Flat superlens by using negative refraction in two-dimensional phononic crystals

We experimentally and theoretically demonstrated a flat superlens by negative refraction imaging for acoustic waves in a two-dimensional phononic crystal. The sample consists of a square array of steel cylinders immersed in water. The dispersion surfaces at the first band for this sample are nearly circular around point M in the first Brillouin zone, which makes the index of the negative refraction for the phononic crystal sample be well defined for all angles of incidence. Both the observed negative refraction behavior and imaging effect are in excellent agreement with numerical simulations by the Multiple Scattering Theory method.