In this article, we present an indium antimonide (InSb)-based metasurface absorber (MA) using a complementary ring structure. The proposed MA exhibits absorption characteristics in the terahertz frequency range spanning from 1.0 to 2.2 THz. Within this frequency range, the MA demonstrates dual-band tunability, achieving approximately 100% absorption. Geometric parameters such as the outer ring radii, ring width, and InSb layer thickness are systematically adjusted to fine-tune the absorption frequency of the MA. In addition, we explore the refractive index sensing capabilities by introducing different refractive index materials into the air-filled complementary ring cavity. Notably, we achieve a peak refractive index sensitivity of 555 GHz per refractive index unit (RIU) for the first absorption peak at a minimum radius of 60 mu m.
