Ústav teoretické a experimentální elektrotechniky

Browse

Now showing 1 - 5 of 49

Modification of Insulating Properties of Surfaces of Dielectric High-Voltage Devices Using Plasma
(MDPI, 2024-05-22) Pernica, Roman; Klíma, Miloš; Londák, Pavel; Fiala, Pavel
Plasma discharges under atmospheric pressure are applicable for modifying the electrical properties of dielectric surfaces. The aim of the plasma discharge treatment of such surfaces is to design a procedure so that its characteristic parameters improve the resulting levels of the breakdown electrical strength Eb when tested under pulsed or alternating electrical voltages. In this research, a set of functional experiments performed by using plasma in samples of two types of materials (thermoset, thermoplastic) were processed and evaluated, and the resulting effect of the magnitude of the breakdown electrical voltage, electrical intensity, and electrical conductivity of the surface were compared. A slit plasma chamber, previously described and parameterized, was employed to treat the surface of the dielectric samples. The surface structure was modified via plasma discharge without precursors, and methodologies were developed to evaluate these modifications with respect to the change in the electrical strength parameters of the insulator surface. Subsequently, the surface strength of the affected and unaffected samples was measured and evaluated as a function of exposure time, and the stability of the modification was assessed. The first methodical test showed that plasma discharge without precursors improved the long-term surface electrical strength of the dielectric surface. The test and its parameters were carried out with respect to feasibility in an industrial environment.
Electric field and higher harmonics of RF plasma slit jet measured by antennas and VI probes
(IOP Publishing, 2024-05-29) Polášková, Kateřina; Drexler, Petr; Klíma, Miloš; Macháč, Jan; Nečas, David; Švanda, Milan; Zajíčková, Lenka
The cold atmospheric plasma jets change their character when interacting with the different surfaces. Since such interaction is the primary area of plasma jet applications, it is essential to monitor the process. The non-linearity of the RF plasma slit jet (PSJ) was analyzed using the VI probes and a novel method, the non-intrusive antenna measurements. Regardless of the experimental setup and gas mixture (Ar, Ar/O2, Ar/N2), the PSJ frequency spectrum consisted of the following main features: dominant fundamental frequency peak, relatively strong odd harmonics, and significantly weaker even harmonics. The lowest degree of non-linearity was recorded for the Ar PSJ ignited against a grounded target. Admixing a molecular gas increased the discharge non-linearity. It was attributed to the enhancement of secondary electron emission from the dielectric surfaces. In addition to the non-linearity analysis, the antenna spectra were for the first time used to determine the semi-quantitative values of the PSJ-radiated electric field. The electric fields decreased by a factor of 2 after the admixing of nitrogen and oxygen molecular gases. Out of the studied targets, the highest electric fields were observed when plasma impinged on the grounded targets, followed by the floating target (2x lower) and the PSJ ignited in the open space configuration (4x lower than in the grounded target configuration).
Effect of high voltage on the development of the plant tissue
(Electrotechnical Institute, 2015-05-14) Vlachová Hutová, Eliška; Marcoň, Petr; Bartušek, Karel
In our experiment the electrical parameters that affect early somatic embryos (ESEs) were investigated. High voltage was generated by a special high voltage generator. High voltages ranging from 5 to 20 kV and frequency of 1Hz were applied longitudinal and transversal directly on the Petri dish with 2 days old ESEs of Picea abies for periods of 3 hours every day. One Petri dish was placed directly on top of the high voltage generator and on the other petri dish were fixed two copper plates for transmission of high voltage. Petri dishes were exposed to high voltage for 14 days. After this time, the influence of high voltage was evaluated.
Classification of brain lesions using a machine learning approach with cross-sectional ADC value dynamics
(Springer Nature, 2023-07-15) Solár, Peter; Valeková, Hana; Marcoň, Petr; Mikulka, Jan; Barák, Martin; Hendrych, Michal; Stránský, Matyáš; Novotná, Kateřina; Kostial, Martin; Holíková, Klára; Brychta, Jindřich; Jančálek, Radim
Diffusion-weighted imaging (DWI) and its numerical expression via apparent diffusion coefficient (ADC) values are commonly utilized in non-invasive assessment of various brain pathologies. Although numerous studies have confirmed that ADC values could be pathognomic for various ring-enhancing lesions (RELs), their true potential is yet to be exploited in full. The article was designed to introduce an image analysis method allowing REL recognition independently of either absolute ADC values or specifically defined regions of interest within the evaluated image. For this purpose, the line of interest (LOI) was marked on each ADC map to cross all of the RELs’ compartments. Using a machine learning approach, we analyzed the LOI between two representatives of the RELs, namely, brain abscess and glioblastoma (GBM). The diagnostic ability of the selected parameters as predictors for the machine learning algorithms was assessed using two models, the k-NN model and the SVM model with a Gaussian kernel. With the k-NN machine learning method, 80% of the abscesses and 100% of the GBM were classified correctly at high accuracy. Similar results were obtained via the SVM method. The proposed assessment of the LOI offers a new approach for evaluating ADC maps obtained from different RELs and contributing to the standardization of the ADC map assessment.
Comparing efficiencies of polypropylene treatment by atmospheric pressure plasma jets
(WILEY-V C H VERLAG GMBH, 2023-07-11) Polášková, Kateřina; Ozkan, Alp; Klíma, Miloš; Jeníková, Zdeňka; Buddhadasa, Madhuwanthi; Reniers, François; Zajíčková, Lenka
Plasma treatment of polypropylene (PP) is a well-established method of improving its surface properties. However, the efficiencies of different plasma discharges are seldom compared. Herein, we discuss the differences in PP treated by three arc-based commercial plasma jets working in dry air, Plasmatreat rotating plasma jet (PT-RPJ), AFS PlasmaJet & REG; (AFS-PJ), and SurfaceTreat gliding arc jet (ST-GA), and by the low-temperature RF plasma slit jet (RF-PSJ) working in argon. The AFS-PJ has a significantly different reactive species composition dominated by nitrogen oxides. It induced higher thermal loads leading to surface damage. The other arc-based jets (PT-RPJ and ST-GA) created the PP surface with higher oxygen and nitrogen concentration than the low-temperature RF-PSJ. It induced a higher adhesion strength measured on PP-aluminum joints.

Browse

Recent Submissions