Fabrication And Performance Optimization Of An Electret Energy Harvester Based On Elastomer Capacitance Structure

With the arrival of the 5G era,the availability of sustainable and renewable energy becomes an urgent requirement for the substantial number of distributed devices required to build smart cities.The traditional chemical batteries exist bulky,need to be replaced in time,easy to pollution and many other defects.Therefore,the mechanical energy harvester,which directly collects mechanical energy from the surrounding environment and converts it into electric energy,has become a research hotspot in recent years.As a type of mechanical energy harvester,electret-based energy harvester(EEH)has been widely studied for its advantages of high sensitivity,low cost,simple manufacturing process and compatibility with MEMS.At present,there is still ample room for enhancement in the output performance of EEH,which requires further research and improvement.The structure of EEH is divided into three parts:electret,capacitive medium(mostly air)and electrodes.The electret materials are the core of EEH.The output performance of EEH is highly dependent on the performance of the electret materials.In general,the energy collected by the EEH is proportional to the square of the charge density in the electret.Therefore,it is important to find electret materials with high charge density and high charge storage stability to improve the output performance of EEH.The capacitive medium is another main component of EEH.However,until now,there has been no research on the capacitive medium of EEH.The main research work and achievements of this paper are as follows:(1)The air and spring in the electret collector are replaced with an elastomer film.The use of elastomer membranes makes the structure simpler and more compact.And the relative permittivity of the elastomer membranes can be varied to investigate the relationship between the capacitive medium and the output performance of EEH.(2)A theoretical model is established for the EEH using elastomer film as capacitive medium.It is evident from the theoretical model that the surface potential of the electret is proportional to the output current and output voltage of the EEH.In addition,through the simplified model and numerical simulation,it is found that the output performance of EEH increases first and then decreases with the increase of the relative permittivity of the capacitor medium,that is,there is an optimal relative permittivity to achieve the best output performance of the EEH.(3)The sandwich structure was used to improve the performance of fluorinated ethylene propylene(FEP)electret membrane.tetrafluoroethylene-hexafluoropropylene-vinylidene terpolymer(THV)membrane is used as the intermediate layer.The surface potential of FEP electret membrane and FEP/THV/FEP electret membrane is measured under three different conditions(room temperature,continuous heating,and alcohol scrubbing).The experimental results show that the sandwich structure improves the charge density and stability of the electret.(4)Using carbon nanotubes(CNTs)doped with polydimethylsiloxane(PDMS),the composite films(CNT@PDMS)with 0-2.8 wt%of carbon nanotubes were prepared.The relative permittivities of CNT@PDMS films are measured.The experimental results show that doping CNT in PDMS can effectively improve the relative permittivity.(5)The experimental testing of the impact of relative permittivity of capacitive medium on EEH output performance is conducted.The experimental results verify the conclusion about the relationship between the relative permittivity of the capacitor medium and the output performance of EEH in the theoretical part of this paper.According to this conclusion,the relative permittivity of the capacitor medium is optimized successfully,and the output performance of EEH is significantly improved.This work provides an intriguing design methodology for the development of EEH.(6)Simulation of the EEH excited by mechanical energy in daily environment.Using a human finger to click the optimized optimal EEH device,it was found that the output power can reach 1.549 m W at an external load of 10 MΩ,corresponding to the power density of 0.948 W/m~2.When the optimal EEH is connected to 100 blue LED lights in series,it can instantly light up all the bulbs.