Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7148
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Article Citation - WoS: 5Citation - Scopus: 5Nonreciprocal Transmission Enabled by Time Modulation of Penetrable Metasurface Assisted by Surface Waves(Aip Publishing, 2024) Yilmaz, H. Onder; Yaman, FatihThis study introduces a novel approach to achieving nonreciprocal transmission by implementing time modulation to the bianisotropic metasurface. For the first time, we present the analytical solution of the excitation of anti-symmetric surface waves on penetrable metasurfaces depending on the excitation direction. Exploiting this finding, we numerically demonstrate asymmetric control of the transmission coefficient under a fast-time scale by employing solely time modulation. This approach lowers the complexity of the modulation scheme and implementation encountered in the space-time modulation technique. We develop and simulate a 3D unit cell model in the microwave domain, which forms a surface cavity that incorporates time-varying capacitors. The impedance transfer matrix method and harmonic balance numerical solutions are applied to the retrieved equivalent circuit for the numerical simulations. The results reveal optimized phase-coherent and incoherent nonreciprocal transmission at the significant isolation level ( >= 40 dB) for forward and backward transmissions. We discuss the consistency and discrepancies between numerical methods and consider the impact of the losses and nonlinearity on the metastructure performance. (c) 2024 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) licenseArticle Citation - Scopus: 2Mixture-Based Dielectric Permittivity Measurements Through Gallium-Excited Cavities(Ieee-inst Electrical Electronics Engineers inc, 2024) Karatay, Anil; Yaman, FatihIn dielectric measurements within resonant cavities, analytical perturbation methods encounter limitations, particularly with nonstandard cavity shapes and lossy materials under test (MUTs) having high dielectric constant. In such cases, the demand for iterative techniques to improve accuracy and flexibility is evident, but the efficiency of the existing iterative techniques, relying on numerical electromagnetic solvers, is often compromised, particularly in terms of time. Therefore, we introduce a novel methodology for measuring the permittivity of dielectric materials using liquid mixtures. This novel method employs a rapid iterative technique in which effective permittivity values are reconstructed at each iteration step based on the volume fraction of liquid mixtures, thus eliminating the dependence on time-consuming 3-D numerical solvers. In addition, we aim to achieve dual-band measurements at 2.45 and 5.8 GHz, enhancing precision by separating mode frequencies. Introducing a re-entrant cavity-like structure, we position the first mode at 2.45 GHz and the second at 5.8 GHz, effectively mitigating intermodal crosstalk and ensuring measurement accuracy. Also, for the first time in the literature, determining which mode will be excited in a cavity by the coupler probe made of gallium can be achieved through the displacement of the liquid metal, which enables measurements to be taken exclusively at the desired frequency.Article Citation - WoS: 3Citation - Scopus: 4Liquid Metal-Controlled Dual-Band Doppler Radar for Enhanced Velocity Measurement(IEEE, 2024) Karatay, Anıl; Yaman, FatihDoppler radars, which are critical instruments for velocity measurement, may need to be reconfigured to adapt to different environmental conditions or for ease of use. However, conventional electrical, optical, and physical reconfiguration methods often come with several disadvantages such as deteriorated radiation pattern, reduced radiation efficiency, and high cost. Therefore, the aim of this article is to integrate microwave components that can be controlled using liquid metal (LM) displacement into a Doppler radar to adjust its main lobe direction and operating frequency to the desired values and enhance the measurement capacity of the respective radar. Through this study, multiple parameters of an operational Doppler radar have been simultaneously adjusted using LM displacement exploitation for the first time, thus avoiding the shortcomings associated with conventional reconfiguration methods. To achieve this objective, initially, a back-to-back Vivaldi antenna operating at 2.45 GHz is designed, and beam switching ability is imparted to the structure using the LM displacement method. Subsequently, various techniques are used to convert the structure into a dual-band antenna capable of simultaneous operation at 2.45 and 5.8 GHz, ensuring the desired beam switching feature at both the frequencies. In addition, a power divider capable of switching between the two operating frequencies through LM assistance is proposed, and its integration into the radar system enables the control of both main lobe direction and frequency using the proposed method.Conference Object Citation - Scopus: 2Compact Proton Accelerator in Uhf Band at Kahvelab(JACoW Publishing, 2022) Esen, S.; Adıgüzel, A.; Koçer, O.; Çağlar, A.; Çelebi, E.; Öz, S.; Özcan, V.E.; Karatay, Anıl; Yaman, Fatih; Yılmaz, Hasan ÖnderProton Test Beam at KAHVELab (Kandilli Detector, Accelerator and Instrumentation Laboratory) project aims to design and produce a radio frequency quadrupole (RFQ) operating at 800 MHz in Istanbul, Turkey using the local resources. The beamline consists of a proton source, a low energy beam transport (LEBT) line including the beam diagnostic section and the RFQ cavity itself. This RFQ is 4-vane, 1-meter-long cavity to accelerate the 20 keV beam extracted from plasma ion source to 2 MeV. Its engineering prototype is already produced and subjected to mechanical, low power RF and vacuum tests. In this study, the results of the first test production, especially the bead-pull test setup will be discussed. © 2022 Proceedings - Linear Accelerator Conference, LINAC. All rights reserved.Conference Object Citation - Scopus: 2Rf Measurements and Tuning of the Test Module of 800 Mhz Radio-Frequency Quadrupole(JACoW Publishing, 2022) Kılıçgedik, A.; Adıgüzel, A.; Esen, S.; Baran, B.; Çağlar, A.; Çelebi, E.; Özcan, V. E.; Kaya, U.; Türemen, G.; Ünel, N. G.; Yaman, FatihThe 800 MHz RFQ (radio-frequency quadrupole), developed and built at KAHVElab (Kandilli Detector, Accelerator and Instrumentation Laboratory) at Bogazici University in Istanbul, Turkey, has been designed to provide protons that have an energy of 2 MeV within only 1 m length. The RFQ consists of two modules and the test module of RFQ was constructed. The algorithm developed by CERN, based on the measurements generated by the tuner settings estimated through the response matrix [1, 2, 3], has been optimized for a single module and 16 tuners. The desired field consistent with the simulation was obtained by bead-pull measurements. In this study, we present low-power rf measurements and field tuning of the test module. © 2022 Proceedings - Linear Accelerator Conference, LINAC. All rights reserved.Conference Object Citation - WoS: 1An Origami-Inspired Low-Cost Waveguide Design, Fabrication and Measurements for X-Band Satellite Communication Systems(IEEE, 2023) Karatay, Anıl; Ataç, Enes; Yaman, FatihIn many applications such as satellite communication, transmission lines are required and waveguides are widely used in these applications. This passive component, which is an indispensable element of microwave systems, is generally not suitable for practical and low-cost applications due to being produced from costly and heavy metals. Therefore, nowadays, the tendency to use low-cost, light and practical components has increased. In this study, origami-inspired waveguide design for X-band satellite communication systems is aimed. This component, which is formed by folding a paper into a three-dimensional structure and covering it with a conductive material, is both practical and fast to produce, portable and adjustable. The obtained simulation results match well with the experimental results, and it has been proven that the paper-based waveguide performs as well as the conventional aluminum waveguide. This makes the proposed method an innovative and cost-effective solution for waveguide fabrication.Conference Object Dalgacık gürültü giderme yöntemiyle mikrodalga bileşen karakterizasyonunun iyileştirilmesi(IEEE, 2023) Karatay, Anıl; Olcay, Bilal Orkan; Yaman, FatihIn this study, an efficient approach is presented to improve the characterization of various microwave components commonly used in communication and radar applications, such as antennas and power dividers. The components were initially simulated and then fabricated using the Computer Simulation Technology (CST) software. Vector Network Analyzer (VNA) measurements of the fabricated components were performed using a low-cost but noisy coaxial cable, and the measurement results were processed using a wavelet-based noise reduction method. For comparison purposes, the Haar and Daubechies-4 (DB4) wavelet functions were applied separately, and the results were examined. It was observed that the correlation and root mean square error between the ideal and measurement results improved in a positive direction with the noise reduction application. This approach provides significant cost and labor advantages, particularly when expensive elements such as gold and silver are used in coaxial cables that are physically free from noise. The experimental and numerical results show good agreement between the ideal simulation results and the filtered measurement results.Article Citation - WoS: 2Citation - Scopus: 2A Non-Resonant Approach for Dielectric Constant Reconstructions Via Newton Iterations(Elsevier, 2023) Özkal, Ceren; Yaman, FatihIn this study, a Newton–Raphson-based iterative method has been proposed to obtain dielectric constants accurately from measurements. The originalities of the approach lie in its applicability at non-resonant frequencies, which brings a significant experimental simplicity by avoiding critical coupling, expansion of available frequencies in different bands with the same cost-efficient low-Q (?60) cavity. The direct problem involves either measuring power values inside a cavity (14.6 × 5 × 20.6) cm via a spectrum analyzer or simulating the complete setup via CST-MWS software at one of the non-resonant modes, 1.5 GHz. The solution to the inverse problem provides fastly converging results with an error rate of 1% for the unknown permittivities. The experiments were carried out using five different liquid samples even though the proposed technique does not have a limitation on solid materials. Applicability and the effectiveness of the introduced method is illustrated in detail and comparisons with the perturbation method is provided. © 2023 Elsevier GmbHArticle Citation - WoS: 3Citation - Scopus: 3Reconstructions of Effective Parameters for a Metamaterial Antenna Via 3d-Printed Components(Taylor & Francis, 2022) Yılmaz, Hasan Önder; Yaman, FatihThis study presents the reconstruction of effective medium parameters for a double negative metamaterial slab from the knowledge of the measured/simulated S-matrix. The structure initially has been designed to embed into a patch antenna for a radar application. To observe the medium characteristics, we locate the slab in a rectangular waveguide for various orientations. The waveguide-based retrieval method is applied to find parameters regarding the biaxial anisotropic medium. Fundamental mode is used for the excitation. Additive printing technology is employed to manufacture a rectangular waveguide and its adapters for the experiments. The metallization is achieved by coating the printed structures with conductive thin layers. Experimental setups for each orientation are simulated as well. We illustrate good agreements between simulation and measurements under the fabrication tolerances. The feasibility and applicability of the additive printing technology for the investigations of the metamaterial anisotropic/bianisotropic nature is reported.Article Citation - WoS: 2Citation - Scopus: 2Electromagnetic Effects of Equatorially Misaligned Rf Cavities(IOP Publishing, 2021) Karatay, Anıl; Yaman, FatihOne of the most challenging problems in modern particle accelerator systems is the manufacture of RF cavities within the desired tolerance limits. In this study experimental and computational investigations to quantify the effects of transversal half-cell misalignments on the fundamental accelerator cavity parameters and beam dynamics are presented. Equivalent circuit components of an equatorially misaligned single-cell aluminum elliptical cavity are obtained from the measured data and are employed to calculate longitudinal impedance and modal wake function. Critical coupling and bead-pull measurements are performed at the TM010-like mode frequency, 2.45 GHz for the quality factor and shunt impedance of the high-beta cavity. We report equivalent circuit analysis for higher-order modes and variations of the equivalent circuit components with respect to considered misalignment errors for the MICE experiment's muon cooling cavity. It is shown that using the equivalent circuit model decreases the computational load significantly for the wake field simulations of resonator cavities. Good agreement between simulations and measurements in terms of accelerating cavity parameters and impedances is illustrated.