This thesis deals with a design of 9DOF module for the evaluation of orientation in space. The thesis includes a theoretical description of sensors, mathematical apparatus for rotating and the Kalman filter. The practical part deals with the design of hardware, firmware and software, whereby the mathematical formulas set out in the theoretical part are applied. In the last part a testing of the created module is presented.

UAVs have become an essential tool in many market segments, particularly the military where critical intelligence can be gathered by them. A tailsitter aircraft is a platform whose purpose is to efficiently merge the range and endurance of fixed-wing aircraft with the VTOL capabilities of rotorcraft and is of significant value in applications where launch and recovery area is limited or the use of launch and recovery equipment is not desirable. Developing autopilot software for a tailsitter UAV is unique in that the aircraft must be autonomously controlled over a much wider range of attitudes than conventional UAVs. Assumptions made in conventional estimation and control algorithms are not valid for tailsitter aircraft because of routine operation around gimbal lock. Quaternions are generally employed to overcome the limitations Euler angles; however, adapting the attitude representation to work at a full range of attitudes is only part of the solution. Kalman filter measurement updates and control algorithms must also work at any orientation. This research presents several methods of incorporating a magnetometer measurement into an extended Kalman filter. One method combines magnetometer and accelerometer sensor data using the solution to Wahba's problem to calculate an overall attitude measurement. Other methods correct only heading error and include using two sets of Euler angles to update the estimate, using quaternions to determine heading error and Euler angles to update the estimate, and using only quaternions to update the estimate. Quaternion feedback attitude control is widely used in tailsitter aircraft. This research also shows that in spite of its effective use in spacecraft, using the attitude error calculated via quaternions to drive flight control surfaces may not be optimal for tailsitters. It is shown that during hover when heading error is present, quaternion feedback can cause undesired behavior, particularly when the heading error is large. An alternative method for calculating attitude error called resolved tilt-twist is validated, improved, and shown to perform better than quaternion feedback. Algorithms are implemented on a commercially available autopilot and validation is performed using hardware in loop simulation. A custom interface is used to receive autopilot commands and send the autopilot simulated sensor information. The final topic covered deals with the tailsitter hovering in wind. As the tailsitter hovers, wind can cause the tailsitter to turn such that the wind is perpendicular to the wings. Wind tunnel data is taken and analyzed to explain this behavior.

The most common equipment used for attitude determination in small satellites are magnetometers. However, using magnetometers gives rise to many challenges. One of these challenges is the calibration of the magnetometer. Magnetometer calibration takes many factors into account. There are external and internal factors. External factors can be the satellite itself. Satellites are built of many complex subsystems. These subsystems can produce magnetic disturbances and affect the measurements taken by the magnetometer ,which also affects the attitude determination of the satellite. Internal factors are nonorthogonalityand scale factors. In this project, we aim to test different calibration methods and compare the results. Another objective is to provide a complete procedure for a calibration of the magnetometer using the Helmholtz coils. The comparison of the results with other methods can help with the decision of which should be used to calibrate the magnetometer onboard the satellite for future calibrations for MIST satellites. / En av de mest vanliga verktyg för attitydbestämning i små satteliter är magnetometer, men att använda magnetometer kan leda till många utmaningar, en av de kalibrering av magnetometern. Magnetometer kalibrering är beroende av många faktorer. Det finns inre och yttre faktorer. Yttre faktorer kan vara själva satelliten. Del system som bildar satelliten kan påverka mätningar i magnetometern och då påverkar attitydbestämning av hela satelliten. Inre faktorer är icke ortogonalitet och skalära faktorer. I det här projektet vi ska testa olika kalibrerings metoder och jämföra resultaten. Ett annat mål är att bygga en komplett procedur för att kalibrera magnetometer med hjälp av Helmholtz spolar. Jämförelsen och resultaten från kalibreringen visar hur det är möjligt att kalibrnetometer som är integrerad i satelliten för kommande kalibreringar i MIST. / Kandidatexjobb i elektroteknik 2022, KTH, Stockholm

A small satellite can be adversely affected by Earth’s magnetic field due to the resulting torque the magnetic field exerts on the satellites magnetic dipole moment. Therefore, this dipole moment needs to be estimated during the development of the satellite to make sure that the torque does not become a problem once the satellite is in orbit. This needs to be done for the MIniture STudent satellite (MIST), built at KTH Royal Institute of Technology. Two methods that make use of different techniques to measure the magnetic dipole moment of objects are evaluated through simulations. The first method holds the promise of being able to accurately estimate the dipole moment on components and the whole satellite alike, but has the downside of having a more complex setup. The second method can be set up easily, and can quickly produce an estimate of the dipole moment of one single object. However, the method is more susceptible to external disturbances in the magnetic field, and placement of the object. Due to time constraints, only the second method is evaluated experimentally. To understand how the second method performs, reference measurements are made on a coil with a known dipole moment. The results from the reference measurements show that the second method works well enough to produce values accurate enough for this project. Measurements are thereafter made on components similar to the flight hardware which are put through a set of tests to see how easily magnetised they are. The resulting values show that the magnetic field from magnetic tools can magnetise the components to the extent of becoming a problem, making the satellite’s dipole moment exceed the set limit. A more thorough investigation of MIST’s magnetic dipole moment should be conducted to determine if the satellites total magnetic dipole moment runs the risk of exceeding the set limit. / Små satelliter kan påverkas negativt av jordens magnetfält då det i samband med satellitens magnetiska dipolmoment kan resultera i ett moment som verkar på satelliten. Därför behöver det magnetiska dipolmomentet uppskattas under utvecklingen av satelliten för att fastställa att problem inte uppstår när satelliten är i omloppsbana runt jorden. Denna uppskattning måste göras på MIniture STudent satelliten MIST, som byggs på Kungliga Tekniska Högskolan i Stockholm. Två metoder som använder sig av olika tekniker för att mäta det magnetiska dipolmomentet på komponenter undersöks genom simuleringar. Första metoden verkar från simuleringarna kunna göra en mätning av det magnetiska dipolmomentet med hög precision på enskilda komponenter och hela satelliten. Metoden har dock en komplex mätuppställning. Andra metoden kan snabbt ställas upp och en uppskattning av en komponent kan fås. Nackdelen med metoden är dess känslighet mot störningar i magnetfältet samt felplacering av dipolen. På grund av projektets tidsram väljs den andra metoden för att göra experimentella mätningar. För att förstå hur den andra metoden presterar görs mätningar på en spole med ett känt magnetiskt dipolmoment. Resultaten från mätningarna på spolen visar att metoden fungerar bra nog för att ge tillräckligt noggranna värden för projektet. Mätningar görs därefter på komponenter som liknar MISTs hårdvara för att undersöka hur lätta de är att magnetisera. Resultaten visar att magnetiska fält från verktyg kan magnetisera komponenterna så pass mycket att den satta gränsen för satellitens magnetiska dipolmomentet överskrids. En mer grundlig utredning av MISTs magnetiska dipolmoment bör göras för att fastställa om dipolmomentet riskerar att överskrida gränsen. / Kandidatexjobb i elektroteknik 2020, KTH, Stockholm

This thesis proposes a set of methods for the purpose of improving the calibration of three-axis magnetometers. Specifically, these methods aim to improve the accuracy of the bias estimation methods currently in use. The first proposed method utilizes a constrained optimization problem based on norm preserving. The second proposed method finds the same bias estimate as the first method, but in a computationally more efficient manner. The last proposed method tackles the case where the value of the local geomagnetic field is only imprecisely known. Computer simulations demonstrate the viability of the proposed methods.

We have investigated the Faraday effect of bismuth-doped rare-earth iron-garnets with varying doping levels of gallium from z = 1.0 to 1.35. We used lutetium to control the film's in-plane magnetic properties and found that gallium doping levels above the compensation point caused a loss of anisotropy control, a canted out-of-plane magnetization in the film, and an extremely weak but linear coercivity above 10 micro-Tesla fields. Using these results we focused on in-plane films to create 8 layer stacks of 500 um thick films to achieve a minimum detectable field of 50 pT at 1 kHz. Unlike previous Magneto-Optic (MO) studies that typically used thin films of approximately 1um thickness, we used approximately 400um thick films to allow experimentation with the final, robust, ideal form the MO sensor would take. We measured what most other MO studies with garnets neglected: the magnetic anisotropy axis or structure within the film. Knowledge of this structure is essential in improving the sensitivity of a stacked MO probe. Studying thick films proved to be key to understanding the magnetic anisotropy and domain properties that can degrade or enhance the sensitivity of the Faraday rotation in bismuth doped rare-earth iron-garnets to an applied magnetic field and to pointing the direction of future research to develop the conditions for rugged magnetometer sensors. / Physics

Yes / This document reviews Legacy Data generated from 10 years’ worth of road scheme activity in Ireland to determine how archaeological geophysical surveys could be carried out on national roads in the future. The geophysical surveys were carried out by several different contractors across a range of challenging field conditions, geologies, weather and seasons. The research is based upon the results of linear schemes but also has validity for wider approaches. The findings of this research are based upon the compilation of all terrestrial archaeological geophysical surveys carried out on behalf of the National Roads Authority (NRA), a review of the success or otherwise of those surveys in comparison with ground-observed excavations and in combination with experimental surveys that tested previously held assumptions or knowledge to determine best practice methods for the future. The use and success of geophysical surveys in Ireland differ quite significantly from those in the UK, from where many of the methods of assessment were derived or adapted. Many of these differences can be attributed to geology. Ireland has a very high percentage of Carboniferous limestone geology, overlain mostly by tills and frequent occurrences of peat. These soils can reduce, to some extent, the effectiveness of magnetometer surveys; the most frequently used geophysical technique in Ireland. However, magnetometer data can be maximised in these cases by increasing the spatial resolution to produce effective results. An increase in spatial resolution is also effective generally, for enhancing the chances of identifying archaeological features by discriminating between archaeological and geological anomalies as well as increasing anomaly definition and visualisation of small and subtle archaeological features. Seasonal tests have determined that Irish soils are generally suitable for year round earth resistance assessments although some counties in the southeast of the country may experience very dry soils at the surface during some periods of the year. A variety of sampling strategies were used in the past, however it is now apparent that detailed assessments across the full length and width of a proposed road corridor are the most appropriate form of geophysical investigation. Magnetometer surveys are generally suitable for most Irish soils and geologies, although exceptions apply in areas of near-surface igneous deposits, deep peat and alluvial soils; however magnetometer surveys are not capable of identifying all types of archaeological features and other methods will be required for a full evaluation. Analysis of the Legacy Data has determined that in general the NRA archaeological geophysical surveys were historically used in a very positive way on road schemes. The range of features assessed or identified account for most types of archaeological sites in Ireland. These have provided a significant archive of case studies that will be of benefit to future archaeological geophysical research and will help to protect the globally dwindling archaeological resource that is threatened by development-led or commercially driven projects.

Earth is under constant influence of the Sun and phenomena driven by the solar wind that may affect man-made technology. These events are summarized under the concept of space weather. This creates variations in Earth’s magnetic field and nearby space. Space weather can affect power grids, gas pipelines and also have effects on human health. Due to these effects, as well as the scientific interest in space and the growing space industry, the need to monitor space weather, the space environment and how Earth is affected by them increases. Accurate magnetic mesurements rely on expensive magnetometers and careful calibration. Swedish Institute of Space Physics IRF, operates two magnetometers in Sweden, one observatory and one variometer to measure local geomagnetic variations. For the purpose of space weather, measurements of local variations have high demands on temporal resolution and precision but not the same need for long-term accuracy. The purpose of this thesis is to define and evaluate an autonomous system for local geomagnetic variations, with future hopes of creating a network of systems for space weather monitoring. The future goal is to be able to place systems in remote locations where they will be able to conduct measurements autonomously. The work was done by analysis and testing of a fluxgate magnetometer that was placed close to one of the IRFs existing magnetometers. Using data from the existing station as a reference, an analysis of the magnetometer could be performed. The results showed that the tested magnetometer had less precision than the existing station but could within a certain frequency range provide good results that make it possible to measure the local geomagnetic variations that may be of use for space weather. Conclusions from this study show that it is possible to create a simpler autonomous system for measurements of the local geomagnetic variations, but that this system requires further development, where future work can be based on this degree project as a basis. / Jorden är under konstant påverkan av solen och fenomen drivna av solvinden som kan påverka mänsklig teknologi. Dessa event sammanfattas under begreppet rymdväder. Genom detta skapas variationer i Jordens magnetfält och närliggande rymd. Rymdväder kan påverka kraftnät, gasledningar och även ha effekter på mänsklig hälsa. På grund av dessa effekter samt det vetenskapliga intresset för rymden och den växande rymdbranschen ökar behovet av att övervaka rymdväder, rymdmiljön samt hur Jorden påverkas av de. Exakta magnetiska mätningar är beroende av dyra magnetometrar och nogrann kalibrering. Institutet för Rymdfysik IRF driver två magnetometrar i Sverige, ett observatorium och en variometer för att mäta lokala geomagnetiska variationer. Då mätningar av lokala variationer har höga krav på temporal upplösning och precision men inte samma behov av kontroll på långsiktig noggrannhet. Syftet med det här examensarbetet är att definiera och utvärdera ett autonomt system för lokala geomagnetiska variationer, med framtida förhoppningar om att skapa ett nätverk av system för övervakning av rymdväder. Framtidsmålet är att kunna placera ut system på avlägsna platser där det autonomt ska kunna bedrivas mätningar. Arbetet gjordes genom analys och tester med en fluxgate-magnetometer som placerades i närheten av en av IRF befintliga magnetometrar. Med data från den existerande stationen som referens kunde en analys av magnetometern utföras. Resultatet visade att den testade magnetometern hade mindre precision än den befintliga stationen men kunde inom ett viss frekvensspann förse goda resultat som gjorde det möjligt att mäta de lokala geomagnetiska variationerna som kan vara till nytta för rymdväder. Slutsatser från denna studie visar att det är möjligt att skapa ett enklare autonomt system för mätningar av de lokala geomagnetiska variationerna men att detta system kräver vidare utveckling, där framtida arbete kan utgå från resultaten som erhölls i detta examensarbete.

A way to obtain materials that show novel phenomena is to explore the interplay between geometry and interactions. When it is not geometrically possible to satisfy all the interactions by a given configuration, then to find the ground state becomes very complicated. This interplay between geometry and interactions defines geometrical frustration. One of the most popular examples of geometrical frustration in magnetism is spin ice. In this system, nearest neighbour ferromagnetic interactions between Ising spins in a pyrochlore structure emulate water ice by showing the same degree of frustration. This is manifested by the same ground state residual entropy. Although the clearest example of spin ice among magnets is shown by Dy₂Ti₂O₇, the behaviour of this material is richer than that of pure spin ice. The large magnetic moments of the rare earth Dy form a spin ice that also interacts via dipolar interactions. These long range interactions give rise to monopolar excitations which dramatically affect the dynamics of the system with respect to the pure spin ice case. In this thesis magnetisation experiments and numerical methods are used to explore the properties of the magnetic insulator Dy₂Ti₂O₇. We study its excitations at low temperature and describe the out-of-equilibrium characteristics of the magnetisation processes, below a temperature where the system freezes out. For temperatures above the freezing temperature, we describe and measure a 3D Kasteleyn transition and the concomitant Dirac strings associated to it, for the field in the [100] crystallographic direction. For temperatures below the freezing temperature, we find new out-of-equilibrium phenomena. Magnetic jumps are measured and their sweep rate dependence analysed. A deflagration theory is proposed and supported by simultaneous magnetisation and sample temperature measurements obtained by a new design of a Faraday magnetometer.

Nous avons évalué les performances et limitations de différents capteurs susceptibles d’aider à orienter un déficient visuel : GPS, magnétomètre, gyroscope, accéléromètre, baromètre ainsi que la façon de les combiner pour guider efficacement les déficients visuels dans trois contextes différents : le milieu urbain, la randonnée et les intérieurs. Nous avons réalisé des prototypes se plaçant sur la hanche ou tenus à la main fournissant une information présentée sous la forme d’un cap et d’une distance au point à atteindre. Cette information se réactualise en temps réel en fonction des changements de position ou d’orientation de la personne.Nous avons montré par des tests en situation réelle sur des parcours urbains et pédestres de plusieurs kilomètres, effectués par différents déficients visuels, l’efficacité de cette approche très différente de celle du guidage automobile. Les tests ont été également effectués dans des zones où les capteurs sont perturbés : forêts denses ou rues avec des bâtiments hauts (signal GPS perturbé), à proximité des lignes électriques (magnétomètre perturbé), etc. Le cas le plus complexe est celui des intérieurs (stations du métro, centres commerciaux) où le signal GPS est absent. Notre approche ne fait appel à aucun équipement du lieu (de type bornes Bluetooth ou Wifi) et utilise uniquement une cartographie préalable ou relevée sur le site. Nous sommes parvenus à des guidages fonctionnels sur quelques centaines de mètres sous certaines conditions : entrainement de l’utilisateur afin d’assimiler les spécificités du langage de la locomotion utilisé pour le guidage et apprentissage des stratégies de déplacement évitant le disfonctionnement de la centrale inertielle. Nous sommes en mesure de proposer à l’issue de ce travail un outil pouvant être diffusé auprès des utilisateurs avec des solutions fiables pour le milieu urbain et la randonnée. Pour les intérieurs les développements complémentaires se poursuivent et ne seront proposés qu’en béta-test. Cet outil va également être proposé pour initier les déficients visuels non autonomes à des randonnées simples afin de tenter de faire naître l’envie d’améliorer son autonomie. / We have evaluated the possibilities and the limitations of different sensors able to help to the orientation of the visually impaired: GPS, magnetometer, gyroscope, accelerometers, and barometers and also the way to mix their information for guiding efficiently the visually impaired in three different contexts: urban areas, hiking and indoor areas. We have implemented some belt mounted and hand held prototypes giving the information in the way of “heading” and “distance” to the destination to reach. This information is updated in real time taking into consideration the change of the position and orientation of the person. We have shown, during real situation tests, in urban pedestrian paths and hiking circuits of many kilometers done by different visually impaired people, the efficiency of this approach which is very different to the car navigation. The tests have been run including zones where the sensors data is perturbed: dense forest or big buildings in urban areas (GPS signal perturbed), proximity to electrical lines (magnetometer data perturbed), etc. The most complicated case is the indoor navigation (metro stations and commercial centers) where the GPS signal is not available. Our approach does not require any equipment apparatus in the building (such as Bluetooth or Wi-Fi hotspots) and uses just a previous cartography or a cartography done in situ. We have achieved functional guidance in few hundred meters under certain conditions: the training of the user in order to make him understand the specific characteristics of the mobility language used for the navigation and the learning of the strategies of displacement in order to avoid the failure of the Inertial Measurement Unit (IMU). We are in position to offer, at the end of this work, one tool which can be distributed to the users with reliable solutions for the urban areas and the hiking. For the indoor navigation, complementary development is carrying on and it will be proposed just like beta-test version. This tool is also going to be proposed for initiating non-autonomous visually impaired people to easy treks in order to try to make them want to improve their autonomy.