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We propose a switchable metamaterial absorber (MMA) for bandwidth tunable broadband and four-band absorption in the terahertz (THz) band based on the phase-transition characteristics of vanadium dioxide (VO2). The proposed MMA can achieve over 90% broadband absorption in the 3.06–7.61, 3.18–8.91, and 2.78–9.22 THz ranges when the conductivity of VO2 is 3 × 1 0 5 , 3 × 1 0 4 , and 2 × 1 0 4 S m − 1 , respectively, and has the advantages of polarization insensitivity and wide-angle absorption. When VO2 is in the insulator phase, the MMA can achieve four-band high absorption, and the absorptance can reach 99% at 2.23, 4.06, 5.80, and 9.82 THz. Through the joint action of the multi-layer structure, the proposed MMA solves the problem that when only VO2 is used to tune the broadband absorption, the decrease in the conductivity of VO2 by 1 order of magnitude will lead to the obvious decrease in the broadband absorption bandwidth. A switchable absorber designed by a simple tuning method without changing the structure has significant development prospects in stealth technology and selective thermal emitters. [ABSTRACT FROM AUTHOR]

A switchable bi-functional optical metamaterial for broadband absorption and broadband cross-polarization conversion is proposed in the terahertz band based on the phase transition of vanadium dioxide (VO 2). When VO 2 is in the metal phase, the designed metamaterial has the function of a broadband absorber. This absorber consists of a VO 2 top structure, a polyimide layer, and VO 2 film. Calculated results show that the absorptance of the absorber is higher than 90% in the 3.33–5.62 THz range. Because of its symmetry, the absorber is insensitive to polarization and maintains high absorptance in incident angles from 0° to 60°. When VO 2 is in the insulator phase, the designed metamaterial has the function of a broadband cross-polarization converter. This polarization converter comprises two gap gold square rings, a polyimide layer, and a gold substrate. The calculated results show that more than 90% cross-polarization conversion can be achieved at the vertical incidence of x and y polarization in the 2.54–4.55 THz range. Nearly 100% cross-polarization conversion can be achieved at 2.62, 3.29, and 4.33 THz. The designed metamaterial has a wide potential application prospect in fields including stealth technology, solar electromagnetism, and radar communication. • Have the dual functions of broadband absorption and broadband polarization. • The switching of dual functions can be realized within similar operating bandwidths. • Function switching can be realized by a small range of temperature changes. • High working efficiency. [ABSTRACT FROM AUTHOR]