This work covers a novel concept for piezoelectric energy harvesting subject to a structural strain excitation for the use in lightweight design. The concept is based on piezoelectric electrets, also called ferroelectrets. Ferroelectrets are piezoelectric polymers that show a higher ecological compatibility and a much higher structural flexibility than piezoceramics. Furthermore they provide charge constants in the same order of magnitude as piezoceramics. For the use of structural strain energy, conventional piezoelectric energy harvesting solutions are based on glued piezoceramics that are comparably difficult to install onto and remove from a metallic host structure. This is a major disadvantage in the context of recycling.The proposed concept is motivated by a strain-excitation in an aircraft wing caused by a stationary dynamic pressure. The used ferroelectret material is parallel-tunnel FEP which provides high transversal piezoelectric d31-coefficients compared to conventional PP-foam-ferroelectrets. The main idea is to split up the two functionalities of the energy harvester of energy transformation and energy conversion into two different materials. The transformation of the strain energy is realized by means of a metallic transmission mechanism to convert a low strain amplitude with a high structural stress to a desired high strain amplitude with a smaller stress. The piezoelectric energy conversion is finally achieved by the transducer material. Due to low stresses needed in the ferroelectret material, the metallic mechanism can be designed in a very light way and the connection of ferroelectret to the mechanism can be accomplished by a simple reversible clamping. Furthermore small concentrated masses are used to tune the energy harvester to a desired eigenfrequency.To optimize the energy harvester, a parametric finite element model is used with the goal of maximizing the power output per total energy harvester mass for a quasistatic and a dynamic case. The best result is investigated in an experimental bending test setup and the simulation model is eventually validated by a model fit. An additional calculation addresses the power output of the used topology in a cluster of energy harvesters in a specific area.The presented work shows that the designed energy harvester can compete with conventional solutions in terms of power output per used mass on the one hand, providing advantages like ecological compatibility on the other hand.

Simulation-Based Design and Experimental Validation of a Ferroelectret Strain Energy Harvester for Lightweight Structures

Paper Proceedings: https://asmedigitalcollection.asme.org/SMASIS/SMASIS2021/volume/85499

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