Fig. 2. Initial realizations of locally resonant acoustic metamaterials.

(A) Images of the sample that first realized a local resonance-induced anomalous mass effect (16). Left: The cut-away view of a sample unit cell consisting of a small metallic sphere coated by a thin uniform layer of silicone rubber. Right: The sample made by using epoxy to glue together the units shown on the left. The effective frequencies for total reflection by the sample were shown to correspond to a wavelength that is between one and two orders of magnitude larger than the size of the lattice constant, which is 1.55 cm. (B) An illustration of the sample, comprising a series of Helmholtz resonators connected to one side of a conduit, that realized the frequency dispersion for the bulk modulus (18).