A split-ring resonator is a component part of a metamaterial (a material with a negative refractive index). When an electromagnetic wave passes from an optically less dense material to an optically denser material, it refracts because it loses some of its energy to the electrons in the optically denser material. The two components of an electromagnetic wave are the electric field and the magnetic field. The electrons move back and forth due to electric field and in circular motion due to magnetic field. So, a magnetic flux penetrating the metal rings (SRRs) induces rotating currents in the rings. This will result in the electrons oscillate at a certain frequency, the resonance frequency, determined by the SSRs' structure and dimensions. When an electromagnetic wave with a frequency higher than the resonance frequency passes through the material, the material acts as a metamaterial.
