Terahertz membrane sensing based on terahertz composite slabs with enhanced fields

Double-layer metal structures show strong fields coupling when the distance between two metal layers is certain. Here, we have investigated the terahertz transmission properties of a composite slab composed of double-layer metal complementary periodic cross-shaped resonators (CPCRs). By carefully altering the spacing between two metal layers, new abnormal peaks are split from the lowest resonant modes and thus multi-band filters can be achieved, which originates from the enhanced coupling between the localized fields on the metal surfaces. Embedded a dielectric layer in the spacing of two layers, the transmission properties of the composite slabs can also be manipulated. A distinct frequency shift and transmittance changes at the resonant peak are observed as the refractive index and material absorption alters. The sensitivity using our proposed slab is up to 0.30 THz/RIU. Furthermore, the transmittance at resonant peak distinctly decreases as the loss of membranes increases. Such transmittance change reaches 67% when the membrane loss is about 0.10 cm−1. These results show that the composite slab has the potential to be applied for molecular fingerprint detection with high sensitivity as well as narrow bandwidth filters in terahertz regions.