临近空间黑障区高温尘埃等离子体中太赫兹波电磁特性研究

There is no perfect method to completely eliminate the ionization blackout phenomena about the communications interruption of high speed spacecraft in near space yet. Recently, the development of Terahertz wave technology provides an efficient way to solve the problem. However, the study on Terahertz wave propagation in plasma theory is comparatively rare. Meanwhile the effects caused by charged dust particles are not included into the theory. Both vibration frequency and rotation frequency of the dust particles' atom and molecule are at Terahertz wave frequency band. The below two issues will be further investigated in the project according to the current development situation. The main contents are as follows. 1) Cutoff frequency of dusty plasma around spacecraft in the blackout zone will be studied with Terahertz wave reflection imaging principle. The constitutive relation and dispersion relation of thermal dusty plasma will be theoretical deduced and consummated. Consequently the theoretical model for thermal dusty plasma in the blackout zone at Terahertz wave frequency band will be built. 2) Research on electromagnetic characteristic of Terahertz wave propagation in thermal dusty plasma of blackout zone in near space will be fully implemented. The effect to Terahertz wave transmission caused by dust charging and electrical temperature will be analyzed. The earlier theoretical basis on ionization blackout problem practically solved with Terahertz wave detection technology in the future will be established. The anticipated research results will greatly facilitate the progress of space plasma physics and electromagnetic wave theory, the application of Terahertz wave technology in information and communications fields, and the cross-development of radar target scattering characteristic and spatial information technology subjects etc.

临近空间高速飞行器发生通信中断的黑障现象尚未有彻底消除的方法，近年来太赫兹波技术的发展为其提供了有效的解决手段，然而太赫兹波在等离子体中传播理论的研究较少，且该理论未考虑原子分子的振动和转动频率都处于太赫兹频段的带电尘埃颗粒作用。针对目前的发展现状，本项目拟将从以下两个方面开展工作，主要内容包括：1) 利用太赫兹反射成像原理确定黑障区飞行器周围尘埃等离子体的截止频率，理论推导和完善高温尘埃等离子体本构关系、色散关系，从而建立黑障区太赫兹频段高温尘埃等离子体理论模型；2) 全面开展太赫兹波在临近空间黑障区高温尘埃等离子体中电磁特性的研究，分析尘埃充电、电子温度等对太赫兹信号传输的影响，为将来实际利用太赫兹波探测解决黑障问题奠定预先理论基础。预期的研究成果将会大大促进空间等离子体物理和电磁场理论的发展，推动太赫兹技术在信息通信领域的应用，以及促进雷达目标特性与空间信息技术等学科的交叉发展。

本项目研究临近空间黑障区高温尘埃等离子体中太赫兹波电磁特性，引入原子分子的振动和转动频率都处于太赫兹频段的带电尘埃颗粒作用，探索了用太赫兹技术消除高速飞行器发生通信中断黑障现象的可行性。本项目在以下几个方面作出了创新性贡献：.(1) 调研飞行器再入过程中等离子体以及工业高温尘埃等离子体物理参数，给出了尘埃等离子体的介质参数。分析了如何求解尘埃等离子体的截止频率和提取各向异性的介质参数，推导尘埃等离子体本构关系、色散关系，给出了太赫兹频段尘埃等离子体和金属铝的相对介电系数，从而建立黑障区太赫兹频段高温尘埃等离子体理论模型。.(2) 发展传播矩阵方法研究了含尘埃等离子体多层板的太赫兹波传播。计算了铝板覆盖尘埃等离子体是否含真空夹层的传播特性，数值结果表明：真空夹层使铝板(模拟一定厚度飞行器蒙皮)双面覆盖等离子体板的透射系数出现了一些谐振峰，但几乎不影响板相对大的反射系数。.(3) 通过引入充电响应因子和电荷弛豫速率，推导了描述尘埃等离子体鞘套的波方程，利用和发展ADE-FDTD(Auxiliary Differential Equation Finite Difference Time Domain，ADE-FDTD)技术将其离散。讨论了其计算铝板失效的原因。数值计算结果表明，薄铝板几乎将太赫兹波全反射。讨论了介质参数对太赫兹波穿透尘埃等离子体板的影响。.(4) 基于FDTD方法计算了Epstein电子密度分布尘埃等离子体鞘套的电磁散射。尘埃粒子的充电响应因子和尘埃等离子体的角等离子体频率均含有随空间呈Epstein曲线变化分布电子密度。讨论了Epstein函数调制因子和梯度比例因子对太赫兹波在尘埃等离子体板中传播的影响。当尘埃等离子体的电子密度达到1021 m–3时，太赫兹波几乎被尘埃等离子体完全吸收。.(5) 将包含不均匀电子密度，尘埃粒子的充电响应因子和电荷弛豫速率的复介电系数模拟时变的尘埃等离子体鞘套。最后搭建了产生尘埃等离子体装置的平台，对尘埃等离子体的实验测试环境及结果进行了理论和数值预测。. 本项目的研究为太赫兹波在空间、工业等尘埃等离子体的检测和诊断中的应用提供有益的数据参考。