Yüksek Lisans Tezleri

Permanent URI for this collectionhttps://hdl.handle.net/20.500.12573/5799

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Department: search.filters.department.AGÜ, Fen Bilimleri Enstitüsü, Elektrik ve Bilgisayar Mühendisliği Ana Bilim DalıSubject: search.filters.subject.Elektrik Ve Elektronik Mühendisliği

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Now showing 1 - 10 of 21
  • Master Thesis
    Ultra Geniş Bantlı Vivaldi Antenlerin Tasarımı ve Performans İyileştirmesi
    (Abdullah Gül Üniversitesi, Fen Bilimleri Enstitüsü, 2024) Güzelkara, İzzet; Kılıç, Veli Tayfun
    Ultra-wideband technology has become a trending topic in the academic community since 2002 due to the release of the spectral mask by Federal Communications Commission, allowing the use of 3.6-10.1 GHz band for commercial and industrial applications. Being one of the fundamental components of ultra-wideband systems, ultra-wideband antennas are an important research area. In this research, Vivaldi antennas for ultra-wideband communications and several performance enhancement techniques for the antennas were studied. Antennas were designed and simulated using a commercially available three-dimensional electromagnetic simulation tool. First, a simple design of a Vivaldi antenna with a rectangular microstrip feed was obtained. The initial design has a -10 dB impedance bandwidth between 3.1 and 13.6 GHz and an average realized gain of 2.75 dBi. A method based on the alignment of the microstrip feed was described for adjusting the bandwidth of the initial design. Then, using several performance enhancement techniques such as implementation of corrugations and a parasitic patch, the antenna design was improved. Thanks to the applied methods, an antenna design with -10 dB impedance bandwidth extending from 1.33 to 10.1 GHz and an average realized gain of 6 dBi was achieved. Findings of this thesis study show that Vivaldi antennas having specific structures designed with the applied techniques are a promising solution for ultra-wideband communication systems, especially where antennas with directive radiation patterns are desired.
  • Master Thesis
    Yarı-Tek-Aşamalı Dört-Anahtarlı Alçaltıcı-Yükseltici Evirici için Pürüzsüz Mod Geçiş Tekniğinin İncelenmesi ve Geliştirilmesi
    (Abdullah Gül Üniversitesi, Fen Bilimleri Enstitüsü, 2023) Keskinkılıç, Ebubekir; Keskinkılıç, Ebubekir; Tekgün, Burak
    In recent decades, given the world's inevitable energy scarcity, increasing energy demand and green energy concerns, high efficiency energy conversion has become more important and attractive than ever, and researchers have directed their interest to energy-efficient converters. Inverters are a commonly utilized type of converter, which can be classified into two categories: single and two-stage inverters. Considering the inherent drawbacks of traditional inverters, a quasi-single-stage inverter (QSSI) has emerged. The QSSI uses a DC-DC converter to shape the rectified version of the desired AC waveform in the first stage and, in the second stage, it switches only once to alternate the polarity. It stands forward in terms of efficiency, control simplicity, and system stability. Among QSSI, a non-inverting buck-boost converter has drawn attention due to its capability to perform both step-up and down modes and its bidirectional power transfer feature. In the first stage of the QSS non-inverting buck-boost converter; smooth transitions between the buck and boost modes and efficient conversion cannot be achieved by the traditional two-mode control method when the output voltage level is close to the input voltage level due to various limitations, non-idealities, and disturbances. Many methods have been applied and studied in the literature to minimize or eliminate the effects of the region which is called the 'dead zone'. In this thesis study, further efficiency and THD improvement for the QSSI is targeted by employing a four-mode control method. The study incorporates a comparative study of the dead zone effects on inverter systems, which have not been previously documented in the literature. Moreover, it places a priority on optimizing efficiency and minimizing distortion in various applications—ranging from motor control and solar energy systems to grid-tied wind turbines and switched-mode power supplies—by comparing existing methods with open-loop voltage control. In conclusion, the theoretical results are verified with experimental studies.
  • Master Thesis
    Yüksek Parlaklık Kuantum Nokta Led Aygıtların Geliştirilmesi
    (Abdullah Gül Üniversitesi / Fen Bilimleri Enstitüsü, 2023) Biçer, Ayşenur; Mutlugün, Evren
    Optoelectronic devices are essential components of optical communication systems, internet and displays. Among these devices, in the category of light emitting diodes (LED), there are quantum dot LEDs (QLED) that emit light by employing quantum dots (QDs) and have rich optoelectronic properties such as varying emission wavelength associated with the its size and excellent brightness [1], [2]. In this thesis, we worked on transparent and solution processible QLEDs in three groups: Indium Phosphide (InP) QLEDs, Carbon Quantum Dot (CQD) LEDs and Cadmium Selenide (CdSe) QLEDs. In the InP study, a QLED was fabricated using InP-based QDs as the emitting layer to demonstrate the feasibility of these QDs. Results found a maximum external quantum efficiency (EQE) of 1.16% and brightness of 1039 cd/m2. For the CQD LEDs, yellow emissive QDs were mixed systematically in Poly(9-vinylcarbazole) (PVK) as the host. A blue-to-white shift was observed in the CIE coordinate with varying ratios. From these, white luminescent devices were obtained with a maximum brightness of 774.3 cd/m2 and an EQE of 0.76%. High-brightness irradiation was obtained compared to other white-luminescent studies in the literature. In CdSe QLEDs, as a proof of concept, devices with a maximum brightness of 111,450 cd/m2 and an EQE of 15.08% were obtained. In these three works, devices with high brightness in their own categories were produced using both heavy metal and non-heavy metal QDs. Keywords: Optoelectronics, LED, QD, CQD LED, InP QLED, CdSe QLED
  • Master Thesis
    Anahtarlamalı Relüktans Motorlarında Tork Dalgalanmasının Azaltılması için Uyarlanabilir Çevrimiçi Tork Paylaşım Fonksiyonu Geliştirilmesi
    (Abdullah Gül Üniversitesi, Fen Bilimleri Enstitüsü, 2023) Genç, Ufuk; Tekgün, Burak
    Electrical machines play a crucial role in modern society by transforming electrical energy into mechanical energy and vice versa. These machines include various types of motors and generators, which are used in a wide range of applications such as electric vehicles, industrial automation, and renewable energy systems. One of the popular electrical machines is the switched reluctance machine (SRM), which is known for its high reliability and efficiency. The key advantages of the SRM include its simple structure, robustness, and low cost. The SRM does not require a permanent magnet or an excitation winding, making it an attractive option for high-volume, low-cost applications. Despite its advantages, the SRM also has some disadvantages that need to be considered. One of the main drawbacks of the SRM is being susceptible to torque ripple, which can result in vibration and noise. In order to overcome these disadvantages, advanced control methods have been developed for the SRM. One such control method is the torque sharing function, which distributes the load among the phases of the motor. This results in improved torque characteristics and reduced torque ripple. However, this control method also has some disadvantages, such as increased complexity and the need for more advanced sensors and controllers. Additionally, the torque sharing function may result in reduced efficiency, especially at high speeds. The purpose of this thesis study is to improve the torque ripple performance of SRM for a wide speed range through the proposed control approach. In conclusion, minimizing the torque ripple is a critical aspect of the operation of SRMs, and a range of control strategies and techniques can be used to achieve this goal. By reducing the torque ripple, SRMs can deliver improved efficiency, performance, and reliability, making them even more attractive for a wide range of applications.
  • Master Thesis
    Erken Orman Yangını Tespiti için Otonom Heterojen Çoklu Robot Sistemi Tasarımı
    (Abdullah Gül Üniversitesi, Fen Bilimleri Enstitüsü, 2022) Serin, Ömer Faruk; Güler, Samet
    The usage of autonomous multi-robot systems for human life-endangering applications is emerging. Early wildfire detection and firefighting are two example applications. In this study, a heterogenous multi-robot system is proposed for both fire detection and response. The system employs an unmanned aerial vehicle for beyond-visual line-of-sight observations and an unmanned ground robot for fire extinguisher carrying. The proposed method uses ultrawideband (UWB) communication and ranging modules for the relative localization of robots during their movements. A specially trained YOLOv7 object detection model is used for robustly detecting forest fires and smoke while a modified version of the Vector Field Histogram Plus (VFH+) algorithm on the ground robot is used for obstacle avoidance while navigating. The structural design of the system requires no odometry or mapping of the environment hence improving the applicability of the system while decreasing system complexity. Additionally, the proposed UWB localization system is shown to be robust in long-lasting operations unlike many odometry-based approaches which accumulate errors with time. Moreover, localization of the UAV is realized with only three independent UWB-based range measurements and the altitude information of the UAV. The system is tested both in a realistic simulation environment and in real experimental setups with multiple runs. Results showed that the proposed system is improvable for better detection and practical to implement even in a dense forest environment without the need for GPS sensors, odometer data, or magnetometer.
  • Master Thesis
    Esnek Kağıt Tabanlı Kapasitif Sensör Kullanarak Solunum İzleme
    (Abdullah Gül Üniversitesi, Fen Bilimleri Enstitüsü, 2022) Solak, İrfan; İçöz, Kutay; Hah, Dooyoung
    Respiration is an action known to be essential and crucial for life. Unfortunately, in some cases such as illnesses and accidents various respiratory problems can be experienced. It might be difficult to maintain normal respiration for the people who have respiratory diseases. It is known that respiration monitoring of people who have respiratory problems, albeit for different reasons, is important in terms of their treatment and maintaining their life quality. Current respiration monitoring systems are expensive and bulky. Many of these systems are only available at hospitals or in laboratories. Low-cost, easy to use and portable respiratory monitoring devices are needed. Having these motivations, we aimed to monitor respiration by designing and producing a paper-based sensor that is easy to manufacture, low-cost, and highly responsive. The sensor, which is the subject of this thesis project, has potential to be used for different purposes such as measuring the humidity in the environment. In this project, we focused on designing a system for people who have respiratory problems by providing respiration monitoring data. In addition, according to the data obtained, we are able to analyze the health status of the users. Therefore, this sensor can be used both for the detection of respiration diseases and monitor the status of the patients. In this way, respiration related unhealthy situation can be detected and treated immediately.
  • Master Thesis
    Elektrik Dağıtım Şirketleri Perspektifinden Blockchain Temelli Enerji Uygulamaları
    (Abdullah Gül Üniversitesi, Fen Bilimleri Enstitüsü, 2022) Yağmur, Ahmet; Tonyalı, Samet
    This thesis discusses blockchain-based energy applications from the distribution system operator (DSO) perspective. Blockchain has a potential impact on emerging actors, such as electric vehicles (EVs), charging facility units (CFUs), Distributed Energy Resources (DERs) and microgrids of the electricity grid. Although, blockchain offers magnificent, decentralized solutions, owing to the reality of the existing grid structure, the central management of DSOs still plays a significant, non-negligible role. Numerous studies of proposed blockchain-based EV systems have investigated the energy costs of EVs, fast and efficient charging, privacy and security, peer-to-peer energy trading, sharing economy, selection of appropriate location for CFUs, and scheduling. Additionally, blockchain in DERs, microgrids and energy market investigated in literature. However, cooperation with DSO organizations has not been adequately addressed. Blockchain-based solutions mainly suggest an entirely distributed and decentralized approach for energy trading. However, converting the entire power system infrastructure is considerably expensive. Building a thoroughly decentralized electricity network is nearly impossible in a short time, particularly at the national grid level. In this regard, the applicability of the solutions is as significant as their appropriateness, especially from the DSO perspective, and must be examined closely. The blockchain applicability of the essential DSO services such as SCADA and AMI are analyzed in this study. Time series analysis applied to forecast future peak load of the grid in a pilot region. Reducing the peak load by using BC based demand side management mechanism scenario evaluated and total saving of grid investment is analyzed. We searched and analyzed DSO-based requirements for potential blockchain applications in the energy sector.
  • Master Thesis
    Mesafe ve Görüntü Kullanan Dronlar ile Koordine Hedef Teşhisi ve Takibi
    (Abdullah Gül Üniversitesi, Fen Bilimleri Enstitüsü, 2022) Alabay, Hüsnü Halid; Güler, Samet
    Robot autonomy refers to the ability to carry out objectives by perceiving the environment and deciding on the actions required without human interruption. Although autonomous aerial robots offer big advantages in our daily life, online localization and control remain the biggest challenge lying ahead of aerial robot implementations. For single robot applications, GPS, and motion capture (mocap) systems can be utilized for outdoor and indoor applications, respectively. However, when it comes to multi-robot systems, the relative localization problem needs to be solved beyond the single robot localization problem. Furthermore, GPS signals are not available everywhere, and mocap systems limit the application space of multi-robot systems. Motivated by the industrial application scenarios, we address the relative localization and docking problem in multi-drone systems where drones do not utilize any external infrastructure for localization. We consider a two-drone system that aims at docking a target object which consists of an ultrawideband (UWB) distance sensor. The drones are equipped with UWB sensors and cameras and try to localize the target object and dock around it in a pre-defined configuration in the absence of GPS and magnetometer sensors and external infrastructures. We design an extended Kalman filter based on the dynamic model of the drone-target configuration that fuses the distance and vision sensor outputs. Particularly, we use the YOLO algorithm for the bearing detection between the drones and the target. Next, we devise and implement a switching-based distributed formation control algorithm and integrate it into the estimation algorithm. We demonstrate the performance of our algorithm in several simulation studies in a realistic Gazebo environment. Finally, we provide primary experimental results and a roadmap to the full implementation of the system.
  • Master Thesis
    Işık Emici Optoelektronik Cihazların Üretimi ve Yeni Uygulamaları
    (Abdullah Gül Üniversitesi, Fen Bilimleri Enstitüsü, 2022) Savaş, Müzeyyen; Erdem, Talha
    Fabrication of optoelectronic devices relies on expensive, energy-consuming conventional tools including chemical vapor deposition, lithography, and metal evaporation. Developing an alternative technology would contribute to the efforts on achieving a sustainable optoelectronics technology. Keeping this in our focus, here we present a simple technique to fabricate visible photodetectors. These fully solution-processed and transparent metal-semiconductor-metal photodetectors employ silver nanowires (Ag NW) as the transparent electrodes replacing the indium-tin-oxide (ITO) commonly used in optoelectronic devices. By repeatedly spin coating Ag NW on a glass substrate followed by the coating of ZnO nanoparticles, we obtained a highly conductive transparent electrode reaching a sheet resistance of 95 Ω/□. The transmittance of the Ag NW-ZnO films was 84% at 450 nm while the transmittance of the ITO films was 90% at the same wavelength. Following the formation of the conductive film, we scratched it using a heated surgical blade to open a gap which is ~30 µm forming an insulating line. As the active layer, we drop-casted red-emitting CdSe/ZnS core-shell colloidal quantum dots (CQDs) onto this gap. These visible CQD-based photodetectors exhibited responsivities and detectivities up to 8.5 mA/W and 0.95x109 Jones, respectively. These proof-of-concept photodetectors show that the environmentally friendly, low-cost, and energy-saving technique presented here can be an alternative to conventional, high-cost, and energy-hungry techniques while fabricating light-harvesting devices.
  • Master Thesis
    Kağıt Tabanlı Magnetoforetik Sensör Geliştirilmesi
    (Abdullah Gül Üniversitesi Fen Bilimleri Enstitüsü, 2022) FAROOQI, MUHAMMAD FUAD; Farooqi, Muhammad Fuad; İçöz, Kutay
    One of the widely used type of biosensors are paper-based lateral flow systems. They are used to detect a wide variety of biomolecules like microorganisms, proteins, chemicals, oligonucleotides among many others. In this research, a setup was created using dual magnet sets in which the flow of cell sample on two kinds of different sample paper was explored. There were two factors which affected the movement of the sample the most, the magnetic field and the wetting. Images were obtained using a cell phone along and/or a bright field optical microscope and then analyzed using image processing. Images were also taken using scanning electron microscope. The effects of the wetting and the magnetic field were tested and studied. It was found that at least 90% of the cells were able to reach the edge of the paper. Although the cells were not able to maintain their shape on the paper due to the unideal conditions of the paper for cells but still this kind of paper-based lateral flow assay setup can be used for cells to see their behavior when they were labelled and exposed to a magnetic field. This research shows support that this technique can be used for separating cells as well as detecting different cells.