A Switchable Wideband Absorber/Reflector using $\text{VO}_{2}$ Based Metasurface in Terahertz Range

In the paper, a thermally switchable wideband terahertz absorber/reflector incorporating patterned vanadium dioxide (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{VO}_{2}$</tex>) metasurface (MS) has been suggested and thoroughly investigated. The proposed MS design consists of two <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{VO}_{2}$</tex> rings at the top, gold as base, and silicon dioxide as a dielectric spacer separating them. It functions as an excellent absorber demonstrating an outstanding absorption bandwidth of 5.07 THz with over 90 % absorbance within the frequency spanning from 5.35 to 10.42 THz when subjected to normal incidence under metallic state (conductivity, <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\sigma=2 \times 5 ~\mathrm{S} / \mathrm{m}$</tex>) of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{VO}_{2}$</tex>. Moreover, when <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{VO}_{2}$</tex> transition in its insulating state (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\sigma= 200 ~\mathrm{S} / \mathrm{m}$</tex>), the intensity of absorption peak falls to merely 1.76 %, reflecting almost all the incident waves. It shows polarization insensitivity owing to its fourfold symmetry. Moreover, the MS absorber maintains of over 90 % absorption efficiency for incident angles up to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\pm 50^{\circ}$</tex> under both transverse electric and transverse magnetic polarization. The electric field, magnetic field, and power loss distribution analyses reveals that the top layer comprising <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{V O}_{\mathbf{2}}$</tex> is primarily responsible for the wideband absorption/reflection. Owing to its peculiar traits, the designed metasurface holds great potential in the fields of modulation, THz imaging, optical switching and other futuristic 6 G applications.