Ultra-thin freestanding terahertz frequency selective surface on flexible cyclic olefin copolymer

Abstract Frequency selective surfaces (FSSs) are widely employed in spectrometers, selective absorbers, energy harvesting, and sensing devices. However, in the terahertz range, the performance of this ideal component is frequently constrained by the choice of material, which introduces a certain degree of attenuation, thereby diminishing the signal-to-noise ratio. Moreover, these FSS are often bulky and demonstrate a low extinction ratio, which limits their usage in wearables and miniaturised devices. In this work, a multi-band FSS composed of periodic microstructures on an ultrathin cyclic olefin copolymer sheet is proposed, analysed, fabricated, and evaluated using terahertz-time domain spectroscopy. The unit cell is composed of triple, evenly spaced, horizontal gold strips, linked around the middle by a fourth vertically oriented gold strip. By displacing the vertical strip, the asymmetric metasurface shows dual narrowband transmission at 1.04 THz and 1.67 THz. However, only a single narrowband transmission at 1.07 THz can be observed on a symmetric metasurface, with no displacement. The calculated Q factors are 4.52 and 16.63 at 1.04 THz and 1.67 THz, respectively, for the asymmetric metasurface. While for the symmetric metasurface, the calculated Q factor at 1.07 THz is 3.63. The proposed flexible metasurface can be tailored easily as single or dual narrowband frequency selective metasurface for channel filtering and broadband sources in emerging terahertz wireless systems.