  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 rotation-al piezoelectric
energy harvesting.
