Thermal micro energy harvesting by thermomagnetic film actuation

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This project on “Thermal micro energy harvesting by thermomagnetic film actuation” investigates a novel approach to generate electrical energy from thermal energy on the miniature scale. It expands a precursor project at KIT, in which thermomagnetic generators (TMGs) have been developed, reaching average power densities of the active material of 118 mW cm-3 and 5% of Carnot efficiency. These specifications already compete with the best thermoelectric generators at the length scale of a centimetre and below. The current project addresses the key characteristics of a TMG: (1) Expansion of the usable temperature range to 30–100°C, (2) increase of electrical power, and (3) improvement of thermodynamic efficiency. As the performance of miniaturized TMGs is intimately connected with the functional properties of the thermomagnetic films used, this joint proposal brings together the complementary competence on microsystem engineering of KIT and thermomagnetic materials science of IFW.For optimization of TMG characteristics (1)-(3), the thermomagnetic properties of Ni-Mn-based Heusler and Ga-based films (transition temperatures, temperature-dependent change of magnetization, dM/dT, hysteresis) will be tailored by varying composition and degree of order. The design of the TMGs will be optimized by improving heat transfer, enhancing magnetic field gradient, as well as tuning mechanical resonance. In particular, for the improvement of heat transfer micromachined films will be applied, containing trenches filled by Cu. The scaling properties of TMG characteristics will be investigated experimentally, as well as by lumped element modelling. Based on the optimum scaling of a single TMG, distributed systems of 1D and 2D arrays of TMGs will be developed in order to bring the total power in line with the practical needs of IoT and industry4.0.