A novel auxetic metamaterial for enhancing piezoelectric energy harvesting performance

Piezoelectric energy harvesters are widely used for scavenging ambient vibrational energy in self-powered sensing systems, but their low output power and high natural frequencies limit practical application, especially under low-frequency excitation. To improve harvesting performance, this study proposes a novel rotating triangular auxetic metamaterial (NRTA) integrated near the clamped end of a cantilever beam to accommodate rectangular piezoelectric patches of different sizes. Analytical models are established for the NRTA under axial deformation and transverse bending, and a coupled bending-response model is developed for the cantilever beam incorporating the NRTA. Based on this structure, an auxetic metamaterial cantilever energy harvester (AEH) is designed, and its first-mode shape and electromechanical coupling behavior are numerically analyzed. Finite element simulations show that the NRTA increases the average stress in the piezoelectric layer and creates partial equivalent negative Poisson's ratio response regions on the patch. Prototype AEHs are fabricated and experimentally tested. Compared with a conventional plain-beam piezoelectric harvester (PEH), the AEH increases output power by 456.4 %–1375.9 % and reduces natural frequency by 7.76 %–24.7 % across the tested geometries. The AEH also successfully powers a temperature–humidity sensor under 0.2 g excitation. In addition, comparisons with four conventional metamaterial configurations demonstrate the superior energy harvesting performance of the NRTA. The proposed models and design strategy provide a useful basis for the analysis and optimization of metamaterial-based piezoelectric energy harvesters.