Analysis of a two-degree-of-freedom beam for rotational piezoelectric energy harvesting

This study introduces a two-degree-of-freedom piezoelectric energy harvester designed to harness rotational motion as an energy source. The harvester is built using a cut-out beam, which enables the first two resonant frequencies to be closely located in the low-frequency range. A distributed continuous model is developed and validated with experimental results. As the beam undergoes significant displacement due to rotational excitations, the geometric nonlinearity arising from longitudinal displacement is considered in the model to enhance its accuracy. It is observed that as the rotating speed increases, the increased centrifugal force causes the first resonant frequency to rise while the second resonant frequency decreases. The rotation-specific mode veering and the interchange of the first two modes are discussed. This study explores the potential to expand the bandwidth of the harvester using two types of nonlinear external force, namely mechanical stoppers and magnetic force. The results indicate that the proposed harvester can broaden the bandwidth of the first and second resonant frequencies. This research addresses the gap of combining multimodal and nonlinear force methods in rotational piezoelectric energy harvesting.