Studies On Power Absorption Of High Frequency Electromagnetic Waves In Partially Ionized Plasma Layer Under Atmosphere Conditions

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.