Browsing by Author "Kuyucuoglu F."
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Item Analysis of thin dielectric cylindrical reflector having an arbitrary conic section profile illuminated by complex line source: H-polarization case(IEEE Computer Society, 2014) Oguzer T.; Kuyucuoglu F.; Avgin I.; Altintas A.Arbitrary conic section profile and thin dielectric reflector is analyzed by using the Method of Analytical Regularization (MAR) technique based on Riemann-Hilbert problem and Fourier inversion procedures. The reflector surface is assumed to be illuminated by an H-polarized complex line source type feed antenna. The convergence of the solution is verified and some changes in the radiation patterns are obtained especially for rather thicker cases. © 2014 IEEE.Item Radiation performance of metamaterial cylindrical reflector antenna having a conic section profile illuminated by An E-polarized complex source line beam(IEEE Computer Society, 2014) Kuyucuoglu F.; Oguzer T.; Avgin I.Parabolic conic section profile, cylindrical metamaterial reflector antenna radiation characteristic is analyzed by using the Method of Analytical Regularization (MAR) techniques. E polarized complex source point is located at the focal point is used to illuminate the antenna. Far field radiation patterns are obtained for metamaterial and dielectric cases. © 2014 IEEE.Item Analysis of a thin, penetrable, and nonuniformly loaded cylindrical reflector illuminated by a complex line source(Institution of Engineering and Technology, 2017) Oğuzer T.; Kuyucuoglu F.; Avgin I.; Altintas A.A thin, penetrable, and cylindrical reflector is illuminated by the incident field of a complex source point. The scattered field inside the reflector is not considered and its effect is modelled through a thin layer generalised boundary condition (GBC). The authors formulate the structure as an electromagnetic boundary value problem and two resultant coupled singular integral equation system of equations are solved by using regularisation techniques. The GBC provides us to simulate the thin layer better than the resistive model which is applicable only for very thin sheets. Hence, the more reliable data can be obtained for high-contrast and low-loss dielectric material. The scattering and absorption characteristics of the front-fed and offset reflectors are obtained depending on system parameters. Also, the effects of the edge loading are examined for both E- and Hpolarisations. The convergence and the accuracy of the formulation are verified in reasonable computational running time. © The Institution of Engineering and Technology 2017.Item Reflection and transmission properties of a graphene-dielectric-thin resistive layer structure in the THz range(Elsevier GmbH, 2022) Oğuzer T.; Kuyucuoglu F.We studied two-dimensional planar dielectric slab, sandwiched by graphene and thin resistive layer from two sides. Problem geometry is illuminated by a H-polarized electromagnetic plane wave from upper side. It is expected to observe the reflection and transmission performance of such a composite slab geometry depending on the electrical and geometrical parameters. We used the local reflection and transmission coefficients method to determine the overall performance. It is seen that the proper selection of the electrical resistivity of the thin resistive layer reduces the reflection from lower boundary of slab and the electrical thickness becomes less important for high THz range. Then, the geometry turns to be an air-dielectric interface. This is a novel finding and completely different from the pure dielectric slab without coatings which has frequency dependent characteristics. Also higher reflections are observed due to the higher conductivity of graphene in the low THz range. Furthermore, a sample finite plate is constructed in a same manner and it is modeled by using CST software. Presented method using equivalent 2D profile model and CST results are compared and very good consistency is observed. In both cases, the reflection can be controlled with the chemical potential at low THz range and the selection of the relative permittivity of the dielectric material determines the reflectance level at higher THz scale. We demonstrate these statements in the numerical results section for various problem parameters and angle of incidence. © 2022 Elsevier GmbHItem A novel approach to the design of multi section ultra-wideband Jaumann absorber(Elsevier GmbH, 2023) Kuyucuoglu F.A novel ultra-wideband Jaumann absorber design and analytical procedure that greatly enhance the absorption bandwidth and absorptivity level using few dielectric layers are described. The absorptivity bandwidth of the proposed structure is much better than the traditional absorbers. In Jaumann absorbers, determining resistivity of resistive sheets is a complex task and optimization techniques are generally utilized for the solution. The new contribution given in this paper is that the reflected waves from each boundary inside the dielectric layers are eliminated. Therefore, input reflection coefficient is obtained analytically using Binomial expansion without any approximation. Then a binomial matching procedure is applied to obtain the ultra-wideband absorption. Absorption enhancement is achieved by quarter wavelength dielectric slabs, resistive sheets with critical resistivities and a metallic ground plane backed final dielectric layer with high permittivity. Proposed structure is designed for normal illumination. Parallel and perpendicular polarizations are also studied for oblique incidences. Absorptivity and reflectivity variations are presented versus frequency in 0–40 GHz band for the 20 GHz design frequency for several structures. It is shown that choosing three layers backed with a final layer (εrb=20) structure gives absorptivity greater than 90% in a 6.8–33.2 GHz band region with a fractional bandwidth of 132%. CST Microwave Studio and AWR programs are used to prove the correctness of the proposed method. Great consistency is observed and demonstrated in the numerical results section. © 2023 Elsevier GmbHItem A new approach to design multi section wideband transmissive absorber using thin resistive sheets and dielectric slabs(Elsevier GmbH, 2023) Oğuzer T.; Kuyucuoglu F.A new design and analytical procedure are presented that greatly enhance the absorption bandwidth and absorptivity level with few dielectric layers without using the metallic ground plane. The performance of the proposed structure is beyond what is possible with Salisbury screen or Jaumann absorber. The performance improvement is obtained using the resistive sheets coated on the surface of each lossless dielectric slab. Reflected waves inside each dielectric layer are eliminated and input reflection coefficient can easily be written with the aid of binomial expansion without any approximation. So we can apply Binomial design and considerable improvement at the absorption level and bandwidth is realized by the selection of the resistive sheets with the critical resistivity values. Alternatively, we observed that transmission is independent from frequency and layer number and it can be controlled only by the initial and final layer's dielectric constants. Two cases are analyzed as air to air and air to dielectric. Absorptivity, transmittivity and reflectivity variations are presented versus frequency in 0–20 GHz band, in both cases. It is shown that choosing three layers backed with a final layer (εrb=20) structure in air to air case gives absorptivity greater than 90% in 5.45–14.55 GHz band where fractional bandwidth is 91% at 10 GHz design frequency. The design is performed at normal incidence and also wide angular stability at a reasonable level is presented. CST Microwave Studio and AWR simulation programs are also used to prove the correctness of the proposed method. © 2023 Elsevier GmbH