Negative mass density and ρ-near-zero quasi-two-dimensional metamaterials: Design and applications

We report the design and the characterization of artificial structures made of periodical distributions of structured cylindrical scatterers embedded in a two-dimensional (2D) waveguide. For certain values of their geometrical parameters they show simultaneously negative effective bulk modulus and negative effective mass density. Here our analysis is focused on the frequencies where they behave like materials with negative density or density near zero (DNZ). The scattering units consist of a rigid cylindrical core surrounded by an anisotropic shell divided in angular sectors. The units are embedded in a 2D waveguide whose height is smaller than the length of the cylinders, which makes the structure quasi-2D. We have obtained the dispersion relation of the surface acoustic waves excited at frequencies with negative effective density. Also, we report phenomena associated with their DNZ behavior, such as tunneling through narrow channels, control of the radiation field, perfect transmission through sharp corners, and power splitting. Preliminary experiments performed on samples with millimeter-scale dimensions demonstrated their single-negative behavior, with the main drawback being the strong losses measured at the frequencies where the negative behavior is observed.