Based on the phase transition of vanadium dioxide(VO₂), an ultra-broadband tunable terahertz metamaterial absorber is proposed. The absorber consists of bilayer VO₂ square ring arrays with different sizes, which are completely wrapped in Topas and placed on gold substrate. The simulation results show that the absorption greater than 90% has frequencies ranging from 1.63 THz to 12.39 THz, which provides an absorption frequency bandwidth of 10.76 THz, and a relative bandwidth of 153.5%. By changing the electrical conductivity of VO₂, the absorption intensity can be dynamically adjusted between 4.4% and 99.9%. The physical mechanism of complete absorption is elucidated by the impedance matching theory and field distribution. The proposed absorber has demonstrated its properties of polarization insensitivity and wide-angle absorption, and therefore has a variety of application prospects in the terahertz range, such as stealth, modulation, and sensing.

In this paper, we reported a theoretical study of a novel Surface plasmon resonance (SPR) biosensor composed of BK7 prism, gold (Au)/silver (Ag) bimetallic layer, silicon and two-dimensional (2D) materials. The bimetallic layer combines the advantages of Au and Ag and the high refractive index silicon layer enhances the electric field on the surface of the sensor, so that the sensor has a better overall performance in terms of sensitivity and figure of merit (FOM). Compared with ordinary dielectrics, 2D materials have excellent photoelectric properties, such as larger specific surface area, higher carrier density and stronger adsorption capacity, which improve the detection ability of the sensor. The sensitivity of the optimized sensor achieves 297.2°/RIU, 274°/RIU and 246°/RIU when the silicon layer is covered with graphene, MXene (Ti₃T₂C_x) and MoS₂, respectively. Compared with the traditional SPR sensor, the sensitivity of the structure has been significantly improved, and its excellent performance has broad application prospects in biosensing and other fields.

Metasurfaces have been reported to boost the signal-to-noise ratio (SNR) of magnetic resonance imaging (MRI) through their magnetic field enhancement capabilities. The varying region-of-interest (ROI) sizes in clinical imaging limit metasurfaces from realizing their potential, since the field enhancement regions of the most metasurfaces are fixed after fabrication. In this paper, a tunable metasurface (TMS) is proposed to significantly boost SNR of 1.5 T MRI in regions with different sizes. The TMS is composed of unit cells that contain a planar metal spiral loaded with a variable capacitor and placed on a square dielectric substrate. The feasibility of switching between a wide enhancement region (WER) mode and a narrow enhancement region (NER) mode by adjusting the capacitance is validated through simulations and experiments. The enhancement of the magnetic field by the WER mode of TMS boosts the SNR of the human brain voxel model by a maximum of 14.01 times, reaching a higher value of 22.81 times with the NER mode. This work offers an effective approach that can change the region sizes of field enhancement flexibly, enabling metasurfaces to adapt for various MRI scenarios such as disease detection in the large region or therapeutic monitoring in the specific small region.