Refraction of a uniform plane wave incident on a plane boundary between two lossy media

The expressions describing the modified propagation constants of the refracted nonuniform transmitted field, produced by a uniform plane wave incident on a plane boundary between two lossy media, are presented. Some examples under which the modified propagation constants must be used are illustrated to determine the limitations.     

A collocation-Galerkin finite element model of cardiac actionpotential propagation

A new computational method was developed for modeling the effects of the geometric complexity, nonuniform muscle fiber orientation, and material inhomogeneity of the ventricular wall on cardiac impulse propagation. The method was used to solve a modification to the FitzHugh-Nagumo system of equations. The geometry, local muscle fiber orientation, and material parameters of the domain were defined using linear Lagrange or cubic Hermite finite element interpolation. Spatial variations of time-dependent excitation and recovery variables were approximated using cubic Hermite finite element interpolation, and the governing finite element equations were assembled using the collocation method. To overcome the deficiencies of conventional collocation methods on irregular domains, Galerkin equations for the no-flux boundary conditions were used instead of collocation equations for the boundary degrees-of-freedom. The resulting system was evolved using an adaptive Runge-Kutta method. Converged two-dimensional simulations of normal propagation showed that this method requires less CPU time than a traditional finite difference discretization. The model also reproduced several other physiologic phenomena known to be important in arrhythmogenesis including: Wenckebach periodicity, slowed propagation and unidirectional block due to wavefront curvature, reentry around a fixed obstacle, and spiral wave reentry. In a new result, the authors observed wavespeed variations and block due to nonuniform muscle fiber orientation. The findings suggest that the finite element method is suitable for studying normal and pathological cardiac activation and has significant advantages over existing techniques     

Reflection of electromagnetic wave from a time-varying medium

For the purpose of radiowave propagation in the ionosphere, in a plasma and in other media, the reflection and transmission of an electromagnetic wave from a suddenly changed conductivity, when a plane wave is normally incident upon an interface separating two conducting media, are studied. The field expressions are exactly obtained through the use of the Laplace transform. The discussion is primarily on the time behaviour of the reflected wave.     

Computation of electromagnetic waves diffraction by spectralmoments method

We solve, for the first time, electromagnetic wave propagation equations in heterogeneous media using the spectral moments method. This numerical method, first developed in condensed matter physics, was successfully applied to acoustic waves propagation simulation in geophysics. The method requires the introduction of an auxiliary density function, which can be calculated by the moments technique. This allows computation of the Green's function of the whole system as a continued fraction in time Fourier domain. The coefficients of the continued fraction are computed directly from the dynamics matrix obtained by discretization of wave propagation equations and from the sources and receivers. We illustrate this method through the study of a plane wave diffraction by a slit in two-dimensional (2-D) media and by a rectangular aperture in three-dimensional (3-D) media. Comparison with analytical results obtained with the Kirchhoff theory shows that this method is a very powerful tool to solve propagation equations in heterogeneous media. Last, we present a comparison with other computing methods     

An approach to include stochastic rough surface scattering into deterministic ray-optical wave propagation modeling

A new method to include stochastic rough surface scattering into deterministic ray-optical wave propagation modeling is derived. It can be utilized in conjunction with the concept of ray launching. Similar to the Kirchoff formulations, the approach is based on a tangential plane approximation, i.e., it is applicable to surfaces with gentle undulations, whose horizontal dimensions are large compared to the incident wavelength. However, in contrast to the Kirchoff models, which are only valid for either slightly rough or very rough surfaces, the proposed stochastic scattering approach includes both the coherent and incoherent components at the same time. The purely deterministic ray-based modeling is expanded by a "stochastic" component, allowing, for the first time, to account for nondeterministic scattering in ray-optical wave propagation modeling.     

Dynamic analysis of a microstrip line over a perforated groundplane

A full wave analysis is presented to compute the characteristic impedance and propagation constant of a microstrip line over a perforated ground plane. The perforations in the ground plane are modeled by equivalent magnetic currents. The method of moments is applied to solve the coupled integral equations for the unknown electric current on the microstrip line and the unknown magnetic currents in the apertures. The fields are formulated using the space domain Sommerfeld type Green's functions. The matrix pencil technique is used to obtain the amplitude and the propagation constant of the fundamental modes for both current and the voltage on the microstrip line. Typical numerical results are given     

Reflection and transmission characteristics of a slab with periodically varying surfaces

Using a plane wave spectral decomposition of the relevant electromagnetic (EM) fields and the T-matrix solution philosophy, a T-matrix is formulated which completely characterizes the EM response of an infinite material plate bounded by two homogeneous half-spaces, the two interfaces being periodically rough. Individual T-matrices for either of the two periodic bimaterial interfaces are used in this derivation. Using the computed results, the anomalies in the scattering response of the rough slab are explained in terms of reflectionless and transmissionless modes, the Brewster angle, and the conditions for propagation or evanescence of a given plane wave mode.     

无线电波传播中的随机射线及其应用

对建模无线电波传播的随机射线进行了详细的阐述,从随机网格信道引出随机射线的概念,介绍了随机射线的产生背景和分类,并给出一种产生随机射线的数学模型随机桥过程。使用最大熵原理得到发生后次反射随机射线的概率分布。最后介绍使用随机射线建模超宽带室内信道的多径传播轨,在此基础上可以得到信道特性建模的基本随机变量,以及无线电波传播的概率模型等应用。     

用复射线展开法计算目标散射场的误差特性分析

复射线展开法是计算目标散射场的一种简捷的方法,其可靠性有赖于对误差特性的系统研究。本文以平面波谱积分为散射场计算的参考标准,以L2空间中由范数定义的距离作为复射线展开法计算结果的误差,从而得到了复射线展开法在目标散射场计算中的误差特性,找到了减小误差的方法并给出这一方法的适用范围。     

建筑物内电磁波传播的计算问题

本文用时域有限差分(FD-TD)法研究了建筑物内电磁波传播的计算问题.首先把计算结果与联合有限元法和边界元法的结果进行了对比,而后计算了不同频率电磁波从不同方向入射时建筑物内电磁场分布的特点.并计算了线源辐射的电磁波在建筑物内的传播及向外辐射的特性以及脉冲电磁波在建筑物内传播和反射的特点.     

The determination of the propagation constant for the travelingwave in an infinite ground plane

The propagation constant for the travelling wave in a trough in an infinite ground plane is examined. The null-field integral is used to determine the electromagnetic field in the trough structure, and pulse basis functions give the distribution of the aperture fields. From this, the propagation constant is solved for, using the Newton-Raphson iterative scheme. Various sizes of geometries are examined. The far-field patterns are calculated and compared with other solutions, thereby validating the integral formulation which subsequently provided the propagation constant. Measurements of two trough geometries are performed to validate the theoretical results     

Rain induced attenuation for 3mm wave band and its measurement system

In this paper, the effect of rain induced attenuation for millimeter wave is discussed. The theory of multiple scattering is used to obtain the solution for the plane wave propagation through a plane parallel medium of thickness L containing randomly distributed nonspherial particles. The coherent field and the total field are studied, respectively. The numerical results are good agreement with experimental data and the multiple scattering effects must be included. A 3mm wave propagation measurement system was made on a 0.8km terrestrial link.     

A Stochastic Model of the Time-Variant MIMO Channel Based on Experimental Observations

This paper proposes a stochastic multipath model that is useful for generating multiple-input–multiple-output (MIMO) channel matrices in time-variant environments. The multipath model is developed by first extracting the relevant multipath cluster characteristics from measured indoor channel data and subsequently capturing these characteristics in an autoregressive stochastic model. This model is then used to generate channel matrices whose space–time characteristics closely match those of realistic scenarios, particularly when birth and death of multipath clusters are included in the stochastic representation. Computational examples reveal the applicability and the accuracy of the approach. While the current implementation is based on data taken assuming that propagation is confined to the horizontal plane, this paper also discusses the extension of the model to describe 3-D propagation, enabling its application to a wide range of physical scenarios and antenna characteristics.      

A novel expression for the mutual admittance of planar radiating elements

The mutual admittance between two identical planar radiating apertures can be expressed as the bidimensional Fourier transform of a function (defined in the wavenumbers plane), obtained by taking the inner product of the plane wave spectrum (representing the field radiated by the element) by another plane wave spectrum obtained from it by reversing the sense of propagation of each component wave. The asymptotic evaluation of the expression shows that (under certain limitations) the mutual admittance, for large spacing among the radiators, tends to be proportional to the power radiation pattern on the plane of the aperture. By using the formalism here introduced the "grating lobes series" for the driving point admittance of an element in an infinite periodic array can be simply derived from the "mutual admittances series." As a check of the theory the mutual admittance between rectangular slots, in different relative positions, has been numerically calculated.     

随机波束研究超宽带室内多径信道特性

从随机桥过程出发引入随机波束概念,使用随机波束研究超宽带（UWB）室内多径信道的传播特性.将UWB信号多径传播轨迹视作随机过程的样本,得到建模多径信道传播特性的随机波束.使用随机波束构建UWB信道的多径传播模型,并给出使用随机波束方法分析UWB室内多径信道特性的算法.使用该信道模型对实际传播环境进行仿真分析,并与其它建模UWB多径信道的方法进行了比较.仿真得到的UWB信道的功率延迟分布特性与实验测量的结果非常一致,证明此方法的有效性.     

Plasmon Resonances in a Glass Nanowire Covered with a Silver Layer of Variable Thickness

A two-dimensional problem of diffraction of a plane electromagnetic wave by a silver shell with the boundaries formed by a circular and an elliptical cylinders is considered. The far fields and the scattering spectra are calculated by rigorous methods in the visible band. The dipole and quadrupole resonance frequencies for thin shells are determined in the quasi-static approximation. It is shown that the quadrupole resonances are degenerate and the dipole resonances are “split”; at the dip frequency, the scattered field can be directed perpendicularly to the direction of propagation of the incident plane wave.     

Wave propagation and dipole radiation in a suddenly created plasma

Propagation and radiation of electromagnetic waves from oscillating sources in a suddenly created plasma are studied in this investigation. Field expressions are derived through the use of Laplace transformations. The spatial distribution of sources is taken to be arbitrary but confined. Two cases are considered in detail: 1) plane wave propagation in a source-free region and 2) electric point dipole radiation. In the case of plane wave propagation, various aspects such as wave split, frequency shift, phase and group velocities, amplitude changes, power flows, and energy relations are discussed. In the case of electric dipole radiation, the electromagnetic fields and instantaneous radiated power are calculated and expressed in terms of Lommel functions of two variables. Asymptotic expressions and graphical results of numerical calculations of these quantities are presented. Many interesting properties of the spherical waves and power radiation are discussed.     

Uncertainty analysis of the specific absorption rate induced in a phantom using a stochastic spectral collocation method

Uncertainty analysis of human exposure to radio waves is studied with a spectral approach of stochastic collocation methods. This approach allows determining in an efficient way the statistical moments of the output variable, the specific absorption rate, with respect to uncertain input parameters. Polynomial chaos expansions are used for the random output, and the spectral coefficients are determined by projection or regression. These techniques are used with an electromagnetic solver based on a finite difference time domain scheme. The convergence of the statistical moments is analyzed for two case studies. Global sensitivity is also analyzed for the uncertain position of a cellular phone in the close vicinity of a human head model.     

瞬态标量平面波的平行三维复源脉冲波束展开

本文从理论上较全面地分析了入射瞬态平面波的三维复源脉冲波束展开,出发点是从频域球面波严格的格林函数导出球面复源点表达式,由此得到频域平面波的复源点展开公式,     

随机介质中波场的双频双点互相干函数的窄带近似解

随机介质中波传播的前向多重散射理论的关键是矩方程的求解，本文从矩方程的叠代解法出发，在窄带近似情况下得到了双频双点互相关函数的解，并讨论了平面波入射和单色波入射情况下的特例。