An Impact‐driven Rotational Piezoelectric Energy Harvester Based on a Two‐Degree‐of‐Freedom Beam for Broadband Harvesting

The power output of traditional cantilevered piezoelectric energy harvesters is often constrained by their narrow harvesting bandwidth. To address this limitation, this study proposes an impact‐driven piezoelectric energy harvester featuring a folded beam structure and evaluates its performance in a rotating environment. The folded beam design has two closely spaced resonant frequencies, with the centrifugal force generated during rotation further narrowing the frequency gap. A theoretical model of the proposed harvester, formulated using Lagrange's equation, includes an impulse force term representing the impact when the beam contacts the stopper. The frequency responses of the folded beam were first analyzed and validated through base excitation experiments using a shaker to ensure model accuracy without centrifugal force or impact. Rotational excitation was then performed using a motor to evaluate the piezoelectric energy harvester's performance and validate the impact model under constant rotational speeds. Variations in beam dimensions and stopper spacing were also analyzed to understand their influences on voltage output. The findings demonstrate that the proposed harvester effectively achieves a broad harvesting bandwidth. Adjusting structural parameters primarily shifts the peak output frequency, while reducing the stopper spacing broadens the bandwidth, albeit with a slight reduction in peak voltage.