Reformative EIT Inspired Ultra-sensitive Terahertz Sensing on Micro-volumetric Microfluidic Metamaterial

Abstract

The ultrasensitive terahertz (THz) microfluidic sensors based on novel metamaterials with enhanced wave-matter interaction, tagged by the label-free sensor, have attracted much attention from researchers owing to its advantages of higher sensitivity and reliability. The electromagnetically induced transparency (EIT) phenomenon has a property of being sensitive to the refractive indices of the surrounding medium, making it possible to apply it to refrac- tometric sensing. However, for minute dielectric change, the quality factor (Q-factor) and the sensing performance still need to be improved. Inspired by the conventional EIT resonator, a micro-volumetric microfluidic sensor based on a double-transparency-window EIT metasurface is proposed here. Firstly, by introducing a dual-wire-SRR resonator, a prototype sensor with two sharp transparency windows was engineered for multiband sensing. Further, in order to maximize the wave-matter overlap, we increased the metal layer thickness and added a dielectric pattern layer underneath the metallic pattern. Observed from the flank electric field distribution and the surface current distribution, the hybrid composite structure not only enlarges the sensing overlap, but also dramatically improves the wave-matter interaction by concentrating the local electromagnetic fields. The optimized sensitivities for both transmission peaks are 0.440/RIU at 0.861 THz and 0.482/RIU at 0.774 THz, which are 34% and 38% more than the original EIT structures. Obviously shown in simulation, much higher sensitivities with stronger resonances have been attained in contrast to previously designed EIT sensors. Furthermore, this metamaterial integrated microfluidic sensor can be extended to other frequency ranges and has promising applications in bio-sensing and matter detection.