Electronically controlled flexible terahertz metasurface based on the loss modulation of strontium titanate

A flexible terahertz metamaterial is designed to control the transmittance through an external electric field. Two different metallic structures, the split ring (type I structure) and the split ring inside a ring (type II structure), were prepared and voltage was applied through a forked finger electrode. The structures were wrapped in a thin film made by mixing strontium titanate nanopowder with polyimide in a certain ratio. Under normal incidence, the transmittance is controlled by applying a voltage to adjust the imaginary part of the permittivity of strontium titanate. The modulation depth of the type I structure at 1.08 THz is 40.1%, and that of the type II structure at 1.16 THz is 44.7%. The working bandwidths of the two structures are 0.07 THz and 0.42 THz, respectively, and are greatly broadened by combining with the ring. The proposed design enriches the modulation method of the transmission of metamaterials and broadens the application range of flexible terahertz metasurfaces.