A shielding apparatus for passively attenuating electromagnetic radiation comprising: a plurality of cells with each cell comprising a plurality of resonators which are spaced from one another; wherein the plurality of cells are arranged in a plurality of unit cells with each unit cell comprising a common loop which surrounds at least two adjacent cells of the plurality of cells ; the plurality of unit cells each having an asymmetric structure so that the shielding apparatus has a negative refractive index for at least one selected frequency whereby electromagnetic radiation at the at least one selected frequency is attenuated; characterized by: the plurality of unit cells each comprise a first cell having a first pair of adjacent resonators and a second cell having a second pair of adjacent resonators wherein a spacing between the first pair of adjacent resonators is different from a spacing between the second pair of adjacent resonators whereby each of the plurality of unit cells has the asymmetric structure; and wherein each unit cell comprises at least two additional resonators surrounding the common loop and the additional resonators are split ring resonators comprising a loop with two open ends forming a gap, wherein the gap in a first additional resonator is positioned at an opposite end of the unit cell to the gap in a second additional resonator. a plurality of cells with each cell comprising a plurality of resonators which are spaced from one another; wherein the plurality of cells are arranged in a plurality of unit cells with each unit cell comprising a common loop which surrounds at least two adjacent cells of the plurality of cells ; the plurality of unit cells each having an asymmetric structure so that the shielding apparatus has a negative refractive index for at least one selected frequency whereby electromagnetic radiation at the at least one selected frequency is attenuated; characterized by: the plurality of unit cells each comprise a first cell having a first pair of adjacent resonators and a second cell having a second pair of adjacent resonators wherein a spacing between the first pair of adjacent resonators is different from a spacing between the second pair of adjacent resonators whereby each of the plurality of unit cells has the asymmetric structure; and wherein each unit cell comprises at least two additional resonators surrounding the common loop and the additional resonators are split ring resonators comprising a loop with two open ends forming a gap, wherein the gap in a first additional resonator is positioned at an opposite end of the unit cell to the gap in a second additional resonator. the plurality of unit cells each comprise a first cell having a first pair of adjacent resonators and a second cell having a second pair of adjacent resonators wherein a spacing between the first pair of adjacent resonators is different from a spacing between the second pair of adjacent resonators whereby each of the plurality of unit cells has the asymmetric structure; and wherein each unit cell comprises at least two additional resonators surrounding the common loop and the additional resonators are split ring resonators comprising a loop with two open ends forming a gap, wherein the gap in a first additional resonator is positioned at an opposite end of the unit cell to the gap in a second additional resonator. <EOS>