Impact-activated programming of electro-mechanical resonators through ferroelectret nanogenerator (FENG) and vanadium dioxide

Abstract

Ferroelectret Nanogenerators (FENG) devices were introduced recently as promising flexible devices for energy harvesting and microphone/loud-speaker applications. Vanadium dioxide (VO2) thin films, on the other hand, have been demonstrated to enable large frequency tunability of miniaturized electro-mechanical structures, which are commonly integrated in transceiver and communication systems. In this work, we integrate these two technologies, to show a system where an electric pulse, supplied by the FENG can be used to tune the resonant frequency of VO2-based micro-electro-mechanical structures. Furthermore, due to the VO2's hysteretic behavior, the applied pulse also programs the tuned frequency, allowing for different frequency states in the device for a single applied DC bias. It is found that the tuning of the frequency states is determined by the supplied energy, and the programming is more efficient for larger, shorter pulses –even if the duration of the pulse is shorter than the system's thermal time constant. We explore two different mechanical structures, bridge and cantilever. A wider tuning range is found for the bridge structure (22%), which is due to the larger frequency sensitivity with stress for this configuration. The tuning/programming action uses harvested mechanical energy, which could come from the user. The potential use of the developed system as an accelerometer or impact sensor for monitoring brain injuries in contact-sports is discussed.