A transformable anisotropic 3D penta-mode metamaterial

Penta-mode metamaterials, composed by solids but behaving as liquid, have great potential in manipulating acoustic wave in fluids. Most work concentrates on 2D penta-mode metamaterial consisting of classic honeycomb lattice and their acoustic applications. However, the 3D penta-mode exploration is still limited to traditional diamond lattice. Here, we propose a novel 3D penta-mode metamaterial design whose geometry is based on truncated octahedron. The configurations of regular truncated octahedron (RTO) and transformed truncated octahedron (TTO) exhibit isotropic and anisotropic penta-mode property, respectively. By introducing the modular origami and boundary constrains, a transformable penta-mode design metamaterial between RTO and TTO configurations is proposed. The tunable anisotropy of the penta-mode is experimentally demonstrated, based on which we analyze the effective acoustic impedance and wave velocity, and illustrate their ability to manipulate the amplitude and wavefront of acoustic waves. Our findings offer a wider 3D transformable penta-mode metamaterial flatform to achieve the tunable control of acoustic wave in fluids.