Electric Field Dropping Effect Enhanced Extraordinary Sensitivity of THz Electromagnetically Induced Transparency Metamaterial

Metamaterial sensors have unique advantages, including non-labeling and non-destructive capabilities in the terahertz (THz) regions. However, the low sensitivity, limited by the poor light-matter interaction, still restricts the implementation of the metamaterial sensors for practical applications. In this paper, we construct a novel THz electromagnetically induced transparency (EIT)-like metamaterial using two resonators with different metal thicknesses (undulated metamaterial), resulting in a coupled mode with electric field dropping distribution. This electric field dropping distribution leads to a remarkable enhancement of the electric field in the space where the analyte is present. The transmission amplitude of the transparency window shows obvious growth with the undulated surface design because of the enhanced coupling between the two resonant modes. The simulation results are also investigated through coupled harmonic oscillator model. Furthermore, the sensitivity of the metamaterial sensor with undulated characteristics is 550 GHz/RIU, surpassing that of the metamaterial sensor with uniform metal thickness by a factor of 1.57 due to the strengthened light-matter interaction. In addition, an experimental demonstration of the enhanced sensing performance and transmission amplitude growth of the undulated metamaterial is conducted, which shows good consistency with the simulations. The THz metamaterial, consisting of different resonators with varying metal thickness, can provide an efficient approach for designing biosensors with ultra-sensitivity and the designing method offers an opportunity for the realization of further enhanced sensitivity without changing the pattern of metamaterial.