Elektronik ve Haberleşme Mühendisliği Bölümü Yayın Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12416/260
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Article Citation - WoS: 38Citation - Scopus: 42Propagation Factor of Partially Coherent Flat-Topped Beam Array in Free Space and Turbulent Atmosphere(Elsevier Sci Ltd, 2012) Yuan, Yangsheng; Cai, Yangjian; Eyyuboglu, Halil T.; Baykal, Yahya; Chen, JunAnalytical expressions for the propagation factor of partially coherent radial flat-topped (FT) beam array in free-space and turbulent atmosphere are derived. Our formulae can be applied to study the beam propagation factors of partially coherent Gaussian beam, partially coherent FT beam and partially coherent radial Gaussian beam array. The evolution properties of the propagation factors of those beams in turbulent atmosphere are studied numerically and comparatively. From the aspect of the propagation factor, our results show that partially coherent radial FT beam array is less affected by turbulence than partially coherent Gaussian beam, partially coherent FT beam and partially coherent radial Gaussian beam array. (C) 2011 Elsevier Ltd. All rights reserved.Article Citation - WoS: 34Citation - Scopus: 39Wavelet Based Flickering Flame Detector Using Differential Pir Sensors(Elsevier Sci Ltd, 2012) Toreyin, B. Ugur; Soyer, E. Birey; Inac, Ihsan; Gunay, Osman; Kose, Kivanc; Cetin, A. Enis; Erden, FatihA Pyro-electric Infrared (FIR) sensor based flame detection system is proposed using a Markovian decision algorithm. A differential PIR sensor is only sensitive to sudden temperature variations within its viewing range and it produces a time-varying signal. The wavelet transform of the FIR sensor signal is used for feature extraction from sensor signal and wavelet parameters are fed to a set of Markov models corresponding to the flame flicker process of an uncontrolled fire, ordinary activity of human beings and other objects. The final decision is reached based on the model yielding the highest probability among others. Comparative results show that the system can be used for fire detection in large rooms. (c) 2012 Elsevier Ltd. All rights reserved.Article Citation - WoS: 18Citation - Scopus: 19Field Correlations of Flat-Topped Gaussian and Annular Beams in Turbulence(Elsevier Sci Ltd, 2011) Baykal, YahyaStarting from the second order moment formulation for multi-beam incidence, field correlations at the receiver plane of flat-topped Gaussian and annular beams are found in turbulence. Reflecting the information on both the randomness due to turbulence and the field profile of the incident field, field correlations of the fiat-topped Gaussian beams are found to become larger at larger source size, smaller flatness parameters and smaller turbulence strengths. For the annular beam structures, field correlations are larger for thicker beams. Field correlations of larger primary beam sized annular incidences are smaller at smaller diagonal distances and larger at larger diagonal distances. As expected, annular beam field correlations are found to be larger at smaller structure constants and at smaller wavelengths. However, at large link lengths, field correlations could be larger than at smaller link lengths due to fact that for annular beams, the field at the centre of the receiver attains very small value at smaller link lengths, however, on propagation in turbulence, receiver field distribution changes to a Gaussian profile. (C) 2011 Elsevier Ltd. All rights reserved.Article Citation - WoS: 7Citation - Scopus: 10Propagation of Various Dark Hollow Beams Through an Optical System in Turbulent Atmosphere(Elsevier Sci Ltd, 2010) Cai, Yangjian; Eyyuboglu, Halil T.; Baykal, Yahya; Eyyubolu, Halil T.The propagation of a dark hollow beam (DHB) of circular, elliptical or rectangular symmetry through aligned and misaligned ABCD optical systems in turbulent atmosphere is investigated. Analytical propagation formulae for the average intensities of various DHBs are derived based on the extended Huygens-Fresnel integral. As a numerical example, the focusing properties of various DHBs in turbulent atmosphere are studied It is found that the focusing properties of various DHBs in turbulent atmosphere are much different from their focusing properties in free space (C) 2010 Elsevier Ltd. All rights reserved.