Ozlem Ozgun

Hacettepe University · Department of Electrical and Electronics Engineering

This paper presents an efficient approach for evaluating the Sommerfeld integrals in the spectral domain, whose integrands typically show an oscillatory and slowly decaying behavior at high frequencies, e.g., in the millimeter wave regime. It is well known that these integrals arise in the representations of the dyadic Green's functions of layered...

The sea clutter phenomenon is investigated from a different perspective by using the finite element domain decomposition (FEDD) method, which is a full -wave numerical method based on the decomposition of the problem into sub-problems with the help of the locally-conformal perfectly matched layer (LC-PML) approach. The numerical model developed in...

A new version of PETOOL (Parabolic Equation Toolbox) is introduced with various additional capabilities. PETOOL is an open-source and MATLAB-based software tool with a user-friendly graphical user interface (GUI) for the analysis and visualization of electromagnetic wave propagation over variable terrain and through arbitrary atmosphere. Four novel...

In this article, a hybrid numerical method, called finite element method (FEM) + dipole moment (DM), is presented for efficient solution of multiscale electromagnetic radiation and scattering problems that involve structures with fine features, such as thin-wire antennas or objects. In this method, the FEM is hybridized with the DM approach to help...

This paper presents a novel computational electromagnetics (CEM) technique, which hybridizes the periodic finite element method (FEM) with the method of moments (MoM), for efficient numerical modeling of electromagnetic scattering from metasurfaces consisting of truncated periodic or locally varying quasi‐periodic array of structures. Based on the...

A high fidelity full-wave simulator is presented to perform numerical experiments for rough sea scattering problem by considering different polarizations, frequencies, grazing angles, wind speeds and sea surface spectra. The simulator is based on a novel Finite Element Domain Decomposition (FEDD) method for solving the problem of two dimensional el...

Link: https://www.crcpress.com/MATLAB-based-Finite-Element-Programming-in-Electromagnetic-Modeling/Ozgun-Kuzuoglu/p/book/9781498784078 This book focuses on finite element methods with emphasis on MATLAB for numerical modeling of electromagnetic problems. Providing readers with knowledge and skills thorough which they can develop their own finite e...

A coordinate transformation based finite element method (called CT‐FEM) is presented for detecting contours of breast cancer tissues in the context of microwave imaging. The geometry and location of a single or multiple cancerous tumors inside a breast tissue are identified by constructing an inverse problem based on the genetic optimization algori...

A comparative study of some theoretical and numerical models is presented in the solution of two-dimensional urban radiowave propagation problems. The path loss is computed by GO+UTD (geometric optics + uniform theory of diffraction), two-way SSPE (split step parabolic equation) and the diffracting screens models, and the results are compared throu...

The finite element method is applied to the modeling of fringe currents and fields in a diffraction problem where a perfectly conducting wedge is illuminated by a line source. A spatial superposition approach is employed to compute the fringe currents. The locally-conformal perfectly matched layer (PML) approach is used to truncate the infinitely-l...

A remesh-free numerical method is developed for shape optimization problem by combining the transformation optics approach, the finite element method and the genetic optimization algorithm. To overcome cumbersome remeshing processes, transformation media are designed within the elements where the contour of the object passes. A simple rectangular m...

Various computational media are designed by using the principles of Transformation Optics (TO) for the purpose of efficient modeling of stochastic electromagnetic problems, such as scattering from rough surfaces, scattering from a random array of obstacles, and propagation in a waveguide with rough or randomly varying surfaces. The stochastic model...

A MATLAB-based tool, GO+UTD, is presented with a user-friendly graphical user interface (GUI) for the simulation of electromagnetic wave propagation and diffraction effects over variable terrain by using the geometrical optics (GO) and the uniform theory of diffraction (UTD) techniques. The theoretical background, structure, capabilities, and limit...

The coordinate transformation technique (with its current name of transformation electromagnetics) is applied to the finite-element method (FEM) with periodic boundary conditions for efficient Monte Carlo simulation of one-dimensional random rough surface scattering problems. In a unit cell of periodic structure, two coordinate transformations are...

Perturbation and transformation electromagnetics methods are hybridized for solving electromagnetic scattering from objects with weakly perturbed surfaces within the context of finite element method. A mesh is generated for smooth surface and a transformation medium layer is designed over the smooth surface by using the coordinate transformation te...

Electromagnetic scattering from a random array of objects is modeled by using special coordinate transformations that are based on the form invariance property of Maxwell's equations. The main motivation is to perform multiple realizations of Monte Carlo simulations corresponding to different positions of objects in an efficient way by using a sing...

A parabolic equation toolbox (called PETOOL) has been developed in MATLAB with a user-friendly Graphical User Interface (GUI) for modeling radio-wave propagation over variable terrain and through homogeneous and inhomogeneous atmosphere (O. Ozgun, G. Apaydin, M. Kuzuoglu, L. Sevgi, Computer Physics Communications, 182, 2638–2654, 2011). The unique...

Finite element (FEM) diffraction modeling of double-tip structure is presented and its accuracy is compared with the uniform theory of diffraction (UTD) and the method of moments (MoM). The locally-conformal perfectly matched layer (PML) approach is utilized to truncate the infinitely-long structure in a finite-sized computational domain. Diffracte...

The subject of single and double diffraction phenomena has long been investigated by high-frequency asymptotic techniques. However, integral or differential equation-based numerical methods suffer from computational complexity due to electrically large geometries encountered in high-frequency problems. The main purpose of this paper is to present t...

The vector analysis graphical user interface (VectGUI), a MATLABbased vector analysis visualization tool, can be used as a supplementary tool in the first course of electromagnetic education. The main purpose of this tool is to provide various visual aids that assist students in developing a mental image of some fundamental concepts in vector calcu...

Electromagnetic scattering from randomly distributed array of scatterers is numerically analyzed by Monte Carlo simulations by utilizing coordinate transformations in the context of finite element method solution of Helmholtz equation. The major goal in proposed approaches is to place transformation media into computational domain by employing the...

A numerical method is proposed for efficient solution of scattering from objects with weakly perturbed surfaces by combining the perturbation theory, transformation electromagnetics and the finite element method. A transformation medium layer is designed over the smooth surface, and the material parameters of the medium are determined by means of a...

The reshaping technique that is based on transformation optics renders an object to be perceived as if it has a different shape irrespective of the location of the observer. This is achieved by coating the object with an anisotropic and spatially varying metamaterial layer by employing the concept of coordinate transformation. This paper presents a...

Monte Carlo analysis of surface roughness in electromagnetic scattering problems is presented by using the principles of transformation electromagnetics/optics in finite methods. The main motivation in the proposed approach is to eliminate the need of mesh generation for each surface in repeated Monte Carlo realizations, and hence, to devise a fast...

The above paper [1] is about the two-way split-step parabolic equation method (2W-SSPE) over irregular terrain, and claims that they have developed the “improved” version of the 2W-SSPE approach that has been proposed and validated by us in literature [2]-[11]. The paper [1] claims to derive the 2W-PE directly from 2D Helmholtz equation. They do th...

A computational model is developed for efficient solution of electromagnetic scattering from obstacles having random surface deformations or irregularities (such as roughness or randomly-positioned bump on the surface), by combining the Monte Carlo method with the principles of transformation electromagnetics in the context of finite element method...

A transformation electromagnetics-based approach is presented to facilitate the use of fixed Cartesian grids for modeling arbitrarily shaped (convex or nonconvex) curved boundaries in finite methods. The basic idea is to design transformation media adapted to the Cartesian grid by using the duality between the material parameters of the media and t...

AbstractA computational model is presented for Monte Carlo simulation of waveguides with ridges, by combining the principles of transformation electromagnetics and the finite methods (such as finite element or finite difference methods). The principle idea is to place a transformation medium around the ridge structure, so that a single and easy‐to‐...

This paper presents computational models employing special transformation-based media—which we call software metamaterials—for the purpose of enhancing the ability of numerical modeling methods for solving multi-scale electromagnetic boundary value problems involving features with multiple length or frequency scales or both. The multi-scale problem...

This paper presents a computational model that utilizes transformation-based metamaterials to enhance the performance of numerical modeling methods for achieving the statistical characterization of two-dimensional electromagnetic scattering from objects on or above one-dimensional rough sea surfaces. Monte Carlo simulation of the rough surface scat...

A computational model is introduced which employs transformation-based media to increase the computational performance of finite methods (such as finite element or finite difference methods) for analyzing waveguides with grooves or rough surfaces. Random behavior of the roughness is taken into account by utilizing the Monte Carlo technique, which i...

A coordinate transformation technique is introduced for the finite difference time domain method to alleviate the effects of errors introduced by the staircasing approximation of curved geometries that do not conform to a Cartesian grid. An anisotropic metamaterial region, which is adapted to the Cartesian grid and designed by the coordinate transf...

This paper presents a comparative study of some analytical and numerical techniques in the solution of a classical problem of electromagnetic scattering from single and double knife edge above ground. The results of the analytical exact and asymptotic techniques (such as uniform theory of diffraction, parabolic equation diffraction method) are comp...

The Monte Carlo-based Characteristic Basis Finite-Element Method (MC-CBFEM) is developed for predicting the statistical properties of the 2-D electromagnetic scattering from objects (such as ship- and decoy-like objects) on or above random rough sea surfaces. At each realization of the Monte Carlo technique, the 1-D rough sea surface is randomly ge...

This paper presents coordinate transformation techniques for solving low-frequency electromagnetic boundary value problems involving electrically-small geometrical features. The major motivation is to eliminate the need for fine mesh and to allow uniform and easy-to-generate meshes by placing transformation media into the computational domain. A sa...

This paper presents a design technique for transformation media that aim to reduce staircasing errors occurring in the numerical solution of electromagnetic boundary value problems by finite methods. The main idea is to place transformation media within the computational domain adapted to the Cartesian grid, and to determine the material parameters...

Program download: http://cpc.cs.qub.ac.uk/summaries/AEJS_v1_0.html A MATLAB-based one-way and two-way split-step parabolic equation software tool (PETOOL) has been developed with a user-friendly graphical user interface (GUI) for the analysis and visualization of radio-wave propagation over variable terrain and through homogeneous and inhomogeneou...

This paper presents coordinate transformation techniques for solving multi-scale electromagnetic boundary value problems involving fine geometrical features. The major purpose of this study is to get rid of fine mesh and to allow uniform and easy-to-generate meshes in the finite element solution of the multi-scale problems by introducing metamateri...

A novel two-way finite-element parabolic equation (PE) (2W-FEMPE) propagation model which handles both forward and backward scattering effects of the groundwave propagation above the Earth's surface over irregular terrain paths through inhomogeneous atmosphere is introduced. A Matlab-based propagation tool for 2W-FEMPE is developed and tested again...

We present numerical solution techniques for efficiently handling multi-scale electromagnetic boundary value problems having fine geometrical details or features, by utilizing spatial coordinate transformations. The principle idea is to modify the computational domain of the finite methods (such as the finite element or finite difference methods) b...

Recently, the solution of multiscale problems that are not only large, but contain fine features as well, has emerged as one of the key areas in Computational Electromagnetics that present a considerable challenge to us. Some examples of such problems are: RFID sensors mounted on complex platforms; nanowire antennas placed close to a relatively lar...

Metamaterials-artificial materials with engineered electromagnetic properties-is a young but rapidly growing topic that breaks down traditional rules, and fascinates scientists in the field of physics, optics and electromagnetics. One of the major breakthroughs in the development of metamaterials is the cloaking device for obtaining electromagnetic...

Helmholtz's wave equation can be approximated by means of two differential equations, corresponding to forward and backward propagating waves each of which is in parabolic wave equation (PWE) form. The standard PWE is very suitable for marching-type numerical solutions. The one-way Fourier split-step parabolic equation algorithm (SSPE) is highly ef...

In this paper, we design and demonstrate various transformation media for the development of numerical models for efficient solution of electromagnetic boundary value problems via finite methods. The governing idea is to alter the computational domain of the finite methods by making use of a suitable transformation media, and hence to devise effici...

This paper, by going one step further in the advancement of the CBFEM approach, presents a memory-efficient technique that derives the CBFs by utilizing a multi-level scheme. This novel approach can be employed in all variety of CBFEM techniques in a similar manner. In the multi-level scheme, the CBFs in each level are progressively combined by gro...

In this paper, we introduce a novel method, which we call Finite Element / Dipole Moment Method (FEDM), with two alternative (iterative and self-consistent) implementations, for handling the multiscale problem mentioned above. In this method, the conventional FEM is modified through the use of dipole moments in such a way that the region around the...

This paper introduces a two-way split-step parabolic equation propagation tool (2W-SSPE), which is capable of handling both forward and backward scattered waves during groundwave propagation over an irregular terrain, through inhomogeneous atmosphere. The algorithm is calibrated and tested against reference data obtained with the help of image meth...

The aim of this study is to introduce, for the first time in the literature, a two-way FEMPE algorithm (2W-FEMPE), and to perform calibration tests of both two-way FEMPE and SSPE algorithms against the Image Method and the Geometric Optic (GO) + Uniform Theory of Diffraction (UTD).

We present spatial-coordinate transformation techniques to control the propagation of electromagnetic fields in several surprising and useful applications. The implementation of this approach is based on the fact that Maxwell's equations are form-invariant under coordinate transformations. Specifically, the effect of a general coordinate transforma...

The authors introduce the iterative leap-field domain decomposition method that is tailored to the finite element method, by combining the concept of domain decomposition and the Huygens' Principle. In this method, a large-scale electromagnetic boundary value problem is partitioned into a number of suitably-defined 'small' and manageable subproblem...

In this article, we introduce a new type of Characteristic Basis Finite Element Method (CBFEM), which is based on the concepts of Physical Optics (PO) and Perfectly Matched Layers (PMLs), for solving large-scale electromagnetic scattering problems in a rigorous and efficient manner. This parallel and iteration-free technique, called CBFEM-PO, decom...

This article presents a noniterative and parallel finite element technique that is tailored for a wide class of electromagnetic boundary problems, covering both quasi-static and time-harmonic regimes. This approach, called the characteristic basis finite element method, combines the domain decomposition technique with the use of characteristic basi...

We introduce a spatial coordinate transformation technique to compress the excessive white space (i.e. free-space) in the computational domain of finite methods. This approach is based on the form-invariance property of Maxwell’s equations under coordinate transformations. Clearly, Maxwell’s equations are still satisfied inside the transformed spac...

We introduce a memory-efficient version of the Characteristic Basis Finite-Element Method (CBFEM), which combines the domain decomposition with the use of characteristic basis functions (CBFs) that are tailored for each individual subdomain. Although the conventional CBFEM is inherently an efficient approach, the final number of unknowns is primari...

The Fourier split-step method is a one-way marching-type algorithm to efficiently solve the parabolic equation for modeling electromagnetic propagation in troposphere. The main drawback of this method is that it characterizes only forward-propagating waves, and neglects backward-propagating waves, which become important especially in the presence o...

In this paper, we present another version of the CBFEM (called CBFEM-PO), which is based on the use of physical optics (PO) and perfectly matched layers (PMLs) for the generation of the CBF. The CBFEM-PO constructs three types of CBFs, namely: (i) primary bases arising from the self-interactions in each subdomain; (ii) secondary bases due to the mu...

We present a novel coordinate transformation technique that controls the propagation of waves inside a waveguide, such that the waveguide behaves as if it is a “reshaped” waveguide. In this technique, the spatial domain of the waveguide is mapped to that of its reshaped equivalent, yielding an anisotropic medium inside the waveguide. In other words...

In this paper, we introduce a parallelized version of a novel, non-iterative domain decomposition algorithm, called Characteristic Basis Finite Element Method (CBFEM-MPI), for efficient solution of large-scale electromagnetic scattering problems, by utilizing a set of specially defined characteristic basis functions (CBFs). This approach is based o...

In this paper, we present a novel, non-iterative domain decomposition method, which has been parallelized by using the message passing interface (MPI) library, and used to efficiently extract the capacitance matrixes of 3-D interconnect structures, by employing characteristic basis functions (CBFs) in the context of the finite element method (FEM)....

In this paper, we introduce "specially-defined" coordinate transformation techniques to produce material specifications which control electromagnetic fields in reshaping objects in electromagnetic scattering (Ozgun et al., 2007), and in reshaping and/or miniaturizing waveguides. We first discuss the design procedure of the anisotropic metamaterials...

Efficient and accurate solution of electromagnetic boundary value problems involving electrically-large and geometrically complex objects continue to challenge us, because they present a heavy burden on the CPU time and memory. During recent years, various domain decomposition schemes that are based on iterative techniques have been proposed to sol...

In this paper, we generalize this algorithm to 3D scattering problems, and we demonstrate that the algorithm is actually non-iterative in problems involving smooth convex geometries (such as sphere, cube, missile, cone, plate, etc.) and some special geometries (such as inlet). The most distinguished feature of the algorithm is the utilization of th...

We introduce the Iterative Leap-field Domain Decomposition Method (ILF-DDM), which is based on the dual employment of Finite Element Method and Huygens' Principle iteratively, for the solution of electromagnetic boundary value problems. The method can be applied to cases involving both multiple objects and a single 'challenging' object using the lo...

We introduce a new technique which remedies the drawbacks in the Finite Element solution of low-frequency electromagnetic scattering problems, through the usage of an anisotropic metamaterial layer which is designed by employing the coordinate transformation approach. The usual finite element method should utilize a “challenging” mesh generation sc...

We present a comparative evaluation of two novel and practical perfectly matched layer (PML) implementations to the problem of mesh truncation in the finite element method (FEM): locally-conformal PML, and multi-center PML techniques. The most distinguished feature of these methods is the simplicity and flexibility to design conformal PMLs over cha...

In the numerical solution of some boundary value problems by the finite element method (FEM), the unbounded domain must be truncated by an artificial absorbing boundary or layer to have a bounded computational domain. The perfectly matched layer (PML) approach is based on the truncation of the computational domain by a reflectionless artificial lay...

We introduce a new approach which enables a waveguide to support propagation of electromagnetic waves below the cutoff frequency, as well as which avoids undesirable reflections in a waveguide. These are achieved through the usage of an anisotropic metamaterial layer by employing the concept of coordinate transformation. The proposed method can be...

We introduce the forward–backward domain decomposition method (FB-DDM), which is basically an improved version of the classical alternating Schwarz method with overlapping subdomains, for electromagnetic boundary value problems. The proposed method is noniterative in some cases involving smooth geometries, or it usually converges in a few iteration...

We introduce a new technique (in the context of time-harmonic electromagnetic scattering), which renders an object (or scatterer) to be perceived as if it has a different shape, irrespective of the location of the observer. This is achieved through the usage of an anisotropic metamaterial layer, which is designed as conformal to the surface of the...

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We present the multicenter perfectly matched layer (PML) technique, which is an easy and practical conformal PML implementation, obtained by the complex coordinate stretching, to the problem of mesh truncation in the finite element method. After developing the analytical background of this method, we demonstrate its performance in electromagnetic r...

We introduce the locally-conformal perfectly matched layer (PML) approach, which is an easy and straightforward PML implementation, to the problem of mesh truncation in the finite element method (FEM). This method is based on a locally-defined complex coordinate transformation which has no explicit dependence on the differential geometric character...

In this article, we introduce the locally conformal perfectly matched layer (PML) technique, which is an easily implementable conformal PML implementation, obtained via complex coordinate transformation, for the purpose of mesh truncation in the finite element method. After deriving the governing equations, we test this technique using electromagne...

In this paper, we discuss two practical implementations of the complex coordinate stretching approach, which we call the locally-conformal and multi-center perfectly matched layers (PMLs), for the mesh truncation of FEM simulations. The performance of the approaches are tested using three-dimensional electromagnetic scattering problems

Dual-frequency operation of antennas has become a necessity for many applications in recent wireless communication systems, such as GPS, GSM services operating at two different frequency bands, and services of PCS and IMT-2000 applications. Although there are various techniques to achieve dual-band operation from various types of microstrip antenna...