Tato disertační práce pojednává o optimalizaci algoritmů pro rekonstrukci obrazu neznámé měrné vodivosti z měřených dat pořízených elektrickou impedanční tomografií. Danou problematiku zde věcně vymezuje několik různých prvků, zejména pak stručný matematický popis dopředné a inverzní úlohy řešené různými přístupy, metodika měření a pořizování dat pro rekonstrukci a přehled dostupných numerických nástrojů. Uvedenou charakteristiku rozšiřuje rozbor optimalizací parametrů modelu ovlivňujících přesnost rekonstrukce, způsoby paralelního zpracování algoritmů a souhrn dostupných zařízení pro měření tomografických dat. Na základě získaných poznatků byla navržena optimalizace parametrů matematického modelu, která umožňuje jeho velmi přesný návrh dle měřených dat. V této souvislosti dochází ke snížení nejistoty rekonstrukce rozložení konduktivity. Pro zefektivnění procesu získávání dat bylo navrženo zařízení k automatizaci tomografie s důrazem na cenovou dostupnost a snížení nejistoty měření. V oblasti tvorby numerického modelu byly dále zkoumány možnosti užití otevřených a uzavřených domén pro různé metody regularizace a hrubost sítě, a to s ohledem na velikost chyby rekonstruované konduktivity a výpočetní náročnost. Součástí práce je také paralelizace subalgoritmů rekonstrukce s využitím vícejádrové grafické karty. Předložené výsledky mají přímý vliv na snížení nejistoty rekonstrukce (optimalizací počáteční hodnoty konduktivity, rozmístění elektrod a tvarové deformace domény, regularizačních metod a typu domén) a urychlení výpočtů paralelizací algoritmů, přičemž výzkum byl podpořen vlastním návrhem jednotky pro automatizaci tomografie.

This master‘s thesis deals with measurement of liquid dielectric materials (insulators). Above all, it is the different kinds of clean and drinking water, but also transformer oils. There was done theoretical information retrieval about the given topic in this project and on the basis of theory there were realized the relevant measurements of selected properties of liquid dielectric, such as permittivity, capacitance, loss number, conductivity, but also temperature dependence of these parameters. The measurements were realized with the help of product manufactured at the faculty FEKT VUT and with the help of measuring system AGILENT 16452A. The measured results were evaluated, graphically processed and compared.

PLC - power line communication is not new. It has been known for many years. But It never be used in massive scale. There were only sporadic applications, for example ripple control system HDO used in the Czechoslovakia. PLC currently experiencing a renaissance thanks to the advent of Smart Grid. PLC offering relatively low bit rates and relatively unreliable transmission, but these disadvantages compensates very low costs to build a communication infrastructure and it offers specific functionalities for Smart Grid. The question is whether the declared parameters will be met in the real world. This thesis tries to find an answer.

The dissertation thesis deals with the analysis of prospective environmentally compatible electrical insulating fluids for electrical engineering in relation to their chemical structure. The thesis starts with the overview of the current state of the art and of the latest trends in the use of synthetic and biodegradable natural oils. In the experimental part were studied these oils: mineral oils, rapeseed oil, sunflower oils, soybean oil, methyl oleate, peanut oil, MCT oil, castor oil and other. Dielectric properties were measured using LRC meter Agilent 4980A including dielectric liquid test fixture Agilent 16452A and also by the Novocontrol Alpha-A analyzer. Electrical properties are presented in the frequency range 10 mHz – 1 MHz range in the temperature interval 253 K to 363 K. The work goes on with the study of the suitability of individual oils for lower temperature, including the impact of the chemical structure and formulation on electrical properties.

My diploma thesis is focused on a comparison of direct-current and high frequency (15-80 kHz) electric discharge, which generates non-thermal plasma in water solution of sodium chloride. Mainly current-voltage and Lissajous charts are discussed in the first part of this thesis. These charts describe different discharge phases: electrolysis, bubble formation, discharge breakdown and discharge regular operation in a pin-hole of a dielectric barrier. Influence of frequency, electrolyte conductivity, thickness of the diaphragm (or length of the capillary) and pin-hole diameter on discharge breakdown and bubble generation was studied, too. Measurements were realized in a polycarbonate reactor with total volume of 110 ml, which was divided by a changeable polyacetal insulating wall. This wall divided the reactor into two approximately equal spaces with one stainless steel planar electrode in each part. The Shapal-MTM ceramic discs (thickness of 0.3–1.5 mm and diameter of the central pin-hole of 0.3-0.9 mm) were mounted in the centre of the insulating wall. Initial conductivity of sodium chloride solution was chosen within the interval of 100900 S/cm. The second part of my thesis compares an influence of the direct-current (DC) and high frequency (HF) power sources on physical solution properties (conductivity, pH and temperature) and generation of hydrogen peroxide. A plasma reactor with total volume of 4 l and with mixing set up was divided into two equal spaces with one planar platinum electrode in each part. Diaphragm with thickness of 0.6 mm and pin-hole diameter of 0.6 mm was installed in the middle of the separating wall. Experiment was held at discharge operation of 45 W for 40 minutes with both power sources. Detection of hydrogen peroxide was realised by using a titanium reagent forming a yellow complex, which was analysed by absorption spectroscopy. If HF discharge power is plotted as a function of applied frequency, exponential decrease of frequency with increasing power can be observed. Higher breakdown voltage is necessary for thicker dielectric barriers, on the other hand for bigger diameter of the pin-hole lower breakdown voltage and higher power is needed in DC as well as in HF regime. Breakdown voltage is decreased by the increasing conductivity in both regimes; due to more charge carriers in the higher conductivity lower breakdown voltage is needed. However frequency in HF regime and DC discharge power increases. HF discharge power is decreased by the increasing conductivity. Solution conductivity and temperature are increased by initial conductivity value in both discharge regimes. Solution pH drops to acidic conditions when HF or DC positive regime is applied due to the generation of reactive species and electrolysis (in DC regime). However solution becomes alkaline when DC negative regime is applied. Concentration of hydrogen peroxide is produced linearly when HF or DC negative regime is applied and it depends on initial solution conductivity.

The exact mechanism of the discharge in liquids ignition is not sufficiently known up to now. Although during the last years was achieved the great progress and overloading which some of them are written in this theoretical part of thesis. This thesis is divided into two experimental parts. When the first part deals with diagnostics of diaphragm discharge in electrolyte solutions and the second part is focused on its use for uncoiling (higher homogenization) of carbon nanotubes in solutions. In experiment 1, three different sized (4 l, 100 ml, 50 ml) diaphragm discharge configurations were used to diagnose diaphragm discharge in electrolyte solutions. Diagnostics is done through current and voltage waveforms with the addition of synchronized ICCD camera images that have been connected to a four-channel oscilloscope. The V-A characteristic can be described by three events occurring in the electrolyte solution with a gradual increase in voltage. Slowly increasing of the voltage in the solution leads first to electrolysis. The next phase is the formation of microbubbles or bubbles, which is characteristic of the curve by a slight decrease in the increase of the current passing between electrodes. The sudden increase in the current flow is characteristic of the last phase, namely the discharge phase. The distance of the electrodes from the diaphragm does not significantly affect the V-A characteristic. The higher diameter of the pin hole, therefore, has a higher voltage, but this does not affect the origin of bubble generation or breakdown. The higher thickness of diaphragm, the higher voltage is needed to the beginning of the bubbles generation, and consequently the discharge breakdown. Comparison of the voltage of the start generation of the bubbles and breakdown for PET diaphragms and diaphragms from the ceramic there was no mark able difference. One of the most important parameters is the conductivity of the electrolyte solution. The lower voltage is needed for the start generation of the bubbles at the higher solution conductivity, and also the discharge generation is observed at a lower breakdown voltage. The second experimental part is focused on the study of the diaphragm discharge effect on carbon nanotubes. A specially designed U-shaped reactor is used to modify carbon nanoparticles. Tap water and aqueous solutions of organic compounds are used as the electrolytic solutions. The discharge is generated by a non-pulsed DC high source with a voltage in the range of 0-2.8 kV supplied to platinum electrodes located in the electrolyte solution. The experimental results have shown that the diaphragm discharge has positive effects on the disintegration of clusters and agglomerates of carbon nanotubes. The primary effect on disintegration is probably the shock waves generated by the discharge. It turned out that it depends on the electrode configuration, where the treatment in anode space has far greater effects than the treatment in cathode half of the reactor. Effects of carbon nanotubes disintegration in solution are long-lasting and the treatment effect is not loosed after several months. There were detected no significant changes in the structure of plasma-treated nanotubes by Infra-red spectroscopy.