Thermal-mechanical-electrical analysis of a nano-scaled energy harvester

Applying nanotechnology to efficiently harvest energy from ambient environment is of great importance owing to its broad application prospects. However, the mechanical analysis of harvesters, especially at the nano-scale, is challenging. This study establishes a general thermal-mechanical-electrical coupling model of a beam-type harvester to exactly depict the working performance of a harvester at the nano-scale. The model considers both the surface effect and flexoelectricity. The size-dependent thermal-mechanical-electrical coupling model is mathematically depicted by introducing an additional thin layer, whose material property is represented by a surface parameter. This model can be reduced to the classical cases if some specific assumptions are made. After the validation, a systematic numerical simulation is carried out for a PZT-5H/silicon composite harvester, which focuses on the performance improvement. The size-dependent property is evident when the surface layer-to-bulk thickness ratio is greater than approximately 10⁻². Correspondingly, a critical beam thickness that quantitatively distinguishes the surface effect from the macro-mechanical behaviors can be proposed if the surface parameter is determined. The proposed general model can be a useful tool to explain the inherent physical mechanism, structural design and eventually system optimization for harvesters both in the nano- and macro-scale.