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Title: SOLUTION OF LAPLACE'S EQUATION USING MULTIPLE PATHS METHOD (MPM)
Abstract: A probabilistic method called the multiple paths method (MPM) is presented to solve the potential equation. Unlike other probabilistic techniques there is no need for the generation of a grid resulting in less computation time and simplicity. The method is based on the calculation of the probability of absorption of a particle at a point on the boundary. The random walk is along a "path" which is a line passing through the starting point, where the potential is to be determined. The results show good agreement with other probabilistic methods and numerical techniques. [Vol. 11, No. 3 (1996), pp 4-8
Author(s): J. Rashed-Mohasselel, M. Fasih
File Type: Journal Paper
Issue:Volume: 11      Number: 3      Year: 1996
Download Link:Click here to download PDF     File Size: 349 KB

Title: A NEW DESIGN METHOD FOR LOW SIDELOBE LEVEL LOG-PERIODIC DIPOLE ANTENNAS
Abstract: A new design procedure for log-periodic dipole arrays is presented in this paper. In this method, either the scale factor or the number of dipole elements is selected, after the boom length, and the operating frequency region are specified. The procedure is applied iteratively, in conjunction to the Numerical Electromagnetic Code, to produce a design with low sidelobe levels. With this new procedure, the antenna designer has more control over the boom length; in older techniques, the boom length and the element spacing were dependent on previous calculations, which frequently resulted on unreasonable values Results for several designs are presented, showing the peak gain to peak-sidelobe level ratio, and the antenna gain as a function of frequency, for different scale factors and boom lengths, for a frequency range of 13 to 30 MHz. [Vol. 11, No. 3 (1996), pp 9-15]
Author(s): James K. Breakall, Rafael A. Rodriguez Solis
File Type: Journal Paper
Issue:Volume: 11      Number: 3      Year: 1996
Download Link:Click here to download PDF     File Size: 445 KB

Title: NUMERICAL EVALUATION OF SINGULAR INTEGRANDS IN THE APPLICATION OF THE CHARGE SIMULATION METHOD WITH DISTRIBUTED CHARGE DENSITY
Abstract: As it is well known the Charge Simulation Method is a numerical method for the computation of the electric field in three-dimensional problems, based on the concept of the substitution of the electrodic geometry with a series of elementary charge suitably arranged. In this paper we will show a possible, useful way to overpass the difficulties arising in the numerical computations on the integral expression of the electric potential in the contour points where the boundary conditions are imposed, when distributed surface charges are used in the simulation. The numerical approach presented here allows us to evaluate with accuracy the potential coefficients on the metallic surfaces, avoiding the presence of oscillatory numerical solutions in the computation of the electric potential and of the electric field strength around the electrodes, that generally occurs when discrete charges are used in the simulation. [Vol. 11, No. 3 (1996), pp 16-24]
Author(s): Ermanno Cardelli, Loris Faina
File Type: Journal Paper
Issue:Volume: 11      Number: 3      Year: 1996
Download Link:Click here to download PDF     File Size: 482 KB

Title: MEASURED RCS POLAR CONTOUR MAPS FOR CODE VALIDATION
Abstract: Measured radar cross-section (RCS) data as a function of the angle of incidence and of the frequency over a wide range provide an excellent basis for code validation. This paper examines the RCS of six targets measured as a function of the angle of incidence of the plane wave, and of the frequency, through and beyond the resonance range of target size. The RCS is presented as a function of frequency and incidence angle using a color contour map in a polar format, with the radius proportional to the frequency. Such polar contour maps exhibit striking patterns to the underlying scattering mechanisms and target geometry. The RCS as a function of incidence angle and frequency is available from the authors for an extensive collection of targets. [Vol. 11, No. 3 (1996), pp 25-43]
Author(s): C.L. Larose, C.W. Trueman
File Type: Journal Paper
Issue:Volume: 11      Number: 3      Year: 1996
Download Link:Click here to download PDF     File Size: 2808 KB

Title: AN EFFICIENT METHOD OF ANALYSIS OF CO-PLANAR DIPOLE ARRAY ANTENNAS
Abstract: Generalized impedance formulas for non-uniform array configurations based on the improved Circuit Theory (ICT) are presented for the first time in an English text. To further enhance the ICT as an accurate and fast method for evaluations, a new and more com pact closed-form formula is derived to replace a function requiring time intensive numerical integration during the implementation of the of the ICT algorithm in co-planar dipole array antenna evaluations. The resulting ICT computational scheme reduces the required CPU time by a factor of two and has the same order of accuracy as the conventional MoM. The new ICT implementation would be of considerable use as a Computer Aided Design (CAD) tool of co-planar dipole array antennas. [Vol. 11, No. 3 (1996), pp 44-54]
Author(s): A. I. Imoro, N. Inagaki, N. Kikuma
File Type: Journal Paper
Issue:Volume: 11      Number: 3      Year: 1996
Download Link:Click here to download PDF     File Size: 848 KB

Title: AN ALGORITHM FOR SOLUTION OF THE INVERSE ELECTROMAGNETIC LIQUID METAL CONFINEMENT PROBLEM
Abstract: The design of an electromagnetic levitation system for large amounts of liquid metal requires the solution of an inverse field problem. The objective is to calculate the electromagnetic pressure distribution which corresponds to a specific metallo-static head. This paper describes an algorithm for the design of coil systems which will produce the desired pressure distribution. The technique is illustrated by the design of a torroidal levitation system. [Vol. 11, No. 3 (1996), pp 55-62]
Author(s): G.J. Bendzsak
File Type: Journal Paper
Issue:Volume: 11      Number: 3      Year: 1996
Download Link:Click here to download PDF     File Size: 687 KB

Title: COMPARISON OF MAGNETICALLY INDUCED ELF FIELDS IN HUMANS COMPUTED BY FDTD AND SCALAR POTENTIAL FD CODES
Abstract: This paper presents a detailed numerical comparison of the magnetically-induced extremely low-frequency electric field and current density within an anatomically realistic model of the full human body, as computed using two different numerical techniques. The first technique is a recently-described full-wave quasi-static finite-difference time-domain (FDTD) method. The use of a time-ramped excitation involving pairs of oppositely-directed plane waves allows for the calculation of decoupled magnetic and electric induction in complex heterogeneous bodies, in relatively short (5 ns) simulation times. The second method is an implementation of Stevenson's method applied for isolated conducting bodies. With the lowest-order external magnetic field represented by a vector potential, the lowest-order internal electric field can be represented by a scalar conduction potential, and the magnetically-induced contribution can be calculated in isolation. Both methods have an underlying similarity in their finite-difference approach, but are nevertheless very distinct. Each code was used to calculate the fields, induced by three orthogonal uniform magnetic fields, in a 7.2 mm-resolution human full-body model. Three-dimensional correlation coefficients of better than 99.9998% were observed between current densities computed by the two methods. Individual edge electric fields typically agree to 3 significant digits. [Vol. 11, No. 3 (1996), pp 63-71]
Author(s): Trevor W. Dawson, Jan De Moerloose, Maria A. Stuchly
File Type: Journal Paper
Issue:Volume: 11      Number: 3      Year: 1996
Download Link:Click here to download PDF     File Size: 693 KB

Title: ANALYTIC VALIDATION OF A THREE-DIMENSIONAL SOLAR-POTENTIAL FINITE- DIFFERENCE CODE FOR LOW-FREQUENCY MAGNETIC INDUCTION
Abstract: This paper presents a detailed comparison of numerical and analytical calculations of the low-frequency electric and current density fields, induced by an applied uniform axial magnetic field, in an equatorially stratified sphere having the conductivity distribution Rho (_)=Rho0e- cos( _) with p {1,2} and > 0. As shown by the analytic solution, the resulting induced fields are fully three-dimensional, and the model therefore serves as a rigorous test of numerical codes The numerical method is a scalar-potential finite-difference scheme based on Stevenson's method for isolated conducting bodies. This computer code was recently shown to provide excellent agreement with results computed independently by a modified Finite-Difference Time-Domain method. Nevertheless, both codes share some underlying similarities, such as their common use of parallelepiped material voxels to represent the conductivity distribution, and of an edge-based staggered to model the electric fields. Therefore, it is of value to compare the numerical results with analytic ones The analytic model has a freely adjustable contrast parameter, and supports both pi and 2pi-periodic conductivity distributions. Numerical and analytical results are compared for several configurations. Full three-dimensional volumetric correlation coefficients are typically of the order of 99% or better. As might be expected, the main differences occur at the surface of the sphere, where the true circumferential fields are most poorly approximated by the staircasing approximation inherent the numerical approximation. [Vol. 11, No. 3 (1996), pp 72-81]
Author(s): Trevor W. Dawson, Maria A. Stuchly
File Type: Journal Paper
Issue:Volume: 11      Number: 3      Year: 1996
Download Link:Click here to download PDF     File Size: 767 KB

Title: THE GRADIENT ASSOCIATED CONJUGATE DIRECTION METHOD
Abstract: A new conjugate direction (CD) based method, GaCD by name, is addressed with its full derivations. Comparison with some commonly used CD methods is made, concluding that the GaCD method is among the best of them, in terms of an assessment number. A practical example is presented in which a waveguide-microstrip transition section is optimized with respect to its transmission parameter S2l. The measurement of the transition agrees very well with the numerical results. [Vol. 11, No. 3 (1996), pp 82-96]
Author(s): Min Zhang
File Type: Journal Paper
Issue:Volume: 11      Number: 3      Year: 1996
Download Link:Click here to download PDF     File Size: 1873 KB