A quadrupolar-symmetric VO ₂ metasurface with edge-plasmonic dipoles for ultrabroadband and polarization-insensitive terahertz absorption

Obtaining broadband terahertz (THz) absorbers with simple structures is crucial for terahertz device research. In light of the temperature-controlled phase transition property of vanadium dioxide (VO₂), this study designed and realized a dynamically tunable broadband terahertz absorber driven by electric dipole resonance. The device achieves broadband absorption over 90% across the frequency range of 3.56-10.53 THz, featuring an absolute bandwidth of 6.97 THz, and exhibits near-perfect absorption characteristics in the frequency bands of 4.04-4.54 THz and 9.4-9.52 THz. Through the comprehensive application of interference theory, impedance matching principles, the multiple-reflection interference model, electric field profile analysis, and multipolar decomposition, the study confirms that its broadband absorption mechanism stems from the edge plasmon resonance associated with the central disk induced by the square arrays at the four corners. Moreover, the slit structure between the squares and the central disk also significantly enhances the plasmon resonance intensity, thereby realizing perfect absorption over a broader frequency band. Benefiting from the highly symmetric configuration of its structure, the device exhibits excellent polarization-independent characteristics and wide-angle stability, maintaining efficient broadband absorption performance even at incident angles up to 50°. Compared with terahertz metamaterial devices previously reported, the VO₂-based device demonstrated in the present work has been significantly optimized with respect to tunable range and absorption bandwidth. This work offers a high-performance and easily integrable approach to terahertz metamaterial absorbers, exhibiting significant application prospects within fields such as solar absorber coatings, terahertz stealth devices, and medical diagnostics.