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Quadrature spatial pulse amplitude modulation and generalized versions for vlc
(Osman Sağdıç, 2021) Çelik, Yasin
Quadrature spatial modulation (QSM) is a promising technique for multiple-input-multiple-output (MIMO) systems that completely prevents inter-channel interference (ICI) and provides spatial multiplexing gain greater than spatial modulation (SM). In QSM, the information conveyed by the indices of the transmit antennas doubles thanks to the in-phase and quadrature components. In this regard, the quadrature spatial pulse amplitude modulation (QSPAM), which enables QSM for visible light communication (VLC) with the help of orthogonal pulses, is proposed in this paper. Generalized versions of QSPAM, i.e. generalized QSPAM (GQSPAM) and variable-length generalized QSPAM (VGQSPAM) have also been proposed and a well-known scheme, spatial pulse amplitude modulation (SPAM), is used as a benchmark. The proposed schemes efficiently use the spatial domain and increase spectral efficiency with fewer light-emitting diodes (LEDs). The angular diversity receiver (ADR) proposed for the channel correlation problem of indoor MIMO VLC systems is used as the receiver unit. Although ADR reduces channel correlation, it is not sufficient in the corner of the room. Therefore, a precoding matrix is generated with the help of convex optimization for demanding conditions. The bit error rate (BER) performance of considered modulation schemes is obtained through Monte Carlo simulations and, the upper bound BER performances are also derived analytically to validate these results. Additionally, spectral efficiency (SE) versus signal-to-noise ratio (SNR) graphs are obtained at a fixed symbol error rate (SER) of 10-5. According to the results, VGQSPAM performs better than the other schemes and benchmarks when the channel correlation is low. However, GQSPAM outperforms VGQSPAM for harsh conditions.
A deep learning-based quality control application
(Osman Sağdıç, 2020) Korkmaz, Mehmet; Barstugan, Mücahid
The study at hand is an implementation of a deep learning strategy on a quality control scheme. The quality control process is a substantial part of product manufacturing. It fundamentally targets to detect and eliminate defective products so that the erroneous ones will not be delivered to the customers. Final product control has been usually performed by experts. Generally, those experts can easily distinguish defective and trouble-free products. On the other hand, growing product lines and human-based natural problems may affect the efficiency of that quality control process. Therefore, there is an increasing demand for computer-aided software that will take the place of those experts. This software or algorithm typically increases the product control rate. Besides, they make it possible to avoid from human-driven faults. The algorithms run at high speed and efficacy under conditional situations i.e. perfectly lightening environment. However, they may easily fail when small changes occur in the environment or the product for some duties that humans can easily achieve. These robustness problems make them not preferable, although they have numerous advantages. At this point, deep learning-based artificial intelligence algorithms have made a significant enhancement. The general development and achievable prices of GPUs pave the way for using numerous training examples so that better networks, meaning more robust, can be created for the applications. To this end, we carried on an experiment that could realize the deep learning strategy on the quality control scheme. For this purpose, the developed algorithms applied to the inverters conveying on a product line to confirm whether they are erroneous or not. Results show that developed strategy could detect defective products similar to the human being.
A revision of the navigation path based on different objects
(Osman Sağdıç, 2020) Korkmaz, Mehmet
This study is about a mobile robot navigation. Navigation algorithms are needed to move mobile robots. Thanks to these algorithms, the navigation of robots from the specified starting point to the target point is provided. However, avoiding obstacles while navigating the robot is one of the requirements that a standard navigation algorithm need. For obstacle avoidance, a navigation path is created by taking into account the obstacles on a known map. Another method is to actively scan during navigation and choose the paths without obstacles. On the other hand, classical obstacle detection or obstacle avoidance algorithms ignore whether objects are human or non- living. Thus, all obstacles are seen the same and the robot follows its path by avoiding these obstacles. On the other hand, treating people as a classic obstacle is one of the most important shortcomings of current navigation algorithms. In such a situation, people may be disturbed by the presence of robots. Especially after a Covid-19 pandemic, people need more space even between other humans. For this reason, obstacle avoidance algorithms encountered in classical navigation algorithms should be revised based on the presence of people so that a better navigation scheme will be created. In this context, a distinction is made between humans and other objects in this study. The robot updates the navigation paths by taking into account a social distance to people based on the proxemics theory. Thus, by providing the social distance people need, it has been able to create a navigation that will make people feel more comfortable.
Optoelektronik sensör kullanarak nefeste bulunan su buharı analizinin araştırılması
(Selçuk Üniversitesi Mühendislik Fakültesi, 2019) Bayraklı, İsmail
Bu çalışma kapsamında, biyomedikal uygulamalar için kullanılabilecek olan eksen-dışı kovuk artırılmış soğurma spektroskopisine dayalı optoelektronik sensör kullanılarak nefeste bulunan su buharı analiz çalışmaları yapılmıştır. İlk önce HITRAN veri tabanı kullanılarak teorik çalışma yapılmış ve subuharı molekülünün algılanması için kullanılabilecek olan soğurma çizgisi tespit edilmiştir. Ardından, bulunan soğurma çizgisi kullanılarak nefesteki su buharı molekülü analiz edilmiştir. Bunun için 1250-1350 nm aralığında dalga boyu taranabilen dış kavite diyot lazer sistemi kullanılmıştır. Lazerden çıkanışın, 50 cm odak uzaklığına sahip bir mercek ve bir ayna kullanılarak eksen dışı (off axis, OA) düzenekte, kovuk artırılmış soğurma spektroskopi kovuğuna bağdaştırılmıştır. Kovuk, 700 nm ile 1650 nm spektral aralığında çok yüksek geri yansıma katsayısına sahip (% 99.96), 1 m eğrilik yarıçapında ve 2.54 cm çapında iki tane aynadan oluşmaktadır. Bildiğimiz kadarıyla, su moleküllerinin analizi için ilgili spektral alan ilk defa bu çalışmada kullanılmıştır.
The Effect of LED Deployment on RSSI-based VLP Systems
(Osman Sağdıç, 2019) Çelik, Yasin
In this paper, the effect of light emitting diode (LED) deployment is investigated based on the received signal strength indication (RSSI)technique for visible light positioning (VLP) systems. The optical code division multiple access (OCDMA) is used as a multiplexingtechnique to transmit the location and RSSI information of LEDs simultaneously. For different highly reflective indoor scenarios, LEDsare placed on the ceiling of a room considering homogeneous illumination. The illuminance of the room is provided particularly with400 lux minimally at the desk height. In order to demonstrate the uniformity of lighting for different indoor scenarios, the uniformityilluminance ratio (UIR) values are also obtained in this study. In addition, electrical signal-to-noise ratio (SNR), an important parameterfor reliable communication, is calculated at desk height for each scenario considered and an SNR level of 45 dB is obtained at aminimum. The simulation results demonstrate that the mean square error (MSE) of the estimated location is reduced with an increase inthe number of visible access points (VAPs). The MSE of the distance for number of VAPs 12 and 16 are the best, however, the scenariowith 16 VAPs is preferable with a better uniformity illuminance ratio (UIR) parameter. In terms of illuminance, all the cases have theaverage illuminance value more than 450 lux.
Double Quadrature Spatial Intensity Modulation for Visible Light Communications
(Osman Sağdıç, 2019) Çelik, Yasin
In this paper, a new spectrally efficient space modulation technique, which is called double quadrature spatial intensity modulation(DQSIM), is proposed for multiple-input multiple-output (MIMO) visible light communication (VLC) systems. Sub-carrier intensitymodulation (SCM), which ensures the use of in-phase/quadrature (I/Q) signals in intensity modulation direct detection (IM/DD)systems, is used as a digital modulation scheme. In RF, quadrature spatial modulation (QSM) transmits the I/Q signals through singleor multiple antennas selected independently from each other. Furthermore, the orthogonality between I and Q components is providedfor the half period of sinusoids. DQSIM utilizes these two features and transmits four fold more bits than spatial modulation (SM) viaspatial constellation. SCM uses two-fold bandwidth compared to on-off keying (OOK), while DQSIM uses three fold. DQSIMoutperforms benchmark modulation schemes, which are SCM-SM and pulse amplitude modulation spatial modulation (PAM-SM), atthe bit error rate (BER) value of $10^{-4}$. Furthermore DQSIM performance has increased with the increasing number of LEDs.
A comparative study: voltage multipliers for rf energy harvesting system
(Ankara Üniversitesi Fen Fakültesi, 2019) Sarı, Filiz; Uzun, Yunus
Voltage multipliers are widely used for energy harvesting processesto convert the received AC signal to DC signal, also enhanced the low levelreceived signal. In this study, Villard, Dickson and Greinacher type voltagemultipliers are analyzed without impedance matching and substrate materials todecide the effective voltage multiplier type depending on the inputs of theharvester. So, load resistance, input power and input frequencies’ effects areanalyzed and compared with each other. Agilent Advanced Design System (ADS)is used for simulations. HSMS 2852 Schottky diode and capacitors are used forthese voltage multipliers. Results show that, determining load resistance isimportant for evaluating high efficiency, e.g. efficiency differences are reached33% between 2kΩ and 20 kΩ for Dickson voltage multiplier at 100 MHz inputfrequency. Furthermore, the best efficiency is obtained by Greinacher voltagemultiplier for low input frequencies which is lower than 1 GHz but there are nosignificant differences are observed for high frequencies. This study shows thatload resistance, input frequency and input power are important parameters forvoltage multiplier selection and Greinacher voltage multiplier is the best choice toobtain high efficiency for low frequency application of RF harvesting.
Performance analysis of adaptive mimo techniques for angular diversity receiver-based visible lıght communication
(Milli Savunma Üniversitesi Deniz Harp Okulu Dekanlığı, 2024) Horunlu, Kardelen; Çelik, Yasin
Correlation between the channels is the primary factor that restricts data rates in multiple-input multiple-output visible light communications (MIMO-VLC). Different receiver designs have been proposed to reduce this correlation value, while adaptive modulations that perform better under the correlated channel effect have been studied on the transmitter side. In this study, we conducted a performance analysis of MIMO-VLC systems by utilizing adaptive MIMO modulations at the transmitter side and angular diversity receiver (ADR) structures at the receiver side. As adaptive modulations, created using spatial diversity (SD) and spatial multiplexing (SMP) modulations, SD/SMP switching, adaptive SMP (aSMP), and SD-assisted adaptive SMP (SD-aSMP) are considered. Analytical and simulation results were obtained for achievable data rates in an indoor environment. Cumulative distribution function (CDF) graphs were used to assess the overall performance based on these data rates. GADR has an advantage over ADR in low SNR regions but performs similarly in high SNR regions. The SD-aSMP scheme demonstrated the best performance across all SNR regions as a hybrid modulation, taking advantage of diversity gain in low SNR and multiplexing gain in high SNR regions. The adaptive SMP schemes benefit from increasing the number of LEDs and increasing the elevation angle up to 60 degrees.
Damage detection in aircraft engine borescope inspection using deep learning
(Springer Science and Business Media Deutschland GmbH, 2025) Uzun, Ismail; Tolun, Mehmet Reşit; Sarı, Filiz; Alpaslan, Ferda Nur
Aircraft engine inspection is a key pillar of aviation safety as it helps to maintain adequate performance standards to ensure engine airworthiness. In addition, it is also vital for asset value retention. Borescope inspection is currently the most widely used visual inspection method for aircraft engines. However, borescope inspection is a time-consuming, subjective, and complex process that heavily depends on the experience and attention level of the inspector. Moreover, the cost savings of airlines and the maintenance, repair, and overhaul (MRO) centers expose pressure and workload on inspectors. These factors make an automated system to support damage detection during borescope inspection necessary in order to mitigate potential risks. In this paper, we propose a deep learning-based automated damage detection framework that employs aircraft engine borescope inspection images. Faster R-CNN-based deep learning model with Inception v2 feature extractor is utilized for the present architecture. Due to the limited number of images, data augmentation and other overfitting methods are also employed. The framework supports crack, burn, nick, and dent damage types across all modules of turbofan engines. It is trained and validated with moderate to complex borescope images obtained from the field. The framework achieves 92.64% accuracy for crack, 92.05% for nick or dent, and 81.14% for burn damage classes, with an overall 88.61% average accuracy.
Modular-Multi-Port-Converter-Based Battery Energy Storage System with Integrated Battery Management Functions
(Multidisciplinary Digital Publishing Institute (MDPI), 2025) Yıldırım, Börteçene; Elgendy, Mohammed A.; Smith, Andrew; Kulan, Mehmet C.; Akbal, Bahadır
Modular converters offer an effective solution for battery energy storage systems (BESSs) by lowering battery pack voltage levels and enabling additional functionalities, such as state of charge (SoC) and state of health (SoH) balancing, temperature regulation, and improved system reliability. However, conventional modular designs often require numerous additional components, including passive elements, switches, and sensing circuits. This paper proposes a modular multi-port converter (MMPC) BESS that combines energy conversion and battery management functions, leveraging the benefits of both modular and multi-port architectures. The proposed system demonstrates promising scalability and adaptability within the tested voltage and power ranges, with potential for extension to higher voltage and power applications through modular expansion. It also introduces an additional control layer, enhancing flexibility for control optimization and cost-effectiveness while improving reliability by reducing dependency on bypass switches. A prototype utilizing three dual-port converters managing six battery packs was developed. The experimental results confirm that the MMPC-based BESS achieves energy conversion and effectively balances the SoC among battery packs during both charging and discharging, under initial SoC mismatches.
Acoustic energy harvesting and modeling from distributed feedback quantum cascade laser based sensor system
(Elsevier B.V., 2025) Sarı, Filiz; Bayraklı, İsmail
This study analyzes acoustic energy harvesting from a distributed feedback quantum cascade laser (DFB-QCL)-based sensor system. The system integrates a DFB-QCL as an optical excitation source and a custom-designed photoacoustic resonator to generate and detect acoustic waves. A Cockcroft–Walton voltage multiplier (CWVM) converts the resulting electrical signal into direct current voltage. Capacitor tests for the VM are conducted under open-circuit and loaded conditions. Considering voltage conversion efficiency, mean voltage, and ripple, 22 µF capacitors are selected as optimal and used in all subsequent analyses. Experiments with up to four-stage VMs are conducted using ten load resistances. The fourth-stage VM delivers 6.4 mW of mean power under a 10 kΩ load, with an energy efficiency of 26.7%. These findings indicate the system's potential to power self-sufficient sensor networks and low-power electronic devices, especially in remote or inaccessible environments. A mathematical model is developed to describe the relationship between acoustic input, load resistance, and VM output. The model reflects the nonlinear characteristics derived from the time-domain analysis of the VM circuit and is constructed from experimental data. Its accuracy is validated using the mean squared error (MSE), root mean squared error (RMSE), and coefficient of determination (R2) metrics, yielding low error rates with R2 values ranging from 0.972 to 0.991. Mean voltage and power outputs are fitted by power series functions of load resistance, achieving goodness of fit above 99%. The high level of agreement between the fitted and modeled results demonstrates the model's reliability in representing stage-dependent system behavior.
Optimum cable bonding with pareto optimal and hybrid neural methods to prevent high-voltage cable insulation faults in distributed generation systems
(Multidisciplinary Digital Publishing Institute (MDPI), 2024) Akbal, Bahadır
The high voltage, current and harmonic distortion in high-voltage cable metal sheaths cause cable insulation faults. The SSBLR (Sectional Solid Bonding with Inductance (L) and Resistance) method was designed as a new cable grounding method to prevent insulation faults. SSBLR was optimized using multi-objective optimization (MOP) with the prediction method (PM) to minimize these factors. The Pareto optimal method was used for MOP. The artificial neural network, hybrid artificial neural network and regression methods were used as the PM. When the artificial neural network–genetic algorithm hybrid method was used as the PM, and the genetic algorithm was used as the optimization method, the voltage and current were significantly reduced in the metal sheath of the cable.
Zırhlı yüksek gerilim kablolarında yalıtım arızalarını önlemek için çok amaçlı optimizasyon ve hibrit yapay zekâ tabanlı kablo topraklama yöntemi
(Oğuzhan YILMAZ, 2024) Akbal, Bahadır
Bir yüksek gerilim kablosunda, yalıtkan tabaka üzerinde kullanılan metal kılıf ve zırh elektrik alanını sınırladıkları gibi mekanik etkilere karşı yalıtkanı korurlar. Ancak kablodan yük akımı geçince, zırh ve metal kılıf üzerinde kablo sıcaklığını artıran ve tehlikeli gerilimlere neden olan akım ve gerilimler oluşur. Aşırı kablo sıcaklığı ve tehlikeli gerilimler yalıtım arızalarına neden olmaktadır. Literatürde bu yalıtım arızalarını önlemek için farklı topraklama yöntemleri önerilmektedir. Ancak, son yıllarda harmonik akımlarının da etkisinin artmasından dolayı bu topraklama yöntemleri yalıtım hatalarını önlemek için yetersiz kalmaktadır. Bu çalışmada yüksek harmonikli akım ve gerilimden dolayı oluşan yalıtım arızalarını önlemek için optimizasyon ve yapay zekâ tabanlı yeni bir topraklama yöntemi önerilmektedir. Bu yöntemde, optimum bir topraklama yapabilmek için metal kılıf ve zırh üzerindeki geriliminin, akımının ve akım harmonik bozunumunun bilinmesi gerekir. Dolayısıyla, bu parametre değerlerinin tespiti için hibrit sinir ağları ve regresyon yöntemlerinden oluşan tahmin yöntemleri kullanılmıştır. Hibrit yapay arı kolonisi-yapay sinir ağı (H-YAK) ve gauss proses regresyon (GPR) yöntemleri minimum eğitim hatalarına göre bu gruplar içinden seçilmiş ve optimizasyon algoritmalarında amaç fonksiyonu olarak kullanılmışlardır. Önerilen topraklama yönteminin optimizasyonunda birçok amaç olduğu için çok amaçlı optimizasyon yöntemi kullanılmıştır. Çok amaçlı optimizasyonda, tahmin yöntemi olarak H-YAK kullanıldığında, metal parçalar üzerinde gerilim, akım ve akım harmoniklerinde optimum değerler sağlanmıştır.
Compact laser spectroscopy-based sensor using a transformer-based model for analysis of multiple molecules
(Optica Publishing Group (formerly OSA), 2024) Bayraklı, İsmail; Eken, Enes
Interest in the development of compact sensors that consume low energy is increasing day by day. This study reports, to our knowledge, such a novel sensor system that can analyze multiple molecules simultaneously with high sensitivity under ambient conditions (900 mbar and 300 K). To quantify molecules, a distributed feedback quantum cascade laser (DFB QCL) was combined with a compact multi-pass absorption (mpass) cell without the need for vacuum components, lock-in amplifier, or any electric filters. By using a transformer-encoder-based model, the noise level was reduced and the pressure-broadened absorption lines of the molecules were separated, narrowed (resolved), and displayed one by one. In this way, molecules can be quantified using pressure-broadened overlapping absorption lines under ambient conditions. To test our sensor system, CO2 and N2O molecules were used. Depending on the concentration values, SNR can be improved by up to 50 times. Better results are obtained at higher concentration values. Detection limits for N2O and CO2 molecules were determined to be 30 ppb and 180 ppm, respectively. The analysis time of molecules is around 80 ms.
Optimal fuzzy P + Dµ controller for cancer chemotherapy
(Elsevier Ltd, 2024) Ay, Sena; Soylu, Selim
This paper aims to develop a robust, effective, and optimal controller for an automatic intravenous drug delivery system for the chemotherapy treatment of cancer patients. For this purpose, a novel hybrid control method, namely the Fuzzy P + Dµ controller, is designed by combining fractional calculus and fuzzy logic controller (FLC). Particle swarm optimization (PSO) algorithm is employed to tune the controller parameters optimally. To evaluate the performance of the proposed controller, a cancer patient model that considers cumulative drug toxicity, one of the most common side effects of chemotherapy, is utilized. Limits on toxicity and drug concentration for patient safety are incorporated into the controller design and optimization process. The graphical and numerical simulation results show that almost no cancerous cells are left at the end of the treatment period. The effectiveness of the controller is proven by the performance index (PI) obtained. Our optimal hybrid Fuzzy P + Dµ outclasses other control techniques in previous related studies with the best PI of 44.426 and the minimum final number of cancerous cells (FNCCs) of 5.084E-08. Moreover, in robustness tests perturbing intra-patient parameters and using different treatment protocols, the cumulative drug toxicity level is kept within safe limits, and almost no cancerous cells remain
Design of Optimal FOPI Controller for Two-Area Time-Delayed Load Frequency Control System with Demand Response
(Korean Institute of Electrical Engineers, 2024) Katipoğlu, Deniz; Soylu, Selim
This study comprehensively investigates modeling and controller design for two-area load frequency control (LFC) system with demand response (DR) and time delays. An optimized fractional order proportional-integral (FOPI) controller is designed both to improve the stability of grid frequencies and to deal with the time delays. Using the stability boundary locus (SBL) method, the stability region for the FOPI controller parameter space is obtained. The boundaries of these stability regions are used in the optimization process of the FOPI controller parameters. A new objective function is used to minimize the integral time-weighted absolute error (ITAE) and time domain specifications such as overshoot (OS) and undershoot (US) of the frequency and tie-line power deviations. The parameters of the FOPI controller are optimized by Artificial Hummingbird Algorithm (AHA). The simulation results are compared with gray wolf optimizer (GWO) and particle swarm optimization (PSO) tuned FOPI controllers. The AHA tuned FOPI (AHA-FOPI) controller gives very promising results, especially in terms of improving the transient response of the system by reducing the settling time (ST) and steady-state error (ess). Additionally, the effectiveness of the AHA-FOPI is demonstrated under increased time delay. It is evident from the simulation results that the AHA-FOPI controller has successfully improved the time domain characteristics of the LFC-DR system.
A novel approach for improving the performance of deep learning-based state of charge estimation of lithium-ion batteries: Choosy SoC Estimator (ChoSoCE)
(Elsevier Ltd, 2024) Korkmaz, Mehmet
Deep learning-based (DL) methods have recently come to the forefront among the data-driven models due to their success in capturing the complexities of the battery. Many previous DL-based studies for SoC estimation have almost exclusively focused on improving DL structure by proposing various architectures. Questions regarding the outlier or atypical predictions have yet to be adequately addressed. Furthermore, few works benefit from optimization algorithms to determine the hyperparameters of DL. In this study, we have addressed the problem of how to obtain the hyperparameter of DL and fix the improper DL predictions. To this aim, we used two different optimization algorithms to determine the hyperparameters of DL and proposed a novel algorithm that considers the previous SoC estimations. The algorithm either approves or rejects the DL predictions for the relevant step and offers new values for the rejected ones. The proposed scheme is evaluated using a battery dataset which includes different driving cycles. According to the results, it is observed that the optimized DL outperforms the empirical one by at least 35% in terms of performance indices. Moreover, the proposed novel algorithm successfully integrates into all variations and significantly improves the performance index scores.
Joint Pulse Index and Spatial Modulation
(Institute of Electrical and Electronics Engineers Inc., 2024) Aldırmaz Çolak, Sultan; Aydın, Erdoğan; Gündem, Sümeyra; Çelik, Yasin; Başar, Ertuğrul
According to the planned key performance indicator (KPI) standards, 6G technology should achieve higher throughput than 5G. More efficiency in transceiver schemes is required to meet this demand. In this study, we take advantage of spatial modulation (SM) and pulse index modulation (PIM) techniques to increase spectral efficiency. The proposed PIM-SM scheme utilizes well-localized and orthogonal Hermite-Gaussian pulses along with spatial indexing. Thanks to the orthogonality between pulses in the set, multiple pulses are transmitted together. The design, simulation, and analytical bit error rate performance derivations of PIM-SM are discussed in this letter to verify the viability and compatibility of pulse-based data transfer utilizing the spatial domain. The performance is compared with generalized code index modulation-spatial modulation (GCIM-SM), code index modulation-quadrature spatial modulation (CIM-QSM), and classical spatial modulation (SM) schemes.
Dinamik talep cevabı içeren zaman gecikmeli iki bölgeli yük frekans kontrol sistemlerinin kararlılık bölgelerinin hesaplanması
(Gazi Üniversitesi, 2024) Katipoğlu, Deniz; Sönmez, Şahin; Ayasun, Saffet
Bu çalışmada, dinamik talep cevabı (DTC) ve haberleşme zaman gecikmesi içeren iki bölgeli yük frekans kontrol (YFK-DTC) sisteminin kararlılık sınır eğrisi yöntemi kullanılarak denetleyici parametre düzleminde kararlılık bölgeleri hesaplanmıştır. DTC kontrol, kontrol edilebilir yük gruplarını frekans kontrol servisine dahil ederek, üretim ve puant yük talebi arasında dengenin daha kısa sürede sağlanması ve yenilenebilir enerji kaynaklarında güç dengesizlikleri problemlerine karşı önemli bir çözüm sunmaktadır. DTC kontrol mekanizmasının yük frekans kontrol sistemlerinde kullanımı, sistemin güvenliği ve güvenilirliğini sağlamasına rağmen, haberleşme ağlarından kaynaklanan zaman gecikmeleri, denetleyici performansını ve sistemin kararlılığını olumsuz etkileyebilmektedir. Dolayısıyla, bu çalışma zaman gecikmesi içeren iki bölgeli YFK-DTC sisteminin kararlılığını garanti edecek tüm oransal-integral (PI) denetleyici kazanç değerlerini elde etmektedir. Bu amaçla, zaman gecikmeli YFK-DTC sisteminin denetleyici parametre düzleminde kararlılık bölgelerini oluşturan kompleks kök sınır (Complex Root Boundary, CRB) eğrisini ve reel kök sınır (Real Root Boundary, RRB) eğrisini bulmak için kararlılık sınır eğrsi yöntemi kullanılmıştır. Elde edilen teorik sonuçların doğruluğu, quasi-polynomial mapping root (QPmR) algoritması ve zaman düzleminde yapılan benzetim çalışmaları ile gösterilmiştir. Sonuçlar, DTC kontrol çevriminin katkısı ile zaman gecikmeli YFK sisteminin kararlılık bölgelerinin ve kararlılık payının arttığını göstermektedir.
Nickel-coated carbon fillers for polyurethane foam with improved microwave absorption performance: A comparative analysis
(Wiley, 2024) Kurt, Gökçe; Korkmaz, Mehmet
In this study, polyurethane foam (PUF) composites were prepared by incorporating different functional fillers, and morphological, rheological, dielectric, and microwave absorption properties of these composite samples were investigated. Graphite (G), nickel (Ni), nickel-coated hybrid carbon (NiC), and iron II-III oxide (Fe3O4) powders were used as functional fillers, while rigid polyurethane foam (PUF) with a 40 kg/m3 density and a closed-cell structure was used as the carrier foam phase. Morphological analyses that were carried out by scanning electron microscopy showed that all fillers were dispersed between the cell walls. In dielectric characterization, the highest electrical permittivity values were obtained by incorporation of G, while the highest magnetic permeability values were obtained by incorporation of Fe3O4 at the same filler concentration. Furthermore, the PUF composites could be prepared using NiC at a higher filler concentration than the others due to the lower viscosity increasing effect of NiC. The highest microwave absorption performance was obtained in the NiC-filled PUF composite at a filler concentration of 120 phr. The minimum reflection loss (RL) value of -45.2 dB at 10.62 GHz and an RL value lower than -10 dB in the entire X-band region were obtained in the NiC-filled PUF composite.HighlightsNickel-coated carbon (NiC) filled polyurethane foam (PUF) was prepared.The absorption performance of NiC was compared to conventional filler.PUF composites containing NiC showed lower viscosity and processability.The highest absorption could be obtained by NiC compared to conventional fillers.

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