Volume 65 (2014): Issue 5 (September 2014)

Some aspects of the numerical modeling of the electromagnetic waves propagation using the “complex-envelope” finitedifferences formulation in the one-dimensional case are here reviewed and discussed in comparison with the standard finitedifferences in time-domain (FDTD) approach. The main focus is put on the stability and the numerical dispersion issues of the “complex envelope” explicit and implicit methods

In this paper authors present the results of identification of emission and capture processes in tandem solar cell structures based on quaternary InGaAsN semiconductor alloys by DLTFS (Deep Level Transient Fourier Spectroscopy) and by ana- lytical evaluation processes. The energies of five trap levels ET1=0.77 eV, ET2=0.47 eV, ET3=0.64 eV, HT1=0.62 eV and HT2=0.53 eV were identified with reliable accuracy. These values were obtained by available analytical procedures, verified by simulations and confirmed by reference structures with basic layer types and compared with possible reference trap data. Native structural defects in GaAs were stated as the origin of these deep energy levels

A simulation model of brushless DC motor (BLDC) control and diagnostics is considered. The model has been developed using a freeware complex “Modeling in technical devices”. Faults and diagnostic parameters of BLDC are analyzed. A logicallinguistic diagnostic model of BLDC has been developed on basis of fuzzy logic. The calculated rules determine dependence of technical condition on diagnostic parameters, their trends and utilized lifetime of BLDC. Experimental results of BLDC technical condition diagnostics are discussed. It is shown that in the course of BLDC degradation the motor condition change depends on diagnostic parameter values

An explicit formula for the resistance between two nodes in a network described by non-symmetric Laplacian matrix L is obtained. This is of great advantage eg in electronic circuit fault analysis, where non-linear systems have to be solved repeatedly. Analysis time can be greatly reduced by utilization of the obtained formula. The presented approach is based on the “mutual orthogonality” of the full system of left and right-hand eigenvectors of a diagonalizable matrix L. Simple examples are given to demonstrate the accuracy of this approach to circuit networks

Orthogonal frequency division multiplexing (OFDM) is a common technique in multi carrier communications. One of the major issues in developing OFDM is the high peak to average power ratio (PAPR). Golay sequences have been introduced to construct 16-QAM and 256-QAM (quadrature amplitude modulation) code for the orthogonal frequency division multiplexing (OFDM), reducing the peak-to-average power ratio. In this paper we have considered the use of coding to reduce the peakto- average power ratio (PAPR) for orthogonal frequency division multiplexing (OFDM) systems. By using QPSK Golay sequences, 16 and 256 QAM sequences with low PAPR are generated

In this paper, selected problems occurring during GaN epitaxy on Si substrates are correlated with in-situ interferometer observations based on structures fabricated using 3×2” Thomas Swan Close Coupled Showerhead MOVPE system. Samples were epitaxially grown on highly resistive (> 500cm) p-type 2” silicon substrates. The growth was observed using an interferometer acquiring reflectance traces in-situ. To avoid issues that are shown in this paper, different approaches of the so-called buffer layer were used by depositing them on Si before the growth of GaN. Different material qualities of grown GaN layers were obtained by variation in films constituting the buffer layer grown before the desirable GaN film. The study shows the evolution of the grown samples, improvement of various parameters and also gradual reduction of material issues discussed in this paper. Improvement in GaN layer was mainly observed by SEM characterization and studying the growth mechanisms through observation of reflectance traces obtained in-situ.

GaInNAs alloys are mostly used as an active part of light sources for long wavelength telecom applications. Beside this, these materials are used as thin quantum wells (QWs), and a need is to grow thick layers of such semiconductor alloys for photodetectors and photovoltaic cells applications. However, structural characterization of the GaInNAs layers is hindered by non-homogeneity of the In and N distributions along the layer. In this work the challenges of the structural characterization of doped thick GaInNAs layers grown by atmospheric pressure metalorganic vapour phase epitaxy (APMOVPE) will be presented

This paper illustrates a promising application of an accelerometer sensor in physiological research, we demonstrated use of accelerometers for monitoring the standard proband physical activity (PA) and also in special applications like respiration and mechanical heart activity, the so-called seismocardiography (SCG) monitoring, physiological activation monitoring and mechanomyography (MMG)

The paper deals with optical characterization of the Al0.295Ga0.705As/GaAs multi-quantum well light emitting diode (LED) structure with photonic crystal (2D PhC) patterned on the top of the structure using Electron Beam Direct Write Lithography (EBDWL). Light-current characteristics measured by integrating sphere shows increase of extracted light intensity as 21.1%. Additionally, extracted light intensity was studied by far-field measurements as a complementary method to light-current characteristics. The far-field measurements show increase of extracted light intensity as 31.2%. We suggest this method as more suitable for evaluation of extracted light intensity because it omits emission from edges of the LED and thus light is measured only from the area where PhC is patterned

Electrical properties of recessed and non-recessed AlGaN/GaN Schottky diodes under off-state stress were investigated. The samples were consecutively stressed by the stepped negative bias (−60 V). Before and after the stress I−V and C−V characteristics were evaluated to verify the device degradation process. Finally, the degradation mechanism and the influence of AlGaN recessed layer thickness on the electrical properties of the Schottky diodes were analysed. It was found that the short time stress influence on I−V characteristics was most negligible for the non-recessed sample. Shallow and deep recessed samples exhibited initial trap filling and reverse current decrease. Generally it was found that the stress voltage near 60 V caused recoverable device degradation

The effect of neutron radiation on the surface properties of the nanocrystalline (Fe_0.25Ni_0.75)₈₁Nb₇B₁₂ alloy was studied. Firstly, amorphous (Fe_0.25Ni_0.75)₈₁Nb₇B₁₂ ribbon was brought by controlled annealing to the nanocrystalline state. After annealing, the samples of the nanocrystalline ribbon were irradiated in a nuclear reactor with neutron fluences of 1×10¹⁶cm⁻² and 1 × 10¹⁷cm⁻² . By utilizing the magnetic force microscopy (MFM), topography and a magnetic domain structure were recorded at the surface of the ribbon-shaped samples before and after irradiation with neutrons. The results indicate that in terms of surface the nanocrystalline (Fe_0.25Ni_0.75)₈₁Nb₇B₁₂ alloy is radiation-resistant up to a neutron fluence of 1 × 10¹⁷cm⁻² . The changes in topography observed for both irradiated samples are discussed

Transmission system in Slovakia is part of a synchronously interconnected system of continental Europe. Besides indisputable technical and economical benefits of cooperation many hazardous factors exist of fault condition spreading with impact on our system. Even today a system break-up escalated into a vast blackout is a real danger. European transmission system operators continually work on preventive measures and develop systems with a goal to handle critical situations. The ambition of the European Awareness System is to signalize the rise of these situations and also assist with system restoration