Electromagnetic interactions in a pair of coupled split-ring resonators

Split-ring Resonators (SRRs) are a fundamental building block of many electromagnetic metamaterials. Typically the response of a metamaterial is assumed to be independent of inter-element interactions in the material. We show that SRRs in close proximity to each other exhibit a rich coupling that involves both electric and magnetic interactions. We study experimentally and computationally the strength and nature of the coupling between two identical SRRs as a function of their separation and relative orientation. We characterise the electric and magnetic couplings and find that, when SRRs are close enough to be in each other's near-field, the electric and magnetic couplings may either reinforce each other or act in opposition. At larger separations retardation effects become important.