Hybrid triboelectric-piezoelectric energy harvesting via a bistable swing-impact structure with a tuneable potential barrier and frequency-up conversion effects

This paper presents a novel piezoelectric-triboelectric hybrid energy harvester, which includes two sub triboelectric energy harvesters (sub-TEHs) working under the alternative impacts between a swinging structure and two plates, and a sub piezoelectric energy harvester (sub-PEH) whose motion is coupled with the swinging structure through magnetic repulsion. With this design, 1:2 frequency-up conversion is achieved for both the triboelectric energy harvesting and piezoelectric energy harvesting because of the nature of swing motion. The introduced magnets also induce bistability with a dynamically tuneable potential barrier to the swinging structure, which improves its ability to get across the barrier to form interwell motion. Through experimental investigation, the frequency-up conversion effect is demonstrated. It also shows that this energy harvester can effectively operate in a broad bandwidth and exhibits good robustness. The practical applications of the energy harvester are also experimentally validated by testing its energy harvesting performance under water wave conditions, which performs well under such operating scenarios. Then, a theoretical model is established and its reliability is experimentally validated. Based on the model, the dynamic behaviours and energy harvesting performance of the energy harvester under different excitation parameters and system parameters are comprehensively investigated, showing that this device can effectively and broadly harvest energy from low-frequency ambient vibration.