Scattering Characteristics Of Electrically Large Targets Coated By Dusty Plasma

Dust plasma is composed of electrons,ions,neutral molecules and dust particles.It is widely found in natural space and aerospace equipment,such as the ionosphere,rocket wakes,and the surface of hypersonic vehicles.Dust plasma will seriously affect the propagation and scattering characteristics of electromagnetic waves.Therefore,there are more and more researches related to dust plasma,which are of great significance to the fields of microwave communication,radar detection,and aerospace science.As the frequency of the radar wave increases,the electrical size of the aircraft will become very large.The physical optics method has the advantages of low storage cost and fast calculation speed.It can be used to analyze the scattering characteristics of dusty plasma-coated electrically large-scale targets.Based on the theory of dust plasma dynamics,using the physical optics method of coating the target,the scattering characteristics of the uniform and non-uniform weakly ionized dust plasma coated target under the modified BGK model and the fully ionized dust plasma coated target based on the FPL model are studied in the commonly used frequency bands for radar detection.The work content of the thesis includes the following 4 aspects:1.Introduced the basic concepts and theories in dusty plasma,deduced the Stratton-Chu equation and the physical optics integral expression of the coated target scattering,and introduced the physical optics approximation and occlusion judgment algorithm in detail.The RCS of the blunt cone coated with lossy material is calculated and compared with the calculation result of the Multilevel Fast Multipole Method to verify the correctness of the physical optics method.2.According to the limited trajectory model,during the charging process of dust particles,the minimum initial electron velocity for collision is not zero,and the collision cross section is different from the area of the dust particles.Therefore,this paper revises the dust charging kinetic theory in the BGK model,and obtains an improved expression for the complex permittivity of the weakly ionized dust plasma.Based on the new dielectric parameter model,RCS of electrically large blunt cones coated with uniform weakly ionized dust plasma was calculated by physical optics,and compared with the calculation results under the traditional model.The influence of dust plasma parameters on electromagnetic wave scattering characteristics under the modified BGK model is analyzed.The results show that the new value is significantly lower than the traditional value.3.Since the flow field distribution around the hypersonic vehicle is non-uniform,the electron density changes particularly sharply in the direction perpendicular to the surface of the vehicle.Therefore,based on the modified BGK model,combined with the flow field data obtained from flight test and simulation,this paper establishes a layered non-uniform dust plasma sheath model,uses the physical optics method to calculate the backward RCS of the aircraft assembly target,and compares it with the calculation results of the uniform plasma target.The effects of flight altitude,flight speed,incident angle and dust plasma parameters on the electromagnetic scattering characteristics of the target covered by the non-uniform weakly ionized dust plasma sheath are analyzed.These research conclusions provide engineering reference and theoretical basis for hypersonic vehicle radar detection.4.In some areas,such as aircraft heads,space plasmas,shock waves and fusion plasmas,the plasma temperature up to tens of thousands K,and there are hardly any neutral molecules,which can be regarded as fully ionized dust plasma.In the fully ionized plasma,long-range and small-angle Coulomb collisions of electrons are dominant,so the FPL collision model is suitable for studying fully ionized dusty plasma.At the end of this paper,the PO method is extended to the calculation of electromagnetic scattering of electrically large targets coated with fully ionized dust plasma under the FPL model.The RCS based on the BGK model and the FPL model for fully ionized dust plasma targets are compared.And the scattering characteristics of fully ionized and weakly ionized dust plasma coated targets were compared,and the variation of RCS of fully ionized dust plasma coated targets under different dust plasma parameters was analyzed.