Research On The Influence Of Component Ratio On THV Electret Performance And Application

Electret,also named as “yong dian ti”,is a dielectric material that can store space charge and dipole charge for a long time.In recent years,electret membrane material has made remarkable progress in the field of sensor application.Micro-vibration energy harvester made of polymer electret material is a hotspot in micro-energy research because it can effectively convert vibration energy in the environment into electrical energy and then supply energy for miniaturized,portable and integrated self-driving system.However,due to less-than-ideal charge storage properties in electret material,charge may decay in the natural environment,and it limits practical application process.Developing electret material with good charge storage stability,high space charge and dipole charge density which can resist the harsh environment has been top priority.Based on the summary of existing polymer electret research results,this paper explores the electret property of TFE/HFP/VDF terpolymer THV material with different component ratio and studies internal charge behavior of THV220 electret(component ratio is 45.8wt%TFE,18.5wt%HFP,35.7wt%VDF),THV500 electret(component ratio is 59wt%TFE,19wt%HFP,22wt%VDF)and THV815 electret(component ratio is 76.1wt%TFE,10.9wt%HFP,13wt%VDF).On this basis,sandwich FEP/THV/FEP composite electret membrane is prepared,micro-vibration energy harvester based on FEP/THV/FEP electret membrane is proposed and the output performance of the energy harvester is studied.The main results are as follows:(1)Using high temperature melting and hot pressing technology,THV220,THV500 and THV815 terpolymer which have different TFE-HFP-VDF component ratios are prepared by controlling hot-pressing temperature appropriately.The XRD spectrum and crystallinity of the membrane are tested by X-ray diffraction technique.The crystallinity analysis shows that crystallinity increases with the order of THV220,THV500 and THV815 and the crystallinity of THV membrane becomes larger after polarization.Testing dielectric performance of three terpolymers shows that the dielectric constant and dielectric loss of THV220 are larger than that of THV500 and THV815.Polymer’s dielectric constant and dielectric loss are related to its polarity,when the polarity of the material increases,its dielectric constant will increase.The content of polar group VDF in THV220 is the highest,so the dielectric constant of THV220 is largest,and the dielectric loss is largest.(2)The THV220,THV500 and THV815 three membranes are injected by thermal polarization method,the electrostatic field stability of electret membranes under natural storage condition are studied by the method of surface potential measurement,which are obtained at two injecting temperatures of 110℃and 155℃.The results show that the surface potential of thesamples increase with the increase of the injecting electric field,and the surface potential decay rates decrease with the order of THV220,THV500,and THV815.At injecting temperature of110℃,the surface potential of the THV220 electret membrane decays quickly to zero,while the THV815 electret membrane would keep steady about 275 V.Under the action of 155℃ and high injecting electric field,THV815 surface has hetero charge which means surface potential is opposite to the polarity of the injecting electric field.Study on comparison of surface potential stability of one-side electrode and non-plated electrode THV electret material shows that one-side plating can improve the electret charge storage stability.(3)Thermally stimulated discharge spectrum shows that the three THV electrets have both dipole charge and trapped charge.THV220,THV500 and THV815 both have a dipole peak related to the crystal structure at approximately 40℃.For the peak temperature caused by space charge and area enclosed by space charge peak and coordinate axis,THV815 is maximum,THV500 is the second,THV220 is minimum.The space charge desorption peak of the thickness of 320μm sample is bigger than that of 110μm sample,which indicates that the 320μm sample has more deep trap charge.(4)Using high-temperature and hot-pressing technique,the PTFE / THV / PTFE composite membrane is prepared by combining non-polar material PTFE with THV220.PTFE/THV/PTFE composite electret membrane is prepared by injecting the composite membrane with one side plated electrode through the thermal polarization method.The charge storage thermal stability of the composite electret sample wiped with alcohol and original sample are studied by thermally stimulated surface potential decay method,the results show that the surface potentials of two samples increase at first and then decrease,and the maximum surface potential is at 125 ℃.But the increase in the surface potential of sample wiped alcohol is 5 times of the initial surface potential,while the increasing scope of original sample is very small.Based on this phenomenon,a charge storage model of the composite membrane is proposed,and the charge storage mechanism is explained.It is concluded that the thermal stability of electrostatic effect of PTFE /THV / PTFE electret membrane is related to the melting temperature of THV220 polymer layer and VDF polar group.(5)A micro-vibration energy harvester based on PTFE / THV / PTFE electret membrane is designed and fabricated.The test results of output performance show that the output power of micro-vibration energy harvester reaches 2.8?W when tapping frequency is 5Hz.Its output power keeps constant during over 2000 times tapping testing and for 100-days testing process.This result further proves that the PTFE/THV/PTFE composite electret membrane has very good charge storage stability.