Compact passively self-tuning energy harvesting for rotating applications

Abstract

This paper presents a compact, passive, self-tuning energy harvester for rotatingapplications. The harvester rotates in the vertical plane and is comprised of two beams: arelatively rigid piezoelectric generating beam and a narrow, flexible driving beamwith a tip mass mounted at the end. The mass impacts the generating beamrepeatedly under the influence of gravity to drive generation. Centrifugal force fromthe rotation modifies the resonant frequency of the flexible driving beam andthe frequency response of the harvester. An analytical model that captures theharvester system’s resonant frequency as a function of rotational speed is used toguide the detailed design. With an optimized design, the resonant frequency ofthe harvester substantially matches the frequency of the rotation over a widefrequency range from 4 to 16.2 Hz. A prototype of the passive self-tuning energyharvester using a lead zirconate titanate generating beam achieved a power density of30.8 µW cm−3 and a more than 11 Hz bandwidth, which is much larger than the 0.8 Hz bandwidthcalculated semi-empirically for a similar but untuned harvester. Passive tuning was alsodemonstrated using the more robust and reliable but less efficient polymer polyvinylidenefluoride for the generating beam.