A Thermal Energy Harvester Using LaFeSi Magnetocaloric Materials

A thermomagnetic generator (TMG) using a Halbach structure as a field source and a first-order LaFeSi magnetocaloric material (MCM) from Vacuumschmelze as the 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 the piezoelectric materials. This system is working between an 18 °C cold end and a 56 °C heat source (i.e., over a temperature difference between the reservoirs \Delta T_{\mathrm{ res}} = 38\,\,^{\circ }\text{C} ) and shows a power of 0.12~\mu \text{W} ( 6.8~\mu \text{W} per 1 cm 3 of MCM). We present and discuss a detailed analysis of the thermodynamic cycle underpinning the device mechanism, relying on the 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 toward further performance improvements.