Browsing by Author "Kuyucuoglu, F"

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    Reflection and transmission properties of a graphene-dielectric-thin resistive layer structure in the THz range
    Oguzer, 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.
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    A new approach to design multi section wideband transmissive absorber using thin resistive sheets and dielectric slabs
    Oguzer, 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 inde-pendent 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 (epsilon rb=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.
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    Analysis Of Thin Dielectric Cylindrical Reflector Having An Arbitrary Conic Section Profile Illuminated By Complex Line Source: H-Polarization Case
    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.
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    Analysis of a thin, penetrable, and non-uniformly loaded cylindrical reflector illuminated by a complex line source
    Oguzer, 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 H-polarisations. The convergence and the accuracy of the formulation are verified in reasonable computational running time.
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    Radiation Performance Of Metamaterial Cylindrical Reflector Antenna Having A Conic Section Profile Illuminated By An E-Polarized Complex Source Line Beam
    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.
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    The effect of ambient temperature on electric power generation in natural gas combined cycle power plant-A case study
    Sen, G; Nil, M; Mamur, H; Dogan, H; Karamolla, M; Karaçor, M; Kuyucuoglu, F; Yörükeren, N; Bhuiyan, MRA
    Natural gas combined cycle power plants (CCPPs) are widely used to meet peak loads in electric energy production. Continuous monitoring of the output electrical power of CCPPs is a requirement for power performance. In this study, the role of ambient temperature change having the greatest effect on electric production is experimentally investigated for a natural gas CCPP. The plant has generated electricity for fourteen years and setup at 240 MW in Aliaga, Izmir, Turkey. Depending on the seasonal temperature changes, the study data were obtained from each gas turbine (GT), steam turbine (ST) and combined cycle blocks (CCBs) in the ambient temperature range of 8-23 degrees C. In electric energy production, an important decrease was in the GTs because of the temperature increase. This decrease indirectly affected the electric energy production of the STs. As a result, the efficiency of each GT, ST and CCB decreased, although the quantity of fuel consumed by the controllers in the plant was reduced. As a result of this data, it has been recommended and applied that additional precautions have been taken in the power plant to bring the air entering the combustion chamber to ideal conditions and necessary air cooling systems have been installed. (C) 2018 The Authors. Published by Elsevier Ltd.