Time-domain analysis of periodic structures at oblique incidence:orthogonal and nonorthogonal FDTD implementations

A novel implementation of periodic boundary conditions incorporated into the finite-difference time-domain (FDTD) technique in both orthogonal and nonorthogonal grids is presented in this paper. The method applied is a field-splitting approach to the discretization of the Floquet-transformed Maxwell equations. As a result, the computational burden is reduced and the stability criterion is relaxed. The results of the two methods are compared to experimental data     

平面波斜入射到有孔腔体的屏蔽效能分析

使用解析方法研究了缝隙偏离中心的有孔屏蔽腔屏蔽效能。将有孔腔体的屏蔽和传输特性用等效传输线的高次模进行分析,推导了平面波以任意角度和极化方向入射时,有孔腔体屏蔽效能的解析计算表达式。分析了入射角度、极化方向、孔缝尺寸、测试点位置、腔体壁损耗、工作频率等参量与腔体屏蔽效能的关系。经与腔体谐振频率比对,表明该解析方法得到的结果可信,而且解析公式计算速度快,利于参量分析,能为屏蔽腔体设计提供依据。     

FDTD等效入射波法分析PSTM

本文提出一种简捷有效的方法，即等效入射波法分析光子扫描隧道显微镜(PSTM)。作为验证，计算了3维情况下，形貌起伏样品和嵌埋的不同折射率样品，S和P极化情况下，等高扫描面上的场分布的PSTM图像，并与其他方法进行比较。比较表明，时域有限差分法(FDTD)等效入射波法与其他方法已有的结果符合相当好，并具有简捷，降低对吸收边界的要求，减小网格数和计算时间等优点。     

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 simple and efficient implementation of CFS-PML in the FDTD analysis of periodic structures

The use of perfectly matched layers (PMLs) is one of the most popular techniques employed for mesh truncation in finite-difference time-domain (FDTD) simulations. Its original form, however, has a poor absorption of evanescent waves, which are highly present in simulations of periodic structures. A better absorption has been achieved using a complex frequency shifted (CFS) PML, which has been implemented via a convolution scheme. In this letter, we present a simple and efficient implementation of the CFS PML and apply it to periodic structures.     

FDTD analysis of plane wave superposition to simulate susceptibility tests in reverberation chambers

The behavior of a device in a reverberation chamber can be analyzed as the same device irradiated by random plane waves. This work proposes an application of the finite difference time domain method to analyze the device by using a superposition of random plane waves, simulating the behavior of a reverberation chamber. The analysis of a transmission line compared with theoretical and experimental results in a reverberation chamber is reported.     

Reflection of a transient plane wave obliquely incident on compressible plasma half-space

The expression for the reflected transient pulses from the sharp surface of a compressible plasma half-space are obtained in a series form with the first perturbation order explicitely evaluated and valid for small to moderate compressibility (α = u/C0≤ 0.3, u is the electron acoustic velocity and C0is the velocity of light in free space). The reflected waveform are close to the waveform of cold plasma (α = 0) with noticeable change of amplitude and time delay of the first maxima.     

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.     

One-third-of-pitch reduction technique for the analysis of ternary azimuthally periodic helical slow-wave structures

This paper presents a technique to reduce the standard single-pitch helical model when performing a full-wave analysis of helical slow-wave structures (SWSs). The technique makes use of azimuthally periodic boundary conditions applied to the conventional helical SWS; the ternary angular symmetry of its dielectric rods allows reducing the standard computational domain by two thirds. It has been demonstrated that this method, as implemented with a commercially available simulator (high-frequency structure simulator), has no impact on the stability and accuracy of the cold parameters but allows a significant reduction of simulation time, which increases with the accuracy of the results. The proposed technique is therefore perfectly suitable for the accurate modeling of complex geometries and is expected to be particularly attractive for optimization analyses and applications in which accuracy and short simulation time are main concerns.     

Finite element analysis of electromagnetic scattering from periodic cylindrical structures at oblique incidence

A hybrid technique which combines the finite element method (FEM) and an expansion of the field in terms of Floquet modes is presented for the analysis of the scattering from, and the transmission through, penetrable periodic cylindrical structures, at skew incidence. The method is very flexible and allows the analysis of practical cylindrical configurations with arbitrary cross-section and material properties.<>     

On the scattering of an obliquely incident plane wave by a biisotropic cylinder

Scattering of an obliquely incident electromagnetic plane wave by an infinitely long, homogeneous, biisotropic cylinder is addressed. The ambient host medium considered is isotropic, homogeneous and dielectric-magnetic. It is observed that the constitutive coupling of the electric and the magnetic fields in the biisotropic material causes the cross-polarization component of the scattered field not to vanish even for the normal incidence case.     

Hybrid finite-element analysis of electromagnetic plane wavescattering from axially periodic cylindrical structures

In many antenna systems the primary feed or the subreflector will most often be supported by struts which obstruct the aperture and therefore cause a reduction in the directivity and an increase in sidelobe levels. So as to be able to design new structures which avoid these drawbacks, the problem of plane wave scattering from an infinite axially periodic cylinder of arbitrary geometric and material parameters is analyzed by a hybrid finite element/boundary element method. Covariant-projection edge elements are employed in the inhomogeneous region of the unit cell and the scattered field is expanded in terms of cylindrical Floquet harmonics. The resulting practical numerical procedure has been tested to ensure that power conservation rules are obeyed and checked satisfactorily against both analytical results and measurements on periodically loaded struts     

Scattering of obliquely incident plane waves from a finite periodic structure of ferrite cylinders

For the scattering of waves obliquely incident on many homogeneous gyrotropic cylinders simultaneous matrix equations are first derived from the reciprocity theorem where the auxiliary electric and magnetic current sources are specially selected. As a numerical example we examine the scattering properties of a finite periodic structure composed of many circular ferrite cylinders, with attention to 1) the frequency characteristics of the scattering cross section where the parameters are the number of cylinders, the incident angle, and the applied static magnetic field; 2) the patterns of the scattered power density; 3) the distributions of the total field in the vicinity of the cylinders; 4) the role of the periodicity of the spacing of the scatterers on the scattering cross section; and 5) the effect of the interactions among the cylinders. The extension of the present method may make it possible to analyse guided modes along an array of gyrotropic cylinders.     

Spectral domain analysis of electromagnetic wave scattering by an infinite plane metallic grating

A new method, based on the spectral domain analysis, is presented for solving the electromagnetic wave scattering by an infinite plane metallic grating. The key point of the present method is discretization of spectral formulation in terms of the sampling theorem. Two different polarizations, transverse magnetic (TM) and transverse electric (TE) excitations, are considered here. Accuracy of the present method is examined numerically by comparison with the rigorous Wiener-Hopf solutions which are applicable only to a special case. Since the end effect of a conducting strip is taken into account analytically, final results show enough convergence to evaluate the near fields as well as the far fields with small matrix calculations. Some numerical examples are shown mainly for surface current distributions to make clear the differences between the two different polarizations.     

Diffraction of a normally incident plane wave at a wedge withidentical tensor impedance faces

Diffraction of a normally incident plane wave by a wedge with identical tensor impedance faces is studied and an exact solution is obtained by reducing the original problem to two decoupled and already solved ones. A uniform asymptotic solution then follows from the exact one and agrees excellently with numerical results due to the method of parabolic equation     

Absorption in human body at 900 MHz for oblique incidence of plane wave

ICNIRP(1998) and IEEE C95.1-2005 limits for human exposure to radio-frequency fields are derived based on the condition of maximal coupling of the field to the body. In this study, at 900 MHz, the whole body average specific absorption rate (SAR_WB) for an adult's and a child's body is computed under these conditions and is shown to be also relatively uniform when explored over a range of oblique angles of incidence and polarisation of a constant amplitude plane wave. The SAR_WB in the body remains below the public limit of 80 mW/kg when the oblique field is maintained at the limit value of 41.1 V/m.     

斜入射条件下“猫眼”目标回波功率分析

建立了斜入射条件下"猫眼"目标回波功率的计算模型,在此基础上建立了非离焦和离焦两种情况下"猫眼"目标反射的几何模型,推导出非离焦和正负离焦条件下入射角的变化范围,引入有效接收面积概念,得到了正负离焦引起的"猫眼"目标的回波发散角和有效接收面积,得到了斜入射条件下"猫眼"目标的回波功率计算公式,对入射角和离焦量对"猫眼"目标回波功率的影响进行了数值模拟.结果表明:入射角和离焦量的共同作用引起"猫眼"目标有效接收面积和回波发散角的改变,进而引起反射光场能量分布的变化,只有满足特定条件的入射角才能产生回波功率,入射角和离焦量的增大引起回波功率的减小,其中离焦量的变化对回波功率的影响作用显著,当入射角和离焦量都为零时接收到的回波能量最强.     

入射平面波复射线展开精度的分析

从复射线展开表达式出发,通过参数变换,得到了入射平面波复射线展开拟合精度的单变量表达式,利用该式对展开面上及离开展开面后的拟表度进行了系统的讨论,建立了一种系统分析入射平面波复射线展开精度的方法。这一方法有助于建立通用的任意目标散射复射线分析软件。     

基于FDTD的微带漏波天线分析的新方法

使用时域有限差分法对微带漏波天线进行数值仿真,得到了微带漏波天线TE01模下的电场分布,对微带漏波天线的电波传播特性进行初步的讨论.提出新的经验计算公式微带漏波天线漏波传播系数,所得漏波传播系数曲线与实测数据以及比较数据十分吻合.     

Scattering of a plane wave by a cascade of two frequency-selective structures

Propagation of a plane electromagnetic wave through a multilayer frequency-selective dielectric structure with biperiodic metallization of two interfaces is considered. A method is proposed for calculation of the reflection and transmission coefficients of the structure. Computation results are presented for a structure with gratings consisting of metal rings. The effects of longitudinal and transverse shifts of gratings on the electrodynamic characteristics of the frequency-selective structure are studied. The computation results are compared to experimental data obtained in the microwave band.