Yazar "Ramahi, Omar M." seçeneğine göre listele

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    Complex Permittivity and Thickness Evaluation of Low-Loss Dielectrics From Uncalibrated Free-Space Time-Domain Measurements
    (IEEE-Inst Electrical Electronics Engineers Inc, 2022) Hasar, Ugur Cem; Kaya, Yunus; Ozturk, Hamdullah; Izginli, Mucahit; Barroso, Joaquim Jose; Ramahi, Omar M.; Ertugrul, Mehmet
    A free-space time-domain method is proposed to retrieve dielectric constant (epsilon r), conductivity (sigma e), and thickness (d) of metal-backed low-loss dielectric samples using calibration-independent reflected power peak measurements. Its algorithm is validated by numerical calculations and simulations (CST Microwave Studio) using a sine-modulated Gaussian window. A sensitivity analysis is followed to examine its performance considering the dependencies of reflected power peaks with respect to epsilon r and sigma e. Free-space time-domain measurements have been implemented after transforming frequency-domain measurements into time-domain ones to extract epsilon r, sigma e, and d of polypropylene, polyethylene, and polyoxymethylene samples.
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    Coupling analysis between resonating metamaterial slabs using scattering parameters
    (Elsevier Sci Ltd, 2021) Hasar, Ugur Cem; Kaya, Yunus; Izginli, Mucahit; Ozturk, Hamdullah; Ertugrul, Mehmet; Ramahi, Omar M.
    Metamaterial (MM) slabs in close proximity can couple with one another. This coupling can modify the electromagnetic response of the overall MM structure involving individual MM resonators. The signal flow graph technique along with the ABCD parameters are applied to quantitatively and qualitatively examine this coupling from simulated/measured scattering parameters of cascade connection of closely or largely separated MM slabs. S-parameter measurements of a MM slab constructed by split-ring-resonators were carried out at X-band (8.2-12.4 GHz) to validate our theoretical analysis.
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    Determination of Propagation Constants and Wave Impedance of Non-Reciprocal Networks From Position-Insensitive Waveguide Measurements
    (IEEE-Inst Electrical Electronics Engineers Inc, 2022) Hasar, Ugur C.; Kaya, Yunus; Izginli, Mucahit; Ozturk, Hamdullah; Barroso, Joaquim J.; Ramahi, Omar M.; Ertugrul, Mehmet
    A microwave method is proposed to determine the forward and backward propagation constants (gamma ? and gamma ?) and the wave impedance ( $z_{w}$ ) of reciprocal and non-reciprocal microwave networks whose positions are not known within their measurement cells (position-insensitive). The proposed method relies purely on analytical expressions and can also evaluate the reference plane transformation distances. Scattering parameter measurements at the X-band (8.2-12.4 GHz) of a reciprocal network (a waveguide straight) and a non-reciprocal network (a microwave phase shifter) arbitrarily positioned into their measurement cells were conducted to retrieve gamma ?, gamma ?, and $z_{w}$ for validation of our method and testing its position-insensitive property. The importance of the method becomes apparent when compared to conventional methods whose accuracy is based on precise determination of the reference planes.
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    Extraction Method for Unique Determination of Complex Permittivity From Graphical Analysis of Natural Frequencies
    (IEEE-Inst Electrical Electronics Engineers Inc, 2023) Hasar, Ugur C.; Ozturk, Gokhan; Kaya, Yunus; Alfaqawi, Mona S. S.; Barroso, Joaquim Jose; Ertugrul, Mehmet; Ramahi, Omar M.
    A time-domain free-space extraction procedure is proposed to uniquely determine the relative complex permittivity epsilon(r)(omega) based on two sets of natural frequencies of the metal- and air-backed dielectric samples. A graphical analysis is applied for evaluating whether unique epsilon(r)(omega) can be extracted using such natural frequencies. The method is numerically validated using two dielectric samples with different epsilon(omega) for the ideal case (no noise) and under the influence of noise with different signal-to-noise ratios (SNRs).
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    Feasible Extraction Method for Electromagnetic Properties of Multilayer Metamaterials With Short-Circuit Termination
    (IEEE-Inst Electrical Electronics Engineers Inc, 2022) Hasar, Ugur Cem; Ozturk, Gokhan; Kaya, Yunus; Bute, Musa; Karaaslan, Muharrem; Barroso, Joaquim J.; Ramahi, Omar M.
    An extraction technique is proposed for electromagnetic characterization of metal-backed multilayer metamaterial (MM) structures demonstrating reflection-asymmetric property. It uses recursive scattering parameters for direct and reversed configurations of a multilayer structure. The algorithm was validated by comparing the extracted electromagnetic properties of multilayer structures composed of different MM unit cells with those determined by one-layer-only S-parameter methods. Two-layer and three-layer multilayer structures composed of MM slabs with C-shaped and Omega-shaped rings and an FR4 material were fabricated and measured for experimental validation. A sensitivity analysis was also conducted to quantitatively evaluate the performance of our method against a small air gap between the multilayer structures and the short-circuit termination and between adjacent MM slabs within these structures. Strong agreement was observed between the resulted obtained using our method and measurements.
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    Improved Method for Permittivity Determination of Dielectric Samples by Free-Space Measurements
    (IEEE-Inst Electrical Electronics Engineers Inc, 2022) Hasar, Ugur Cem; Kaya, Yunus; Ozturk, Hamdullah; Izginli, Mucahit; Ertugrul, Mehmet; Barroso, Joaquim Jose; Ramahi, Omar M.
    A new deembedding technique is proposed for relative complex permittivity epsilon(r) determination of dielectric materials using gated free-space measurements. Its three main features are 1) it does not require any formal calibration procedure (calibration-free); 2) it is position-insensitive; and 3) it extracts ripple-free epsilon(r) due to gating process. The objective function derived to determine epsilon(r) by the proposed method is validated by free-space measurements of three dielectric samples (polypropylene, polyethylene, and polyoxymethylene). Besides, the accuracy of our method is compared with the accuracy of other calibrationfree and calibration-dependent methods in the literature.
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    Temporal Reflection Response of Plane Waves Within an N-Layer Structure Involving Bianisotropy
    (IEEE-Inst Electrical Electronics Engineers Inc, 2023) Hasar, Ugur C.; Ozturk, Gokhan; Kaya, Yunus; Barroso, Joaquim Jose; Ertugrul, Mehmet; Ramahi, Omar M.; Alfaqawi, Mona S. S.
    The temporal reflection response of an N-layer composite structure involving bianisotropic behavior is examined for the first time in the literature. Toward this goal, the wave matrix (WM) method, which is fundamental, relatively easier to apply, and compact and iterative suitable for analysis of multilayer structures, is first extended to the analysis of an interface separating two different media involving bianisotropy. Next, the reflection response of the whole structure is derived in terms of series form to better analyze its temporal behavior. Then, frequency-domain and time-domain responses of the whole structure are expressed using a special reflection coefficient (the reduced reflection coefficient) by way of the concept of subregions. A numerical analysis is performed to demonstrate the applicability of our formalism for two different polarization types (perpendicular and parallel).