Study On The Characteristics Of DBD Plasma And Its Attenuation To Electromagnetic Waves

Plasma stealth technology is a new concept stealth technology that is different from the traditional structure stealth technology,coating stealth technology.It achieves the purpose of aircraft stealth through the absorption,reflection,refraction of the incident electromagnetic wave.As an auxiliary means of structural stealth technology and coating stealth technology,it has a great application prospect in local stealth of aircraft.The key technology is to realize the controllability of plasma electron density and the broadband attenuation of electromagnetic wave.Dielectric Barrier Discharge can produce large and uniform plasma,and has a good application prospect in the field of plasma stealth.Therefore,this dissertation aims at the large area of DBD plasma electron density characteristics and attenuation characteristics of wideband electromagnetic waves,starting from the diagnosis method of DBD plasma electron density,discussing the rule of the radial distribution of the plasma electron density,studying the wide range of regulatory mechanism of large area DBD plasma,putting forward a kind of electromagnetic wave attenuation band broadening multilayer structure of plasma and two methods of the determination of multi-layer plasma parameters.Gradually thorough,the research of the characteristics of DBD plasma and the attenuation of electromagnetic wave is carried out.Accurate diagnosis of electron density is very important for the determination of plasma frequency.This dissertation presents a method for determining electron density based on a simplified collision radiative model of discharge gas at medium and high pressures,which provides a basis for the study of the regulation mechanism of electron density.The accurate diagnosis of electron density is the basis of studying the influencing factors of electron density and the interaction between plasma and electromagnetic wave.Based on the simplified collision radiative model,a diagnosis method of electron density of plasma with large area（discharge gap larger than 1cm）and low ionization degree(electron density lower than 10¹⁷m^-3)under medium and high pressure（0.01-1 atm）is presented in this dissertation,which provides a method basis for the study of the spatial distribution law of electron density and the regulation mechanism of wide range.The distribution of plasma in a closed space has a great influence on the propagation and attenuation of electromagnetic waves in it.In this dissertation,the effect of partial discharge on internal parameters of discharge is analyzed by establishing equivalent circuit model of pseudo-glow discharge mode.The radial distribution law of electron density is studied.It is found that the adjustable range of electron density in single gas discharge is narrow.In addition,it is found that the edge region of the plasma is narrow and the electron density has a larger gradient.The engineering application of plasma stealth needs to produce a large area of uniform plasma and realize wide range of electron density adjustment.Aiming at the problem of narrow adjustable range of electron density in single gas discharge,this dissertation studies the characteristics of large-area plasma discharge mode and electron density regulation of He-Ar mixed gas under different reaction conditions,and analyzes the two-dimensional distribution characteristics of large-area DBD plasma electron density.It is found that the He-Ar mixed gas can combine the advantages of He and Ar and obtain a plasma with high electron density and wide parameter adjustment range.For the problem of a large gradient of electron density variation at the plasma edge,this dissertation proposes a multilayer plasma structure,and puts forward two multilayer plasma parameters（plasma frequency,electron collision frequency,plasma layer thickness）optimization and selection methods.The influence of the number of plasma layers and the incidence Angle of electromagnetic wave on the electromagnetic wave attenuation is analyzed.It is found that the multilayer plasma structure can widen the attenuation band of electromagnetic waves,and the more the number of layers,the more obvious the attenuation effect.The research work in this dissertation is helpful to further understand and master the wide range regulation mechanism of DBD plasma electron density and the method of broadening the attenuation band of electromagnetic wave,and provide certain theoretical basis and technical reference for the application of plasma stealth of aircraft.