A bifunctional sensor metasurface enabling efficient simultaneous absorption and polarization conversion

Abstract This study presents a bifunctional terahertz metasurface sensor whose unit cell consists of three different aluminum patterns layers, four layers dielectric-slab of silicon dioxide (SiO ₂ ) and an aluminum backplate. The metasurface enables simultaneous dual-peaks absorption and dual-broadband linear-to-linear polarization (LP-LP) conversion. The absorption rate of the metasurface is above 90% at 7.75 THz and 8.57 THz. Owing to the sharpness of the absorption peaks, it has applications in sensing that possess surrounding environmental and dielectric sensing corresponding to different peaks, respectively. The surrounding environmental sensing demonstrates a high sensitivity of 696 GHz frequency shift with refractive index changing at the second peak. While at the first peak, it sensitives to the different dielectric-slab, and it exhibits a sensitivity of 123 GHz RIU ⁻¹ (Refractive index unit). In addition, the polarization conversion rate of the proposed metasurface surpasses 90% in the range of 7.83–8.51 THz and 8.63–9.43 THz. The corresponding reflection spectra, calculated by multiple interference theory, show good agreement with the simulation results. Furthermore, the physical mechanisms of absorption and polarization conversion are analyzed by the surface current distributions. Thus, the designed metasurface has potential applications in THz biomolecule detection, environmental pollutant monitoring, and relevant communication fields.