【作者】 黄海；

【导师】 陈伟；

【作者基本信息】 安徽大学 ， 电磁场与微波技术， 2024， 硕士

【摘要】 尘埃等离子体作为一种独特的物质形态,存在范围极其广泛,跨越了从星际空间到近地环境的多个尺度。主要由电子、离子、中性分子和尘埃粒子组成,其中尘埃粒子会与带电粒子相互作用而带电,改变等离子体的特性,表现出一些与普通等离子体不一样的现象。电磁波在穿过尘埃等离子体区域时会发生强烈的相互作用,导致电磁波信号强度减弱,相位改变等,严重时会出现通信“黑障”现象,这对飞行器的制导和测控系统非常的不利。因此,深入研究尘埃等离子体对电磁波的散射特性,不仅具有重大的理论价值,而且对解决飞行器通信受阻的问题具有不可忽视的实际意义。此外,时域有限差分(finite-difference time-domain,FDTD)方法因其易于理解,计算效能高等优点得到了快速普及与发展。但基于传统YEE网格的FDTD法的采样点稀疏,导致各向异性和数值色散问题的出现。因此,本文将面中心网格(face-centered cube,FCC)应用到FDTD方法中,对尘埃等离子体的后向雷达散射截面(radar cross section,RCS)进行计算,针对计算结果对尘埃等离子体包覆目标的后向散射特性进行了分析。论文主要工作如下:(1)从玻尔兹曼方程出发,推导了全电离非均匀尘埃等离子体FPL(Fokker-Planck-Landau)碰撞模型下FDTD的迭代表达式。结合尘埃等离子体的碰撞效应和充电效应,得到了FPL碰撞模型下全电离尘埃等离子体的电导率表达式。利用Z变换时域有限差分(Z-transform finite-difference time-domain,Z-FDTD)法计算了二维情况下尘埃等离子体涂覆金属钝头锥的RCS值。分析了尘埃粒子密度、尘埃粒子半径、电子密度与尘埃粒子密度比值、尘埃粒子充电频率以及电磁波的入射角对目标散射特性的影响。结果表明,在全电离空间非均匀尘埃等离子体中,随着尘埃粒子半径的增大会削弱德拜屏蔽效应,导致RCS增大;此外,受到尘埃等离子体的碰撞效应和充电效应的影响,会对目标的RCS产生较大的影响。(2)结合弱电离弱碰撞尘埃等离子体的电导率表达式,采用电流密度卷积面中心网格时域有限差分(JE convolution face-centered cube finite-difference time-domain,JEC-FCC-FDTD)法得到含有尘埃等离子体的电场与磁场迭代式,分别对不同飞行高度、飞行速度、尘埃粒子半径、尘埃粒子密度、电子温度、碰撞频率以及时变尘埃等离子体包覆目标的后向RCS进行了计算。结果表明,飞行高度增加以及飞行速度的减小都会使电子密度减小,减弱尘埃等离子体对电磁波能量的吸收效应,使RCS增大。尘埃粒子密度和半径的增大,导致更多的电磁波被反射,进而使后向RCS值增大。电子温度的增大导致尘埃等离子体对电磁波能量的吸收减少;电子与中性粒子的碰撞频率减小,减小了碰撞所需能量,吸收能量减小;电磁波入射角度的减小,避开了电子密度最高的区域,对RCS产生较大的影响。同时发现尘埃等离子的时变特性会对电磁波的散射特性产生影响,RCS值与电子密度随时间的变化率成正相关。本文为研究尘埃等离子体的电磁波散射特性以及解决高声速飞行器在进行超高声速飞行时遇到的通信“黑障”问题提供了理论基础。更多还原

【Abstract】 As a unique form of matter,dusty plasma exists in an extremely wide range,spanning multiple scales from interstellar space to near-earth environment.It is mainly composed of electrons,ions,neutral molecules and dust particles,of which dust particles will be charged by interacting with charged particles.This changes the characteristics of the plasma and exhibits some phenomena different from ordinary plasma.Electromagnetic(EM)wave will have strong interaction when passing through the dusty plasma region,resulting in weakening of EM wave signal strength,phase change,etc.In serious cases,there will be a communication"blackout"phenomenon,which is very unfavorable to the guidance and measurement and control system of aircraft.Therefore,the in-depth study of the scattering characteristics of dusty plasma to EM waves not only has great theoretical value,but also has practical significance to solve the problem of communication obstruction of aircraft.In addition,the finite-difference time-domain(FDTD)method has been rapidly popularized and developed because of its advantages of easy to understand and high computational efficiency.However,the sampling points of the FDTD method based on the traditional YEE grid are sparse,which leads to anisotropy and numerical dispersion problems.Therefore,in this paper,face-centered cube(FCC)is applied to the FDTD method to calculate the radar cross section(RCS)of dusty plasma.Based on the calculated results,the backscattering characteristics of the dusty plasma coated target are analyzed.The main work of this paper is as follows:(1)Based on Boltzmann equation,the iterative expression of FDTD under Fokker-Planck-Landau(FPL)collision model of fully ionized inhomogeneous dusty plasma is derived.Combining the impact effect and charging effect of dusty plasma,the expression of conductivity of fully ionized dusty plasma under FPL collision model is obtained.Using Z-transform finite-difference time-domain(Z-FDTD)method,the RCS values of dusty plasma coated metal blunt cone in two dimensions are calculated.The effects of dust particle density,dust particle radius,electron density to dust particle density ratio,dust particle charging frequency and EM wave incidence angle on target scattering characteristics are analyzed.The results show that with the increase of dust particle radius,Debye shielding effect is weakened and RCS is increased in non-uniform dusty plasma in fully ionized space.In addition,the impact effect and charging effect of dusty plasma will have a great impact on the RCS of the target.(2)Combined with the conductivity expression of weak ionization and weak collision dusty plasma,the iterative formula of electric and magnetic fields containing dusty plasma is obtained by using the JE convolution face-centered cube finite-difference time-domain(JEC-FCC-FDTD)method.The backward RCS values of targets are calculated under different flight altitude,flight speed,dust particle radius,dust particle density,electron temperature,collision frequency and time-varying dusty plasma.The results show that the increase of flight altitude and the decrease of flight speed will reduce the electron density,weaken the absorption effect of dusty plasma on EM wave energy,and increase the RCS.As the density and radius of dust particles increase,more EM waves are reflected,which increases the backward RCS value.The increase of electron temperature leads to the decrease of the absorption of EM wave energy by dusty plasma.The collision frequency between electron and neutral particle decreases,the energy required for collision decreases,and the absorbed energy decreases.The decrease of EM wave incidence angle avoids the region with the highest electron density,which has a great influence on RCS.At the same time,it is found that the time-varying characteristics of dusty plasma will affect the scattering characteristics of EM wave,and the RCS value is positively correlated with the change rate of electron density with time.This paper provides a theoretical basis for studying the scattering characteristics of EM wave of dusty plasma and solving the communication"blackout"problem encountered by high sound velocity aircraft during ultra-high sound speed flight.更多还原