An enhanced nonlinear piezoelectric energy harvester with multiple rotating square unit cells

In this paper, a new method is proposed to enhance the performance of auxetic nonlinear piezoelectric energy harvesting by increasing the unit cell number of auxetic structure. This method is validated through an auxetic nonlinear piezoelectric energy harvester, which combines a clamped–clamped beam with multiple rotating square unit cells. On one hand, the key structural parameter of the square rotating unit cell is adjusted to obtain desired broad operating bandwidth. On the other hand, the number of the unit cell is increased to improve the output power of the proposed design with minor influence on the operating bandwidth. Therefore, by tuning the parameter and unit cell number, the proposed harvester can obtain both broad operating bandwidth and high output power, to reduce the trade-off between these two aspects in the previous auxetic nonlinear energy harvesters. FEM simulation is conducted to investigate the characteristics of the proposed design. A dynamic model is built to theoretically analyse the proposed harvester, which matches with the testing results well. In the experiments, under 0.3 g base excitation, the output power of the proposed harvester is enhanced by 77% as the unit cell number increases from single to 4 × 4, without obvious reduction on the operating bandwidth. In addition, the bandwidth and output power of the proposed harvester are increased by 14% and 268%, respectively, compared with the conventional nonlinear energy harvester.