Two-dimensional octagonal phononic crystals for highly dense piezoelectric energy harvesting

Piezoelectric energy harvesting at multi-scales has received considerable attention as an attractive powering technology which enables sustainable self-powered operation of small electronics such as wireless sensors. Self-powered wireless sensors for structural health monitoring, biomedical and wearable applications would be great potential applications with high market demand. A key challenge has been insufficient power generation for practical applications, which necessitates a new paradigm in the design of energy harvesting systems. In this work, drastic enhancement of harvesting performance along with energy focusing is demonstrated both analytically and experimentally by introducing metamaterial-based energy harvesting (MEH) systems. Metamaterials, artificially engineered structures, exhibit unique properties including band gap and negative refractive index and thus enable us to manipulate mechanical wave propagations. Wave guide and localization toward a desired position can lead to amplification of harvestable input mechanical energy. In this work, systematic design of two-dimensional octagonal phononic crystals (PnCs) through geometric and band gap optimization process is proposed and followed by experimental demonstration. Energy confinement and localization at the defect of proposed PnCs leads to successful enhancement of harvesting power up to 22.8 times compare to the case without the presence of metamaterial.