Πλοήγηση ανά Συγγραφέα "Magafas, L."
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Τεκμήριο Digital chaotic synchronized communication system(2009) Stavrinides, S. G.; Anagnostopoulos, A. N.; Miliou, A. N.; Valaristos, A.; Magafas, L.; Kosmatopoulos, K.; Papaioannou, S.The experimental study of a secure chaotic synchronized communication system is presented. The synchronization between two digital chaotic oscillators, serving as a transmitter-receiver scheme, is studied. The oscillators exhibit rich chaotic behavior and are unidirectionally coupled, forming a master-slave topology. Both the input information signal and the transmitted chaotic signal are digital ones.Τεκμήριο Non-linear analysis in RL-LED optoelectronic circuit(2008) Hanias, M.; Magafas, L.; Kalomiros, J.In this paper we present the chaotic state of a LED as a diode element in a non linear LRD. Multisim is used to simulate the circuit and show the presence of chaos. Time series analysis performed by the method proposed by Grasberger and Procaccia. The correlation and minimum embedding dimension ν and m respectively were calculated. Also the corresponding Kolmogorov entropy was calculated.Τεκμήριο The nonlinear current behaviour of a driven R–L-Varactor in the low frequency range(2009-04) Kalomiros, J. A.; Stavrinides, S. G.; Miliou, A. N.; Antoniades, I. P.; Magafas, L.; Anagnostopoulos, A. N.The nonlinear behaviour of an R–L-Varactor circuit, simulated by Multisim 7.0 at a driving frequency that is below the circuit resonance frequency, is reported and evaluated. A new high amplitude oscillation is observed and attributed to the emergence of a large diode junction capacitance. Increasing the driving signal amplitude, the circuit is led to a non-periodic mode of operation, producing trajectories of increasing chaotic content in a four-dimensional phase space. At specific amplitudes a two-dimensional tori was monitored, where trajectories are periodic, like in a two oscillator system with commensurate frequencies. Poincaré cross-sections, FFT spectra and correlation dimension calculations, suggest the quasi-periodicity route to chaos.Τεκμήριο Optimization of Al/a-SiC:H optical sensor device by means of thermal annealing(2007-12) Magafas, L.; Kalomiros, J.The optimization of optoelectronic properties of Al/a-SiC:H Schottky diodes grown as Al/a-SiC:H/c-Si(n) structures is studied by means of thermal annealing of a-SiC:H thin films. According to the spectral response of the Schottky diodes the measured quantum efficiency, ηmeasured, increases with increasing annealing temperature (400–600 °C), whereas ηmeasured decreases for Ta>600 °C. For Ta=600 °C, optimum material quality of a-SiC:H films is achieved and the spectral response of the Al/a-SiC:H/c-S(n) structures present very high and almost constant values (ηmeasured⩾80%) for the whole range of wavelengths from 500 up to 850 nm. These results show that our Al/a-SiC:H/c-S(n) structures can be very attractive as optical sensors. Diffusion length calculations as well as the mobility by lifetime product (μτ)p of the minority carriers (holes) of a-SiC:H films present a dependence on Ta similar to that of the measured quantum efficiency. Finally, the quantum efficiency of films processed with Ta=675 °C is found to increase when the Al/a-SiC:H/c-S(n) structures are exposed to hydrogen, a result that could be promising for the construction of a hydrogen detection sensor.Τεκμήριο Optimization of the electrical properties of Al/a-SiC:H Schottky diodes by means of thermal annealing of a-SiC:H thin films(2006-11) Magafas, L.; Kalomiros, J.; Bandekas, D.; Tsirigotis, G.The present work reports on the optimization of the electrical properties of Al/a-SiC:H Schottky diodes by means of thermal annealing of a-SiC:H thin films. Optical transmission experiments have shown that the optical properties of the films are affected by thermal annealing when Ta>600 °C, due to emission of hydrogen bonded to silicon. Although the electrical properties of Al/a-SiC:H Schottky diodes are invariant for Ta⩽400 °C, for higher Ta these properties are improved with the optimum result achieved at View the MathML source. At this annealing temperature the linear log I–V characteristics span about eight orders of magnitude and the ideality factor is 1.09±0.04, making these diodes very interesting for many potential applications. For higher Ta (>600 °C) the electrical properties of Al/a-SiC:H Schottky diodes deteriorate with complete degradation at View the MathML source. For temperatures up to 600 °C this behavior is attributed to relaxation of the strain in the amorphous network which is possibly combined with weak hydrogen emission for temperatures up to 600 °C, leading to an optimum material quality. For further increase of Ta (>600 °C) the observed deterioration of the electrical properties of Al/a-SiC:H Schottky diodes is due to the intensive emission of hydrogen atoms bonded to silicon that cause voids in the amorphous network. These results are also supported by the experimental values of the room temperature apparent barrier height of the Al/a-SiC:H junction ϕbRT and its temperature coefficient γ.