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

Abstract Frequency-selective surfaces are widely employed in spectrometers, selective absorbers, energy harvesting, and sensing devices. In the terahertz range, this ideal component is often limited by the choice of material that adds some degree of attenuation, reducing signal-to-noise ratio. Moreover, these frequency-selective surfaces are often bulky and demonstrate low extinction ratio, that limit their usage in wearables and miniaturised devices. In this work, a multi-band frequency-selective surface composed of periodic microstructures on ultrathin polyimide sheet, is proposed, analysed, fabricated, and evaluated using THz-TDS. 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 show 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 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.