Slow propagation of electromagnetic waves in a dielectric slab waveguide with a left-handed material substrate

The dispersion properties of the guided modes propagating along a dielectric slab waveguide with a left-handed material substrate are studied. It is shown that both the oscillating and surface modes can propagate very slowly along such a waveguide if the thickness of the core layer is chosen appropriately. The propagation speed of the guided waves can even approach zero and this slow propagation is illustrated with an finite-difference time-domain simulation in a tapered waveguide. The influence of the material loss on the slow propagation is also discussed.     

In-plane propagation of millimeter waves in periodic magnetoactive semiconductor structures

Non-transmission bands of electromagnetic waves propagating along the layers in periodic structures are studied in the steady magnetic field perpendicular both to the uniaxis and the direction of propagation. The band control range (36÷75 GHz) inn-InSb/Al₂O₃ structures with the carrier densities 4 10¹³ ≤n ≤ 8 10¹⁴ cm^?3 in magnetic fieldsB _o ≤ 2 T at temperatures 77 ≤T ≤ 200 K is found to agree with the calculated in the effective medium approximation. Attenuation down to ?50 dB within the band is observed. The band lineshape is found to indicate additional effects related to the finite layer thickness and periodicity termination predicted by a more rigorous theory of dispersion.     

Interaction of electromagnetic waves in a waveguide with very thin wires

Absorption and scattering of electromagnetic radiation by thin metal wires in a waveguide are investigated experimentally and theoretically. It is shown that, when the wavelength many times exceeds the diameter of a cylindrical wire, this wire strongly absorbs the radiation and weakly scatters it, and the absorption efficiency factor depends on the wavelength only slightly. This phenomenon can be used for developing radiation absorbers in the meter-wavelength range.     

等离子体中的涡旋电磁波传播研究

目前对涡旋电磁波的产生方法及应用已经有很多理论及实验上的研究,但对于其传播过程的研究还非常缺乏,尤其是在电离层等离子体中的传播过程的研究.本文建立了柱坐标系下的时域有限差分方法模型,推导了柱坐标系下的边界吸收方法,在此基础上计算了涡旋电磁波在真空及等离子体中的传播过程,同时模拟了等离子体密度在涡旋电磁波作用下的时空演化过程.模拟结果表明：通过阵列天线模型产生的涡旋电磁波在真空中传播时涡旋的形状不会改变;在等离子体介质中,涡旋波的传播依然遵循线性理论,当涡旋电磁波遇到截止频率的等离子体时也会有明显的反射,并产生驻波;同时,在等离子体中涡旋波依然可以保持涡旋形态;涡旋波对等离子体的线性作用使得等离子体也呈现出涡旋态,与实验中的观测相符.以上的模拟结果能为涡旋电磁波加热电离层的实验以及未来在短波通信方面的应用提供理论支持.本文建立的涡旋波在等离子体中的传播模型也为进一步研究涡旋波与等离子体的非线性相互作用打下了基础.     

Calculation of the propagation constants and fields of polarized electromagnetic TM waves in a nonlinear anisotropic layer

Propagation of polarized electromagnetic TM waves through a nonlinear homogeneous nonmagnetic dielectric layer located between two homogeneous isotropic half-spaces is considered. The dispersion equation is derived for the propagation constants (eigenvalues) of waves in the layer. The propagation constants for nonlinear and linear media in the layer are compared. The propagation constants and fields (eigenfunctions) are calculated.     

Natural propagation of electromagnetic waves in tunnels

An experimental study of the electromagnetic wave propagation in various tunnels at frequencies between 1 MHz and 1000 MHz is presented. The results provide a better understanding of various propagation mechanisms in underground galleries. The analysis shows the existence of a cutoff frequency, and enables one to distinguish three different ranges of frequency characterized by three different modes of propagation. Experimental verification was made in road and mine tunnels of various shapes and sizes. The results show a strong correlation between the propagation characteristics and the transverse dimensions of the tunnel.     

Ultrahigh-frequency surface electromagnetic waves in an open waveguide

An experiment in which guided propagation of surface electromagnetic waves (SEWs) on a free curved metal-dielectric interface was observed in the ultrahigh-frequency band (at frequencies of 850 and 1200 MHz) is described. The data on signal propagation over various paths and under various propagation conditions is presented. It has been found that the decrease of the wave field with increasing distance from the source follows the exponential law.     

On the propagation of light waves in a multilayer planar dielectric waveguide

Dispersion equations for the eigenvalues of effective refractive index β of a planar dielectric waveguide supporting an optic TE wave are investigated. A relation between the traditional dispersion equation obtained on the basis of the characteristic-matrix method and the so-called multilayer equation is revealed. It is shown that all of the roots of the traditional dispersion equation are roots of the multilayer equation for the same problem. It is found that the roots of the multilayer equation may include the values of the refractive indices of inner layers of the waveguide and that these values are not the eigenvalues of quantity β.     

Approximate 3D model of electromagnetic modes in waveguide cross-shaped junctions with dielectric filling

Athree-dimensional electrodynamic model of hybrid electromagnetic modes in a waveguide junction of cylindrical and rectangular waveguides with dielectric filling of a cylindrical waveguide is proposed in this study. To solve the vector problem, the mode matching technique (MMT) is applied with the separation of the common waveguide junction region and the representation of the field in this region in the form of superposition of the fields of the partial eigenwaves of waveguides. Classification of eigenmodes is carried out: intrinsic resonances of junction based on transcendental modes and resonances of a waveguide-dielectric type. The investigated structure can be used for measuring the electrical parameters of dielectric samples of both cylindrical and rectangular cross-section shape. Since the spectral characteristics of the junction are determined mainly by the size of the central coupling region of the waveguides and the electrical parameters of the dielectric in the junction, the measurements are of a local nature.     

VLF propagation across discontinuous daytime-to nighttime transitions in anisotropic terrestrial waveguide

Discontinuity effects are analyzed after referring the ionospheric surface impedance of daytime and nighttime waveguide portions to the same common altitudeh. The properties of the waveguide junction are determined by field matching, and the resulting linear equations are rearranged in a form that permits a sequential determination of transmission and reflection coefficients. Simple dominant mode approximations of the transmission and reflection coefficients are also developed. Field calculations of reciprocal geometries illustrate the consistency of the formulation and reflection coefficients are found to be of negligible magnitudes. The discontinuous surface impedance tends to excite higher order waveguide modes of larger amplitudes than a ground based source in homogeneous waveguide.     

Normal mode model for electromagnetic propagation in the earth crust waveguide

Propagation of modes in an idealized model of the earth-crust waveguide is considered. The two-layer region is bounded above and below by a perfectly conducting plane. For this structure, there are an infinite number of discrete modes without any contribution from a continuous spectrum. The excitation factor for the structure is derived for voltage-type and electric, current line sources. Specific numerical results for 1 to 1000 Hz are given for the case where the lower conductive region is effectively of infinite depth. It is found that the conductivity of the upper region is the main controlling factor on the attenuation rate.     

Calculation of the propagation constants of TM electromagnetic waves in a nonlinear layer

Propagation of TM electromagnetic waves through a nonlinear homogeneous isotropic nonmagnetic dielectric layer is considered. The layer is located between two homogeneous isotropic half-spaces. The dispersion equation for the propagation constants of the waves in the layer and the first approximation for these constants are presented. The propagation constants for the cases of a linear medium and a nonlinear medium in the layer are compared. The linear and nonlinear cases and the first approximation are analyzed. Calculation results are presented.     

Scattering of electromagnetic waves by an anisotropic plasma-coated conducting cylinder

This paper considers the scattering of electromagnetic waves by an infinitely long anisotropic plasma-coated conducting cylinder. The source is assumed to be a magnetic current filament which gives rise to an incident magnetic field with only an axial component. Complete expressions for the scattered electric and magnetic fields are obtained. Scattering by an anisotropic plasma column and that by an isotropic plasma-coated conducting cylinder are special cases of the present problem.     

Eigen Q-factor of electromagnetic oscillations of E-type in waveguide junction of plane waveguides with anisotropic dielectric

The electrodynamic and numerical analysis of eigen Q-factor of electromagnetic modes of E-type in waveguide junction of plain waveguides, fulfilled with anisotropic dielectric in depending on a permittivity tensor components and dielectric loss have been carried out in the paper. The recommendations on using of waveguide junctions for measurement of dielectric losses of the materials are given.     

矩形隧道围岩电参数对电磁波传播的影响

隧道围岩电参数对电磁波的传播特性有很大影响.基于矩形隧道传播模型和软件模拟的方法,研究了隧道顶、底板和侧壁电参数的不同变化对不同极化方式电磁波的影响.结果表明:矩形隧道的顶、底板电参数的变化对垂直极化模式有很大影响,对水平极化模式没有影响;而侧壁电参数的变化只对水平极化模式的电磁波有影响,对垂直极化模式的影响很小.     

Scattering of electromagnetic pulse waves by conducting wedge in uniaxially anisotropic plasma

Asymptotic expansion for the transient response of radiation fields due to electric dipole located above the conducting wedge with an arbitrary angle embedded in a simple plasma is derived by using the saddle point method of integration. The transient time, which is defined as the time required to reach steady state, is discussed for various kinds of wedge angles and plasma frequencies.     

Kinetic theory of electromagnetic waves obliquely incident upon a plasma slab

The problem of an electromagnetic wave obliquely incident upon a plasma slab is considered as a boundary-value problem, using a self-consistent solution of the coupled linearized Vlasov and Maxwell equations for the electrons, with the ions treated as a fixed, uniform background. Power reflection, transmission, and absorption coefficients are derived under the assumption that electrons undergo specular reflection at the surfaces of the plasma slab. Although our analysis is valid for arbitrary slab thickness, computational results are presented for slabs which are thin compared to a free-space wavelength. The results show a series of resonances which are attributed to the kinetic behavior of the plasma. The results further show that the resonances are Landau damped as the thermal velocity of the plasma electrons increases. While similar resonances can be predicted from the coupled linearized hydrodynamic Maxwell equations, such a model does not predict Landau damping. The effects of a finite collision frequency are then included via a simple Bhatnager-Gross-Krook collision term. The numerical computations vividly indicate that the resonances undergo severe damping for extremely small ratios of the collision frequency to signal frequency.     

A FDTD scheme for the computation of VLF-LF propagation in the anisotropic earth-ionosphere waveguide

Due to the presence of the natural magnetic field, the ionosphere surrounding the earth is a gyrotropic medium. This paper presents a finite-difference time-domain scheme that can deal with such an anisotropic medium, allowing the propagation of VLF-LF radiowaves to be computed in the waveguiding structure composed of the earth surface and the ionosphere. The numerical scheme is described in detail, with a special emphasis on the problem of the numerical stability.     

矩形波导中主模电磁波传播特性研究

矩形波导主模电磁波是波导传输中使用最多的模式。为了能深入了解其传播特征。从波导的截至波长入手,讨论了电磁波单模传播的条件。得出结论：主模传播需要电磁波波长和波导尺寸之间满足一定关系。推导出主模电磁波的场方程,利用该场方程,结合一定尺寸的矩形波导管,模拟出一定频率的主模电磁波分布图,进而总结了主模电磁波传播的主要特征。这...     

Some new results on propagation of electromagnetic waves in strongly turbulent media

New results for the covariance of the intensity fluctuations of a plane wave propagating in a strongly turbulent medium are presented, and the consequences of these new results on aperture averaging, angle of arrival fluctuations, and the temporal frequency spectrum of the intensity scintillations are evaluated. The differences between the strong turbulence and weak turbulence cases are generally quite significant.