Tunable elastic wave energy localization and harvesting in phononic crystals with decoupled double incomplete line defects

Using phononic crystals (PnCs) to enhance the electrical performance of piezoelectric energy harvesting (PEH) devices is an effective strategy for enabling self-powered operation in low-power electronic systems. Building on prior studies of PnCs with incomplete line defects, this study proposes a PnC with decoupled double incomplete line defects. In the upper (y-direction) subsystem, the defect was extended stepwise from the second to the sixth supercell layer, while the other subsystem was kept fixed, yielding five supercells. Their dispersion relations, elastic wave localization, and energy harvesting characteristics were systematically examined. All supercells exhibited effective decoupling between the two subsystems. As the size of defects in the upper subsystem increased, the total system's electrical performance first increased and then decreased. Specifically, when the defect extended to the fourth layer, the total system reached its optimum, yielding 17.58 mW of output electric power and representing a 349-fold improvement compared with conventional materials. Furthermore, because incomplete line defects induce waveguide-localized coupling modes, an efficient, tunable, relatively broad energy harvesting bandwidth of elastic waves was achieved by adjusting the subsystem's defect size. Therefore, a practical route is provided to optimize PEH electrical output and tune the operating frequency range through multi-defect PnC designs.