Cilt:63 Sayı:02 (2021)

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https://dspace.ankara.edu.tr/handle/20.500.12575/86463

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    Estimating the frequency and bandwidth of square-split ring resonator (S-SRR) designs via support vector machines (SVM)
    (Ankara Üniversitesi Mühendislik Fakültesi, 2021) CAN, Sultan; Elektrik-Elektronik Mühendisliği; Mühendislik Fakültesi
    In this study Support Vector Machine (SVM) based estimation technique is proposed for estimating the bandstop frequency and bandwidth of square-split ring resonators. Artificially engineered surfaces especially the planar frequency selective surfaces like the SRRs have narrowband properties so that estimating the filtering frequencies and the bandwidth is essential in a cost and design-effective way. The proposed method, which is superior to optimization methods and 3D electromagnetic solvers in terms of cost and computational burden, achieved accurate results via SVMs generalization capability. This study represents two SVM regression models one for predicting frequency and the other for predicting bandwidth having fast response and accuracy. Results of the proposed model reveal that resonance frequency estimation error, in terms of percentage, is bounded in the interval [0.0542, 3.5938], with an overall error of 0.89 % for the test data. The mean and standard deviation of the percentage error is obtained as 0.9861 and 0.9376, respectively. In addition to that -10dB bandwidth is estimated with the bounded error where estimation error in terms of percentage would be lie in the interval [0.068925, 6.876800] with an overall error of 3.68% for the test data.
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    Geant4 based dosimetry evaluation for gamma knife using different phantom materials
    (Ankara Üniversitesi Mühendislik Fakültesi, 2021) Bostancı, Gazi Erkan; Elektrik-Elektronik Mühendisliği; Mühendislik Fakültesi
    This study examines the dose difference for a variety of phantom materials that can be employed for “Leksell Gamma” Knifes. These materials resemble human tissue by not including the skull bone. Geant4 was utilized in the analysis of the dose distributions for collimator helmet sizes of 4mm and 8mm. The phantom is illustrated with a radius of 80mm. Water, brain, Poly-methyl methacrylate (PMMA) and polystyrene were being considered as the main material types. Results proved that there is no considerable differences for radiation dosimetries depending on the material types. In addition, the polystyrene and PMMA (phantom is also quite appropriate in terms of evaluating the dose profiles of the Gamma Knife unit.
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    Design and implementation of a low cost, high performance ionizing radiation source detection and source direction finding system
    (Ankara Üniversitesi Mühendislik Fakültesi, 2021) Cuhadaroğlu, Burak; Elektrik-Elektronik Mühendisliği; Mühendislik Fakültesi
    This study shows the design, implementation, and test results of a low-cost portable radiation-detector system relies on a directionally designed multi detector probe that works in Geiger-Müller counting mode with a single chip solution. The proposed system can perform the functions of detecting the ionizing radiation source, counting gamma and showing the direction and angle of the gamma source relative to the position of the device. The radiation direction finding (RDF) system consists of a radiation probe and electronic sections that are mounted in a metal box. The probe has a has a cast housing made of lead material and it has 8 directional slots for placing the optically isolated PIN diode arrays where each array consists of 4 parallelly connected BPW 34 PIN model diode. The lead housing also blocks incident rays from unintended directions and provides a directional sensing for PIN diodes. The metal box contains 8 low noise amplifiers and pulse shaping detector boards that are assigned to each channel of PIN diode arrays, a signal inverter board, a step-up high voltage board, a 12 V battery and a parallel processing FPGA board with an embedded VHDL software that can process all 8 channels simultaneously and execute the direction estimation algorithm. The system also has an adjustable detector bias voltage and the applied voltage can be displayed on a seven-segment display located in front of the unit so that different models of PIN diodes can be used and tested with different bias voltage levels. It also has a HMI touch screen unit and user interface for displaying the Cpm or Cps values of each channel; a 360-degree scale showing the direction of the source with its pointer and an indicator showing the direction of the source numerically in degrees. The system works as a gamma detector and the source direction can also be detected within ±45° interval. The success of system within this interval is 99.22%. The detector was tested with low to high energy gamma sources (241Am, 9.761 μCi, 59.54 keV, 137Cs 661, 3.7 MBq, keV and 60Co, μCi, 1173 and 1332 keV) and showed good sensitivity performance level in gamma ray detection. The major outcome of this study and the major contribution of this work to the literature is therefore is the design and production details of a hand-held detector and source direction locator prototype; which is a light, portable and compact system.