Resilient electret film-based vibrational energy harvesters with a V-shaped counter electrode

Vibrational energy harvesters, which can convert mechanical energy distributed widely in the surrounding environment to electrical energy in a convenient, eco-friendly and sustainable way, have attracted great attention in both academia and industry. In this study, a resilient electret film-based vibrational energy harvester with a V-shaped counter electrode is introduced, simulated and constructed. A negatively charged fluorinated polyethylene propylene (FEP) electret film with a wavy shape was adopted in the devices, achieving simultaneously a stable embedded biased voltage and a large tensile deformation during vibration. The influences of the factors on the performance of the device, including the initial stretching state of the resilient electret film, seismic mass and depth of the V-shape counter electrode, were analyzed comprehensively with finite element simulation and compared to experiments. Further, the structure of the device was optimised for generating a high output power, and a good agreement between the simulation and experimental data was achieved. Additionally, the resonant frequency of the device can be easily tuned between 28 and 68 Hz by merely adjusting the initial stretching state of the wavy FEP electret film, guaranteeing great superiority for broad bandwidth energy harvesting applications. For an optimised energy harvester with a volume of only 15 × 5 × 1.7 mm³ and a tiny seismic mass of 25 mg, and a normalized output power referring to 1 × g (g is the gravity of the Earth) up to 547 μW was obtained at its resonant frequency of 28 Hz. These results demonstrate that such a miniaturised vibrational energy harvester is a promising electrical energy supplier for low-power-consumption electronic devices, in particular in wireless sensor networks.