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

Abstract

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 ϕs and duration Δϕ can be adjusted. The control of ϕs and Δϕ allows to electrically adapt the dynamics of the electromechanical harvester. In a first part, we analytically derive the influences of ϕs and Δϕ 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 μW for vibration frequencies ranging from 90 to 140 Hz, under an external acceleration of 0.2 G.