Thermal micro energy harvesting by thermomagnetic film actuation
Metallurgical, Thermal and Thermomechanical Treatment of Materials
Final Report Abstract
This project addressed the development of miniature-scale thermomagnetic generator (TMG) devices based on the principle of resonant self-actuation combining microsystems engineering (KIT) and thermomagnetic material science (HZDR). As the performance of a TMG is intimately connected with the functional materials used within, we developed guidelines for efficient and cost-effective thermomagnetic materials. From the large set of relevant materials we evaluated, we identified Heusler alloys as particular promising for microsystems. Accordingly, we optimized systematically Ni-Mn-Ga films by adding Cu and an additional heat treatment. This quaternary system allows tailoring the thermomagnetic properties over a broad range and disentangling the effects in changing the number of valence electrons through the addition of Cu, and the alteration of chemical order before and after heat treatment. A validated lumped element model (LEM) was developed to comprehensively describe the dynamic properties of TMG devices and to identify key performance parameters. The effect of scaling the active material volume was investigated in terms of increasing the film thickness and the number of devices operating in parallel. Upscaling the film thickness resulted in a substantial increase in electrical power per footprint by a factor of 3.4. Thus, TMG devices reached up to 50 μW/cm² with a mere 3 °C temperature change in the TM material. Additional studies identified the critical distance between parallel-operating TMG devices causing thermal cross-coupling. The minimal heat source temperature, at which the TMG device was capable to operate under resonant self-actuation conditions near room temperature, could be reduced down to ~50 °C by implementing TM films with decreasing Curie temperature while maintaining the large power output.
Publications
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Upscaling of Thermomagnetic Generators Based on Heusler Alloy Films. Joule, 4(12), 2718-2732.
Joseph, Joel; Ohtsuka, Makoto; Miki, Hiroyuki & Kohl, Manfred
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Coupling Effects in Parallel Thermomagnetic Generators Based on Resonant Self-Actuation. 2021 21st International Conference on Solid-State Sensors, Actuators and Microsystems (Transducers) (2021, 6, 20), 463-466. IEEE.
Joseph, Joel; Wehr, Mira; Miki, Hiroyuki; Ohtsuka, Makoto & Kohl, Manfred
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Efficient and affordable thermomagnetic materials for harvesting low grade waste heat. APL Materials, 9(1).
Dzekan, Daniel; Waske, Anja; Nielsch, Kornelius & Fähler, Sebastian
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Lumped Element Model for Thermomagnetic Generators Based on Magnetic SMA Films. Materials, 14(5), 1234.
Joseph, Joel; Ohtsuka, Makoto; Miki, Hiroyuki & Kohl, Manfred
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Thermal processes of miniature thermomagnetic generators in resonant self-actuation mode. iScience, 25(7), 104569.
Joseph, Joel; Ohtsuka, Makoto; Miki, Hiroyuki & Kohl, Manfred
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A Gd‐Film Thermomagnetic Generator in Resonant Self‐Actuation Mode. Advanced Functional Materials, 33(22).
Joseph, Joel; Fontana, Erika; Devillers, Thibaut; Dempsey, Nora M. & Kohl, Manfred
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Integration of Multifunctional Epitaxial (Magnetic) Shape Memory Films in Silicon Microtechnology. Advanced Functional Materials, 33(51).
Fink, Lukas; Kar, Satyakam; Lünser, Klara; Nielsch, Kornelius; Reith, Heiko & Fähler, Sebastian
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Power Generation by Resonant Self-Actuation. Karlsruhe Institute of Technology, 2023
Joseph, J.
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Resonant Self-Actuation Based on Bistable Microswitching. Actuators, 12(6), 245.
Joseph, Joel; Ohtsuka, Makoto; Miki, Hiroyuki & Kohl, Manfred
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Tailoring of thermomagnetic properties in Ni-Mn-Ga films through Cu addition. Journal of Alloys and Compounds, 966(2023, 12), 171435.
Fink, Lukas; Nielsch, Kornelius & Fähler, Sebastian
