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Modelling of bioelectronic devices
Truksa, Jan ; Vala, Martin (referee) ; Salyk, Ota (advisor)
Tématem této práce je počítačové modelování organického elektrochemického tranzistoru (OECT). Pro vytvoření modelu bylo třeba vypočítat rozložení elektrického pole a koncentrace iontů elektrolytu. Výpočet byl proveden numericky pomocí metody konečných prvků. Bylo vypočítáno rozložení elektrického potenciálu na povrchu kanálu OECT, dále byly vypočítány změny vodivosti a výstupní proud OECT. Výpočty byly provedeny na osobním počítači pomocí komerčního softwaru COMSOL Multiphysics. Kvůli nedostatečnému výpočetnímu výkonu musel být model rozdělen na části a drasticky zjednodušen. Prezentované výsledky se liší od literatury, protože se nepodařilo správně modelovat saturaci tranzistoru. Odchylky od reálného chování OECT jsou pravděpodobně způsobeny zjednodušením modelu.
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Transport and optical properties of CdTe/CdZnTe single crystals
Uxa, Štěpán ; Belas, Eduard (advisor) ; Humlíček, Josef (referee) ; Drbohlav, Ondřej (referee)
Title: Transport and optical properties of CdTe/CdZnTe single crystals Author: Štěpán Uxa Department: Institute of Physics of Charles University Supervisor: Assoc. Prof. Eduard Belas, PhD, Institute of Physics of Charles University Abstract: The thesis is focused on a study of internal electric field and temperature dependence of the absorption edge of CdTe and CdZnTe samples. In the first part of the thesis the transient-current technique (TCT) is used for investigations of electric fields within planar radiation detectors. The original comprehensive theory that links together TCT measurements with measurements of detector's charge-collection efficiency (CCE) is presented. This approach results in the development of two new iterative methods for processing of experimental data which can be used in any situation when the internal electric field can be approximated by a linear profile. In the second part of the thesis high temperature measurements of transmittance of thin polished CdTe samples are presented, leading to the estimation of the temperature dependence of the bandgap energy from calculated spectra of absorption coefficient. This is for the first time when measurements in a Cd overpressure have been performed which significantly reduces sample sublimation. Keywords: CdTe, transient-current technique,...
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Studium elektrického pole v detektorech záření pomocí Pockelsova jevu
Hakl, Michael ; Franc, Jan (advisor) ; Richter, Ivan (referee)
Study of electric field in radiation detectors by Pockels effect (Master Thesis) by Michael Hakl Abstract Cadmium Telluride (CdTe) is a convenient candidate for room tem- perature detection of X-ray and gama radiation due to 1.5 eV band- gap energy and high atomic mass. Since CdTe has the highest linear electro-optical coefficient among II-VI compounds, the detector rep- resents a Pockels cell. Transmittance of the crystal is modulated by the internal electric field. Processing of infrared camera photographs results in an electric field profile between biasing electrodes. The elec- tric field in semi-insulting CdTe is influenced with deep level traps causing charge polarization under the electrodes. Occupation of traps is dependent on metal-semiconductor interface. Relation of charge accumulation and band bending for gold and indium contacts was studied. Repolarization/depolarization induced by additional illumi- nation with sub/above bandgap excitation laser was observed and ex- ploited for determination of the deep level energy. Results obtained by the Pockels-effect method were supported with luminescence measure- ments. Correlation between the occurrence of deep levels and surface point defects was discovered. Keywords: Pockels electro-optical effect, Cadmium Telluride ra- diation detector, Electric field, Schottky...
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Electrooptic Pockels effect in X-ray radiation detectors
Rejhon, Martin ; Franc, Jan (advisor) ; Moravec, Pavel (referee)
In this work, we have added a temperature controller to an apparatus for measuring Pockels effect, which comprises of an integrated circuit and a Peltier element. Then the course of the electric field was measured in the sample of high resistance CdTe, a suitable detector on the high-energy radiation, depending on the voltage and temperature of the sample. Also the charge distribution in the sample was determined depending on time after the voltage and sample's temperature were reached. Finally, the activation energies of deep levels were determined, which are responsible for the polarization. Powered by TCPDF (www.tcpdf.org)
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Degradation of liquid insulators for high voltage
Komárek, Filip ; Štěpánek, Jaroslav (referee) ; Krbal, Michal (advisor)
This bachelor's thesis deals with measurement of liquid insulators. Mainly it deals with diagnostic tests of transformer oil. Diagnostic tests are needed to identify oil status and to determine the parameters of the oil. The status of the used oil determines its type of degradation and progress of degradation. For the determination of degradation it is necessary to know the composition of the essential oil, to determine how it has changed the structure of the oil and the oil did not contain before use. To determine the basic electrical properties of the oil are used in diagnostic tests such as dielectric strength and dissipation factor. This work is in addition to a summary of diagnostic tests observation of mineral oil with an unknown degree of degradation and behavior of impurities in mineral oil once the electric field.
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Modelling of organic electrochemical transistors
Truksa, Jan ; Omasta, Lukáš (referee) ; Salyk, Ota (advisor)
The topic of this work is the making of a virtual model of a circular organic electrochemical transistor (OECT) and its electric field, and comparison of the computed results to a real system of rotationally symmetrical electrodes. The electric potential field in the transistor was modelled using the finite element method and the electric field and current field were determined using the results. Later, the electric potential field was mapped in a real system of aluminium electrodes, submerged in water. The electric field model of an unusually configured circular OECT is presented in this work. Due to insufficient computing capacity, the model had to be significantly simplified. The computed results agree with the experimentally determined potential field despite the simplification. The deviations of the model output characteristic from real OECT characteristic were caused by simplifying the model in respect to reality.
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Simulation of electric field in the area of switchgear busbars
Müller, Michal ; Janda, Marcel (referee) ; Bušov, Bohuslav (advisor)
The aim of this work is to simulate the electric field in the space of busbar HV switchgear. More precisely, the aim is to find a place with the most critical value of the electric field, the design of measures to reduce the size of the field at this point. The simulation was performed using the finite element method program. The simulation found the most critical area. Using the basic physical principles it has been proposed solution. This solution reduced twice the magnitude the electric field in this area.
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Experimental drying and desalination of bricks, sandstones and masonry under an applied electric field
Matyščák, Ondřej ; Katunský,, Dušan (referee) ; Ostrý, Milan (referee) ; Doc.Ing. Karel Kubečka, Ph.D (referee) ; Novotný, Miloslav (advisor)
Dewatering and desalination of building constructions is currently a discussed topic. At the present time, different techniques for dewatering and desalination can be used. The existing methods are efficient but it is necessary to improve these methods and to develop new ones. The moisture in the building constructions is directly connected with the salts, which can be dissolved in it and together with the moisture further to move. The salts can cause damage of constructions and change mechanical and physical properties of the buildings materials. The basic demands for dewatering and desalination are the speed, efficiency and economical factors. Presented dissertation focuses on dewatering and desalination with the use of electrokinetic methods together with the technique of the clay poultices. In the first part of the thesis, basic theoretical principles of moisture and salts are described. In the second part (experimental part), the series of experimental measurements were conducted both in the laboratory and in situ. In this part of dissertation, I was dewatering and desalinating bricks and sandstones under an applied electric field. The main focus was on the optimization of a laboratory setup in order to get the highest efficiency for dewatering and desalination. Other measurements were done in situ, where the same technique was used.
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Voltage amplifier for Electrical field generation
Nedbal, Jan ; Szabó, Zoltán (referee) ; Kubásek, Radek (advisor)
This bachelor’s thesis is about design and practical realization of the voltage amplifier for generating an electric field defined trace. First part is introduced design of function generator and a DC power supply symmetric. In the second part is the design and simulation of power amplifier in class A and high voltage DC source. The last part is consists of measurements on a function generator, power amplifier and high voltage DC source.
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