Symmetric and antisymmetric modes of electromagnetic resonators

In this paper, we numerically study a new type of infrared resonator structure, whose unit cell consists of paired split-ring resonators (SRRs). At different resonant frequencies, the magnetic dipoles induced from the two SRRs within one unit cell can be parallel or antiparallel, which are defined as symmetric and antisymmetic modes, respectively. Detailed simulation indicates that the symmetric mode is due to magnetic coupling to resonators, in which the effective permeability could be negative. However, the antisymmetric mode originating from strong electric coupling may contribute to negative effective permittivity. Our new electromagnetic resonators with pronounced magnetic as well as electric responses could provide a new pathway to design negative index materials (NIMs) in the optical region.