A monostable hybrid energy harvester for capturing energy from low-frequency excitations

Efficient energy extraction from ubiquitous low-frequency excitations is still an open problem due to the high challenge in constructing an energy harvester with sufficiently low resonant frequency. To address this problem, this article reports a monostable hybrid energy harvester that consists of a piezoelectric power unit and an electromagnetic power unit. The proposed hybrid energy harvester can capture energy simultaneously from one excitation through the two power units. Theoretical models for the monostable hybrid energy harvester are established, and theoretical results fit well with the experimental measurements. Under a harmonic excitation with amplitude of 0.5g (g = 9.8 m/s(2)), the power output of the monostable hybrid energy harvester is experimentally measured to be 0.39 mW, which is obviously higher than that (piezoelectric unit: 0.25 mW; electromagnetic unit: 0.3 mW) produced by the individual power units when they work separately. More importantly, compared with the linear hybrid energy harvester, the monostable hybrid energy harvester has an operating frequency range that is shifted toward the lower frequency and achieves a slightly enhanced peak power, making the monostable hybrid energy harvester well suited for harnessing low-frequency excitations. In addition, employing two transduction mechanisms to synchronously and parallelly generate electricity from ambient excitations, the monostable hybrid energy harvester may also enjoy improved reliability and robustness.