Communications - Scientific Letters of the University of Zilina, 2015 (vol. 17), issue 1A
Articles
Spectrum Renting with Two Finite Source Pools in Mobile Cellular Networks
Adam Horvath, Tamas Berczes
Communications - Scientific Letters of the University of Zilina 2015, 17(11):4-11 | DOI: 10.26552/com.C.2015.1A.4-11 
Spectrum renting is a technique for improving the efficiency of spectrum usage and alleviating the scarcity of the available spectrum in mobile cellular networks. Since the first proposal of spectrum pooling, several works have been done in this area. In this paper, we propose a finite-source queuing model in which service providers may rent each other's unutilized frequency bands. Our model contains two source pools: one for subscribers generating fresh calls in the investigated mobile cell, and another for modeling handover calls. The model considers the traveling of subscribers over the borders of the investigated mobile cell, too. Moreover, we...
Biomaterial Real Cracks Evaluation by Eddy Current Testing Method
Milan Smetana, Klara Capova
Communications - Scientific Letters of the University of Zilina 2015, 17(11):12-16 | DOI: 10.26552/com.C.2015.1A.12-16
The paper deals with identification of real biomaterial`s cracks using electromagnetic non-destructive sensing. Advanced types of the magnetic field sensors are used for this purpose. New modular eddy current probe is used for the evaluation. Harmonic excitation is used for the excitation of the eddy currents. The real biomaterial stress corrosion cracks (SCC) and fatigue cracks (FC) are inspected. Gained results are discussed and presented in the paper. The main aim of the paper is to compare the sensitivity of the various magnetic field sensors under the same conditions.
Progress in Three-Dimensional Non-Destructive Assessment of Real Cracks from Eddy Current Testing Signals
Ladislav Janousek, Mihai Rebican, Milan Smetana, Anton Duca
Communications - Scientific Letters of the University of Zilina 2015, 17(11):17-22 | DOI: 10.26552/com.C.2015.1A.17-22
Enhancement in three-dimensional non-destructive evaluation of real cracks from two-dimensional simulated eddy current testing signals is reported in the paper. A new uniform eddy current testing probe is employed for the inspection. All three spatial components of the perturbation electromagnetic field are acquired during two-dimensional scan of the probe. The ECT signals due to partially conductive cracks are simulated by a fast forward FEM-BEM solver using a database. Two crack models are proposed for the inversion using the tabu search stochastic method. The former model has a cuboid shape and the latter one reflects a more complex geometry. Numerical...
Impact of Parallel Operation of AC Traction Motors on Locomotive Performance
Matej Pacha, Jiri Stepanek
Communications - Scientific Letters of the University of Zilina 2015, 17(11):23-27 | DOI: 10.26552/com.C.2015.1A.23-27
Presented paper deals with common problems of parallel operation of AC traction motors and presents some methods to investigate the basic impacts of the concept. A complex simulation model is introduced as well as results of simulations. Based on the results, a conclusion is made on locomotive performance impact.
Magamp Regulated Isolated AC-DC Converter with High Power Factor
Volodymyr Yaskiv, Alexander Abramovitz, Keyue Smedley, Anna Yaskiv
Communications - Scientific Letters of the University of Zilina 2015, 17(11):28-34 | DOI: 10.26552/com.C.2015.1A.28-34
This paper evaluates the performance of magnetic amplifier regulator in isolated off-line power supplies with power factor correction stage. A research of operation modes of power converter, based on high frequency magnetic amplifiers, with power factor correction was conducted for the first time. Simplified controller circuitry is suggested and analyzed. Experimental results are reported.
Statistical Analysis of Fast Fluctuating Random Signals with Arbitrary-Function Envelope and Unknown Parameters
Oleg V. Chernoyarov, Martin Vaculik, Armen Shirikyan, Alexandra V. Salnikova
Communications - Scientific Letters of the University of Zilina 2015, 17(11):35-43 | DOI: 10.26552/com.C.2015.1A.35-43
We find a new expression for the solving statistics of fast fluctuating Gaussian pulses with arbitrary-function envelope, based on which we can receive much simpler processing algorithms of random signals with unknown parameters in comparison with available analogues. For example, the synthesis and analysis of maximum likelihood detector and measurer of a high-frequency random pulse with unknown time parameter is carried out. The asymptotically exact expressions for detection and estimation characteristics including anomalous effects are presented. By methods of statistical computer modeling the adequacy of the considered analytical approach of the...
Reliability Analysis of Logic Network with Multiple Outputs
Elena Zaitseva, Miroslav Kvassay, Vitaly Levashenko, Jozef Kostolny
Communications - Scientific Letters of the University of Zilina 2015, 17(11):44-50 | DOI: 10.26552/com.C.2015.1A.44-50
Reliability analysis of a logic network with multiple outputs is considered in this paper. One of the principal tasks of reliability engineering is identification of those system components that have the most influence on the system activity. There exist several measures that are used for this purpose. One of them is Structural Importance Measure (SIM) which focuses on topological importance of individual system components. This measure is calculated from the system structure function, i.e. function that defines dependency between system activity and activity of its components, using logical differential calculus. In this paper, we present a method...
New Approach to Metal Biomarker Detection Using Nonionizing Electromagnetic Field
Roman Radil, Jan Barabas, Patrik Kamencay
Communications - Scientific Letters of the University of Zilina 2015, 17(11):51-57 | DOI: 10.26552/com.C.2015.1A.51-57
Medical detection techniques used for preoperative scanning of certain marked areas are mostly based on ionizing radiation as it is in case of CT. This paper provides an unusual approach to detection of metal biomarkers implanted into the human body, based on nonionizing radiation and discusses problems and complications connected with chosen technique.
Wireless Telemetry: Channel Characterization and Statistical Imputation of Missing Values
Vasilios Zarikas, Theofilos Chrysikos, Konstantinos E. Anagnostou, Stavros Kotsopoulos, Panagiotis Avlakiotis, Charalambos Liolios, Theodoros Latsos, Georgios Perantzakis, Athanasios Lygdis, Dimitirios Antoniou, Asimakis Lykourgiotis
Communications - Scientific Letters of the University of Zilina 2015, 17(11):58-65 | DOI: 10.26552/com.C.2015.1A.58-65
An implemented communication wireless telemetric system is presented. It has been built to serve as a measuring station at Thermopiles hot springs. The present work analyzes the method applying several models for adjusting and optimizing the functions of the system. The system also includes a unit that receives and stores data in an appropriate form, ready to be used for statistics. Data of critical physicochemical parameters are continuously measured, processed and transmitted over a wireless link. Path loss is investigated in order to ensure reliable signal reception. In the examined case study of low SNR region with the integrated in the open field...
Resonant Frequencies of Small Arterial Segments as Determining Factors For Estimation of Terminal Segments in Electromechanical Arterial Tree Model
Stefan Borik, Ivo Cap, Branko Babusiak
Communications - Scientific Letters of the University of Zilina 2015, 17(11):66-70 | DOI: 10.26552/com.C.2015.1A.66-70
A model of the nonsymmetrical arterial tree was analyzed. The arterial branching model was based on the principle of the electromechanical analogy. The nonsymmetrical arterial tree was divided to 7 arterial generations, starting from larger arteries towards small arteries and arterioles. For each generation the resonant frequency and the transfer function were calculated and there are presented the pressure simulation results for each arterial generation. Terminal segments were determined regarding to calculation of the resonant frequencies and the transfer functions and simulation results.
Evaluation of Power Quality in Off-Grid Power System
Stanislav Misak, Lukas Prokop, Petr Bilik, Petr Krejci
Communications - Scientific Letters of the University of Zilina 2015, 17(11):71-76 | DOI: 10.26552/com.C.2015.1A.71-76
The energy independence, reliability and safety of energy distribution system operation as well as use of renewable resources have been hot research topics in recent years. This research leads to the development of active distribution grids with specific requirements. The Power Quality problems can arise when using renewable sources in active distribution grids. Problems are caused by decreased short-circuit power of local renewable sources, stochastic supply of electric energy from renewable sources and operating the active distribution grid in off-grid regime without connection to the external distribution system. In case of these conditions, the...
Construction Aspects of System for Wireless Low Power Transfer on Moving Parts of Electric Machinery
Vladimir Kindl, Tomas Kavalir, Roman Pechanek
Communications - Scientific Letters of the University of Zilina 2015, 17(11):77-82 | DOI: 10.26552/com.C.2015.1A.77-82
The paper discuses important construction aspects of resonant wireless power transfer (WPT) system for moving parts of electric machinery. It focuses mainly on key electrical parameters of the systems resonant linkage and its simple and durable construction shape. All presented theoretical presumptions are consequently verified by detailed measurement.
Sinusoidal and Relaxation Wide Range Voltage Controlled Oscillators
Milan Stork
Communications - Scientific Letters of the University of Zilina 2015, 17(11):83-88 | DOI: 10.26552/com.C.2015.1A.83-88
This paper presents a sinusoidal Wien-bridge and square wave wide range voltage controlled oscillators. The square wave oscillator is based on relaxation (Schmitt trigger) topology. All described oscillators have potential use in different applications, e.g. phase locked loops, modulation and detection. The frequency changing is based on optically coupled resistor with 100 dB dynamic range. The oscillators were constructed and measured. The new method for amplitude control for quadrature oscillator is also described.
Operational Non-Contact Diagnostics of Induction Machine Based on Stray Electromagnetic Field
Petr Bernat, Petr Kacor
Communications - Scientific Letters of the University of Zilina 2015, 17(11):89-94 | DOI: 10.26552/com.C.2015.1A.89-94
Paper deals with one new method of testing and operational diagnostics of induction machines using a stray electromagnetic field. This leakage field on the surface or on surroundings of machine frame is the carrier for diagnostic information and we can make simultaneous comparisons of utility, advantages and disadvantages of the existing and most common methods of diagnostics performed using the measurement of the machine supply current. This method is patented as Czech Patent CZ 303 470, UPV 2012.
Torque Smoothing of a Fault Tolerant Segmental Stator Switched Reluctance Motor
Lorand Szabo, Mircea Ruba, Daniel Fodorean, Pavol Rafajdus, Peter Dubravka
Communications - Scientific Letters of the University of Zilina 2015, 17(11):95-101 | DOI: 10.26552/com.C.2015.1A.95-101
The relatively high torque ripples are one of the main disadvantages of the switched reluctance motors. By smoothing their torque they can become more competitive for variable speed drives used in automotive and industrial applications. One of the most promising approaches to reduce the torque ripples of a SRM is the use of a direct instantaneous torque controller. In the paper the effectiveness of this type of control will be proved for a fault tolerant segmental stator SRM. By advanced simulation techniques the working principle of the direct instantaneous torque controlled drive system is illustrated, and its performances are demonstrated.
Sine Wave Filters Design for AC Motor Drives with Genetic Algorithms
Mario Cacciato, Giuseppe Scarcella, Giacomo Scelba, Pavol Spanik
Communications - Scientific Letters of the University of Zilina 2015, 17(11):102-109 | DOI: 10.26552/com.C.2015.1A.102-109
This paper proposes a suitable design methodology of the filter used at the output of inverters for AC motor drives. While it allows to achieve the best tradeoff among different design constraints that are difficult to include in standard design methods, such an approach is able to simultaneously consider several technical issues such as losses and voltage drops of the filter, total harmonic distortion of currents and voltages as well as economic aspects. Accordingly, the proposed procedure determines the optimal values of the filter parameters by exploiting simulations of accurate model of the electrical drive and genetic algorithms. Hence, no rough...