Comments on "Refraction at a Curved Dielectric Interface Geometrical Optics Solution"

In the above paper, Lee et al. consider the refraction of waves at a curved dielectric interface between media of uniform refractive index. They quote an earlier paper by us [2], and infer that our results are either inadequate or incorrect. We should like to have the opportunity to state that we have no reason to doubt the validity of our results, which. in any case were independently verified by Jones [3], and to point out how the erroneous conclusions of Lee et al. arise.     

Reflection at a Curved Dielectric Lnterface--- Electromagnetic Tunneling

The reflection of a locally plane wave from a curved interface between two nonabsorbing dielectric media is investigated. Our analysis is applicable to an interface of general shape, defined at each point by the two principal radii of curvature. When the wave is incident from the denser medium at angles greater than the critical angle it is only partially reflected, due to a form of electromagnetic tunneling. Generalized Fresnel transmission coefficients and an extension of Snell's law are derived to account for this transmission into the less dense medium. Ray tracing can then be applied to determine such phenomena as the bending losses in optical slab waveguides, and the curvature loss of skew rays within straight optical waveguides of circular cross section.     

利用单轴晶体实现的负折射现象

运用k空间的等频率线,分析研究了单轴晶体界面上e光独特的折射行为,指出在光轴与界面具有一定夹角的情况下,当入射角小于某临界角将会发生负折射的现象。通过对晶体色散关系的分析,给出了发生负折射的角度范围与光轴倾角之间的依赖关系。对单轴晶体而言,当光轴与界面的夹角为45°时,发生负折射的入射角度范围最大。     

Small Hemielliptic Dielectric Lens Antenna Analysis in 2-D: Boundary Integral Equations Versus Geometrical and Physical Optics

We assess the accuracy and relevance of the numerical algorithms based on the principles of geometrical optics (GO) and physical optics (PO) in the analysis of reduced-size homogeneous dielectric lenses prone to behave as open resonators. As a benchmark solution, we use the Muller boundary integral equations (MBIEs) discretized with trigonometric Galerkin scheme that has guaranteed and fast convergence as well as controllable accuracy. The lens cross-section is chosen typical for practical applications, namely an extended hemiellipse whose eccentricity satisfies the GO focusing condition. The analysis concerns homogeneous lenses made of rexolite, fused quartz, and silicon with the size varying between 3 and 20 wavelengths in free space. We consider the 2D case with both - and -polarized plane waves under normal and oblique incidence, and compare characteristics of the near fields.     

Theoretical Reflection Coefficient of Metal Grid Reflectors at a Dielectric Interface

Reflection properties of square apertures metal mesh mirrors are studied theoretically with the Finite-Difference Time-Domain (FDTD) method associated to Floquet Boundary Conditions. The reflector is illuminated by a normally incident plane wave and is located at an interface between two semi infinite low loss dielectric materials. Reflectivity and phase of the reflection coefficient are given in the non diffraction region for a wide range of square apertures, and for the four situations corresponding to an interface between free space and fused quartz.     

傍轴黎曼几何光学应用——光束自聚焦

利用光流体模型 ,计算模拟了激光束的自聚焦传输特性 ,得到与实验相一致的结果。     

Probing of a Stratified Medium by Means of a Magnetic Dipole: A Geometrical Optics Approach

The propagation of a field radiated by a vertical magnetic dipole located in a plane stratified medium is described in terms of rays obeying geometrical optics laws. This leads to a simple equation linking the field to the complex permittivity of each layer. This equation is then solved to obtain the real permittivity and the conductivity of each layer. In addition it is shown, by rigorously simulating measured values, that the knowledge of the phase of the field provides valuable information on the location of the interfaces.     

Design of Absorber-Lined Chambers for EMC Measurements Using a Geometrical Optics Approach

Absober-lined chambers (ALC's) have been found useful for EMC measurements over an extremely wide frequency range. However, only limited information about the field structure inside ALC's can be efficiently determined by measurements, while the characteristics of the rough absorbing surface do not render their analysis amenable to formal methods. The computation of field structure as a function of various parameters must thus resort to empirical modeling. A simple computational technique presented here predicts fields inside ALC's to a good approximation. Use is made of the Geometrical Theory of. Optics (GO). The absorber material is empirically modeled by its reflectivity as a function of frequency and angle of incidence. To establish the validity of the technique, computed results are compared to measured data. The methodology is then extended to compute fields inside a variety of ALC configurations. A study of the effect of shape, size, and absorber characteristics on these fields is presented to demonstrate the utility of the technique as a tool for ALC design purposes.     

电磁波在正负折射率介质界面上的传输特性

为了研究负折射率介质这种新型复合材料的电磁性质，利用麦克斯韦电磁理论对电磁波在正、负折射率介质交界面上的反射和透射特性进行了分析。得到了Snell反射定律和折射定律，反射系数和透射系数随入射角的关系（Fresnel公式）。结果发现Snell反射定律和折射定律仍然适用。但折射线与入射线位于法线的同侧；不论是腰波还是TM波，当以某一入射角入射时，反射系数都有可能变为零。这些结果对于设计新型的电磁学和光学器件具有指导性的意义。     

三维情况下平面介质交界面处二阶精度FDTD方程

提出了一种新的二阶精度时域有限差分法(FDTD)算法,针对研究区域介质填充不均匀,包含平面介质交界面的情况.新算法在交界面处利用非均匀网格建模,通过积分形式Maxwell方程的离散和交界面处连续场分量的泰勒级数展开,给出了平面介质交界面处三维情况下的二阶精度FDTD方程.该方法在保证介质交界面处电磁场量二阶精度的同时,合理划分不同介质区域粗细网格,在不增加计算容量和计算时间的基础上,有效地提高算法整体的计算精度.最后对介质谐振腔结构和微带电路进行模拟,验证了本文算法的精度高于标准的FDTD方法.     

The Impedance of a Wire Grid Parallel to a Dielectric Interface

Analysis is given for the problem of reflection of a plane wave at oblique incidence on a wire grid which is parallel to a plane interface between two homogeneous dielectrics. It is assumed that the wire grid is a periodic structure and consists of thin cylindrical wires of homogeneous material. The equivalent circuit is derived where it is shown that the space on either side of the interface can by a transmission line, and the grid itself is represented by a pure shunt element across one of the lines.     

Slant Dielectric Interface Discontinuity in a Waveguide (Short Papers)

The reflection and transmission of electromagnetic waves by a slant interface between two dielectric media is investigated. By using suitable Green's functions and a geometrical optics approximation for the field on the dielectric interface, expressions for the transmitted and reflected fields are derived. The approximate results obtained in this manner are compared with the available numerical data and are shown to be fairly accurate for a number of cases of interest.     

Numerical Solution of Dielectric Loaded Waveguides: I-Finite-Element Analysis

A variational expression of the electromagnetic fields in dielectric loaded waveguides is derived. This expression is discretized using the finite-element method and an electromagnetic coupling matrix is derived and evaluated. No restriction is placed on the shapes of the triangular elements or the order of the polynomial approximation. A general finite-element computer program is described and dispersion curves and field plots of some dielectric loaded waveguides are presented.     

Numerical Solution of Dielectric Loaded Waveguides: II---Modal Approximation Technique

A numerical method is described for the solution of the electromagnetic fields in dielectric loaded waveguides. The method uses the cutoff modes of the waveguide, obtained by finite-element analysis, to determine by matrix methods the fields above cutoff. A theoretical comparison with the conventional finite-element method is given and a general, highly efficient computer program for the analysis of dielectric loaded waveguides by the new method is described. Dispersion curves and contour plots obtained from the program are shown for several geometrical configurations, and these results are compared with analytic values and those obtained by the conventional finite-element method.     

Interior Green's Function Solution for a Thick and Finite Dielectric Slab

An interior Green's function solution is presented for a two-dimensional thick and finite dielectric slab. In the present development, the source and the field points are assumed to be inside the dielectric slab. The result is composed of two parts. The first part which has a discrete spectrum of eigenfunctions includes the surface wave multiple interactions, and is obtained by using the generalized scattering matrix and method of moments. The second part, which is a closed-form integral, is obtained for a separable dielectric slab that is closely related to the finite slab. The closed form integral is evaluated numerically and added to the surface wave solution. The solution accounts for the mode conversions at the end caps which occur when surface waves are reflected and diffracted. Test cases show very good agreement with a finite-element solver, even when the source is near the end caps.     

Measurement of Small Dielectric Losses in Material with a Large Dielectric Constant at Microwave Frequencies

A method is described for measuring dielectric losses at microwave frequencies in materials with a large dielectric constant. By observing a dielectric resonance in a sufficiently large sample, the loss tangent of the material can be obtained. Results on SrTiO/sub 3/, single crystals at 20 kMc are presented.     

Physical Optics Curved-Boundary Dielectric Plate Scattering Formulas for an Accurate and Efficient Electromagnetic Characterization of a Class of Natural Targets

Closed-form representations of the physical optics (PO) field scattered in the far zone by plane penetrable dielectric angular sectors of arbitrary opening angle featuring a conical-section boundary are derived in terms of incomplete cylindrical functions (ICFs). The proposed expressions, possibly in combination with PO formulas for the scattering from polygonal plates, allow one to evaluate the scattering from flat dielectric plates with both convex and concave curved edges in a very efficient manner and constitute a useful tool to improve the accuracy of the geometrical characterization of a class of natural scatterers. In order to check the correctness and computational effectiveness of the proposed scattered-field solutions, comparisons with results obtained by accurate completely numerical PO calculations are provided. Simulation data by the method of moments are also presented to assess the applicability of the PO approximation to the considered sample scattering geometries.     

Calculation of Coefficients of Capacitance of Multiconductor Transmission Lines in the Presence of a Dielectric Interface

A method is given for the numerical determination of the coefficients of capacitance for a class of multiconductor transmission-line systems. This class includes systems without ground planes, or with one or two ground planes, with the lines embedded in one or two layers of dielectrics. The conductors can be of any cross section that can be approximated adequately by polygons. The method is a refinement of the subareas method in which the assumption of a "staircase function" surface charge density, that is, constant charge density over each subarea, is replaced by the assumption of a piecewise linear charge density over the conductor surfaces, and the charge density parameters are determined by making a least-squares fit to the potential to the boundary conditions of the problem.     

变温介电参数测量系统研制

介绍自行研制的变温介电参数测量系统，对该系统的组成，测量方法作了详细说明，并给出应用实例，整个系统由计算机控制，采用双通道锁相放大技术，使测量结果更加精确可靠。利用该测量系统，可以同时得到介电常数、介质保耗与温度的关系，将有助于热释电材料研究。     

Scattering of Surface Waves at a Dielectric Discontinuity on a Planar Waveguide

A theoretical treatment is presented of the scattering of a surface-wave mode on a planar surface waveguide at an abrupt axial transition. The latter is due to a dielectric obstacle that covers the line completely up to a given height. The analysis involves the matching of the tangential fields, expressed in terms of complete sets of eigenmodes, on the transition plane. The problem arises in certain obstacle detection schemes currently being proposed for guided transportation, which use the principle of guided RADAR.