Elektrik Elektronik Mühendisliği Bölümü

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Citation - WoS: 28
Citation - Scopus: 30
Effect of Anisotropy on Intensity Fluctuations in Oceanic Turbulence
(Taylor & Francis Ltd, 2018) Baykal, Yahya
For an optical spherical wave propagating in an oceanic turbulent medium, the effect of anisotropy on the received intensity fluctuations is investigated. For different anisotropy factors, the variations of the scintillation index vs. the ratio that determines the relative strength of temperature and salinity in the index fluctuations, the rate of dissipation of the mean squared temperature, the rate of dissipation of the turbulent kinetic energy, viscosity, link length and the wavelength are plotted. It is found that, for all the oceanic turbulence and the link parameters of interest, as the medium becomes more anisotropic, the intensity of the optical spherical wave fluctuates less. It is concluded that the performance of an optical wireless communication systems (OWCS) operating in anisotropic oceanic turbulence is better than the performance of OWCS operating in isotropic oceanic turbulence.
Citation - WoS: 10
Citation - Scopus: 10
Cross-Beam Scintillations in Underwater Medium
(Spie-soc Photo-optical instrumentation Engineers, 2016) Baykal, Yahya
The fluctuation in the intensity, which is quantified by the scintillation index, is evaluated for cross beams when such beams propagate in an underwater medium experiencing turbulence. The variations in the scintillation index are investigated against the changes in the size of the cross beams, the ratio of temperature to salinity contributions to the refractive index spectrum, the rate of dissipation of mean-squared temperature, and the rate of dissipation of kinetic energy per unit mass of fluid. (C) 2016 Society of Photo-Optical Instrumentation Engineers (SPIE)
Citation - WoS: 22
Citation - Scopus: 20
Scintillation Index of Optical Spherical Wave Propagating Through Biological Tissue
(Taylor & Francis Ltd, 2017) Baykal, Yahya; Arpali, Caglar; Arpali, Serap Altay
Effects of the tissue turbulence on the propagation of an optical spherical wave are analysed. For this purpose, scintillation index of an optical spherical wave which is propagating in a soft tissue is formulated and evaluated in weakly turbulent soft tissue. Scintillation index of the optical spherical wave is examined against the changes in the tissue parameters which are the tissue length between the optical spherical wave source and the detector, random variations in the refractive index of the tissue and the outer scale of the tissue turbulence. According to our graphical outputs, it is observed that increase in the random variations of the refractive index of the tissue results in an increase in the scintillation index at a certain realization of the turbulence spectrum. On the other hand, larger outer scales and longer tissue lengths yield larger scintillations. The variation of the scintillation index of the optical spherical wave versus the wavelength is also investigated. It is found that at small tissue lengths, wavelength has almost no effect on the scintillations; however, when the tissue length reaches a certain value, shorter wavelengths give rise to larger intensity fluctuations.
Citation - WoS: 5
Citation - Scopus: 5
Intensity Correlations of Flat-Topped Beams in Oceanic Turbulence
(Taylor & Francis Ltd, 2020) Baykal, Yahya
Intensity correlations of flat-topped beams are formulated and evaluated in oceanic turbulence. Variations of the intensity correlations are examined against the diagonal distance from different starting points at the receiver plane, for the various number of beams composing the flat-topped beam, for various starting points at the receiver and for various source sizes. Also, the variations of the intensity correlations are investigated against the ratio of temperature to salinity contributions to the refractive index spectrum for the various number of beams composing the flat-topped beam, against the rate of dissipation of mean-squared temperature for various starting points at the receiver plane and against the rate of dissipation of kinetic energy per unit mass of fluid for various source sizes.
Citation - WoS: 6
Citation - Scopus: 10
Application of Adaptive Optics on Bit Error Rate of M-Ary Pulse-Position Oceanic Optical Wireless Communication Systems
(Iop Publishing Ltd, 2020) Gokce, Muhsin C.; Ata, Yalcin; Baykal, Yahya
An adaptive optics correction arising from the sum of tilt, focus, astigmatism and coma components is applied to the bit error rate (BER) of M-ary pulse-position-modulated (PPM) oceanic optical wireless communication systems. The percentage reduction in BER is evaluated versus the oceanic turbulence parameters of the ratio of temperature to salinity contributions to the refractive index spectrum, the rate of dissipation of mean-squared temperature and that of kinetic energy per unit mass of fluid under different data bit rates, avalanche photodiode (APD) average current gains and the M values of the M-ary PPM. Our findings indicate that the percentage reduction in BER becomes larger when the ratio of temperature to salinity contributions to the refractive index spectrum or the rate of dissipation of mean-squared temperature or the data bit rate or the M value of the M-ary PPM is smaller, and when the rate of dissipation of kinetic energy per unit mass of fluid or the APD average current gain is larger.
Citation - WoS: 3
Citation - Scopus: 6
Grid Connected Three-Phase Boost-Inverter for Solar Pv Systems
(int Journal Renewable Energy Research, 2021) Demirkutlu, Eyyup; İskender, İres; Iskender, Ires; Elektrik-Elektronik Mühendisliği
This paper presents a transformerless grid-connected three-phase boost-type inverter derived from the Swiss Rectifier (SR) and can be used in solar systems. The proposed boost-inverter retains the great advantages of the Swiss rectifier. Since the number of switches that are instantly switched with high frequency is only two, the switching losses are very low, therefore the proposed boost-inverter is very advantageous in terms of efficiency. Without having large transformer and electrolytic bus capacitors, the boost-inverter has an advantage in terms of size and weight. The switching states of the topology are given in detail. The operation principle of the boost-inverter is described with the help of equivalent circuits. A cascaded control method including current and voltage loops is designed. Simulation results are presented to validate the operation of the boost-inverter and show quality performance of the designed control approach.
Citation - WoS: 1
Citation - Scopus: 1
Calculation of the Spin-Lattice Relaxation Time and the Activation Energy Near the Iv-Iii Phase Transition in Pyridinium Fluorosulfonate (C5nh6)fso3
(Taylor & Francis Ltd, 2022) Kara, N.; Kiraci, A.; Yurtseven, Hamit
The spin-lattice relaxation time T-1(H) for protons nuclei is calculated in term of the pseudospin-phonon (PS) coupled and the energy fluctuation (EF) models close to the IV-III solid-solid phase transition of T-C = 235 K in (C5NH6)FSO3. This calculation was performed by associating the observed second moment of the H-1 as the order parameter below k and the disorder parameter above T-C. Values of the activation energy for the cation reorientation in this crystal are also deduced by using both models. In addition, the observed dielectric permittivity of this crystal is analyzed within the framework of the Landau theory and values of the spontaneous polarization (P-s) are determined as a function of temperature. The normalized values of P-s are used in the PS and EF models to extract the activation energy for the reorientation of the dipole moment of this compound arising from cation-anion interaction. Our results show that the PS and EF models can describe the observed behavior of the spin-lattice relaxation time adequately for the IV-III solid-solid transition in (C5NH6)FSO3.
Üç Fazlı Kuru Tip Transformatör Verimliliği İçin Meta Sezgisel Algoritma Tabanlı Yaklaşımlar
(2021) İskender, İres; Kül, Seda; Celtek, Seyit Alperen
Transformatörler, elektrik enerjisinin verimli iletimi ve dağıtımına önemli katkı sağlayan unsurlar olarak kabul edilir. Gerilim ve akım seviyelerini ters orantılı olarak değiştirme yeteneği, iletken kayıplarının azaltılmasına yardımcı olur. Bununla birlikte, günümüzün daha önemli verimlilik işaretlerine yönelik katı gereksinimleri, bir güç sistemindeki bireysel bileşenlerin verimliliğine dikkat çekiyor. Bu nedenle, temel işlevlerinden ödün vermeden transformatörlerin verimliliğini en üst düzeye çıkarmak için büyük çaba sarf edilmektedir. Bu karmaşık bir sorundur ve gelişmiş tasarım araçlarının kullanılmasını gerektirir. Son yıllarda geliştirilen meta-sezgisel yöntemler, tasarım süresinde tasarruf ve optimum çözümü bulmada büyük başarı sağladıklarından elektrik mühendisliğinde kullanılmaktadır. Bu çalışmada sırasıyla Parçacık Sürü Optimizasyonu (PSO), Benzetimli Tavlama (SA) ve Ağaç Tohum Algoritması (TSA) yöntemlerini kullandık. Amaç, üç fazlı kuru tip transformatörler için bir tasarım metodolojisi geliştirmek ve verimliliklerini en üst düzeye çıkarmaktır. Üç algoritmanın sonuçları, optimum çözümü doğrulamak için karşılaştırılır. Prosessin gösterimi için üç fazlı 100 kVA kuru tip bir transformatör kullanılır. Transformatörün matematiksel modeli oluşturulduktan sonra transformatör parametreleri, akım yoğunluğu (s) ve transformatör demir kesiti kabul edilebilirliği (C) optimize edilmiştir. Sonuç olarak, transformatörlerin verimlerinin geleneksel tekniklerle elde edilenin üzerinde artırılabileceği gözlemlenmiştir. Verimlilik optimize edilmiş ve 0.975'ten 0.9844'e yükseltilmiştir.
High-Gain Low-Profile Rectangular Microstrip Patch Antenna With Yagi Elements
(Taylor & Francis Ltd, 2020) Sener, Goker
This paper presents a novel high gain rectangular microstrip patch antenna (RMSA) with vertically placed Yagi elements. The antenna is fed by a coaxial probe to excite TM01 fundamental waves at 2.4GHz, which is suitable for wireless local area network (WLAN) applications. In order to increase the antenna gain, Yagi elements are placed in groups of 5, on each side of the substrate in order to serveas directors for the radiating slots as well as the ground reflections. The proposed antenna offers 1.3dB gain improvement and %3 .1 impedance bandwidth increase in comparison to the plain rectangular microstrip antenna with the same specifications. The advantage of this antenna is to provide an easy and cost effective solution to increase microstrip antenna gain, particularly in 8-10dB range, without disruptingits planar structure.
Citation - WoS: 6
Citation - Scopus: 8
Effects of Adaptive Optics on Bit Error Rate of M-Ary Ppm Oceanic Optical Wireless Communication Systems With Aperture Averaging in Strong Turbulence
(Iop Publishing Ltd, 2021) Baykal, Yahya; Ata, Yalcin; Gokce, Muhsin Caner
Scintillation is the result of oceanic turbulence reducing the bit error rate (BER) performance of oceanic optical wireless communication (OWC) systems. The scintillation, also known as intensity fluctuations, occurs due to the turbulence-induced wavefront deformations. The correction of deformations by adaptive optics (AO) reduces the scintillation effect of turbulence and results in improved BER performance. In this paper, an oceanic OWC (OOWC) system that has a Gaussian laser beam at the transmitter, finite-sized circular aperture at the receiver, employing M-ary pulse position modulation (PPM) and operating in strong oceanic turbulence, is considered. Improvement in the BER performance of the OOWC system is examined with the implementation of AO correction. Comparison of BER performances between the AO and non-adaptive optics OOWC systems is shown by calculating the metric defined. BER of M-ary PPM OOWC links is evaluated over gamma-gamma fading channels. The modified Rytov theory together with the Zernike filter functions is used to find the AO corrected aperture averaged scintillation index where extended Huygens-Fresnel technique is used to obtain the average received signal power.
Citation - WoS: 3
Citation - Scopus: 6
Case Study on Thermal Optimization of Oil Immersed Transformer Used in Solar Power Plant Based on Genetic Algorithm and Computational Fluid Dynamics
(Vinca inst Nuclear Sci, 2023) Iskender, Ires; Yukselen, Emir
Transformers are one of the most capital investments in the solar power generation. Their safe and stable operations in the electrical networks are important. The main failure factor of transformers is the high temperature generated by the losses during operation, which increases the probability of insulation damage that significantly affects the useful life of transformer. Considering the importance of oil temperature and its effects on the life of the transformer, a numerical method is developed in this paper to optimize the cooling system of the transformer. In this regard, genetic algorithm is used as an optimization method to minimize the total cost of the cooling system while maintaining the required thermal conditions of the transformer. A comprehensive parametric study is carried out among the effective cooling geometry parameters using 3-D electromagnetic and thermal models of the photovoltaic transformer to evaluate and analyze the temperature distribution. The accuracy and feasibility of the proposed method is established by comparing the numerical results with those obtained from the experimental test. The results of the proposed method are found to be in a good agreement with the experimental and simulation results.
Citation - WoS: 29
Citation - Scopus: 35
Ber Evaluations for Multimode Beams in Underwater Turbulence
(Taylor & Francis Ltd, 2016) Arpali, Serap Altay; Baykal, Yahya; Arpali, Caglar
In underwater optical communication links, bit error rate (BER) is an important performance criterion. For this purpose, the effects of oceanic turbulence on multimode laser beam incidences are studied and compared in terms of average BER (< BER >), which is related to the scintillation index. Based on the log-normal distribution, < BER > is analysed for underwater turbulence parameters, including the rate of dissipation of the mean squared temperature, the rate of dissipation of the turbulent kinetic energy, the parameter that determines the relative strength of temperature and salinity in driving index fluctuations, the Kolmogorov microscale length and other link parameters such as link length, wavelength and laser source size. It is shown that use of multimode improves the system performance of optical wireless communication systems operating in an underwater medium. For all the investigated multimode beams, decreasing link length, source size, the relative strength of temperature and salinity in driving the index fluctuations, the rate of dissipation of the mean squared temperature and Kolmogorov microscale length improve the < BER >. Moreover, lower < BER > values are obtained for the increasing wavelength of operation and the rate of dissipation of the turbulent kinetic energy in underwater turbulence.
Design of a Novel Converter Between Li-Ion Battery and Supercapacitor To Feed Synthetic Aperture Radar Loads for Satellite Applications
(int Journal Renewable Energy Research, 2020) Tulay, Gencer; İskender, İres; Iskender, Ires; Elektrik-Elektronik Mühendisliği
For satellite applications the active duty life of a satellite depends mainly on the battery lifespan. The charging or discharging current has an important role in useful life of batteries. For this purpose, the converters used in power supplies including batteries should be accurately designed such that the large current of batteries can be prevented. The power converter proposed in this paper is used to transfer energy from battery to supercapacitor when SAR (Synthetic Aperture Radar) load is active. Accordingly, the lifespan of battery and hence the lifespan of satellite will be extended. Parallel to preventing the large discharging current of batteries the proposed converter has another important property such that it is able to vary the input voltage without having any stability problems. The operating performance of the converter that is composed of Weinberg and Buck converters is analyzed using PSpice software and the results of simulations are verified through experiments. The results show that how well the converter operates satisfying the conditions required for satellite applications.
Citation - WoS: 8
Citation - Scopus: 10
Aperture Averaging in Multiple-Input Single-Output Free-Space Optical Systems
(Spie-soc Photo-optical instrumentation Engineers, 2015) Baykal, Yahya; Kamacioglu, Canan; Uysal, Murat; Gokce, Muhsin C.
Multiple-input single-output systems are employed in free-space optical links to mitigate the degrading effects of atmospheric turbulence. We formulate the power scintillation as a function of transmitter and receiver coordinates in the presence of weak atmospheric turbulence by using the extended Huygens Fresnel principle. Then the effect of the receiver aperture averaging is quantified. To get consistent results, parameters are chosen within the range of validity of the wave structure functions. Radial array beams and a Gaussian weighting aperture function are used at the transmitter and the receiver, respectively. It is observed that the power scintillation decreases when the source size, the ring radius, the receiver aperture radius, and the number of array beamlet increase. However, increasing the number of array beamlets to more than three seems to have negligible effect on the power scintillation. It is further observed that the aperture averaging effect is stronger when radial array beams are employed instead of a single Gaussian beam. (C) 2015 Society of Photo-Optical Instrumentation Engineers (SPIE)
Citation - WoS: 8
Citation - Scopus: 8
M-Ary Pulse Position Modulation Performance With Adaptive Optics Corrections in Atmospheric Turbulence
(Taylor & Francis Ltd, 2020) Gokce, Muhsin C.; Baykal, Yahya; Ata, Yalcin
The performance of M-ary pulse position modulated (PPM) optical wireless communication (OWC) systems in atmospheric weak turbulence medium is evaluated by using adaptive optics corrections. Piston, tilt, defocus and coma components of adaptive optics corrections are applied to the avalanche photodetector (APD) type of receiver and the results are obtained depending on various turbulence and receiver parameters. The lognormal channel distribution is used to model the weak atmospheric turbulence conditions. Adaptive optics correction increases the bit-error-rate (BER) performance of an OWC system operating in atmospheric turbulence conditions. Piston component yields the highest BER performance, followed by the tilt, defocus and coma adaptive optics correction components respectively.
Citation - Scopus: 9
Improvement of Underlay Cooperative Cognitive Networks Bandwidth Efficiency Under Interference and Power Constraints
(Ksii-kor Soc internet information, 2019) Preveze, Barbaros; Alkhayyat, Ahmed; Al-Mishmish, Hameed R. M.
The definition of the bandwidth efficiency (BE) of cognitive cooperative network (CCN) is the ratio between a number of the licensed slot(s) or sub-channel(s) used by the unlicensed users to transmit a single data packet from the unlicensed transmitter to unlicensed destination, and from unlicensed relay(s) to unlicensed destination. This paper analyzes and improves the BE in the underlay CCN with a new reactive relay selection under interference and power constraints. In other words, this paper studies how unlicensed cooperative users use the licensed network slot(s) or sub-channel(s) efficiently. To this end, a reactive relay selection method named as Relay Automatic Repeat Request (RARQ) is proposed and utilized with a CCN under interference and power constraints. It is shown that the BE of CCN is higher than that of cooperative transmission (CT) due to the interference and power constraint. Furthermore, the BE of CCN is affected by the distance of the interference links which are between the unlicensed transmitter to the licensed destination and unlicensed relay to the licensed destination. In addition, the BE for multiple relays selection over a CCN under interference and power constraints is also analyzed and studied, and it is shown that the BE of CCN decreases as the number of relays increases.
Citation - WoS: 7
Citation - Scopus: 9
Flat-Topped Beam Transmittance in Anisotropic Non-Kolmogorov Turbulent Marine Atmosphere
(Spie-soc Photo-optical instrumentation Engineers, 2017) Ata, Yalcin; Baykal, Yahya
Turbulence affects optical propagation, and, as a result, the intensity is attenuated along the path of propagation. The attenuation becomes significant when the turbulence becomes stronger. Transmittance is a measure indicating how much power is collected at the receiver after the optical wave propagates in the turbulent medium. The on-axis transmittance is formulated when a flat-topped optical beam propagates in a marine atmosphere experiencing anisotropic non-Kolmogorov turbulence. Variations in the transmittance are evaluated versus the beam source size, beam number, link distance, power law exponent, anisotropy factor, and structure constant. It is found that larger beam source sizes and beam numbers yield higher transmittance values; however, as the link distance, power law exponent, anisotropy factor, or structure constant increase, transmittance values are lowered. Our results will help in the performance evaluations of optical wireless communication and optical imaging systems operating in a marine atmosphere. (C) 2017 Society of Photo-Optical Instrumentation Engineers (SPIE)
Citation - WoS: 1
Citation - Scopus: 1
Antenna Synthesis by Levin's Method Using a Novel Optimization Algorithm for Knot Placement
(Applied Computational Electromagnetics Soc, 2023) Sener, Goker
- Antenna synthesis refers to determining the antenna current distribution by evaluating the inverse Fourier integral of its radiation pattern. Since this inte-gral is highly oscillatory, Levin's method can be used for the solution, providing high accuracy. In Levin's method, the integration domain is divided into equally spaced sub-intervals, and the integrals are solved by transfer-ring them into differential equations. This article uses a new optimization algorithm to determine the location of these interval points (knots) to improve the method's accuracy. Two different antenna design examples are pre-sented to validate the accuracy and efficiency of the pro-posed method for antenna synthesis applications.
Citation - WoS: 6
Citation - Scopus: 6
Intensity Correlation of Collimated Gaussian Beams Propagating in Biological Tissues
(Taylor & Francis Ltd, 2021) Baykal, Yahya
Intensity correlations in turbulent biological tissues are evaluated when collimated Gaussian laser beam is used. Variations of the intensity correlations in biological tissues are investigated versus the diagonal distance from the origin of the observation plane for various tissue distances, biological tissue types, strength coefficients of the refractive-index fluctuations, starting points at the observation plane. Also, intensity correlations in biological tissues for various biological tissue types versus the strength coefficient of the refractive-index fluctuations, small length-scale factor, fractal dimension. It is found that intensity correlations become smaller at larger diagonal distance, tissue distance, strength coefficients of the refractive-index fluctuations, and at smaller source size, small length-scale factor and fractal dimensions. Behaviour of the intensity correlations is found to depend on the type of the biological tissue. Our results can be used in tissue identification and to find the disorders in biological tissues.
Citation - WoS: 5
Citation - Scopus: 4
Laser Array Field Correlations in Underwater Turbulence
(Taylor & Francis Ltd, 2022) Gokce, Muhsin C.; Baykal, Yahya; Ata, Yalcin
In underwater turbulent medium, field correlations are found when the incidence is a laser beam array. Variations of the field correlations against the variations in the ring radius of laser array beam, number of beamlets composing the laser array, source size, underwater turbulence parameters, i.e. the ratio of temperature to salinity contributions to the refractive index spectrum, rate of dissipation of mean-squared temperature and rate of dissipation of kinetic energy per unit mass of fluid, are investigated. Field correlations of laser arrays are found to be larger than the field correlations of the single beams. The effect of underwater turbulence is to reduce the field correlation of laser arrays.

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