Lubomir Ivanek

Patch antenna optimization in COMSOL multiphysics

This paper deals with the different kinds of optimization. Especially, it uses COMSOL Multiphysics software and its subsequent utilization at the patch antenna. The article deals with optimization of basic dimensions the patch antenna depending on the parameter S11 and the field strength at a defined point. This feature is very important, because it helps determine whether the antenna is properly built or modelled. From this reason, it helps save time and resources of development teams.

Distribution of the Density of Current in the Base of Railway Traction Line Posts

This paper deals with modelling stray currents in the concrete base of traction line post in one of the most frequent defects - short-circuit of the surge arrester. If these defects occur more frequently, the concrete may be degraded and the post base firmness may deteriorate. The results of the modelling will be subjected to further processing by Construction Material Laboratories at VSB - Technical University in Ostrava.

Remote earth in the electrified railway traction

This paper describes principles and methods for determining the remote earth (remote ground) of traction systems used in electrified railway traction. Remote earth is determined for the purposes of measuring transition resistance between the rails and remote earth. Transition resistance is needed to calculate the distribution of the current between the rail and the ground. There are presented results of modeling voltage drop at various ratios of conductivity of rail top and soil.

Examination of current fields in the vicinity of railway L - type platform

This paper deals with the examination of current fields in the vicinity of railway L - type platform. We consider for comparison the case with iron fittings in concrete foundations and the case without iron fittings. To answer this we use program Comsol Multiphysics, which solves partial differential equations using finite element methods.

Structure and properties of polyaniline/montmorillonite nanocomposites prepared under various conditions

Abstract Three different methods have been used for the preparation of polyaniline/montmorillonite nanocomposites: (i) two-step process: first intercalation of anilinium into Ca–montmorillonite structure followed with oxidisation; (ii) two-step process: first oxidisation with subsequent addition of Ca–montmorillonite aqueous suspension; (iii) one-step process: oxidisation and polymerisation in the presence of Ca–montmorillonite aqueous suspension. Structure and properties of samples have been investigated using combination of X-ray powder diffraction, Fourier transform infrared and Raman spectroscopy, elemental analysis and conductivity measurements in order to find the relationship between technology, structure and electrical properties. Results confirmed the crucial effect of the preparative procedure on polyaniline/montmorillonite composites.

Track occupancy detection using ratio of open-circuit impedance to short-circuit impedance

This paper deals with the change of the ratio of the open circuit impedance to short-circuit impedance of the electric traction depending on the distance of the traction vehicle from the beginning of the section. This ratio is calculated in order to estimate the traction vehicle speed and the distance at which the track occupancy can be indicated. Therefore, the impedance moduli and the impedance phases of the open track circuit and the impedance of the occupied track (short-circuit impedance) is compared at different short-circuit distances. The impedances ratio varies with changing weather conditions. It is different in dry weather than in the rain. Therefore, in practical use, the track occupancy indicator must always be updated and the ratio must always be recalculated for the new situation. In this paper, the impedances ratio is calculated for specific parameters measured in the section of the track in Orlova. The distance between a reference point (place of short circuit rails) from a measuring point is for the impedance module ratio of F = 10 about 218 m.

Estimating of traction capacity in track circuits using computer modelling

This paper deals with estimates of capacity between rails of the traction tracks. The determination of capacity was performed using software for numerical processing of electromagnetic fields: QField, COMSOL, together with the ATP program. The model comprised a traction section with the track clearance of 10 cm above the ground. The result then provides the estimate of capacity changes between rails together with changes in frequency, ground clearance, earth conductivity etc.

Propagation measurements and estimation of channel propagation models in urban environment

Wireless communication is a telecommunication technology, which enables wireless transmission between the portable devices to provide wireless access in all types of environments. In this research, the measurements and various empirical models are analysed and compared in order to find out a suitable propagation model to provide guidelines for cell planning of wireless communication systems. The measured data was taken in urban region with low vegetation and some trees at 900 MHz frequency band. Path loss models are useful planning tools, which permit the designers of cellular communication to obtain optimal levels for the base station deployment and meeting the expected service level requirements. Outcomes show that these empirical models tend to overestimate the propagation loss. As one of the key outputs, it was observed that the calculations of Weissberger model fit with the measured data in urban environment.

The Sensitivity of the Input Impedance Parameters of Track Circuits to Changes in the Parameters of the Track

This paper deals with the sensitivity of the input impedance of an open track circuit in the event that the parameters of the track are changed. Weather conditions and the state of pollution are the most common reasons for parameter changes. The results were obtained from the measured values of the parameters R (resistance), G (conductance), L (inductance), and C (capacitance) of a rail superstructure depending on the frequency. Measurements were performed on a railway siding in Orlova. The results are used to design a predictor of occupancy of a track section. In particular, we were interested in the frequencies of 75 and 275 Hz for this purpose. Many parameter values of track substructures have already been solved in different works in literature. At first, we had planned to use the parameter values from these sources when we designed the predictor. Deviations between them, however, are large and often differ by three orders of magnitude (see Tab.8). From this perspective, this article presents data that have been updated using modern measurement devices and computer technology. And above all, it shows a transmission (cascade) matrix used to determine the parameters.

Coupling of finite and boundary elements for transient eddy current problems

A symmetric coupling of methods of finite and boundary elements for numerical solution of transient eddy current problems is described. This is an essential step in modelling of electromagnetic forming of metalic sheets. The finite element method is employed in the conducting region of the metalic sheet. The boundary element method relies on the Stratton-Chu representation formula and it models the electromagnetic field in the air including its decay at infinity. We impose external currents by the Biot-Savart law.