基于全波法的甚低频波对低电离层扰动分析

通过全波解反射系数和波模振幅递归算法,文中分析了平面波在水平电离层分层结构中的能流分布规律,结合电离层化学反应模型对电离层参量的扰动情况进行仿真,并与其他文献中使用的方法相比.全波计算方法考虑到了各层反射、透射波相互叠加的情况,仿真结果对比发现,用全波法得到的能流吸收和电子温度扰动幅度更大.不同入射波参数、地磁场参数、...     

多层双各向同性媒质中电磁波的传输特性

用不对称传输线模型分析了平面电磁波垂直入射于多层双各向同性媒质的反射和透射问题，导出了形式上较简单的计算多层双各向同性媒质界面反射和透射系数公式。为了便于和已有的文献结果相比较，给出计算实例，结果表明，用此公式得出的结果和文献结果一致，为计算多层双各向同性媒质的反射和透射带来方便；同时，对双各向同性媒质，非互易参数和手征参数的改变对反射和透射系数都有较大的影响。     

Integral equation method in problems of electromagnetic-wave reflection from inhomogeneous interfaces between media

Problems on reflection of a plane electromagnetic wave from various irregular interfaces between media are studied by the integral equation method in the cases of two- and three-dimensional incident electromagnetic field. The reflecting surfaces are meant as periodic transparent interfaces between two media and plane boundaries with locally inhomogeneous and transparent sections. The boundary value problems for the system of Maxwell’s equations in an infinite domain with an irregular boundary are reduced to Fredholm or singular integral equations, depending on the problem considered. Numerical algorithms for solving such integral equations are developed. Results of calculation of currents induced on inhomogeneities and characteristics of the electric field in the far zone are presented.Problems on reflection of a plane electromagnetic wave from various irregular interfaces between media are studied by the integral equation method in the cases of two- and three-dimensional incident electromagnetic field. The reflecting surfaces are meant as periodic transparent interfaces between two media and plane boundaries with locally inhomogeneous and transparent sections. The boundary value problems for the system of Maxwell’s equations in an infinite domain with an irregular boundary are reduced to Fredholm or singular integral equations, depending on the problem considered. Numerical algorithms for solving such integral equations are developed. Results of calculation of currents induced on inhomogeneities and characteristics of the electric field in the far zone are presented.     

球形分层媒质中并矢格林函数的求解 I:并矢格林函数的推导

首先,在球坐标系下,通过德拜位函数得到均匀各向同性介质中矢量波动方程的解。然后,分析了内、外向波的单界面和多层界面的反射和透射,得到了相应的反射系数和透射系数以及广义反射系数和透射系数。接着,推导了啄源在球形分层介质中的不同位置产生的德拜位。最后,根据得到的德拜位,用球坐标系下的矢量波函数表达出场点在不同位置时的电并矢格林函数和磁并矢格林函数。     

分层媒质中声波传输规律的研究

利用声波在分层媒质中的传播理论,分析了平面声波在由不同固体,液体构成的多层媒质中声波的透射规律,计算得到透射系数公式,并进行了数值计算。结果为激光扫描声学显微镜的设计及实际应用提供了参考依据。     

1维光子晶体中TM波的传输公式及其辨析

为了得到1维光子晶体中TM波的传输公式,采用传输矩阵的方法和电磁波的边界条件,推导出TM波在介质层中的特征矩阵及其反射系数和透射系数公式。结果表明,用TE波反射系数和透射系数公式做代换的方法不能得到正确的TM波的反射系数和透射系数公式;对推导出TM波的反射系数和透射系数公式进行了分析,由TM波的反射系数和透射系数公式得出的光强透射率和反射率满足能量守恒;并且推出的TM波反射系数公式不仅能够反映反射波与入射波的数量关系,且能够反映反射波与入射波的位相关系。这些结果对研究1维光子晶体中TM波的传输性质是有帮助的。     

泡沫对激光传输能量衰减的研究

为了定量研究泡沫对激光传输的影响,基于电波吸收、反射和散射特性对泡沫衰减遮蔽机理进行了分析.根据泡沫状态的不同,将泡沫分为离散泡沫和粘连泡沫,运用朗勃-比尔定律定量计算了离散泡沫的激光透过率及能量衰减值,运用几何光学和电磁波传播理论定量计算了粘连泡沫的激光透过率及能量衰减值,并利用MATLAB中仿真工具进行了数值仿真.结果表明,泡沫对激光衰减作用明显,且随着泡沫厚度的增加,激光透过率逐渐减小,与测得的实验值基本一致,进一步验证了模型的合理性.     

等离子体鞘套中太赫兹波传输特性研究

采用散射矩阵方法(SMM)研究太赫兹波在非磁化、非均匀等离子体鞘套中的传输特性。在假定等离子体电子密度分布为双指数分布条件下,对太赫兹波斜入射等离子体时的功率反射系数、透射系数及吸收系数进行了仿真,还对其随太赫兹波的入射角度、太赫兹波的频率、等离子体的碰撞频率、等离子体分布形态的变化规律进行了总结。研究结果表明,在上述条件下,太赫兹波在等离子体中均有较好的传输特性。总体上来说,随着太赫兹波频率的提高,太赫兹波在等离子体中的透射性更好,可以考虑提升载频至太赫兹波段来解决通信黑障问题。     

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.     

微波的特点及应用

微波在一系列现象的反映中都呈现与电磁波相同的性质,包括在介质传播过程中呈现的反射、及衍射现象.同时,微波在能量传输方面相较于以往的普通电波呈现显著优势,尤其是在其产生及应用过程中呈现的特点比较明显.本文针对微波展开深入研究,主要分析其呈现的特点及在各个领域的应用,从而为微波领域在今后的深入发展提供理论支持.     

太赫兹波在介质中传播的FDTD分析

时域有限差分法是电磁场领域中应用最为频繁的数值方法之一,它可以有效地处理复杂媒质中颗粒对电磁脉冲信号的散射问题,以及超宽带电磁脉冲信号在色散媒质中的传播问题。几乎所有介质,无论其在太赫兹（THz）波段是否有吸收峰,对太赫兹波的传播都有影响。研究太赫兹波在介质中的传播情况,对优化太赫兹系统,分析与设计太赫兹应用技术有重要意义。本文模拟了太赫兹波在散射介质中的传播,说明了太赫兹波在内弹道干涉测速应用中的可能性;模拟了太赫兹脉冲在色散介质中的传播情况,为太赫兹时域光谱系统中晶体选择提供依据。     

类回旋各向异性媒质电磁特性及参数反演研究

讨论了类回旋各向异性媒质参数在对称、共轭对称以及反对称等条件下的有耗性、互易性.然后利用不同极化、不同角度入射条件下类回旋各向异性材料平板的自由空间反射、透射系数及其与媒质参数的特点,通过设计不同的目标函数,提出了在对称、共轭对称以及反对称条件下分步反演该类媒质参数的方法.算例中考虑了有噪声条件下的反演,并讨论了频率的选择、初始值的正确选择以及纵向参数的反演.结果表明,分步反演方法是可行的,为任意复杂电磁媒质的反演提供了一条新的思路.     

Implementation of a surface impedance formalism at obliqueincidence in FDTD method

The authors point out that modeling of interfaces between two media, using time-domain surface impedances, permits one to reduce the discretization volume in the finite-difference-time-domain (FDTD) technique. The method presented here is based on an exact formulation of surface impedances, starting from Fresnel reflection coefficients for oblique incidence of the incident wave. The concept, valid for homogeneous and frequency-independent media, is then introduced into an FDTD algorithm where it is converted into a surface-impedance boundary condition (SIBC) for vertical or horizontal polarizations of locally plane waves. Two- and three-dimensional results are compared to those computed with classical FDTD or Fresnel reflection coefficients involving a Fourier transform     

Improved bidirectional beam propagation method for analysis ofreflection on nonparallel interfaces

An improved bidirectional beam propagation method (IBBPM) is proposed, to allow the analysis of optical wave reflection and transmission in waveguiding structures with multiple nonparallel interfaces     

基于平面波斜入射的人体信道远场路径损耗建模

人体信道路径损耗计算对植入式通信链路预估具有重要意义.文章利用有耗媒质的电磁场边界条件、反射和透射定理并引入切向等效波阻抗定义,推导出平面波向人体斜入射时各人体组织分界面上的入射角、透射角、反射系数、透射系数、切向等效波阻抗以及各人体组织中的电磁合成波,提出了一种基于平面波向多层有耗媒质斜入射的人体信道远场路径损耗解析模型.然后以植入在肌肉为例,计算了TM波和TE波在5个常用工业通信频率以不同角度斜入射的人体信道电磁场分布与路径损耗,结果显示,电磁波在入射面的反射是影响人体信道路径损耗的关键因素,当频率在1.4 GHz附近时总路径损耗最小,TM波性能优于TE波,且当入射角小于等于30°时,总路径损耗基本保持不变.最后采用COMSOL Multiphysics建立了有限元仿真模型验证解析模型,二者结果高度吻合,最大误差仅为0.039,有力证明了解析模型的正确性和有效性.     

平面波在双负和双正参数媒质界面的反射与折射

研究了平面波在均匀无耗的、各向同性的、介电常数和磁导率同时为正和同时为负的媒质界面的反射与折射.理论分析了反射波和透射波在两种媒质中的传播特性,从而解释了负折射发生的原理.还给出了反射系数和透射系数的表达式.讨论了发生全反射和全折射的可能条件.     

分层手征介质中电磁波的传播矩阵法及其传播特性研究

本文首先建立了任意分层手征介质中的电磁波传播矩阵法,给出了正向和反向传播矩阵的一股形式。并且分析了两种不同手征介质界面处,有无金属板衬底的单层手征介质板的反射和透射特性,特别考虑了手征导纳的影响。     

Transmission of horizontally polarized waves and trapped waveguide modes in inhomogeneous media

A generalized Wentzel-Kramer-Brillouin (WKB) approach is used to obtain full wave solutions for horizontally polarized waves in inhomogeneous media when no closed form analytic solutions are known. This approach is suitable for complex permittivity profiles with critical coupling regions even when the permittivity gradient approaches zero. The transmission and reflection coefficients and the characteristic surface impedance for inhomogeneous layers of finite thickness are computed for several permittivity profiles. Excitation of propagating and evanescent waves is considered and the results are shown to satisfy the realizability and reciprocity relationships in electromagnetic theory. Sinusoidal permittivity profiles for which closed form analytical solutions are known are also considered to provide an additonal check on the generalized WKB solutions. For permittivity profiles with several spatial periods, transmission windows with very narrow beamwidths are found to exist. When conditions for total internal reflection in the inhomogeneous dielectric layer are satisfied, the reciprocal of the reflection coefficient vanishes and propagating waves are trapped in the layer. For these trapped waveguide modes the inhomogeneous dielectric is characterized by a surface reactance.     

Pulsed beam propagation in inhomogeneous medium

Pulsed beams (PB) are localized space-time wavepackets that propagate along ray trajectories. This paper deals with general PB solutions in inhomogeneous medium. We derive an approximate form of the time-dependent wave equation (termed the wavepacket equation), valid within a moving space-time window that brackets the wavepacket, and then construct its exact PB solutions. This is done first in a free-space and latter on in a general smoothly varying medium where the propagation trajectories are curved. We also determine the reflection and transmission laws at curved interfaces. These new PBs are related to the so called complex source pulsed beams which are exact solutions in free-space, but they have more general form that admits wavepacket astigmatism and medium inhomogeneity. Since they maintain their wavepacket structure throughout the propagation process they are identified as eigen-wavepacket solutions of the time dependent wave equation     

Full wave physical models of nonspecular scattering in irregularstratified media

A physical interpretation is given of each term in the full-wave expansion of the vertically or horizontally polarized electromagnetic fields scattered by irregular stratified media. These solutions provide a basis for the construction of physical models of nonspecular scatter in complex, irregular, layered structures. The full wave solutions involve a pair of nonspecular reflection scattering coefficients and a pair of nonspecular transmission scattering coefficients that reduce to the familiar Fresnel reflection and transmission coefficients for the specular case. The full-wave solutions are shown to satisfy the reciprocity and duality relationships in electromagnetic theory, and they are invariant to coordinate transformations. The relationships between the full-wave solution, the high-frequency physical optics solution, and the low-frequency perturbation solution are demonstrated. The analysis is relevant to problems of communication in irregular stratified media and to problems of remote sensing