Highly sensitive 3D metamaterial sensor based on diffraction coupling of magnetic plasmon resonances

We theoretically investigate the diffraction coupling of magnetic plasmon (MP) resonances in three-dimensional (3D) metamaterials comprising a rectangular array of metallic vertical split-ring resonators (VSRRs). By suspending 3D metamaterials into air to reduce the substrate effect, the interaction between MP resonances of VSRRs and a collective surface mode signaled by Wood anomaly in the periodic array can cause a narrow-band mixed mode with greatly enhanced magnetic fields. Due to the interaction, an anti-crossing phenomenon similar to Rabi splitting in atomic physics, is also observed and explained satisfactorily with the help of a coupled oscillator model. For the narrow-band mixed mode, the greatly enhanced magnetic fields in VSRR gaps are lifted off from the substrate to be fully exposed to the sensing medium. Therefore, the 3D metamaterials have good sensing performance factors (S = 900 nm/RIU, FOM = 38, and FOM* = 125), which are promising for label-free biochemical sensors.