【作者】 郭斌；

【导师】 王晓钢；

【作者基本信息】 大连理工大学 ， 等离子体物理， 2006， 博士

【摘要】 现代技术的许多方面都与电磁场,尤其是高频电磁场有关。作为电磁理论的一个重要分支,电磁波与等离子体的相互作用,特别是电磁波在等离子体中的传播和吸收问题,无论从等离子体物理本身还是它的实际应用方面来说,都是一个古老而且又是十分活跃的研究领域。尤其是进入到90年代,由于新兴技术的发展,诸如等离子体隐身技术、等离子体天线技术、等离子体波加热技术等,又激起了众多研究人员的兴趣,并成为等离子体物理、电离层物理、大气物理、雷达通信、等离子体天线和等离子体源等领域的一个研究热点。 本文主要研究了高频电磁波在大气压等离子体层中传播和吸收的特性,着重考虑了大气中的负离子、电子与中性气体的碰撞频率、外加磁场、以及非线性现象对高频电磁波在大气压等离子体层中的传播的物理机制和吸收的影响。 第一章,简要介绍了等离子体概念、波在等离子体中传播的各种情形和基本特性、等离子体隐身技术以及研究等离子体隐身技术的方法和研究概况等。 第二章,考虑了更加实际情况下的放电条件下的大气等离子体,将等离子体视为由正离子、负离子和电子以及中性气体组成的系统。研究了高频电磁波在大气等离子体层中的传播特性,尤其是研究了大气中负离子的存在对高频电磁波在等离子体层中吸收的影响。结果发现,负离子的存在使得电子相对密度减少,从而显著减少了高频电磁波在大气等离子体层中的吸收。 第三章,结合更为实际的情况,考虑了覆盖在金属表面上的等离子体层,首次推导出了电磁波在覆盖在金属表面上的大气等离子体层中的多次反射和吸收公式,研究了负离子对高频电磁波在覆盖在金属表面上的大气等离子体层中的吸收的影响,并且还探讨了电子与中性气体的碰撞频率对高频电磁波在等离子体层中吸收的影响。进一步,考虑了外加磁场对高频电磁波在等离子体层中的吸收的影响,发现外加磁场可以增强大气等离子体层对高频电磁波的吸收。而且比较了电子相对密度和外加磁场对电磁波吸收的影响,结果发现,在较低频情况下,电子的相对密度起着主要作用,而在高频情况下,外加磁场起着主要作用。 第四章,首先简要介绍了时域有限差分法的基本思想和基本实现方法以及数值稳定性和吸收边界条件。其次,采用了自洽的多流体等离子体运动方程模型研究了高频电磁波在等离子体层中的非线性吸收现象,并且比较了线性情况下的吸收和非线性情况下的更多还原

【Abstract】 Many aspects of modern technology relate to electromagnetic waves, especially high frequency electromagnetic waves. As an important branch of electromagnetics theory, the interaction of electromagnetic waves with plasmas, partiularly the problem of electromagnetic wave propagation and absorption in plasmas, is an old but still active area, both in plasma physics and its applications. In recent years, especially till 1990s, as developments of new technologies, such as plasma stealth, plasma antenna, and wave heating in plasmas, etc., is attracting much attention of many researchers in the world. Therefore, it becomes a hotspot of researches in plasma physics, ionosphere physics, atmospheric physics, radar communication, and plasma sources.The present thesis aims mainly at studying power absorption of high frequency electromagnetic waves in partially ionized plasma layer in atmospheric conditions, with effects of negative ions in atmosphere, collision rate between electron and neuter gas, the external magnetic field, and nonlinear effects on power absorption of high frequency electromagnetic waves in partially ionized plasma layer under atmospheric conditions.First, a briefly introduction is made in Chapter 1 to the concept and examples of electromagnetic wave propagation in plasmas, the characteristics of the propagation, plasma stealth, and the means and general situation of the research.Then, we in Chapter 2 consider plasma as a there-component fluid with electron, positively and negatively charged ions, according to the real condition of atmospheric plasma. Numerical simulation for characteristics of electromagnetic wave propagation in such a plasma is presented, especially with effects of negatively charged ions. Results show that the presence of negatively charged ions can significantly reduce the relative electron density, and therefore the power absorption.In Chapter 3, considering a plasma layer covering a metal surface in atmosphere conditions, we for the first time derive a general formula of total power absorption and reflection in the plasma layer with infinite times of reflections between the atmosphere-plasma interface and the metal surface. The power absorption of electromagnetic waves the in plasma layer and effects of collision rate between electron and neuter gas have been studied. Then, theeffect of external magnetic field on power absorption has also been studied. The results show that the external magnetic field can enhance the absorption. Also the effect of relative electron density is in comparison with that of the external magnetic field. It is founded that in the weak magnetic field range, the dependence on the magnetic field strength is not significant, and the electron population is then a key factor for power absorption. In the strong magnetic field range however, the effect of the magnetic field becomes dominant.In Cahpter 4, we briefly introduce the basic ideas and methods of finite-difference time-domain (FDTD), as wellas numerical stability and absorbing boundary conditions. Then numerical simulations based on FDTD approximation to multi-fluid equations for positive ions, negative ions and electrons are used to study high frequency electromagnetic wave propagation and nonlinear absorption in the plasma layer. Results show that the nonlinear absorption effect can reduce power absorption in comparison with the linear absorption, in particular for the very high frequency regime.Based on the other mechanism of plasma stealth technology (refraction stealth), we in Chapter 5 briefly study the characteristics of electromagnetic wave absorption in suddenly created plasmas. Results show that the incident electromagnetic wave can be splited into two new waves which with frequencies different from the incident wave. And the direction of propagating for one of them is opposite to the incident. At the same time, it is founded that the new wave frequency can depart from the original incident wave by as much as 35%. It significantly reduces the radar cross section.Finally, conclusions and the future work are given in Chapter 6.更多还原