Improved TL-RLC model for terahertz circular split-ring resonators

Three geometries of split-ring resonators (SRRs) including circular geometry and two elliptical geometries were fabricated by modern photolithography process. The samples were measured by terahertz time-domain transmission spectroscopy. These spectra clearly revealed the lower-frequency LC resonances and the higher-frequency dipole resonances; meanwhile, the coupling effect between the LC and dipole resonance had played an important role in the overall response. Comparing the results shows that the LC resonance, dipole resonance, and the coupling effect can be designed. A simple transmission-line (TL) RLC circuit model was used to help us understand this coupling behavior and the extent of its effects. But the simple model has some disadvantage. For better matching TL-RLC model results with measured data, an improved model was introduced for the circular and y-direction stretched elliptical geometry SRRs. Other resonances and modes existing at higher frequencies except the typical LC and dipole resonances were revealed by the improved model.