Behavioral Resonance Alteration Using Phase Transitions in VO $_{2}$ Resonator for Thermal-Brewster Operated THz Absorber

Metal-insulator phase transitions in vanadium dioxide (VO $_{2})$ ring resonator can convert its resonance behavior to find the dual-band terahertz (THz) absorption. The surface charge distribution following the metallic boundaries in VO $_{2}$ establishes the dipolar and multipolar resonance in the lower and upper bands at frequencies 1.8 and 4.32 THz, respectively. In the insulating phase, resonance is obtained by standing waves created in the dielectric ring resonator of VO $_{2}$ with the effect of formed electric and magnetic dipole in the lower and upper bands at frequencies 3.75 and 4.45 THz, respectively. Thus, thermal variation in VO $_{2}$ can result in tunable conductivity, and hence, the upper-to-lower resonance frequency ratio (FR) can be tuned over a wide range of $1.8$ $-$ $12.4$ . Moreover, Brewster’s effect excites an extra resonance based on the quad-pol field in between the metallic dipolar and multipolar arrangement at a frequency of 3.32 THz. The proposed absorber can also offer angle-based tunability in the device response for TM-polarized incident waves. The absorber structure can offer an ultrathin geometry of thickness $\approx \lambda /15$ . The operation of the absorber is validated using electrical circuit analysis.