Triggering high-energy orbits in rotational nonlinear energy harvesters via time-varying external excitation and internal parameter modulation

The nonlinear dynamics of rotational piezoelectric energy harvesters can enhance power output and broaden the operational bandwidth. However, their practical application is severely constrained by uncontrollable switching between the high-energy orbit (HEO) and low-energy orbit (LEO) induced by nonlinearity and time-varying effects. In addition, centrifugal effects significantly raise the energy threshold required for the harvester to reach the HEO state. To address these challenges, this study proposes an HEO-excitation strategy that combines time-varying external excitation with internal system parameter modulation, enabling synergistic improvements in both power output and operational bandwidth. First, an analytical model of a centrifugal-force-affected rotational harvester is established. A representative nonlinear rotational piezoelectric energy harvester is then designed, and its theoretical model is derived using the method of multiple scales. Next, HEO excitation is investigated through two mechanisms: external rotational frequency modulation and internal electrically induced damping modulation. The corresponding orbit-jump behaviors and performance enhancement effects are validated experimentally. For implementation, rotational frequency modulation is realized through a motor controller, while electrically induced damping modulation is achieved using a bidirectional energy conversion circuit. By inducing and stabilizing the HEO state, the proposed method achieves a maximum 911% increase in output power and a 62.5% expansion of the operational bandwidth. In addition, the harvester operating in the HEO state enables self-powered LoRa-based wireless temperature sensing. Through coordinated parameter modulation, this work presents a new strategy for rotational energy harvesting, providing an effective route for HEO excitation and self-powered sensing.