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Measurement of gradient magnetic field decay in MR tomograph
Kubásek, Ondřej ; Kubásek, Radek (referee) ; Bartušek, Karel (advisor)
The objective of my thesis is to measure magnetic field gradient decay in an MR tomograph, process and evaluate the data measured and analyse the issue. The theoretical section focuses on the reasons for the gradient distortion which has a negative impact on NMR measuring techniques and it also describes options to eliminate the negative effects, focusing mainly on pre-emphasis filtration. It also lists methods of gradient magnetic field measuring. The practical section contains results of magnetic field decay measurements taken with the tomograph in the Institute of scientific instruments of the Academy of sciences in Brno using the method of instantaneous frequency with and without pre-emphasis compensation. The data are processed with MAREVISI and MATLAB programmes. MATLAB is used to develop a modern method of filtration to eliminate noise in useful signal leading to more accurate measurements of MR magnetic fields. This filtration uses a method of time-dependent variable thresholds and two-channel filter banks. MATLAB is also used to design a programme for approximation of the measured gradient magnetic field decay. The decay must be approximated in order to obtain time constants and the degree of exponential decay, which serve to set up the pre-emphasis compensation.
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Using repeaters to enhance cellular communication signals
Kubásek, Ondřej ; Kubánek, David (referee) ; Koutný, Martin (advisor)
This thesis examines possibile applications of RF repeaters to improve the mobile networks signal coverage. An overview of various types of repeaters is given, while advantages and disadvantages of particular types are discussed. The questions of antenna isolation and resulting repeater gain settings are solved here as well. The thesis also considers a proposal of repeater system to improve the signal coverage in the trains of the České dráhy, a.s. company. This proposal analyses the questions of signal penetration and propagation in trains, possibilities of implementing repeaters into carriages, system diagnostics and the financial issues. The proposal is supported by the results of a trial measurement taken out in the cooperation among T-Mobile Czech Republic a.s., Vodafone Czech Republic a.s., Telefónica O2 Czech Republic a.s., České dráhy a.s. (Czech Railways Company) a ČD-Telematika a.s. on the Prague – Ostrava line.
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Using repeaters to enhance cellular communication signals
Kubásek, Ondřej ; Kubánek, David (referee) ; Koutný, Martin (advisor)
This thesis examines possibile applications of RF repeaters to improve the mobile networks signal coverage. An overview of various types of repeaters is given, while advantages and disadvantages of particular types are discussed. The questions of antenna isolation and resulting repeater gain settings are solved here as well. The thesis also considers a proposal of repeater system to improve the signal coverage in the trains of the České dráhy, a.s. company. This proposal analyses the questions of signal penetration and propagation in trains, possibilities of implementing repeaters into carriages, system diagnostics and the financial issues. The proposal is supported by the results of a trial measurement taken out in the cooperation among T-Mobile Czech Republic a.s., Vodafone Czech Republic a.s., Telefónica O2 Czech Republic a.s., České dráhy a.s. (Czech Railways Company) a ČD-Telematika a.s. on the Prague – Ostrava line.
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Measurement of gradient magnetic field decay in MR tomograph
Kubásek, Ondřej ; Kubásek, Radek (referee) ; Bartušek, Karel (advisor)
The objective of my thesis is to measure magnetic field gradient decay in an MR tomograph, process and evaluate the data measured and analyse the issue. The theoretical section focuses on the reasons for the gradient distortion which has a negative impact on NMR measuring techniques and it also describes options to eliminate the negative effects, focusing mainly on pre-emphasis filtration. It also lists methods of gradient magnetic field measuring. The practical section contains results of magnetic field decay measurements taken with the tomograph in the Institute of scientific instruments of the Academy of sciences in Brno using the method of instantaneous frequency with and without pre-emphasis compensation. The data are processed with MAREVISI and MATLAB programmes. MATLAB is used to develop a modern method of filtration to eliminate noise in useful signal leading to more accurate measurements of MR magnetic fields. This filtration uses a method of time-dependent variable thresholds and two-channel filter banks. MATLAB is also used to design a programme for approximation of the measured gradient magnetic field decay. The decay must be approximated in order to obtain time constants and the degree of exponential decay, which serve to set up the pre-emphasis compensation.
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