Split Ring Resonator

A split-ring resonator (SRR) is a component part of a negative refractive index material. SRRs are a pair of concentric annular rings with splits in them at opposite ends. The rings are made of nonmagnetic metal like copper and have small gap between them.

A magnetic flux penetrating the metal rings induces rotating currents in the rings, which produces it's own flux to enhance or oppose the incident field (depending on SRR's resonant properties). This field pattern is dipolar. Due to splits in the rings the structure can support resonant wavelengths much larger than the diameter of the rings. This would not happen in closed rings. The small gap between the rings produces large capacitance which lowers the resonating frequency as time constant is large then.The dimension of structure is small compared to the resonant wavelength resulting in low radiative losses and so very high quality factors.

At frequencies below resonant frequency the real part of magnetic permeability of SRR becomes large (positive) and goes to negative values at frequencies higher than the resonant one. This negative permeability can be used with negative dielectric constant of another structure to produce negative refractive index materials.