Fig. 1From: Acoustic wave science realized by metamaterialsEffective mass density and bulk modulus diagram. v ph denotes the phase velocity. R and I indicate purely real and imaginary parts of phase velocity, respectively. Normal materials in nature belong to a with double positive parameters. Metamaterials can be classified as negative mass density (b), double negative parameters (c), negative bulk modulus (d) and near-zero mass density (e)Back to article page