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Öğe A new error reduction technique for reflection coefficient measurements for use in quick laboratory tests(Taylor & Francis Ltd, 2019) Çolak, Bektaş; Helhel, SelçukReflection coefficient measurement is one of those fundamental methods for determining the performance of radar absorber materials, and reflections due to these measurements are originated from the discontinuities in the measurement system and they result in error. In this paper, a new technique for the calibration of the scalar reflection coefficient measurements in the frequency range of 3-18 GHz in a portable two-sectioned metallic chamber is being proposed for use in quick laboratory tests with reasonable error (redacted error). Calibration measurements are performed by two calibration standards in frequency domain and transformed to time domain for further calculation. Proposed technique exhibits a good agreement with the theoretical values for especially in compact chambers where plane-wave conditions are not fully satisfied, and it is not in need of any complex time gating process. Furthermore, it does not require considering the phase differences which occurs at the measurement plane, providing a cheap and faster solution, reducing time and complexity in characterization of radar absorber materials. This technique with the mentioned test set-up could supply scalar reflection coefficient measurements with overall 0.55 dB error level and useful for practical applications where high level of accuracy is not required.Öğe Absorbing properties and structural design of PVB/Fe 3 O 4 nanocomposite(Elsevier Ltd, 2019) Akınay, Yüksel; Hayat, Fatih; Çolak, BektaşRecently, 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 (PANI) coated-Fe 3 O 4 (COM1) and PVB/Fe 3 O 4 (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 (? ’ ,? ’’ ) and permeability (? ’ ,? ’’ ) 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). © 2019 Elsevier B.V.Öğe Development of multifrequency MW detection device to scan liquids in security checkpoints(Ieee, 2019) Yengejeh, M. Vafadar; Mamadazizov, Sultonazar; Çolak, Bektaş; Rameev, BulatDevelopment of both technical devices and effective methods for the detection of various dangerous substances is one of the critical task in providing airport and critical infrastructure security. In this work, we propose to use MW technique, based on probing dielectric permittivity parameters of liquids, as a prospective technique for detection of most frequently used energetic, flammable, chemically-active and other classes of dangerous liquids. Approaches for the MW detection with increased discrimination ability are presented. A device, combining several sensors for various frequencies with various probing distances, has been designed and tested. Several issues have been successfully resolved in the process of the development of this device: 1) placing various sensors in the most effective and compact manner to scan of bottles of various size; 2) a minimal cross-talk between various sensors; 3) effect of distance variations between the sensors and a scanned bottle. For minimization of the device cost and easy commercial implementation, low MW electronic components and units have been used to construct this device. A set of various sensors for frequencies between 1-4 GHz have been developed. A signal acquisition, processing and user-interface software have been also developed. The first experiments with the PET bottles with various liquids have been done.Öğe Investigation of the characteristics of low-cost and lightweight horn array antennas with novel monolithic waveguide feeding networks(Elsevier Gmbh, 2018) Genç, Abdullah; Başyiğit, İbrahim Bahadır; Çolak, Bektaş; Helhel, Selçuk3D printed X-Ku band single horn antenna and 2 x 1 and 2 x 2 pyramidal horn array antennas with novel lightweight and monolithic waveguide feeding networks (WFNs) are proposed at 10-15 GHz for satellite communications and radar systems to increase the gain. Proposed novel fabrication method consists of two main steps that are to make the skeleton of horn array antenna from acrylonitrile butadiene styrene (ABS) thermoplastic via 3D printer and to perform copper plating over all surface of antenna by using the electroless plating and electroplating processes. The WFN structures with 3 lambda element spacing designed and realized by using WR75 waveguide T-junction, E-type bend, and UDR 120 flange. Qualitative agreement between measurement and simulation via CST Microwave Studio is obtained with max 1 dB due to high precision and surface roughness. The gains of array antennas are increased by about 1.5 dB and 3 dB, respectively compared to the single antenna. VSWRs of array antennas are 0.3 dB and 0.6 dB, respectively higher than the single one. In the study, proposed 3D printed components not only with 90% lighter weight than, but also with 80% cheaper than commercial products, and horn arrays with -40 dB cross-polarization values.Öğe Moisture content effect of banana leaves to radio frequency absorbing(Wiley, 2019) Çolak, BektaşThe aim of this paper is to express the importance of the moisture content of banana leaves to the evaluation of radio frequency (RF) absorbing performance. Radar absorbing material (RAM) is generally used in electromagnetic compatibility chambers to minimize reflections within the chamber. These materials also reduce the radar traces of air elements by minimizing RF radiation in stealth technology. Chemical substances that are used in fabricating RAM with pyramidal shape are neither cheap nor harmless to the environment. So, vegetable wastes such as bananas, coconut, and rice are studied to use as RAM. In this study, transmission line technique has been used to measure dielectric properties of the sample (banana leaves) in 8.2-12.4 GHz. It was concluded that dried banana leaves are so sensitive to environmental moisture and the RAM produced from banana leaves gives different return loss values relative to the moisture content of the sample. The water content of the sample is reduced by 5.0% and 4.9%, respectively. In this case, there is nearly 16% and 12% reduction on relatively dielectric constant, about 54% and 33% reduction on dielectric loss, finally approximately 56% and 31% reduction on return loss.Öğe PCB soğutucuların besleme noktasına göre elektromanyetik girişim davranışlarının 1-10 GHz bandında deneysel olarak incelenmesi(Gazi Üniversitesi, 2023) Karaman, Alpaslan Bozkurt; Başyiğit, Bahadır; Doğan, Habib; Genç, Abdullah; Kocakuşak, Atalay; Çolak, Bektaş; Helhel, SelçukPCB devre elemanlarının çalışma frekanslarındaki artış sonucu devrenin minyatürleşmesi, ortamdaki ısı miktarını daha fazla arttırır. Artan ısı miktarının transferi için metal soğutucular yaygın olarak kullanılır. Ancak soğutucular, belli frekanslarda yayılan elektromanyetik (EM) emisyona neden olurlar. Bu emisyon, soğutucu çevresindeki devre elemanlarının çalışma performansını olumsuz etkiler. Bu çalışmada, eşit taban alanına sahip dikdörtgen ve dairesel soğutuculardaki farklı besleme noktalarının, EM davranışları üzerindeki etkisi 1-10 GHz bandında incelenmiştir. Yansıma katsayısı, EM emisyon, normalize ışıma örüntüsü, ve E-alan dağılımları elde edilmiştir. Benzetim ve ölçüm sonuçları birbirleriyle uyumludur. Dikdörtgen soğutucuda 1. ve 2. besleme noktaları için ilk rezonans frekansı 3 GHz olup bu frekanstaki yansıma katsayısı değerleri sırasıyla -10,1 ve -12,3’dür. Dairesel soğutucuda 3. ve 4. besleme noktaları için ilk rezonans frekansı 2,2 GHz olup bu frekanstaki yansıma katsayısı değerleri sırasıyla -14,9 ve -17,3’dür. Ayrıca, dairesel soğutucularda 1,3-3,9 GHz ve 5,8-10 GHz frekans bantlarında 1. besleme noktası için yayılan emisyon, diğer besleme noktalarına göre ~2-8 dBmV/m daha az olduğu için tercih edilmelidir. Dikdörtgen soğutucularda 1-2 GHz ve 6-10 GHz frekans bantlarında 1. ve 2. besleme noktası için yayılan emisyon ~5-6 dBmV/m daha az olduğu için tercih edilmelidir. Sonuç olarak, her iki soğutucu merkezden beslendiğinde daha az emisyon yaydığı için elemanların soğutucu merkezine yerleştirilmesi önerilir.Öğe Remote sensing for the detection of explosives and energetic materials by N-14 NQR and N-14 NMR(Ieee, 2019) Mozzhukhin, Georgy; Maraşlı, A.; Mamadazizov, S.; Çolak, Bektaş; Rameev, BulatIn this work, technical approaches for remote detection of explosives and energetic materials by N-14 NQR and NMR are presented. In the case of N-14 NQR, a problem of the detection of ammonium nitrate (AN) and AN-based explosives have been considered. Special accent is made on the technical solutions with use of cross-relaxation enhanced NQR. In the second part of the work, applications of N-14 NMR (TD-NMR) for detection of hazardous liquids are discussed. A method of the fast discrimination of dangerous liquids by the low-field N-14 NMR relaxation parameters have been proposed and tested using a set of energetic, toxic and electrolyte liquids. A surface coils for the detection of liquids in NMR is also studied.
