Lämpötilanmittaus magneettikuvausympäristössä optista tehon- ja tiedonsiirtoa käyttäen

Lääketieteellisen magneettikuvantamisen yhteydessä on tarpeen mitata mm. potilaan lämpötilaa. Kuvantamisessa käytettävät kentät asettavat suuret vaatimukset kuvauksen aikana käytettäville mittalaitteille. Magneettikuvausympäristöön soveltuva lämpötilanmittausjärjestelmä on mahdollista toteuttaa käyttämällä sekä lämpötilatiedon että sähkötehon siirtämiseen valokuitua, jolloin järjestelmä on täysin galvaanisesti erotettu. Valokuidusta tuleva optinen teho muunnetaan sähkötehoksi valosähkömuuntimella. Tämä diplomityö keskittyy magneettikuvauksessa käytettävän lämpötilanmittausjärjestelmän suunnitteluun. Haasteena oli optisesta tehonsiirrosta johtuva tarve minimoida tehonkulutus ja lämpötilamittauksen tarkkuusvaatimus. Järjestelmän prototyyppi voidaan rakentaa suunnittelun mukaisesti. Diplomityössä suunnittelutuloksia testattiin koekytkennän avulla ja näin varmistuttiin mittausperiaatteen toimivuudesta.

Physical Realization of an Optical Automatic Target Recognition System

In the modern warfare there is an active development of a new trend connected with a robotic warfare. One of the critical elements of robotics warfare systems is an automatic target recognition system, allowing to recognize objects, based on the data received from sensors. This work considers aspects of optical realization of such a system by means of NIR target scanning at fixed wavelengths. An algorithm was designed, an experimental setup was built and samples of various modern gear and apparel materials were tested. For pattern testing the samples of actively arm engaged armies camouflages were chosen. Tests were performed both in clear atmosphere and in the artificial extremely humid and hot atmosphere to simulate field conditions.

RF disturbances produced by high-power photovoltaic solar plants

In this thesis, analysis of electromagnetic compatibility of high-power photovoltaic solar plant is made. Current standards suitable for photovoltaic applications are given. Measurements of antenna factor for experimental setup are shown. Also, measurements of common mode disturbance voltages in high-power solar plant are given. Importance of DC-side filter is shown. In the last part of the work, electromagnetic simulations are made. These simulations show influence of several factors to EMC of power plant. Based on these simulations and measurements recommendations are given.

Spin-Dynamics in Cold Gases of 87Rb and Atomic Hydrogen. The spins they are a-changin’

In this thesis the dynamics of cold gaseous atoms is studied. Two different atomic species and two different experimental techniques have been used. In the first part of the thesis experiments with Bose-Einstein condensates of Rb-87 are presented. In these experiments the methods of laser cooling and magnetic trapping of atoms were utilized. An atom chip was used as the experimental technique for implementation of magnetic trapping. The atom chip is a small integrated instrument allowing accurate and detailed manipulation of the atoms. The experiments with Rb-87 probed the behaviour of a falling beam of atoms outcoupled from the Bose-Einstein condensate by electromagnetic field induced spin flips. In the experiments a correspondence between the phases of the outcoupling radio frequency field and the falling beam of atoms was found. In the second part of the thesis experiments of spin dynamics in cold atomic hydrogen gas are discussed. The experiments with atomic hydrogen are conducted in a cryostat using a dilution refrigerator as the cooling method. These experiments concentrated on explaining and quantifying modulations in the electron spin resonance spectra of doubly polarized atomic hydrogen. The modifications to the previous experimental setup are described and the observation of electron spin waves is presented. The observed spin wave modes were caused by the identical spin rotation effect. These modes have a strong dependence on the spatial profile of the polarizing magnetic field. We also demonstrated confinement of these modes in regions of strong magnetic field and manipulated their spatial distribution by changing the position of the field maximum.

Quantum Hall effect in 2 dimensional GaInAs structure

Transport properties of GaAs / δ – Mn / GaAs / InxGa1-xAs / GaAs structure with Mn δ – layer, which is separated from InxGa1-xAs quantum well (QW) by 3 nm thick GaAs spacer was investigated. This structure with high mobility was characterized by X-ray difractometry and reflectometry. Transport and electrical properties of the structure were measured by using Pulsed Magnetic Field System (PMFS). During investigation of the Shubnikov – de Haas and the Hall effects the main parameters of QW structure such as cyclotron mass, Fermi level, g – factor, Dingle temperature and concentration of holes were estimated. Obtained results show high quality of the prepared structure. However, anomalous Hall effect at temperatures 2.09 K, 3 K, 4.2 K is not clearly observed. Attempts to identify magnetic moment were made. For this purpose the polarity of the filed was changed to the opposite at each shot. As a result hysteresis loop was not observed in the magnetic field dependences of the anomalous Hall resistivity.This can be attributed to the imperfection of the experimental setup.

Power semiconductor nonlinearities in active du/dt output filtering

This doctoral thesis introduces an improved control principle for active du/dt output filtering in variable-speed AC drives, together with performance comparisons with previous filtering methods. The effects of power semiconductor nonlinearities on the output filtering performance are investigated. The nonlinearities include the timing deviation and the voltage pulse waveform distortion in the variable-speed AC drive output bridge. Active du/dt output filtering (ADUDT) is a method to mitigate motor overvoltages in variable-speed AC drives with long motor cables. It is a quite recent addition to the du/dt reduction methods available. This thesis improves on the existing control method for the filter, and concentrates on the lowvoltage (below 1 kV AC) two-level voltage-source inverter implementation of the method. The ADUDT uses narrow voltage pulses having a duration in the order of a microsecond from an IGBT (insulated gate bipolar transistor) inverter to control the output voltage of a tuned LC filter circuit. The filter output voltage has thus increased slope transition times at the rising and falling edges, with an opportunity of no overshoot. The effect of the longer slope transition times is a reduction in the du/dt of the voltage fed to the motor cable. Lower du/dt values result in a reduction in the overvoltage effects on the motor terminals. Compared with traditional output filtering methods to accomplish this task, the active du/dt filtering provides lower inductance values and a smaller physical size of the filter itself. The filter circuit weight can also be reduced. However, the power semiconductor nonlinearities skew the filter control pulse pattern, resulting in control deviation. This deviation introduces unwanted overshoot and resonance in the filter. The controlmethod proposed in this thesis is able to directly compensate for the dead time-induced zero-current clamping (ZCC) effect in the pulse pattern. It gives more flexibility to the pattern structure, which could help in the timing deviation compensation design. Previous studies have shown that when a motor load current flows in the filter circuit and the inverter, the phase leg blanking times distort the voltage pulse sequence fed to the filter input. These blanking times are caused by excessively large dead time values between the IGBT control pulses. Moreover, the various switching timing distortions, present in realworld electronics when operating with a microsecond timescale, bring additional skew to the control. Left uncompensated, this results in distortion of the filter input voltage and a filter self-induced overvoltage in the form of an overshoot. This overshoot adds to the voltage appearing at the motor terminals, thus increasing the transient voltage amplitude at the motor. This doctoral thesis investigates the magnitude of such timing deviation effects. If the motor load current is left uncompensated in the control, the filter output voltage can overshoot up to double the input voltage amplitude. IGBT nonlinearities were observed to cause a smaller overshoot, in the order of 30%. This thesis introduces an improved ADUDT control method that is able to compensate for phase leg blanking times, giving flexibility to the pulse pattern structure and dead times. The control method is still sensitive to timing deviations, and their effect is investigated. A simple approach of using a fixed delay compensation value was tried in the test setup measurements. The ADUDT method with the new control algorithm was found to work in an actual motor drive application. Judging by the simulation results, with the delay compensation, the method should ultimately enable an output voltage performance and a du/dt reduction that are free from residual overshoot effects. The proposed control algorithm is not strictly required for successful ADUDT operation: It is possible to precalculate the pulse patterns by iteration and then for instance store them into a look-up table inside the control electronics. Rather, the newly developed control method is a mathematical tool for solving the ADUDT control pulses. It does not contain the timing deviation compensation (from the logic-level command to the phase leg output voltage), and as such is not able to remove the timing deviation effects that cause error and overshoot in the filter. When the timing deviation compensation has to be tuned-in in the control pattern, the precalculated iteration method could prove simpler and equally good (or even better) compared with the mathematical solution with a separate timing compensation module. One of the key findings in this thesis is the conclusion that the correctness of the pulse pattern structure, in the sense of ZCC and predicted pulse timings, cannot be separated from the timing deviations. The usefulness of the correctly calculated pattern is reduced by the voltage edge timing errors. The doctoral thesis provides an introductory background chapter on variable-speed AC drives and the problem of motor overvoltages and takes a look at traditional solutions for overvoltage mitigation. Previous results related to the active du/dt filtering are discussed. The basic operation principle and design of the filter have been studied previously. The effect of load current in the filter and the basic idea of compensation have been presented in the past. However, there was no direct way of including the dead time in the control (except for solving the pulse pattern manually by iteration), and the magnitude of nonlinearity effects had not been investigated. The enhanced control principle with the dead time handling capability and a case study of the test setup timing deviations are the main contributions of this doctoral thesis. The simulation and experimental setup results show that the proposed control method can be used in an actual drive. Loss measurements and a comparison of active du/dt output filtering with traditional output filtering methods are also presented in the work. Two different ADUDT filter designs are included, with ferrite core and air core inductors. Other filters included in the tests were a passive du/dtfilter and a passive sine filter. The loss measurements incorporated a silicon carbide diode-equipped IGBT module, and the results show lower losses with these new device technologies. The new control principle was measured in a 43 A load current motor drive system and was able to bring the filter output peak voltage from 980 V (the previous control principle) down to 680 V in a 540 V average DC link voltage variable-speed drive. A 200 m motor cable was used, and the filter losses for the active du/dt methods were 111W–126 W versus 184 W for the passive du/dt. In terms of inverter and filter losses, the active du/dt filtering method had a 1.82-fold increase in losses compared with an all-passive traditional du/dt output filter. The filter mass with the active du/dt method was 17% (2.4 kg, air-core inductors) compared with 14 kg of the passive du/dt method filter. Silicon carbide freewheeling diodes were found to reduce the inverter losses in the active du/dt filtering by 18% compared with the same IGBT module with silicon diodes. For a 200 m cable length, the average peak voltage at the motor terminals was 1050 V with no filter, 960 V for the all-passive du/dt filter, and 700 V for the active du/dt filtering applying the new control principle.

Mäntyöljyn tislauksen esikäsittely

Raakamäntyöljy on selluteollisuuden sivutuote. Suopa erotetaan mustalipeästä ja palstoitetaan tuottaen siten raakamäntyöljyä. Raakamäntyöljy tislataan tavanomaisesti viiteen pääjakeeseen: rasvahapot, hartsihapot, mäntyöljytisle, esiöljy ja mäntyöljypiki. Näiden jakeiden lisäksi raakamäntyöljyssä on erityisesti mustalipeästä siihen erottuneita epäpuhtauksia, jotka haittaavat raakamäntyöljyn prosessointia. Epäpuhtauksia ovat orgaaniset ja epäorgaaniset yhdisteet, kuten metallit, suolat ja ligniini. Nämä epäpuhtaudet aiheuttavat haitallisia reaktioita prosessissa huonontaen siten lopputuotejakeiden laatua. Tämän lisäksi epäpuhtaudet aiheuttavat saostumia prosessilaitteissa alentaen siten prosessointitehokkuutta. Raakamäntyöljyn esikäsittelyllä tehostetaan tislauksen toimintaa. Työssä esitetään esikäsittelymenetelmistä mm. degumming-menetelmä, laimea happopesu, hiilidioksidikäsittely, valkaisu ja lämpökäsittely. Menetelmien pohjalta valitaan tätä työtä varten yksi menetelmä, jonka pohjalta suunnitellaan kokeellisessa osassa suoritettavat kokeet. Kokeellinen osuus koostuu esikokeista, varsinaisista kokeista ja lisäkokeista. Menetelmän tarkoituksena on saavuttaa epäpuhtauksille 90–95 % reduktioaste. Kokeiden onnistumista tutkitaan analysoimalla alkuperäinen raakamäntyöljy, sekä jokaisen kokeen jälkeen erotetut faasit. Työssä saavutettiin hyvä erotustehokkuus. Alkuperäisen tavoitteen mukaista reduktioastetta ei pystytty määrittämään eri analyysimenetelmien ja niiden analyysituloksissa ilmenneiden eroavaisuuksien vuoksi, mutta lisäkokeiden ansiosta pystyttiin vahvistamaan kyseisen koejärjestelmän optimaalinen poistoaste. Lisäksi työssä havaittiin että esikäsittelytulos on hyvin riippuvainen käsiteltävän raaka-aineen koostumuksesta.