Piezoelectric energy harvesting from multifunctional wing spars for UAVs - Part 2: experiments and storage applications

This paper is the second part of a two-part series investigating the development of multifunctional piezoelectric energy harvesting devices to be used in unmanned aerial vehicle and micro air vehicle applications. The proposed self-charging structures include piezoelectric layers and novel thin-film battery layers bonded to a substrate layer in order to create a multilayer, self-charging, load bearing energy harvesting device. Part 1 of this work (coupled modeling and preliminary analysis) presents a distributed parameter electromechanical model used to predict the response of the proposed selfcharging structures under harmonic base excitation. The model is compared to experimental results and found to be quite accurate. This paper investigates the fabrication and experimental evaluation of the self-charging structures. A detailed analysis of the thin-film batteries used in the self-charging structures is carried out, and their electrical and mechanical performance is evaluated. Typical charge and discharge curves are generated and analyzed. The fabrication process involved in creating self-charging structures is also outlined, including details on bonding of the layers and establishing electrical connections. A simple energy harvesting circuit is designed to allow the transfer of energy from the piezoelectric layers to the battery layers. Lastly, the energy harvesting performance of the self-charging structure is evaluated and typical charge and discharge time histories are recorded for the structure under base excitations.