频域吸收边界条件的构造理论

在频域中推导了适用于差分类数值方法的吸收边界条件的构造方法，并通过选取不同参数导出了几种现有的吸收边界条件。在计算了一般形式的吸收边界条件的反射系数之后，提出了一种简单实用的自适应吸收边界条件。     

柱坐标系下FDTD算法的吸收边界条件

本文借助二阶准波方程式研究了柱坐标系下FDTD算法的一种吸收边界条件.根据这一边界条件,编制了相应的计算程序检验其吸收特性,并与均匀柱面波传播的简单吸收条件作了比较.计算结果表明,该吸收边界条件具有较好的吸收性能.     

一种改进的Mur吸收边界条件

吸收边界条件是时域有限差分(FDTD)算法解决电磁问题的重要条件。提出一种改进的吸收边界条件。将惠更斯面推广到二维的时域有限差分算法中,并利用惠更斯面来改进Mur吸收边界。惠更斯面具有理论基础成熟、编程简单、占用的计算内存少等优点,可以方便地插入到FDTD计算域中。FDTD数值仿真证明,惠更斯面在增加少量计算量的同时大幅度提高了Mur边界的吸收性能。而在应用的截断边界元胞数目相同的情况下,改进的Mur吸收边界能达到比PML吸收边界更好的吸收效果。     

Efficient High-Order Absorbing Boundary Condition for the ADI-FDTD Method

In this letter, an efficient high-order absorbing boundary condition for the alternating-direction-implicit-finite-difference time-domain (ADI-FDTD) method is developed. The proposed high-order absorbing boundary condition (ABC) has very high numerical efficiency because it can keep the tri-diagonal matrix form during the ADI iteration. The absorbing performance of the proposed ABC is analyzed theoretically. To verify the performance of the proposed high-order ABC, a rectangular waveguide problem which has very strong dispersion characteristic is analyzed with the ADI-FDTD method. Numerical results show that the proposed high-order ABC has excellent absorbing performance.     

数值吸收边界条件在OSRC方法中的应用

本文引入一种数值吸收边界条件,将其应用于解决开放空间电磁散射问题的表面辐射条件法(OSRC)之中。本文使用这种边界条件对理想导电及均匀电磁可穿透材料圆柱散射体的表面场进行了数值计算,并与使用二阶微分算子B_2型的吸收边界条件的结果作了比较。所有结果说明,这种数值吸收边界条件特大大改善OSRC方法的精度。     

采用PML的FDTD方法对矩形微带天线的研究

将完全匹配层(PML)吸收边界应用于微带结构中，对矩形微带天线进行了分析计算，给出了其时域和频域的仿真结果。结果表明，与传统的Mur边界相比，采用PML吸收边界具有反射小、馈源模型简单、收敛速度快等优点。     

PML吸收边界的时域有限差分法的数值色散研究

PML吸收边界以其优异的吸收能力与效果而倍受人们的关注。本文针对运用PML吸收边界的时域有限差分法的数值色散问题进行了研究,并得到了较为满意的结果,PML吸收边界在有效减少电磁 波在边界上的反射的情况下,并没有带来对数值色 散的不良影响。     

一种有效的吸收边界条件及其应用

从二维波动方程出发 ,经过相关理论分析 ,充分利用其内含的局域性特点 ,得出了局域边界条件 ;并把它和Mur二阶边界条件相比较 ,发现从理论到数值仿真 ,新边界条件都比Mur二阶边界更有效。而且 ,和Mur二阶边界条件相比 ,它只增加非常少的计算量和计算机内存。最后 ,应用新边界条件来模拟平面波在多层媒质中的传播 ,发现新吸收边界更适合解决此类问题     

Absorbing Boundary Conditions for the Finite-Difference Approximation of the Time-Domain Electromagnetic-Field Equations

When time-domain electromagnetic-field equations are solved using finite-difference techniques in unbounded space, there must be a method limiting the domain in which the field is computed. This is achieved by truncating the mesh and using absorbing boundary conditions at its artificial boundaries to simulate the unbounded surroundings. This paper presents highly absorbing boundary conditions for electromagnetic-field equations that can be used for both two-and three-dimensional configurations. Numerical results are given that clearly exhibit the accuracy and limits of applicability of highly absorbing boundary conditions. A simplified, but equally accurate, absorbing condition is derived for two- dimensional time-domain electromagnetic-field problems.     

Standing-travelling wave boundary condition (STWBC) forfinite-difference time-domain mesh truncation

The standing-travelling wave boundary condition (STWBC) is presented for the truncation of the finite-difference time-domain (FDTD) grid. This new boundary condition represents an improvement over the perfectly matched layer (PML) and the one-way wave absorbing boundary condition (ABC) in that it includes no additional absorbing region, no field splitting, and is composed of simple FDTD updating expressions. Numerical results demonstrate the stability and efficiency of this new boundary condition     

理想匹配层及模式匹配法分析多段平面光波导结构

将理想匹配层（PML）吸收边界条件和模式匹配法用于多段平面光波导结构分析，给出了一种改进的平面光波导结构的PML吸收边界条件，并对光波导的光场分布进行数值模拟，所得结果表明了PML吸收边界条件应用于多段平面光波导结构分析的有效性。该方法也可用于分析复杂结构的平面光波导。     

Absorbing boundary conditions applied to model wave propagation inmicrowave integrated-circuits

A general expression of an absorbing boundary condition is presented in this paper to model wave propagation in passive microwave integrated-circuits by the finite-difference time-domain method. Unlike previously developed absorbing boundary conditions which can only absorb propagating waves, this boundary condition can also absorb evanescent waves effectively. The microstrip line is used as an example to demonstrate how to impose this absorbing boundary condition on different outer boundaries of a computation-domain. It is also demonstrated that the numerical stability of this absorbing boundary condition, when it is applied in its high order form, can be maintained by properly selecting its parameters     

波导模场分布采用模式匹配的PML处理方法

理想匹配层(PML)是近年来迅速发展起来的一种非常有效的吸收边界.本文基于模式匹配法将PML吸收边界条件用于平面光波导结构计算中,从理论上分析了PML吸收边界条件的有效性,并在PML边界条件下模拟计算了一个三段平面光波导结构的模场分布.     

采用PML吸收边界条件的FDTD法在分析平面微带结构中的应用

本文将理想匹配层(PML)吸收边界条件用于平面微带结构的时域有限差分法(FDTD)分析中,给出平面微带结构的PML吸收边界条件,并编制程序,进行数值计算。结果表明,与传统的Mur吸收边界条件相比,采用PML吸收边界条件只需采用最简单的馈源模型就可明显地减小计算网格空间和加快收敛速度,并且可用于分析任意复杂结构的微带电路。本文方法对微带电路及微带天线的CAD设计将具有实际意义。     

The effect of curvature on the reflection coeffiecient of layered absorbers

The backscattering solutions for a metallic cylinder and a metallic sphere coated with single and double layers of absorbing material are investigated. In each case, attention is confined to the high-frequency specular return. The formal series solution obeying exact boundary conditions is expanded asymptotically into a Luneberg-Kline series whose first term, geometric optics, would be obtained by using an impedance boundary condition. The second term may be viewed as a correction term which depends upon the coating characteristics and radii of curvature of the body; in the case of the cylinder, its form for the TE polarization component differs from that for the TM polarization component. No practical conditions can be imposed upon the absorbing layers to cause cancellation of second order terms simultaneously for both polarization components. However, it is possible to adjust the flat-plate reflection coefficient of the absorber coat to cancel second order terms for one polarization component. The reflection coefficient will then depend ,upon curvature; for example, the voltage reflection coefficient must be i/(SkQ) for polarization parallel to a cylinder with a thin magnetic absorber coat. Comparison of the sphere solution with the cylinder solution yields information concerning absorbers on a general convex body.     

Unconditionally stable FDTD formulation with UPML-ABC

A new unconditionally stable finite-difference time-domain (US-FDTD) formulation is established in combination with the uniaxial anisotropic perfectly matched layer absorbing boundary condition. This approach exhibits improved absorbing performance yet maintains unconditional stability. Numerical results show that the reflection error of this scheme is limited even when the time-step size is beyond the Courantndash;Friedrichndash;Levy stability bound, and the absorbing performance is better than that of the US-FDTD with the dispersive boundary condition.     

完全匹配层（PML）吸收边界条件的理论分析

本文以屏蔽微带线为例,应用谱域方法推导了时域差分(FDTD)法中所用的完全匹配层(PML)吸收边界条件的公式,并且严格证明了有关参数的选择原则.计算表明,在屏蔽微带线中,这种吸收边界条件的反射系数可以小于-80dB.本文所给出的推导方法对于平面分层介质结构是普遍适用的,因为谱域中的每一个波谱实际上都代表一个平面波.文中所给出的推导揭示了这种吸收边界条件的机理,它对于正确使用以及进一步改进这种吸收边界条件都是有意义的.     

Shape optimization of corrugated coatings under grazing incidence using a genetic algorithm

We report on the use of a genetic algorithm (GA) to design optimal shapes for a corrugated coating under near-grazing incidence. A full-wave electromagnetic solver based on the boundary integral formulation is employed to predict the performance of the coating shape. In our GA implementation, we encode each shape of the coating into a binary chromosome. A two-point crossover scheme involving three chromosomes and a geometrical filter are implemented to achieve efficient optimization. A standard magnetic radar absorbing material (MAGRAM) is used for the absorber coating. We present the optimized coating shapes depending on different polarizations. A physical interpretation for the optimized structure is discussed and the resulting shape is compared to conventional planar and triangular shaped designs. Next, we extend this problem from single to multiobjective optimization by using a Pareto GA. The optimization results with two different objectives, viz. height (or weight) of the coating versus absorbing performance, are presented.     

一种新的吸收边界条件及三维微波结构的FDTD分析

本文基于Ｚ－变换域上导出的一种新的有效的吸收边界条件和ＦＤＴＤ法对三维微波无源集成结构进行了分析。与Ｍｕｒ吸收边界条件、色散吸收边界条件等相比,这种新的吸收边界条件更精确有效。相应的软件可应用于复杂三维微波集成结构等效网络参数的精确快速提取。     

The Improvement of PML Approach for the Calculation of Microwave and Millimeter Waves Circuit

The improved PML absorbing boundary condition have been introduced in this paper. The reflection coefficient of the absorbing boundary condition is less than the reflection coefficient of Berenger's PML algorithm. And in order to validate the theory and its effectiveness, We have applied the absorbing boundary condition to the calculation of microwave and millimeter waves circuit and get its reflection coefficient S ₁₁. The numerical result is shown in this paper.