Energy harvesting of a frequency up-conversion piezoelectric harvester with controlled impact

Frequency up-conversion is an effective approach to increase the output power of a piezoelectric energy harvester (PEH). In this work, we studied a piezoelectric energy harvesting system, which converts low-frequency vibration from ambient sources to the resonant vibration of the PEH to improve the energy harvesting efficiency. The PEH includes two beams, a pair of rack and pinions, and a slider crank mechanism to retrieve energy from ambient low-frequency vibrations through impacts. The soft driving beam is subjected to a sinusoidal base excitation along the transverse direction. The piezoelectric bimorph undergoes both slow longitudinal motion as well as transverse vibrations. The transverse vibration of the bimorph is induced by impacts which is the vibration source to generate output power. The longitudinal motion of the bimorph is used to control the impact with the soft driving beam, which guarantees the harvester to pump in more kinetic energy from the driving beam. Using the discontinuous dynamic theory, the energy harvesting performance of the impact-controlled system was studied in period one and period two motions. The stability of periodic solutions was investigated and bifurcation diagrams of impact velocities, times and displacements were obtained. The harvested power of the piezoelectric beam versus the based excitation frequency was also obtained, and the results were compared to the power generation of a piezoelectric beam directly subjected to the base excitation along the transverse direction.