Radiation propagating transverse to the external magnetic field from an electromagnetic source in an unbounded plasma

The radiation characteristics of a line source of magnetic current embedded in an unbounded plasma are investigated for the case in which a uniform magnetic field is impressed externally throughout the medium in the direction of the source. The plasma is assumed to be a homogeneous and macroscopically neutral mixture of compressible gas of electrons and ions. A two-fluid continuum theory of plasma dynamics is employed. It is shown that it is possible to define three suitable wave functions which satisfy separately simple wave equations whose solutions are written down by inspection. These wave functions specify the three possible modes which are identified, respectively, to be the modified forms of the electromagnetic, the electron plasma and the ion plasma modes. The limiting behavior of these modes are discussed for the following two cases: 1) infinite source frequency and 2) vanishing external magnetic field. The dispersion relations for the three modes are examined in detail for the general case using a perturbation procedure. It is shown that the modified ion plasma (MIP) mode propagates for all frequencies whereas both the modified electron plasma (MEP) mode and the modified electromagnetic (MEM) mode have a low-frequency cutoff. Explicit expressions for the cutoff frequencies are obtained. The power radiated in each of the three modes is also evaluated. It is found that the power radiated in the MEM mode is always lower than that due to the line source in free space, whereas the power radiated in the two plasma modes is higher than that value for certain ranges of frequency.     

Excitation of Plasma Waves in an Unbounded Homogeneous Plasma by a Line Source

The radiation characteristics of a line source of magnetic current embedded in a homogeneous electron plasma of infinite extent are investigated for the case in which a uniform magnetic field is impressed externally throughout the medium in the direction of the source. The single-fluid theory of magnetohydrodynamics is employed. A very simple model is assumed for the plasma. Under this assumption, it is found that there are two modes of propagation of waves of small amplitude. By examining the behavior of these modes in the limiting cases of vanishing external magnetic field or infinite source frequency, they are identifiable as the modified forms of the usual plasma and optical modes which exist in an isotropic electron plasma. The dispersion relations for these two modes are discussed. The power radiated in each of the two modes is also evaluated. It is found that the power radiated in the optical mode is always lower than that due to the line source in free space, whereas the power radiated in the plasma mode is higher than that value for certain ranges of the source frequency.     

Radiation from a line source in a ground plane covered by a warm plasma slab

The problem of a magnetic line source in a ground plane coated with a warm plasma slab is investigated. Consideration is given to electromagnetic and plasma waves in the slab and to the coupling at the boundaries between these waves and the free-space fields. An integral expression for the radiation field is obtained and is evaluated by the method of steepest descent. The resulting radiation patterns display interesting effects due to electron pressure near the electron plasma frequency, and these are discussed with the help of the transmission line analog to the problem. The surface-wave poles are located and discussed using this same analog.     

电磁波在等离子体中的传播衰减

针对通信黑障的问题,文中从电磁波在等离子体中的传播特性出发,利用Matlab数值仿真,研究不同电磁波频段,不同等离子体参数,包括等离子频率、碰撞频率、等离子温度、压强等对电磁波传播衰减的影响,以及外加磁场作用下,不同极化的电磁波在等离子体层的传播衰减特性。研究结果表明:外加磁场可明显降低圆极化电磁波衰减,并且当外加磁场满足一定条件,大于最小磁场强度时,电磁波衰减小于10 dB;且同等条件下右旋极化比左旋极化电磁波的衰减更小,为了获得较小的电磁波衰减,右旋极化电磁波所需的磁场强度也小于左旋极化。     

表面波放电狭缝天线辐射电磁场的三维数值分析

针对平板型表面波放电等离子体源,建立了表面波放电狭缝天线辐射电磁波模型,对狭缝天线辐射电磁场分布进行了三维数值计算,并与表面波电磁场进行对比分析,讨论了平板型表面波放电机理。结果表明:整个狭缝天线阵激发的电磁场是每个狭缝天线激发电磁场的线性叠加;狭缝天线阵直接激发的电磁场强度在临近波导壁面处很大,并且随着空间距离的增大迅速衰减;狭缝天线阵直接激发和表面波的电场均远大于各自的磁场,分析电、磁场对带电粒子的力作用时可以忽略磁场力的作用;表面波电磁场远大于狭缝天线阵直接辐射的电磁场,强电磁场范围也远大于狭缝天线阵直接激发的强电磁场范围,等离子体有增强电磁场强度、扩大强电磁场范围的作用。     

Transient Analysis of the Electromagnetic Field for a Wave Absorber in Three-Dimensional Space

In recent years, large-scale structures such as tall buildings, large bridges, and towers cause severe reflection and diffraction in the propagation of electromagnetic waves. The most effective means for improvement of these characteristics is coating an electromagnetic wave absorber on the surfaces of structures. At the present time, determination of the performance of a coating and the estimation of its effects are carried out on a practical basis. Beforehand, however, theoretical clarification of absorbing characteristics is necessary for better design of a structure. This analysis demands the unified treatment involving both characteristics of absorber materials and the shapes in three-dimensional space of structures to which they are applied. Also, the analysis of propagation characteristics of a pulse wave in the time domain will be important. In this paper, we report the fundamental treatment of absorbing characteristics, including boundary conditions of the structure. The method of time-domain analysis in three-dimensional space and time is used. This method is formulated by Bergeron's method and based upon the equivalent circuit of both Maxwell's equation and characteristics of the medium. As an example, the performance of a very thin coating of absorber with magnetic loss is presented. The variations of field distribution for changes of magnetic-loss term including permeability and the frequency of incident wave, are shown. The absorbing characteristics for a pulse wave in the time domain are also given as a parameter of incidence angle.     

Dispersion Characteristics of Plasma Mode in Corrugated Plasma Waveguide

The dispersion equation of electromagnetic wave is derived for corrugated waveguide filled with plasma immersed in magnetic field under assumption of small corrugation, the dispersion characteristics of low frequency plasma mode are calculated and analyzed, the dense spectrum of plasma mode is demonstrated.     

空间电荷波传播特性的PIC粒子模拟

采用周期性边界条件的二维准静电PIC粒子模拟程序对空间电荷波的产生及传播过程进行了数值模拟,给出了静止和一维定向漂移空间电荷波的产生及传播特性随等离子体参数变化的关系,通过单电子跟踪的方法,得到了波动过程带电粒子的空间状态的变化规律。其结果,将作为进一步实现空间电荷波与电磁波产生波一波相互作用过程模拟的基础。     

Radiation from a uniaxially anisotropic plasma half space

A line source of magnetic currents is located in a half space with uniaxially anisotropic dielectric constant, with the optic axis inclined at an arbitrary angle to the interface. This two-dimensional, scalar diffraction problem is solved by Fourier integral techniques, and the solution is examined in the asymptotic range of large distance from the source. The radiation field comprises incident, reflected and refracted ray contributions whose properties are determined from a study of the refractive index curves for the medium. In addition, there may exist a lateral wave which is excited by a critically refracted incident ray, and which sheds energy back into the anisotropic medium by refraction. If the medium is a plasma with an externally impressed infinite dc magnetic field, and if the source oscillates below the plasma frequency, there exist shadow regions from which the direct and reflected rays are excluded but which can be penetrated by the lateral waves.     

Superheterodyne Amplification of Sub Millimeter Electromagnetic Waves in an n-GaAs Film

The superheterodyne amplification of sub-millimeter electromagnetic waves in GasAs due to negative differential mobility is analyzed. The nonlinearity arises from the current and the magnetic field of the electromagnetic waves. The case of interaction of two traveling counter propagating electromagnetic waves and the following space charge wave in an n-GaAs film, placed onto i-GaAs substrate, is considered, under a 2D electron gas model. The simulation of this nonlinear interaction shows a certain amplification of the sub-millimeter electromagnetic wave.     

高密度螺旋波等离子体源的应用进展

首先介绍了螺旋波的定义、螺旋波等离子体源产生等离子体所需条件的工作范围以及螺旋波等离子体源主要的一些应用.按照所加磁场范围的不同(分为在磁感应强度为100～1 600 Gs和在强磁场中两部分),分别进一步讨论了国内外各研究小组研制的等离子体源的运行参数及技术特点.随后介绍了螺旋波等离子体源在刻蚀、薄膜沉积和火箭推进三个...     

Radiation from a uniformly moving distribution of electric charge in an anisotropic, compressible plasma

The radiation characteristics of a linear distribution of electric charge moving with a uniform velocity in a homogeneous electron plasma of infinite extent are investigated for the case in which a uniform static magnetic field is impressed externally throughout the medium. The linear distribution of charge and its direction of motion are assumed to be parallel and perpendicular, respectively, to the direction of the external magnetic field. Of the two possible modes of waves of small amplitude, namely, the modified electromagnetic mode and the modified electron plasma mode, the uniformly moving charge distribution excites the modified electron plasma mode. The emitted radiation has no frequencies less than the plasma frequency. For a particular value of the ratio of the gyrotropic to the plasma frequency of the electrons, the frequency and the angular spectrum of the emitted radiation are determined for two values of the velocity of the charge.     

Radiation from a vertical dipole in a warm plasma--Part II

A numerical evaluation of the integrals that constitute the formal solution of the problem of a vertical dipole, which is situated in a homogeneous, warm plasma half-space above a perfectly conducting plane, is considered. An asymptotic series expansion is obtained for these integrals by the double saddle point method of integration. The dominant terms of the solution in the far field are shown to consist of a surface wave, which arises from the residue of a pole, and a space wave, which is the leading term of the saddle point contribution. The space wave is identified as the geometrical ray approximation to the solution. It is demonstrated that the surface wave can propagate when the source frequency is either above or below the plasma frequency. The transfer of power from an incident acoustical (p) mode to a boundary-generated electromagnetic (e) mode, and from an incident e mode to a boundary-generatedpmode, is investigated at a plasma-conductor interface. It is evident in both situations that only a small percentage of the incident power is transformed into the boundary-generated mode. In the case of a vertical dipole, however, it is shown that, at source frequencies which are near to the plasma frequency, the power in the incidentpmode is much larger than that in theemode. Thus, the boundary-generatedemode, which is due to the incidentpmode, is as large as the reflectedemode due to an incidentemode. As a result of this effect, it is pointed out that one can represent the reflectedemode by two image sources.     

含单负材料对称三层平板波导的模式特性

由电磁场的波动方程和边界条件建立了单负材料作为芯层的对称三层平板波导的模式本征方程,用图解法研究其色散特性。研究发现,单负介质波导不支持快波的传播,只支持表面波的传播。在负磁材料平板波导中只存在TE表面模,不存在TM表面模。分析了在负磁材料平板波导中TE模受磁导率的比值-μ2／μ1和波导参数的影响,给出了横向场分布图。在-μ2/μ1〈1时,偶对称只有TE0表面模存在,奇对称只有TE1表面模存在,高阶模式并不存在,且两种模式都没有低频截止;-μ2/μ1〉1时,TE1表面模始终不出现;TE0模的存在与否和波导参数有关,在一定条件下TE0模可出现双模并存。给出的结果可望对表面波器件的设计提供理论基础。     

On instability of low-frequency waves in a stream-magnetized plasma system

The interaction of low-frequency electromagnetic waves propagating at an arbitrary angle to the static magnetic field with a nearly synchronous charged stream along the field in a cold plasma is analyzed. The temporal growth of the waves is found to increase with the signal frequency, the stream density, and the propagation angle off the field line. Explicit forms of maximum growth rate are derived for VLF and ELF waves, and a numerical example is given for a typical ionospheric plasma near the magnetic equator.     

非对称单脊波导的特性计算

从矢量波函数空间的偏微分算子理论出发,给出完备的旋量波函数空间的本征函数系及电磁波基本方程组,由此推导出数学形式简洁的并矢格林函数及基于旋量波算子空间本征函数系的电磁场量,在脊波导的耦合边界上模式匹配,推导出计算公式,给出了两个分析脊波导的实例,得到主模和第一个高阶模的截止频率,非对称脊波导的电中心线偏移量.     

Electromagnetic waves in a suddenly created magnetized Lorentzmedium (transverse propagation)

The interaction of electromagnetic waves in a suddenly created Lorentz medium with impressed steady uniform magnetic field is considered. It was shown that for the case of the incident electric field normal to the static magnetic field, the source wave splits into six new extraordinary waves whose frequencies are different from the incident waves. Three of those six new waves are transmitted waves, and the other three are reflected waves. The dispersion relation, power transmission, and reflection coefficients are derived and discussed     

Ka 波段方同轴线中TM 波的全波算法*

对方同轴线中TM波的FDM(Finite Difference Method)全波算法进行了研究,推导了方同轴线TM波在临界和传播状态下各个电磁分量的全波计算公式,得到了传播状态与临界状态场分量之间的关系式,简化了对传播状态场分量计算,利用Yee氏网格单元对各电磁场分量进行有限差分,采用Matlab编程得到了TM波两个最低模式的色散与电磁场分布情况,与亥姆霍兹法、CST仿真计算结果进行了比较,三者结果均一致,并且研究了网格精度和不同内导体边长对截止频率的影响.全波算法是所有电磁分量参与计算,具有一次求解得到所有电磁场分量、计算速度快的优点,此法同样适用于方同轴线中其它模式的求解,也能求解其它类型传输线中模式的色散特性和电磁场分布问题,具有推广应用的潜力.     

An effect of excitation of a transverse magnetic creeping wave when a transverse electric wave crosses the line of the coincidence of propagation constants

Transverse electromagnetic electric (TE) and transverse magnetic (TM) creeping waves on a surface with an anisotropic impedance boundary condition are considered. An asymptotic theory is developed for creeping waves. The theory is valid near the line where the attenuation parameters of two different types of waves coincide and, therefore, standard asymptotics are inapplicable. Asymptotic formulas describing physical effects that occur when a creeping wave propagates across the degeneracy line are derived. It is found that, behind the degeneracy line, a propagating TE wave excites a TM wave with a small amplitude (of order O(k ^−1/6)) and a propagating TM wave excites a TE wave.     

Guided Waves on an Infinite Cylindrical Cavity in a Magneto-ionic Medium II. Dipolar Modes†

The characteristics of the guided waves supported by an infinitely long cylindrical cavity of free-space immersed in a magneto-ionic medium are investigated for the case of the magnetostatic field in the direction of the axis of the column. The dipolar case for which the fields have an exp (imφ) azimuthal variation, where φ is the angular variable and m ± 1, is treated. The characteristics of the transition, the resonance and the cut-off frequencies of the guided waves ore discussed with particular reference to their dependences on the radius of the free-space column. The dispersion characteristics under propagating conditions are studied in detail both for the special case of vanishing static magnetic field and for the general case of finite magneto-static field corresponding to the two typical values of the ratio R of the gyromagnetic to the plasma frequencies. The lowest-order mode is found to be of the modified TE type and has special features such as that it can have forward or backward wave and fast or slow wave regions in certain portions of its characteristics, depending on the radius of the free-Space column and the azimuthal variation of the fields. All the other higher-order modes are found to be fast forward waves, whose phase velocity monotonically decreases as the frequency is increased and approaches the free-space velocity of electromagnetic waves. For an extremely small radius of the free-space column, the group velocity is vanishingly small for a major portion of the range of propagation of the only existing, lowest-order surface wave.