Acoustic metamtaterial and metasurface composed of meta-atoms and meta-molecules

Acoustic metamaterials (AMMs) and acoustic metasurfaces (AMSs) are artificially structured materials with the unique properties not found in natural materials. We reviewed herein the properties of AMM and AMS that have been designed using the meta-atoms of split hollow spheres (SHSs) and hollow tubes (HTs) or meta-molecules of split hollow tubes (SHTs) with local resonance. AMMs composed of SHSs or HTs display a transmission dip with negative modulus or negative mass density. AMMs composited with SHSs and HTs present a transmission peak and a phase fluctuation in the overlapping resonant frequency region, indicating that they simultaneously have a negative modulus and a negative mass density. Furthermore, the meta-molecule AMMs with SHTs also exhibit double-negative properties. Moreover, the acoustic meta-atoms or meta-molecules can be used to fabricate acoustic topological metamaterials with topologically protected edge states 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 the anomalous manipulation for acoustic waves. The various tunability of the meta-molecules provides a feasible path to achieve broadband AMS.