WoS İndeksli Yayınlar Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12573/394
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Article Microstrip Stub Filter Design with Enhanced Performance Inspired by SIW Structures Operating at 1.93 GHz GSMBand(Gazi Univ, 2026-03-29) Tosun, Huseyin; Yentur, Abdulkadir; Kilic, Veli TayfunThis paper reports a microstrip stub filter design operating at 1.93 GHz GSM band with enhanced performance inspired by SIW structures. In the designed filter additional vias are placed around the microstrip lines to enhance the encasing of the electromagnetic fields while propagating through the filter to develop the filter performance. The filter was examined with electromagnetic simulations for various numbers of vias and different via to microstrip line distances. Results show that the maximum transmission coefficient (S21 parameter) magnitude value reached in the pass band of the filter increases with the number of the vias and as the vias get closer to the lines. On the other hand, when the via number increases and the space between them and the lines narrows, the frequency at which the maximum S21 value is attained shifts to lower frequencies. The designed filters were manufactured, too. Results obtained in the measurements agree well with the simulation results. Additionally, a receiver system operating at 1.93 GHz band was constructed. System experiments were carried out with the constructed prototype for the manufactured filters. Results show that a greater signal level in the filter pass band is achieved and unwanted signals outside the filter pass band are suppressed more in the system where the filter with vias is used instead of the filter without any additional via. The findings indicate that the designed filters inspired by SIW structures are promising for applications requiring high signal quality.Conference Object Citation - WoS: 2Citation - Scopus: 194.8 Km-Range Direct Detection Fiber Optic Distributed Acoustic Sensor(Optica Publishing Group (Formerly OSA), 2019) Uyar, F.; Onat, T.; Unal, C.; Kartaloǧlu, T.; Ozdur, I.; Özbay, E.This work demonstrates an ultra-long range direct detection fiber optic distributed acoustic sensor which can detect vibrations at a distance of 94.8 km with 10 m resolution along the sensing fiber. © 2023 Elsevier B.V., All rights reserved.Conference Object Citation - WoS: 2Citation - Scopus: 2Cascade Control of Magnetic Levitation with Sliding Modes(EDP Sciences edps@edpsciences.com, 2016) Eroǧlu, Y.; Ablay, G.The effectiveness and applicability of magnetic levitation systems need precise feedback control designs. A cascade control approach consisting of sliding mode control plus sliding mode control (SMC plus SMC) is designed to solve position control problem and to provide a high control performance and robustness to the magnetic levitation plant. It is shown that the SMC plus SMC cascade controller is able to eliminate the effects of the inductance related uncertainties of the electromagnetic coil of the plant and achieve a robust and precise position control. Experimental and numerical results are provided to validate the effectiveness and feasibility of the method. © 2016 Elsevier B.V., All rights reserved.Article Fluctuations in the European Housing Market: Forecasting the House Price Index Change with Time-Series Models(Gazi Univ, 2026-03-15) Soylemez, Ismet; Nalici, Mehmet Eren; Unlu, RamazanThis study presents a comparative analysis of a time series models for forecasting changes in the Housing Price Index (HPI) in 27 European countries. Accurate HPI forecasting is essential for the development of effective policies and investment strategies. The study uses quarterly data from Q4 2013 to Q3 2024. Methodologically, the stationarity of the data is tested using the Dickey-Fuller test and differencing is applied to non-stationary series. The ARIMA, Holt Linear Trend, Additive Damped Trend and Exponential Smoothing models are evaluated based on the lowest mean squared error (MSE) value for each country. The findings confirmed the heterogeneous structure of the European housing market, showing that no single model is suitable for all countries. The ARIMA model provided the most accurate results for nine countries, while the Holt Linear Trend and Additive Damped Trend models performed best in seven countries each. Forecasts for the period 2025-2026 are generated based on these results. This study highlights the importance of adopting country-specific and adaptable forecasting approaches to accommodate the varying dynamics of European housing markets.Article Effect of Different Pitch Ratios on the Flow Around Tandem Circular Cylinders with Spoilers(Elsevier Ltd, 2025-12) İlkentapar, M.; Akşit, S.; Öner, A.A.; Genç, M.S.This study experimentally investigates the unsteady aerodynamic characteristics of two tandem circular cylinders subjected to various pitch ratios and spoiler configurations in a controlled wind tunnel environment. The primary objective is to understand how the placement and presence of spoiler's influence flow separation, wake interference, surface pressure distributions, and overall aerodynamic performance. The experiments were conducted for three pitch ratios (2D, 4D, and 7D) and four spoiler configurations: NN (no spoilers on either cylinder), NS (spoiler on the downstream cylinder only), SN (spoiler on the upstream cylinder only), and SS (spoilers on both cylinders). Measurements included surface pressure, velocity distribution via hot-wire anemometry, and aerodynamic forces, while qualitative flow patterns were assessed using smoke-wire visualization. The results indicate that the usage of spoilers substantially alters the wake structure and pressure profiles, especially in closely spaced configurations. In the NN configuration, increasing the pitch ratio led to a progressive decoupling of the flow between the cylinders, transitioning from a merged wake to more isolated vortex shedding. In the SN and NS configurations, the asymmetrical placement of spoilers induced unsteady wake interactions and altered reattachment dynamics on the downstream body. The SS configuration exhibited the most disturbed flow regime at low pitch ratios, which gradually stabilized as the spacing increased. Violin plots derived from velocity measurements provided statistical insight into flow symmetry and turbulence intensity, while smoke visualizations captured coherent structures and transition zones across the configurations. The combined analysis demonstrates that both pitch ratio and spoiler configuration are critical parameters in controlling aerodynamic interference and unsteady wake behavior in tandem arrangements. These findings offer valuable implications for flow management and control strategies in offshore structures, cylindrical risers, and heat exchanger tube banks, where vortex-induced vibrations and flow separation play crucial roles. © 2025 Elsevier B.V., All rights reserved.Conference Object Range-Based Wireless Sensor Network Localization by a Circumnavigating Mobile Anchor Without Position Information(IEEE, 2024-06-11) Guler, SametTypical range-based wireless sensor network (WSN) localization approaches aim at estimating the sensor node positions by using a set of anchors with known positions. In some applications, assuming the knowledge of the anchors' positions may be impractical, and estimation of the sensors' positions in an arbitrary fixed frame may be sufficient. Considering such scenarios, we propose a WSN localization algorithm by single mobile anchor without self location information. The mobile anchor obtains distance measurements from the sensors while tracking a custom trajectory which is shown to improve the localization performance over time for high signal-to-noise ratio cases. By utilizing two stationary reference nodes within the WSN, the proposed framework generates sensor node position estimation up to translation and rotation with sufficient precision in the absence of global positioning aids. We foresee that the proposed framework can demonstrate benefits in several WSN applications ranging from internet-of-things to service robotics.Conference Object Quasi-Static Operation of 2-Axis Microscanners With AlN Piezoelectric Quad-Actuators(Institute of Electrical and Electronics Engineers Inc., 2021-08-25) Hah, D.Aluminum nitride (AlN) started to draw attentions as a material for piezoelectric actuation owing to its CMOS process compatibility and safeness for biomedical applications. Due to its relatively low piezoelectric coefficients, AlN-based piezoelectric actuators have been mostly operated in resonance modes, especially in optical scanning. This paper presents a novel design of a 2-axis-tilt microscanner with AlN piezoelectric quad-actuators and meander-shaped hinges for reasonable quasi-static operation. Through finite-element-method simulation, it is shown that the proposed device can have about 9 degree of optical scan angle in two dimensions with the voltage amplitude of 50 V. Lissajous scanning operation of the device is demonstrated as well via simulation. © 2021 Elsevier B.V., All rights reserved.Conference Object Power Factor Improvement of a Permanent-Magnet Vernier Machine with Harmonic Injected Excitation Currents(IEEE, 2025-06-11) Karatepe, Hasan Can; Tekgun, DidemPermanent-magnet vernier machines (PMVM) are recognized for their high torque density but low power factor (PF) due to high inductive reactance. This paper presents a method for improving the PF of a PMVM by injecting additional harmonics into the excitation currents. This injection is done through the motor drive, unlike many proposed methods for enhancing PF, thus eliminating any modifications needed on the machine's geometric design. In this paper, different sets of harmonic injected currents are fed to a 14-rotor pole 12-slot PMVM with short-pitched coils on Finite Element Analysis (FEA) to demonstrate the effects of individual and combined harmonic currents. Corresponding performance characteristics of each simulation case, such as PF and torque density, are investigated. Simulation results indicate that PF can be improved by the proposed method of harmonic current injection. A comparison with a similarly sized permanent-magnet synchronous machine (PMSM) is made to demonstrate that the proposed method can be an alternative to widely used PMSMs.Conference Object Citation - Scopus: 1NLP-Driven Fake News Detection: A Machine Learning Perspective(IEEE, 2025-05-23) Coban, Mert Korkut; Bakal, GokhanThe rapid spread of fake news poses a significant challenge, impacting public opinion, decision-making, and societal trust. This study explores the application of Natural Language Processing (NLP) and Machine Learning (ML) techniques for robust fake news detection. Using datasets such as ISOT Fake News, WELFake, and Football Fake News, the project employs advanced preprocessing methods and feature extraction techniques, including TF-IDF, Word2Vec, and GloVe. A comprehensive evaluation of machine learning models-Random Forest, Support Vector Machines (SVM), and Neural Networks-was conducted to identify the optimal configuration. Results demonstrate that Random Forest with TF-IDF excels in in-domain detection, achieving an F1-score of 99.70%, while Neural Networks paired with Word2Vec and GloVe embeddings outperform in cross-dataset scenarios. The study highlights the importance of dataset size, domain relevance, and feature representation in achieving high generalizability. These findings provide a scalable framework for combating misinformation on digital platforms.Conference Object Citation - WoS: 2Citation - Scopus: 2Influence of Eccentricity Faults on IPM Motor Equivalent Circuit Characteristics(IEEE, 2025-06-11) Tekgun, DidemInterior Permanent Magnet (IPM) machines are preferred in various modern applications due to their high efficiency, compact design, and reliability. They are especially favored in electric vehicle (EV) powertrains but also play a key role in hybrid vehicles, electric motorcycles, industrial automation systems, robotics, and home appliances such as air conditioners and washing machines. Eccentricity is a critical and challenging issue since it causes an unbalanced airgap magnetic flux and forces, eventually resulting in vibration, noise, and a higher likelihood of motor malfunction over time. This study investigates the effects of eccentricity faults on the motor's magnetic flux density and corresponding equivalent circuit parameters through Finite Element Analysis (FEA). The results show that the two types of eccentricity, static and dynamic, produce noticeable variations in the airgap magnetic flux as well as in key equivalent circuit parameters. Specific equivalent circuit parameters are particularly sensitive to different eccentricity faults, making them key indicators for early fault detection.