Abstract: A shielding apparatus which is for passively attenuating electromagnetic radiation and which comprises a plurality of cells. Each cell comprises a plurality of resonators (26) which are spaced from one another. The cells are arranged in a plurality of unit cells with each unit cell comprising a common loop (32) which surrounds at least two adjacent cells of the plurality of cells. The plurality of unit cells each have an asymmetric structure. The shielding apparatus thus has a negative refractive index for at least one selected frequency whereby electromagnetic radiation at the at least one selected frequency is passively attenuated.