Harnessing ultra-low-frequency vibration energy by a rolling-swing electromagnetic energy harvester with counter-rotations

While ultra-low-frequency vibration is a common energy source, electromagnetic energy harvesting from such vibrations presents a challenge due to the low output performance caused by the slow variation of the magnetic field. In this work, we propose a rolling-swing electromagnetic energy harvester (RS-EMEH) that creates the counter-rotations between magnets and coils, thereby amplifying the magnetic field variation within a single cycle of ultra-low-frequency excitation. Simplified dynamic modeling, rigid-body simulation and finite-element analysis are performed to confirm its working mechanism. A unique alternating pole arrangement of magnets is adopted that enhances the output voltage by 2 times as compared to the traditional uniform pole arrangement. Moreover, the experiment of the RS-EMEH prototype validates the above simulation and demonstrates the positive correlation between electrical output and excitation in terms of both frequency (1.10 Hz to 1.50 Hz) and acceleration amplitude (0.05 g to 0.40 g). Further experiment shows that the harvested energy by the RS-EMEH can sustain the operation of a thermometer and calculator simultaneously for 161.3 s under the excitation at 0.4 g, 1.4 Hz for 92.6 s. Specifically, the RS-EMEH can provide milliwatt-level output at the walking speed ≤3.5 km/h, sufficient to power portable wireless low-power electronic devices. The findings of this work unveil the promising power generation and application potential of the rolling-swing electromagnetic energy harvesters for self-powered systems subject to ultra-low-frequency vibrations.