Sensitive Detection of Doped Polymer Thin Films Using Terahertz Metamaterial Based on Analog of Electromagnetically Induced Transparency

Abstract

We propose a novel terahertz (THz) metamaterial (MM)-based sensor for the sensitive detection of doped polymer thin films. The MM constructed by periodic quasi-ring resonators can generate the analog of electromagnetically induced transparency (EIT) at the THz region and work in a wide range of incident angles. The simulated results show that the frequency and magnitude of the EIT-like resonance can be, respectively, affected by the refractive index and dielectric loss of the analyte, which is further explained by a coupled harmonic oscillator model. The theoretical sensitivity of the proposed sensor is calculated as 185 GHz/RIU [refractive index unit (RIU)], showing a good sensing capability. In experiments, the dispersed red 1 (DR1)-doped polymethylmethacrylate (PMMA) thin films with a subwavelength thickness of 600 nm were covered on the MM surface. The measured results show that the EIT-like resonance experiences frequency redshift and magnitude attenuation as the doping concentration increases, indicating the addition of DR1 can lead to the increase in both refractive index and dielectric loss of the PMMA thin film. The proposed MM-based sensor can successfully identify the dielectric change of extremely thin polymer films caused by doping, offering a novel way to achieve high-sensitivity thin-film sensing.