Acoustic omni meta-atom for top-down, decoupled access to all octants of a wave parameter space

Abstract

The common behavior of a wave is determined by wave parameters of its medium, which are generally associated with the characteristic oscillations of its corresponding elementary particles. In the context of metamaterials, the decoupled excitation of these fundamental oscillations would provide an ideal platform for top-down and reconfigurable access to the entire space of constitutive wave parameters; however, this has remained as a conceivable problem that must be accomplished, after being pointed out by Pendry. Here, by focusing on acoustic metamaterials, we achieve the decoupling of density $\rho$ , modulus B$^{-1}$, and bianisotropy {\xi} near the Dirac point, by separating the paths of particle momentum to conform to the characteristic oscillations of each macroscopic wave parameter. Independent access to all octants of wave parameter space ($\rho$ , B$^{-1}$, $\xi$) = (+/-,+/-,+/-) is thus realized using a single platform that we call an omni meta-atom; as a building block that achieves top-down access to the target properties of metamaterials. With precision access to the target ($\rho$ , B$^{-1}$, $\xi$ ), we also propose a bianisotropic meta-surface for independent shaping of transmission- and reflection-wave fronts, and a zero-index anisotropic waveguide for pressure-velocity conversion.