The presence of magnetic fields has increased significantly during the last hundred years due to technology development and increased consumption of electricity. Sweden follows recommended maximum values from the International Commission on Non-Ionizing Radiation Protection (ICNIRP), which are to prevent acute effects and are generally not exceeded in the environment. For long-term effects, such as increased cancer risk, today's knowledge is not sufficient to establish any limit values. The study aims to determine the variation of daily exposure of low-frequency magnetic fields in individuals with different occupations and living environments. Measurements of low-frequency magnetic fields were performed with an EMDEX-meter to get a 24-hour magnetic field exposure for ten test subjects. Measurement with an SMPS-meter was performed to measure magnetic fields at some common objects in the home environment that emit low frequency magnetic fields. The average value for exposure of low-frequency magnetic fields for 24-hours varied between 0.03–0.10 µT, exposure in the home environment varied between 0.00–0.17 µT, working environment varied between 0.02–0.27 µT, night environment varied between 0.00–0.09 µT. The daily mean values from the measurements are at what can be regarded as a normal exposure 0.01–0.20 µT. The average value that was picked up from home-, joband night-environment can be considered as normal exposure level. Based on the increased presence of electronics and magnetic fields and the lack of knowledge in the research on health effects, it may be interesting to discuss the introduction of further new technology, limit values, safety and supervision.

I och med att båtar har med tiden blivit allt mer tystare både akustiskt och magnetiskt, är det av stort intresse att mäta den elektriska signaturen. Den elektriska signaturen uppstår fram för allt från den galvaniska effekten mellan båtens skrov och propeller och ger upphov till en potentialskillnad. Denna potentialskillnad propagerar i vattnet med en väldigt låg frekvens (0-3kHz). Med hjälp av specifika undervattensensorer kan dessa signaturer mätas för att detektera och lokalisera båtar. Varje sensor måste kalibreras i dess rätta omgivning (vatten) på grund av deras individuella geometri. För kalibreringen behövs ett känt homogent elektrostatiskt fält användas som referens. Examensarbetet avser att modellera den faktiska vattentanken som är tänkt som kalibreringsanläggning för sensorerna och simulera det elektrostatiska fältet som uppstår. Examensarbetet har ett ingående tillvägagångsätt för hur modellen och simuleringen implementeras i COMSOL Multiphysics® 5.5 som baseras på den finita elementmetoden (FEM). Ett teoretisk homogent elektriskt fält är svårt konstruera i verkligheten, därför är examensarbetet huvudsyfte att analysera homogeniteten för praktiska elektriska fält som finns i vattentanken. Olika konfigurationer av hur laddningsplattor fördelas simulerades och analyserades. Den väsentliga slutsatsen från simuleringarna är att homogeniteten på det elektriska fältet är bra så länge laddningsplattorna är symmetriska mot varandra men på en bekostnad av att fältstyrkan minskar. Examensarbete inkluderar även simuleringar hur undervattensensorn i sig själv påverkar det elektriska fältet som den skall kalibreras i, sensorn introducerar en störning. Slutligen finns det förslag för förbättring av arbete och förslag för ett fortsatt arbete. / With time, boats have become more quiet, both acoustic and magnetic. Therefore, it is of great interest tomeasure the electric signature. The electric signature is a low-frequency (0-3 kHz) electric field generatedby a potential difference that appears due to the galvanic effect between the boat's hull and propeller.With assistance from specific under-water sensors, these signatures can be measured to detect andlocalize boats. Due to the individual geometry of the sensors, each sensor must be calibrated in its rightenvironment (water). To perform this, a known homogeneous electrostatic field must be used forreference. This master Master-degree project purpose is to modulate a water tank, which is supposed to beused as a calibration facility for the sensors and simulate the electrostatic field that will evolve. Thisproject presents the approach for how the model and simulation will be implemented in COMSOLMultiphysics® 5.5, which is based on the finite element method. A theoretically homogeneous electricfield is difficult to build in reality, hence this project main objective is to analyse the homogeneity forpractical electric fields in the water tank. Different electric fields were analysed depending how the metalplates were distributed. The main conclusion from the simulations is that the homogeneity on theelectrical field is good enough to use for calibration purposes. The plates shall to be symmetricallydeployed with respect to each other. A drawback is that the field strength decreases when parts of thefield diverts. This project also simulates how the under-water sensor itself affects the electrical field it issupposed to be calibrated in; the sensor introduces disturbances to the field. Finally, this report proposesseveral improvements as well as direction for further work.

Energiskördning är idag ett växande område och är framstående sett till hållbarhetsaspekterna. Vibrationsbaserad sådan har blivit allt populärare där man kan utnyttja mekanisk energi från olika källor till att generera elektrisk energi. Piezoelektricitet fungerar enligt denna princip och piezoelektrisk energiskördning har varit ett område som fler och fler utnyttjar på grund av dess effektivitet, exempelvis till trådlösa sensornätverk. Ett krav på att piezoelektrisk energiskördning ska fungera optimalt är att vibrationerna sker med en satt frekvens utan större variation, ofta i väldigt höga frekvenser. Syftet med detta projekt är att anpassa denna teknik till mänskliga rörelser vilket kan göra den mer användbar och ett tänkt ändamål kan vara ett demonstrationsexempel för oregelbundna rörelser vid låga frekvenser, precis som mänskliga rörelser. Utmaningen lägger därmed i att utveckla en piezoelektrisk energiskördare som har ett frekvensområde inom mänskliga rörelsers frekvenser på 4 till 7 Hertz, där effektiviteten fortfarande kan vara hög. Detta har beprövats med vibrationsplatta. Vad som observerades var att med flera piezoelektriska material på konsolbalkar i kolfiber av olika dimensioner med olika vikter längst ut, uppstod ett frekvensområde inom mänskliga området med höga spänningar. För att göra det möjligt behövdes vikterna ha en stor massa av upp till hundratals gram så att resonansfrekvenserna kunde vara inom nämnt frekvensområde. Då piezoelektriska material ger en växelspänning, måste spänningen likriktas. Detta gjordes med två olika gränssnitt med ett mönsterkort tillverkat för vardera. Dessa gränssnitt är ett klassiskt som helt enkelt likriktar spänningen, medan den andra, Parallel Synchronized Switch Harvesting on the Inductor (P-SSHI), ska maximera spänningen och effekten. Det visade sig att det inte blev lika lyckat som planerat. Det klassiska gränssnittet gav en likspänning som var nästan lika hög som den inmatade växelspänningen medan det inte gällde för P-SSHI. / Today energy harvesting is an area on the rise and is outstanding in regards to the environmental aspects. Vibration based energy harvesting has become popular where it uses mechanical energy from different sources to produce electrical energy. Piezoelectricity operates according to this principle and piezoelectric energy harvesting has been an area more are using because of its efficiency, with applications such as wireless sensor networks. One demand for piezoelectric energy harvesting to work optimally is that the vibration source must have a well known frequency with minor deviations and this in usually very high frequencies. The purpose of this thesis is to adapt this technology to human motions which could make it even more useful and a proposed usage is a demo product for irregular motions of low frequency, just like human motions. The challenge is hence to create a piezoelectric energy harvester which has a frequency range within the human motions’ frequencies of 4 to 7 Hertz, where the efficiency still could be high. This has been tested using a vibration exciter. What was noticed was that with multiple piezoelectric materials on cantilever beams of carbon fibre with different dimensions and tip masses, a frequency range within human range with high voltages could be created. To make this possible, the masses needed to have a significant mass of up towards hundreds of grams in order for the resonance frequencies to be within the stated frequency range. As the piezoelectric materials provide an AC voltage, the voltage needs to be rectified. This was done with two different interfaces with a PCB created for each. These interfaces are a classic one which simply rectifies the voltage, while the other, Parallel Synchronized Switch Harvesting on the Inductor (PSSHI), is supposed to maximize the voltage and power. This did not turn out to be as successful as predicted. The classical interface delivered a DC voltage almost as much as the provided AC voltage while the P-SSHI interface did not.

Geomagnetic disturbances that result from solar activities can affect technological systems such as power networks. They may cause DC currents in power networks and saturation of the core in power transformers that leads to destruction in the transformer performance. This phenomena result in unwanted influences on power transformers and the power system. Very asymmetric magnetization current, increasing losses and creation of hot spots in the core, in the windings, and the metallic structural parts are adverse effects that occur in transformers. Also, increasing demand of reactive power and malfunction of protective relays menaces the power network stability. Damages in large power transformers and blackouts in networks have occurred due to this phenomenon. Hence, studies regarding this subject have taken the attention of researchers during the last decades. However, a gap of a comprehensive analysis still remains. Thus, the main aim of this project is to reach to a deep understanding of the phenomena and to come up with a solution for a decrease of the undesired effects of GIC. Achieving this goal requires an improvement of the electromagnetic models of transformers which include a hysteresis model, numerical techniques, and transient analysis. In this project, a new algorithm for digital measurement of the magnetic materials is developed and implemented. It enhances the abilities of accurate measurements and an improved hysteresis model has been worked out. Also, a novel differential scalar hysteresis model is suggested that easily can be implemented in numerical methods. Two and three dimensional finite element models of various core types of power transformers are created to study the effect of DC magnetization on transformers. In order to enhance the numerical tools for analysis of low frequency transients related to power transformers and the network, a novel topological based time step transformer model has been outlined. The model can employ a detailed magnetic circuit and consider nonlinearity, hysteresis and eddy current effects of power transformers. Furthermore, the proposed model can be used in the design process of transformers and even extend other application such as analysis of electrical machines. The numerical and experimental studies in this project lead to understanding the mechanism that a geomantic disturbance affects power transformers and networks. The revealed results conclude with proposals for mitigation strategies against these phenomena. / <p>QC 20150210</p>