Browsing by Author "Ergül, Özgür"
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Accuracy and efficiency considerations in the solution of extremely large electromagnetics problems
Gürel, Levent; Ergül, Özgür (IEEE, 2011)This study considers fast and accurate solutions of extremely large electromagnetics problems. Surface formulations of largescale objects lead to dense matrix equations involving millions of unknowns. Thanks to recent ... 
Accurate modeling of metamaterials with MLFMA
Ergül, Özgür; Ünal, Alper; Gürel, Levent (ESA Publications, 2006)Electromagnetic modelling of large metamaterial (MM) structures employing multilevel fast multipole algorithm (MLFMA) is reported. MMs are usually constructed by periodically embedding unit cells, such as splitring ... 
Accurate solutions of scattering problems involving lowcontrast dielectric objects with surface integral equations
Ergül, Özgür; Gürel, Levent (Institution of Engineering and Technology, 2007)We present the stabilization of the surface integral equations for accurate solutions of scattering problems involving lowcontrast dielectric objects. Unlike volume formulations, conventional surface formulations fail to ... 
Analysis of composite objects involving multiple dielectric and metallic partswith the parallel multilevel fast multipole algorithm
Ergül, Özgür; Gürel, Levent (Applied Computational Electromagnetics Society, 201204) 
Analysis of dielectric photoniccrystal problems with MLFMA and Schurcomplement preconditioners
Ergül, Özgür; Malas, T.; Gürel, Levent (IEEE, 20110113)We present rigorous solutions of electromagnetics problems involving 3D dielectric photonic crystals (PhCs). Problems are formulated with recently developed surface integral equations and solved iteratively using the ... 
Analysis of photoniccrystal problems with MLFMA and approximate Schur preconditioners
Ergül, Özgür; Malas, Tahir; Kılınç, Seçil; Sarıtaş, Serkan; Gürel, Levent (IEEE, 200907)We consider fast and accurate solutions of electromagnetics problems involving threedimensional photonic crystals (PhCs). Problems are formulated with the combined tangential formulation (CTF) and the electric and magnetic ... 
Approximate MLFMA as an efficient preconditioner
Malas, Tahir; Ergül, Özgür; Gürel, Levent (IEEE, 2007)In this work, we propose a preconditioner that approximates the dense system operator. For this purpose, we develop an approximate multilevel fast multipole algorithm (AMLFMA), which performs a much faster matrixvector ... 
Circular arrays of logperiodic antennas for broadband applications
Ergül, Özgür; Gürel, Levent (IEEE, 2006)Circular arrays of logperiodic (LP) antennas are designed for broadband applications. A sophisticated electromagnetic simulation environment involving integral equations and fast solvers is developed to analyze the LP ... 
Combinedfield solution of composite geometries involving open and closed conducting surfaces
Ergül, Özgür; Gürel, Levent (IEEE, 200504)Combinedfield integral equation (CFIE) is modified and generalized to formulate the electromagnetic problems of composite geometries involving both open and closed conducting surfaces. These problems are customarily ... 
Comparison of integralequation formulations for the fast and accurate solution of scattering problems involving dielectric objects with the multilevel fast multipole algorithm
Ergül, Özgür; Gürel, Levent (Institute of Electrical and Electronics Engineers, 2009)We consider fast and accurate solutions of scattering problems involving increasingly large dielectric objects formulated by surface integral equations. We compare various formulations when the objects are discretized with ... 
Comparisons of FMM implementations employing different formulations and iterative solvers
Gürel, Levent; Ergül, Özgür (IEEE, 200306)The implementation of multilevel fast multipole algorithm (MLFMA) requires the consideration of several parameters. The preferred combination of the parameters given is not trivially obvious and requires a careful ... 
Computational analysis of complicated metamaterial structures using MLFMA and nested preconditioners
Ergül, Özgür; Malas, Tahir; Yavuz, Ç; Ünal, Alper; Gürel, Levent (IEEE, 200711)We consider accurate solution of scattering problems involving complicated metamaterial (MM) structures consisting of thin wires and splitring resonators. The scattering problems are formulated by the electricfield ... 
Computational study of scattering from healthy and diseased red blood cells
Ergül, Özgür; ArslanErgül, A.; Gürel, Levent (Society of Photo Optical Instrumentation Engineers, 20100805)We present a comparative study of scattering from healthy red blood cells (RBCs) and diseased RBCs with deformed shapes. Scattering problems involving threedimensional RBCs are formulated accurately with the electric and ... 
Contamination of the accuracy of the combinedfield integral equation with the discretization error of the magneticfield integral equation
Gürel, Levent; Ergül, Özgür (Institute of Electrical and Electronics Engineers, 2009)We investigate the accuracy of the combinedfield integral equation (CFIE) discretized with the RaoWiltonGlisson (RWG) basis functions for the solution of scattering and radiation problems involving threedimensional ... 
Design and simulation of circular arrays of trapezoidaltooth logperiodic antennas via genetic optimization
Gürel, Levent; Ergül, Özgür (Electromagnetics Academy, 2008)Circular arrays of logperiodic (LP) antennas are designed and their operational properties are investigated in a sophisticated simulation environment that is based on the recent advances in computational electromagnetics. ... 
Discretization error due to the identity operator in surface integral equations
Ergül, Özgür; Gürel, Levent (ELSEVIER, 20090503)We consider the accuracy of surface integral equations for the solution of scattering and radiation problems in electromagnetics. In numerical solutions, secondkind integral equations involving welltested identity operators ... 
Effective preconditioners for large integralequation problems
Malas, Tahir; Ergül, Özgür; Gürel, Levent (IET, 200711)We consider effective preconditioning schemes for the iterative solution of integralequation methods. For parallel implementations, the sparse approximate inverse or the iterative solution of the nearfield system enables ... 
Efficient parallelization of the multilevel fast multipole algorithm for the solution of largescale scattering problems
Ergül, Özgür; Gürel, Levent (Institute of Electrical and Electronics Engineers, 200808)We present fast and accurate solutions of largescale scattering problems involving threedimensional closed conductors with arbitrary shapes using the multilevel fast multipole algorithm (MLFMA). With an efficient ... 
Efficient solution of the combinedfield integral equation with the parallel multilevel fast multipole algorithm
Gürel, Levent; Ergül, Özgür (IEEE, 200708)We present fast and accurate solutions of largescale scattering problems formulated with the combinedfield integral equation. Using the multilevel fast multipole algorithm (MLFMA) parallelized on a cluster of computers, ... 
Efficient solution of the electric and magnetic current combined‐field integral equation with the multilevel fast multipole algorithm and block‐diagonal preconditioning
Ergül, Özgür; Gürel, Levent (WileyBlackwell Publishing, Inc., 200912)We consider the efficient solution of electromagnetics problems involving dielectric and composite dielectricmetallic structures, formulated with the electric and magnetic current combinedfield integral equation (JMCFIE). ...