Elektrik Elektronik Mühendisliği Bölümü Yayın Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12416/411
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Article Citation - WoS: 5Citation - Scopus: 4Laser Array Field Correlations in Underwater Turbulence(Taylor & Francis Ltd, 2022) Gokce, Muhsin C.; Baykal, Yahya; Ata, YalcinIn 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.Article Citation - WoS: 1Citation - Scopus: 1Calculation 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, HamitThe 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.Article Citation - WoS: 2Citation - Scopus: 1Signal-To Ratio With Adaptive Optics Compensation in Non-Kolmogorov Weak Turbulent Atmosphere(Taylor & Francis Ltd, 2021) Baykal, Yahya; Gokce, Muhsin Caner; Ata, YalcinThis study investigates the average signal-to-noise ratio < SNR > at the shot-noise limited receiver of an optical wireless communication system (OWC) that uses collimated Gaussian beam with adaptive optics correction in non-Kolmogorov weak turbulent atmosphere. < SNR > and the variation in the percentage < SNR > are calculated and the results are presented against various adaptive optics correction modes, non-Kolmogorov power-law exponent, receiver aperture size, Gaussian beam source size, photodetector quantum efficiency, electronic bandwidth, link length, and turbulence strength. Adaptive optics correction is analyzed for tilt, defocus, astigmatism, coma and trefoil modes and their variations. The effects of adaptive optics compensation are examined that cause an increase in SNR, hence improve the performance of an OWC system using collimated Gaussian beam and operating in the non-Kolmogorov weak turbulent atmosphere.Article Citation - WoS: 8Citation - Scopus: 9Multimode Laser Beam Scintillations in Weak Atmospheric Turbulence for Vertical Link Laser Communications(Taylor & Francis Ltd, 2022) Sayan, Omer F.; Gercekcioglu, Hamza; Baykal, YahyaScintillation index of multimode laser beams used for communication systems in vertical paths of weak atmospheric turbulent medium are examined by employing the Rytov method. On-axis scintillation index is examined versus the source size, propagation distance and zenith angle for vertical link including uplink and downlink. At the selected values of source sizes and propagation distances, scintillation responses of multimode laser beams are evaluated. In general, it is found for both uplink and downlink that the laser beam with multimode content has larger scintillation noise as compared to a Gaussian laser beam. However, for the downlink at L=700 km, at the chosen parameters, the multimode beam possessing larger mode content, is found to attain slightly smaller scintillations.Article Citation - WoS: 6Citation - Scopus: 6Intensity Correlation of Collimated Gaussian Beams Propagating in Biological Tissues(Taylor & Francis Ltd, 2021) Baykal, YahyaIntensity 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.Article Citation - WoS: 6Citation - Scopus: 5Effects of Underwater Turbulence on Average Transmittance of Cos-Gaussian and Cosh-Gaussian Optical Beams(Taylor & Francis Ltd, 2021) Baykal, Yahya; Keskin, AysanThe impacts of underwater turbulence on the average optical transmittance are investigated when optical cosine-Gaussian and optical cosine-hyperbolic-Gaussian (cosh-Gaussian) beam propagate in weakly turbulent underwater medium. Findings obtained by using MATLAB reveal that when the displacement parameter is smaller (larger) for the cos-Gaussian (cosh-Gaussian) beam, the average transmittance increases. Also, an increase in the source size results in elevated average transmittance values. Rate of dissipation of kinetic energy per unit mass of fluid is found to be directly proportional to the average transmittance. However, the rate of dissipation of the mean-squared temperature is inversely proportional to the average transmittance. Average transmittance is found to be essentially the same when the temperature-induced optical turbulence is dominant. An increase in the salinity-induced optical turbulence suddenly reduces the average transmittance of the cos-Gaussian and cosh-Gaussian beam in underwater turbulence. Finally, it is observed that for the same sized beams in the same underwaterturbulent medium, cosh-Gaussian beam will have larger average transmittance than the corresponding cos-Gaussian beam. As the influence and value of our research conclusion on the development of our research, we comment that cosh-Gaussian beams can be preferred over the cos-Gaussian and Gaussian beams in obtaining larger average transmittance in underwater turbulence.Article Citation - WoS: 1Citation - Scopus: 2Ber Performance Ofm-Ary Pulse Position Modulated Communication Systems in Anisotropic Non-Kolmogorov Turbulent Atmosphere(Taylor & Francis Ltd, 2022) Gokce, Muhsin Caner; Ata, Yalcin; Baykal, YahyaWe investigated the effect of anisotropic non-Kolmogorov atmospheric turbulence on the performance of the optical wireless systems whenM-ary Pulse Position Modulation (PPM) is applied to a Gaussian beam. The performance of the optical wireless systems that use avalanche photodetector at the receiver is evaluated in terms of the bit error rate (BER). The effects of the parameters, such as the anisotropy factors inx-ydirections, modulation order, data bit rate, equivalent load resistor, photodetector quantum efficiency, non-Kolmogorov turbulence power law exponent, beam source size, link length, photodetector gain and structure constant on BER of theM-ary PPM Gaussian beam propagating in anisotropic non-Kolmogorov atmospheric turbulence, are examined.Article Citation - WoS: 6Citation - Scopus: 5Anisotropic Non-Kolmogorov Turbulence Effect on Transmittance of Multi-Gaussian Beam(Taylor & Francis Ltd, 2020) Ata, Yalcin; Baykal, YahyaThe effect of anisotropic non-Kolmogorov turbulent atmosphere on multi-Gaussian beam is investigated and the results are presented against different beam and medium parameters. Results show that anisotropy increases the power efficiency of wireless communication systems. Besides anisotropy, turbulence effects on the multi-Gaussian optical beam are represented versus the beam source size, beam flatness order, propagation distance, inner scale length, turbulence strength, non-Kolmogorov turbulence power law exponent, wavelength, inner and outer source sizes for flat-topped and annular beams.Article High-Gain Low-Profile Rectangular Microstrip Patch Antenna With Yagi Elements(Taylor & Francis Ltd, 2020) Sener, GokerThis 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.Article Citation - WoS: 5Citation - Scopus: 5Intensity Correlations of Flat-Topped Beams in Oceanic Turbulence(Taylor & Francis Ltd, 2020) Baykal, YahyaIntensity 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.