Acoustic and mechanical metamaterials for energy harvesting and self-powered sensing applications

Metamaterials are artificially engineered structures that exhibit extraordinary properties beyond the constituent materials, making them attractive for various applications in optics, acoustics, and mechanics. Energy harvesting is an eco-friendly technology that recycles ambient wave and mechanical energy by converting it into valuable electricity. The unique properties of metamaterials offer exciting opportunities to enhance energy harvesting performance by manipulating input wave direction and amplitude or increasing strain levels on energy conversion materials and devices. Recently, there has been a surge in research on incorporating energy manipulation capabilities of phononic crystals, locally-resonant acoustic metamaterials, and mechanical metamaterials into energy harvesting systems, including acoustic and elastic wave focusing and localization and mechanical energy trapping phenomena. In this review, we provide a classification of acoustic and mechanical metamaterials utilized for energy harvesting and self-powered sensing, followed by a comprehensive comparison of how each metamaterial has been integrated and the extent to which it contributes to quantitative improvements in energy and sensing performance. We also discuss the potential of unexplored metamaterials whose concepts are intriguing but have not yet been applied to energy harvesting or self-powered sensing, and discuss the vision and future direction of metamaterial research in this exciting field.