Selectively VO2-loaded terahertz metasurface for dual-state broadband polarization conversion and near-unity absorption

A selectively VO 2 -loaded terahertz metasurface is studied for dual-state polarization conversion and absorption. The ground-backed unit cell consists of a broken diamond-shaped Au resonator, two square VO 2 loading regions, a circular VO 2 ring, and a polyimide spacer. With VO 2 in the insulating conductivity state, the structure operates as a reflective cross-polarization converter. PCR x remains above 0.90 from 1.5150 to 2.5849 THz, while PCRγ exceeds 0.90 from 1.5270 to 2.6726 THz. In the metallic conductivity state, A x remains above 0.90 from 1.5700 to 1.9970 THz and reaches 0.9997 at 1.8050 THz. At this frequency, the normalized impedance is 0.970 − j 0.014, and VO 2 accounts for 97.14% of the dissipated power. The conversion mechanism is supported by polarization-resolved reflection, rotated-axis phase response, and asymmetric current paths. The absorber state is associated with reflection suppression, resonator-ground coupling, and loss in the metallic VO 2 regions. Four-pass and six-pass mesh solutions differ by less than 1% in the principal response measures. Angular and tolerance analyses further show that the main features of both operating states are retained under the investigated conditions. The results numerically demonstrate dual-state terahertz operation through conductivity-state switching of selectively loaded VO 2 within a single planar unit cell.