Browsing by Subject "Electromagnetism"

Now showing 1 - 20 of 32

Open Access
Accuracy and efficiency considerations in the solution of extremely large electromagnetics problems
(IEEE, 2011) Gürel, Levent; Ergül, Özgür
This study considers fast and accurate solutions of extremely large electromagnetics problems. Surface formulations of large-scale objects lead to dense matrix equations involving millions of unknowns. Thanks to recent developments in parallel algorithms and high-performance computers, these problems can easily be solved with unprecedented levels of accuracy and detail. For example, using a parallel implementation of the multilevel fast multipole algorithm (MLFMA), we are able to solve electromagnetics problems discretized with hundreds of millions of unknowns. Unfortunately, as the problem size grows, it becomes difficult to assess the accuracy and efficiency of the solutions, especially when comparing different implementations. This paper presents our efforts to solve extremely large electromagnetics problems with an emphasis on accuracy and efficiency. We present a list of benchmark problems, which can be used to compare different implementations for large-scale problems. © 2011 IEEE.
Open Access
Analysis of double-negative materials with surface integral equations and the multilevel fast multipole algorithm
(IEEE, 2011) Ergül O.; Gürel, Levent
We present a fast and accurate analysis of double-negative materials (DNMs) with surface integral equations and the multilevel fast multipole algorithm (MLFMA). DNMs are commonly used as simplified models of metamaterials at resonance frequencies and are suitable to be formulated with surface integral equations. However, realistic metamaterials and their models are usually very large with respect to wavelength and their accurate solutions require fast algorithms, such as MLFMA. We consider iterative solutions of DNMs with MLFMA and we investigate the accuracy and efficiency of solutions when DNMs are formulated with two recently developed formulations, namely, the combined tangential formulation (CTF) and the electric and magnetic current combined-field integral equation (JMCFIE). Numerical results on canonical objects are consistent with previous results in the literature on ordinary objects. © 2011 IEEE.
Open Access
Analysis of photonic-crystal problems with MLFMA and approximate Schur preconditioners
(IEEE, 2009-07) Ergül, Özgür; Malas, Tahir; Kılınç, Seçil; Sarıtaş, Serkan; Gürel, Levent
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.
Open Access
Calculation of radome-enclosed aperture antenna in 3-D
(IEEE, 2010-09) Sukharevsky, I.; Altintas, Ayhan
The exact mathematical model of an aperture antenna and the image theory are used to develop exact and PO integral representations of the fields radiated by radome-enclosed aperture antenna. The desired problem is reduced to finding fields of a plane wave diffracted on the "symmetrized" radome. The passage of the wave through the wall of the radome is analysed by means of geometrical optics. Caustic influence is taken into account, and the contribution of stationary phase points of reflected field to the far-side radiation is discussed. Radiation patterns for antennas with a specified ampliphase distribution enclosed in spherical and parabolic radomes are analysed. © 2010 IEEE.
Open Access
Characteristic equations for the lasing Modes of infinite periodic chain of quantum wires
(IEEE, 2008-06) Byelobrov, V. O.; Benson, T. M.; Altıntaş, Ayhan; Nosich, A.I.
In this paper, we study the lasing modes of a periodic open optical resonator. The resonator is an infinite chain of active circular cylindrical quantum wires standing in tree space. Characteristic equations for the frequencies and associated linear thresholds of lasing are derived. These quantities are considered as eigenvalues of specific electromagnetic-field problem with "active" imaginary part of the cylinder material's refractive index - Lasing Eigenvalue Problem (LEP). ©2008 IEEE.
Open Access
Effect of disorder on magnetic resonance band gap of split-ring resonator structures
(Optical Society of American (OSA), 2004) Aydın, K.; Güven, K.; Katsarakis, N.; Soukoulis, C. M.; Özbay, Ekmel
We investigated the influence of periodicity, misalignment, and disorder on the magnetic resonance gap of split-ring resonators (SRRs) which are essential components of left handed-metamaterials (LHMs). The resonance of a single SRR which is induced by the split is experimentally demonstrated by comparing transmission spectra of SRR and closed ring resonator. Misaligning the SRR boards do not affect the magnetic resonance gap, while destroying the periodicity results in a narrower band gap. The disorder in SRR layers cause narrower left-handed pass band and decrease the transmission level of composite metamaterials (CMMs), which may significantly affect the performance of these LHMs. © 2004 Optical Society of America.
Open Access
Effect of the off-focus shift of the feed on the radiation characteristics of a 2-D parabolic reflector antenna
(IEEE, 2010) Oğuzer, T.; Altıntaş, A.; Nosich, Alexander
The parabolic reflector antennas are widely used in the telecommunication systems and generally have large aperture sizes like 50λ to 80λ and larger. Their reliable full-wave analysis with the conventional Method of Moments (MoM) or with the other numerical methods is difficult because of inaccessible speed and accuracy. This statement is valid both for 3D and 2D reflector antennas in both polarizations. The Method of Analytical Regularization (MAR) constitutes an alternative solution compared to the ordinary MoM, which can provide only 1-2 digit accuracy. It provides finer accuracy within a reasonable computation time because the computational error can be decreased simply by increasing the matrix size in MAR. We have previously developed this method for the accurate simulation of the arbitrary conical section profile 2D reflector antennas, and the corresponding codes have provided us with accurate benchmark data. Here we study a similar problem however with the feed simulated by Complex Source Point (CSP) source located at an off-focus point on the symmetry axis of a front-fed reflector antenna. The numerical results are presented for the radiation characteristics including the forward and backward directivities and the radiation patterns in all directions. © 2010 IEEE.
Open Access
Efficient analysis of large finite arrays via mom formulation with dft based acceleration algorithms
(2003) Çivi, Ö. A.; Ertürk, Vakur B.; Chou, H.-T.
A DFT based acceleration algorithm is combined with iterative methods to accelerate the computation of Method of Moments (MoM) analysis of electromagnetic radiation/scattering from large, finite free-standing and printed elements of phased arrays. Computational complexity of this approach is O(Ntot), where Ntot is the number of unknowns. Numerical results are presented to validate the efficiency and accuracy of the method.
Open Access
An efficient parallel implementation of the multilevel fast multipole algorithm for rigorous solutions of large-scale scattering problems
(IEEE, 2010) Ergül O.; Gürel, Levent
We present the solution of large-scale scattering problems discretized with hundreds of millions of unknowns. The multilevel fast multipole algorithm (MLFMA) is parallelized using the hierarchical partitioning strategy on distributed-memory architectures. Optimizations and load-balancing algorithms are extensively used to improve parallel MLFMA solutions. The resulting implementation is successfully employed on modest parallel computers to solve scattering problems involving metallic objects larger than 1000λ and discretized with more than 300 million unknowns. © 2010 IEEE.
Open Access
Efficient solution of the combined-field integral equation with the parallel multilevel fast multipole algorithm
(IEEE, 2007-08) Gürel, Levent; Ergül, Özgür
We present fast and accurate solutions of large-scale scattering problems formulated with the combined-field integral equation. Using the multilevel fast multipole algorithm (MLFMA) parallelized on a cluster of computers, we easily solve scattering problems that are discretized with tens of millions of unknowns. For the efficient parallelization of MLFMA, we propose a hierarchical partitioning scheme based on distributing the multilevel tree among the processors with an improved load-balancing. The accuracy of the solutions is demonstrated on scattering problems involving spheres of various radii from 80λ to 110λ. In addition to canonical problems, we also present the solution of real-life problems involving complicated targets with large dimensions. © 2007 IEEE.
Open Access
Electromagnetic modeling of split-ring resonators
(IEEE, 2007) Gürel, Levent; Ünal, Alper; Ergül, Özgür
In this paper, we report our efforts to model splitring resonators (SRRs) and their large arrays accurately and efficiently in a sophisticated simulation environment based on recent advances in the computational electromagnetics. The resulting linear system obtained from the simultaneous discretization of the geometry and Maxwell's equations is solved iteratively with the multilevel fast multipole algorithm. As an example, we present an array of 125 SRRs showing a negative effective permeability about 92 GHz.
Open Access
Electromagnetically induced left-handedness in a dense gas of three-level atoms
(The American Physical Society, 2004) Oktel, M. Ö.; Müstecaphoǧlu, Ö. E.
Ways in which a three-level system can be used to change the frequency-dependent magnetic permeability of an atomic gas were discussed. The resulting macroscopic electrodynamics was also discussed. The two levels were separated at optical frequencies while having a nonvanishing magnetic dipole matrix element. It was found that such level splittings require large external magnetic fields.
Open Access
EU NoE metamorphose: Metamaterials research activities
(SPIE, 2005) Özbay, Ekmel
We will present the activities of METAMORPHOSE a network of excellence (NoE) formed under EU-FP6 on the area of metamaterials. The main scientific objective of the partners of this consortium is to develop new types of artificial materials, referred to below as metamaterials, with electromagnetic properties that cannot be found among natural materials. The results of this development should lead to a conceptually new range of radio, microwave, and optical technologies, based on revolutionary new materials made by large-scale assembly of some basic elements (nanoscopic and microscopic) in unprecedented combinations. Further information on this NoE can be found in http://www.metamaterials-eu.org.
Open Access
Experimental demonstration of sub-wavelength imaging by left handed metamaterials
(SPIE, 2007) Özbay, Ekmel
We review the studies conducted in our group concerning electromagnetic properties of metamaterials and photonic crystals with negative effective index of refraction. In particular, we demonstate the true left handed behavior of a 2D composite metamaterial, by analyzing the electric and magnetic response of the material components systematically. The negative refraction, subwavelength focusing, and flat lens phenomena using left handed metamaterials and photonic crystals are also presented.
Open Access
Extension of forward-backward method with DFT-based acceleration algorithm for the efficient analysis of large periodic arrays with arbitrary boundaries
(John Wiley & Sons, 2005) Civi, Ö. A.; Ertürk, V. B.; Chou, H.-T.
An extension of the discrete Fourier transform (DFT)-based forward-backward algorithm is developed using the virtual-element approach to provide a fast and accurate analysis of electromagnetic radiation/scattering from electrically large, planar, periodic, finite (phased) arrays with arbitrary boundaries. Both the computational complexity and storage requirements of this approach are O(Ntot) (Ntot is the total number of unknowns). The numerical results for both printed and freestanding dipole arrays with circular and/or elliptical boundaries are presented to validate the efficiency and accuracy of this approach.
Open Access
Extracting power from sub-wavelength apertures by using electrically small resonators: Phenomenology, modeling, and applications
(IEEE, 2012) Bilotti F.; Di Palma L.; Ramaccia, D.; Toscano, A.; Vegni L.; Ateş, Damla; Özbay, Ekmel
In this contribution, we review our recent work on the extraction of the electromagnetic power from electrically small apertures by using metamaterial-inspired resonators. First, we present an antenna interpretation of the power transmission through sub-wavelength apertures and discuss the questioned concept of 'enhanced transmission'. Then, we present the so-called 'connected bi-omega particle' and the related analytical model. After that, exploiting proper numerical and experimental examples, we also show that the electromagnetic response of such a particle is not influenced by the surrounding environment. This unique property makes the particle a suitable candidate for the implementation of microwave components based on the selective power extraction from electrically small apertures. Finally, the application of the proposed concepts to the design of innovative microwave components, such as waveguide filters, diplexers, power-splitters, modal filters, horn antennas, etc. will be considered and demonstrated through proper numerical and experimental results. © 2012 IEEE.
Open Access
Fast and accurate analysis of complicated metamaterial structures using a low-frequency multilevel fast multipole algorithm
(2009-09) Ergül, Özgür; Gürel, Levent
We present efficient solutions of electromagnetics problems involving realistic metamaterial structures using a low-frequency multilevel fast multipole algorithm (LF-MLFMA). Ordinary implementations of MLFMA based on the diago-nalization of the Green's function suffer from the low-frequency breakdown, and they become inefficient for the solution of metamaterial problems dis-cretized with very small elements compared to the wavelength. We show that LF-MLFMA, which employs multipoles explicitly without diagonalization, significantly improves the solution of metamaterial problems in terms of both processing time and memory. © 2009 IEEE.
Open Access
Fast and accurate analysis of optical metamaterials using surface integral equations and the parallel multilevel fast multipole algorithm
(IEEE, 2013) Ergül, Özgür; Gürel, Levent
We present fast and accurate simulations of optical metamaterials using surface integral equations and the multilevel fast multipole algorithm (MLFMA). Problems are formulated with the electric and magnetic current combined-field integral equation and solved iteratively with MLFMA, which is parallelized using the hierarchical strategy on distributed-memory architectures. Realistic metamaterials involving dielectric, perfectly conducting, and plasmonic regions of finite extents are solved rigorously with the developed implementation without any periodicity assumptions.
Open Access
Fast and accurate solutions of scattering problems involving dielectric objects with moderate and low contrasts
(IEEE, 2007-08) Ergül, Özgür; Gürel, Levent
We consider the solution of electromagnetic scattering problems involving relatively large dielectric objects with moderate and low contrasts. Three-dimensional objects are discretized with Rao-Wilton-Glisson functions and the scattering problems are formulated with surface integral equations. The resulting dense matrix equations are solved iteratively by employing the multilevel fast multipole algorithm. We compare the accuracy and efficiency of the results obtained by employing various integral equations for the formulation of the problem. If the problem size is large, we show that a combined formulation, namely, electric-magnetic current combined-field integral equation, provides faster iterative convergence compared to other formulations, when it is accelerated with an efficient block preconditioner. For low-contrast problems, we introduce various stabilization procedures in order to avoid the numerical breakdown encountered in the conventional surface formulations. © 2007 IEEE.
Open Access
Hybridizing physical optics with MLFMA for efficient scattering computations of three-dimensional complex targets
(IEEE, 2009-07) Manyas, Alp; Ergül, Özgür; Gürel, Levent
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.