Terahertz metamaterial sensing on polystyrene microbeads: shape dependence

Abstract

The shape dependence of target materials on the sensitivity of terahertz metamaterial sensors was investigated. Polystyrene microbeads with a known dielectric constant and spherical, ovular, lens-shaped, and star-shaped structures were studied. The resonant frequency showed a clear red-shift after the deposition of low-density microbeads owing to the change in the dielectric environment in the gap area of the metamaterials. Results of simulations based on a finite-difference time-domain (FDTD) method, in which the known dielectric constant of a polystyrene sphere was used, showed excellent agreement with experimental results. The shift in the resonant frequency increased linearly with the surface density, saturating at 60–80 GHz when the gap area was full of microbeads. More importantly, the resonant frequency shift was higher for non-spherical microbeads, such as the star-shaped microbeads. Therefore, the shape of the individual target material was a crucial factor in determining metamaterial sensor sensitivity.