Browsing by Author "Oğuzer T."
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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 Improving radiation performance of the cylindrical dielectric reflector sandwiched by thin resistive layer illuminated by a complex line source(Elsevier GmbH, 2021) Kuyucuoğlu F.; Oğuzer T.We studied two-dimensional (2-D) thin dielectric parabolic reflector, sandwiched by thin resistive layer from both sides. It is illuminated by an E-polarized electromagnetic plane wave from front side. It is expected to observe the radiation performance of such a composite reflector depending on the electrical and geometrical parameters. We applied two-sided generalized boundary conditions which are modified for a thin multilayer structure. The electromagnetic boundary value problem is formulated and it finally produced a set of two coupled singular integral equations (SIEs). They are handled with the analytical regularization method based on the Riemann-Hilbert Problem solution. The final numerical results are in the Fredholm second-kind matrix equation form and any desired accuracy can possibly be obtained. Also the solution procedure guarantees the convergence. It is observed that the proper selection of the electrical resistivity of the thin resistive layer produces wider bandwidth in the aperture efficiency and the directivity variation approaches to the perfect electric conductor (PEC) reflector case for higher dielectric constants. This selection can increase the allowable frequency band in the applications by coating dielectric layer from both sides. We demonstrate these statements in the numerical results section in the microwave frequency range. © 2021 Elsevier GmbHItem 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 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