Electromagnetically induced transparency in planar complementary metamaterial for refractive index sensing applications

We report on numerical work concerning a planar complementary metamaterial analogue of electromagnetically induced transparency (EIT) capable of exhibiting refractive index sensing with high sensitivity. The unit cell of the proposed complementary metamaterial consists of two cut-out nanostructures in a homogeneous metallic film, and can exhibit a sharply narrow reflectance transparency peak at near-infrared region breaking its structural symmetry. Moreover, the transparency peak shows highly sensitive response to the refractive index change in the surrounding medium. A complementary metamaterial sensor based on the EIT-like effect can yield a sensitivity of 928.9 nm/refractive index unit (RIU) and a figure of merit (FOM) of 19.2 increasing a supporting layer between the metamaterial and the substrate. The high sensitivity is attributed to the well-confined electric field and the increased spatial overlap between the induced local electric field and the surrounding medium. In addition, the sensitivity and FOM can be further improved by optimizing the asymmetric degree of two cut-out structures.