Snap-through energy harvester with buckled mechanism and hierarchical auxetic structures for ultra-low-frequency rotational excitations

In this Letter, a snap-through energy harvester is proposed to break through the energy output bottleneck of ultra-low-frequency (<1 Hz) rotational energy harvesting. On one hand, a buckled mechanism provides large-amplitude snap-through motion that enhances the output power. On the other hand, the hierarchical auxetic structures enable the simultaneous operation of d31 and d32 modes of piezoelectric buzzers and boosts the energy harvested. Moreover, both the buckled mechanism and auxetic structures can reduce the fundamental natural frequency of the total system. A finite element model is established to predict the harvester performances, which are validated via experiments. Experimental results show that the integration of the buckled mechanism and auxetic structures can improve the output power by 3224.75% at 0.5 Hz. Specifically, the proposed harvester can achieve an output power of 146.2 μW and a normalized power density of 1.392 μW/mm3 Hz2 at 0.5 Hz, which are superior to other state-of-the-art rotational piezoelectric energy harvesters. Therefore, the proposed harvester can provide sufficient energy for low-power sensors at ultra-low rotational frequencies and has a great application potential in the structural health monitoring of wind turbine blades.