Tunable toroidal Fano resonance in the multiple split-ring resonators metamaterials

Abstract

We investigate the tunable toroidal Fano resonance in the multiple split-ring resonators (SRRs) metamaterial. The toroidal Fano resonance is theoretically and experimentally demonstrated. The Fano resonance can be excited by introducing a big-SRR in the multiple small-SRRs. Fano resonance results from the mutual coupling between toroidal and magnetic dipoles. The Fano lineshape can be tuned by changing the size of big-SRR. Moreover, the authors discover that the direction of toroidal dipole also can be tuned by properly controlling the size of big-SRR. The strength of Fano resonance can be enhanced by introducing two small-SRRs. The double Fano resonances can be excited by tuning the size ratio between two small-SRRs. The structure provides more dielectric information of the analyte. In the design, by introducing two small-SRRs in the structure and using Fano resonance, the sensitivity has been improved. The two small-SRRs structure increases the sensitivity of the final design, up to two times compare to the one small-SRRs structure. The tunable toroidal Fano resonance offers the potential for application in the microwave and terahertz sensing.