Constitutive relations for a rotating electron plasma

The constitutive relations for small-signal electromagnetic fields propagated in a cylindrical electron plasma rotating around its axis are derived with the use of the electron-theoretical approach. A rotating electron plasma is found to be equivalent to a moving dispersive dielectric with an appropriate dielectric constant, as far as small-signal electromagnetic fields are concerned.     

弱纵向外电场对磁化等离子体中哨声波的影响

本文以等离子体动力论为基础讨论存在纵向外电场时磁化等离子体的哨声波。由于外电场的影响,等离子体偏离平衡态。取电子稳态分布函数为局域的麦克斯韦分布,用沿无扰轨道积分方法求出系统的介电张量,并分别用介电张量的厄米部份和反厄米部份分析哨声的色散关系和增长率。对于波矢在以电场方向为轴顶角为2c锥角范围内的哨声,外电场的作用使波增长;波矢在此锥角范围之外,外电场的作用使其衰减。波的增长率随频率增高而增大,随波矢倾角增大而减小。ee时,波矢与外电场平行对应的最大增长率与等离子体密度成正比,与磁场强度成反比。文中还给出了以电离层F层作背景参数的数值计算结果。     

Resistance of a plane grid condenser moving through a plasma

The resistance of a plane grid condenser, moving in a magnetized plasma, is calculated using the quasi-hydrodynamic approximation for the plasma dielectric tensor. It is shown that, as a consequence of the anomalous Doppler effect, the resistance may become negative. Some implications for antenna measurements in the ionosphere are discussed.     

Diffraction by a perfectly conducting semi-infinite screen in an anisotropic plasma

The scattering of a plane electromagnetic wave by a perfectly conducting semi-infinite screen embedded in a homogeneous plasma is investigated. A uniform magnetic field is assumed to be impressed externally in a direction parallel to the edge of the half plane. The plasma is idealized to be a dielectric characterized by a tensor dielectric constant. The direction of the incident wave is assumed to be in a plane perpendicular to that of the screen. This vector problem is separable into two equivalent scalar problems for which either the electric or the magnetic vector is parallel to the edge of the half plane. It is found that for the case of theEmode, the magnetic vector parallel to the edge of the half plane satisfies a simple wave equation and a new type of impedance boundary condition on the screen. This problem is formulated in terms of an integral equation which specifies the current induced on the screen. The integral equation is of the Wiener-Hopf type and is solved by the usual function-theoretic methods. For a given orientation of the external magnetic field, a surface wave is found to exist along the screen but on one side only. The characteristics of this surface wave are determined.     

THE THEORETICAL INVESTIGATION OF THz ELECTROMAGNETIC WAVES IN A ROD DEGENERATE PLASMA-WAVEGUIDE

By using the Fourier components of dielectric tensor elements of cold collisionless degenerate plasmas, the dispersion relation of electromagnetic waves in a cylindrical metallic waveguide with a degenerate plasma column protected by an annular dielectric layer are obtained. The permissible frequency regions for slow and fast waves in E-mode (TM) are presented. Furthermore, the graph of cutoff frequency versus the radius of plasma column for the fast waves is investigated. In addition, the time growth rate for excitation of symmetric slow E-modes (TM) by a thin annular relativistic electron beam (TAREB) is studied. The graph of time growth rate respect to radius of dielectric layer and accelerating voltage are presented.     

Waveguides Containing Moving Dispersive Media

Perturbation formulas are derived for the changes in the dispersion curves and phase velocity for the modes in an arbitrary composite waveguide structure containing dispersive media in relative motion. The formulas are also valid when the media are fluids with arbitrary velocity distributions. It is shown that the relativistic transformation laws for the frequency and wave vector of uniform plane waves are also valid for waveguide modes provided that all moving media that make up the guide move with the same velocity. There are also difficulties when the moving media are dispersive. In general, one most therefore obtain the dispersion relation directly from the field equations or from the perturbation formulas. An example involving a simple surface wave along the interface of a moving plasma and a dielectric is worked out by both methods. As an interesting side result, it is found that plane waves in an unbounded isotropic plasma have phase velocities independent of the motion of the plasma.     

Improvement of Linear Model of Plasma Filled Dielectric Cerenkov Maser

The plasma filled dielectric Cerenkov maser considering the effect of the plasma grating has been studied. The plasma grating is formed by the modulation of the strong fields. According to the plasma-grating model, An equivalent model is constructed. The modified dispersion relation has been derived .The numerical results show that when the modulation over the background plasma increases, the operation frequency also increases, however, the growth rate varies slightly. Compared with the calculation results obtained by treating the plasma as uniform fluids, the calculation results with the equivalent model describe the bounded bandwidth of the dielectric oscillator more precisely.     

Simulation of a periodic dielectric corrugation with an equivalent anisotropic layer

A periodic, corrugated, dielectric layer is simulated by an anisotropic dielectric layer of equal thickness. The tensor elements of the equivalent dielectric layer are given in terms of the permittivity of the dielectric material, the period of the surface corrugation, and the width of the corrugations. The validity of this technique is verified by comparing the reflection coefficient of the equivalent layer with that of the corresponding corrugated layer using the moment method. Employing a multiple layer approach, the technique is extended to handle periodic surfaces with arbitrary cross sections which can be used to design millimeter wave dielectric plate polarizers and absorbers.     

A technique for solution of Maxwell's equations in a moving dielectric medium

A simple technique is presented for converting a known solution for the electric and magnetic vector fields in a dielectric medium at rest into the corresponding fields in a moving dielectric medium. The technique combines methods presented by Tai [1] with a scaling procedure developed by Clemmow [2]. Tai's work reduces the moving medium problem to the solution of Maxwell's equations in a uniaxial medium, and Clemmow's procedure enables one to convert a known solution in an isotropic medium to the corresponding solution in a uniaxial medium. Thus by first solving for the fields in the medium at rest, then following Clemmow's procedure to obtain the fields in Tai's uniaxial medium, and finally applying Tai's reasoning, one may easily obtain the solution of Maxwell's equations in the moving medium.     

EFFECT OF A WEAK LONGITUDINAL ELECTRIC FIELD ON WHISTLER WAVES

The effect of a longitudinal electric field on whistler waves is studied based onkinetic theory.A local Maxwellian distribution is taken as stationary distribution function ofelectrons which departs from thermodynamic equilibrium due to the applied electric field.Thedielectric tensor is derived by integrating along orbit of the particle in the unperturbed field.Dispersion relation and growth rate are analysed from Hermitian and anti-Hermitian parts ofthis tensor respectively.It is found that the waves are growing when the angle between the wavevector and the electric field is in range of θ<2θ_c, otherwise the whistler waves are damping.Thegrowth rate increases with wave frequency and decreases with the angle between the wave vectorand the applied field.In the case of ω_e(?)Ω the maximum of growth rate,which is at θ=O_l isproportional to the plasma density and anti-proportional to the magnetic field.Some computedresults for parameters at top of the F layer are given.     

束-离子通道系统的电磁慢波特性

 利用荷流体线性微扰理论分析了无外加磁场时相对论电子束在离子通道中的三维扰动效应,导出了系统的等效介电率张量.对电磁波沿轴向传播的情况进行了详细研究和数值模拟计算,得到了系统的色散关系.结果表明,此系统存在电磁慢波的传输特性.电磁波与电子的Betatron振荡相互耦合,可能是该系统出现电磁辐射的物理原因.研究结果也旁证了:由此系统电磁不稳定性所带来的电磁辐射,在一定条件下可能是切连科夫辐射.     

铁电液晶显示的交流稳态技术与等效电路模型改进

针对交流稳态技术提出了一种改进的能体现铁电液晶电学、光学各向异性的等效电路模型.通过将介电张量与电场的耦合作用和由表面定向层引起的锚定能量以等效源的形式表达在电路模型中,成功地将模型拓展到介电各向异性情况下.分别就正、负性介电各向异性及应用交流稳态技术时的光响应特性和动力学机制进行了模拟,并给出了对应的介电扭矩、铁电扭矩和极化反转电流.模拟结果吻合于理论分析及文献报道的结果,表明了电路模型的有效性.     

Finite-difference time-domain solution of Maxwell's equations forthe dispersive ionosphere

The application of the finite-difference time-domain (FDTD) technique to problems in ionospheric radio wave propagation is complicated by the dispersive nature of the ionospheric plasma. In the time domain, the electric displacement is the convolution of the dielectric tensor with the electric field, and thus requires information from the entire signal history. It is shown that this difficulty can be avoided by returning to the dynamical equations from which the dielectric tensor is derived. By integrating these differential equations simultaneously with the Maxwell equations, temporal dispersion is fully incorporated. An FDTD approach utilizing the vector wave equation is also presented. The accuracy of the method is shown by comparison for a special case for which an analytic solution is available. The method is demonstrated with examples of pulse propagation in one and two dimensions. The computational limitations of present-generation computers are discussed. The application of this approach to the study of wave propagation in randomly structured ionization is addressed     

Reflection and transmission of electromagnetic waves normally incident on a plasma slab moving uniformly along a magnetostatic field

Power reflection and transmission coefficients are found for linearly and circularly polarized plane electromagnetic waves, normally incident on a plasma slab, moving uniformly along a magnetostatic field, normal to the slab boundaries. The solution is found by applying the boundary conditions in the rest frame, and then using relativistic transformations for the fields and the plasma parameters to find the reflection and transmission coefficients observed in the laboratory frame. The results for the circularly polarized incident waves are found in closed form. Numerical results are presented for linearly polarized incident waves. It is found that with an increase in the magnetostatic field, the absolute maximum of the reflection coefficient increases at different velocities. An increase in the magnetostatic field makes the slab more transparent at velocities for which the transmission coefficient with no magnetostatic field is very small. A dielectric-like behavior is observed for large magnetostatic fields. The sum of the power reflection and power transmission coefficients is found to be no longer equal to unity for velocity different from zero.     

Numerical Determination of Potential in Inhomogeneous Dielectrics by Earnshaw's Theorem

Earnshaw's theorem, a characterization of potential functions equivalent to Poisson's equation, expresses a relation between the value of the potential at a point and an average of the function over a spherical surface centered at the point. The theorem therefore lends itself to use in numerical computation of the potential. A formulation of the theorem is presented with particular reference to determination of the potential in a region which is inhomogeneously occupied by dielectric media. This provides a rigorous basis for the formulas used to determine the potential at points on a dielectric interface, in that it avoids the ambiguity which arises in the evaluation of the finite-difference approximation to the Laplacian at such points. The use of the formulation is illustrated by examples of computer-generated graphs giving the potential in the presence of irregular dielectric objects.     

A New Approach to Dyadic Green''s Function in Spectral Domain

A new method is proposed to derive the dyadic Green's function for stratified dielectric layers from the wave equation in spectral domain. The result is a clear equivalent circuit of the whole structure which combines the TE and TM modes by hybrid block matrices. It is simple to apply and evaluate. The relation to the conventional immittance approach is shown by means of a similarity transform which diagonalizes the submatrices. The simplicity of the method is demonstrated in the application to the well-known example of a single microstrip patch on a grounded dielectric layer as well as structures with multiple layers and metallizations in arbitrary interfaces     

On Radial Transmission Line Representations of Electromagnetic Fields in an Anisotropic Moving Medium

The problems of electromagnetic waves in moving isotropic or uniaxial mediums have been dealt with by numerous authors. Chawla and Unz considered the fields in a moving anisotropic plasma, and Chen and Cheng analyzed waves in an isotropic plasma in a moving dielectric medium. In this note we consider electromagnetic fields in a moving anisotropic medium and propose the network formulation of electromagnetic fields in the moving medium in the radial cylindrical coordinate. The method is an extension of the transmission line representation of electron beams on infinite magnetic fields. We can apply these results to the cases of any magnetic field intensity and, further, solve the complex problems for a stationary anisotropic plasma by a similar method.     

Radar cross sections of dielectric or plasma coated conducting spheres and circular cylinders

Radar cross sections for a variety of spherical and cylindrical scatterers having homogeneous dielectric or plasma shells are obtained by using both the exact boundary value solutions and approximate, semi-empirical methods based on physical principles. The plasma is assumed to have the macroscopic properties of a lossless dielectric with a permittivity less than that of free space. A superposition approximation for the radar cross section of a dielectric coated conducting body is obtained by considering the scattered field to be the phasor sum of two principal components, the field scattered by the air-dielectric interface and the field scattered by an equivalent conducting body which differs from the actual body because of the lens action of the shell. This approximation yields very good agreement with the exact solutions for both spherical and cylindrical dielectric clad scatterers with radii in the Rayleigh region and in the resonant region, and for bistatic scattering as well as for backscatter. The echo area of a conducting sphere with nonconcentric spherical dielectric shell calculated by means of the superposition approximation is in excellent agreement with experimental measurements, thus demonstrating the validity of this method in a case for which the exact solution cannot be obtained.     

矩形波导铁氧体移相器的有限元分析

本文从麦克斯韦方程推出适合于解决导磁率为张量形式的各向异性介质加载波导本征值问题的全电场有限元方程,讨论识别主模的方法和如何把两种不同媒质界面上的边界条件引入有限元方程。通过所建立的有限元方程,分析了双板铁氧体加载矩形波导的传播特性,并同解析解作比较,两者所得结果吻合得很好。     

An Analysis of the Tensor Dielectnc Constant of Sea Ice at Microwave Frequencies

The bilocal approximation of strong fuctuation theory is used to develop a model for the tensor dielectric constant of sea ice that is treated as a random anisotropic medium. The application is a twofold one: first the individual ice grains are treated as pure ice with embedded elongated brine cells with random spacings and sizes and secondly as the combined ice-brine system, which has tensor dielectric properties, with random orientations of the principal axes and random embedded air bubbles. Comparisons with measurements on a variety of ice types over the temperature range 0 to -32 ° C and frequencies from 0.1 to 40 GHz show that the theory is able to account quantitatively for large parts of the published data including expected scattering corrections to the quasi-static dielectric constant at low salinities and high frequencies.