This thesis reports on two graphene-based structures that have been proposed and fabricated as possible prototypes for high-spatial-resolution Hall sensors with potential application in research on high-density magnetic recording technology such as bit patterned magnetic recording (BPMR) and other areas where the measurement of highly inhomogeneous fields is required. There is a direct graphene-metal contact in the first structure, which is named as TYPE I in this thesis, so that the anomalous Hall effect (AHE) in the ferromagnetic islands deposited on the graphene could be detected. Meanwhile, the graphene and the metal are isolated by an h-BN layer in the second structure which is named as TYPE II, so that only the stray field from the islands can be detected using the ordinary Hall effect (OHE).The transport measurements performed on TYPE I devices revealed there is no AHE or stray field signal detectable, and their Hall resistance relations are non-linear and do not pass through the origin point. A finite element simulation comparing the resistance of the empty graphene cross and the island-occupied cross indicates that the current in the graphene may not redistribute through the metallic islands due to interface current blocking, resulting in the non-appearance of the expected AHE signal. Moreover, an analysis on the data of the longitudinal magnetoresistance (MR) reveals that a two-fluid model and effective medium theory (EMT) model might be the major graphene MR mechanisms in the regime away from and near to the charge neutrality point (CNP) respectively. As a combined result of the above findings, a joint MR-Hall effect model under the condition of the presence of a pre-existing transverse offset current, is proposed to explain the unusual behaviour of the Hall measurement data of the TYPE I devices. The model gives qualitatively correct fitting for all longitudinal and transverse transport data of TYPE I devices. In addition, the nature of the graphene/metal contact is considered as the reason responsible for the non-appearance of the expected AHE and stray field signal, although further experimental work is needed, and suggested in the thesis, to clarify this issue. On the other hand, the TYPE II devices have shown their potential to be developed as a Hall sensor being able to detect a sub-micron magnetic island in the future, but there is still a large space for the performance of the devices to be improved. At the end of the thesis, future experimental work, which could lead to the eventual development of a high-sensitivity high-spatial-resolution Hall sensor on the basis of TYPE I and TYPE II structures, are suggested and described.

This research proposes the architecture of motor driver IC for the application of small BLDC motors. Both analog and digital mixed-mode techniques are employed here to design BLDC fan motor driver IC. The controlling method of this motor driver IC mainly utilizes analog approach. Besides, in order to prevent any damages on motors due to abnormal operations, digital control circuit is also involved in this IC. This motor driver IC is used in heat-sinking fan on notebooks as well as on the motors with very small impedance, so the IC is designed to be able to work in low supply voltage, and has high driving capability at the output stage. Via the feedback signal generated by the Hall sensor, it controls the motor driver IC so that the IC can supply current accordingly to stator coil. Therefore, the purpose of controlling motors is then achieved.

There is always a need for more effective ways to store energy in order to reduce the human impact on the environment. One step on the way can be the use of flywheels as kinetic energy storage devices. Low frictional losses are essential for a flywheel to be effective. To minimize these losses active magnetic bearings (AMB) can be used to keep the shaft centered instead of the more conventional ball-bearings. AMBs use actuators and a fast control system that needs correct and noise-free measurement data of the shaft position and the current in the actuators to work properly. This thesis explains the process of constructing power electronics and a current measurement system for active magnetic bearings (AMB). The focus of the thesis is on how to minimize noise in the circuits, including practical considerations on circuit design and theoretical explanations of the origin of noise in electric circuits. In addition there are discussions on factors to consider when designing a PCB and the importance of choosing the right component for the right application. Finished PCB-designs for both power electronics and current measurement along with specifications of the circuits and calibration data is presented. The finished circuits works well and have low noise levels and high reliability.

Hall Effect integrated circuits are used in a wide range of applications to measure the strength and/or direction of magnetic fields. These sensors play an increasingly significant role in the fields of automation, medical treatment and detection thanks largely to the enormous development of information technologies and electronic industries. Commercial Hall Effect ICs available in the market are all based on silicon technology. These ICs have the advantages of low cost and compatibility with CMOS technology, but suffer from poor sensitivity and detectability, high power consumption and low operating frequency bandwidths. The objective of this work was to develop and fabricate the first fully monolithic GaAs-InGaAs-AlGaAs 2-Dimensional Electron Gas (2DEG) Hall Effect integrated circuits whose performance enhances pre-existing technologies. To fulfil this objective, initially 2 µm gate length pHEMTs and 60/20 µm (L/W) Greek cross Hall Effect sensors were fabricated on optimised GaAs-In.18Ga.82As-Al.35Ga.65As 2DEG structures (XMBE303) suitable for both sensor and integrated circuit designs. The pseudomorphic high electron mobility transistors (pHEMTs) produced state-of-the-art output conductance, providing high intrinsic gain of 405, current cut-off frequency of 4.8 GHz and a low negative threshold voltage of -0.4 V which assisted in designing single supply ICs with high sensitivity and wide dynamic range. These pHEMTs were then accurately modelled for use in the design and simulation of integrated circuits. The corresponding Hall sensor showed a current sensitivity of 0.4 mV/mA.mT and a maximum magnetic DC offset of 0.35 mT at 1 V. DC digital (unipolar) and DC linear Hall Effect integrated circuits were then designed, simulated, fabricated and fully characterised. The DC linear Hall Effect IC provided an overall sensitivity of 8 mV/mT and a power consumption as low as 6.35 mW which, in comparison with commercial Si DC linear Hall ICs, is at least a factor of 2 more power efficient. The DC digital (unipolar) Hall Effect IC demonstrated a switching sensitivity of 6 mT which was at least ~50% more sensitive compared to existing commercial unipolar Si Hall ICs. In addition, a novel low-power GaAs-InGaAs-AlGaAs 2DEG AC linear Hall Effect integrated circuit with unprecedented sensitivity and wide dynamic range was designed, simulated, fabricated and characterised. This IC provided a sensitivity of 533 nV/nT, minimum field detectability of 177 nT (in a 10 Hz bandwidth) at frequencies from 500 Hz up to 200 kHz, consuming only 10.4 mW of power from a single 5 V of supply. In comparison to commercial Si linear Hall ICs, this IC provides an order of magnitude larger sensitivity, a factor of 4 higher detectability, 20 times wider bandwidth and over 20% lower power consumption (10.4 mW vs. 12.5 mW). These represent the first reported monolithic integrated circuits using a CMOS-like technology but in GaAs 2DEG technology and are extremely promising as complements, if not alternatives, to CMOS Si devices in high performance applications (such as high temperatures operations (>150 °C) and radiation hardened environment in the nuclear industry).

The purpose of this project is to design and construct a portable lightweight elevator for transportation of goods to rooftops. The elevator should be easy to transport, assemble and disassemble, it should also be useful at various heights and for a wide range of roof inclinations. The elevator contains a railway consisting of four separable modules. A carriage rides the railway and is pulled to the top with a winch powered by a DC-motor. The carriage starts and stops using a Rocker switch and a Hall sensor that detects magnets placed at the end and beginning of the railway. After performing tests with the elevator the conclusion is that the elevator is practical to assemble and transport, but the carriage derails too easily when the railway has angular changes. / Målet med projektet är att designa och konstruera en portabellättviktshiss som kan transportera gods från marknivå till hustak. Den ska vara lätt att transportera och att montera ner och upp, den ska också gå att anvåanda för olika höjder och på hus med olika taklutningar. Hissen består av en räls som går att ta isär i fyra olika delar. En vagn åker på fyra hjul uppför rälsen och lyftkraften kommerfrån en vinsch som drivs av en likströmsmotor. Vagnen kan starta och stanna med hjälp av en knapp, den stannar även automatisk då en hallsensor på vagnen känner av magneter som är placerade vid början och slutet av rälsen. En arduino Uno skickar signaler mellan de elektriska komponenterna och motorn får ström via en H-brygga, vilket gör att den kan rotera i båda riktningarna. Efter att hissen testats kan det konstateras att konstruktionen är enkel att bygga ihop och smidig att fästa vid olikavinklar och höjder. Däremot spårar vagnen ofta ur då hissen körs med för branta vinklar mellan de olika delarna av rälsen.

A Escola Politécnica da Universidade de São Paulo (EPUSP, Brasil) e o Instituto Dante Pazzanese de Cardiologia (IDPC, Brasil) estão desenvolvendo conjuntamente um Dispositivo de Assistência Ventricular (DAV) baseado numa bomba de vazão mista e utilizando mancais magnéticos que objetivem substituir os mancais convencionais, pois o uso de mancal magnético neste dispositivo minimiza a hemólise e melhora o tempo de vida do DAV, isso em razão da ausência e contato de um mancal com a crase sanguínea o que, por fim, aumenta a vida útil do dispositivo. O mancal magnético utilizado para o DAV será o mancal do tipo híbrido. Este tipo de mancal combina ímãs permanentes com eletroímãs para realizar a levitação do rotor com controle apenas na direção axial do rotor. Na configuração original desse mancal magnético, um sensor indutivo detecta a posição axial do rotor. Esta posição é enviada a um controlador do tipo PID e processada, amplificada e enviada aos atuadores eletromagnéticos. A corrente enviada aos eletroímãs é controlada de maneira a manter o rotor sempre em uma posição axial fixa. No entanto, essa configuração exige o uso de um atuador eletromagnético contendo um furo para a instalação do sensor indutivo, impondo limitações no desempenho do atuador. Além disso, o sensor indutivo limita a miniaturização do mancal. Assim, para minimizar as limitações impostas pelo uso do sensor indutivo, este trabalho faz, primeiramente, um levantamento das diversas técnicas conhecidas para a medição da posição do rotor em mancais magnéticos. Como resultado, este trabalho identifica o uso do sensor Hall como a alternativa mais promissora. Este sensor responde à magnitude de um campo magnético que nele é aplicado. Fixando-se um ímã permanente ao rotor, obtém-se uma saída no sensor Hall proporcional ao deslocamento do rotor. Contudo, a leitura do sensor Hall é afetada ainda pelo campo magnético gerado pelos atuadores eletromagnéticos, o que é indesejável. Buscando minimizar essa influência, este trabalho apresenta algumas estratégias para eliminar, da saída do sensor Hall, a influência do campo gerado pelo atuador eletromagnético. Os métodos são testados através de experimentos de levitação em mancal magnético e a eficácia dos mesmos comprovada. / The Escola Politécnica of the University of São Paulo (EPUSP, Brazil) and the Institute Dante Pazzanese of Cardiology (IDPC, Brazil) are jointly developing a Ventricular Assist Device (VAD) based on a mixed flow pump with magnetic bearings. The VAD rotor has a conical shape with spiral impellers that impels and pressurizes the blood. The magnetic bearing eliminates mechanical contact between the pump rotor and the VAD body, minimizing hemolysis and improving the lifetime of the VAD. The magnetic bearing studied is the hybrid type that combines permanent magnets with electromagnets to execute active control in the axial direction of the rotor. In the original configuration, the bearing uses inductive sensor to detect the axial position of the rotor. The sensor readings are sent to a PID type controller, processed, amplified and sent to the electromagnets. The current supplied to the electromagnets are controlled in a manner to keep the rotor in a fixed axial position. However, this configuration requires the use of a hollowed core in the electromagnetic actuator, imposing limitations in its efficiency. Moreover, the use of an inductive sensor imposes limitations to pump downsizing. In order to minimize the limitations, this work conducts firstly a study about alternative techniques for measuring the rotor position in a magnetic bearing. As result, the Hall sensor is identified as the most promising alternative. The Hall sensor is a small semiconductor element available in the market that gives an electric signal with amplitude corresponding to the magnet field intensity applied to it. By fixing a permanent magnet to the rotor, the Hall sensor gives a signal according to the rotor displacement. However, the Hall sensor output is also affected by the magnetic field generated by the electromagnetic actuator of the bearing. This is not desirable for controlling the bearing. In order to minimize the mentioned influence, this work presents some methods to eliminate the influence of the actuator from the Hall sensor readings. The methods are tests in a magnetic bearing and the efficiency of these methods is demonstrated.

A Escola Politécnica da Universidade de São Paulo (EPUSP, Brasil) e o Instituto Dante Pazzanese de Cardiologia (IDPC, Brasil) estão desenvolvendo conjuntamente um Dispositivo de Assistência Ventricular (DAV) baseado numa bomba de vazão mista e utilizando mancais magnéticos que objetivem substituir os mancais convencionais, pois o uso de mancal magnético neste dispositivo minimiza a hemólise e melhora o tempo de vida do DAV, isso em razão da ausência e contato de um mancal com a crase sanguínea o que, por fim, aumenta a vida útil do dispositivo. O mancal magnético utilizado para o DAV será o mancal do tipo híbrido. Este tipo de mancal combina ímãs permanentes com eletroímãs para realizar a levitação do rotor com controle apenas na direção axial do rotor. Na configuração original desse mancal magnético, um sensor indutivo detecta a posição axial do rotor. Esta posição é enviada a um controlador do tipo PID e processada, amplificada e enviada aos atuadores eletromagnéticos. A corrente enviada aos eletroímãs é controlada de maneira a manter o rotor sempre em uma posição axial fixa. No entanto, essa configuração exige o uso de um atuador eletromagnético contendo um furo para a instalação do sensor indutivo, impondo limitações no desempenho do atuador. Além disso, o sensor indutivo limita a miniaturização do mancal. Assim, para minimizar as limitações impostas pelo uso do sensor indutivo, este trabalho faz, primeiramente, um levantamento das diversas técnicas conhecidas para a medição da posição do rotor em mancais magnéticos. Como resultado, este trabalho identifica o uso do sensor Hall como a alternativa mais promissora. Este sensor responde à magnitude de um campo magnético que nele é aplicado. Fixando-se um ímã permanente ao rotor, obtém-se uma saída no sensor Hall proporcional ao deslocamento do rotor. Contudo, a leitura do sensor Hall é afetada ainda pelo campo magnético gerado pelos atuadores eletromagnéticos, o que é indesejável. Buscando minimizar essa influência, este trabalho apresenta algumas estratégias para eliminar, da saída do sensor Hall, a influência do campo gerado pelo atuador eletromagnético. Os métodos são testados através de experimentos de levitação em mancal magnético e a eficácia dos mesmos comprovada. / The Escola Politécnica of the University of São Paulo (EPUSP, Brazil) and the Institute Dante Pazzanese of Cardiology (IDPC, Brazil) are jointly developing a Ventricular Assist Device (VAD) based on a mixed flow pump with magnetic bearings. The VAD rotor has a conical shape with spiral impellers that impels and pressurizes the blood. The magnetic bearing eliminates mechanical contact between the pump rotor and the VAD body, minimizing hemolysis and improving the lifetime of the VAD. The magnetic bearing studied is the hybrid type that combines permanent magnets with electromagnets to execute active control in the axial direction of the rotor. In the original configuration, the bearing uses inductive sensor to detect the axial position of the rotor. The sensor readings are sent to a PID type controller, processed, amplified and sent to the electromagnets. The current supplied to the electromagnets are controlled in a manner to keep the rotor in a fixed axial position. However, this configuration requires the use of a hollowed core in the electromagnetic actuator, imposing limitations in its efficiency. Moreover, the use of an inductive sensor imposes limitations to pump downsizing. In order to minimize the limitations, this work conducts firstly a study about alternative techniques for measuring the rotor position in a magnetic bearing. As result, the Hall sensor is identified as the most promising alternative. The Hall sensor is a small semiconductor element available in the market that gives an electric signal with amplitude corresponding to the magnet field intensity applied to it. By fixing a permanent magnet to the rotor, the Hall sensor gives a signal according to the rotor displacement. However, the Hall sensor output is also affected by the magnetic field generated by the electromagnetic actuator of the bearing. This is not desirable for controlling the bearing. In order to minimize the mentioned influence, this work presents some methods to eliminate the influence of the actuator from the Hall sensor readings. The methods are tests in a magnetic bearing and the efficiency of these methods is demonstrated.

This diploma thesis deals with the creation measuring instruments and program for controlling model hydropower plant intended for laboratory use. The first step is to improve the mechanical performance of the original model of hydroelectric power. The second step is to select a revive measuring instruments for electric values of the plant. The third step is to create a program for displaying electrical parameters and control the plant. The final step was re-measuring the operating characteristics of the generator model hydropower plant.

Title: Development and application of methods for measurement of magnetic field on tokamaks Author: Ing. Karel Kovařík Department: Department of Surface and Plasma Science, Faculty of Mathematics and Physics, Charles University in Prague Institute of Plasma Physics of the Czech Academy of Sciences, v. v. i. Supervisor: Ing. Ivan Duran, PhD. (Institute of Plasma Physics of the Czech Academy of Sciences, v. v. i.) Abstract: Thesis describes two parts of my work in frame of magnetic confined fusion research. First part describes irradiation testing of the Hall sensors based on InSb semiconductor. It evaluates radiation effects of fast and thermal neutrons on the Hall sensors sensitivity. Tests indicate low level of changes for fluence lower only by order of magnitude than expected in the whole lifetime of ITER tokamak. Second part describes measurement of turbulent plasma structures parameters in scrape--off layer of the COMPASS tokamak, particularly the parallel electric current flowing along them. Design of novel combined probe allowing measurement of not only electrostatic parameters but also the parallel electric current is presented. Evaluation of parallel electric current is discussed and compared with experiment. Statistical analysis of the plasma structures is presented. Empirical formulas of the...

This diploma theisis deals with the theoretical analysis of the known types of current sensors, including for example, current transformers, shunts, and advanced sensors using Hall sensor or Rogowski coil. Subsequently, the rest of the work deals with the issue of current transducers with Hall sensors, without using a ferromagnetic circuit. For optimal currnet measure and overall precision, several possible options are designed and calculated. This includes number of sensing elements and distribution of sensors around the wires. Based on calaculation of magnetic intensity, related 3D charts ale plotted unsing Excel software. These charts illustrate the theoretical calculations of field distribution around conductors for various number of sensor. In the last part, components ale designed for practical implementation and scheme of electrical wiring. According to this scheme there is PCB designed as well. Whole current meter ir practically build and its results are compared with theoretical assumtions that are discussed in conclusion part of this theisis.