Approximate formulas for lateral electromagnetic pulses from a horizontal electric dipole on the surface of one-dimensionally anisotropic medium

In this paper, approximate formulas are derived for the electromagnetic pulse due to a delta-function current in a horizontal electric dipole on the planar boundary between a homogeneous isotropic medium and one-dimensionally anisotropic medium. The components of the electric field consist of two delta-function lateral pulses which decrease with the amplitude factor /spl rho//sup -2/ and travel along the boundary with different velocities and different amplitudes. Also, it is noted that the formulas for the time-dependent magnetic field components obtained by Fourier transforms from the approximate formulas in the frequency domain are not adequate.     

On waves in an anisotropic plasma imbedded in a moving dielectric medium

The governing equations for electromagnetic fields in an anisotropic plasma imbedded in a moving dielectric medium are obtained. Examination of the wave and dispersion equations yields information on the elliptically or linearly polarized waves which may exist when the external magnetic field is parallel or perpendicular to the direction of motion, respectively.     

An effective medium description for a random uniaxial anisotropic medium with small-scale fluctuations

Some properties of the electromagnetic field are determined for an unbounded medium characterized by a permittivity tensor whose elements can be expressed as the sum of two terms, one deterministic and the other random. The deterministic and random parts of the permittivity tensor are considered to be uniaxial anisotropic; thus it is a diagonal tensor where two of the three elments are equal. Starting from the bilocal approximation to Dyson's equation, an effective permittivity tensor and mean dyadic Green's function are obtained for small-scale fluctuations. Some important properties of the ordinary and extraordinary waves are also made known.     

A low-frequency model for wedge or pyramid absorber arrays-I:theory

The interaction of electromagnetic waves with an array of absorbing wedges or pyramid cones is studied in the low-frequency limit; i.e., when the period of the array is small compared with wavelength. A theoretical model is obtained using the method of homogenization, which replaces the transversely periodic structure with a transversely uniform medium possessing a certain (generally anisotropic) effective permittivity and permeability. Plane-wave reflection from such structures can then be modeled using well-known techniques for one-dimensionally inhomogeneous media; a Riccati equation for the reflection coefficient is used in this work. This model is appropriate for use with absorbers found in anechoic chambers used for electromagnetic compatibility and electromagnetic interference (EMC/EMI) measurements over the frequency range of 30-1000 MHz     

Electromagnetic radiation in drifting tellegen anisotropic medium

The electromagnetic waves in a homogeneous, drifting, general, linear, anisotropic Tellegen medium are evaluated in terms of the electric and magnetic current density sources. The fields are shown to be expressible in terms of the characteristic waves of the medium. The solution is in agreement with the particular cases for a nondrifting medium worked out originally by Bunkin.     

水平电偶极子在负折射媒质半空间激励的场

讨论了水平电偶极子在由介电常数和磁导率都为负数的媒质和普通媒质构成的均匀半空间中激励的电磁场,并得出了远区场的解析表达式.理论分析和数值计算结果表明:位于普通介质中的水平电偶极子在普通媒质和负折射媒质分界面能够有效激励表面波.该表面渡是一种"慢波",沿分界面传播的波数小于波在两种均匀媒质中传播的波数.当两种介质均无损耗时,沿径向传播的幅度按波的几何扩散衰减.由于存在三种传播波数,表面波、侧面波、直达波和反射波共同作用形成的总场将发生复杂的干涉现象.     

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.     

Analysis of radiowave propagation in a four-layered anisotropicforest environment

Propagation of electromagnetic waves in forest environments is examined in which both the transmitting and receiving points are located in the trunk layer of a four-layered anisotropic forest model. This propagation model considers the forest as a horizontally stratified, anisotropic media of canopy and trunk, bounded by ground below and air above. The electromagnetic fields are obtained using dyadic Green's functions in their eigenfunction expansion forms for an anisotropic four-layered geometry. Analytical results are found for the fields, which consist primarily of three wave modes: a direct wave, multiply reflected waves, and lateral waves. These field constituents are compared, and their domains of preponderance are calculated; it is found that the lateral wave plays a major role in communication at large distances. Radio losses for typical forest are calculated to illustrate numerical application of the forest model     

Radiation of elementary sources in a chiral medium

The classical problem of radiation of elementary sources is generalized to the case of a chiral medium. The electromagnetic fields of right- and left-hand polarized waves are expressed in terms of vector potentials, and formulas for the components of the fields radiated by a vertical electric dipole in a chiral medium are obtained.     

Magnetic susceptibility of a composite medium with variable parameters that consists of arbitrarily oriented anisotropic ferrite particles

The dynamic high-frequency tensor susceptibility of a composite medium consisting of independent chaotically oriented uniaxially anisotropic ferrite spheres is calculated by averaging over directions under the conditions of an orientation transition. It is established that the tensor magnetic susceptibility has all nine components, among which the maximum components are those responsible for oscillations of the magnetization vector in the directions perpendicular to the constant magnetic field. It is shown that these peculiarities of the tensor make it possible to analyze waves in the medium with the help of the methods known in the electromagnetics of gyrotropic media.     

导体球涂覆各向异性铁氧体介质电磁散射的解析解

该文用球矢量波函数对各向异性铁氧体介质涂覆导体球的电磁散射解析解开展研究。各向异性铁氧体介质中电磁场的球矢量波函数解可表示成第一、二、三、四类球矢量波函数之和。根据球Bessel函数的性质,可以得出导体球涂覆各向异性铁氧体介质的球矢量波函数解析解。应用铁氧体与自由空间分界面上电磁场切向连续和在导体球面上切向电场等于零的边界条件以及球矢量波函数切向正交性质,可分别得出铁氧体介质中电磁场和散射场的展开系数。给出了平面波入射情况下的数值计算结果。该文的结果可应用于有关微波器件、天线以及目标特征的分析和计算。     

利用表面电磁波进行能量分配的研究

研究了二维分界面上的表面电磁波,推导得出二维分界面上TE表面电磁波的电场强度、磁场强度和能流密度的表达式,得到分界面上表面波的存在条件,根据总能流把分界面分为左手分界面和右手分界面,对二维分界面上表面电磁波的传播进行仿真,最后提出利用表面电磁波进行能量分配,并给出了仿真结果.     

Excitation of electromagnetic waves in a gyroelectric cylinder

The coupling of electromagnetic waves originating from a dipole to an infinite gyroelectric cylinder is treated analytically. The anisotropy axis of the gyrotropic medium is assumed to coincide with the cylinder axis. An electric dipole type primary excitation, with an arbitrary axis of orientation, is considered and the dyadic Green's function is derived for the gyroelectric cylinder. The field inside the anisotropic medium is expressed as a superposition of transverse magnetic (TM) and transverse electric (TE) type waves and a purely longitudinal wave. Excitation of guided modes along the gyroelectric guide and radiation patterns of dipoles radiating in the proximity of the gyroelectric cylinder are analyzed and computed for several cases.     

分层介质中平面电磁波的传播与Zenneck波

平面电磁波作为一种理想的电磁波型,其在均匀介质中的传播特性分析是电磁场理论基础教学的核心内容.特别是均匀平面波由理想介质入射到与导电媒质平面分界面时的传播规律,是地球物理勘探、陆地移动通信工程及光纤传输技术的理论基础.本文分别以理想介质与理想介质和导电介质构成的两层平面分层媒质为例,应用场匹配方法,给出反射波和传输波分析求解的统一描述.与传统的处理方法相比,具有数学分析简洁严密与物理概念准确清晰的特点.     

Radiation and low-frequency scattering of EM waves in a generalanisotropic homogeneous medium

This paper focuses on a boundless homogeneous medium with general anisotropy of electromagnetic properties. The explicit exact form of the four spectral Green's dyads Gˆ_νξ(k) is obtained and a coordinate-free representation of the four spatial Green's functions Gˆ_νξ(x-x') in terms of one scalar potential W(x-x') is developed. On this basis, asymptotic expressions for the radiation field due to arbitrary sources are derived that show that the associated modes and the eigenmodes determine radiation along a singular optic axis and in all other directions, respectively. Using an integral equation approach and the theory of Newtonian potential, the problem of low-frequency scattering by a small anisotropic ellipsoidal body immersed into an anisotropic medium is solved analytically     

截断各向异性介质的修正NPML吸收边界条件

基于各向异性介质中的时域有限差分（Finite-Difference Time-Domain,FDTD）方法及近似完全匹配层（Nearly Perfect Match Layer,NPML）原理,提出一种截断各向异性介质的修正的NPML吸收边界条件.通过对Maxwell旋度方程中的空间偏导数进行坐标拉伸并结合空间插值方法,推导出易于在FDTD方法中实现的吸收边界公式.计算了电偶极子辐射场的反射误差,验证了这种吸收边界截断二维各向异性介质的有效性.三维算例中数值模拟了时谐场的相位分布,以及不同网格NPML吸收层随时间变化的反射误差.数值结果表明NPML吸收边界能有效吸收各向异性介质中的电磁波.     

Resonant modes of a concentric spherical cavity with conicallystratified medium

An analysis on electromagnetic fields of a cavity formed by two concentric conducting spheres with a conically stratified medium is presented in this paper. Angular transmission formulation and the radial eigenfunction expansion are used to formulate the field components. Boundary matching methods are applied to obtain the characteristic equations containing various infinite series of spherical Hankel functions and Legendre functions of complex order for resonant frequencies. The first two resonant frequencies and field expansion coefficients are determined numerically. The distribution pattern of angular field components and the forms of typical electric field lines and magnetic field lines for the first resonant fields are also indicated     

Uniaxial IB-Medium Interface and Novel Boundary Conditions

The class of uniaxial electromagnetic IB media involving five medium parameters is defined as a special case of the previously defined class of general IB media (or skewon-axion media) involving 16 parameters. The problem of plane-wave reflection from and transmission through the interface of a uniaxial IB-medium half space is analyzed. It is shown that, for general values of the medium parameters, waves polarized TE and TM with respect to the normal direction are reflected as from the respective PEC and PMC boundaries. Unlike the anisotropic soft-and-hard surface which has a somewhat similar property, the uniaxial IB interface is isotropic in the plane of the interface. As a consequence, a novel class of electromagnetic boundaries can be defined for general fields requiring vanishing of the normal components of both D and B vectors at the boundary. Another realization of such a boundary in terms of an anisotropic metamaterial with zero axial permittivity and permeability is discussed.     

Axisymmetric spherical traveling electromagnetic waves in an isotropic medium

The problem of propagation of spherical electromagnetic waves traveling in an isotropic space in the absence of sources is solved in the axisymmetric case for the first two modes varying along the latitude. The solution is obtained from the homogeneous Maxwell equations represented in spherical coordinates in a real form. Analytic expressions for the components of the fields of these E and H waves are used to derive the equations of the corresponding field lines. Field-line patterns are displayed that illustrate the dynamics of propagation of converging and diverging spherical electromagnetic waves in the case when the former are transformed into the latter.     

On Guided Waves in Moving Anisotropic Media

Based upon the Maxwell-Minkowski theory, the equations governing the propagation of electromagnetic waves in a cylindrical waveguide of an arbitrary cross section filled with a moving anisotropic medium are derived. The governing equations are reducible to a pair of coupled wave equations in the axial components of the electric and magnetic fields, which in turn can be solved through the solution of a single second order scalar homogeneous Hehnholtz equation. For a general anisotropic medium no pure TM or TE modes can exist in the waveguide. However, if the moving medium is uniaxially anisotropic, TM and TE modes are possible. It is interesting to note that the cutoff frequencies are always lowered by a factor which depends upon the velocity of the medium and is independent of the guide geometry. The formulas for the characteristic wave impedance and power flow in a waveguide for a moving uniaxial medium, if expressed in terms of the new cutoff frequency, have the same forms as those for a moving isotropic medium. The propagation characteristics of waveguides of rectangular and circular cross sections filled with a moving uniaxial gyroelectric medium are discussed.