Browsing by Author "Apaydin, Gokhan"

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Citation Count: 1
Comments on "Wave diffraction by a soft/hard strip: Modified theory of physical optics solution"
(Elsevier Gmbh, Urban & Fischer verlag, 2018) Apaydin, Gokhan; Sevgi, Levent; Ufimtsev, Pyotr Ya.
Modified theory of physical optics (MTPO) solution for a soft/hard strip is analyzed. It is shown that this solution is incorrect because the MTPO Green function does not satisfy boundary conditions. Defects of MTPO in calculations of fringe waves are also noticed. (C) 2018 Elsevier GmbH. All rights reserved.
Citation Count: 0
Diffraction and Fringe Effects in EMC Problems
(Ieee, 2017) Apaydin, Gokhan; Sevgi, Levent
Understanding the nature of electromagnetic (EM) wave interference is essential in EMC engineering. EM wave interference mainly includes the diffraction and fringe effects. This paper aims to visualize the diffraction and fringe effects using the canonical wedge structure.
Citation Count: 11
Diffraction at a Rectangular Plate: First-Order PTD Approximation
(Ieee-inst Electrical Electronics Engineers inc, 2016) Apaydin, Gokhan; Hacivelioglu, Feray; Sevgi, Levent; Gordon, William B.; Ufimtsev, Pyotr Ya.
Physical theory of diffraction (PTD) is developed for the field scattered at a perfectly conducting rectangular plate. Grazing incidence and grazing scattering are analyzed. High-frequency asymptotic estimations are derived. Bistatic and monostatic scenarios are considered. Comparison is presented with known experimental and numeric results obtained by the method of moments (MoM).
Citation Count: 6
Diffraction at Rounded Wedges: MoM Modeling of PTD Fringe Waves
(Applied Computational Electromagnetics Soc, 2017) Apaydin, Gokhan; Sevgi, Levent; Ufimtsev, Pyotr Ya
The paper examines diffraction at rounded wedges with perfectly conducting faces. This topic was a subject of many publications which investigated mainly the total diffracted waves. In the present paper, we calculate specifically their fringe components to illustrate their sensitivity to the edge curvature. Such fringe waves provide substantial contributions to the scattered field in certain directions and represent a key element in extension of the physical theory of diffraction (PTD) for objects with rounded edges.
Citation Count: 2
Diffraction at trilateral cylinders with combinations of soft and hard faces: first-order PTD approximation
(Taylor & Francis inc, 2018) Hacivelioglu, Feray; Apaydin, Gokhan; Sevgi, Levent; Ufimtsev, Pyotr Ya.
The paper investigates diffraction at trilateral cylinders with combinations of soft (electric) and hard (magnetic) faces. Scattered field in far zone is calculated according to the physical theory of diffraction. The first-order high-frequency approximation is constructed as a sum of single-diffracted edge waves. Plotted numerical data clearly demonstrate the difference for objects with different faces. Substantial suppression of backscattering is observed for cylinders with soft-hard illuminated faces. Fringe wave contributions to the scattered field are shown. Physical theory of diffraction results are compared with those of the physical optics and confirmed by the method of moments.
Citation Count: 9
Diffraction Modeling by a Soft-Hard Strip Using Finite-Difference Time-Domain Method
(Ieee-inst Electrical Electronics Engineers inc, 2017) Uslu, Alper; Apaydin, Gokhan; Sevgi, Levent
Diffraction by a strip with one face soft and the other face hard boundary condition is modeled numerically using finite-difference time-domain method, and the results are compared to the method of moments, which was validated against physical theory of diffraction.
Citation Count: 1
Diffraction of acoustic waves at two-dimensional hard trilateral cylinders with rounded edges: First-order physical theory of diffraction approximation
(Acoustical Soc Amer Amer inst Physics, 2018) Apaydin, Gokhan; Sevgi, Levent; Ufimtsev, Pyotr Ya.
The paper explores diffraction of acoustic waves at a two-dimensional hard trilateral cylinder with rounded edges. It represents the extension of the physical theory of diffraction (PTD) for finite objects with rounded edges. A first-order PTD approximation is developed. Integral equations are formulated for acoustic fringe waves and solved by method of moments (MoM). Good agreement is observed with the exact solution found by MoM when the object size exceeds a few wavelengths. (C) 2018 Acoustical Society of America.
Citation Count: 15
Double Tip Diffraction Modeling: Finite Difference Time Domain vs. Method of Moments
(Ieee-inst Electrical Electronics Engineers inc, 2014) Uslu, Mehmet Alper; Apaydin, Gokhan; Sevgi, Levent
Discontinuities such as tips and edges cause diffracted electromagnetic waves interact with objects. Two-dimensional (2D) wedge with non-penetrable boundaries is a canonical structure which has long been investigated analytically and numerically for the understanding and extraction of diffracted waves. Multiple-diffraction has also been investigated. Here, double tip diffraction is modeled with both finite-difference time-domain and method of moments and reference data are generated.
Citation Count: 5
Extension of PTD for Finite Objects With Rounded Edges: Diffraction at a Soft Trilateral Cylinder
(Ieee-inst Electrical Electronics Engineers inc, 2017) Apaydin, Gokhan; Sevgi, Levent; Ufimtsev, Pyotr Ya
The letter extends the physical theory of diffraction (PTD) for objects with rounded edges. It represents a combination of the fundamental PTD concept of fringe currents and the method of moments (MoM). The objects in the vicinity of edges are considered as parts of appropriate tangential wedges. Integral equations are formulated for fringe currents on these wedges and solved by the MoM. Then, a far field radiated by these currents is calculated. A very good agreement is observed with the field produced by the currents induced on the actual scattering object when its size exceeds a few wavelengths.
Citation Count: 2
Finite Difference Time Domain Modeling of Fringe Waves
(Applied Computational Electromagnetics Soc, 2017) Uslu, Mehmet Alper; Apaydin, Gokhan; Sevgi, Levent
A novel method is introduced for calculating fringe currents and fringe waves around the tip of a perfectly reflecting wedge under line source illumination. The time-domain fringe (non-uniform) currents are extracted with the finite-difference time-domain (FDTD) method. These currents are then fed into a free-space FDTD and fringe waves are excited. Alternatively, fringe waves are also obtained using the Green's function approach. The validation of the proposed method and the verification of the results are done against the physical theory of diffraction (PTD) as well as the method of moments (MoM). The factors affecting the accuracy are also discussed.
Citation Count: 5
Fringe integral equations for the 2-D wedges with soft and hard boundaries
(Amer Geophysical Union, 2016) Apaydin, Gokhan; Sevgi, Levent; Ufimtsev, Pyotr Ya.
Novel, fringe wave integral equations that account for the diffraction from nonpenetrable wedges with both soft and hard boundaries are derived. Method of moments simulation of fringe waves generated by a plane wave that excites the wedge is performed using this fringe wave integral equation. The results are compared with the exact physical theory of diffraction fringe waves.
Citation Count: 9
Fringe Waves from a Wedge With One Face Electric and the Other Face Magnetic
(Ieee-inst Electrical Electronics Engineers inc, 2016) Apaydin, Gokhan; Hacivelioglu, Feray; Sevgi, Levent; Ufimtsev, Pyotr Ya
Fringe waves represent the diffracted field generated by the nonuniform/fringe surface currents concentrated in vicinity of sharp scattering edges. For perfectly conducting wedges, they have been studied in a number of publications. In this communication, fringe waves for a wedge with one face electric and the other magnetic are analyzed analytically and numerically.
Citation Count: 3
A Groundwave Propagation Model Using a Fast Far-Field Approximation
(Ieee-inst Electrical Electronics Engineers inc, 2017) Apaydin, Gokhan; Lu, Cai-Cheng; Sevgi, Levent; Chew, Weng Cho
A fast far-field approximation (FAFFA), which is simple to use, is applied to groundwave propagation modeling from a nonpenetrable surface with both soft and hard boundaries. The results are validated against available reference models as well as compared to other numerical methods such as split step parabolic equation model and the method of moments.
Citation Count: 6
A MATLAB-Based Virtual Tool for Simulations of Wave Propagation Inside a Parallel-Plate Waveguide
(Ieee-inst Electrical Electronics Engineers inc, 2017) Apaydin, Gokhan; Sevgi, Levent
[No Abstract Available]
Citation Count: 16
Method of Moments Modeling of Backscattering By a Soft-Hard Strip
(Ieee-inst Electrical Electronics Engineers inc, 2015) Apaydin, Gokhan; Sevgi, Levent
Method of moments (MoM) is applied in modeling and simulation for backscattering from a strip with one face soft and the other face hard (i.e., with Dirichlet and Neumann boundary conditions, respectively). The results are compared with high-frequency asymptotics (HFA), such as physical theory of diffraction (PTD) and theory of edge diffraction (TED) approximations.
Citation Count: 13
A Novel Wedge Diffraction Modeling Using Method of Moments (MoM)
(Applied Computational Electromagnetics Soc, 2015) Apaydin, Gokhan; Sevgi, Levent
Scattering from edges and/or tips (i.e., diffraction) has long been modeled using different approaches. Initially, it was handled analytically using high frequency asymptotics (HFA). Parallel to the development in computer technology diffraction has begun to be modeled using numerical approaches also. Here, method of moments (MoM) is used to model the canonical wedge scattering problem and a novel, generally applicable procedure is introduced to extract diffracted fields and diffraction coefficients.
Citation Count: 1
Parabolic Equation Toolbox for Radio Wave Propagation
(Ieee, 2015) Ozgun, Ozlem; Apaydin, Gokhan; Kuzuoglu, Mustafa; Sevgi, Levent
[No Abstract Available]
Citation Count: 32
PETOOL v2.0: Parabolic Equation Toolbox with evaporation duct models and real environment data
(Elsevier, 2020) Ozgun, Ozlem; Sahin, Volkan; Erguden, Muhsin Eren; Apaydin, Gokhan; Yilmaz, Asim Egemen; Kuzuoglu, Mustafa; Sevgi, Levent
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 features of the second version are as follows: (i) Several evaporation duct models have been developed. (ii) Real atmosphere data have been included in the form of "Binary Universal Form for Representation (BUFR)" data developed by "World Meteorological Organization (WMO)". (iii) Real terrain data have been incorporated into the toolbox in the form of "Digital Terrain Elevation Data (DTED)" developed by "National Imagery and Mapping Agency (NIMA)". (iv) A special add-on has been developed to generate a 3D coverage map of propagation factor/loss on real terrain data. The toolbox can be used for research and/or educational purposes to analyze more realistic propagation scenarios in an easier and flexible manner. Program summary Program title: PETOOL v2.0 (Parabolic Equation Toolbox v2.0) CPC Library link to program files: http://dx.doi.org/10.17632/v8f42rn2zs.1 Licensing provisions: GNU General Public License 3 Programming language: MATLAB (MathWorks Inc.) R2019a. Partial Differential Toolbox, Curve Fitting Toolbox and Mapping Toolbox required. Journal Reference of previous version: O. Ozgun, G. Apaydin, M. Kuzuoglu, and L. Sevgi, PETOOL: MATLAB-based one-way and two-way split-step parabolic equation tool for radiowave propagation over variable terrain, Computer Physics Communications 182 (2011) 2638-2654. Does the new version supersede the previous version?: Yes Reasons for the new version: The new version of the toolbox has been enriched with several add-ons which allow the toolbox to make more realistic analyses with real terrain and atmospheric data. The toolbox has the ability to read real atmospheric data in the form of BUFR data and real terrain data in the form of DTED data. A wide range of evaporation duct models has been incorporated into the toolbox. A special add-on has been developed to generate a 3D coverage map of propagation factor/loss on real terrain data. Hence, the toolbox can be used to analyze more realistic propagation scenarios in an easier and flexible manner. Summary of revisions: (i) Several evaporation duct models have been included with real atmospheric data in BUFR format. (ii) Real terrain data in DTED format have been incorporated into the toolbox. (iii) A special add-on has been developed to generate a 3D coverage map of propagation factor/loss on real terrain data. Nature of problem: This program is designed with a user-friendly GUI for the analysis and visualization of radio-wave propagation over variable terrain on the Earth's surface, and through homogeneous and inhomogeneous atmosphere by using real atmosphere and terrain data. It can easily model both horizontally- and vertically-varying atmospheric refraction (especially ducting) and multipath effects. Solution method: The program employs one-way and two-way Split-Step Parabolic Equation (SSPE) algorithms with a wide-angle propagator. The SSPE is an initial-value problem starting from a reference range (typically from an antenna), and marching out in range by obtaining the field along the vertical direction at each range step, through the use of step-by-step Fourier transformations. The two-way algorithm incorporates the backward-propagating waves into the standard one-way SSPE by utilizing an iterative forward-backward scheme for modeling multipath effects over a staircase-approximated terrain. (C) 2020 Elsevier B.V. All rights reserved.
Citation Count: 0
Three-dimensional split-step-fourier and finite difference time domain-based rectangular waveguide filter simulators: Validation, verification, and calibration
(Wiley, 2016) Apaydin, Gokhan; Sevgi, Levent
The split-step-Fourier-based three-dimensional wave propagation prediction and finite-difference time-domain-based simulators are developed to show network scattering parameters of rectangular waveguide filters with horizontal and/or vertical windows as capacitive and/or inductive irises, respectively. The three-dimensional-split-step parabolic equation simulator is applied to rectangular waveguide filters, and the results are compared with finite-difference time-domain model through tests inside a rectangular waveguide. (c) 2016 Wiley Periodicals, Inc. Int J RF and Microwave CAE 26:660-667, 2016.