A hybrid energy harvester with dual-frequency-up-conversion mechanism for ultra-low frequency rotational motion under 1.5 Hz

This paper proposes a hybrid energy harvester (HEH) based on dual-frequency-up-conversion mechanism, which is suitable for ultra-low frequency rotation. This mechanism takes full advantage of the periodic excitation provided by gravity to achieve two harvesting responses in one cycle. HEH consists of the piezoelectric energy harvester (PEH) and electromagnetic energy harvester. The magnet component achieves frequency up-conversion of PEH by impact, and also induces electrical energy from the coil, thus coupling two parts together to form continuous energy harvesting. The electromechanical coupling model of HEH is established, and the characteristics are in-depth analyzed via experiments and simulations. PEH can attain a bandwidth of 1.4 Hz with an open-circuit output voltage above 5.6 V, which indicates the frequency up-conversion helps the piezoelectric cantilevers to break through the resonance limit and obtain the higher output. HEH can combine the advantages of two energy harvesting parts, obtaining the maximum power of 6.598 mW under 1.5 Hz. The results show that the dual-frequency-up-conversion mechanism greatly improves the efficiency of energy conversion and HEH has the ability to power low-power sensors at ultra-low frequencies.