National Repository of Grey Literature 174 records found  1 - 10nextend  jump to record: Search took 0.02 seconds. 
Numerical Modeling of Periodical Structures
Nešpor, Dušan ; Bartušek, Karel (referee) ; Brančík, Lubomír (referee) ; Fiala, Pavel (advisor)
The thesis discusses the dynamic electromagnetic field on periodic structures. The author focuses on three principal types of resonant structures, considering their application possibilities. In general, these types can be individually defined as follows: materials exhibiting a negative refractive index of the incident electromagnetic wave; structures with gradual changes in impedance, characterised by their usability as reflectionless surfaces; and periodic structures able to conveniently shape the magnetic field distribution. Materials of the third group within the above-shown short list facilitate the fabrication of magnetoinductive lenses for nuclear magnetic resonance. The presented analysis of the properties of periodic resonant structures is mainly based on numerical models utilising the finite element method, and this approach is combined with both the derivation of the corresponding analytical relations and an experimental measurement of the non-radiating component of the electromagnetic field. The thesis includes a physical description of the basic elements of periodic resonant structures. Physical properties of the elements were examined in detail via numerical analysis. In the course of the research, the data acquired through this analysis and the related experimental measurement enabled the author to propose a method for optimising the most widely used resonant structures. Moreover, several new versions of resonant elements, structures, and fabrication techniques were also designed. The results obtained from the numerical analyses carried out to examine the central physical properties of the fabricated structure samples were all verified via the designed method for measuring the non-radiating component of the magnetic field.
Optimizing Image Reconstruction in Electrical Impedance Tomography
Dušek, Jan ; Brančík, Lubomír (referee) ; Sikora, inž Jan (referee) ; Mikulka, Jan (advisor)
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.
Audio pre-amplifier for two satellites and subwoofer
Štaud, Stanislav ; Brančík, Lubomír (referee) ; Kratochvíl, Tomáš (advisor)
The aim of this thesis was to design, simulate and construction audio pre-amplifier for two satellites and subwoofer and monolithic amplifier for subwoofer in the class AB. Audio pre-amplifier provides bass, treble and switch loudness volume control. It includes subsonic filter and active crossovers Sallen-Key with approximation Linkwitz-Riley. There are low noise operating amplifiers LM833 and TL081 at the place of active amplifiers with very low distortion. End-amplifier can delivers power 50 W to 4 ohms. Of consists delayed switch speaker and supports security against direct voltage on the output of amplifier.
Optimization of Basic Magnetic Field Homogeneity in MR Tomography
Hadinec, Michal ; Brančík, Lubomír (referee) ; Frollo, Ivan (referee) ; Bartušek, Karel (advisor)
This thesis is concerned with problems of measuring and mapping of magnetic field in MR tomograph, for purpose of magnetic flux density homogeneity optimization. Attention is paid to mapping techniques on rotary symmetric volume and to ways of magnetic fields optimization with utilization of passive and active correction systems. Theoretical analysis of magnetic field decomposition with utilization of spherical harmonics and numerical decomposition is made. Mapping and approximation techniques of basic magnetic field are verified by experiments in the laboratory at the Institute of Scientific Instruments AS CR in Brno.
Design of switching low-frequency power amplifier
Janáč, Josef ; Kratochvíl, Tomáš (referee) ; Brančík, Lubomír (advisor)
This bachelor project maps out switching technologies used in LF power electronics and gained information was consequentially used to design switching lf power amplifier as independent unit. Content of design is LF power amplified level, working on switching technology principle. Correction pre-amplifier with possibility of adjusting volume, balance h/l frequency and switching power supply is content as well too. Next part of project is familiarization s design program Eagle and optimizing program for switching power supply PXLS expert and creating constrictive basis for complete device. Last part of project is basically activation all functional part of device in one unit. Than measurement basic parameters on created functional device, graphical elaborating measurement-gained values and confrontation with catalog values. Conclusion of this project is evaluation achieved results in compare with supposed result of project.
Design of class AB stereo audio power amplifier
Podr, Michal ; Šotner, Roman (referee) ; Brančík, Lubomír (advisor)
This thesis describes the design of a complete amplifier operating in class AB. It contain two power amplifiers with working in the bridge mode correction amplifier with volume control, bass, treble, and also with the choice of loudness. Preamplifier with three different inputs and the choice between stereo and mono modes.
Class AB audio amplifier for two satellites and subwoofer
Cupák, Jan ; Brančík, Lubomír (referee) ; Kratochvíl, Tomáš (advisor)
This bachelor’s thesis deals with design of AB class audio amplifiers. Further more it deals also with other functional blocks, e.g. preamplifier, tone equalizer and active crossover. Outcome of this work is a complete solution of the amplifier with it's simulation. In final solution is also included scheme of a high quality power supply unit, speaker protection and heat sinks for high performance transistors. In this project is also included a solution of task about optimal mechanical arrangement of the single parts in the case of this amplifier. This thesis contains results of measurement and photo document of functional prototype.
Model of four-quadrant analog multiplier AD835 for PSpice
Kuřátko, David ; Brančík, Lubomír (referee) ; Šotner, Roman (advisor)
This bachelor's thesis deals with the analog behavioral modeling of the AD835 multiplier and its simple applications in PSpice. The first part of this thesis is focused to the theoretical analysis of analog multiplier in general. This is followed by an analysis of individual elements, which are suitable for modeling of this multiplier AD835 and possibility of substitution by other elements. The next part deals with the description of the multiplier AD835, an analysis of the proposed model and confirmation of several parameters with measurement. Finally, there was noted several applications with analog multiplier AD835. Simulation results of these applications are compared with ideal expectations.
Design of class-D audio power amplifier
Fiala, Roman ; Götthans, Tomáš (referee) ; Brančík, Lubomír (advisor)
This semestral thesis describes class D low frequency power amplifiers and design of specific 2x100W class D power amplifier. The designed amplifier contains a second order sigma-delta modulator in which the quantization is controlled only by the delay of modulator components. This design does not include the clock generator which usually controls the quantization in sigma-delta modulators. This semestral thesis also includes design of a switched-mode power supply for the power amplifier and for the preamplifier. The PSpice program has been used for the design and verification of some sections of circuits. All designs have been built. Also basic parameters of completed circuits were measured.
Design of stabilized dual power supply
Svoboda, Tomáš ; Kubíček, Michal (referee) ; Brančík, Lubomír (advisor)
This bachelor’s thesis is focused on design and construction of stabilized dual power supply with adjustable output voltage in range 0 – 30 V and adjustable current limit in range 0 – 3 A. Power supply consists of line transformer, switching regulator and subsequent application of linear regulator for better output properties. Measurement of output voltage and current is realized by microcontroller ATmega644, which has optical separated inputs. In this thesis the device is designed and simulated. The design is verified by prototype device and then full construction is done. Construction is tested by measurements, which confirm a proper design.

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