Study On Electrostatic Field Stability And Charge Distribution Uniformity Of FEP Film Electret

Electret was proposed in 1892 by Heaviside,a British physicist.The electret is a dielectric material that can be permanently polarized.The first electret in the world was prepared by Japanese physicist Eguchi in 1919.In recent years,with the development of science and technology and the continuous efforts of researchers,great success has been achieved in both theoretical research and practical applications.As a dielectric material capable of permanently storing charge,electrets can be used as sensing media in various types of acoustic and electrical sensors,micro-power generation systems,and micro-energy harvesters.In the electret acoustic and electrical sensor industry,the use of fluoroethylenepropylene(FEP)electrets accounts for the majority.At present,the main problem of the electret acoustic sensor is that the sensitivity of the device changes greatly during use,which leads to uneven performance of the market products.The main reason for this problem is that the mechanism affecting the charge storage stability and charge distribution uniformity of the FEP film electret is still unclear,and there is no theoretical guidance for the control of product performance.Therefore,in-depth study of the storage mechanism of FEP film electrets,and improve their charge storage stability and charge distribution uniformity,is of great significance to promote the development of research on electret acoustic sensors and other sensor devices.In this paper,two kinds of FEP film materials with excellent performance and poor performance provided by the electret acoustic sensor manufacturer and FEP film prepared with domestic FEP powder are taken as research objects,and the crystal phase structure is controlled by controlling the melting temperature.Different charging methods were used to change the charge trapping properties.Materials such as X-ray diffraction analysis,differential scanning calorimetry,thermal stimulation surface potential attenuation technique and surface potential distribution measurement were used to study the materials and electret research techniques.Correlation between crystal phase structure and electret performance.The main conclusions are as follows:(1)In order to study the effect of the injection temperature on the charge storage performance of the material,the surface potential stability of the FEP samples from different sources at 30?,150? and 200? was tested by the thermal stimulation surface potential attenuation method.The results show that increasing the injection temperature can significantly improve its charge storage stability.Although there are differences between different samples,the overall performance is as follows: Increasing the injection temperature can cause the surface potential decay temperature of the FEP sample to move toward the high temperature region,the attenuation rate is obviously slowed down,and the complete attenuation temperature is increased by nearly 20?.(2)The crystal phase structure of FEP materials from different sources was studied by X-ray diffraction.The results show that the crystal phase structures of different samples are different.In the FEP sample with excellent performance,in addition to the typical FEP crystal phase diffraction peak,there are diffraction peaks which are not found in the other two samples.This result indicates that FEP samples with excellent performance may have different crystal phase structures.Analysis of crystallinity showed that the FEP sample with excellent performance had higher crystallinity than other samples.Specifically,the excellent FEP sample has a crystallinity of 49%,the poorer crystallinity of the sample is 42%,and the laboratory prepared FEP crystallinity is only 40%.(3)The melting-solidification law of FEP materials from different sources was studied by differential scanning calorimetry.The results show that the endothermic peaks in the melting process are different from the exothermic peaks in the curing process.The endothermic peak corresponds to a temperature higher than the temperature corresponding to the exothermic peak,and the exothermic peak is sharper than the endothermic peak.The temperature of the endothermic peak and the exothermic peak of the FEP material with excellent performance is higher than the other two samples.After half-width analysis of the exothermic peak and the endothermic peak,it was found that the FEP sample with excellent performance had a narrower half-width of the exothermic peak and the endothermic peak.(4)In order to study the effect of melt temperature on the crystallization properties and charge storage properties of the material,the thermal stimulation surface potential decay test combined with X-ray diffraction analysis was used to test the rapid cooling and solidification of the melt at 310? and 320?.Crystallization properties and charge storage performance correlation.The results show that when the melt temperature is 320?,the crystallinity of the obtained sample is larger,the temperature corresponding to the initial decay of the surface potential is higher,and the decay rate is slower in the high temperature region.(5)In order to study the influence of polarization method on the uniformity of charge distribution,the charge distribution of corona polarization and interfacial polarization samples was measured by semi-automated test platform.The results show that the interface polarization sample has better than corona polarization sample.Better charge distribution uniformity.For corona-polarized samples,the uniformity of charge distribution deteriorates with increasing storage time;while the interfacial polarized sample maintains good charge distribution uniformity over a 500-hour storage period.(6)In order to study the effect of the vapor-deposited electrode on the uniformity of charge distribution on the back side,the charge distribution uniformity of the back vapor-deposited electrode and the non-vapor-deposited electrode sample under the same polarization method was studied by a semi-automated test platform.The results show that: For the interface-polarized sample,the vapor-deposited electrode can significantly improve the uniformity of the charge distribution;however,for the corona-polarized sample,the uniformity of the charge distribution after evaporation of the electrode is deteriorated.(7)The charge storage stability of the samples obtained by different polarization methods during the 500-hour storage period after polarization was tested using a semi-automated test platform.The results show that the corona-polarized sample has a faster charge decay rate,while the interfacial polarized sample has a much slower charge decay and exhibits better stability.However,the stable surface potential of the corona-polarized sample is higher than that of the interface-polarized sample.The reason may be related to the higher initial surface potential of the corona-polarized sample.(8)The charge storage stability in the 500-hour storage period after polarization of the back vapor-deposited electrode and the non-vapor-deposited electrode sample was tested using a semi-automated test platform.The results show that the charge storage stability of the vapor-deposited electrode is significantly better than that of the non-evaporated electrode,whether it is corona polarization or interfacial polarization.This shows that the vapor-deposited electrode can delay the decay of the charge in the material,thereby improving the charge storage stability.In summary,the charge storage stability of the FEP film electret is related to the internal crystallization properties of the material.The higher the internal crystallinity of the material,the better the charge storage performance of the FEP electret.By controlling the melt temperature,the crystallinity of the FEP material can be improved,thereby improving the electret charge storage stability of the FEP.The single-sided plating electrode can delay the charge decay rate of the FEP film electret and improve the charge storage stability.The FEP film electret charge distribution uniformity that can be obtained by the interface polarization method is better.The results obtained in this paper can provide theoretical and technical guidance for the preparation of more excellent FEP film electrets.