A compact dual-rotor wrist-worn energy harvester based on axial-flux topology for self-powered wearable devices

Human biomechanical energy is increasingly recognized as an ideal power source for wearable devices. To address the challenge of harvesting low-frequency kinetic energy from arm swing within the constrained space of the wrist, this paper proposes a compact, direct-drive electromagnetic energy harvester (EMEH) utilizing an axial-flux topology. Incorporating a dual-rotor, single-stator “sandwich” magnetic circuit structure and an eccentric inertia modulation strategy implemented by tungsten alloy, the device significantly enhances electromechanical conversion performance, achieving a 2.5-fold higher peak magnetic flux density and an approximate 2-fold increase in output power. An electromechanically-coupled theoretical model was established to explore the system behaviors and elucidate the mechanisms underlying large-amplitude nonlinear oscillations induced by higher-frequency excitations. Experimental results demonstrate that the device achieves an average power of 1.93 mW (273μW/cm³) at 1.5 Hz, and an instantaneous peak power of approximately 6 mW during running (7km/h). Furthermore, this energy harvester successfully powered a wireless sensing node, validating its potential as a sustainable power source for wearable Internet of Things (IoT) applications.