Multifunctional Unmanned Aerial Vehicle Wing Spar for Low-Power Generation and Storage

This paper presents the investigation of a multifunctional energy harvesting and energy-storage wing spar for unmanned aerial vehicles. Multifunctional material systems combine several functionalities into a single device in order to increase performance while limiting mass and volume. Multifunctional energy harvesting can be used to provide power to remote low-power sensors on unmanned aerial vehicles, where the added weight or volume of conventional harvesting designs can hinder flight performance. In this paper, a prototype self-charging wing spar containing embedded piezoelectric and battery elements is modeled, fabricated, and tested to evaluate its energy harvesting and storage performance. A coupled electromechanical model based on the assumed modes method is developed to predict the vibration response and voltage response of a cantilevered wing spar excited under harmonic base excitation. Experiments are performed on a representative self-charging wing spar, and the results are used to verify the electromechanical model. The power-generation performance of the self-charging wing spar is investigated in detail for harmonic excitation in clamped free boundary conditions. Experiments are also conducted to demonstrate the ability of the wing spar to simultaneously harvest and store electrical energy in a multifunctional manner. It is shown that, for an input base acceleration level of +/- 0.25 g at 28.4 Hz at the base of the structure, 1.5 mW of regulated dc power is delivered from the piezoelectric layers to the thin-film battery, resulting in a stored capacity of 0.362 mAh in 1 h.