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Title: ACES November 2007 Full Journal
File Type: Journal Paper
Issue:Volume: 22      Number: 3      Year: 2007
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Title: November 2007 Front/Back Matter
File Type: Journal Paper
Issue:Volume: 22      Number: 3      Year: 2007
Download Link:Click here to download PDF     File Size: 378 KB

Title: Eliminating Interface Reflections in Hybrid Low-Dispersion FDTD Algorithms
Abstract: The numerical phase mismatch across FDTD lattice layers with different sets of update equations has been investigated. A predictive equation of numerical reflections across high-order/low-order layers has been derived. Based on this equation the standard Yee (S22) update equations have been modified to allow their implementation around PEC boundaries and other special situations in an otherwise global high-order implementation, while keeping spurious reflections at the hybrid interface to a practical minimum and independent of the traversing wave direction. S22 Phase matching has been developed and verified in both S24 and M24 high-order hybrid algorithms.
Author(s): Mohammed F. Hadi, Rabie K. Dib
File Type: Journal Paper
Issue:Volume: 22      Number: 3      Year: 2007
Download Link:Click here to download PDF     File Size: 2458 KB

Title: Finite Difference Time Domain Method for the Analysis of Transient Grounding Resistance of Buried Thin Wires
Abstract: For the analysis of grounding resistance with the finite-difference time-domain (FDTD) method for solving Maxwell's equations, an equivalent radius of a naked thin wire in a lossy medium is derived by means of the static field approximation, proposed for derivation of that of an aerial thin wire. It is 0.23 times the size of each cell employed, which is the same as that of an aerial thin wire. The validity is tested by comparing the grounding-resistance values obtained through FDTD simulation on simple buried structures with the theoretical values.
Author(s): Md. Osman Goni, Eiji Kaneko, Akihiro Ametani
File Type: Journal Paper
Issue:Volume: 22      Number: 3      Year: 2007
Download Link:Click here to download PDF     File Size: 266 KB

Title: Accelerated GRECO Based on a GPU
Abstract: For obtaining the electromagnetic scattering characteristic of a complex target efficiently, GRECO (Graphical Electromagnetic COmputing) is implemented by a programmable pipeline of a modern GPU (Graphics Processing Unit). The speed of the simulation can be improved up to 20 times compared with the raw GRECO. The ray tracing algorithm based on a GPU is implemented to obtain the multiple reflection contribution of a target with concave structure. This approach will redound to research works such as radar target identification and Inverse Synthetic Aperture Radar (ISAR) imaging.
Author(s): Yang ZhengLong, Jin Lin, Li WeiQing
File Type: Journal Paper
Issue:Volume: 22      Number: 3      Year: 2007
Download Link:Click here to download PDF     File Size: 317 KB

Title: An Efficient Preconditioner (LESP) for Hybrid Matrices Arising in RF MEMS Switch Analysis
Abstract: The small dimensions of Radio Frequency Micro-ElectroMechanical Switches (RF MEMS) raise significant modeling challenges in terms of accuracy and solver efficiency. This paper introduces a practical RF MEMS switch analysis based on an extended finite element-boundary integral (EFE-BI) method with an iterative solver incorporating a new sparse-matrix preconditioner whose large eigenvalues are very close to those of the original matrix. This sparse preconditioner is key to successfully solving the ill-conditioned EFE-BI matrix. The smaller condition number and almost positive-definite eigenvalue spectrum after preconditioning leads to fast convergence. Specific RF MEMS simulations are presented to demonstrate the accuracy and effectiveness of the methodology and solution process.
Author(s): Zhongde Wang, John L. Volakis, Katsuo Kurabayashi, Kazuhiro Saitou
File Type: Journal Paper
Issue:Volume: 22      Number: 3      Year: 2007
Download Link:Click here to download PDF     File Size: 273 KB

Title: A Parallelized Monte Carlo Algorithm for the Nonlinear Poisson-Boltzmann Equation in Two Dimensions
Abstract: This paper presents the parallelization of a previously-developed two-dimensional floating random walk (FRW) algorithm for the solution of the nonlinear Poisson-Boltzmann (NPB) equation. Historically, the FRW method has not been applied efficiently to the solution of the NPB equation which can be attributed to the absence of analytical expressions for volumetric Green’s functions. Stochastic approaches to solving nonlinear equations (in particular the NPB equation) that have been suggested in literature involve an iterative solution of a series of linear problems. As a result, previous applications of the FRW method have examined only the linearized Poisson-Boltzmann equation. In our proposed approach, an approximate (yet accurate) expression for the Green’s function for the nonlinear problem is obtained through perturbation theory, which gives rise to an integral formulation that is valid for the entire nonlinear problem. As a result, our algorithm does not have any iteration steps, and thus has a lower computational cost. A unique advantage of the FRW method is that it requires no discretization of either the volume or the surface of the problem domains. Furthermore, each random walk is independent, so that the computational procedure is highly parallelizable. In previously published work, we have presented the fundamentals of our algorithm and in this paper we report the parallelization of this algorithm in two dimensions. The solution of the NPB equation has many interesting applications, including the modeling of plasma discharges, semiconductor device modeling and the modeling of biomolecules.
Author(s): Kausik Chatterjee, Jonathan Poggie
File Type: Journal Paper
Issue:Volume: 22      Number: 3      Year: 2007
Download Link:Click here to download PDF     File Size: 264 KB

Title: Electromagnetic Scattering Computation Using a Hybrid Surface and Volume Integral Equation Formulation
Abstract: This paper presents a hybrid integral equation formulation for computation of electromagnetic scattering by composite conducting and dielectric materials. In the hybrid formulation, multiple material regions in a scatterer are classified into two categories, one is the surface integral equation (SIE) region, and the other is the volume integral equation (VIE) region. For the SIE region, the boundary conditions for tangential E-field and tangential H-field are applied to formulate the surface integral equation for the equivalent surface currents. For the VIE region, the equivalent principle is applied to formulate the volume integral equation for the induced volume currents. The hybrid formulation takes the advantageous of both the SIE and VIE. The integral equations are cast into a set of linear equations using the method of moments. For regions that are electrically large, the multilevel fast multipole algorithm is applied to accelerate the matrix-vector multiplication needed by iterative solvers. Numerical results are provided to verify the accuracy and the application of the program developed from the hybrid formulation.
Author(s): Chong Luo, Cai-Cheng Lu
File Type: Journal Paper
Issue:Volume: 22      Number: 3      Year: 2007
Download Link:Click here to download PDF     File Size: 238 KB

Title: Accurate Computational Algorithm for Calculation of Input Impedance of Antennas of Arbitrarily Shaped Conducting Surfaces
Abstract: In the present work, a Galerkin’s electric field integral equation (EFIE) solution is applied to get the current flowing on a conducting surface of arbitrary shape when excited by a gap generator as well as when illuminated by an incident plane wave. The main objective of this work is to get a fast, accurate and efficient computer algorithm that optimizes the use of computer resources and reduces the computational time and to accurately evaluate the input impedance of conducting surface antennas. The singular integrals arising in such a Galerkin’s formulation are accurately evaluated and obtained as analytic expressions. An efficient method is described for accurate evaluation of the input impedance for antennas of arbitrarily-shaped conducting surface. The efficiency of the applied Galerkin’s algorithm is examined by calculating the input impedance of well known antennas of conducting surfaces such as the strip-dipole, bow-tie and planar equiangular spiral antennas. To investigate the accuracy of the applied technique the results concerning these antennas are presented and compared with some published results.
Author(s): Khalid F. A. Hussein
File Type: Journal Paper
Issue:Volume: 22      Number: 3      Year: 2007
Download Link:Click here to download PDF     File Size: 290 KB

Title: Electric and Magnetic Dual Meshes to Improve Moment Method Formulations
Abstract: A new Moment Method (MM) scheme to solve the Electric Field Integral Equation (EFIE) for some ill-conditioned problems is presented. The approach is an alternative to the Combined-Field Integral Equation (CFIE). The proposed formulation employs the Impedance Boundary Condition (IBC) to compute the scattering from conducting bodies uncoated or coated by dielectric materials. The scheme uses dual meshes to represent the currents: one mesh for the electric current and another mesh for the magnetic current. Each mesh is defined by a grid of quadrangles that can be conformed to arbitrarily curved surfaces. The quadrangle grids are interlocked; the corners of the quadrangles of one mesh are the centers of the quadrangles of the other mesh and vice versa. Several examples showing the potential of the approach to solve ill-conditioned problems are included.
Author(s): M. Felipe Cátedra, Oscar Gutiérrez, Iván González, Francisco Saez de Adana
File Type: Journal Paper
Issue:Volume: 22      Number: 3      Year: 2007
Download Link:Click here to download PDF     File Size: 389 KB

Title: Optimum Plannar Antenna Design Based on an Integration of IE3D Commercial Code and Optimization Algorithms
Abstract: The optimum planar antenna design utilizing a simulation tool based an integration of IE3D commercial code as an electromagnetic computational engine and an add-on optimization algorithm is proposed in this paper. The work is motivated by the popularity of planar antennas and the need of customized designs in industrial applications, which can be effectively achieved by using simulation tools. Currently available commercial codes are reliable and relatively accurate in the analysis with more efforts tending to enhance the efficiency. The quality of the antenna design will mainly rely on an effective optimization algorithm that can be and should be developed independently according to engineers’ own need since the variables and cost functions for optimization can be flexibly selected. The integration of existing analysis codes, as mentioned above, and self-developed algorithms will be most effective for an engineer in the customized antenna design. The concepts and strategies are addressed with numerical examples to validate.
Author(s): Hsi-Tseng Chou, Yuan-Chang Hou, Wen-Jiao Liao
File Type: Journal Paper
Issue:Volume: 22      Number: 3      Year: 2007
Download Link:Click here to download PDF     File Size: 775 KB

Title: Analysis and Design of Quad-Band Four-Section Transmission Line Impedance Transformer
Abstract: The design of four-section transmission line matching transformer, operating at four arbitrary frequencies, is presented. Standard transmission line theory is used to obtain a closed form expression that is solved using particle swarm optimization technique to find the required transformer parameters (lengths, and characteristic impedances). Different examples are presented which validate the design approach. To further validate the analysis and design approach, a microstrip line four-section quad-band transmission line transformer is designed, analyzed, fabricated and measured.
Author(s): Hussam Jwaied, Firas Muwanes, Nihad Dib
File Type: Journal Paper
Issue:Volume: 22      Number: 3      Year: 2007
Download Link:Click here to download PDF     File Size: 207 KB

Title: Analysis of Dielectric Loaded Scalar Horn Radiators
Abstract: The dielectric loaded horn radiators are commonly used in various applications due to their distinguished features, such as low cross-polarization, pattern symmetry and simple production. The analysis of this kind of horn, mode matching (MM) and integral equation methods have been preferred in the literature. In the present study, the radiation of plane harmonic scalar waves from a dielectric loaded circular horn radiator is treated by using the mode matching method in conjunction with theWiener- Hopf technique. The solution is exact but formal since infinite series of unknowns and some branchcut integrals with unknown integrands are involved. Approximation procedures based on rigorous asymptotic are used and the approximate solution to the Wiener-Hopf equations are derived in terms of infinite series of unknowns, which are determined from infinite systems of linear algebraic equations. Numerical solution of these systems is obtained for various values of the parameters, of the problem. Their effect is presented on the directivity of the circular feed horn.
Author(s): Bahattin TÜRETKEN
File Type: Journal Paper
Issue:Volume: 22      Number: 3      Year: 2007
Download Link:Click here to download PDF     File Size: 315 KB

Title: Electromagnetic Scattering Problems Utilizing a Direct, Parallel Solver
Abstract: Finite-element discretization of the vector wave equation is a common method of analyzing the electromagnetic field scattered by an object. One of the most challenging aspect of the this research concerns the solution of the system of equations resulting from the finite-element analysis. Advanced solution algorithms have enabled researchers to generate more realistic computational models for scattering problems.
Author(s): William R. Dearholt, Steven P. Castillo
File Type: Journal Paper
Issue:Volume: 22      Number: 3      Year: 2007
Download Link:Click here to download PDF     File Size: 1592 KB

Title: Scattering from a Semi-Elliptic Channel in a Ground Plane Loaded by a Lossy or Lossless Dielectric Elliptic Shell
Abstract: An analytic solution to the problem of scattering of a plane electromagnetic wave by a lossy or lossless dielectric confocal elliptic shell loading a semielliptic channel is derived. The incident, scattered and transmitted fields in every region are expressed in terms of complex Mathieu functions. Applying the boundary conditions at various faces and interfaces along with the partial orthogonality properties of angular Mathieu functions, the unknown scattered and transmitted field coefficients are obtained. The presented numerical results show a good agreement with the published data especially for the case of a lossless dielectric shell loading a semi-circular channel.
Author(s): A-K. Hamid
File Type: Journal Paper
Issue:Volume: 22      Number: 3      Year: 2007
Download Link:Click here to download PDF     File Size: 112 KB

Title: Investigation of Wire Grid Modeling in NEC Applied to Determine Resonant Cavity Quality Factors
Abstract: Numerical computer simulations using the NEC Method of Moments (MoM) code were performed on wire grid models of resonant cavities in order to study how well conductive structures and their surface impedances can be modeled by wire meshes. The resonant cavity quality factor, or Q, was examined due to its high sensitivity to surface impedance. Several half-wave coaxial cavities were simulated using various mesh element sizes. The cavities’ outer conductor radius was varied to obtain different geometries. The quality factor Q was determined from the simulated input impedance spectra. The wire grid model results were compared to well known theoretical and experiment results. Qualitative agreement between simulation, theoretical, and experimental results was achieved for fixed mesh parameters, giving confidence in comparative simulation using the same wire grid meshing parameters. Quantitative agreement of simulation results was achieved through repeated simulation with varying mesh element lengths and extrapolating the simulation results to a conceptual mesh element length of zero. This shows that simulations to determine quantities sensitive to surface impedances can be successfully performed with codes such as NEC.
Author(s): Franz A. Pertl, Andrew D. Lowery, James E. Smith
File Type: Journal Paper
Issue:Volume: 22      Number: 3      Year: 2007
Download Link:Click here to download PDF     File Size: 297 KB