A new energy harvester design for high power output at low frequencies

•A new composite beam design is proposed for cantilever based energy harvesters.•A simple lumped parameter model is proposed for composite beam based energy harvester.•The design is demonstrated to be more efficient at energy harvesting at low operating frequencies.•Energy harvester is characterized using stopper at one side to increase the operating bandwidth. The energy harvesters (EHs) using resonant mechanism have encountered two major issues: low output power scavenged from low frequency vibrations, and limited effectiveness of harvesting mechanism in a narrow range near resonant frequency. To overcome these issues, we have proposed a piezoelectric EH comprising a composite cantilever and a proof mass at the free end. The composite cantilever is formed by a piezoelectric bimorph and a polymer beam (soft spring) mechanically connected along the longitudinal direction. Comparing with the resonant frequency of 275Hz of a standalone piezoelectric bimorph, the composite cantilever design enables the resonant frequency of the EH to be as low as 36Hz. Moreover, this kind of EH is demonstrated to be 3.12 times and 1.32 times (at 0.1g) more efficient at output power generation than a standalone piezoelectric bimorph and piezoelectric bimorph with a proof mass at the free end, respectively. With the aid of spring hardening effect, the operating bandwidth (BW) can be increased from 5Hz to 16.4Hz.