A compact architecture for passively-switched energy harvesters

This paper presents the design and experimental characterization of a compact parallel-beam architecture for low-frequency energy harvesters that switch passively among dynamical modes to extend their operational range. Two beams interact to generate power; a driving beam couples into low frequency vibrations, and a higher frequency generating beam outputs power upon impact by the driving beam. The system switches between modes in which the driving beam bounces off the generating beam (coupled motion) and modes in which the driving beam passes the generating beam (plucked motion). The compact structure is realized by mounting the generating beam within a U-shaped driving beam on a single support. A flexible tip is mounted inside the driving beam's U shape to enable robust interactions. This new architecture reduces system volume by 80% compared with an earlier model that has the same resonance frequency, but it also changes the flexible tip's role in the contact dynamics. The flexible tip is experimentally tailored to optimize performance. The harvester generates power over the measured range of acceleration from 0.2 g to 2 g and driving frequency from 5 Hz to 20 Hz. With one tip design, the harvester offers peak power of 0.267 mW with plucked operation covering 32% of the tested range. With a second tip design, the harvester offers a lower peak power of 0.036 mW with plucked operation covering 73% of the tested range.