Acoustic metafluids of shear modulus enabling surface waves

Abstract

Metafluids, the version of metamaterials with fluid background, are generally characterized by two parameters: the effective mass density and bulk modulus. However, we recently theoretically demonstrated that a metafluid, with built-in quadrupolar resonances, can counterintuitively accommodate a third parameter, the effective shearlike modulus. In this letter, we go further to experimentally implement this metafluid, realized as a square lattice array of hollow steel cylinders in water. The effective parameters are extracted by matching the measured dispersion curves with the effective medium theory. By virtue of the emergent parameter, the metafluid can intrinsically support surface waves at the interface with water, which updates the knowledge that surface waves cannot exist at the interface of two fluids. Our work has potential in expanding the applications of metafluids.