A Hexa-Band Refractive Index Sensor Using a Symmetrical Boss-Cross Terahertz Metamaterial Absorber with Biomedical Applications

Terahertz (THz) metamaterial absorbers have become a prominent research topic in recent years. In this paper, a hexa-band metamaterial absorber is designed for bio-medical sensing applications. The design can detect changes in the surrounding medium's refractive index and operates in the refractive index range of 1.3 – 1.4, with six prominent absorption peaks. The proposed structure comprises a square ring resonator made up of gold with a boss-cross structure at the center, on top of a Gallium Arsenide (GaAs) substrate with a thickness of 8 μm. When the surrounding medium’s refractive index is 1.4, it offers six absorption peaks at 0.537 THz, 2.573 THz, 3.025 THz, 3.146 THz, 3.493 THz, and 3.739 THz, with corresponding peak absorptions of 75%, 92.9%, 98.4%, 95.3%, 94.1%, and 97.7%, respectively. The structure was designed at n = 1.4 instead of n = 1, as several biological specimens, such as blood, breast cells, etc., have a refractive index in the range of 1.3 - 1.4, and it offers six bands for n = 1.4. This choice was made because many biomedical applications have a refractive index around 1.4. The design parameters were selected through a parametric analysis so as to achieve maximum absorption peaks. The design was also tested with different polarization angles, and it was discovered that the absorber is polarization-insensitive. This design can inspire future research on the biomedical application of THz absorbers.