Acoustic metamaterials and metasurfaces composed of meta-atoms and meta-molecules

Acoustic metamaterials (AMMs) and acoustic metasurfaces (AMSs) are artificially structured materials with unique properties not found in natural materials. We review herein the properties of AMMs and AMSs that have been designed using different kinds of meta-atoms or meta-molecules with local resonance. AMMs composed of meta-atoms display a transmission dip with a negative modulus or a negative mass density. AMMs composed of two kinds of meta-atoms present a transparent transmission, indicating that they simultaneously have a negative modulus and a negative mass density. Furthermore, meta-molecule AMMs also exhibit double-negative properties. Moreover, acoustic meta-atoms or meta-molecules can be used to fabricate acoustic topological metamaterials with topologically protected edge state propagation. These meta-atoms and meta-molecules can also attain phase discontinuity near the resonant frequency, and thus they can be used to design AMSs with anomalous manipulation for acoustic waves. The tunability of meta-molecules provides a feasible path to achieve broadband AMS.