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In this paper, mechanically bistable microelectromechanical systems devices are investigated for energy harvesting from mechanical vibrations. This approach is particularly suitable when random, weak, and broad-band vibrations in the low-frequency range are considered. These working conditions are, in fact, quite challenging and are often approached via arrays of linear resonant microdevices. Our approach allows, with a single device, to efficiently collect kinetic energy in the whole spectrum of frequencies of the incoming signal. Bistable behaviors are achieved through purely mechanical and fully compliant micromechanisms. Different structures have been analytically and numerically investigated, both in static and dynamic working conditions, and optimized results are proposed. The advantages of the proposed device, which exploit bistable dynamic behaviors, over linear and monostable strategies are presented in this paper: In the case of the incoming kinetic energy spread over a large bandwidth and confined at low frequencies, a larger fraction of the input mechanical energy is transferred to the mechanical-to-electrical conversion section of the harvester and, therefore, to the final user. A complete device design is proposed in this paper by taking into account a dedicated fabrication process which allows to obtain large inertial masses; electrostatic conversion has been considered and embedded into the device to evaluate the device performances in terms of the electric energy scavenged.
Date of Publication: Aug. 2012