Papers by yasemin altuncu
A Microwave Subsurface Imaging Technique for Rough Surfaces
IEEE Geoscience and Remote Sensing Letters, Dec 31, 2022
IEEE Geoscience and Remote Sensing Letters, Apr 1, 2007
We present a method to detect and locate dielectric objects buried under a rough surface. The met... more We present a method to detect and locate dielectric objects buried under a rough surface. The method is based on the determination of appearing surface impedance of the half-space, where the dielectric objects are located. The equivalent surface impedance is obtained directly from the impedance boundary condition, which requires the knowledge of the electric field and its normal derivative on the surface. These field values are obtained by measuring the far-field data and using single-layer-potential representation of the scattered field. Using the equivalent surface impedance, one can detect and locate the buried objects. The efficiency and efficacy of the method are tested via numerical simulations.
Microwave and Optical Technology Letters, 2007
14.0 mm, W 4 ϭ 2.8 mm, W 5 ϭ 1.0 mm, L ϭ 60.0 mm, W ϭ 60.0 mm, respectively. Based on the dimensi... more 14.0 mm, W 4 ϭ 2.8 mm, W 5 ϭ 1.0 mm, L ϭ 60.0 mm, W ϭ 60.0 mm, respectively. Based on the dimensions, many samples have been fabricated and measured. The return loss of the antenna is measured on a HP-8720ET vector network analyzer. The simulated and measured return losses are shown in Figure 2. It may be seen that two results agree well with each other. The result shows that the impedance bandwidth for S 11 Յ Ϫ10 dB of the antenna is about 10% at 2.4 GHz and 15% at 5 GHz, respectively. Radiation patterns of the antenna are measured in a chamber and the results are given in Figure 3. In the figure, it may be seen that the radiation patterns at the dual-band are almost the same. And its cross-polarization is better than 15 dB over the operation frequency band. The measured gain of the antenna is given in Figure 4. 3. CONCLUSION A novel dual-band slot-antenna for WLAN applications is presented. The antenna is composed of two narrow slots fed by a microstrip-line. Its configuration is very simple but it has a good performance. Therefore, it is a useful candidate antenna for WLAN application.
On the Relation between Surface Impedance and Shape of the Perfectly Conducting Objects
A new, simple and fast method for the solution of electromagnetic scattering problems related to ... more A new, simple and fast method for the solution of electromagnetic scattering problems related to perfectly conducting objects of arbitrary shape is presented. The method is based on the representation of the conducting object in terms of a circular one having higher order impedance boundary condition on its surface. Through the Taylor expansion of the total field on the minimum circle covering the object, a universal relation between higher order surface impedances and the shape of the object is obtained. Numerical simulations show that the method yields quite accurate results
IEEE Transactions on Geoscience and Remote Sensing, Jun 1, 2006
Düzlemsel Elektromagnetik Dalgaların Periyodik Bir Empedans Yüzeyinden Saçılması
Elektromagnetik dalgaların düzgün olmayan yüzeye sahip bir yarı-uzay içine gömülü cisimlerden saçılması
Bu calismada, engebeli yuzeyler altina gomulu cisimlere iliskin elektromagnetik sacilma problemle... more Bu calismada, engebeli yuzeyler altina gomulu cisimlere iliskin elektromagnetik sacilma problemlerinin cozumu icin yeni ve efektif bir yontem verilmistir. Soz konusu problemler dielektrik mayinlarin tespiti, tahribatsiz muayene, yer kabugu altindaki catlak ve faylarin belirlenmesi gibi pek cok uygulama alanina sahip olmalari sebebiyle elektromagnetik teoride buyuk oneme sahiptirler. Her ne kadar bu uygulamalar ters sacilma problemlerinin konusu olarak bilinse de bunlara iliskin duz sacilma problemlerinin cozumu, ters problem algoritmalarinin elde edilmesi sirasinda ortaya cikan zorluklarin ustesinden gelinmesine buyuk katkilar saglamaktadir. Bu calismada verilen yontemde ilk olarak duzlemsel olmayan bir arayuzeyle birbirinden ayrilmis iki parcali uzaya iliskin Green fonksiyonu kullanilarak engebeli yuzey altina gomulu cisimlerden sacilma problemi ikinci tip bir Fredholm integral denkleminin cozumune indirgenmistir. Elde edilen integral denklemin cozumu Moment yontemi kullanilarak yapilmistir. Diger taraftan, arayuzeyi engebeli iki parcali uzayin Green fonksiyonunun belirlenmesi de ayri ve zor bir problemdir. Bu problemin cozumu “gomulu cisim yaklasimi” adini verdigimiz ve yuzeydeki puruzluluk ve engebelerin, duzlemsel arayuzeyle birbirinden ayrilmis olan iki parcali uzaya gomulu cisimler olarak kabul edilmesi esasina dayali bir yaklasim kullanilarak yapilmistir. Bu tur bir yaklasim, problemi duzlemsel arayuzeyle birbirinden ayrilmis iki parcali uzaya gomulu silindirik cisimlerden, silindirik dalgalarin sacilmasi problemine donusturmeye olanak vermektedir. Yontem, lokal bir aralikta, degisimi nasil olursa olsun duzgun olmayan tum yuzeyler icin oldukca iyi sonuclar vermektedir. Yapilan sayisal uygulamalar ile yontemin dogrulugu ve cesitli parametrelerin sacilan alana etkisi gosterilmistir. Anahtar Kelimeler: Gomulu cisim yaklasimi, elektromagnetik sacilma, engebeli yuzey.
Electromagnetic Scattering Analysis from Rough Surfaces via Buried Object Approach and FDTD
ABSTRACT In this study the analysis of electromagnetic wave scattering from one dimensional local... more ABSTRACT In this study the analysis of electromagnetic wave scattering from one dimensional locally rough interface between two dielectric half-spaces is realized using buried object approach (BOA). The validation and verification of the this method are fulfilled by the comparison of the results with the data obtained via Finite Difference Time Domain (FDTD) Technique. Analysis of electromagnetic scattering from rough surfaces constitutes an important and inter-esting class of problems in electromagnetic theory due to its potential applications in modeling of ground wave propagation, remote sensing of geophysical terrains such as snow, soil and vegetation, detection of buried objects under rough surfaces etc. Due to the enormous efforts devoted in the last five decades several analytical and numerical techniques, such as perturbation theories, physical optic approximations in frequency domain and FDTD in time domain, have been developed [1–3] for the investigation of scattering from rough surfaces. The aim of this work is to apply buried object approach (BOA) [4] to the solution of scattering problems related to rough interfaces between two lossy dielectric half-spaces in the case of line source illumination as well as to analyze the validity of the proposed technique by comparing with FDTD for different scattering scenarios. We consider one dimensional locally rough surfaces for the sake of simplicity. In our approach we consider the irregularities of the rough surface as buried objects in a two half-spaces medium with planar interface, which allows us to formulate the problem as a scattering problem related to cylindrical bodies of arbitrary cross sections. Through the Green's function of the two half spaces medium where the irregularities are buried, the problem is reduced to the solution of a Fredholm integral equation of second kind which can be treated by using one of the known techniques. In this work, we solved the integral equation via an application of Method of Moments (MoM) by reducing it to a linear system of equations. The computational cost is directly proportional to the number of irregularities of the surface and their sizes. As a result the method is very effective for surfaces having a localized roughness, arbitrary rms height and slope. The method permits us to obtain both the near and far field expressions of the scattered wave. The results obtained from presented method are compared with the data obtained using FDTD. The time domain data, accumulated at required observation points in a single FDTD run, are transformed into frequency domain using an off-line discrete Fourier transform algorithm. The good agreement is observed between BOA and FDTD results in the range of their validity regions.
Surface Impedance Modelling of Perfectly Conducting Rough Surface
Impedance boundary conditions (IBC) are widely used to simplify the mathemat- ical and numerical ... more Impedance boundary conditions (IBC) are widely used to simplify the mathemat- ical and numerical complexities in the solution of scattering problems in electromagnetic theory and have been the subject of the several research activities (1{3). Along this line, efiective impedance boundary conditions have been developed for such objects as the earth surface, thin layers of dielectrics and multilayered dielectric structures. The surface impedance is in general a tensor and it may be an inhomogeneous scalar under an isotropic assumption. The determination of the IBC for a given scatterer constitutes an important class of problems in the electromagnetic theory and various approximate methods have been established in the literature for special kind of geometries and surfaces (4). In all these methods one flrst tries to solve the direct scattering problem for a given scattering structure and then express the IBC in terms of the electric and magnetic fleld on the boundary. The aim of this paper is to derive a special kind of impedance boundary condition for perfectly conducting rough surfaces. In the approach that we consider here, the rough surface is replaced by a plane which is parallel to the mean surface having a standard impedance boundary condition (SIBC) or higher order impedance boundary condition (HIBC) on its surface. Through the Taylor expansion of the scattered wave it can be shown that the surface impedances which appear in the impedance boundary condition are directly related to the surface variation of the perfectly conducting rough surface. It is shown that the surface impedances are independent of the incidence angle and then yield to have an universal equivalent boundary condition for perfectly conducting surfaces. Representing the perfectly conducting rough surface in terms of a plane surface with inhomogeneous impedance boundary condition yields a simpler scattering problem. Clearly, the scattering from perfectly conducting objects have been extensively studied in the open literature and surface based integral equation techniques have been developed. Such a formulation generally yields a singular integral equation which need to pay a special care in the numerical solution. On the other hand scattering from plane surface with inhomogeneous impedance boundary conditions can be solved easily with a Fourier transform representation of the scattered wave. In such a case the problem can be easily reduced to the solution of a Fredholm integral equation of second kind in the spectral domain. Numerical simulations show that when the roughness has a smooth and local variation, the SIBC yield very accurate results.
On the Relation between Surface Impedance and Shape of the Perfectly Conducting Objects
Proceedings of XIth International Seminar/Workshop on Direct and Inverse Problems of Electromagnetic Acoustic Wave Theory, 2006
A new, simple and fast method for the solution of electromagnetic scattering problems related to ... more A new, simple and fast method for the solution of electromagnetic scattering problems related to perfectly conducting objects of arbitrary shape is presented. The method is based on the representation of the conducting object in terms of a circular one having higher order impedance boundary condition on its surface. Through the Taylor expansion of the total field on the minimum circle covering the object, a universal relation between higher order surface impedances and the shape of the object is obtained. Numerical simulations show that the method yields quite accurate results
2006 IEEE International Symposium on Geoscience and Remote Sensing, 2006
Scattering of Electromagnetic Waves by Periodic Rough Surfaces
Periodic structures often appear in the applications such as antenna design, microwave systems, m... more Periodic structures often appear in the applications such as antenna design, microwave systems, metamaterials etc. and the analysis of electromagnetic wave propagation in such structures has an important place in the electromagnetic theory. Among them scattering of electromagnetic waves from rough surfaces is important due to both theoretical and practical points of view. For the periodic surfaces having a slow variation, one can obtain the solution under the Rayleigh hypothesis in terms of Floquet modes. On the other hand, for surfaces which does not satisfy the Rayleigh condition it is required to develop new methodologies. In this paper, it is aimed to give two methodologies for the solution of scattering problems related to periodic dielectric rough surfaces which are valid beyond the limits of the Rayleigh Hypothesis. The first method is the extension of buried object approach (BOA) given in (4) to the present problem. The basic idea here is that the irregularities of the rough...
Imaging of dielectric objects buried under a rough surface via distorted born iterative method
Journal of Physics: Conference Series, 2008
ABSTRACT A method is given for the shape, permittivity and conductivity reconstruction of lossy d... more ABSTRACT A method is given for the shape, permittivity and conductivity reconstruction of lossy dielectric objects buried under rough surfaces using the Distorted Born Iterative Method (DBIM). The method is based on the refreshing of the Green's function of the two-part space media with rough interface by updating the complex permittivity of the reconstruction domain at each iteration step. The scattered field data are measured at multiple locations for multiple transmitters operating at a single frequency where both transmitters and receivers are located above the rough surface interface. The Green's function of the problem is obtained by using the buried object approach (BOA) method where the fluctuations of the rough surface from the flat one are assumed to be buried objects in a two-part space with planar interface. The performance of the method is tested by some numerical applications and satisfactory results are obtained.
IEEE Transactions on Geoscience and Remote Sensing, 2008
A new approach for the scattering of electromagnetic (EM) waves from periodic dielectric rough su... more A 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.
IEEE Transactions on Geoscience and Remote Sensing, 2006
IEEE Geoscience and Remote Sensing Letters, 2007
We present a method to detect and locate dielectric objects buried under a rough surface. The met... more We present a method to detect and locate dielectric objects buried under a rough surface. The method is based on the determination of appearing surface impedance of the half-space, where the dielectric objects are located. The equivalent surface impedance is obtained directly from the impedance boundary condition, which requires the knowledge of the electric field and its normal derivative on the surface. These field values are obtained by measuring the far-field data and using single-layer-potential representation of the scattered field. Using the equivalent surface impedance, one can detect and locate the buried objects. The efficiency and efficacy of the method are tested via numerical simulations.
Canadian Journal of Physics, 2007
A new method for the scattering of electromagnetic waves from a locally rough interface between t... more A new method for the scattering of electromagnetic waves from a locally rough interface between two dielectric half-spaces is addressed. The method is based on the assumption that the perturbations of the rough surface from the planar interface are objects buried in a two-half spaces media with a planar boundary, which allows one to reduce the problem to the scattering of electromagnetic waves by cylindrical bodies of arbitrary cross section. Then through the Green's function of the background medium one obtains a Fredholm integral equation of the second kind, which is solved via an application of the Method of Moments. The present formulation permits one to get the near and far field expressions of the scattered wave. The method is effective for surfaces having a local roughness and arbitrary root mean square heights but does not work in the case of a highly conductive background medium.PACS Nos.: 41.20.–q, 41.20.Jb, 03.50.De
Microwave and Optical Technology Letters, 2007
14.0 mm, W 4 ϭ 2.8 mm, W 5 ϭ 1.0 mm, L ϭ 60.0 mm, W ϭ 60.0 mm, respectively. Based on the dimensi... more 14.0 mm, W 4 ϭ 2.8 mm, W 5 ϭ 1.0 mm, L ϭ 60.0 mm, W ϭ 60.0 mm, respectively. Based on the dimensions, many samples have been fabricated and measured. The return loss of the antenna is measured on a HP-8720ET vector network analyzer. The simulated and measured return losses are shown in Figure 2. It may be seen that two results agree well with each other. The result shows that the impedance bandwidth for S 11 Յ Ϫ10 dB of the antenna is about 10% at 2.4 GHz and 15% at 5 GHz, respectively. Radiation patterns of the antenna are measured in a chamber and the results are given in Figure 3. In the figure, it may be seen that the radiation patterns at the dual-band are almost the same. And its cross-polarization is better than 15 dB over the operation frequency band. The measured gain of the antenna is given in Figure 4. 3. CONCLUSION A novel dual-band slot-antenna for WLAN applications is presented. The antenna is composed of two narrow slots fed by a microstrip-line. Its configuration is very simple but it has a good performance. Therefore, it is a useful candidate antenna for WLAN application.
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Papers by yasemin altuncu