Multiscale metamaterials: a new route to isotropic double-negative behaviour at visible frequencies

We propose a systematic method of producing isotropic, double-negative metamaterials which operate in the visible spectrum. The material comprises two sets of inclusions dispersed in a host medium. We demonstrate that if the inclusions in one set are much smaller than those in the other, then the larger will behave as though they are submerged in a composite background material, rather than the true host material. This hierarchy effect is shown to enrich the designer's capacity to induce strong, simultaneous electric and magnetic resonance at an arbitrary visible frequency, leading to double-negative behaviour. The predictions of Mie theory are verified using full-wave analysis and backward waves directly measured in the proposed designs.