Dynamic phenomena and analysis of MEMS capacitive power harvester subjected to low-frequency excitations

We study power harvesting using MEMS capacitors with single and dual air cavities that have been fabricated in our laboratory. Our goal is to achieve power harvesting from vibration sources with limited amplitude and with frequencies that are well below the resonance frequency of the fabricated device. The mathematical model includes the electrostatic forces and the forces provided by stoppers which are designed to prevent the direct contact between the capacitive plates. Global bifurcation analysis of the model illustrates the effect of the electrostatic force on the static equilibrium, the resonance frequency, and the regions of stability surrounding the equilibrium. The electrostatic forces are shown to reduce the resonance frequency at the cost of shrinking the stable domain of oscillation near the equilibrium. The inclusion of the mechanical stoppers make power harvesting still possible when the plate motion exceeds the stable domain so long as the two capacitive plates are kept at a distance to prevent the electrostatic force to dominate. Moreover, when the two plates are kept sufficiently separated, rocking instability the instability leading to non-parallel motion between the two plates is also prevented.