  Using both multiple scattering theory and effective medium theory, we find
that an acoustic metamaterial consisting of an array of spinning cylinders can
possess a host of unusual properties including folded bulk and interface-state
bands in the subwavelength regime. The folding of the bands has its origin in
the rotation-induced antiresonance of the effective compressibility with its
frequency at the angular velocity of the spinning cylinders, as well as in the
rotational Doppler effect which breaks the chiral symmetry of the effective
mass densities. Both bulk and interface-state bands exhibit remarkable
variations as the filling fraction of the spinning cylinders is increased. In
particular, a zero-frequency gap appears when exceeds a critical value. The
uni-directional interface states bear interesting unconventional
characteristics and their robust one-way transport properties are demonstrated
numerically.
