Computational Electromagnetics Research Center (BiLCEM)No Descriptionhttps://hdl.handle.net/11693/482392023-11-28T13:16:49Z2023-11-28T13:16:49Z841Modeling and synthesis of circular‐sectoral arrays of log‐periodic antennas using multilevel fast multipole algorithm and genetic algorithmsErgül, ÖzgürGürel, Leventhttps://hdl.handle.net/11693/492062021-04-01T08:41:13Z2007-06-17T00:00:00Zdc.title: Modeling and synthesis of circular‐sectoral arrays of log‐periodic antennas using multilevel fast multipole algorithm and genetic algorithms
dc.contributor.author: Ergül, Özgür; Gürel, Levent
dc.description.abstract: Circular‐sectoral arrays of log‐periodic (LP) antennas are presented for frequency‐independent operation and beam‐steering capability. Specifically, nonplanar trapezoidal tooth LP antennas are considered in a circular array configuration, where closely spaced antennas occupy a sector of the circle. Electromagnetic interactions of the array elements, each of which is a complicated LP antenna structure, are rigorously computed with the multilevel fast multipole algorithm (MLFMA). Genetic algorithms (GAs) are also employed in combination with MLFMA for synthesis and design purposes. By optimizing the excitations of the array elements via GAs, beam‐steering ability is achieved in addition to the broadband (nearly frequency‐independent) characteristics of the designed arrays. Computational results are presented to demonstrate the important properties of LP arrays.
2007-06-17T00:00:00ZReply to "Comments on 'The Use of curl-conforming basis functions for the magnetic-field integral equation'"Ergül, ÖzgürGürel, Leventhttps://hdl.handle.net/11693/488882020-07-09T06:11:45Z2008-01-01T00:00:00Zdc.title: Reply to "Comments on 'The Use of curl-conforming basis functions for the magnetic-field integral equation'"
dc.contributor.author: Ergül, Özgür; Gürel, Levent
2008-01-01T00:00:00ZEfficient parallelization of the multilevel fast multipole algorithm for the solution of large-scale scattering problemsErgül, ÖzgürGürel, Leventhttps://hdl.handle.net/11693/488872020-07-09T06:11:45Z2008-08-01T00:00:00Zdc.title: Efficient parallelization of the multilevel fast multipole algorithm for the solution of large-scale scattering problems
dc.contributor.author: Ergül, Özgür; Gürel, Levent
dc.description.abstract: We present fast and accurate solutions of large-scale scattering problems involving three-dimensional closed conductors with arbitrary shapes using the multilevel fast multipole algorithm (MLFMA). With an efficient parallelization of MLFMA, scattering problems that are discretized with tens of millions of unknowns are easily solved on a cluster of computers. We extensively investigate the parallelization of MLFMA, identify the bottlenecks, and provide remedial procedures to improve the efficiency of the implementations. The accuracy of the solutions is demonstrated on a scattering problem involving a sphere of radius 110 discretized with 41 883 638 unknowns, the largest integral-equation problem solved to date. In addition to canonical problems, we also present the solution of real-life problems involving complicated targets with large dimensions
2008-08-01T00:00:00ZEfficient solution of the electric and magnetic current combined‐field integral equation with the multilevel fast multipole algorithm and block‐diagonal preconditioningErgül, ÖzgürGürel, Leventhttps://hdl.handle.net/11693/483122020-07-09T06:11:44Z2009-12-01T00:00:00Zdc.title: Efficient solution of the electric and magnetic current combined‐field integral equation with the multilevel fast multipole algorithm and block‐diagonal preconditioning
dc.contributor.author: Ergül, Özgür; Gürel, Levent
dc.description.abstract: We consider the efficient solution of electromagnetics problems involving dielectric and composite dielectric-metallic structures, formulated with the electric and magnetic current combined-field integral equation (JMCFIE). Dense matrix equations obtained from
the discretization of JMCFIE with Rao-Wilton-Glisson functions are solved iteratively, where the matrix-vector multiplications are performed efficiently with the multilevel fast multipole algorithm. JMCFIE usually provides well conditioned matrix equations that are easy to solve iteratively. However, iteration counts and the efficiency of solutions depend on the contrast, i.e., the relative variation of electromagnetic parameters across dielectric interfaces. Owing to the numerical imbalance of off-diagonal matrix partitions,
solutions of JMCFIE become difficult with increasing contrast. We present a four-partition block-diagonal preconditioner (4PBDP), which provides efficient solutions of JMCFIE by reducing the number of iterations significantly. 4PBDP is useful, especially when the contrast increases, and the standard block-diagonal preconditioner fails to provide a rapid convergence.
2009-12-01T00:00:00ZAccelerating the multilevel fast multipole algorithm with the sparse-approximate-inverse (SAI) preconditioningMalas, T.Gürel, Leventhttps://hdl.handle.net/11693/483092020-07-09T06:11:44Z2009-01-01T00:00:00Zdc.title: Accelerating the multilevel fast multipole algorithm with the sparse-approximate-inverse (SAI) preconditioning
dc.contributor.author: Malas, T.; Gürel, Levent
dc.description.abstract: With the help of the multilevel fast multipole algorithm, integral-equation methods can be used to solve real-life electromagnetics problems both accurately and efficiently. Increasing problem dimensions, on the other hand, necessitate effective parallel preconditioners with low setup costs. In this paper, we consider sparse approximate inverses generated from the sparse near-field part of the dense coefficient matrix. In particular, we analyze pattern selection strategies that can make efficient use of the block structure of the near-field matrix, and we propose a load-balancing method to obtain high scalability during the setup. We also present some implementation details, which reduce the computational cost of the setup phase. In conclusion, for the open-surface problems that are modeled by the electric-field integral equation, we have been able to solve ill-conditioned linear systems involving millions of unknowns with moderate computational requirements. For closed surface problems that can be modeled by the combined-field integral equation, we reduce the solution times significantly compared to the commonly used block-diagonal preconditioner.
2009-01-01T00:00:00ZEfficient surface integral equation methods for the analysis of complex metamaterial structuresYla-Oijala, P.Ergül, ÖzgürGürel, LeventTaskinen, M.https://hdl.handle.net/11693/287372020-07-09T06:11:44Z2009-01-01T00:00:00Zdc.title: Efficient surface integral equation methods for the analysis of complex metamaterial structures
dc.contributor.author: Yla-Oijala, P.; Ergül, Özgür; Gürel, Levent; Taskinen, M.
dc.description.abstract: Two approaches, the multilevel fast multipole algorithm with sparse approximate inverse preconditioner and the surface equivalence principle algorithm, are applied to analyze complex three-dimensional metamaterial structures. The efficiency and performance of these methods are studied and discussed.
dc.description: Date of Conference: 23-27 March 2009; Conference Name: 3rd European Conference on Antennas and Propagation, IEEE 2009
2009-01-01T00:00:00ZAnalysis of photonic-crystal problems with MLFMA and approximate Schur preconditionersErgül, ÖzgürMalas, TahirKılınç, SeçilSarıtaş, SerkanGürel, Leventhttps://hdl.handle.net/11693/287022020-07-09T06:11:45Z2009-07-01T00:00:00Zdc.title: Analysis of photonic-crystal problems with MLFMA and approximate Schur preconditioners
dc.contributor.author: Ergül, Özgür; Malas, Tahir; Kılınç, Seçil; Sarıtaş, Serkan; Gürel, Levent
dc.description.abstract: We consider fast and accurate solutions of electromagnetics problems involving three-dimensional photonic crystals (PhCs). Problems are formulated with the combined tangential formulation (CTF) and the electric and magnetic current combined-field integral equation (JMCFIE) discretized with the Rao-Wilton-Glisson functions. Matrix equations are solved iteratively by the multilevel fast multipole algorithm. Since PhC problems are difficult to solve iteratively, robust preconditioning techniques are required to accelerate iterative solutions. We show that novel approximate Schur preconditioners enable efficient solutions of PhC problems by reducing the number of iterations significantly for both CTF and JMCFIE. ©2009 IEEE.
dc.description: Date of Conference: 20-23 July 2009; Conference name: Computational Electromagnetics International Workshop, CEM 2009
2009-07-01T00:00:00ZHybridizing physical optics with MLFMA for efficient scattering computations of three-dimensional complex targetsManyas, AlpErgül, ÖzgürGürel, Leventhttps://hdl.handle.net/11693/287002020-07-09T06:11:44Z2009-07-01T00:00:00Zdc.title: Hybridizing physical optics with MLFMA for efficient scattering computations of three-dimensional complex targets
dc.contributor.author: Manyas, Alp; Ergül, Özgür; Gürel, Levent
dc.description.abstract: The multilevel fast multipole algorithm (MLFMA) provides accurate and efficient solutions of electromagnetic scattering problems involving large and complicated structures. On the other hand, whenever applicable, accelerations provided by approximation techniques can be useful to further improve the efficiency of solutions. In this paper, we present a hybrid technique, which combines the physical-optics (PO) method and MLFMA for efficient scattering computations of three-dimensional objects. We show that, with a careful choice of MLFMA and PO regions on the structure, the number of unknowns can be reduced and solutions can be accelerated significantly, without sacrificing the accuracy. The proposed hybrid technique is easy to implement by modifying existing MLFMA codes. ©2009 IEEE.
dc.description: Date of Conference: 20-23 July 2009; Conference name: Computational Electromagnetics International Workshop, CEM 2009
2009-07-01T00:00:00ZFast and accurate solutions of extremely large scattering problems involving three-dimensional canonical and complicated objectsErgül, ÖzgürGürel, Leventhttps://hdl.handle.net/11693/286922020-07-09T06:11:44Z2009-07-01T00:00:00Zdc.title: Fast and accurate solutions of extremely large scattering problems involving three-dimensional canonical and complicated objects
dc.contributor.author: Ergül, Özgür; Gürel, Levent
dc.description.abstract: We present fast and accurate solutions of extremely large scattering problems involving three-dimensional metallic objects discretized with hundreds of millions of unknowns. Solutions are performed by the multilevel fast multipole algorithm, which is parallelized efficiently via a hierarchical partition strategy. Various examples involving canonical and complicated objects are presented in order to demonstrate the feasibility of accurately solving large-scale problems on relatively inexpensive computing platforms without resorting to approximation techniques. ©2009 IEEE.
dc.description: Date of Conference: 20-23 July 2009; Conference name: 2009 Computational Electromagnetics International Workshop
2009-07-01T00:00:00ZAn effective preconditioner based on schur complement reduction for integral-equation formulations of dielectric problemsMalas, TahirGürel, Leventhttps://hdl.handle.net/11693/286912021-04-01T13:06:16Z2009-01-01T00:00:00Zdc.title: An effective preconditioner based on schur complement reduction for integral-equation formulations of dielectric problems
dc.contributor.author: Malas, Tahir; Gürel, Levent
dc.description.abstract: The author consider effective preconditioning of recently proposed two integral-equation formulations for dielectrics; the combined tangential formulation (CTF) and the electric and magnetic current combined-field integral equation (JMCFIE). These two formulations are of utmost interest since CTF yields more accurate results and JMCFIE yields better-conditioned systems than other formulations.
dc.description: Date of Conference: 1-5 June 2009; Conference name: 2009 IEEE Antennas and Propagation Society International Symposium
2009-01-01T00:00:00Z