FLuttering Energy Harvester for Autonomous Powering (FLEHAP): A synergy between EMc and Dielectric Elastomers Generators

Energy Harvesting is the main solution to ensure the powering of sensors and micro-processors, especially in extreme environmental conditions where the use of batteries can be expensive or even impractical. In this work, a coupled-mode aero elastic fluttering system, exploiting self-sustained oscillations to harvest electrical energy from the mechanical one, is proposed. An airfoil can freely turn around its rotational axis, bounded to two elastomers parallel to the flow: in the presence of a fluid in motion, under particular mechanical conditions, the system exhibits limit cycle oscillations characterized by noteworthy amplitude and frequency. Moving in the space of parameters every flow speed range is theoretically achievable for the purposes of electrical extraction; this work will focus on low wind speed conditions. By positioning a pair of coils at the ends of the rotational axis of the wing and fixing magnets in an alternated polarity in front of their quasi-vertical harmonic motion, an electro-magnetic coupling (EMc) is obtained: during the oscillations an alternated voltage at the ends of the coils is measured. Dielectric Elastomer Generators (DEGs), composite material formed by coupling two stretchable electrodes to a high permittivity rubber, forming a capacitor in which the capacitance changes with the stretching, replace traditional elastomers: this permits, by charging the DEGs in the maximal stretched status and discharging it in the pre-stretch status, to amplify the input voltage. DEGs cannot be an autonomous powering, because they need an external electrical energy source. Synergistically, the use of an integrated circuit designed for storing efficiently the charges from the EMc in a supercapacitor (SC), and electronics able to manage the DEGs by a 'charge pumping' process supplying a second SC, allows to ensure an excellent and adaptable autonomous powering. A further synergy is introduced exploiting intrinsic effects of the two electrical extraction strategies adopted in the system: EM damping due to the resistance load, and the change in stiffness of DEGs when a voltage is applied, can extend the operating speed range, increasing its global efficiency. Centimeter-sized devices exploiting EMc and DEGs, and an overview about DEGs materials are presented in this work