Enhancing piezoelectric energy harvesters with rotating triangular auxetic structures

The development of piezoelectric energy harvesters is currently constrained by factors such as output power, bandwidth, and natural frequency, which limit their capacity to efficiently capture the low-frequency vibrational energy prevalent in the environment. To address these challenges, this paper proposes a novel approach to enhance the performance of piezoelectric energy harvesters by integrating a rotating triangular auxetic structure. A method for analyzing the mechanical performance of the auxetic structure under lateral constraints is introduced, demonstrating that the structure exhibits favorable negative Poisson's ratio characteristics and design flexibility. Furthermore, the auxetic structure is incorporated into a cantilever beam piezoelectric energy harvester to design and fabricate a novel auxetic-enhanced energy harvester (AEH), alongside a plate substrate energy harvester (PEH) for comparison. Finite element method (FEM) simulations and experimental results show that the auxetic structure increases the average stress in the piezoelectric patch, creating a distinct negative Poisson's ratio region. Under varying geometric parameters and unit cell numbers, the proposed AEH outperforms the conventional PEH, with output power improvements ranging from 96.3 % to 266.1 %, and reductions in natural frequency between 15.35 % and 42.65 %. By appropriately selecting geometric parameters, the AEH also broadens the energy harvesting bandwidth. This enhancement makes the AEH particularly well-suited for capturing low-frequency vibrational energy from the environment. The large negative Poisson's ratio of the auxetic structure, as demonstrated in this study, contributes to an increased energy density in the piezoelectric patch.