Scattering of electromagnetic waves by bodies buried in a half-space with rough surface

Bu çalışmada, engebeli yüzeyler altına gömülü cisimlere ilişkin elektromagnetik saçılma problemlerinin çözümü için yeni ve efektif bir yöntem verilmiştir.  Söz konusu problemler dielektrik mayınların tespiti, tahribatsız muayene, yer kabuğu altındaki çatlak ve fayların belirlenmesi gibi pek çok uygulama alanına sahip olmaları sebebiyle elektromagnetik teoride büyük öneme sahiptirler. Her ne kadar bu uygulamalar ters saçılma problemlerinin konusu olarak bilinse de bunlara ilişkin düz saçılma problemlerinin çözümü, ters problem algoritmalarının elde edilmesi sırasında ortaya çıkan zorlukların üstesinden gelinmesine büyük katkılar sağlamaktadır. Bu çalışmada verilen yöntemde ilk olarak düzlemsel olmayan bir arayüzeyle birbirinden ayrılmış iki parçalı uzaya ilişkin Green fonksiyonu kullanılarak engebeli yüzey altına gömülü cisimlerden saçılma problemi ikinci tip bir Fredholm integral denkleminin çözümüne indirgenmiştir. Elde edilen integral denklemin çözümü Moment yöntemi kullanılarak yapılmıştır. Diğer taraftan, arayüzeyi engebeli iki parçalı uzayın Green fonksiyonunun belirlenmesi de ayrı ve zor bir problemdir. Bu problemin çözümü “gömülü cisim yaklaşımı” adını verdiğimiz ve yüzeydeki pürüzlülük ve engebelerin, düzlemsel arayüzeyle birbirinden ayrılmış olan iki parçalı uzaya gömülü cisimler olarak kabul edilmesi esasına dayalı bir yaklaşım kullanılarak yapılmıştır. Bu tür bir yaklaşım, problemi düzlemsel arayüzeyle birbirinden ayrılmış iki parçalı uzaya gömülü silindirik cisimlerden, silindirik dalgaların saçılması problemine dönüştürmeye olanak vermektedir. Yöntem, lokal bir aralıkta, değişimi nasıl olursa olsun düzgün olmayan tüm yüzeyler için oldukça iyi sonuçlar vermektedir. Yapılan sayısal uygulamalar ile yöntemin doğruluğu ve çeşitli parametrelerin saçılan alana etkisi gösterilmiştir.  Anahtar Kelimeler: Gömülü cisim yaklaşımı, elektromagnetik saçılma, engebeli yüzey.In this work, a novel and effective method is presented for the solution of the problems related to objects buried beneath rough surfaces. Such problems are of great importance in electromagnetic theory due to the their potential applications in practice such as detection and location of dielectric mines, non-destructive testing, determination of underground cracks and earthquake etc. Although these applications are recognized as an “inverse scattering problem” in electromagnetic theory, the solutions of the related direct scattering problems make a valuable contribution to overcome difficulties which may occur in the investigation of inversion algorithms. In this work we consider cylindrical bodies buried in a half-space having one dimensional locally rough surface in the case of plane wave illumination. The upper and lower half spaces separated by a rough interface are filled with simple non-magnetic materials. The material of the buried bodies are assumed to be inhomogeneous. Geometry of the problem is homegenoeus in the direction. The scattering problem considered here is to determine the effect of the buried body as well as the roughness of the surface on the propagation of electromagnetic waves excited in the upper half space. To this end the bodies are illuminated by a time harmonic plane wave whose electric field vector is always parallel to direction namely; where is the incidence direction and  is the wave number of the upper half space. Then the problem is reduced to scalar one and the total field function satisfies the reduced wave equation in the sense of distributions (İdemen, 1973), where  denotes the wave number of the whole space and. The contributions of the buried body to the total field i.e.: scattered field consists in the difference and satisfies the equation  under Sommerfeld radiation condition. Here  stands for the so called object function related to buried body and it is zero outside the body.  Through the Green’s function of the two-part space with rough interface differential equation  for the scattered field is reduced to the solution of a Fredholm integral equation of second kind, namely where B is the cross section of the  body in Ox1x2 plane. The above integral equation is solved here by using Method of Moments (MoM). On the other hand the determination of the Green's function constitutes a separate and difficult problem in the case of two-half spaces characterized by different media and separated by a rough interface. Here we give a new and general method called “buried object approach” (BOA) which is based on the assumption that the perturbations of the rough surface from the planar one are objects located at both sides of the planar boundary. The Green’s function can be written as where is the well known Green’s  function related to two-part space with planar boundary. The second term is the contribution of the surface roughness and satifies the equation where  is the object function related to surface roughness. Modelling the roughness in such a way lead us to formulate the problem as scattering of cylindrical waves from finite number of buried homogeneous cylindrical bodies, which is solved through a numerical method based on MoM. The present method is very effective for surfaces having a localized roughness, arbitrary rms height and slope. The locality limitation of the surface is to guarantee to have finite number of objects in the evaluation of the Green’s function. The method permits us to obtain both near and far field expressions of the scattered wave for buried objects of arbitrary number and shapes and there is no restriction on the level of the roughness. Keywords: Buried object approach, electromagnetic scattering, rough surface

A Numerical Method for Electromagnetic Scattering by 3-D Dielectric Objects Buried Under 2-D Locally Rough Surfaces

WOS: 000359251200032In 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.TUBITAK, Turkish Scientific and Technological Research Council [108E175]This work was supported by TUBITAK, Turkish Scientific and Technological Research Council under Grant 108E175

Design of a novel dual-wideband filtenna

In 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 %

Farklı İki Kontrolör Kullanılarak Kuplajlanan Senkron FHN Nöronları Arasındaki Hata Değerlerinin Belirlenmesi

Bu çalışmada kuplajlı iki FHN nöron modeli kullanılarak yapılan senkronizasyon ve kontrol çalışmaları ele alınmıştır. İki nöron dinamiği arasındaki senkronizasyonu sağlamak için Lyapunov ve geri adımlamalı kontrol yöntemleri kullanılmış olup, kuplajlı iki FHN nöronunun dinamik davranışları arasındaki farklılıkların tespit edilmesi amacıyla çeşitli hata değerleri hesaplatılmıştır. Kuplajlı iki nöron arasındaki senkronizasyonun sağlanmasında kullanılan yöntemlerin etkinlikleri hem genlik hem de faz hatası açısından “ortalama karesel hata” fonksiyonu ve “faz hata” fonksiyonu kullanılarak değerlendirilmiştir.</p

On the scattering of electromagnetic waves by periodic rough dielectric surfaces: A BOA solution

WOS: 000259231600012A 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.Turkish Scientific and Technological Research Council (TUBITAK) [105E029]Manuscript received November 13, 2007; revised January 28, 2008. This work was supported by the Turkish Scientific and Technological Research Council (TUBITAK) under Grant 105E029

An extensive FPGA-based realization study about the Izhikevich neurons and their bio-inspired applications

In 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

Evaluating the effectiveness of several synchronization control methods applying to the electrically and the chemically coupled hindmarsh-rose neurons

© 2020 Elsevier B.V.This 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