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Charge Transport and Storage in a Supercapacitor Structure
Kuparowitz, Tomáš ; Zedníček, Tomáš (referee) ; Hájek, Karel (referee) ; Sedlák, Petr (advisor)
Práce se zabývá studiem superkondenzátorů (SC). Výstupem je detailní studie principů přenosu náboje ve struktuře SC, ukládání energie a nový náhradní model SC, který je založen na fyzikálních zákonitostech a principech SC. Dále byl vytvořen matematický model SC, který popisuje chování náboje v jeho aktivní vrstvě. SC byly testovány metodami umělého stárnutí. Závislosti poklesu parametrů SC vlivem různých metodik stárnutí jsou v práci shrnuty.
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Synthesis of Modern Structures of Frequency Filters
Friedl, Martin ; Hájek, Karel (referee) ; Brančík, Lubomír (referee) ; Sedláček, Jiří (advisor)
Within modern frequency structures, the filter frequency region of up to 10 MHz constitutes a promising research topic that currently attracts intensive attention of specialists interested in the problem. The main reason of this fact consists in that the rapid development of modern technology allows the production of innovated structures of the analog frequency filters required in the defined band. In this context, however, it is also necessary to refine the methods applied in the synthesis and optimization of these structures; such improvement should be carried out with respect to fundamental properties and usability of today's active elements (operational amplifiers with voltage feedback whose Gain Bandwidth Product ranges within units of GHz, operational amplifiers with current feedback, conveyors, transimpedance operational amplifiers). In this thesis, active blocks of synthesis inductors (SIs) and frequency dependent negative resistors (FDNRs) are examined in detail, and the author provides novel formulas to define the basic parameters of the dual circuits. Due emphasis was placed on optimizing the basic building blocks of the second order and defining the variation of their properties caused by the addition of modern active elements. The blocks were analyzed and modified in view of their possible use in higher-order circuits. For active filters of a higher order, simulations were performed to indicate the actual sensitivity of the cascade and non-cascade ARC structures. The following phase of the research comprised mainly the designing of several filters, and this activity was further completed with the verification of the methodology for the synthesis and optimization of higher-order loss ladder filters with modern active blocks. Special attention was paid also to the methods enabling the optimization of such filters, which are invariably based on RLC prototypes. In order to verify the theoretical conclusions, the author materialized a large number of sample optimized filters and measured their parameters. The closing section of the thesis describes the use of the filters in specific applications.
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A Method to Supress Interferences in Wigner-Ville Distribution
Pikula, Stanislav ; Pazdera, Luboš (referee) ; Hájek, Karel (referee) ; Beneš, Petr (advisor)
The doctoral thesis focuses on signal representation in the time-frequency domain with constant resolution. In theoretical introduction the possibilities of displaying a signal in time and frequency are summarized. Attention is concentrated on comparison of short-time Fourier Transform (STFT) and Wigner-Ville Distribution (WVD). The latter achieves a significantly better resolution, especially for a linearly modulated signal. The disadvantage of WVD, which is the presence of interferences resulting from the calculation of the instantaneous autocorrelation function, is described in detail. These interferences are due to the presence of multiple components in the signal or its non-linear modulation. Subsequently, several methods are discussed, which can suppress these interferences, but at the cost of resolution loss. One of the interference suppression methods is smoothed pseudo Wigner-Ville distribution. It is further used in this thesis for the analysis of interference suppression when various filtrations in the time-frequency plane are applied. Several signals with multiple components or various non-linear modulations are used. Based on the analysis, a method using a set of variously smoothed pseudo Wigner-Ville distributions is designed to estimate the time-frequency representation with high resolution and minimal interferences. To compare the results to other methods, the quantitative metrics used in the literature are compared. To select the appropriate one a new metric is suggested. It is applicable to simulated signals and uses mean square error. Based on the comparison, the Stankovi\'{c} measure is selected as the most appropriate for comparing results. The selected metric is used to determine the appropriate minimal number of differently smoothed pseudo Wigner-Ville distributions. Using the selected metric, the proposed method is compared with other methods. These are STFT with optimized window length, S-method with optimized parameter and optimization method using radial Gaussian kernel (RGK). These methods are compared based on the set of signals previously used for interference suppression analysis. In addition, noises are added to the signals. Finally, the methods are also compared based on the real bat echo signal. In conclusion, the proposed method outperforms the compared methods in suppressing interference and resolution.
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Development of a New Generation of Devices with Advanced Diagnostics for Determining Contact Degradation
Dvořáček, Jiří ; Hájek, Karel (referee) ; Náhlík, Luboš (referee) ; Pazdera, Luboš (referee) ; Mazal, Pavel (advisor)
The thesis proposes a methodology for damage identification of thrust bearings using acoustic emission method. The work is the way of the hydraulic loading of specimens and thrust bearings with programmable settings severity and duration of load cycles during contact fatigue tests at stations Axmat. They are designed structural adjustment elements (waveguides) to capture the acoustic emission signal selected apparatus, including the modification of software to capture the data. At the described experiments is verified functionality of the circular test specimens and axial bearings . Part of this work is to propose a new methodology for identifying early stages of contact fatigue using a combination of diagnostic methods.
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Electrical installation of family house - implementing documentation
Hájek, Karel ; Morávek, Jan (referee) ; Mastný, Petr (advisor)
Main goals of this bechelor´s thesis are devided into three parts. First part introduces reader with power and data instalations issues including legislation necessary for project creation in electrickal engineering, object connection to distribution network, basic electric wiring including circuit breakers and electric wiring design in residential buildings, which mainly speaks about ways of installation of electric wiring and elektrical zones. In addition internal and external lighting protection and basic information about switchgear. Second part defines of project documentation creation, both design and text part. The last part is the practical part that looks into complete electrical installation of family house project, which contains marking both low-power and high-power circuits into plan view, house switchgear and electro meter scheme, LPS design and technical report with economical evaluation.
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Primary Calibration of Acoustic Emission Sensors
Keprt, Jiří ; Mazal, Pavel (referee) ; Hájek, Karel (referee) ; Beneš, Petr (advisor)
The aim of the doctoral thesis is the problem of the primary calibration of acoustic emission sensor. In the introductory chapters, there are the results from the study of literature in field of AE and primary calibration of AE sensor summarized. The practical part of the thesis is aimed on realization of the primary calibration of AE sensors by different methods. The standardized methods of step function calibration and reciprocity calibration were practically realized as a part of the research on the same aparature. The method of reciprocity calibration with wideband excitation was practically realized too. The comparison between results from each used method was realized and the influences of the different sources of uncertainty and the different configuration of the calibration aparature on the step function calibration and the reciprocity calibration were determined. The uncertainties were determined for each realized methods. The recommendations for the calibration by the different methods on the available calibration aparature were presented. All the proceses of the reciprocity primary calibration was automated by the programmed software and the channel switcher. The UT 1000 (s.n. 169) by Physical Acoustic Corporation was used as the calibrated sensor for the comparison of the results of the calibrations.
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Adaptive frequency filter
Kříž, Petr ; Hájek, Karel (referee) ; Sedláček, Jiří (advisor)
The aim of this work is to design a filter of the type low–pass of order 5th with Butterworth’s approximation in the range of over-tuning 10 – 100 kHz and if it will be possible so! achieve even higher marginal frequencies. To compare two typical representatives of the frequency filters cascading and non-cascading synthesis from the viewpoint the accuracy of an! approximation function, sensitivity to the tolerance values of components, number of the components (mainly OZ) and viability, especially the possibility of electronic over-tuning in selected frequency range. On the basis of these conditions will be chosen one design, which will be realized later. Further it will be necessary to consider the possibilities of electronic over-tuning and to choose for this over-tuning suitable component, to design user management changes of marginal frequency fm by the help of keyboard + LCD and control application on the PC. For this hardware will be programmed appropriate control software. At the end of this work will be constructed appropriate device, which fullfils requirements written above and will be subjected to the laboratory measurements that verify function of this device. The constructional details of the filter are presented in the enclosure at the end of this work. At the CD are available all materials, which were created during the master’s thesis or which are necessarily concerned.
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Eddy Current Probe Design and its Application on Aircraft Composite Structures
Boháčová, Marie ; Hájek, Karel (referee) ; Kopec, Bernard (referee) ; Mazal, Pavel (advisor)
This thesis deals with design of an eddy current transducer which enables non-destructive inspection of composite aircraft structures primarily carbon fiber reinforced plastic (CFRP) in areas of manufacture and maintenance. The design of the transducer is based on analytical-experimental approach and its electrical and mechanical parameters were optimized to ensure a good signal to noise ratio at the six composite samples. These samples contain artificial discontinuities in the form of various types of defects. These defects are simulating the various types of damage created in the aircraft structure, especially delamination or thickness changes of composite materials. The experimental measurements, data collection and non-destructive evaluation were performed during the period. The result of this work is functional eddy current probe, which is reliably able to detect some damage of the carbon composite structures to the depth of 3,9 mm.
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A Contribution to Optimal Synthesis of Filters
Szabó, Zoltán ; Hájek, Karel (referee) ; Král, Bohumil (referee) ; Sedláček, Jiří (advisor)
The presented dissertation thesis is focused on the optimization of filtering circuit synthesis. In the five main sections of this work, the author analyzes partial problems related to several areas within the synthesis of modern filtering circuits. The first chapter constitutes an examination of elementary aspects which characterize present-day integrated circuits in voltage feedback operational amplifiers, and this main content is further complemented with a view on possible application of these circuits for the designing of filtering circuits as proposed within subsequent parts of the thesis. In this context, the second chapter contains a description of the design and optimization of digitally controlled universal filters tunable by means of digital potentiometers originally produced for audio technology. These digitally controlled circuits are increasingly utilized as analog preprocessing blocks in digital signal processing systems. The most extensive portion of the dissertation is dedicated to a complex analysis of individual configurations of economical, purposely lossy active function blocks and modern voltage operational amplifiers. This part of the thesis aims at providing a detailed insight into the characteristics of individual configurations of examined circuits; furthermore, in this respect, the author proposes a comparison of various application possibilities relating to these circuits and their wider use in the field of active frequency filters optimization. The described section of the work also includes a definition and examples of application of the designed and realized program, which facilitates significant simplification of purposely lossy ARC filters. In the penultimate part of the dissertation thesis, the design, development, and verification of a suitable synthesis procedure are presented together with the optimization of data and (in particular) power models of EMC filters. Based on the verification of characteristics inherent with the designed models of EMC filters, the suggested measuring procedure related to these filters is described, including the design of a station for measuring elementary parameters of line anti-interference devices up to very high frequencies. In the last section of the thesis, the author discusses the procedure of air ions concentration measurement through an aspiration condenser and analyzes the systematic and random errors as well as the optimization of filtration characteristics of the applied measurement method. This part includes the description of the design and characteristics of the realized fully automated measurement system with an aspiration condenser.
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Microplasma Noise as a Diagnostic Tool for PN Junctions of High-Voltage Rectifier Diodes
Raška, Michal ; Chobola, Zdeněk (referee) ; Hájek, Karel (referee) ; Koktavý, Pavel (advisor)
The doctoral thesis deals with diagnostics of local defects in PN junctions and brings new information about microplasma noise behaviour and its usage for the temperature changes detection inside PN junctions. Defects in PN junctions are the source of microplasma noise. There were deviations observed in microplasma noise from the common known rectangle shape pulses during the measurements. These deviations were correlated with the temperature change directly in the defect area and in the defect area surroundings. Generation and recombination coefficients are commonly thought to be constant. However, these coefficients were observed to be not stable with time and this effect is explained in this work. The doctoral thesis then focuses on the PN junction parameters determination in the case when it is not possible to define unambiguously whether it is abrupt or linearly graded PN junction. The most significant parameters which are to be determined are barrier capacity, diffusion voltage and depleted area width in dependence on the voltage. The correlation between local avalanche discharge in PN junction and negative differential resistance appearance on VA characteristics of reverse-biased diode was qualitatively verified. The last important point in the work is computer modelling of temperature behaviour in the defect area and its surroundings during local avalanche breakdown. Thus the method of real diodes heating area parameters determination was introduced.
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