Self-oscillation and heat management in a LaFeSi based thermomagnetic generator

•Waste heat energy harvesting.•Autonomous thermomagnetic generator.•Self-actuating devices.•Phase portrait analysis.•Caloric materials for energy conversion. Harvesting and directly converting the largely untapped and omnipresent low-grade heat into electricity has huge technological potential for supplying internet of things (IoT) devices, and wireless sensors in smart buildings applications. To this end, we present a self-actuating, autonomous, thermomagnetic generator (TMG) showing state-of-the-art net power output 4.2μW (240μW cm−3), working over a 35.1 °C temperature difference. The core of our design is made of cheap and easily available piezoelectric buzzers and of commercial LaFeSi magnetocaloric materials from Vacumschmelze. The device self oscillating cycle is studied as a dynamical system with particular attention to the interplay between mechanical and thermal dynamics.