Yazar "Iliev, Teodor" seçeneğine göre listele

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    Broadband Multilayer Absorber Design Using Double-Stage Cognitive Seeker Optimization Algorithm
    (Ieee-Inst Electrical Electronics Engineers Inc, 2025) Hasar, Ugur Cem; Kaya, Yunus; Korkmaz, Huseyin; Iliev, Teodor
    In this paper, a double-stage cognitive seeker optimization (DSC-SO) algorithm is developed for evaluating optimum design parameters of broadband microwave absorbers. The algorithm not only gives freedom of selecting different number of layers and optimizing the order of layers and their thickness in different stages (double-stage) but also utilizes a cognitive search to improve the optimization. Contributions of the cognitive search and the two stages of our algorithm are first examined to show its efficiency. Then, its performance has been evaluated for two different optimization problems (a broadband absorber for one incidence angle and a broadband absorber with multiple incidence angles) in comparison with similar algorithms in the literature. It has been shown that our algorithm determines either fewer number of layers or smaller overall absorber thickness or both when compared with the results of other algortihms. Finally, the effect of fabrication tolerance is conducted to examine the importance of fewer number of layers.
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    De-Embedding Technique for Parameter Extraction of Biaxial Bianisotropic Metamaterial Slabs
    (Ieee-Inst Electrical Electronics Engineers Inc, 2024) Hasar, Ugur Cem; Kaya, Yunus; Korkmaz, Huseyin; Iliev, Teodor
    Among material classes of isotropic, anisotropic, bi-isotropic, and bianisotropic, the latter classis important because, as different from other classes, the bianisotropic class can describe complex behavior of various materials through tensor expressions between electric and magnetic fields via electric and magnetic flux densities. All electromagnetic parameters (a total of seven) of a general bianisotropic material need to be accurately extracted for understanding its response and characteristic. Extraction methods can be utilized for such a goal. However, the extraction methods in the literature either require a formal calibration procedure or are limited to the extraction of three electromagnetic parameters only. In this study, an attractive self-calibrating waveguide method has been devised for determination of electromagnetic parameters of biaxial biansiotropic metamaterial (MM) slabs. Its first advantage is that it uses a thru connection in addition to the MM-loaded line connection (three different configurations - Case A, Case B, and Case C) and empty-line connection next to the MM-loaded line connection to extract all (seven) constitutive parameters together with the magnetoelectric coupling coefficient. Its second advantage is that it relies on explicit expressions and does not require any calibration process for such an extraction. Simulations and uncalibrated scattering parameter waveguide measurements at X-band (8.2-12.4 GHz) were performed for a biaxial bianisotropic MM slab made by C-patterned resonators to validate the proposed method. It is observed that extracted electromagnetic parameters by the proposed method satisfy the passivity conditions over the entire frequency band except for a few frequency points or regions (e.g.,f=8.2 GHz). Its reason is expected to be associated with the difficulty in satisfying the continuous medium property at such frequencies. Besides, it is noted that two of the constitutive parameters (epsilon 2and mu 3) illustrate a thickness-resonance behavior revealed by additional measurements of the Case B - MM structure with different lengths (7.675 mm, 9.21 mm, and10.475 mm). Besides, it is noted that the resonance behavior of the Case C - MM structure changes with a change in periodicity. Specifically, when the periodicity in the x direction of this MM structure changes from approximately 3.26 mm to 2.29 mm, the resonance frequency shifts from nearly 10.43 GHz to 10.30 GHz(a 1.25% variation). Finally, sensitivity, uncertainty, and error analyses were also performed to evaluate and improve its accuracy. It is observed that|partial derivative epsilon 3/partial derivative|31A
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    Soil Permittivity Extraction by Time-Domain Free-Space Calibration-Free Microwave Measurements With No Thickness Information
    (Ieee-Inst Electrical Electronics Engineers Inc, 2025) Hasar, Ugur Cem; Korkmaz, Huseyin; Kaya, Yunus; Iliev, Teodor
    An attractive microwave free-space method is proposed for permittivity extraction of soil samples using calibration-free time-domain measurements. Different from other similar methods in the literature which use the layer-stripping approach in the forward direction in the extraction process, its formalism is based on the layer-stripping approach in the backward direction, whereby allowing extraction of permittivity from interfacial reflection coefficient only without resorting to any thickness information, especially useful for time-domain analysis of multilayer structures having multiple reflection terms. Effects of angle misalignment, loss, and surface roughness on the extraction performance of the proposed method (PM) are analyzed by numerical examples. Permittivity measurements of three low-loss flat solid samples [polypropylene (PP), polyethylene (PE), and polyoxymethylene (POM)] were first performed by a free-space setup operating over 1-18-GHz frequency range to validate our methodology and compare its accuracy against other similar methods in the literature. Thereafter, permittivity measurements of two soil samples sieved with similar and different sizes (coarse- and fine-grained soil samples) by the same free-space setup were then considered to assess the applicability and performance of our method for electromagnetic property analysis of homogeneous and partially inhomogeneous soil samples.
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    Transient Plane Wave Transmission Through an N-Layer Multilayer Structure With Bianisotropic Behavior
    (Ieee-Inst Electrical Electronics Engineers Inc, 2025) Hasar, Ugur Cem; Kaya, Yunus; Korkmaz, Huseyin; Iliev, Teodor
    An analysis based on electromagnetic reflection and transmission properties of multilayerstructures are in general needed to get more information about their electromagnetic responses beforetheir implementation for some specific applications involving absorption, shielding, and diagnosis. Suchan analysis could be exercised by either frequency-domain or time-domain. While the former one is basedon the steady-state response, the latter one is based on the transient response which thus provides moreinformation about electromagnetic properties of multilayer structures. A procedure relying on a directtheoretical time-domain analysis is preferable to a time-domain analysis based on computational proceduressuch as the finite-time-difference-domain or the fast Fourier transform. In this study, a series presentationof transient plane wave transmission coefficient of N-layer composite structures involving bianisotropicbehavior is derived for the first time in the literature in terms of reduced transmission coefficients (the conceptofsubregion). The wave matrix approach is applied for the theoretical analysis of the reduced transmissioncoefficient after application of the concept ofsubregion. Implementation of this concept to our problem ispresented step-by-step to make a clear understanding of its application to bianisotropic multilayer structures.The derived reduced transmission coefficient is validated by different multilayer structures (differentlayer numbers, different layer lengths, and different polarizations) composed of individual layers whoseelectromagnetic responses are synthesized by the Lorentz dispersion model. Advantages and limitations ofthe derived formalism are also presented