Dual-band ultrasensitive THz sensing utilizing high quality Fano and quadrupole resonances in metamaterials

• Proposed a new metamaterial structure functioning in the THz regime.
• Low loss, high Q Fano and quadrupole resonances can be simultaneously acquired.
• The mechanism of two high-Q resonances was investigated.
• Thickness sensing using the two high-Q resonances was performed.
• Refractive index sensing using the two high-Q resonances was performed.

High quality (Q) factor resonances are extremely promising for designing ultrasensitive sensors. In this paper, we proposed a metamaterial functioning in the THz regime, which exhibited low loss, high Q Fano and quadrupole resonances simultaneously. Ultrasensitive THz sensing was performed based on the redshifts of the two high Q resonances when analyte was coated at the surface of the metamaterial. Results indicated that both the Fano and quadrupole resonances can sensitively detect slight changes of the analyte (e.g. the thickness or refractive index). The refractive index sensitivity levels are 2.06×104 nm/RIU for the Fano resonances and 5.07×103 nm/ RIU for the quadrupole resonance, respectively. Both of the two sensitivities have an order of magnitude higher than schemes based on the low Q dipolar resonances in metamaterials. This planar metamaterial would open new degrees of freedom for designing advanced chemical and biological sensors and detectors in the terahertz regime.