Elektronik ve Haberleşme Mühendisliği Bölümü Yayın Koleksiyonu

Permanent URI for this collectionhttps://hdl.handle.net/20.500.12416/260

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  • Conference Object
    Citation - WoS: 1
    Propagation of a Generalized Beam in Abcd System
    (Cemal Ardil-IEC Barbaros Mah Hasret Sitesi, 2005) Eyyuboglu, HT; Elektronik ve Haberleşme Mühendisliği
    For a generalized Hermite sinosiodal/hyperbolic Gaussian beam passing through an ABCD system with a finite aperture, the propagation properties are derived using the Collins integral. The results are obtained in the form of intensity graphs indicating that previously demonstrated rules of reciprocity are applicable, while the existence of the aperture accelerates this transformation.
  • Conference Object
    Citation - WoS: 2
    Bit Error Rates for Focused General-Type Beams
    (Electromagnetics Acad, 2009) Arpali, Serap; Arpali, Serap Altay; Baykal, Yahya Kemal; Baykal, Yahya; Elektrik-Elektronik Mühendisliği; Elektronik ve Haberleşme Mühendisliği
    Using the scintillation index of general beam formulation, bit error rate (BER) is investigated for focused Gaussian, cos-Gaussian, cosh-Gaussian and annular beams in weak atmospheric turbulence. We have employed our previously derived formulation of the scintillation index of these beams by Rytov method. Rytov method scintillation theory is known to yield accurate results for focused beams on horizontal paths under certain regions. Therefore we find the scintillation indices of the mentioned beams for the valid region. Using the log-normal distributed intensity, BER values versus signal-to-noise ratio (SNR) are calculated for Gaussian, cos-Gaussian, cosh-Gaussian and annular beams. In our study, the focal lengths (radius of curvature) of all the mentioned focused beams are equal to the propagation distance. The improvement of BER is observed for variations of propagation length, source size and wavelength of operation. Based on these parameters, BER values of Gaussian, cos-Gaussian, cosh-Gaussian and annular beams are compared. BER values we found for the focused Gaussian, cos-Gaussian, cosh-Gaussian and annular beams decrease with increasing source sizes. Likewise, BER values of focused Gaussian, cos-Gaussian, cosh-Gaussian and annular beams decrease with increasing wavelength. The focused annular beam attains the lowest BER value for small source sizes and long propagation distances. Moreover, BER for focused beams is compared with their collimated counterparts. We observe that focused beams have lower BER values than the collimated beams on horizontal paths. Our formulation can easily be extended to cover corresponding higher order beams, however in this paper we concentrate mainly on the zero order beams.
  • Conference Object
    Design of Led Circuit Card for an Off-Road Lamp
    (2010) Yakişir, B.; Çil, Celal Zaim; Çil, C.Z.; Elektronik ve Haberleşme Mühendisliği
    In this study a working lamp used on the working machines is designed by using the LED diodes instead of a halogen bulb. In the design, firstly a LED or a LED array and a proper driver circuit that can provide the required optical power are designed, and the working lamp developed are tested under various conditions. The luminous output values of the designed LED working lamp are compared with those of a commercial working lamp using a halogen bulb. It is evaluated that in automotive applications working lamps using LEDs could be successfully utilized depending on the optical efficacy of the LED used, the designs of the LED driver and the reflector.
  • Conference Object
    Citation - WoS: 1
    Citation - Scopus: 1
    Off-Axis Field Correlations in Turbulence
    (Ieee, 2013) Baykal, Yahya Kemal; Baykal, Yahya; Elektrik-Elektronik Mühendisliği
    The field correlations in atmospheric turbulence are evaluated for off-axis optical incidence. Within the practical range of the source and the medium parameters, increase in the diagonal length at the receiver plane is found to decrease the off-axis field correlations in turbulence. At a fixed diagonal length at the receiver plane, off-axis beams that have smaller displacement parameters and larger source sizes possess larger field correlations. When the field correlations of the off-axis beams in atmospheric turbulence are compared to their no turbulence counterparts, it is observed that the behaviour of the field correlation variations do not change, however the field correlations in turbulence diminish at smaller diagonal lengths.
  • Conference Object
    Aperture Averaging of Focused Multi-Gaussian Beams
    (Electromagnetics Acad, 2013) Baykal, Yahya Kemal; Kamacioglu, Callan; Baykal, Yahya; Yazgan, Erdem; Elektrik-Elektronik Mühendisliği
    We investigate the behavior of the power fluctuations of the focused annular and flat-topped beams when a realistic receiver possessing a finite sized aperture is employed in turbulent atmospheric optics links. Employing our previously derived formulation for the power scintillation index, the variations of the power scintillations and the receiver aperture averaging factor of the focused annular and flat-topped beams are scrutinized. Receiver aperture averaging factor is deduced from the ratio of power scintillation index detected by a finite sized aperture to that obtained by a point aperture. Influence of the receiver aperture radius, the propagation length, the structure constant, the inner and the outer beam sizes for an annular type incidence, flatness parameter for a flat-topped incidence and the focusing parameter for the multi-Gaussian beam in general, on the power scintillation and the receiver aperture averaging factor are studied. It is found that for the focused multi-Gaussian beams, the effect of the receiver aperture averaging factor increases as the aperture radius increases for larger link lengths. Additionally, for the annular incidences in turbulence, the effect of the receiver aperture averaging factor is stronger for larger inner beam source sizes. At a fixed receiver aperture radius, receiver aperture averaging becomes more effective when the structure constant becomes larger. When focused multi-Gaussian beams are compared to their collimated counterparts, it is seen that the receiver aperture averaging is more beneficial for the focused annular and focused flat-topped beams. At large link lengths, increase in the receiver aperture radius decreases the power scintillations.
  • Conference Object
    Citation - WoS: 2
    Diffraction Properties of Partially Coherent Elegant High-Order Beam
    (Electromagnetics Acad, 2010) Eyyuboğlu, Halil Tanyer; Wang, Fei; Baykal, Yahya Kemal; Cai, Yangjian; Eyyuboglu, Halil T.; Baykal, Yahya; Elektronik ve Haberleşme Mühendisliği; Elektrik-Elektronik Mühendisliği
    The diffraction properties of a partially coherent elegant higher-order beam in free space are investigated in detail. It is found that the diffraction properties of a partially coherent elegant higher-order beam upon propagation are closely related to its initial coherence. A partially coherent elegant higher-order beam spreads more slowly than a partially coherent standard higher-order beam, which has potential application in free-space optical communications.
  • Conference Object
    Fluorescent On-Chip Imager by Using a Tunable Absorption Filter
    (Ieee, 2017) Arpali, Caglar; Yıldırım, Ender; Yildirim, Ender; Arpali, Çağlar; Arpali, Serap Altay; Arpali, Serap; Makine Mühendisliği; Mekatronik Mühendisliği; Elektronik ve Haberleşme Mühendisliği
  • Conference Object
    Effects of Focusing on Scintillations of Higher Order Laser Modes in Non-Kolmogorov Turbulence
    (Electromagnetics Acad, 2014) Baykal, Yahya Kemal; Baykal, Yahya; Elektrik-Elektronik Mühendisliği
    The scintillation index of focused higher order laser beam propagating in non-Kolmogorov atmospheric turbulence is formulated by employing the Rytov method and the equivalence of the structure constant. Our evaluations are performed for even modes. The equivalence formula for the structure constant is extracted from our earlier work in which the equivalence is obtained by equating the scintillation indices found in the Kolmogorov and the non-Kolmogorov turbulence. If not specified otherwise, the focused beam is defined when the focal length is equal to the link length. For the focused higher order laser beams, as the power law exponent of the non-Kolmogorov spectrum decreases, the scintillations decrease. At any power law exponent, the scintillations tend to become larger when the mode order of the focused beam becomes larger, i.e., the focused Gaussian beam is advantageous over the focused higher order laser beams for any realization of the non-Kolmogorov turbulence. Again being valid for any power law exponent, increase in the source size is found to decrease the intensity fluctuations of all the focused higher order mode scintillations. Especially for the larger order beams, focusing the higher order beam at a distance smaller than the link length results in a change in the behaviour of the scintillation index versus the power law exponent. In such cases, the scintillations are observed to increase. Comparison of the focused higher order beam scintillations with the previously obtained collimated higher order beam scintillations yields that the focused higher order beam scintillations are lower. Collimated higher order beams exhibit lower scintillations than the collimated Gaussian beams whereas this is reversed in the focused case. Another observation in such comparison shows that the difference of the intensity fluctuations between the Gaussian and the higher order beams are much larger in the focused case, especially at larger power law exponent values.
  • Conference Object
    Propagation of Partially Coherent Beams After a Source Plane Ring Aperture
    (Electromagnetics Acad, 2008) Eyyuboğlu, Halil Tanyer; Eyyuboglu, H. T.; Baykal, Yahya Kemal; Baykal, Y. K.; Cai, Y.; Elektronik ve Haberleşme Mühendisliği; Elektrik-Elektronik Mühendisliği
    The propagation properties of partially coherent beams passing through a source placed ring aperture are examined. The derivation is based on the lowest order general beam formulation, such that our results are applicable to a wide range of beam. In this study, our focus is on fundamental Gaussian, cosh-Gaussian, cos-Gaussian, sinh-Gaussian, sine-Gaussian and annular beams. The aperture consists of inner and outer parts, thus the middle hollow part appears in the form of a ring. The propagation environment is turbulent. From the graphical outputs of the beams investigated, it is seen that despite the existence of the circular ring, during propagation, the beams tend to retain the basic profiles similar to the case of no aperture, but depending on the inner and outer radius dimensions, the propagated beams are reduced in intensity levels and become more spread. It is further observed that, when the inner part of the aperture has nonzero radius, ring formations are developed at the outer edges of the receiver plane intensities.
  • Conference Object
    Power Consumption of Novel Throughput Improvement Methods
    (2010) Preveze, B.; Preveze, Barbaros; Şafak, A.; Elektrik-Elektronik Mühendisliği
    The novel proposed method as a combination of Time Division Multiple Access (TDMA) and Orthogonal Frequency Division Multiple Access (OFDMA) called Orthogonal Frequency Division Most Congested Access First (OFDMCAF) provides spectrum sharing, buffer management and improves the throughput. In this work the power consumed by activating each cognitive method is analyzed in addition to the throughput improvement provided by each method used with OFDMCAF. It is shown at the end of the analysis that activation of each method also decreases the average power consumption even the same routing algorithm is used in all cases.