A metamaterial comprises a substrate and a plurality of resonators supported by the substrate, each resonator including a first conducting segment and a second conducting segment, there being at least one adjustable capacitor and at least one bias capacitor located between the first and second conducting segments. In some examples, the first conducting segment, second conducting segment, bias capacitor, and adjustable capacitor are substantially coplanar and may be formed by patterning a metal film supported by the substrate. Bias lines may be configured so as to allow a bias potential to be applied between the first and second conducting segments so as to vary the capacitance of the adjustable capacitor.