Coil Optimization Unlocks 10-400x Gains in Thermomagnetic Waste-Heat Generators

A new preprint by Rasmus Bjørk models thermomagnetic generators (TMGs) by explicitly coupling magnetic and electric circuits, revealing that output power scales linearly with coil volume regardless of wire radius or turn count. The work is an analytical-numerical study validated against experimental data rather than a large empirical trial, so sample size is limited to existing literature prototypes. Because it remains an unreviewed arXiv submission (May 2026), claims of immediate commercialization must be treated cautiously. The analysis shows that published TMG devices used coils far smaller than the optimum, capping performance by one to two orders of magnitude. Related experimental work on La-Fe-Si-based thermomagnetic materials (Kitanovski et al., 2023, Applied Thermal Engineering) and earlier coil-design studies in electromagnetic harvesters (Beeby et al., 2006, J. Micromech. Microeng.) suggests the same scaling law applies across solid-state thermal harvesters. Consequently, everyday devices such as IoT sensors or phone chargers could harvest usable power from processor or battery heat once coil volume is increased, lowering grid demand and extending battery life. Limitations include the assumption of ideal thermal cycling and neglect of mechanical fatigue in the active material, both of which will require long-term testing before deployment.