Analysis of thermal energy harvesting using ferromagnetic materials

•Ferromagnetic materials show a sharp change in their permeability near the Curie temperature.•A bias magnetic field permits changing the magnetic flux with the temperature.•The variable magnetic flux can be converted into electrical energy by using a coil.•Theoretical and experimental measurements show an energy density up to 7.35 μJ cm−3 K−2 cycle−1.•Optimization issues should focus on coil quality and global magnetic reluctance variation.

This Letter aims at giving a preliminary investigation of the thermal energy harvesting capabilities of a technique using the temperature-dependent permeability of ferromagnetic materials. The principles lie in the modification of the magnetic field caused by the variation of the permeability due to the temperature change, hence generating a voltage across a coil surrounding the circuit. The technique can be made truly passive by the use of magnets for applying bias magnetic field. Theoretical results, validated by experimental measurements, show a voltage output of 1.2 mV at optimal load of 2 Ω under 60 K temperature variation in 5 s (with a maximum slope of 25 K s−1). Further improvements, such as the use of low resistivity coil and magnet with high remnant magnetic field, indicate that it is possible to convert up to 7.35 μJ cm−3 K−2 cycle−1.