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    Absorbing properties and structural design of PVB/Fe3O4 nanocomposite
    (Elsevier Science Sa, 2019) Akinay, Yuksel; Hayat, Fatih; Colak, Bektas
    Recently, a wide range of studies has been carried out on microwave absorber composites for use in telecommunications, electromagnetic pollution, stealth technology, and other applications. In this study, the microwave absorption properties of polyvinyl butyral (PVB)/polyaniline (PAM) coated-Fe3O4 (COM1) and PVB/Fe3O4 (COM2) nanocomposites with single and double layer were investigated in the 1-14 GHz for different thickness (t(m)) of composites. XRD, FT-IR, TEM, and SEM were used to determine the structure properties of the composites. The Coaxial transmission line method was used to obtain permittivity (epsilon', epsilon '') and permeability (mu', mu '')parameters of the composites. The reflection loss of the single and multilayers of different thicknesses was calculated. It was figured out that the higher value of reflection loss (R-L) (-51.5 dB at 11.9 GHz) was obtained with COM2 composite. However, using PANI has provided a wider absorption range in COM1 composites. It was found that multilayer composites (COM4) provide broadband absorption compared to COM2 and double-layer design (COM3).
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    A Comparative Study on the Calibration of Frequency Domain Reflection Measurements for a Compact Test Chamber
    (Ieee, 2016) Colak, Bektas
    In this paper, a comparative study is performed for the calibration of Frequency domain reflection measurements for a compact test chamber. A time domain averaging technique and a three standard calibration technique is applied to the frequency domain reflection measurements.
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    Development of Earth's Field Nuclear Magnetic Resonance (EFNMR) Technique for Applications in Security Scanning Devices
    (Springer Wien, 2016) Balci, Erdem; Rameev, Bulat; Acar, Hakki; Mozzhukhin, Georgy V.; Aktas, Bekir; Colak, Bektas; Kupriyanov, Pavel A.
    In this work Earth's field nuclear magnetic resonance (EFNMR) technique for applications in security scanning devices has been presented. The EFNMR setup has been build based on Magritek low-frequency (0-1 MHz) KEA-2 NMR console. Excepting the NMR console, all components are home-made units, which are a first-order gradiometer RF probe, pre-polarization system, magnetic field shimming system, RF shielding box and passive filters. Our measurements have shown that even in very noisy lab conditions the EFNMR signals of small amounts (similar to 5 ml) of liquid samples could be measured. EFNMR measurements of various liquids have been performed and their spin-lattice T (1) and spin-spin T (2) relaxation constants have been obtained. A possibility to detect, at the same time, both fluorine and proton resonance has been shown by EFNMR measurements of trifluoroacetic acid. A good spectral resolution of EFNMR setup has been demonstrated by the spectroscopic measurements of heteronuclear J-coupling of trimethyl phosphate and fluorobenzene. Furthermore, we have shown that the EFNMR measurements of T (1) and T (2) constants as well as heteronuclear J-coupling of liquids enclosed in metallic containers are feasible. Possible applications of the EFNMR technique in security scanners for the detection of illicit and energetic substances are discussed.
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    The electromagnetic wave absorption properties of woven glass fiber composites filled with Sb2O3 and SnO2 nanoparticles doped mica pigments
    (Wiley, 2022) Akinay, Yuksel; Colak, Bektas; Turan, Muhammet Emre; Akkus, Ihsan Nuri; Kazici, Hilal Celik; Kizilcay, Abdullah Oguz
    In this study, the electromagnetic wave absorption properties of woven glass fiber reinforced epoxy composites with Sb2O3 and SnO2 nanoparticles doped mica pigments were investigated. Herein, we synthesized SnO2/mica, Sb2O3/mica, and Sb2O3:SnO2/mica pigments using the sol-gel method. Subsequently, mica pigments filled glass fiber/epoxy composite panels were fabricated with a vacuum assisted resin mold. The phase, crystal, and morphological examinations of particles confirm the deposition of SnO2 and Sb2O3 nanoparticles on the mica surfaces. The electromagnetic wave absorption properties of samples were measured using the S parameters and obtained dielectric data. Sb2O3:SnO2/mica particles display higher complex permittivity and dielectric loss values due to the strong interfacial polarization between conductive nano metal-oxide shells and mica surfaces. According to the calculated reflection loss values, Sb2O3:SnO2/mica particles exhibit superior electromagnetic wave absorption performance with a minimum reflection loss of -25.62 dB for 2.4 mm thicknesses with effective bandwidth between 9.3 and 12.4 GHz. The S parameters of the prepared structural composites with the size of 30 cm x 30 cm x 3 mm was determined by the free-space technique using the transmission line technique. According to the S-12 parameters, filled glass fiber/epoxy composite containing 25 wt% Sb2O3:SnO2/mica show a minimum reflection loss of -20.426 dB at 8.2 GHz with effective bandwidth between 8.2 and 9.67 GHz. These results indicate that Sb2O3:SnO2/mica-filled fiber/epoxy composite is an excellent candidate for the practical application of electromagnetic wave absorbers.
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    Frequency dependent complex dielectric permittivity of rubber and magnolia leaves and leaf water content relation
    (Taylor & Francis Inc, 2016) Kocakusak, Atalay; Colak, Bektas; Helhel, Selcuk
    A mathematical model based on both frequency and relative water content of two tropical crops' rubber and magnolia' leaves derived from s(21) measurements has been proposed in the frequency range of 37 GHz. Leaf samples sandwiched with Plexiglas side holders are inserted within waveguide sections, and the dielectric constants are calculated from the complex transmission coefficient S-21. In general, complex dielectric constant of materials (leaves in this case) is a function of frequency and water content. A model obtained from the data of rubber based on both frequency and relative water content is compared with the models in the literature and verified by measurements of control samples (magnolia in this case). From the comparisons, it is observed that proposed model has been found to show more promise in prediction of the dielectric constants, and model has, at most, +/- 10% error in relative dielectric constant (epsilon(r)) in broad band measurements. Relative dielectric constant is decaying by similar to 1/f(2) and shifts down by relative moisture constant by similar to M-r.
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    Optimization of Shielding Effectiveness of Coaxial Double Braided Screens in Contact
    (Ieee, 2016) Colak, Bektas; Cerezci, Osman; Ari, Niyazi; Helhel, Selcuk
    In this paper, the optimization of the shielding effectiveness of double braided coaxial screens in contact is obtained using semi-empirical single braid optimization formulas. Also the effect of the mutual inductance term between the double braided screens in contact is investigated. A sample optimization has been obtained practically, on one of the standard double braided RF coaxial cable namely, RG-142.
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    Plane wave scattering by a dielectric loaded slit in a thick impedance screen
    (Taylor & Francis Ltd, 2017) Tayyar, Ismail Hakki; Colak, Bektas
    The electromagnetic scattering of the plane wave by a slit loaded with dielectric in a thick impedance screen is considered for a rather general case where the surface impedances of the screen planes and vertical sides of the slit have different values. Because of the symmetry of the scattering structure, the image bisection principle is used and the original problem is splitted up into even and odd excitation cases. By introducing the Fourier transform for each case yields a modified Wiener-Hopf equation of the second kind for each excitation. After decoupling these equations by standard transformation, each modified Wiener-Hopf equation is reduced to a pair of coupled Fredholm integral equations of the second kind. The solution of each integral equation involves two sets of infinitely many constants satisfying two infinite systems of linear algebraic equations and Branch-cut integrals which are evaluated approximately. Numerical solutions of these systems are obtained for various values of the parameters such as the surface impedance of the screen, the vertical wall impedance of the slit, the width and the thickness of the slit and the permittivity of the filling material of the slit which permit one to study the effect of these parameters on the diffraction phenomenon. In order to validate the present Wiener-Hopf solution, experimental verification of the dielectric loaded thick metallic slit has been implemented in microwave frequencies with good agreements.