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Pyroelectric effect in technical applications
Motlová, Tereza ; Tofel, Pavel (referee) ; Hadaš, Zdeněk (advisor)
The focus of this bachelor thesis is pyroelectric effect and its use for energy harvesting. Mathematical model of pyroelectric harvester was described, and then recreated in MATLAB-based graphical programming environment Simulink. Various applications of pyroelectric materials were researched, and their use as sources of electricity was evaluated.
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Analysis of passive and semi-active damping of cantilever oscillation
Václavík, Tomáš ; Tofel, Pavel (referee) ; Hadaš, Zdeněk (advisor)
In this thesis passive and semi-active damping methods on a model of cantilever beam with piezoelectric patch are analyzed. Explanation of piezoelectric effect, classification of damping methods used for vibration control, description of their properties, their benefits and disadvantages, and lastly the challanges of their implementation is presented. Models of specified methods are carried out in MATLAB Simulink and the results are compared. Basic concept of electrical design of circuits for semi-active damping by SDDNC and SSD methods is introduced.
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Flexible generators of electrical energy
Tesařová, Tereza ; Holcman, Vladimír (referee) ; Tofel, Pavel (advisor)
This bachelor thesis is focused on actual research part of energy harvesting technologies – flexible electrical generators, which mean the special generating of electricity using specific flexible materials. The net charge result is affected by the incidental mechanism to transform certain energy form into electrical power and is influenced of material range, which determines what will be harnessed as a source of energy. The energy harvesting is aiming at producing alternative and efficient ways instead of harmful and strained manufacture processing.
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Development of PVDF nanofibers sensor
Klásek, Matyáš ; Tofel, Pavel (referee) ; Hadaš, Zdeněk (advisor)
This diploma thesis deals with the feasibility of using PVDF nanofibers as an active sensor layer generating electrical signal. PVDF and related electromechanical effects are described. A research study is conducted regarding existing PVDF nanofiber applications and based on it, an event sensor design utilizing triboelectric effect and electrostatic induction is proposed. The electrical response of the layers is experimentally investigated and a pulse detection algorithm is conceived and implemented. Finally, a way of integrating the sensor into a rail track is proposed.
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Electrical characterization of flexible nanofiber piezoelectric materials
Pokorná, Romana ; Holcman, Vladimír (referee) ; Tofel, Pavel (advisor)
This bacherol thesis is focused on piezoelectric nanofibrous materials. The first part describes the formation, use and possible aplications of nanofibers. It further analyze the principle of piezoelectric effect. It is a conversion of mechanical energy into electric energy and conversely. The second part is focused on design of experimental workplace for measurement of functional material properties. The last section of the thesis is dedicated to the electrical characterization of PVDF nanofibers and to the measurement of the piezoelectric charge constant.
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Characterization of lead-free piezoelectric ceramics
Šťastná, Magdaléna ; Holcman, Vladimír (referee) ; Tofel, Pavel (advisor)
This project is focused on lead-free piezoelectric ceramics which are meda in CEITEC. Behaviour of these ceramics is quite different from the lead one. The first part is dedicated to dielectrics and its polarisation techniques. These techniques also include the piezoelectric effect which occurs only in crystals without central symmetry. The following part is focused on piezoelectric materials, piezoelectric polymers and piezoelectric ceramics respectively. The next section of the project is dedicated to the design of an experimental workplace for direct measurement of the piezoelectric charge coefficient đť‘‘33. The experimental part of the work is focused on electric characterisation of lead-free piezoceramics.
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Preparation and optimization of piezoelectric materials based on BCZT for energy harvesting
Fojtík, Ondřej ; Holcman,, Vladimír (referee) ; Tofel, Pavel (advisor)
This thesis deals with fabrication and optimization of lead-free piezoceramics based on (Ba0,85Ca0,15Zr0,1Ti0,9)O3 (BCZT). The BCZT precursor powder was synthesized by sol-gel method. Dependence of relative density, microstructure, phase structure and piezoelectric properties on the sintering temperature in a range from 1300–1500 °C was studied on disc shaped samples, which were prepared by cold isostatic pressing (CIP) using pressure of 700 MPa. It was found, that sintering at 1300 and 1350 °C leads to ceramics with fine-grain microstructure, which exhibits poor piezoelectric properties (d*33 = 50 pC·N1 and 65 pC·N1, respectively). The highest value of piezoelectric charge coefficient was obtained by sintering at 1500 °C (d*33 = 390 pC·N1). Furthermore, BCZT thick films were prepared by tape casting. The composition of the ceramic slurry was optimized and various sintering techniques were tested to obtain completely flat films of BCZT ceramics. The correct sintering configuration has not been found. The least deformation of the films was achieved when the samples were sintered hung on the ZrO2 rod. The highest value of d*33 for BCZT films was measured when the sample was sintered at 1400 °C with the dwell time for 4 h (d*33 = 340 pC·N1).
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Non-Linear Electro-Ultrasonic Spectroscopy of Resistive Materials
Tofel, Pavel ; Koktavý, Bohumil (referee) ; Smulko, Janusz (referee) ; Šikula, Josef (advisor)
Elektro-ultrazvuková spektroskopie je založena na interakci dvou signálů, elektrického střídavého signálu s frekvencí fE a ultrazvukového signálu s frekvencí fU. Ultrazvukový signál mění vzdálenost mezi vodivými zrny ve vzorku a tím mění jeho celkový elektrický odpor R. Změna odporu R je proměnná s frekvencí ultrazvukového signálu fU. Vzorek, který obsahuje mnoho defektů ve své struktuře, vykazuje vysokou změnu odporu R v porovnání se vzorkem bez defektů při stejné hodnotě ultrazvukového a elektrického signálu. V disertační práci je popsána elektro-ultrazvuková metoda na tlustovrstvých rezistorech, hořčíkových slitinách, monokrystalech Si a CdTe, varistorech a také jeden z prvních pokusů aplikace elektro-ultrazvukové spektroskopie na horninové vzorky a tak diagnostikovat jejich stav poškození. V našem případě byl proměřen vzorek žuly. Jelikož se jedná o nedestruktivní metodu testování, tak má tato metoda velmi perspektivní budoucnost. Tato metoda je citlivá na všechny defekty ve vzorku. Její výhodou je, že se měří velikost signálu ne frekvenci danou rozdílem nebo součtem budících frekvencí fE a fU a tím se dá dosáhnout vysoké citlivosti. V mém případě byl vždy měřen signál na rozdílové frekvenci fi = fE-fU.
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Principle of Argument Increment For Searching Polynomial Roots
Tošer, Pavel ; Tofel, Pavel (referee) ; Sadovský, Petr (advisor)
Several methods exist for searching multinominal roots. Methods in more cases are used only for special solves. The goal of this thesis is to discover solution for searching multinominal roots. The process is based on optimal iterative method in combination with priciple of argument increment. There is no procedure solving it in this way up to now. This method removes shortcomings already existing methods and she could also complement them with a new knowledge.
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Signal analysis of transport and stochastic processes of emission detectors
Míšek, David ; Tofel, Pavel (referee) ; Andreev, Alexey (advisor)
This Diploma thesis deals with properties of CdTe detectors. This material is ranked among optical sensitive group. This thesis can be thematically divided into two basic parts. The first part describes properties of both elements and the chemical adduct. Selected properties show perfections of the material, which are specializing it to optical area of application. The end of this part contains description of contact metal-semiconductor. This problem is important to comprehension principle the material contact. In second part there were making many measurements. For more accurately compare were first measurements doing without light and then with light. During making measurement was changed wave length and temperature of sample. Key factors were Volt-Ampere characteristics and resistance result with changed temperature and wave length impact to the sample. For better accuracy measurements were done many times. All of data from measurement were cultivate by PC Easyplot programme.
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