Study On Electromagnetic Wave Propagation Characteristics In Plasma Under Cross-electromagnetic Field

During reentry of high-speed aircraft,a plasma layer is generated on the surface due to compression of shock wave and high temperature cause by friction,which is called plasma sheath.Plasma sheath is one of the main factors causing communication blackout during re-entry of high-speed aircraft.Maintaining a good communication state is an important condition for aircraft to return to land safely.Therefore,communication blackout is a problem that has to be solved in aerospace vehicle study.In this thesis,the electromagnetic wave propagation characteristics in plasma are studied based on the method of cross-electromagnetic field,which provides theoretical support and experimental guidance for solving communication blackout.The main research of this thesis is as following:(1)The characteristic parameters of plasma,the phenomenon of electromagnetic wave propagation and the causes of the electromagnetic wave propagation failure in plasma layer are discussed.(2)Based on Matlab numerical simulation,the effects of different electromagnetic wave frequency,plasma parameters,such as plasma frequency,collision frequency,plasma temperature and pressure on the attenuation of electromagnetic wave propagation are studied.On the basis of RAMC flight test and the propagation characteristics of electromagnetic wave in plasma,the absorption,reflection,transmission and attenuation coefficients of electromagnetic wave in plasma within 0-30 GHz frequency band are studied and analyzed.The effects of plasma density and collision frequency on propagation characteristics are also discussed.The results show that reducing plasma density is beneficial to the electromagnetic wave propagation.When the frequency of electromagnetic wave is less than the plasma frequency,the collision frequency will help the propagation of electromagnetic wave.When the frequency of electromagnetic wave is larger than the plasma frequency,the collision frequency will hinder the propagation of electromagnetic wave.Compared with the uniform,exponential and normal plasma density distribution,the transmission loss of electromagnetic wave in plasma with parabola density distribution is the smallest.(3)The model of magnetic window is established,and the propagation and attenuation characteristics of electromagnetic waves with different polarization in plasma layer are studied under magnetic field.The plasma layer is simulated by CST software based on Drude model,and the propagation characteristics of electromagnetic wave in plasma are verified.The study shows that the applied magnetic field can obviously reduce the attenuation of circular polarized electromagnetic wave,and the attenuation of right-hand circular polarized electromagnetic wave is smaller than that of left-hand polarization under the same conditions.In order to obtain a smaller attenuation,the magnetic field intensity required for the right-hand circular polarized electromagnetic wave is also smaller than that for the left-hand polarization.(4)Several plasma generation techniques are discussed,and a new plasma generator is designed based on glow discharge principle.The simulation results show that it is capable of producing plasma section with large area,long duration,continuous controllable density and no electrode shielding.It provides an experimental method and basis for the electromagnetic wave propagation in the plasma.