Design of wave absorber for small conducting sphere

An electromagnetic wave absorber for a small sized conducting sphere is designed by applying the Newton-Raphson method to the eigenfunction series solution for a coated conducting sphere. The parameters for the perfect absorbing condition are the constitutive parameters and the thickness of coating for a given radius of conducting sphere. The wave absorber designed by this method exhibits a superior absorption performance to that designed using flat plate absorber theory     

强电磁脉冲电离大气三维FDTD仿真

强电磁脉冲在大气中传播时会导致大气分子电离,且电离气体又会反作用于传播的电磁波,因此是 一个传播状态动态实时变化的物理过程。要准确模拟该过程需要综合考虑电磁波传播、大气电离、带电粒子运动等 物理过程。为解决该问题,文中结合麦克斯韦方程、等离子体方程、磁流体动力学方程等,构建多物理场分析方程 组,该方程组能够考虑强电磁脉冲传播时大气电离、扩散、附着、复合等物理效应。进而结合三维时域有限差分方法 (FDTD)来构建动态仿真模型,对强电磁脉冲在大气中的传播过程进行仿真并分析其宏观大气电离效果。     

内置负载开缝腔体谐振效应抑制方法研究

开缝腔体谐振特性放大了进入腔内的耦合能量,对内部电子设备构成严重威胁。文中建立内含金属 隔板、吸波体等负载的圆柱腔体模型,提出了在隔板上涂覆吸波材料以抑制谐振的新方式,研究了吸波体电磁特性 对谐振的影响。结果表明:隔板越靠近腔体前壁放置、板间距越大,对内部场影响越小,谐振点出现位置越接近空腔 固有模式;谐振点处屏蔽效能(Shielding Efficiency, SE)的提升是隔板和吸波材料综合作用的结果,隔板可迫使谐振 点迁移,吸波材料能改善谐振特性,并且涂覆磁性吸波材料性能更优;在隔板双面涂敷吸波材料抑制高次谐振效果 更好;适当增加隔板上涂覆材料厚度或提高材料相对磁导率,都能实现和全腔内壁涂覆相同的谐振抑制效果,效费 比也更高;场强分布因传播模式不同而不同,强电场区应放置电性吸波体才有效。     

Transient Analysis of a Directional Coupler Using a Coupled Mlcrostrip Slot Line in Three-Dimensional Space (Short Paper)

In recent MIC techniques, double-sided MIC has been studied because its advantages in propagation characteristics are greater than that conventional MIC's. A coupled microstrip slotline is one of them. Its application to various circuit elements has often been discussed. But the coupled microstrip slotline is essentially three-dimensional structure, so the analysis demands a rigorous three-dimensional treatment. Also, the recent high-speed pulse technique demands analysis in the time domain. The present paper treats a directional coupler using the coupled microstrip slotline in three-dimensional space and time. The results of the directional coupler analysis is presented with the complicated time variation of the three-dimensional electromagnetic field. So, the mechanism of the directional coupling phenomena that is produced by the propagation characteristics of the even and odd modes is presented in the time domain, In particular, the instantaneous diagram of the Poynting vector details the energy flow in the transient process. For the analysis of the characteristics of the complex microwave device, these results present the utilities of the various field distributions that are obtained by the three-dimensional vector analysis in the time domain.     

多媒质区域中电磁波传播的时域特征波模拟

将时域特征波法用于模拟多媒质区域的电磁波传播。与时域有限差分法相比，时域特征波法在处理媒质交界面和吸收边界上具有优越性。     

计算周期性导波结构的时域有限差分方法

本文提出一种计算周期性导波结构的时域有限差分方法.由Floquet定理建立边界条件,在电场边界和磁场边界上两次使用Floquet定理,从而将计算域限制在一个周期结构内,并且在导波结构侧面引入吸收边界条件,保证了计算精度.通过预先给出传播常数,经FDTD迭代计算,其谐振频率就是该传播常数所对应的工作频率.     

Application of an anisotropic perfectly matched layer absorber for open boundary truncation in the multiresolution time domain scheme

We apply an anisotropic perfectly matched layer (APML) absorber for open boundary truncation in implementation of the multiresolution time domain (MRTD) scheme. We develop an APML update algorithm to handle a general APML region in the MRTD formulations with the content of the leapfrog algorithm applied in the conventional finite-difference time-domain method. We also discuss the boundary truncations for both perfectly electric conductor (PEC) and perfectly magnetic conductor (PMC) walls using the image techniques. We validate the algorithm by analyzing various guided wave and antenna structures. It is found that the APML performs well for absorbing electromagnetic waves in the MRTD algorithm.     

一种基于吸波材料的屏蔽领结天线的研究与应用

设计了一种基于吸波材料的屏蔽领结天线, 采用金属腔体提高天线的方向性, 并起到屏蔽作用.通过在腔体内部填充吸波材料, 来降低电磁波在金属腔内部的反射, 并改善天线的频率域特性和时间域信号的拖尾.通过有限元电磁仿真软件HFSS设计天线模型, 优化天线参数.实际天线的各项参数较加吸波材料和金属腔之前得到了有效改善:频率域上, 天线的中心频率有所降低, -10 dB以下带宽从原来的100 MHz提高至200 MHz; 时间域上, 脉冲信号的宽度降低, 信号拖尾得到了明显改善.实际探测证明, 在天线背部加填有吸波材料的金属屏蔽罩, 可以有效降低来自上方的干扰, 分离直达波和有用信号, 提高探测精度.     

FDTD法的计算机可视化技术

本文应用计算机图形学的方法探讨了FDTD法计算机可视化的途径.对FDTD法进行可视化处理后,可直观地看到FDTD法的计算过程,形象地显示出电磁波与物体相互作用的过程,从而可观察到电磁波传播、穿透、散射和吸收等重要现象,这有利于研究电磁波与物体相互作用的机理.两个例子表明,本文提出的方法是非常有用的.     

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。     

垂直人射HEMP近地面电磁环境特性研究

高空核爆电磁脉冲(HEMP)具有覆盖范围广、峰值场强高等特点,对电子设备构成严重威胁.针对有关HEMP标准中主要涉及自由空间HEMP波形描述的情况,研究了双指数HEMP平面波垂直入射地面时,地面附近的电磁脉冲环境特性.基于时域有限差分(FDTD)法提出使用一维合成平面波解决总场空间激励源的引入问题.通过设置不同的入射波...     

一种带宽展宽的等离子体超材料吸波体的设计

为了在TE波下获得带宽可展宽（11GHz~14GHz频带内）且可调谐的吸收曲线，提出了一种新型超材料吸波体，其周期性结构单元采用蜂窝状特有的六边形结构。对该吸波体的参量分析图进行了计算，研究了变量g和d的数值不同时，对吸波体吸收频带及吸收带宽的影响，并解释了蚀刻"十"字形结构吸波体带宽展宽的成因。结果表明，该吸波体在9.17GHz~9.5GHz低频频域的吸收率达到90%以上，当不同的等离子体谐振区域被激励时，可以实现吸波体的分时分频域吸收以及改善吸波体的吸收性能，改变变量g和d可以实现对吸收频带的动态调控；可以通过在方形结构中蚀刻"十"字形结构的方式拓宽高频频域的吸收带宽，其在12.08GHz~13.91GHz频域的吸收率高于90%，改变变量s可以明显展宽吸收频带，且该吸波体对入射电磁波的角度不敏感。该吸波体的设计思路为拓宽吸波体的吸收带宽提供了一种有效的方法。     

Analysis and modeling of multilevel parallel and crossing interconnection lines

Analytical and numerical techniques to study the pulse propagation characteristics such as delay, distortion, and crosstalk in multilevel interconnections associated with high-speed digital IC's including VLSI chips are presented. The parallel and crossing interconnections at various levels are modeled as lossy coupled lumped distributed parameter systems, which are analyzed for their time domain characteristics. The characterizing electrical parameters of the structures are computed by utilizing the network analog method that has been formulated to solve for the lossy line constants and parasitic coupling associated with a three-dimensional multiconductor system in a layered lossy medium. It is shown that the time domain response of the multiport structures can be computed by using standard CAD programs such as SPICE by utilizing compatible circuit models developed from the solution of such systems. Examples of the step and pulse response of typical systems are included to demonstrate the versatility, usefulness, and accuracy of the techniques presented in the paper.     

一种波长可调的近红外波段完美吸收体

一般将电磁波完美吸收体简称为完美吸收体,它可用于很多行业。用有限时域差分法研究了一种可以在近红外波段工作的完美吸收体。模拟结果表明,这种完美吸收体可以实现98%的单峰1400 nm左右宽谱吸收,或者可以实现90%以上的1320 nm和1640 nm波长的双峰吸收效率。通过调节共振腔结构的大小可以调节吸收波长和吸收宽度。电磁波完美吸收体是一种背靠背双共振腔模式的完美吸收体,有非常广泛的应用前景。     

一种新的简化行波边界条件在FDTD算法中的实现

本文提出一种新的边界条件。这种边界条件在边界处强加理想导体对计算场区进行截断,而将由此产生的反射场分离去除,从而减小反射所产生的干扰。与PML边界条件相比,由于它不需要吸收层,不需要PML层中人为的场量分解,因此节约了内存,提高了计算速度。文中给出一维、二维空间的计算实例,计算结果表明原理是可行的。     

强激光打靶产生电磁脉冲特性与传导防护研究

为了降低电磁脉冲的场强大小,加强强激光打靶产生电磁脉冲的传导防护性能,提出了强激光打靶产生电磁脉冲特性与传导防护研究.由于强激光打靶产生电磁脉冲对各种电子设备和电气设备都会造成一定威胁,采用双指数函数,分析了强激光打靶产生电磁脉冲的时域波形频谱,完成了强激光打靶产生电磁脉冲的特性研究;为了消除强激光打靶产生的电磁脉冲波...     

基于全局透射边界条件的宽角抛物方程电波预测模型

提出了一种新型的基于全局透射边界条件（non-local boundary condition,NLBC）的Greene近似宽角抛物方程（wide-angle parabolic equation,WAPE）电波预测模型,用于求解对流层远距离复杂环境中的电磁波传播特性.采用有限差分法（finite difference method,FDM）求解WAPE得到了三对角线性方程组,可以快速地求解整个空间的电场分布,也可以对不规则的地表环境进行精确建模.本文提出的WAPE模型解决了传统的PE离轴传播角度偏小的问题,将电波的最大传播仰角提升至约50°,同时大大减小了计算区域中上边界吸收层的设置尺寸,从而提高了PE的计算效率.实验证明,当伪微分算子的相位误差不超过0.002时,Tappert、Claerbout和Greene近似形式得到的最大传播角分别为20°、35°和45°.最后,通过与经典的光学双射线模型进行对比,证明本文提出的基于NLBC的Greene近似WAPE模型的可计算传播仰角更大,对上边界处反射电磁波有良好的吸收效果.因此,本文的模型适用于对流层远距离复杂环境中电磁波传播特性的精确预测.     

Finite-element time-domain analysis of axisymmetrical radiators

A method of analysis which permits the computation of electromagnetic fields directly in the time domain using the finite element method (FEM) is presented. The method considers coaxially-driven axisymmetrical structures. A new way of implementing absorbing boundary conditions for the coaxial feed is discussed. The method has been successfully used to model coaxially-driven axisymmetrical monopole antennas for a Gaussian pulse excitation. Generally, the results obtained show good agreement with previously published numerical and experimental data     

Analysis of electromagnetic scattering from anisotropic cylindrical structures using state space method

Scattering of the electromagnetic waves from anisotropic cylindrical structures (ACS) is investigated using an exact and analytical frequency domain method in the most general case. The state space approach is used for analyzing of wave propagation in cylindrical structures for the first time. The validity of the proposed method is verified for the anisotropic cylindrical structures which have closed-form solutions. Comparing the results obtained by closed-form solution, the proposed approach and other commonly used methods in literature shows that the method is accurate, fast and simple. The presented study is covered all practical considerations in the field of electromagnetic scattering from ACS's such as polarization and incident angle of excitations, the geometry and configuration of the structure. This comprehensiveness is one of the biggest advantages of the investigation. Regarding the applications of the state space method in parameters retrieval of planar structures, the present study can be effective as the first and basic step in opening a new way toward further studies on inverse scattering of the cylindrical structures consisting complex media.