Frequency tuning of piezoelectric energy harvesters thanks to a short-circuit synchronous electric charge extraction

This paper introduces a new electrical strategy for maximizing the energy scavenged from highly coupled and lowly damped piezoelectric energy harvesters (PEHs). The proposed strategy named Short-circuit synchronous electric charge extraction (SC-SECE) introduces a SC phase whose start time ϕ s and duration Δ ϕ can be adjusted. The control of ϕ s and Δ ϕ allows to electrically adapt the dynamics of the electromechanical harvester. In a first part, we analytically derive the influences of ϕ s and Δ ϕ on the harvester dynamics, and prove that they both affect the damping induced by the electrical interface on the mechanical resonator and its resonant frequency. Thereafter, we numerically evaluate the SC-SECE performances as a function of the intrinsic harvester’s characteristics. We expose that if the coupling and/or mechanical quality factor of the harvester are important enough, the SC-SECE leads to enhanced power frequency responses compared to SECE and SEH strategies. Experimental results on a high coupling PEH associated with the SC-SECE strategy have been realized and are in good agreement with the analytical predictions. Under various vibrations amplitudes, the harvester’s resonant frequency has been tuned on a frequency range as large as 35% of its natural resonant frequency. We have been able to harvest more than 92 μ W for vibration frequencies ranging from 90 to 140 Hz, under an external acceleration of 0.2 G.