A thermal energy harvester using LaFeSi magnetocaloric materials

A thermomagnetic generator (TMG) using an Halbach structure as a field source and a first order LaFeSi magnetocaloric material (MCM) from Vacuumschmelze as active substance, is presented. The MCM, suspended on a cantilever beam self oscillates between a hot source and a heat sink. The mechanical energy associated with the oscillation is harvested and converted into electricity using piezoelectric materials. This system is working between a 18°C cold end, and a 56°C heat source (i.e. over a temperature difference between reservoirs ∆Tres = 38°C) and shows a power of 0.12µW (6.8 µW per 1 cm 3 of MCM). We present and discuss a detailed analysis of the thermodynamic cycle underpinning the device mechanism, relying on direct measurements on the working prototype and on a full laboratory characterization of the MCM. Although our system shows a state-of-the-art power output, our analysis gives useful clues towards further performance improvements.