A broadband adjustable absorber operating in the terahertz (THz) range is presented based on a vanadium dioxide (VO₂) multiple ring structure with a certain gap design. The dynamic absorption regulation of the absorber is realized by utilizing the phase-change characteristics of VO₂, which is easily affected by external temperature. The simulation results show that when the external temperature reaches 350 K, the conductivity of VO₂ can reach 2 × 10⁵ S/m, and the absorber can obtain an absorption efficiency of over 90% from 3.01 THz to 7.27 THz. At this time, the absorption bandwidth reaches 4.26 THz with 82.9% of the relative bandwidth. When the external temperature reaches 300 K, the conductivity changes to 200 S/m, and the absorption efficiency is less than 4%, indicating the strong THz absorption dynamic adjustable ability. Further, through analyzing the optimal impedance matching and the electric field distribution under different conductivities, the broadband absorption mechanism of the absorber can be obtained. Finally, this paper shows that the absorption spectrum cannot be influenced by small angle incidences in both polarization modes. Therefore, the ultra-wideband adjustable absorber is expected to have applications in the terahertz fields of detecting, modulating, and switching.

A novel non-planar coding metasurface optimized by discrete particle swarm algorithm (DPSO) is proposed in terms of the property of wideband radar cross-section (RCS) and diffuse scattering. The design consists of two unit cells, “0” and “1”, which have a 180° ± 37° phase difference for phase interference cancellation. The 10 dB monostatic RCS reduction frequency range of the metasurface is from 6.4 to 29.6 GHz, and its bandwidth ratio is 4.62:1, under normal incidence of the two polarizations. Compared to the planar surface, the non-planar surface has a greater bandwidth with respect to the monostatic and bistatic RCS reduction. The results declare its properties of ultra-wideband, angle insensitivity, and polarization insensitivity. Finally, the theoretical analysis, simulation, and experimental results match perfectly, indicating that the metasurface can be used in the RCS reduction or other microwave applications with wider RCS reduction and diffuse scattering.