Thermally Switchable Broadband Terahertz Metamaterial Absorber Based on VO 2 for Low‐Reflection Absorptive Shielding

Abstract

Thermally reconfigurable terahertz absorbers are of interest for active electromagnetic control, particularly where broadband absorption and low‐reflection shielding are required. In this work, a VO 2 ‐based thermally switchable metamaterial absorber is numerically investigated in the 1–4 THz range. The proposed unit cell consists of one patterned VO 2 resonator located on a polyimide substrate and positioned above a continuous silver ground plane. The optimized structure has a compact subwavelength footprint, corresponding to at 1.58 THz. When VO 2 is in the metallic state, the absorber maintains more than 90% absorption from 1.58 to 3.26 THz, giving an absolute bandwidth equal to 1.68 THz, corresponding to a fractional bandwidth of 69.42%. Two near‐perfect absorption peaks are obtained at 1.82 and 2.93 THz, with absorptance values of 99.83% and 99.91%, respectively. Within the 1.58–3.26 THz absorption band, the silver‐backed structure provides a transmission‐based shielding effectiveness from 54.32 to 62.22 dB, while more than 90% of the incident power is absorbed rather than reflected. In the insulating state, the absorption remains very low over the same band, confirming a clear thermally controlled OFF/ON response. The broadband absorption is attributed to the spectral overlap of two resonant modes, supported by reflection suppression from the metal‐backed configuration and improved impedance matching in the metallic VO 2 state. Field distribution and power‐loss‐density analyses further clarify the electromagnetic energy confinement and dissipation mechanisms. These results support the proposed structure as a compact platform for thermally switchable broadband THz absorption and low‐reflection absorptive shielding.