In this paper, a photo-excited switchable terahertz metamaterial (MM) polarization converter/absorber has been presented. The switchable structure comprises an orthogonal double split-ring resonator (ODSRR) and a metallic ground, separated by a dielectric spacer. The gaps of ODSRR are filled with semiconductor photoconductive silicon (Si), whose conductivity can be dynamically tuned by the incident pump beam with different power. From the simulated results, it can be observed that the proposed structure implements a wide polarization-conversion band in 2.01–2.56 THz with the conversion ratio of more than 90% and no pump beam power incident illuminating the structure, whereas two absorption peaks operate at 1.98 THz and 3.24 THz with the absorption rates of 70.5% and 94.2%, respectively, in the case of the maximum pump power. Equivalent circuit models are constructed for absorption states to provide physical insight into their operation. Meanwhile, the surface current distributions are also illustrated to explain the working principle. The simulated results show that this design has the advantage of the switchable performance afforded by semiconductor photoconductive Si, creating a path towards THz imaging, active switcher, etc.

The design of an optically transparent and flexible metamaterial absorber was presented and fabricated. For this purpose, we use two different patterned silver nanowire films separated by the space layer, forming a transparent sandwiched structure with an ultrathin thickness. By analyzing the equivalent circuit model and distribution of electric field and current, the absorption physical mechanism has been theoretically investigated. The results show that the structure can achieve above 0.8 absorptions from 6 GHz to 18 GHz, and at the same time, this absorber also can obtain wide-angle property. The optical transmittance of the fabricated absorber exceeds 82% in the visible band. The results demonstrate that transparency and flexibility are the additional benefits that make the proposed absorber suitable for various potential applications.