TMFABC及其在传输线参数提取中的应用

本文发现将一阶Ｍｕｒ吸收边界条件分别应用到ｘ－ｔ,ｙ－ｔ,ｚ－ｔ平面上两相邻对角节点时,电磁波的反射误差可以互相抵消,从而提出了二重一阶Ｍｕｒ吸收边界条件（ＴＭＦＡＢＣ）。ＴＭＦＡＢＣ可以很方便地应用到多层结构上去,吸收效率比一阶Ｍｕｒ吸收边界条件及其超吸收算法明显提高,尤其在低频端的效果更好,而且ＴＭＦＡＢＣ对衰减波的吸收也很有效。我们将ＴＭＦＡＢＣ移植到一个时域有限差分（ＦＤＴＤ）程序中,用来     

A new absorbing boundary condition structure for waveguide analysis

The existence of evanescent waves and waves near cutoff frequencies limits the accuracy of the fields computed in waveguides using the finite-difference time-domain method, and prompted several researchers to design complicated boundary conditions, including combinations of perfectly matched layers and Higdon's higher order absorbing boundary conditions (ABCs). Instead, we employ a terminating structure in which the lateral walls are made absorbing in addition to the longitudinal walls. The undesirable lateral waves at the normal boundary interface are slowed down and effectively attenuated in the lateral walls, while the propagating waves are absorbed in the longitudinal walls. Numerical calculations for pulse excitation of a rectangular waveguide, using the simple Mur's first-order ABC, demonstrate the usefulness of the method     

Mur吸收边界条件的校正

本文分析了Mur吸收边界条件产生误差的原因,讨论了用散射中心法校正Mur吸收边界条件的问题,以二维情况下线源的辐射及方柱形导体的散射问题为例进行编程计算,且与未校正的同阶和高阶近似的Mur吸收边界条件作了比较,证明该方法是有效的,最后提出用坡印亭矢量的方向来校正Mur吸收边界条件的思想.     

FDTD analysis of a metal-strip-loaded dielectric leaky-wave antenna

The finite-difference time-domain (FDTD) method is used to analyze a dielectric leaky-wave antenna comprising metal strips etched on a rectangular dielectric rod. The radiation patterns of the leaky-wave antenna with and without the transition are determined by using FDTD. The effects of the launching discontinuity on the performance of the antenna are discussed. In addition, the application of the perfectly matched layer (PML) technique to the three-dimensional (3-D) dielectric waveguide and its performance, compared to those of the Mur's (1981) first-order and super-absorbing Mur's first-order absorbing boundary conditions (ABCs) are described. In addition, the effects caused by perturbation on the wave propagation characteristics of dielectric waveguide are also discussed. The FDTD results are verified by a W-band experiment and found to be in good agreement     

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。     

Fuzzy-based artificial bee colony optimization for gray image segmentation

In this article, we have proposed an image segmentation algorithm FABC, which is a kind of unsupervised classification (clustering), where we combine the concept of artificial bee colony optimization (ABC) and the popular fuzzy C means (FCM) and named it as fuzzy-based ABC or FABC. In FABC, we have used fuzzy membership function to search for optimum cluster centers using ABC. FABC is more efficient than other optimization techniques such as genetic algorithm (GA), particle swarm optimization (PSO) and expectation maximization (EM) algorithms. FABC overcomes the drawbacks of FCM as it does not depend on the choice of initial cluster centers and it performs better in terms of convergency, time complexity, robustness and segmentation accuracy. FABC becomes more efficient as it takes the advantage of the randomized characteristics of ABC for the initialization of the cluster centers. The experiments with FABC, GA, PSO and EM have been done over various grayscale images including some synthetic, medical and texture images, and segmentation of such images is very difficult due to the low contrast, noise and other imaging ambiguities. The efficiency of FABC is proven by both quantitative and qualitative measures.     

Techniques for implementation of the FDTD method on a CM-5 parallelcomputer

In this paper, techniques for efficiently parallelizing the FDTD method for radiation problems are presented. Methods of parallelizing the core FDTD algorithm, PML ABC, Mur's ABCs, and the near-zone-to-far-zone transformation are discussed. A technique which makes the parallel FDTD more efficient can be applied to Berenger's PML in a straightforward manner, and apparently makes the code for PML ABC faster. Performance of the code is shown, and the computer-time usage for various parts of the code is given. On a 32 processor CM-5, the core FDTD algorithm is 100 times faster than an existing serial code, run on a SUN SPARC-2 workstation, and the calculation of the radiation patterns for two orthogonal planes is approximately 27 times faster. The techniques can easily be extended to other cases, not included in this paper, such as FDTD codes for magnetic materials, and non-uniform-mesh FDTD codes     

频域Mur条件差分近似的构造和应用

本文构造了Mur条件的频域有限差分近似。结合推导的非均匀、各向异性媒质中有限差分方程,可以有效、方便地计算电大尺寸复杂媒质体的电磁散射问题。运用稀疏矩阵压缩存贮技术和迭代求解算法,大大减少了所占用的计算机内存,与矩量法相比计算时间也大为减少。文中计算了几种媒质情况上圆柱和方柱的雷达散射截面,并与已有数据作了比较,结果一致性较好。     

Hysteresis compensation in electromagnetic actuators throughPreisach model inversion

In this paper, the classical Preisach independent domain model is used to capture the essential characteristics of hysteresis nonlinearity in electromagnetic (EM) actuators made of soft ferromagnetic material. Experimental results demonstrate its ability to accurately model electromagnetic hysteresis for variations in input current, airgap, and orientation. The Preisach model is then inverted and incorporated in an open-loop control strategy that regulates the EM actuator and compensates for hysteretic effects; hysteresis-free regulation of the EM actuator is obtained, for variations in input current, airgap, and orientation. Hysteresis is also effectively compensated for desired force trajectories of frequencies up to 100 Hz. Thus, the experimental results demonstrate consistent performance of the open-loop control strategy based on Preisach model inversion, in satisfactorily regulating the output of the EM actuator to the desired trajectories     

Mur Absorbing Boundary Condition for Efficient Fundamental 3-D LOD-FDTD

This letter presents the implementations of Mur first-order absorbing boundary condition (ABC) for efficient fundamental scheme of 3-D locally one-dimensional finite-difference time-domain (LOD-FDTD) method. The Mur ABC is incorporated into the efficient fundamental scheme using consistent implementation and a novel implementation with lower reflection coefficient. Both implementations in the efficient fundamental scheme are compared and validated with the conventional LOD-FDTD scheme. By comparing the CPU time of both conventional and efficient fundamental schemes, it is ascertained that substantial gain in the overall efficiency may be achieved for the latter even with Mur ABC incorporated.      

Electromagnetic Field Emission From Gas-to-Air Bushing in a GIS During Switching Operations

Very fast transient overvoltages (VFTO) and the associated very fast transient currents (VFTC) generated during switching operations in a gas-insulated substation (GIS) radiate electromagnetic (EM) fields, which in turn can leak into the external environment through apertures like SF₆ gas-to-air bushing. Therefore, it becomes necessary to characterize and quantify the EM fields when sensitive control devices are used for the operation of such substations. Keeping this in view, a numerical model using a finite-difference time-domain (FDTD) technique was developed to compute the transient field emission from a 245-kV-rated gas- to-air bushing. Shielding effectiveness (SE) of the bushing for these transient fields was evaluated using a derivative Gaussian current excitation of the high-tension (HT) conductor. The variation in EM field levels along the axis of bushing at various radial distances for different frequencies of the transient current were analyzed. The enhancement of the field levels due to the presence of a metallic structure on the ground plane, which simulates the control cubicle or the grounded enclosures of the GIS, were studied. Finally, the emission levels from different bushing models were calculated for the VFTC generated during a switching event, and the dominant frequencies were identified.     

An IE-ODDM-MLFMA Scheme With DILU Preconditioner for Analysis of Electromagnetic Scattering From Large Complex Objects

For electrically large complex electromagnetic (EM) scattering problems, huge memory is often required for most EM solvers, which is too difficult to be handled by a personal computer (PC) even a workstation. Although the multilevel fast multipole algorithm (MLFMA) effectively deals with electrically large problems to some extent, it is still time and memory consuming for very large objects. In order to further reduce the CPU time and the memory requirement, a hybrid algorithm, based on the overlapped domain decomposition method for integral equations (IE-ODDM), MLFMA and block-diagonal, incomplete lower and upper triangular matrices (DILU) preconditioner, is proposed for the analysis of electrically large problems. The dominant memory requirement for plane wave expansions in the three processes of aggregation, translation and disaggregation in the MLFMA is drastically reduced by the first two techniques. The iterative procedure for each overlapped subdomain solved by the MLFMA is effectively sped up by the DILU preconditioner. After integrating these techniques, the proposed hybrid algorithm is more efficient in computing time and memory requirement compared to the conventional MLFMA and is more suitable for analyzing very large EM scattering problems. Enough accurate solution can be obtained within quite a few outer iterations, where an outer iteration means a complete sweep for all the subdomains. Some numerical examples are presented to demonstrate its validity and efficiency.     

An EM Tuning Procedure for Planar Filters Based on Individual Resonator Decomposition

Planar filters directly implemented by design formulas yield a distorted frequency response, especially at higher frequencies, due to dispersion and discontinuities. In this letter, an electromagnetic (EM) tuning procedure based on individual resonator decomposition for a fifth order stepped impedance resonator (SIR) filter is presented. The EM simulation of the SIR filter composed by the tuned resonators shows remarkable agreement with the design formula and requires no further tuning. The procedure is experimentally verified by comparing the measured and the simulation results.     

A new statistical methodology predicting chip failure probability considering electromigration

We present a new approach to analyze chip reliability due to electromigration (EM). This new approach utilizes the statistical nature of EM failure in order to assess overall EM risk. It includes within-die temperature variations from the chip’s temperature map extracted by an Electronic Design Automation (EDA) tool to estimate the failure probability of a design. We first used the traditional EM approach to analyze the design with a single temperature across the entire chip that involves six metal and five via layers. Next, we used the same traditional approach but with a realistic temperature map. A comparison between these two results confirms that using a temperature map yields a less pessimistic estimation of the chip’s EM risk. Finally, we employed the statistical methodology developed by us considering a temperature map and different use-condition voltages and frequencies to estimate the overall failure probability of the chip. The results of this statistical analysis confirm that the chip level failure probability is higher (i) at higher use-condition frequencies for all use-condition voltages, and (ii) when a single temperature instead of a temperature map across the chip is considered.     

用时域变换的方法计算微带线的有效介电常数

使用了各向异性的PML吸收边界条件来截断时域有限差分网格,对具有匹配负载的微带线中的电磁波的传播进行了模拟,并通过时域变换来计算微带线的有效介电常数,首次把各向异性的PML吸收边界 数值模拟终端负载以及时域变换等技术结合起来,引入到有关微带线的计算中来,以替代分别用完全电壁和守全磁壁进行两次计算的边界条件,从计算结果看,该结果同分别使用完全电壁和完全磁壁进行两次计算的边界条件所得的结果符合得很好,并且在计算上更简洁。可以看出各向异性的PML吸收边界条件对用时域近似这类方法来解决微带线问题非常适用。     

Radiation in a warm plasma from an electric dipole with a cylindrical column of insulation

The radiation in a warm plasma due to an axially oriented electric dipole on the axis of a cylindrical column of insulation of infinite length is studied using the linearized continuum plasma theory, and approximate boundary conditions. Two types of surface waves are excited along the cylindrical column of free space immersed in a plasma and their dispersion and power relations are examined. The uncoupled electromagnetic (EM) and the plasma (P) space waves are excited. The radiation pattern and the normalized radiation resistance of the EM and the P modes are studied both as a function of frequency and as the radius of the insulating column. The effect of the insulating column is found to be very significant only in the case of the P mode. It is found that the power transfer into the P mode becomes less at higher frequencies and larger thickness of the insulation. The results of this investigation may be used to predict in a crude manner the effect of the "ion sheath" that is formed around the antenna in the ionosphere.     

Acoustic and electromagnetic wave interaction: analyticalformulation for acousto-electromagnetic scattering behavior of adielectric cylinder

An analytical solution for the bistatic electromagnetic (EM) scattering from an acoustically excited vibrating dielectric circular cylinder is presented. The incident acoustic wave causes a boundary deformation as well as a dielectric inhomogeneity within the dielectric cylinder. First, a perturbation method is developed to calculate the EM scattering from a slightly deformed and inhomogeneous dielectric cylinder. Then, assuming the vibration frequency is much smaller than the frequency of the incident EM wave, a closed form expression for the time-frequency response of the bistatic scattered field is obtained. The solution for acoustic scattering from an elastic cylinder is applied to give the displacement on the surface as well as the compression and dilation within the cylinder. Both the surface displacement and the variation in material density (dielectric constant fluctuation) within the cylinder contribute to the Doppler component of the EM scattered field. Results indicate that the Doppler frequencies correspond to the mechanical vibration frequencies of the cylinder and that the Doppler components only become sizeable near frequencies corresponding to the natural modes of free vibration in the cylinder. These resonances depend only on the object properties and are independent of the surrounding medium. Thus, utilizing the information in the Doppler spectrum scattered by an acoustically excited object vibrating at resonance could provide a means for buried object identification     

THz Thermal Radiation Enhancement Using an Electromagnetic Crystal

Thermal radiation in the terahertz (THz) range only occupies a tiny portion of the whole blackbody power spectrum at room temperature. We demonstrate that a thermal radiator, which is constructed from an electromagnetic (EM) crystal, can be designed so that its photon density of states (DOS) is enhanced in the THz frequency range. We also demonstrate, as a consequence, that this source may lead to large enhancements of the radiated power over the values associated with normal blackbody radiation at those frequencies. The THz thermal radiation enhancement effects of various EM crystals, including both silicon and tungsten woodpile structures and a cubic photonic cavity (CPC) array, are explored. The DOS of the woodpile structures and the CPC array are calculated, and their thermal radiation intensities are predicted numerically. These simulations show that the radiated power can be enhanced by a factor of 11.8 around 364 GHz and 2.6 around 406 GHz, respectively, for the silicon and tungsten woodpile structures in comparison to the normal blackbody radiation values at those frequencies. It is also shown that an enhancement factor of more than 100 may be obtained by using the CPC array. A silicon woodpile EM crystal with a band gap around 200 GHz was designed and fabricated. The transmission property of this woodpile structure was verified using the THz time-domain spectroscopy (TDS). Thermal emissions from the fabricated silicon woodpile and a control blackbody sample were measured. Enhancements of the woodpile source radiation over the blackbody were observed at several frequencies which are consistent with the theoretical predictions.      

Electromigration characteristics in dual-damascene copper interconnects by difference of via structures

In order to improve the interconnect performance, copper has been used as the interconnect material instead of aluminum. One of the advantages of using copper interconnects instead of aluminum is better electromigration (EM) performance and lower resistance for ultralarge-scale integrated (ULSI) circuits. Dual-damascene processes use different approaches at the via bottom for lowering the via resistance. In this study, the effect of a Ta/TaN diffusion barrier on the reliability and on the electrical performance of copper dual-damascene interconnects was investigated. A higher EM performance in copper dual-damascene structures was obtained in barrier contact via (BCV) interconnect structures with a Ta/TaN barrier layer, while a lower EM performance was observed in direct contact via (DCV) interconnect structures with a bottomless process, although DCV structures had lower via resistance compared to BCV structures. The EM failures in BCV interconnect structures were formed at the via, while those in DCV interconnect structures were formed in the copper line. The existence of a barrier layer at the via bottom was related to the difference of EM failure modes. It was confirmed that the difference in EM characteristics was explained to be due to the fact that the barrier layer at the via bottom enhanced the back stress in the copper line.     

New frequency-dependent parametric modeling of dielectric materials

The recent increase in the use of electromagnetic (EM) waves raises more and more concern about the impact of EM radiation. Dielectric properties of materials are important indications of the depth of EM propagation and dispersion. This led to substantial research on the parametric modeling of dielectric properties of materials. In this paper, such modeling of material is studied for frequencies up to 100 GHz. The new model proposed was developed to describe the variation of dielectric properties of dielectricity as a function of frequency using experimental results on dielectric dispersion. Approximate modeling of electrical parameters can be very useful in that it allows the engineer to avoid complex equations of conventional models. Specifically, this work analyzes the dielectric properties of human parts, water, soil and vegetation. The new model is proposed for those materials. The theoretical background on those materials was investigated and simulation results on complex permittivity, the attenuation and phase constants of wave, of each of those materials were performed to assess the accuracy of the new approximate model. This model has further enabled conclusions in terms of measurable biophysical parameters.