Browsing by Subject "Electromagnetic field theory"

Now showing 1 - 8 of 8

Open Access
Comparative evaluation of absorbing boundary conditions using Green's functions for layered media
(IEEE, 1995) Aksun, M. İrşadi; Dural, G.
Absorbing boundary conditions are comparatively studied using the Green's functions of the vector and scalar potentials for multilayer geometries and general sources. The absorbing boundaries are introduced as additional layers with predefined reflection coefficients into the calculation of the Green's functions. The Green's functions are calculated using different reflection coefficients corresponding to different absorbing boundaries and compared to those obtained with no absorbing boundary. This approach provides an absolute measure of the effectiveness of different absorbing boundaries.
Open Access
Comparative study of acceleration techniques for integrals and series in electromagnetic problems
(IEEE, 1995-06) Kinayman, Noyan; Aksun, M. I.
Most of the electromagnetic problems can be reduced down to either integrating oscillatory integrals or summing up complex series. However, limits of the integrals and the series usually extend to infinity. In addition, they may be slowly convergent. Therefore, numerically efficient techniques for evaluating the integrals or for calculating the sum of infinite series have to be used to make the numerical solution feasible and attractive. In the literature, there are a wide range of applications of such methods to various EM problems. In this paper, our main aim is to critically examine the popular series transformation (acceleration) methods which are used in electromagnetic problems and compare them by numerical examples.
Open Access
Comparison of surface-modeling techniques
(IEEE, 1997-07) Sertel, Kubilay; Gürel, Levent
Solution techniques based on surface integral equations are widely used in computational electromagnetics. The accurate surface models increase the accuracy solutions by using exact and flat-triangulation models for a sphere. For a required solution accuracy, the problem size is significantly reduced by using geometry models for the scatterers. The dependence of the accuracy of the solution on the geometry modeling is investigated.
Open Access
Fast direct (noniterative) solvers for integral-equation formulations of scattering problems
(IEEE, 1998) Gürel, Levent; Chew, W. C.
A family of direct (noniterative) solvers with reduced computational complexity is proposed for solving problems involving resonant or near-resonant structures. Based on the recursive interaction matrix algorithm, the solvers exploit the aggregation concept of the recursive aggregate T-matrix algorithm to accelerate the solution. Direct algorithms are developed to compute the scattered field and the current coefficient, and invert the impedance matrix. Computational complexities of these algorithms are expressed in terms of the number of harmonics P required to express the scattered field of a larger scatterer made up of N scatterers. The exact P-N relation is determined by the geometry.
Open Access
Fast direct solution algorithm for electromagnetic scattering from 3D planar and quasi-planar geometries
(IEEE, 1997) Gürel, Levent; Chew, W. C.
A non-iterative method and its application to planar geometries in homogeneous media is presented. The method is extendable to the cases of quasi-planar structures and/or layered-media problems. The fast direct algorithm (FDA)/steepest descent path (SDP) takes advantage of the fact that the induced currents on planar and quasi-planar geometries interact with each other within a very limited solid angle. Thus, all the degrees of freedom required to solve a `truly 3D' geometry are not required for a planar or quasi-planar geometry, and this situation can be exploited to develop efficient solution algorithms.
Open Access
Fast multipole method in layered media: 2-D electromagnetic scattering problems
(IEEE, 1996) Gürel, Levent; Aksun, M. İrşadi
In this study, the Fast Multipole Method (FMM) is extended to layered-media problems. As an example, the solution of the scalar Helmholtz equation for the electromagnetic scattering from a two-dimensional planar array of horizontal strips on a layered substrate is demonstrated.
Open Access
On the choice of basis functions to model surface electric current densities in computational electromagnetics
(Wiley-Blackwell Publishing, Inc., 1999-11) Gürel, Levent; Sertel, K.; Şendur, İ. K.
Basis functions that are used to model surface electric current densities in the electric field integral equations of computational electromagnetics are analyzed with respect to how well they model the charge distribution, in addition to the current. This analysis is carried out with the help of the topological properties of open and closed surfaces meshed into networks of triangles and quadrangles. The need for current basis functions to properly model the charge distribution is demonstrated by several examples. In some of these examples, the basis functions seem to be perfectly legitimate when only the current distribution is considered, but they fail to deliver a correct solution of the electromagnetic problem, since they are not capable of properly modeling the charge distribution on some surfaces. Although the idea of proper modeling of the charge distribution by the current basis functions is easy to accept and can even be claimed well known, the contrary uses encountered in the literature have been the motivation behind the investigation reported in this paper.
Open Access
Solution of radiation problems using the fast multipole method
(IEEE, 1997-07) Gürel, Levent; Şendur, İbrahim Kürşat
Electromagnetic radiation problems involving electrically large radiators and reflectors are solved using the fast multipole method (FMM). The FMM enables the solution of large problems with existing computational resources by reducing the computational complexity by a faster equivalent of O(N) complexity in each iteration of an iterative scheme. Three dimensional radiation problems involving complicated geometries are modeled using arbitrary surface triangulations. Piecewise linear basis functions defined on triangular domains due to Rao, Wilton, and Glisson (RWG) basis functions are used to approximate the induced currents. Using delta-gap voltage sources and prescribed current distributions, the operations of various antennas are simulated.