Fig. 1. Schematic of the proposed gap-tuned metasurface linear cross-polarization converter. (a) Illustration of the cross-section of the metasurface LP polarizer, highlighting the unconventional configuration with an air cavity between the periodic arrays comprising the top and bottom layers. (b) 3D view of the metasurfaces and the unit cell geometry. (c) Illustrations of the top and bottom metallic layers. The top and bottom metallic layers share the same pattern, but the bottom layer is rotated by 90° around the z-axis with respect to the top layer.

Fig. 2. Simulation results for the proposed gap-tuned metasurface LP converter. (a) Cross-polarization amplitude transmission, (b) co-polarization amplitude transmission, and (c) PCR spectrum as a function of d from 150 to 800 µm under normal incidence within the frequency range from 0.1 to 0.13 THz. (d) Bandwidth and amplitude transmission of the cross-polarization component at the center frequency of 0.115 THz as a function of d from 150 to 800 µm.

Fig. 3. E_y-field amplitude distributions in the top and bottom layers at the center frequency of 0.115 THz with different d values of 260, 460, and 660 µm.

Fig. 4. Structure of the proposed gap-tuned metasurface LP converter and schematic of the experimental setup. (a) Photograph of the fabricated sample and (b) part of its magnified microscopic image. (c) Simplified schematic of the experimental setup. (d) Diagram of the stretching device to adjust the spacing between the top and bottom layers.

Fig. 5. Measurement results for the proposed gap-tuned metasurface LP converter. (a) Cross-polarization amplitude transmission, (b) co-polarization amplitude transmission, and (c) PCR spectrum as a function of d from 150 to 800 µm under normal incidence within the frequency range from 0.1 to 0.13 THz. (d) Bandwidth and amplitude transmission of the cross-polarization component at the center frequency of 0.115 THz as a function of d from 150 to 800 µm.