Optimization of the Performance of Bimorph Piezoelectric Energy Harvesters with Honeycomb Metamaterials Using Artificial Neural Networks and NSGA-II

Honeycomb-based metamaterials have recently attracted considerable interest for their potential in energy-harvesting applications. In this paper, we focus on two types of bimorph harvesters incorporating honeycomb substrates with positive and negative Poisson’s ratios (PPR and NPR). The substrates are coupled with piezoceramic (PZT) layers to enable electromechanical conversion. To improve energy-harvesting efficiency, we propose an optimization framework that integrates finite element (FE) simulations for data generation, a pretrained neural network for rapid performance prediction and the NSGA-II evolutionary algorithm for multiobjective optimization. The proposed strategy enables the identification of optimal geometric parameters of the honeycomb cells, particularly for cantilever resonators where the fundamental vibration modes are critical and must be tuned to specific eigenfrequencies for engineering applications. The optimization is applied to an initially unoptimized bimorph harvester with a honeycomb substrate. The simulation results indicate that an optimized harvester with an NPR metamaterial substrate can increase the power-to-mass ratio at a resonance frequency of 160 Hz by approximately 14.72% compared to the unoptimized honeycomb harvester. Moreover, compared to a harvester with a solid substrate, the improvement reaches 5%. Furthermore, a life cycle analysis was conducted, showing that the honeycomb substrate can significantly increase the operational lifetime of the piezoceramic layer. This improvement arises because the honeycomb substrate reduces the equivalent stress on the active layer. At high acceleration levels, the predicted operational lifetime is enhanced by more than tenfold compared to the solid substrate, since the PZT material is brittle and lacks flexibility. This improvement is notable because it surpasses the typical lifespan of both standard button batteries and rechargeable batteries highlighting a strong potential of this design for future applications.