Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7148
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Editorial Comments on “Relaxed Conditions for the Input-to-State Stability of Switched Nonlinear Time-Varying Systems”(Ieee-inst Electrical Electronics Engineers inc, 2025) Sahan, Gokhan; Trenn, StephanThis study addresses the deficiencies in the assumptions of the results in (Chen and Yang, 2017) due to the lack of uniformity. We first show the missing hypothesis by presenting a counterexample. Then, we prove why they are wrong in that form and show the errors in the proof of the main result of (Chen and Yang, 2017). Next, we compare the assumptions and related results of (Chen and Yang, 2017) with similar works in the literature. Lastly, we give suggestions to complement the shortcomings of the hypotheses and thus correct them.Article A Framework for Adaptive Load Redistribution in Human-Exoskeleton Systems(Ieee-inst Electrical Electronics Engineers inc, 2025) Mobedi, Emir; Solak, Gokhan; Ajoudani, ArashWearable devices like exoskeletons are designed to reduce excessive loads on specific joints of the body. Specifically, single- or two-degrees-of-freedom (DOF) upper-body industrial exoskeletons typically focus on compensating for the strain on the elbow and shoulder joints. However, during daily activities, there is no assurance that external loads are correctly aligned with the supported joints. Optimizing work processes to ensure that external loads are primarily (to the extent that they can be compensated by the exoskeleton) directed onto the supported joints can significantly enhance the overall usability of these devices and the ergonomics of their users. Collaborative robots (cobots) can play a role in this optimization, complementing the collaborative aspects of human work. In this study, we propose an adaptive and coordinated control system for the human-cobot-exoskeleton interaction. This system adjusts the task coordinates to maximize the utilization of the supported joints. When the torque limits of the exoskeleton are exceeded, the framework continuously adapts the task frame, redistributing excessive loads to non-supported body joints to prevent overloading the supported ones. We validated our approach in an equivalent industrial painting task involving a single-DOF elbow exoskeleton, a cobot, and four subjects, each tested in four different initial arm configurations with five distinct optimisation weight matrices and two different payloads.Article Finite-Dimensional Backstepping Controller Design(Ieee-inst Electrical Electronics Engineers inc, 2025) Kalantarov, Varga K.; Ozsari, Turker; Yilmaz, Kemal CemIn this article, we introduce a finite-dimensional version of backstepping controller design for stabilizing solutions of partial differential equations (PDEs) from boundary. Our controller uses only a finite number of Fourier modes of the state of solution, as opposed to the classical backstepping controller which uses all (infinitely many) modes. We apply our method to the reaction-diffusion equation, which serves only as a canonical example but the method is applicable also to other PDEs whose solutions can be decomposed into a slow finite-dimensional part and a fast tail, where the former dominates the evolution in large time. One of the main goals is to estimate the sufficient number of modes needed to stabilize the plant at a prescribed rate. In addition, we find the minimal number of modes that guarantee the stabilization at a certain (unprescribed) decay rate. Theoretical findings are supported with numerical solutions.Article Regression Via Classification for Fingerprint Orientation Estimation(Ieee-inst Electrical Electronics Engineers inc, 2024) Erdogmus, NesliEstimating the direction in which the ridges and valleys of the fingerprint pattern are aligned often serves as a pivotal first step in fingerprint recognition systems. The ridge orientation map is a fundamental reference for subsequent processing stages, such as image enhancement, feature extraction, and matching. Therefore, its accuracy is essential to achieve high recognition rates. Ridge orientation estimation entails a regression problem since the task is to estimate an angle between 0 degrees and 180 degrees for each sub-region in the fingerprint image. However, the majority of the approaches in the literature pivot towards framing this regression task as a classification problem. This paper systematically analyzes the regression via classification methodology for fingerprint orientation estimation, exploring various discretization and encoding strategies. Specifically, we examine single and multiple discretization schemes designed to ensure that resulting bins maintain uniform length or uniform probability or are allocated randomly, paired with one-hot, ordinal, and cyclic encoding techniques. Our experiments are conducted on the FOE-TEST database from FVC-onGoing, the sole publicly available fingerprint orientation dataset. The findings highlight the efficacy of cyclic encoding over the one-hot encoding prevalent in prior research, while equal-length and equal-probability discretization strategies yield comparable results.Article Citation - WoS: 1Citation - Scopus: 1Torque-Current Relationship of an Mr Brake for Its Open-Loop Control(Ieee-inst Electrical Electronics Engineers inc, 2024) Kucukoglu, Sefa Furkan; Bozelli, Muhammed Rza; Dede, Mehmet Ismet CanActive and semiactive actuators have been widely preferred for designing an actuation system for kinesthetic-type haptic devices. Among them, magnetorheological fluid-based brakes (MR brakes) offer potent properties, such as high torque/inertia ratio and less power consumption. However, one of the most critical issues to be resolved is their hysteresis behavior. Various methods for modeling the input/output relationship with hysteresis behavior exist. However, hysteresis compensation approaches, i.e., torque-current hysteresis model, are not widely studied for MR Brakes. Therefore, a hysteresis compensation model approach to account for the nonlinear behavior of MR Brake is proposed, and the model is experimentally validated in this article. The model consists of multiple splines and an algorithm that uses these splines in hysteresis compensation. Being relatively simple and easily implementable are the distinguished features of the presented model since an optimization method is not required. Furthermore, the performance of the proposed method is compared with two methods, torque-to-current mapping and inverse Prandtl-Ishlinskii method. The obtained experimental results are investigated with three performance metrics. Finally, the effect of the operational speed on the performance of the hysteresis compensation model is also discussed.Article Citation - WoS: 1Citation - Scopus: 1Multi-Haps Thz Satellite Communication: Error and Capacity Analyses Under I/Q Imbalance(Ieee-inst Electrical Electronics Engineers inc, 2024) Ahrazoglu, Evla Safahan; Altunbas, Ibrahim; Erdogan, EylemSatellite communication (SatCom) has become an important field of research to accomplish the requirements of next-generation wireless communication systems such as high data rates and capacity while providing global coverage. Besides traditional communication applications, SatCom is gathering more and more attention as it enhances the performance of sensing applications, such as environmental monitoring, atmospheric pollution monitoring, and so on. To deliver worldwide service and improve accurate data collection in sensor networks, high-altitude platform station (HAPS) systems can be employed in SatCom. Moreover, utilizing terahertz (THz) frequencies in HAPS-assisted SatCom systems offers incredibly high bandwidths, enabling extreme data rates and higher resolution in sensing applications. In this article, a THz SatCom system model is considered where K number of HAPS systems are deployed to assist the transmission between a low-Earth-orbit satellite and a ground station by utilizing variable-gain amplify-and-forward (AF) relaying. The symbol error rate (SER) and ergodic capacity analyses are performed in the presence of attenuation depending on the atmospheric conditions, fading, pointing error (PE), and in-phase and quadrature (I/Q) imbalance. Theoretical findings are validated through Monte-Carlo simulations.Article Citation - Scopus: 2Mixture-Based Dielectric Permittivity Measurements Through Gallium-Excited Cavities(Ieee-inst Electrical Electronics Engineers inc, 2024) Karatay, Anil; Yaman, FatihIn dielectric measurements within resonant cavities, analytical perturbation methods encounter limitations, particularly with nonstandard cavity shapes and lossy materials under test (MUTs) having high dielectric constant. In such cases, the demand for iterative techniques to improve accuracy and flexibility is evident, but the efficiency of the existing iterative techniques, relying on numerical electromagnetic solvers, is often compromised, particularly in terms of time. Therefore, we introduce a novel methodology for measuring the permittivity of dielectric materials using liquid mixtures. This novel method employs a rapid iterative technique in which effective permittivity values are reconstructed at each iteration step based on the volume fraction of liquid mixtures, thus eliminating the dependence on time-consuming 3-D numerical solvers. In addition, we aim to achieve dual-band measurements at 2.45 and 5.8 GHz, enhancing precision by separating mode frequencies. Introducing a re-entrant cavity-like structure, we position the first mode at 2.45 GHz and the second at 5.8 GHz, effectively mitigating intermodal crosstalk and ensuring measurement accuracy. Also, for the first time in the literature, determining which mode will be excited in a cavity by the coupler probe made of gallium can be achieved through the displacement of the liquid metal, which enables measurements to be taken exclusively at the desired frequency.Article Phase Shift Optimization for Ris Enabled Pnc System With Multiple Antennas(Ieee-inst Electrical Electronics Engineers inc, 2024) Ilguy, Mert; Ozbek, Berna; Musavian, Leila; Mumtaz, ShahidReconfigurable intelligent surfaces (RIS) have been developed to exploit the stochastic characteristics of the propagation environment for next generation wireless systems. On the other hand, the integration of wireless physical network coding (PNC) and multiple antennas yields notable enhancements in system performance. This paper presents a multiuser system, employing RIS enabled PNC alongside multiple antennas to minimize both delay and error probability. Our aim is to establish reliable communication between the user pairs, which communicate through a base station (BS) via RIS. Therefore, the reflecting coefficients including both phases and amplitudes of the RIS are optimized by using the alternating direction method of multipliers (ADMM) algorithm for both single and multiple RIS cases. Extensive results are presented to compare the proposed algorithm with random phase shift, network coding (NC) and the search algorithm to illustrate its superiority.Article Citation - WoS: 3Citation - Scopus: 3Liquid Metal-Tunable Miniaturized Bimodal Cavity for Enhanced Measurement Accuracy in the Ism Bands(Ieee-inst Electrical Electronics Engineers inc, 2024) Karatay, Anil; Yaman, FatihEnhancing measurement accuracy or reducing the effect of the neighboring modes in resonant cavities may necessitate the separation of mode frequencies. However, in ISM-band measurement configurations utilizing a rectangular or cylindrical cavity, the placement of the first two modes at 2.45 and 5.8 GHz is unattainable, necessitating the presence of additional modes in between that would potentially degrade measurement accuracy. This article begins with an analytical approach, employing Lagrange multipliers for the first time to reveal the level of separation achievable in the frequency domain between the initial two modes within these types of conventional cavities. The analytical results were also verified with a numerical grid search. Subsequently, innovative strategies have been introduced to surpass this intrinsic constraint that reduces the measurement accuracy in various applications. A novel miniaturized cavity configuration has been proposed to operate bimodally at 2.45 and 5.8 GHz and manufactured with a 3-D printer. It has been ensured that there are no physical modes present in between, and measurements of the structure have been conducted. Another notable innovation of the article is the capability of tuning the proposed cavity structure by means of liquid metal displacement. Thus, a more flexible tuning method compared to mechanical tuning techniques can be achieved, enabling precise adjustment of the desired measurement frequency. Good agreement between the simulation and measurement results has been reported.