Robust flexural wave energy harvesting via topologically protected interface modes of defect-enhanced performance in a phononic crystal beam-foundation system

Abstract Topologically protected interface modes offer a novel approach to concentrate vibration energy in the structural interfaces with robustness to defects and disorders preserved, but seldom validated via high-frequency experiment. This paper proposes a flexural wave energy harvester driven by nanoscale-amplitude excitations, and both characterized via numerical simulation and ultrasonic experiment to verify the robust harvesting and defect-enhanced voltage output. The band structures and topological phase transitions are investigated in the designed elastically supported phononic crystal (PnC) beam. The band crossing point is shifted from 2670 Hz to 3982 Hz by an added elastic support, and then transformed to an extra bandgap by the adjustment of rubber pillar distance. The flexural wave energy at the interface of two substructures are converted into the electrical energy via piezoelectric disc efficiently. Specifically, the introduction of section defects and spring disorder highlight the exceptional topological robustness to preserve energy harvesting performance. A novel and feasible route about intelligent control is provided to actively tune the operational frequency by adjusting the support spring stiffness. Compared to the plain beam, the topological beam yields 11.51 and 9.19 times higher output voltages with and without section defects, respectively, which indicates the reliable high-performance design strategy of defect-tolerant PnC energy harvesters. Studies demonstrate that rather than acting as limitations, designed defects can be strategically exploited to enhance localization and thereby improve energy harvesting.