Terahertz metamaterial sensing on polystyrene microbeads: shape dependence

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. (C) 2015 Optical Society of America.