Research On Interaction Between Plasma And Electromagnetic Wave Based On FDTD Method

In recent years,the interaction between plasma and electromagnetic wave has aroused great interest of researchers with the attention paid to the influence of plasma sheath around hypersonic vehicle on its radar scattering characteristics and the "communication blackout"situation phenomenon occurring when spacecraft reentry capsule enters the atmosphere.This topic is derived from "Mechanism research of the interaction between dynamic plasma sheath and electromagnetic wave",which is one of the sub-projects of the State Key Development Program of Basic Research of China(973 Program)entitled "the theoretical basis of information transmission of high-speed aircraft under plasma sheath in the space".The purpose of this dissertation is to establish a simulation model of the interaction between an electromagnetic wave and plasma,thus,to explore the interaction law between them,and to provide a reference for overcoming hypersonic target recognition and "communication blackout" phenomenon.In this dissertation,the interaction between an electromagnetic wave and plasma is studied.Based on the finite-difference time-domain(FDTD)method,several high-order algorithms which can be uniformly applied to solve different electromagnetic problems of medium type are derived.Topics including the transmission characteristics of an electromagnetic wave through the plasma,the distribution of the high-temperature flow field in the shock tube,the influence of the flow on the radar scattering characteristics of the ontology target and the scattering characteristics of the target illuminated by vortex electromagnetic wave are studied systematically.The main work can be summarized as follows:1.High-order FDTD method based on the unified dielectric coefficient form of different media was developed.By combining the conductivity with the Drude model which is used to describe the dielectric permittivity of plasma,a new Drude model is obtained to describe the dielectric parameters of different media.Several different high-order FDTD methods which are suitable to dispersive media are then derived.The accuracy and efficiency of each method are compared which provides a reference for the algorithm selection of different electromagnetic problems.2.The flow field distribution in the shock tube was analyzed.Several kinds of shock tube models with different size are established and the high-quality grid distribution of them are obtained.Based on the high-quality grid distribution,the flow field are calculated by using the two temperature and seven component chemical reaction models.The flow field distribution with different parameters at a different time during shock wave propagating through the shock tube is obtained.The scale model of the hypersonic target which is named RAM C-? is set up in the low-pressure section of the shock tube to simulate the situation of plasma sheath covering the hypersonic target.3.The interaction between obliquely incident terahertz waves and plasma was studied.Aiming at the problem of "communication blackout",the feasibility of using high-frequency terahertz wave to overcome that phenomenon is investigated.Combined with the location of the electromagnetic wave emitted by the transmitting antenna through the plasma sheath,the calculation model of the terahertz wave propagation in the plasma layer at a certain incidence angle is established.By the law of continuity of the tangential component of the interface wave vector,the transmission process of terahertz wave in plasma which is the two-dimensional case is equivalent to the quasi-one-dimensional case.The equivalent differential equation is solved based on the shift operator finite-difference time-domain(SO-FDTD)method,which greatly reduces the complexity of the problem and saves computational resources.According to the electron density distribution characteristics of the plasma sheath around the hypersonic vehicle at different altitudes,the transmission characteristics of terahertz wave in different plasma layers are studied.The results show that terahertz wave can effectively overcome the "communication blackout" problem,but the frequency band with high transmission coefficient should be selected and the corresponding frequency of absorption peak should be excluded according to the characteristics of communication conditions.4.A simulation model for the transmission system of the electromagnetic wave through the plasma in the shock tube was established.Based on the high-order Z transform FDTD(ZT-FDTD)method,the simulation model of antenna-shock tube-antenna system simulation model was established.The high-temperature flow field parameters obtained by the shock tube simulation are transformed into plasma parameters and then filled into the plasma region of the system.The transmission characteristics of the electromagnetic wave through the shock tube when the shock wave moves to different positions are investigated by the simulation model.5.Scattering characteristics of an electromagnetic wave by the target coated with plasma was investigated.By placing the hypersonic vehicle scale model in the shock tube,the composite model of the target and its surrounding flow field which is obtained after the shock wave passed is obtained.The composite model is extracted and introduced into the open space and then the electromagnetic wave scattering model is established.Then the model is calculated by using the Auxiliary Differential Equation FDTD(ADE-FDTD)method.At the same time,the Radar Cross Section(RCS)of the scale model is calculated and the results are analyzed.6.Scattering characteristics of the vortex electromagnetic beam by targets was analyzed.Based on the expansion formula of each component of the vortex electromagnetic wave in its own coordinate system and the coordinate transformation,field component values of the vortex electromagnetic wave at each point in the problem space are obtained which are used directly as the incident wave in the scattered field formalism,thus the FDTD method is used to study the scattering problem of the vortex electromagnetic beam by objects.In order to improve the calculation accuracy,the high-order scattered field formula based on FDTD method is derived,which obtains higher accuracy with the same resources The influence of different vortex electromagnetic beam parameters on the scattering characteristics is analyzed.