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

This work covers a novel concept for piezoelectric energy harvesting for the use in lightweight design. It is motivated by a structural strain excitation in an aircraft wing caused by a dynamic pressure. The concept uses piezoelectric electrets, also called ferroelectrets. Ferroelectrets are piezoelectric polymers that show a higher ecological compatibility and a much higher structural flexibility than piezoceramics. The used ferroelectret material for piezoelectric energy conversion is fluorinated ethylene propylene (FEP) assembled in a parallel-tunnel structure that provides high transversal piezoelectric d31-coefficients. The transformation of strain energy is realized by a metallic mechanism converting a low strain amplitude with a high structural stress to a desired high strain amplitude. Due to low stresses required in the ferroelectret material, the metallic mechanism is designed in a very light way. An analytical model is presented to show the main design parameters and a finite element model is used with the goal of investigating the power output per total energy harvester mass. The model is eventually validated with experimental results. A power output of 344.2 nW and a ratio of power per mass of 302.6 mWkg−1 can be reached for a single harvester under a realistic quasistatic load. For a suggested cluster this can be increased up to 2.6 mW/m2 which is enough to power many devices with a low power consumption.