasing its volume.The output characteristics of the multimode hybrid up-conversion based vibration energy harvester under harmonic excitation and random ambient vibration are studied by experimental test methods.The experimental results show that the multimode hybrid up-conversion based vibration energy harvester designed in this thesis can convert part of the vibration energy which frequency between 2 Hz and 36 Hz into electrical energy under the action of the excitation load with the amplitude is10 m/s~2.Compared to a single up-conversion V-VEHs,the energy convert efficiency of the multimode hybrid up-conversion based vibration energy harvester is increased by 292%under harmonic excitation.