Metal-substrate-enhanced magnetic dipole resonance in metamaterials for high-performance refractive index sensing

In this work, we theoretically investigate metal-substrate-enhanced magnetic dipole resonance in metamaterials for high-performance refractive index sensing. The metamaterials are composed of periodic arrays of vertical U-shaped split-ring resonators, dielectric spacer, and metal substrate. Because the metal substrate blocks the transmission channel of light, the radiative damping of magnetic dipole resonance is nearly completely suppressed and thus its quality factor is increased noticeably. Owing to the narrow bandwidth, nearly-zero reflectance, and huge enhancement of electromagnetic fields at the magnetic dipole resonance, our designed metamaterial sensor has very high sensitivity (S = 1308 nm/RIU, S* = 26/RIU) and figure of merit (FOM = 52, FOM* = 1187). The good sensing capability allows for a much more sensitive detection of small refractive index changes and suggests potential applications in biosensing.