We design and demonstrate a thermally switchable terahertz metamaterial absorber consisting of an array of orthogonal coupled split-ring metal resonators involving a VO₂ phase transition. Numerical results indicate that the active metamaterial always absorbs the TE wave in dual-band regardless of insulating and metallic VO₂, while the insulator-to-metal phase transition enables a switchable effect between dual-band and broadband absorption of the TM wave with the resonant frequency tunability of 33%. Especially under the metallic VO₂ state, the absorption properties are polarization-dependent and exhibit a switching effect between dual-band and broadband absorption with the increase of the polarization angle. The tunable absorption mechanism can be explained by effective impedance theory and electric energy density distributions. The proposed dual-band to broadband metamaterial switching absorber may have broad applications in sensors, imaging and emitters.

Coding metasurfaces have received tremendous interest due to their unprecedented control of beams through the flexible design of coding sequences. However, realizing tunable coding metasurfaces with scattering-pattern shifts in the terahertz range is still challenging. Here, we propose a VO₂-integrated coding metasurface to realize a thermally controlled scattering-pattern shift by convolution operation. The required phase profiles and high amplitudes of 1-bit and 2-bit coding metasurfaces are easily obtained only by changing the length of the VO₂ cut-wires. The insulator–metal phase transition of the VO₂ cut-wires leads to an ultrafast switching effect between multiple deflected scattering beams and one normally reflected beam. In particular, the VO₂ phase transition contributes to dynamical convolution operations of the 2-bit coding metasurface. The proposed VO₂-integrated coding metasurfaces are important for realizing tunable terahertz beam manipulation as well as arbitrary required scattering beams.

A multilayer gradient double-corrugated sandwich plate was designed, and the finite element method was employed to investigate numerically the dynamic responses of the sandwich plate subjected to underwater blast loads. ALE modeling method was adopted to simulate the fluid-structure interaction between the water and sandwich plate. TNT explosive was modeled by the JWL model, and the 304 stainless steel used for the double-corrugated sandwich plate was modeled by Johnson-Cook constitutive model. The peak deflection of the back face sheet, the support reaction at the edge of the sandwich plate, and the energy absorption of the structure were discussed to assess the underwater blast resistance of the double-corrugated sandwich structure. The results show that the configuration P₂ with the increasing core relative density has a better blast resistance ability and the weakest upper core layer of the configuration P₂ has the greater contribution to reducing the impulse transmission to the sandwich structure.

Closed-cell polyvinyl chloride foam (PVC) possesses many advantages, including its light weight, moisture protection, high specific strength, high specific stiffness, and low thermal conductivity, and is widely used as the core material in composite sandwich structures. It is increasingly used in fields with light weight requirements, such as shipbuilding and aerospace. Some of these structures can be affected by the action of dynamic loads during their lifespan, such as accidental or hostile blast loads as well as wind-loaded debris shocks. Examining the material properties of PVC foams under dynamic load is essential to predict the performance of foam sandwich designs. In this study, the compressive responses of a group of PVC foams with different densities were investigated under a broad range of quasi-static conditions and high strain rates using a universal testing machine and a lengthened Split Hopkinson press bar (SHPB) fabricated from titanium alloy. The results show that the mechanical properties of foam materials are related to their density and are strain rate-sensitive. The compressive strength and plateau stress of the foams were augmented with increased foam density. In the quasi-static strain rate range, the compressive strength of PVC foams at 10⁻¹ s⁻¹ was 27% higher than that at 10⁻⁴ s⁻¹. With a strain rate of 1700 s⁻¹, the strength was 107% higher than the quasi-static value at 10⁻⁴ s⁻¹.

Due to its unique deformation form, Negative Poisson’s ratio sandwich structure has excellent energy absorption, but the low load capacity limits its engineering applications. In this paper, we design a new negative Poisson’s ratio rectangular tube periodic sandwich structure. There are many beams in this structure which appear plastic hinges when compressed. After further compression, the rectangular tube wall buckles and the core shrinks inward, which realizes that the structure exhibits high-performance energy absorption ability and excellent mechanical properties. Three-dimensional finite element model of sandwich structure with negative Poisson’s ratio of periodic rectangular tube quasi-static compression test and low-velocity impact were investigated by the use of ABAQUS/Explicit software. The accuracy of the simulation method was verified by the comparison of test and simulation results. Based on the validated numerical models were further investigated to comprehensively understand the influence of rectangular tube unit cell wall thickness ( t) and cell height ( h) on the load capacity and energy absorption capacity of the specimen. The energy absorption capacity and mechanical properties of the proposed negative Poisson’s ratio sandwich structure could be enhanced by optimizing the design of rectangular tube unit cell wall thickness ( t) and rectangular tube unit cell height ( h). The present findings offer insights into the application of negative Poisson’s ratio sandwich structure impact energy-absorbing structures in aerospace, automotive and other fields.