Finite Element Analysis of a UAV Wing Spar with Piezoceramics for Vibration Energy Harvesting

Abstract

The research goal in vibration-based energy harvesting is to convert waste vibration energy available in the environment of remotely operated systems or wireless systems with limited energy sources to usable electrical energy. Unmanned Air Vehicles (UAVs) and Micro Air Vehicles (MAVs) constitute unique applications for vibration-based energy harvesting. An additional energy source to run small electronic devices during the flight has the practical value of relieving auxiliary power sources of such systems. Aspect ratios of piezoelectric harvesters in several cases are plate-like and predicting the power output to general (symmetric and asymmetric) excitations requires a plate-type formulation. In this paper, an electromechanically coupled finite element (FE) plate model is presented for predicting the electrical power output of piezoelectric energy harvester plates. Generalized Hamilton’s principle for electroelastic bodies is reviewed and the FE model is derived based on the Kirchhoff plate assumptions as typical piezoelectric energy harvesters are thin structures. Presence of conductive electrodes is taken into account in the FE model. The predictions of the FE model are verified against the analytical solution for a unimorph cantilever and then against the experimental and analytical results of a bimorph cantilever with a symmetric tip mass reported in the literature. The electromechanical behavior of a bimorph cantilever with an asymmetric tip mass is also investigated. Cancellation of the potential of electrical energy that can be extracted from torsional modes is investigated when continuous electrodes are used. Possible solutions to avoid the cancellation of electrical output are discussed in this paper. Finally, an optimization problem is solved where the aluminum wing spar of a UAV is modified to obtain a generator spar by embedding piezoceramics for the maximum electrical power without exceeding a prescribed mass addition limit.