Highly Sensitive Sensing of Refractive Index Using Surface Lattice Resonance in Capacitive Metal Meshes at Millimeter Wave Frequencies

We propose the use of surface lattice resonance (SLR) in capacitive metal meshes (CMMs) to permit highly sensitive measurement of the refractive index (RI) in the millimeter wave (MMW) range. CMMs, which comprise 2-D periodic arrays of square metal patches on thin quartz substrates, are one of the simplest and most classical metasurfaces. Experiments and numerical simulations performed at frequencies around 0.1 THz show that SLRs in such CMMs have extraordinarily high unloaded Q factors of greater than 1000, when the ratio of the length of the metal patch to the mesh period of the CMM and the thickness of the quartz substrate are optimized. An intense and sharp dip in transmission in excess of -60 dB at the SLR frequency with this high unloaded Q factor was produced in a CMM. Using a CMM as an RI sensor, a figure of merit (FoM) of greater than 340 for frequency interrogation and an RI resolution of better than 1.9× 10-6 RI units for phase interrogation were experimentally demonstrated. These results indicate that CMMs are superior sensors with high performance in the MMW region.