Multimode auxetic piezoelectric energy harvester for low-frequency vibration

Abstract Herein, we propose a piezoelectric energy harvester (PEH) capable of vibrating in multi-degrees-of-freedom. The resonant frequency, working bandwidth, and output power of the PEH were improved by introducing an auxetic structure (AS). The proposed PEH exhibited a symmetric serpentine structure with a doubly clamped configuration comprising several proof masses at the junctions. Finite element method (FEM) simulation was conducted to investigate the characteristics of an AS PEH and a plain-structure PEH. Prototypes of the PEHs were manufactured by three-dimensional (3D) printing technology, and their performance was evaluated through vibrational energy-harvesting experimental tests. The results showed that introducing the AS reduced the first and second resonant frequencies by 49% and 44%, respectively, considerably improved the output power in the first mode (up to 2548%) and narrowed the frequency bandgap between the first two resonance modes by 29%. The proposed multimode AS PEH can operate in a low-frequency environment of less than 20 Hz. Finally, we discussed several ways of optimizing the AS. It has been found that the PEH performance could be further improved by selecting a reasonable thickness for the AS, increasing the number of periodic unit cells, and using an AS with a variable cross-section unit cell.