Demonstration and optimization of Energy Harvesting with piezoelectrets in Aircraft-Structures subject to bending host structures
Throughout the flight of an airplane vibrations occur in the mechanical structure through aerodynamics or engine-unbalances. The vibration-energy is dissipated by the structure and remains unused. The research question of the project EnerVib is if and to what extent this energy can be used to power devices like wireless sensors or remote displays and therefore to save cables with associated weights. Electrets are polymers that exhibit a quasi-permanent electric field. Due to their high flexibility, low density, good recyclability and high piezoelectric constants, piezoelectrets appear to be a suitable electromechanical transducer for the application compared to common piezoceramics. Testing on real planes is costly and potentially difficult regarding safety standards. Hence a model-based approach with experiments on simplified structures is used. An essential part of the research is the derivation of realistic loads that are used on representative models to determine the mechanical loads resulting for attached piezoelectret-transducers.
The purpose of this work is the demonstration of Energy Harvesting with piezoelectrets based on the bending of thin aluminum-plates in a four-point flexural test setup representing the behaviour of periodically deforming parts of aircraft-structures. The aim is to show the capability of piezoelectrets for the use under realistic circumstances. With analysis-results of the NASA Common Research Model strain distributions within the structure at different frequencies can be calculated as a reference. Based on a material model for piezoelectric electrets, Finite Element models for Energy-Harvesters are developed. The models are validated with experimental results with respect to the mechanical and electromechanical behaviour with amongst others the generated power in the frequency range up to 300 Hz. In an optimization process the power output in an optimal load-resistance of the harvesters is increased using different piezoelectret-materials and improved geometry for the adjustment of local strains by the change of distance to the neutral axis. Furthermore a model-based comparison to common piezoceramics is conducted for both the simple plate and the optimized geometry, showing advantages of piezoelectrets due to their high flexibility.