Elektrik Elektronik Mühendisliği Bölümü Yayın Koleksiyonu

Permanent URI for this collectionhttps://hdl.handle.net/20.500.12416/411

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Now showing 1 - 10 of 28
  • Article
    Citation - WoS: 11
    Citation - Scopus: 9
    Multimode Beam Propagation Through Atmospheric Turbulence
    (Pergamon-elsevier Science Ltd, 2024) Baykal, Yahya; Ata, Yalcin; Gercekcioglu, Hamza; Gokce, Muhsin Caner
    The investigation focuses on studying the propagation characteristics of multimode lasers in the turbulent amosphere. By employing the Huygens-Fresnel integral, we develop analytical formulations for various propagation parameters. These include the average intensity distribution, kurtosis parameter, beam spread, and the average transmittance of multimode beams in turbulent atmosphere. Our findings reveal that as the propagation distance or the structure constant of the atmosphere increases, i.e., turbulence becomes stronger, the kurtosis parameter and the beam spread increase. The multimode beam exhibits a Gaussian like intensity profile when the propagation distance is significantly increased or when the structure constant becomes sufficiently large. For the case of the Gaussian beam, the kurtosis parameter is found to be 3. The multimode beam's kurtosis parameter rises as the turbulence becomes stronger and eventually approaches 3. Raising the mode content leads to a rise in the average transmittance; however, it leads to a decline in the Kurtosis parameter and the beam spread.
  • Article
    Citation - WoS: 3
    Citation - Scopus: 3
    Performance Evaluation of Aeronautical Uplink/Downlink Free-Space Optical Communication System With Adaptive Optics Over Gamma-Gamma Turbulence Channel
    (Iop Publishing Ltd, 2022) Baykal, Yahya; Gokce, Muhsin Caner; Ata, Yalcin
    In this study, we analyze the effect of adaptive optics corrections on the performance of an aeronautical free-space optical (FSO) system with bidirectional slant path uplink and downlink communication channels. The aeronautical FSO communication (FSOC) system operates in a gamma-gamma atmospheric turbulence channel and employs adaptive optics corrections for the distorted wave front of the Gaussian beam wave. The modulation type of the aeronautical FSOC system is chosen to be M-ary phase-shift-keying-subcarrier intensity modulation and the type of the employed photodetector is positive-intrinsic-negative. In analysis, the effect of system parameters such as zenith angle, the height of transmitter/receiver on the ground, M-ary level, filter bandwidth, link distance, and the adaptive optics correction modes on bit-error-rate are demonstrated.
  • Article
    Citation - WoS: 9
    Citation - Scopus: 8
    Effect of Partial Coherence on Signal-To Ratio Performance of Free Space Optical Communication System in Weak Turbulence
    (Elsevier, 2022) Aymelek, Goerkem; Yolcu, Beguem; Kayam, Orkun; Unal, Onur; Caner Gokce, Muhsin; Baykal, Yahya; Akbucak, Volkan; Gökçe, Muhsin Caner
    The effect of source coherence on the average signal-to-noise ratio ((SNR)) performance of free space optical communication (FSOC) systems operating in weak atmospheric turbulence is investigated with the help of the extended Huygens-Fresnel principle. For an FSOC system that uses a partially coherent laser source, first, the received power at the finite-sized receiver aperture is derived. Then, the power scintillation index is evaluated that reflects the aperture averaging. Using these derived optical entities, the variations of (SNR) are examined versus parameters such as the degree of source coherence, wavelength, link distance, source size, structure constant of atmosphere and the receiver aperture radius. Obtained results show that a decrease in the degree of source coherence has a positive effect on (SNR).
  • Article
    Citation - WoS: 7
    Citation - Scopus: 6
    Adaptive Optics Correction of Beam Spread in Biological Tissues
    (Pergamon-elsevier Science Ltd, 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 com-pared 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 co-efficient 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 char-acteristic 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%.(C) 2022 Elsevier Ltd. All rights reserved.
  • Article
    Citation - WoS: 7
    Citation - Scopus: 5
    Tissue Turbulence and Its Effects on Optical Waves: a Review
    (Elsevier, 2023) Ata, Yalcin; Baykal, Yahya; Gokce, Muhsin Caner
    Tissue turbulence and the effects of tissue turbulence on the propagation of optical waves are reviewed. After the introduction of a survey on the reported research in this area, various topics are elaborated. These topics include the spectrum of tissue turbulence, propagation of light in the tissue, average intensity, beam spread that occur at the receiver plane in the tissue. Other entities examined are the signal to noise ratio (SNR), intensity correlation, beam wander, mutual coherence function and the spectral degree of coherence. Furthermore, spectral change, cross spectral density, spectral correlation function, scintillation, bit error rate (BER), coupling efficiency in tissue turbulence are investigated. The refractive index structure of tissues, imaging in the presence of turbulence in the tissue, scattering, absorption and polarization aspects in tissues are reported. Finally, optical coherence tomography applications in turbulent tissues are reviewed.
  • Article
    Citation - WoS: 3
    Citation - Scopus: 3
    Finite Element Method-Based Optimisation of Magnetic Coupler Design for Safe Operation of Hybrid Uavs
    (Mdpi, 2023) Iskender, Ires; Navruz, Tugba Selcen; Arslan, Sami
    The integration of compact concepts and advances in permanent-magnet technology improve the safety, usability, endurance, and simplicity of unmanned aerial vehicles (UAVs) while also providing long-term operation without maintenance and larger air gap use. These developments have revealed the demand for the use of magnetic couplers to magnetically isolate aircraft engines and starter-generator shafts, allowing contactless torque transmission. This paper explores the design aspects of an active cylindrical-type magnetic coupler based on finite element analyses to achieve an optimum model for hybrid UAVs using a piston engine. The novel model is parameterised in Ansys Maxwell for optimetric solutions, including magnetostatics and transients. The criteria of material selection, coupler types, and topologies are discussed. The Torque-Speed bench is set up for dynamic and static tests. The highest torque density is obtained in the 10-pole configuration with an embrace of 0.98. In addition, the loss of synchronisation caused by the piston engine shaft locking and misalignment in the case of bearing problems is also examined. The magnetic coupler efficiency is above 94% at the maximum speed. The error margin of the numerical simulations is 8% for the Maxwell 2D and 4.5% for 3D. Correction coefficients of 1.2 for the Maxwell 2D and 1.1 for 3D are proposed.
  • Article
    Citation - WoS: 1
    Citation - Scopus: 2
    Entangled State Engineering in the 4-Coupled Qubits System
    (Elsevier, 2023) Salmanogli, Ahmad
    This article studies the behavior of the avoided level crossing in the 4-coupled qubit to each other and mainly focuses on how to engineer it. This phenomenon occurs due to the two transitions out of the ground state in a two-coupled qubit, contributing to the entangled states. This essential and unique behavior can be engineered in a quantum circuit. For this reason, a quantum circuit containing 4 qubits is designed, and its quantum Hamiltonian and dynamic equation of the motion are theoretically derived. Analysis of the entanglement between each coupled qubit using the entanglement metric reveals that the strength of the qubit-qubit coupling factor and the qubit's non-linearity play an essential role in engineering the photonic mode entanglement. The results show that the avoided level crossing appears in the photonic mode entanglement. In other words, two or more transitions from the ground state to the multiple excited states for each bias current. However, the interesting point is that the avoided level crossing just occurs for the qubits connected capacitively to the driven field (the first qubit in this work), not for all.& COPY; 2023 Elsevier B.V. All rights reserved.
  • Article
    Citation - WoS: 4
    Citation - Scopus: 4
    Design and Implementation of a Mhz Frequency Transformer With a Ferromagnetic Fluid Core
    (Mdpi, 2023) Hatem, Sude; Kurt, Erol
    Design and optimization of a magnetic fluid cored transformer are studied for high frequency applications. An easy and cheap fluid core is designed and used to decrease the eddy current and loses, thereby low conducting and paramagnetic features are added. The core exhibits both fluid and solid characteristics exerting high frequency modes in the fluid and low current due to the iron powder inside. The finite element analysis simulations are performed via COMSOL Multi-physics package for different mass fractions of iron powder. The maximum peak-to-peak voltage and power are found as 526 mV and 188.8 mW at 12 MHz from the simulations. 3D patterns prove that the magnetic flux and magnetization exhibit turbulence in the core, thereby localized magnetic values indicate an arbitrary attitude for various frequencies. Optimum mass fraction is found as 0.7, which is parallel with experimental results. The transformer operates between 11 MHz and 13.5 MHz optimally.
  • Article
    Citation - WoS: 4
    Citation - Scopus: 4
    Coupling Efficiency of Multimode Beam To Fiber in Atmospheric Turbulence
    (Pergamon-elsevier Science Ltd, 2023) Baykal, Yahya; Ata, Yalcin; Gokce, Muhsin Caner
    Atmospheric turbulence causes wavefront distortions in the propagated laser beam. By the beam shaping of the transmitted laser, wavefront distortions can be mitigated effectively. In this paper, we consider a shaped laser modeled by multimode beams at the transmitter and investigate the coupling of the light wave to a single-mode fiber under the atmospheric turbulence effect. We derive the light power on the coupling lens and light power accepted by the fiber core using the extended Huygens-Fresnel princi-ple. Then, the fiber coupling efficiency (FCE) is scrutinized for different system parameters such as the number of modes of the transmit laser, link distance, structure constant of atmosphere, focal length and radius of the coupling lens, wavelength, source size, and the number of speckles (NOS).(c) 2023 Elsevier Ltd. All rights reserved.
  • Article
    Citation - WoS: 15
    Citation - Scopus: 19
    Adaptive Optics Effect on Performance of Bpsk-Sim Oceanic Optical Wireless Communication Systems With Aperture Averaging in Weak Turbulence
    (Pergamon-elsevier Science Ltd, 2020) Baykal, Yahya; Ata, Yalcin; Gokce, Muhsin Caner
    Turbulence-induced wavefront deformations cause the irradiance of an optical signal to fluctuate resulting a in serious degradation in the bit-error-rate (BER) performance of optical wireless communication (OWC) system. Adaptive optics is an effective technique to compensate for the wavefront aberrations to reduce the fluctuations in the received intensity. In this paper, we investigate how the adaptive optics technique affects the BER performance of an oceanic OWC (OOWC) system employing binary phase shift keying-subcarrier intensity modulation (BPSK-SIM) and aperture averaging. To evaluate BER performance in weak oceanic turbulence, the required entities such as the received optical power captured by a circular aperture and the aperture averaged scintillation index measuring the fluctuations in the received irradiance are derived. The effect of adaptive optics correction of various wavefront aberrations (i.e., tilt, defocus, astigmatism and the coma) on the BER performance is illustrated and the performance of the adaptive optics-OOWC system is compared to that of a non-adaptive optics OOWC system by the metric defined. (C) 2020 Elsevier Ltd. All rights reserved.