Conductive coupling for efficient generation of multiple Fano resonances in multiple two-split-ring-resonators and its application in refractive index sensor

The properties of two and three two-split-ring-resonators (TSRRs) are investigated in this paper, which shows a remarkable Fano resonance in the microwave frequency. In two TSRRs, the Fano resonance results from the interference between two TSRRs by conductive coupling, both experiments and numerical simulations are in good agreement. The structure shows strong magnetic dipole at the intersection of two TSRRs. In three TSRRs, the double Fano resonances can be excited and double magnetic dipoles produce at two intersections. Because of the interaction between two magnetic dipole, symmetric magnetic dipole and anti-symmetric magnetic dipole (toroidal dipole) modes are presented, respectively. An almost doubled Q factor is observed in the three TSRRs compared to the two TSRRs. In addition, we experimentally demonstrate that the double Fano resonances are sensitivity to the refractive index of background. The sensitivity changes with the change of position of detected material. The highly sensitive areas of double Fano resonances locate at two intersections. This study paves the way to excite the multiple Fano resonances. Such Fano resonance can be applied to the sensors.