Optimization of compact electromagnetic energy harvesters for wireless sensor applications

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2017
Yaşar, Oğuz
The developments in wireless sensor systems force researchers to analyze how to satisfy power requirements of these systems. Batteries can be the main candidate to be used as power source; however, they affect negatively the continuity of the wireless systems due to their limited lifetime. In order to provide continuous power source, energy harvester modules are proposed. With the advancements on IC technology, it is possible to convert extracted energies to power sources for the sensors operating in wireless environments. Therefore, the optimized design of the harvester to generate desired power for wireless sensor nodes is essential. The aim of this thesis study is to design, optimize, fabricate and test the electromagnetic (EM) energy harvesters to be used as power source for wireless systems. Since most of the vibrations in nature exist in low frequency levels (< 10 Hz), the proposed harvester should be capable of operating at low frequency and low amplitude vibrations. Additionally, the design should be compact enough is size; hence, device volume is limited with 8 cm3. This thesis study presents an optimization study for decreasing the operation frequency and increasing the output power of a miniature EM energy harvester. Incorporating a non-magnetic inertial mass (tungsten) along with the axially oriented moving magnets is the main strategy to reach optimum results. Dimensions of the magnets are optimized according to the harvester dimensions and magnetic flux gradients. Additionally, coil length, width, resistance and position have been optimized through finite element analysis (FEA) and experimentally validated. Simulation results show that using a single-magnet structure is not sufficient for increasing the output power of the system. Also, test results reveal that multi-magnet structures yield to higher output voltages and smaller resonance frequencies. Effects of the improvements on the moving structure are analyzed in detail and experimentally validated. The operation frequency of the harvester decreases with axially oriented moving magnets, while the output power increases due to greater magnetic flux contributions provided by repulsive forces. Compared to the single-magnet structure, a modified design with a similar size yields to a decrease in the resonance frequency (from 15 Hz to 7.2 Hz) and an increase in the output power. The optimized harvester has a volume of 7 cm3 and generates 0.53 VRMS, 266 µWRMS output power (@7.2 Hz and 0.5g peak acceleration). 

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Citation Formats
O. Yaşar, “Optimization of compact electromagnetic energy harvesters for wireless sensor applications,” M.S. - Master of Science, Middle East Technical University, 2017.