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Öğe A compact 4 x 4 reconfigurable MIMO antenna design with adjustable suppression of certain frequency bands within the UWB frequency range(Elsevier Gmbh, 2023) Durukan, Tulun; Altuncu, YaseminThis paper introduces a novel 4 x 4 multiple-input multiple-output (MIMO) antenna design with a reconfigurable operating band within the Ultra-Wideband (UWB) range. The antenna consists of four rectangular radiating elements arranged symmetrically and orthogonally on a defected ground plane. The design incorporates switching elements that allow adjustable and reversible suppression of specific bands within the UWB range, enabling the antenna to operate in three different modes: UWB, X-band, and dual-band with sub-6GHZ and X-band. Thus, a single UWB antenna can serve as three different antennas, suppressing certain frequencies as required. To mitigate mutual coupling between adjacent antenna elements, four thin stubs are strategically placed at the center of the ground plane, forming a square with open corners. When one of the antenna elements is excited, this structure acts as an insulator, ensuring that the surface current is confined solely to that element and not induced in others. Experimental verification of the proposed design was performed by fabricating and testing the antenna. The results indicated good agreement between simulation and measurement data for various parameters, including S-parameters, radiation patterns, gains, and MIMO parameters such as envelope correlation coefficients (ECC), diversity gain (DG), mean effective gain (MEG), and total active reflection coefficient (TARC).Öğe A Microwave Subsurface Imaging Technique for Rough Surfaces(IEEE-Inst Electrical Electronics Engineers Inc, 2023) Ozdemir, Ozgur; Altuncu, YaseminSubsurface microwave imaging is the image reconstruction of objects buried below the surface of a medium, such as soil. Modeling the interactions between the background medium and objects, as well as artifacts due to the limited view of objects, are the major concerns in the image reconstruction process. In this work, we have presented an efficient subsurface microwave imaging technique for the reconstruction of targets in a two-layered medium with an arbitrary rough interface. The use of a computationally expensive two-layered background Green's function in the classical integral equation model is avoided by exploiting the boundary data model where only a simple homogeneous Green's function is required. The contrast source imaging technique is reformulated in terms of boundary data and total variation (TV) regularization is included in the cost function multiplicatively to handle limited view and noisy data in a robust way. Numerical simulations demonstrated that the proposed method dramatically reduces the computational time while keeping the same accuracy in comparison to the classical approach.Öğe A Novel Dual-Wideband Four-Port MIMO Filtenna for Sub-6 GHz 5G Communication Systems(IEEE, 2023) Turkeli, Alper; Gorur, Ali Kursad; Altuncu, YaseminIn this study, a new dual-wideband four-port multi-input multi-output (MIMO) filtenna structure is presented for sub-6 GHz 5G communication systems. Each filtenna element on the MIMO structure is constructed by coupling a dual-wideband filter to the feeding line of a conventional broadband monopole antenna. Four identical filtenna elements are arranged perpendicular to each other for the sake of high isolation and polarization diversity. Furthermore, a new isolation performance improvement approach is introduced by locating a patch decoupling element on the ground plane. The designed four-port MIMO filtenna was fabricated and measured in a very good agreement. The frequency bands were measured at the center frequencies of 3.3 and 5.75 GHz with the fractional bandwidths of 42.4 and 22.6 %, respectively.Öğe A Numerical Method for Electromagnetic Scattering by 3-D Dielectric Objects Buried Under 2-D Locally Rough Surfaces(IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2015) Altuncu, YaseminIn this work, a numerical method is developed to solve a forward-scattering problem of three-dimensional (3-D) objects buried into two half-space media with two-dimensional (2-D) locally rough interface. The proposed method exploits the electric field integral equation (EFIE) formulation of the scattered field which involves the dyadic Green's function of the background medium. Since the required Green's function has no analytical expression (in general), buried object approach (BOA) is applied to calculate it numerically. Method of moments (MoM) is then used to solve the EFIE. The presented method is numerically validated by comparing it with finite difference time-domain (FDTD) method. Furthermore, an elaborative numerical analysis of the proposed method is presented to show its feasibility for various roughness profiles and buried objects.Öğe An extensive FPGA-based realization study about the Izhikevich neurons and their bio-inspired applications(Springer, 2021) Karaca, Zuhra; Korkmaz, Nimet; Altuncu, Yasemin; Kilic, RecaiIn this study, a comprehensive comparison about the hardware costs of the original and the modified Izhikevich neuron models and their applications have been presented to the literature. The chaotic behavior, the coupled version, the synchronization applications, and the control of the synchronization states of the original and the modified Izhikevich neurons have been handled and all of these structures have been also emulated with the FPGA-based realizations for the first time. The aim of this article is to show the suitability and the practicality of the Izhikevich neuron model to the electronic realization applications. According to this aim, firstly, the chaotic behaviors of the original and the modified Izhikevich neuron models have been observed with the numerical simulations. Then, the dynamical behaviors of two coupled original and two coupled modified Izhikevich neurons have been examined via the numerical analyses. After that, the synchronization status of two coupled original and two coupled modified Izhikevich neurons have been controlled by the Lyapunov method and these processes have been simulated numerically. Finally, all of these structures have been implemented with the FPGA device, separately. Therefore, it has been overcome the shortcomings in terms of the electronic realization applications of the Izhikevich neuron model. Besides, the device utilizations of the original and the modified Izhikevich neurons in the FPGA-based implementations have been compared inclusively.Öğe Design of a Novel Dual-Wideband Filtenna(IEEE, 2022) Turkeli, Alper; Gorur, Ali Kursad; Altuncu, YaseminIn this paper, a novel microstrip-fed filter-antenna (filtenna) exhibiting dual-wideband response is introduced. In this direction, a dual-wideband bandpass filter is designed first and then it is integrated into the feed line of a wideband monopole microstrip antenna. The dual-wideband bandpass filter is constructed by stub loaded multi-mode resonators. Two types of stub-loaded multi-mode resonators are coupled to the feeding lines from the filter's input and output ports. The proposed topology allows controlling both bandwidths independently. The designed filtenna was fabricated for the experimental verification. Measurements of the fabricated filtenna show a good agreement with the simulated results. Center frequencies of the proposed filtenna are 3.23 and 5.65 GHz with the fractional bandwidths (FBWs) of 46 % and 21.6 %.Öğe Determination of Guided Wavelength in Multi-layer Microstrip Structures via Open Circuit T-resonator(Institute of Electrical and Electronics Engineers Inc., 2023) Oner, Gulden Gunay Bulut; Basbug, Suad; Altuncu, YaseminIn this work, an open circuit T-resonator is used to determine the guided wavelength of a dielectric structure with multiple layers having different relative permittivity values. The multi-layer substrate consists of two single-sided copper clad FR4 laminates and a layer of PETG material between these laminates to form a sandwich structure. In a T-resonator model, standing waves impacts the insertion loss of the transmission line based on the electrical length of the stub resonator that is linked to this microstrip line. By taking advantage of this property, the wavelength determination is achieved with the help of the results obtained by the Comsol software simulations. Additionally, to illustrate the feasibility of the method, we have simulated a classical microstrip antenna designed by considering the results of the T-resonator simulations. The overall results indicates that the suggested method is useful to determine the guided wavelength of multi-layered structure with different dielectric constants. © 2023 IEEE.Öğe Evaluating the effectiveness of several synchronization control methods applying to the electrically and the chemically coupled hindmarsh-rose neurons(Elsevier Sci Ltd, 2020) Cimen, Zuehra; Korkmaz, Nimet; Altuncu, Yasemin; Kilic, RecaiThis study focuses on the synchronization control between the coupled neurons. The achievements of several synchronization control methods have been checked by evaluating the effects of the synaptic coupling weight alteration on the synchronization. Here, a neural ensemble has been constructed by utilizing the Hindmarsh Rose (HR) Neuron Model. The HR neurons have been linked to each other with the bidirectional coupling. The synchrony or the asynchrony states between these coupled neurons have been observed by using the standard deviation results. Here, firstly, the electrically and the chemically coupled HR neurons have been handled without using any control method, separately and the effects of the synaptic coupling weight alteration on the synchronic firing have been assessed by considering the features of the coupling types. Then, while the electrically coupled HR neurons are generally preferred in the available synchronization control studies; the Lyapunov, the back-stepping, and the feedback synchronization control methods have been adapted to both the electrically and the chemically coupled HR neurons. Thus, a remarkable contribution has been provided to the limited number of studies, which are about the synchronization control of the chemically coupled HR neurons. Also, the synchronization control between the electrically or the chemically coupled HR neurons has been provided by the back-stepping method for the first time. Finally, the differences between the membrane potentials of the coupled neurons have been calculated by utilizing an alternative error function. Since this function calculates the amplitude and the phase errors, separately; the effectiveness of these methods can be evaluated correctly in terms of the performing the minimum differences between the neural dynamics.Öğe İki boyutlu düzgün olmayan yüzeyler altına gömülü üç boyutlu cisimlere ilişkin düz saçılma problemlerinin çözümü(2012) Altuncu, Yasemin; Yapar, Ali[Abstract Not Available]Öğe Multi-Layer I-Slot Microstrip Antenna for Internet of Things Applications(Institute of Electrical and Electronics Engineers Inc., 2023) Oner, Gulden Gunay Bulut; Basbug, Suad; Altuncu, YaseminIn this study, an antenna design is presented for the Internet of things applications that need directional antennas. The antenna design includes a multilayer I-slot microstrip patch antenna and two copper director rod elements. The multilayer I-slot microstrip patch antenna comprises three different layers. The first and third layers are FR4 materials with a dielectric constant of ?1 = 4.15 and a height of h = 1.6 mm while the second layer consists of PETG material with a dielectric constant of ?2 = 2.62 and a height of h = 4 mm. The copper rods utilized in our design are used to increase the directivity of the antenna and have a diameter of R = 2.7 mm. PETG material used in the antenna design is produced with a 3D printer. The simulations of the designed antenna in this study are carried out by using Comsol Multiphysics software. The proposed antenna produced after the design and the simulation studies. The simulation and measurement results are compared and found compatible. The antenna designed in this study for 2400-2483.5 MHz ISM band applications has a gain of 7.2 dBi and a bandwidth from 2398 MHz to 2554 MHz. © 2023 IEEE.Öğe On the scattering of electromagnetic waves by periodic rough dielectric surfaces: A BOA solution(IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2008) Yildiz, Selda; Altuncu, Yasemin; Yapar, Ali; Akduman, IbrahimA new approach for the scattering of electromagnetic (EM) waves from periodic dielectric rough surfaces is addressed. The method is an extension of the buried object approach (BOA), which is developed for rough surfaces of infinite extend, to the present problem. The BOA allows to model the original problem as the scattering of EM waves from cylindrical objects located in a two-half-space medium with planar interface. Then, the problem is reduced to the solution of a Fredholm integral equation of second kind through the periodic Green's function of two-half-space medium. The periodic Green's function of two-half-space medium is calculated via the Floquet mode expansion, whose numerical evaluation can be accelerated by using effective methods. The method can also be used to solve the scattering problems of rough surfaces of infinite extend and having a localized roughness. Numerical simulations show that the method yields effective and accurate results for surfaces of arbitrary variation.Öğe Reconstruction of 3D Objects Buried Under Into Half-Space by Using Variational Born Iterative Method(IEEE, 2019) Akdogan, Riza Erhan; Altuncu, YaseminThis paper propose a method based on variational Born iterative method to solve the inverse scattering problem of three-dimensional objects buried into two-part space. The addressed problem is substantially complex in both mathematical and computational aspect, because of the fact that the objects to be reconstructed are both three-dimensional and embedded into half-space. Variation born iterative method (VBIM) is as successful as distorted born iterative method (DBIM) that is the most widely used method in the reconstruction of high-contrast objects among Born-based methods. Furthermore, VBIM is much faster than DBIM because it doesn't require a forward problem solution for the calculation of background Green's function in every iteration step, such as DBIM. Various numerical implementations have been performed to reveal the effectiveness of the method and it is observed that the method is very successful in the reconstruction of multiple objects with arbitrary geometry.Öğe Reconstruction of 3D Objects Buried under into Half-Space by Using Variational Born Iterative Method(Institute of Electrical and Electronics Engineers Inc., 2019) Akdogan, Riza Erhan; Altuncu, YaseminThis paper propose a method based on variational Born iterative method to solve the inverse scattering problem of three-dimensional objects buried into two-part space. The addressed problem is substantially complex in both mathematical and computational aspect, because of the fact that the objects to be reconstructed are both three-dimensional and embedded into half-space. Variation born iterative method (VBIM) is as successful as distorted born iterative method (DBIM) that is the most widely used method in the reconstruction of high-contrast objects among Born-based methods. Furthermore, VBIM is much faster than DBIM because it doesn't require a forward problem solution for the calculation of background Green's function in every iteration step, such as DBIM. Various numerical implementations have been performed to reveal the effectiveness of the method and it is observed that the method is very successful in the reconstruction of multiple objects with arbitrary geometry. © 2019 IEEE.Öğe Reconstruction of Two-Dimensional Objects Buried into Three-Part Space with Locally Rough Interfaces via Distorted Born Iterative Method(Emw Publishing, 2019) Altuncu, Yasemin; Durukan, Tulun; Akdogan, Riza ErhanIn this paper, the reconstruction problem of inaccessible objects buried into a three-part space with locally rough interfaces is solved by Distorted Born Iterative Method (DBIM). DBIM requires the calculation of the background electric field and Green's function in every iteration step via the solution of the direct scattering problem. Here, they are calculated numerically by using the buried object approach (BOA) which is very useful in the solutions of the problems including stratified media with locally rough interfaces. Various numerical applications have been performed to demonstrate the applicability and efficiency of the method. The method was found to be very successful in reconstructing moderate contrast objects when they were buried in the middle space. In this case, the method works effectively even if the buried objects and interface roughnesses have complex geometric structures. Moreover, the multiplicity of buried objects has no negative effect on the reconstruction results. Nevertheless, the results of reconstruction deteriorate when objects are buried in the bottom space. However, the accuracies of them are still on an acceptable level in this situation.Öğe Reconstruction of two-dimensional objects buried into three-part space with locally rough interfaces via distorted born iterative method(Electromagnetics Academy, 2019) Altuncu, Yasemin; Durukan, Tulun; Akdogan, Riza ErhanIn this paper, the reconstruction problem of inaccessible objects buried into a three-part space with locally rough interfaces is solved by Distorted Born Iterative Method (DBIM). DBIM requires the calculation of the background electric field and Green’s function in every iteration step via the solution of the direct scattering problem. Here, they are calculated numerically by using the buried object approach (BOA) which is very useful in the solutions of the problems including stratified media with locally rough interfaces. Various numerical applications have been performed to demonstrate the applicability and efficiency of the method. The method was found to be very successful in reconstructing moderate contrast objects when they were buried in the middle space. In this case, the method works effectively even if the buried objects and interface roughnesses have complex geometric structures. Moreover, the multiplicity of buried objects has no negative effect on the reconstruction results. Nevertheless, the results of reconstruction deteriorate when objects are buried in the bottom space. However, the accuracies of them are still on an acceptable level in this situation. © 2019, Electromagnetics Academy. All rights reserved.Öğe Yer altına gömülü üç boyutlu cisimlerin bozulmuş born iteratif yöntemi ile tespitedilmesi(2021) Akdoğan, Rıza Erhan; Dilaver, Kamil Fatih; Durukan, Tülün; Altuncu, YaseminBu çalışmada, yer altında gömülü üç boyutlu (3B) cisimlerin geometrik ve elektriksel özelliklerinin yer üstünden yapılan ölçümlerle belirlenmesine yönelik bir elektromanyetik ters saçılma problemi ele alınmıştır. Problemin çözümü bozulmuş born iteratif yöntemi (Distorted Born Iterative Method - DBIM) kullanılarak yapılmıştır. Hava ve toprak ortamlarını birbirinden ayıran ara yüzey yukarıdan bir elektromanyetik dalga kaynağı ile aydınlatılmış ve yine yukarıdaki bir bölge boyunca elektrik alan ölçümleri yapılmıştır. Elektromanyetik dalga kaynağı olarak peş peşe farklı geliş açılarıyla gönderilen düzlem dalgalar kullanılırken ölçümler bir düzlem boyunca birden fazla noktada alınmıştır. İlgilenilen hacimsel bir bölgede bulunan cisimlerin geometrik ve elektrikselözellikleri, bu bölgenin kompleks dielektrik sabitinin belirlenmesi sonucu ortaya çıkartılmaktadır. Sunulan yöntemin, yer altındaki rastgele geometrili üç boyutlu nesnelerin tespitindeki başarısını göstermek için çeşitli sayısal sonuçlar sunulmuştur. Elde edilen sonuçlar, bozulmuş born iteratif yönteminin düşük ve orta düzeyde kontrasta sahip cisimlerin hem geometrik hem de dielektrik özelliklerinin belirlenmesinde oldukça başarılı olduğunu ortaya koymaktadır. Yüksek kontrastlı cisimlerin ise yeri ve geometrik özellikleri başarıyla bulunurken bağıl dielektrik sabiti ve iletkenlikleri gerçek değerlerinden daha düşük seviyelerde bulunmuştur.
