Elektrik Elektronik Mühendisliği Bölümü

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Citation Count: İnan, Tolga; Narbaev, Timur; Hazır, Öncü (2022). "A Machine Learning Study to Enhance Project Cost Forecasting", IFAC-PapersOnLine, Vol. 55, No. 10, pp. 3286-3291.
A Machine Learning Study to Enhance Project Cost Forecasting
(elsevier, 2022) İnan, Tolga; Narbaev, Timur; Hazır, Öncü
In project management it is critical to obtain accurate cost forecasts using effective methods. This study presents a Machine Learning model based on Long-Short Term Memory to forecast the project cost. The model uses the seven-dimensional feature vector, including schedule and cost performance factors and their moving averages as a predictor. Based on the cost variation patterns from the training phase, we validate the model using three hundred experiments in the testing phase. Overall, the proposed model produces more accurate cost estimates when compared to the traditional Earned Value Management index-based model.
Citation Count: Mezaal, Yaqeen S.; Eyyuboglu, Halil Tanyer, "A New Narrow Band Dual-Mode Microstrip Slotted Patch Bandpass Filter Design Based on Fractal Geometry", 2012 7th International Conference On Computing and Convergence Technology (Iccct2012), pp. 1180-1184, (2012)
A New Narrow Band Dual-Mode Microstrip Slotted Patch Bandpass Filter Design Based On Fractal Geometry
(IEEE, 2012) Mezaal, Yaqeen S.; Eyyuboğlu, Halil T.; 7688
A narrowband, compact, and easily fabricated microstrip bandpass filter design is introduced in this paper as a candidate for use in modern wireless systems. The proposed filter design is based on the use of dual-mode (two pole) square slotted microstrip resonator. This microstrip bandpass filter has the advantages of possessing much narrower and sharper performance responses than those of the single mode resonator and conventional square patch filter. The proposed microstrip filter structure is fractally generated using Sierpinski fractal curve geometry applied to the conventional square microstrip patch. Filter structures resulting from the successive iterations in the fractal generation process show a considerably low insertion loss, and sharper response of about 1% fractional bandwidth as compared with the conventional microstrip square patch filter of 3% fractional bandwidth designed at the same frequency using the same substrate material. The performance of filter structures, based on dual-mode resonators up to the third iterations, has been evaluated using a full-wave based electromagnetic simulator Sonnet software package. Performance simulation results show that these filter structures offer narrower fractional bandwidth percentages as compared with other types of non- fractalized filter structures.
Citation Count: Preveze, B. (2015). A novel cognitive method for throughput ımprovement of mobile multi-hop ad hoc networks. Wireless Personal Communications, 82(1), 229-243. http://dx.doi.org/10.1007/s11277-014-2205-1
A novel cognitive method for throughput improvement of mobile multi-hop ad hoc networks
(Springer, 2015) Preveze, Barbaros; 17573
We had previously defined a novel cognitive method for throughput improvement of IEEE 802.16j mobile multi-hop ad-hoc network which enables better management of the spectral access and buffer management of the nodes in the network. By this method we had minimized the packet loss ratio and improved the throughput of IEEE 802.16j network. In this study, a novel cognitive buffer management algorithm is proposed that arranges the packets stored in the buffers of the nodes in a probabilistic way and selects correct packet of the correct node to transmit first to provide fewer packet losses and also fewer average hop-counts for more throughputs. It is shown that the novel proposed buffer management algorithm provides about 19.45 % more throughput improvement (on average) with respect to the results evaluated by the buffer management algorithm used before (which was also shown to provide 12 % throughput improvement with respect to a First In First Out buffer management algorithm). All the results evaluated in this study are also confirmed by the results of analytical calculations, the results of the developed simulation program and the results evaluated in the literature.
Citation Count: Şener, G. (2017). A novel method to solve 2nd order neumann type boundary value problems in electrostatics. Applied Computational Electromagnetics Society Journal, 32(4), 289-294.
A novel method to solve 2nd order neumann type boundary value problems in electrostatics
(Applied Computational Electromagnetics Soc., 2017) Şener, Göker; 17740
In this paper, the numerical method of nonpolynomial spline approximation is used to solve 2nd order Neumann type boundary value problems (bvp's) in electrostatics. This new approach provides more accurate results than the polynomial approximations and the spectral methods. The literature contains very little on the solution of Neumann type bvp's because of the fact that a unique solution does not exist for all problems. In electrostatics, Neumann type bvp's are encountered for finding the electrostatic potential inside closed surfaces where the normal derivative of the electric potential is specified everywhere on the surface. Two examples are presented to prove the accuracy of the proposed method. In these examples, the governing differential equation is solved to find the electrostatic potential inside a region bounded by conductors that are maintained at constant voltages. The results are compared with the analytic solutions.
Citation Count: Preveze, B. (2023). "A Novel Solution for Network Flexibility Problem in Mobile Multi-hop Tunneling Networks", Wireless Personal Communications, Vol.129, No.2, pp. 1049-1068.
A Novel Solution for Network Flexibility Problem in Mobile Multi-hop Tunneling Networks
(2023) Preveze, Barbaros; 17573
Since the network throughput performance is limited by the available technology limits, there are too many attempts in the literature to improve the throughput performance of the network by modifying the routing algorithms currently in use. Although application of the tunneling on IP networks provides reserved paths for the higher priority packet streams and succeeds in providing faster communication performances, it is also determined in the literature that, the greatest up to date problem of tunneling networks is the flexibility problem, which is defined as the problem of difficulty to have minimal delay and highest throughput when congestions or node failures occur and the throughput decreases due to high traffic loads on the network. sIn this work, a high performance solution, called LB-ACN (Location Based- Avoid Congested Node) is proposed to solve this flexibility problem and to compensate the increased delay which came up due to the high traffic load and also due to inflexible tunneling network structure, considering the locations of the nodes in addition to their traffic loads. And it is shown that, it is succeeded to carry the throughput of the highly traffic loaded network back to 48.6 Mbps from 36.9 Mbps by about 31.7% performance improvement for which we could improve it from 36.9 Mbps up to 45.9 Mbps by 24.3% using the proposed ACN (Avoid Congested Node) algorithm in our previous work. As a result, we have succeeded in having about 7.4% more improvement on throughput performance in comparison with the previously proposed ACN algorithm.
Citation Count: Toreyin, Behcet Ugur; Aktas, Hakan; Sever, Refik, "A Two Stage Template Matching Algorithm and Its Implementation on FPGA", 23nd Signal Processing and Communications Applications Conference (SIU), pp. 2214-2217, (2015).
A Two Stage Template Matching Algorithm and Its Implementation on FPGA
(IEEE, 2015) Aktaş, Hakan; Sever, Refik; Töreyin, Behçet Uğur; 19325
In this paper, to decrease the computational cost and number of cycles in Template Matching Algorithm, a novel two-stage algorithm is proposed. The Sum of Absolute Differences method is used for matching. The proposed algorithm is implemented on Field-Programmable-Gate-Array (FPGA). The algorithm is accelerated with the effective usage of Block RAMs distributed on FPGA. Thus, the proposed algorithm became fast enough for real time object tracking applications on UAVs.
Citation Count: Salmanogli, Ahmad; Gecim, H. S. (2022). "Accurate method to calculate noise figure in a low noise amplifier: Quantum theory analysis", Microelectronics Journal, Vol.128.
Accurate method to calculate noise figure in a low noise amplifier: Quantum theory analysis
(2022) Salmanogli, Ahmad; Gecim, H. Selcuk; 182579
In this study, a low-noise amplifier is quantum-mechanically analyzed to study the behavior of the noise figure. The analysis view has been changed from classic to quantum, because using quantum theory produces some degrees of freedom, which may be ignored when a circuit is analyzed using classical theory. For this purpose, the Lagrangian is initially derived by considering the related nonlinearity of the transistor, and then using the Legendre transformation and canonical quantization procedure, the quantum Hamiltonian is derived. As an interesting point of this study, the low-noise amplifier is deliberately considered as two oscillators connecting to each other to share the photonic modes between them; accordingly, the voltage and current as measurable observations and the noise figure as a critical quantity in a low-noise amplifier are theoretically expressed in terms of the oscillator's mean photon number. The main goal of this work is to study quantities such as the noise figure in a sufficient detail using quantum theory. In addition, as an advantage of this theory, one can control and manipulate the noise figure only by manipulation of the oscillator's mean photon number and coupling it between two oscillators. Finally, the circuit is classically designed and simulated to verify the derived results using quantum theory. The comparison results show that there is a partial consistency between the two approaches; as the frequency increases, the noise figure becomes minimized at a particular frequency.
Citation Count: Baykal, Y. (2022). "Adaptive optics correction of beam spread in biological tissues", Journal of Quantitative Spectroscopy and Radiative Transfer, Vol.283.
Adaptive optics correction of beam spread in biological tissues
(2022) Baykal, Yahya
Beam spread in turbulent biological tissues is examined when the tissue is excited with a collimated Gaussian laser beam. Adaptive optics correction is applied to the beam spread in the form of piston only (P Only), tilt only (T Only), piston+tilt (P+T), and the reduction in the beam spread is evaluated as compared to the no adaptive optics (No AO) corrected beam spread. No AO and adaptive optics corrected beam spread are expressed for various biological tissue types, against the variations in the strength coefficient of the refractive-index fluctuations, source size, small length-scale factor of turbulence, tissue length, fractal dimension, characteristic lengths of heterogeneity and the wavelength. For the examined tissue types of liver parenchyma (mouse), intestinal epithelium (mouse), upper dermis (human) and deep dermis (mouse), No AO beam spread and the adaptive optics corrected beam spread are found to increase as the strength coefficient of the refractive-index fluctuations, tissue length, fractal dimension, the characteristic lengths of heterogeneity increase, and to decrease as the source size, small length-scale factor, wavelength increase. Reduction ratio of P+T correction is almost the same for all the evaluated cases which is 74%.
Citation Count: Preveze, Barbaros; Safak, Aysel, "Alternative Enhancement of Associativity Based Routing (AEABR) for Mobile Networks", Vol. 32, pp. 67-+, (2010).
Alternative Enhancement of Associativity Based Routing (Aeabr) for Mobile Networks
(Springer, 2010) Preveze, Barbaros; Safak, Aysel; 17573
This study proposes an alternative enhancement for the Enhanced Associativity Based Routing (EABR) method which is a derivation of ABR (Associativity Based Routing) by relative speed and relative distance estimation using the received power strength (RPS) of the nodes. In this study, it is shown that EABR outperforms some other well known protocols. The performance of EABR is improved in terms of number of route reconstructions (RRC) and connected status percentage (CSP). Message overhead and bandwidth utilization is also investigated.
Citation Count: Najafi, Atabak; İskender, İ. (2021). "Amorf Çekirdekli Transformatörün Çoklu Fizik Yöntemiyle Elektromanyetik - Sıcaklık Analizi", Afyon Kocatepe Üniversitesi Fen ve Mühendislik Bilimleri Dergisi, Vol.21, No.5, pp.1086-1096.
Amorf Çekirdekli Transformatörün Çoklu Fizik Yöntemiyle Elektromanyetik - Sıcaklık Analizi
(2021) Najafi, Atabak; İskender, İres; 133746
Bu makalede, Amorf nüveli transformatörün sıcaklık analizini detaylı incelemek için, ısı transferi, akışkan akışı ve elektromanyetik analizlerini kapsayan çok disiplinli bir yaklaşım kullanılmıştır. Transformatörün bobini ve çekirdeğindeki güç kayıpları incelenip, sıcaklık ve akışkan akış analizleri elektromanyetik bir model ile birleştirilmiştir. Önerilen yöntem, Amorf çekirdekli gibi özel transformatörlerde, önceki noktasal sıcaklık bilgisine ya da sıcaklık Gradyan değerlerine ihtiyaç duymadan, sıcaklık değişimini detaylı olarak tahmin edebilmektedir. Teorik çalışma sonuçları uluslararası standartlara göre Dyn11, 34.5/0.4-kV, 630-kVA’lik amorf çekirdekli transformatör üzerine uygulanan deneysel çalışma sonuçlarıyla doğrulanmıştır. Teorik ve pratik çalışma sonuçlarının karşılaştırılması, sonuçların büyük bir uyum içinde olduğunu göstermekte olup, kullanılan yöntem genç mühendislere güç transformatörlerin sıcaklık analiz çalışmalarında faydalı bir araç oluşturmaktadır.
Citation Count: Uzun, E.; Akagunduz, E., "An Analysis On the Effect of Skip Connections in Fully Convolutional Networks for License Plate Localization [Tam Evrişimli Aǧlardaki Atlama Baǧlantilarinin Plaka Konumu Bulmaya Etkisi Üzerine Bir İnceleme]", 27th Signal Processing and Communications Applications Conference, Sıu 2019, (2019).
An Analysis On the Effect of Skip Connections in Fully Convolutional Networks for License Plate Localization [Tam Evrişimli Aǧlardaki Atlama Baǧlantilarinin Plaka Konumu Bulmaya Etkisi Üzerine Bir İnceleme]
(Institute of Electrical and Electronics Engineers Inc., 2019) Akagündüz, Erdem; Uzun, Engin; 233834
In this study, the effect of the skip connections, which are seen in fully convolutional networks, on object localization is analyzed. For this purpose, a local data set for plate detection is created. Experiments are carried out using this data set. Due to the small size of the image set, data augmentation method is used to overcome the danger of over-fitting. The learning rates of the first layers are frozen for analysis and finetuning is applied to only the last layer and deconvolution layers. The results obtained are compared with the results of other image sets. The results indicate the importance of the information provided by the skip connections on object localization.
Citation Count: Yükselen, Emir; İskender, I. (2022). "Analysis and Design of a Special Type Power Transformer Used in Solar Power Plants", International Journal of Renewable Energy Research, Vol.12, No.2, pp.667-673.
Analysis and Design of a Special Type Power Transformer Used in Solar Power Plants
(2022) Yükselen, Emir; İskender, Ires
Due to growing of greenhouse gas emissions and lack of the fossil sources, governments encouraged all scientists and utilities for looking to the alternative energy sources such as solar renewable energy which can help to reduce carbon dioxide emissions. In this respect, Photovoltaic (PV) power plants have become more important in recent years and renewable energy sources integrated into the power system are increasing day by day. Transformers are the main components of electrical grids and are widely used in renewable power plants to transfer the energy they produce to the grid. Accordingly, transformers are one of the most critical equipment of PV plants, and their safe operation and stability in the electrical network are important. This type of transformer is supplied from solar panels through inverters and needs to be customized to work with each system. In this type of transformer, the losses are higher than those for transformers used in electrical power systems supplied by sinusoidal voltage considering existence of different voltage and current harmonics content produced by the inverter. In this study, a special type of PV transformer was designed in accordance with the target performance criteria, taking into account the effects of harmonics, and keeping the transformer losses and temperature rise at a safe level. In this paper also the simulation results are compared with those of experiments test to verify the design procedures.
Citation Count: Baykal, Yahya; Uysal, Murat, "Analysis of Field Correlations in Atmospheric Optical MIMO Systems", 3rd International Workshop in Optical Wireless Communications (IWOW), pp. 30-34, (2014).
Analysis of Field Correlations in Atmospheric Optical MIMO Systems
(IEEE, 2014) Baykal, Yahya; Uysal, Murat
In this paper, we evaluate the absolute field correlations for a free space optical (FSO) multiple-input multiple-output (MIMO) link operating in a turbulent atmosphere. Such knowledge is needed in heterodyne reception to keep all the optical detectors within the region in which a predefined correlation value is fulfilled. The variations of the absolute field correlations versus the longest distance between the detectors are found for different array, medium and receiver parameters such as the number of beamlets, the radius of the radial array, beamlet size, link length, wavelength, structure constant and the position of the detectors.
Citation Count: Yükselen, Emir; İskender, İres. "Analysis of Lightning Impulse Effects on Three Winding Transformer Used in Solar System Based ANSYS Maxwell", 2022 9th International Conference on Electrical and Electronics Engineering (ICEEE), IEEE, pp. 71-75.
Analysis of Lightning Impulse Effects on Three Winding Transformer Used in Solar System Based ANSYS Maxwell
(IEEE, 2022) Yükselen, Emir; İskender, İres; 133746
Transformers are in more critical applications in the renewable energy world and having a transformer fail in such a cyclical power station can be disastrous. Over voltage or voltage strike is the most important phenomena for the transformers. Thus, the evaluating and estimating the effects and stresses of these sudden high voltages is important during the transformers life time operation and design stage. Accordingly in this paper the electromagnetic field analyses of the lightning impulse on Photovoltaic (PV) transformer are investigated using ANSYS Maxwell software. The 3D and 2D model simulation of the PV transformer is carried out to determine the electric field and voltage distribution on critical regions which can cause breakdown on insulation material and damage transformer windings and affects transformer working. Afterwards according to the simulation result, the subjected transformer was designed considering the relative critical regions and performs the full wave lightning impulse test in factory area to verify the dielectric strength of the transformer. This study provides better understanding of the lightning impulse voltage effects with localization of the critical regions on the PV transformer and helps to improve the withstand capability of the transformer against the lightning impulse voltages during the design and production stage.
Citation Count: Jahi, Amir; İskender, İres. "Analysis of Short Circuit Electromagnetic Force in a Three Winding Transformer Used in Solar System", 2021 13th International Conference on Electrical and Electronics Engineering (ELECO), IEEE, pp. 393-397, 2021.
Analysis of Short Circuit Electromagnetic Force in a Three Winding Transformer Used in Solar System
(IEEE, 2021) Jahi, Amir; İskender, İres; 133746
Due to the increasing of the fossil fuels prices in the past years and lack of these sources, all scientists encouraged to looking for the alternative energy sources. One of these energy sources is renewable solar energy. Power transmission from solar systems to grid is achieved using step up transformers. This type of transformer is energized from two inverter with or without variable frequency. Power transformers are deals with a variety of mechanical, electrical and thermal stresses during normal life time operation. Transient electromagnetic forces cause mechanical stress on transformer parameters where calculation of these forces with traditional methods is extremely complex due to the geometry of the transformer. Accordingly in this study, the electromagnetic forces takes place in the windings of a Photovoltaic (PV) transformer are investigated and for calculation of these forces, the 3D and 2D model of transformer is adapted in the ANSYS Workbench. The analysis of electromagnetic forces during the three line fault on high voltage side of the transformer are performed by the Finite Element Method (FEM) and compared with the analytical results. The numerical modeling technique discussed in this study would be useful in the design stage of PV transformer with regard to evaluate ability of transformer to withstand the short circuit current.
Citation Count: Ata, Yalçın; Baykal, Yahya; Gökçe, Muhsin C. (2022). "Analysis of wander and spreading of an optical beam by using the oceanic turbulence optical power spectrum", Journal of the Optical Society of America B: Optical Physics, Vol.39, No.8, pp.2129-2137.
Analysis of wander and spreading of an optical beam by using the oceanic turbulence optical power spectrum
(2022) Ata, Yalçın; Baykal, Yahya; Gökçe, Muhsin Caner
Variance of beam displacement and short-term and long-term spreading of a Gaussian beam propagating in the presence of underwater turbulence are examined by using the oceanic turbulence optical power spectrum (OTOPS). Analytical expressions for both beam wander displacement variance and beam spreading are presented. Results show that the underwater turbulent channel causes deflection from the on-axis mean irradiance and brings significant wander and spreading effects to the propagating Gaussian beam wave. The variations of beam wander and short- and long-term spreading are obtained depending on the underwater medium parameters such as the average temperature, average salinity concentration, temperature-salinity gradient ratio, and temperature and energy dissipation rates. In particular, the real values of the average temperature and salinity concentration of turbulent water are used to obtain the results. In addition, the effects of propagation distance, Gaussian beam source size, and wavelength are shown. The results demonstrate that the underwater turbulent channel brings displacements in the centroid and spreading of the optical beam.
Citation Count: Ata, Y., Baykal, y. (2018). Anisotropy effect on multi-Gaussian beam propagation in turbulent ocean. Chinese Laser Press, 16(8). http://dx.doi.org/10.3788/COL201816.080102
Anisotropy effect on multi-Gaussian beam propagation in turbulent ocean
(Chinese Laser Press, 2018) Ata, Yalçın; Baykal, Yahya; 7812
Average transmittance of multi-Gaussian (flat-topped and annular) optical beams in an anisotropic turbulent ocean is examined analytically based on the extended Huygens-Fresnel principle. Transmittance variations depending on the link length, anisotropy factor, salinity and temperature contribution factor, source size, beam flatness order of flat-topped beam, Kolmogorov microscale length, rate of dissipation of turbulent kinetic energy, rate of dissipation of the mean squared temperature, and thickness of annular beam are examined. Results show that all these parameters have effects in various forms on the average transmittance in an anisotropic turbulent ocean. Hence, the performance of optical wireless communication systems can be improved by taking into account the variation of average transmittance versus the above parameters.
Citation Count: Baykal, Yahya, "Anisotropy effect on performance of PPM optical wireless oceanic communication links", Journal of Quantitative Spectroscopy & Radiative Transfer, Vol. 228, pp. 73-78, (2019).
Anisotropy effect on performance of PPM optical wireless oceanic communication links
(Pergamon-Elsevier Science LTD, 2019) Baykal, Yahya; 7812
The performance, quantified by the bit-error-rate (BER), of M-ary pulse position modulated (PPM) optical wireless oceanic communication (OWOC) link is investigated when such a link operates in anisotropic weak oceanic turbulence. For this purpose, formulations of the average received power and the scintillation index of collimated Gaussian optical beam detected by a point detector are developed for anisotropic weak oceanic turbulence, which in turn are employed in the BER expression of the PPM OWOC links. BER is evaluated under various turbulence parameters of anisotropic oceanic turbulence, M of M-ary PPM, data bit rate, average current gain of avalanche photodiode (APD). For any investigated parameter, it is found that the BER performance of M-ary PPM OWOC links is improved as the ocean becomes more anisotropic. (C) 2019 Elsevier Ltd. All rights reserved.
Citation Count: Şener, Göker (2023). "Antenna Synthesis by Levin’s Method using Reproducing Kernel Functions", Applied Computational Electromagnetics Society Journal, Vol. 38, No 7, pp. 482-488.
Antenna Synthesis by Levin’s Method using Reproducing Kernel Functions
(2023) Şener, Göker; 17740
An antenna synthesis application is presented by solving a highly oscillatory Fourier integral using a stable and accurate Levin’s algorithm. In antenna synthesis, the current distribution is obtained by the inverse Fourier integral of the antenna radiation pattern. Since this integral is highly oscillatory, the Levin method can be used for its solution. However, when the number of nodes or the frequency increases, the Levin method becomes unstable and ineffective due to the large condition number of the interpolation matrix. Thus, an improved scheme of the method is used in an antenna synthesis application in which reproducing kernel functions are used as the basis of the approximation function. The accuracy of the new method is verified by a log-periodic antenna example. The error and stability analysis results show that the new method is more stable and accurate than other well-known kernels, especially for a large number of nodes.
Citation Count: Gökçe, M.C., Baykal, Y.K. (2018). Aperture averaging and BER for Gaussian beam in underwater oceanic turbulence. Optic Communications, 410, 830-835. http://dx.doi.org/10.1016/j.optcom.2017.11.049
Aperture averaging and BER for Gaussian beam in underwater oceanic turbulence
(Elsevier Science BV, 2018) Gökçe, Muhsin Caner; Baykal, Yahya; 28643; 7812
In an underwater wireless optical communication (UWOC) link, power fluctuations over finite-sized collecting lens are investigated for a horizontally propagating Gaussian beam wave. The power scintillation index, also known as the irradiance flux variance, for the received irradiance is evaluated in weak oceanic turbulence by using the Rytov method. This lets us further quantify the associated performance indicators, namely, the aperture averaging factor and the average bit-error rate (). The effects on the UWOC link performance of the oceanic turbulence parameters, i.e., the rate of dissipation of kinetic energy per unit mass of fluid, the rate of dissipation of mean-squared temperature, Kolmogorov microscale, the ratio of temperature to salinity contributions to the refractive index spectrum as well as system parameters, i.e., the receiver aperture diameter, Gaussian source size, laser wavelength and the link distance are investigated.

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