Broadband acoustic energy harvesting via topological edge and bulk states in phononic cavity chains

Topological phononic crystals (PnCs) offer innovative approaches for controlling acoustic waves, garnering significant attention owing to their potential for designing acoustic devices. In this work, we propose the topological PnC chains that achieve multimodal and broadband energy harvesting of acoustic waves through the synergistic effect of edge and bulk states. The phononic cavities support both the monopole- and quadrupolelike cavity modes that could be used for sound confinement and amplification. Based on Su-Schrieffer-Heeger model, the phononic cavity chain is designed, where the cavity coupling can be described by the tight-binding model with long-range couplings. By adjusting the coupling strength between phononic cavities, the system transitions from the topologically trivial phase to the nontrivial one, thereby generating topological edge states (TESs) and broadband bulk states (BSs). Two phononic chain configurations are constructed to generate TESs and BSs, which are validated by full-wave simulations and experimental measurements. The PVDF films are placed at the edge and bulk of the phononic cavity chain for piezoelectric energy harvesting. Compared with the reference harvester, both the TESs and BSs of the PnC structure exhibit much higher electrical outputs, achieving efficient broadband energy harvesting with a relative bandwidth exceeding 23%. The measured maximum area power density of the PnC structure reaches $0.00933\phantom{\rule{0.2em}{0ex}}\text{\ensuremath{\mu}}\mathrm{W}/({\mathrm{cm}}^{2}\phantom{\rule{0.2em}{0ex}}{\mathrm{Pa}}^{2})$, which is approximately 100 times higher than that of the reference structure. Furthermore, the experiments confirm the robustness of the TESs against structural disorders.