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Title: July 2005 Journal Front/Back Matter and Index
File Type: Journal Paper
Issue:Volume: 20      Number: 2      Year: 2005
Download Link:Click here to download PDF     File Size: 342 KB

Title: July 2005 Journal Full Issue
File Type: Journal Paper
Issue:Volume: 20      Number: 2      Year: 2005
Download Link:Click here to download PDF     File Size: 5276 KB

Title: Effective Preconditioners for the Solution of Hybrid FEM/MoM Matrix Equations Using Combined Formulations
Abstract: Hybrid FEM/MoM modeling codes generate large systems of equations that are generally solved using inward-looking, outward-looking or combined formulations. For many types of problems, the combined formulation is preferred because it does not require a direct inversion of the coefficient matrices and can be solved using iterative solution techniques. An effective preconditioner is a crucial part of the solution process in order to guarantee convergence. However, it can be difficult to generate effective, memory-efficient preconditioners for large problems. This paper investigates preconditioners that use the FEM solution and an absorbing boundary condition (ABC). Various techniques are explored to reduce the memory required by the preconditioner while maintaining effectiveness. Practical problems are presented to evaluate the effectiveness of these preconditioners in various situations.
Author(s): C. Guo, T. H. Hubing
File Type: Journal Paper
Issue:Volume: 20      Number: 2      Year: 2005
Download Link:Click here to download PDF     File Size: 602 KB

Title: A 2D Pseudo-Spectral Approach of Photonic Crystal Slabs
Abstract: We consider an L1  periodic dielectric slab which is characterized by the dielectric function a 2D model for photonic crystals. We assume that there is no variation in ydirection, with fields varying time-harmonically according to exp  j ωt  . In order to solve electromagnetic wave propagation in such structures, we diagonalize the Maxwell’s equations with respect to the z coordinate. As demonstrated in this paper, diagonalized forms greatly facilitate the implementation of the finite difference method. The L1 periodicity of the fields suggests expansions in terms of spatially harmonic functions. However, contrary to the commonlyused Bloch inhomogeneous plane waves, we utilize expansions of the form. For the determination of the coefficient functions ψn  z we employ a sophisticated, yet, easy-to-apply implementation of a finite difference discretization scheme in the zdirection which permits virtually arbitrary L1  periodic profile functions. It will be demonstrated that the proposed hybridization of the plane-wave decomposition and the finite difference method leads to a robust and flexible method of analysis with a wide range of applications. As an example, we consider TE-polarized electromagnetic waves which propagate in the assumed dielectric slab along the x axis.
Author(s): K. Varis, A. R. Baghai-Wadji
File Type: Journal Paper
Issue:Volume: 20      Number: 2      Year: 2005
Download Link:Click here to download PDF     File Size: 630 KB

Title: The behavior of smart obstacles in electromagnetic scattering: mathematical models as optimal control problems
Abstract: We consider a bounded obstacle characterized by a boundary electromagnetic impedance contained in the three dimensional real Euclidean space filled with a homogeneous isotropic medium. When an incoming electromagnetic field illuminates the obstacle a scattered field is generated. A smart obstacle is an obstacle that in the scattering process, circulating a surface electric current density on its boundary, tries to achieve a given goal. We consider four possible goals: making the obstacle undetectable (i.e.: furtivity problem), making the obstacle to appear with a shape and impedance different from its actual ones (i.e.: masking problem), making the obstacle to appear in a location different from its actual one eventually with a shape and impedance different from its actual ones (i.e.: ghost obstacle problem) and finally one of the previous goals limited to a given subset of the frequency space (i.e.: definite band problems). We consider the problem of determining the optimal electric current density to achieve the given goal. The relevance in many application fields (i.e. stealth technology, electromagnetic noise control, etc.) of these problems is well known. The previous problems are modelled as optimal control problems for the Maxwell equations. Some numerical results on test problems obtained solving the optimal control problems proposed are shown.
Author(s): L. Fatone, M. C. Recchioni, A.Scoccia, F. Zirilli
File Type: Journal Paper
Issue:Volume: 20      Number: 2      Year: 2005
Download Link:Click here to download PDF     File Size: 1965 KB

Title: Performing 3-D FDTD Simulations in less than 3 Seconds on a Personal Computer and its Application to Genetic Algorithm Antenna Optimization
Abstract: FDTD simulations generally require significant computational resources and time. This paper systematically reduces the number of time steps and the grid size to determine the shortest simulation time that returns results with tolerable error for microstrip antenna simulations and their optimization of insertion loss with the genetic algorithm. Although the error would generally be unacceptable for traditional antenna simulations, it is sufficiently small to optimize their design. Simulations in less than 3 seconds on a P4 2.8 GHz processor were shown to be usable, with error approximately equal to manufacturing tolerances. A dual band ‘waffle’ antenna is designed that has better performance than the traditional dual band “F” antenna.
Author(s): L.A. Griffiths, C.M. Furse
File Type: Journal Paper
Issue:Volume: 20      Number: 2      Year: 2005
Download Link:Click here to download PDF     File Size: 313 KB

Title: Cubic-Spline Expansion with GA for Half-Space Inverse Problems
Abstract: In this paper we address an inverse scattering problem whose aim is to determine the geometrical as well as the physical properties of a perfectly conducting cylindrical body buried in a halfspace. We use cubic-spline method instead of trigonometric series to describe our shape and reformulated into an optimization problem and solved by the genetic algorithm. The genetic algorithm is employed to find out the global extreme solution of the object function. As a result, the shape of the scatterer, which is described by using cubic-spline, can be reconstructed. In such a case, fourier series expansion will fail. Even when the initial guess is far away from the exact one, the cubic-spline description and genetic algorithm can avoid the local extreme and converge to a global extreme solution. Numerical results are given to show that the shape description using cubic-spline method is much better than the Fourier series.
Author(s): W. Chien, C-C. Chiu
File Type: Journal Paper
Issue:Volume: 20      Number: 2      Year: 2005
Download Link:Click here to download PDF     File Size: 451 KB

Title: On the Physical Interpretation of the Sobolev Norm in Error Estimation
Abstract: Error estimates for the moment method have been obtained in terms of Sobolev norms of the current solution. Motivated by the historical origins of Sobolev spaces as energy spaces, we show that the Sobolev norm used in these estimates is related to the forward scattering amplitude, for the case of 2D scattering from a PEC circular cylinder and for 3D scattering from a PEC sphere. These results provide a physical meaning for solution error estimates in terms of the power radiated by the error in the current solution. We further show that bounds on the Sobolev norm of the current error imply a bound on the error in the computed backscattering amplitude.
Author(s): C. P. Davis, K. F. Warnick
File Type: Journal Paper
Issue:Volume: 20      Number: 2      Year: 2005
Download Link:Click here to download PDF     File Size: 826 KB

Title: Induced Currents on a Moving and Vibrating Perfect Plane Under the Illumination of Electromagnetic Pulse: One-Dimensional Simulation using Characteristic-Based Algorithm
Abstract: This paper provides one-dimensional simulation results of the induced currents on constantly moving and vibrating perfect conductors under the normal illumination of plane Gaussian electromagnetic pulses. The characteristic-based algorithm is employed for the solutions of time-dependent Maxwell curl equations. In the numerical model, the size of the computational cell adjacent to the moving boundary, and its corresponding numerical time step become timedependent since the boundary is not stationary. By comparing the computational results with the theoretical Doppler shift values, we show that the present method successfully predicts the induced currents on the perfect conductor surface. The computed electric and magnetic field intensities and induced currents are demonstrated as well.
Author(s): M. Ho
File Type: Journal Paper
Issue:Volume: 20      Number: 2      Year: 2005
Download Link:Click here to download PDF     File Size: 204 KB