11 April 2017 Design and experimental verification of an improved magnetostrictive energy harvester
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This paper summarizes and extends the modeling state of the art of magnetostrictive energy harvesters with a focus on the pick-up coil design. The harvester is a one-sided clamped galfenol unimorph loaded with two brass pieces each containing a permanent magnet to create a biased magnetic field. Measurements on different pick-up coils were conducted and compared with results from an analytic model. Resistance, mass and inductance were formulated and proved by measurements. Both the length for a constant number of turns and the number of turns for a constant coil length were also modeled and varied. The results confirm that the output voltage depends on the coil length for a constant number of turns and is higher for smaller coils. In contrast to a uniform magnetic field, the maximal output voltage is gained if the coil is placed not directly at but near the fixation. Two effects explain this behavior: Due to the permanent magnet next to the fixation, the magnetic force is higher and orientates the magnetic domains stronger. The clamping locally increases the stress and forces the magnetic domains to orientate, too. For that reason the material is stiffer and therefore the strain smaller. The tradeoff between a higher induced voltage in the coil and an increasing inductance and resistance for every additional turn are presented together with an experimental validation of the models. Based on the results guidelines are given to design an optimal coil which maximizes the output power for a given unimorph.
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M. Germer, M. Germer, U. Marschner, U. Marschner, A. B. Flatau, A. B. Flatau, } "Design and experimental verification of an improved magnetostrictive energy harvester", Proc. SPIE 10164, Active and Passive Smart Structures and Integrated Systems 2017, 101643A (11 April 2017); doi: 10.1117/12.2263971; https://doi.org/10.1117/12.2263971

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