An optically transparent metamaterial structure with simultaneously broadband microwave absorptivity and low infrared (IR) emissivity is proposed. Two specifically designed optically transparent metasurfaces were combined to realize radar and IR bi-stealth. One was designed to control the microwave absorption though properly modifying the impedance and resonance peaks of the meta-atom. The other was designed to control the IR radiation. Within a wide incident angle of ±60°, the proposed structure displays high absorptivity greater than 90% in the region of 6.28–12.29 GHz for TE polarization. For TM polarization, the absorptivity in the region of 7.19–15.26 GHz is greater than 90%. The IR emissivity of the metamaterial structure is about 0.30 in the IR region from 3 µ m to 14 µ m. The perfect consistency between experimental results and simulation results demonstrates that the proposal has practical application of multispectral stealth technology.

Achieving ultrawide-angle absorption is urgently required in stealth technology. In this article, we propose a promising scheme to push the development of this issue and achieve wide-angle electromagnetic (EM) absorption in a dynamically controllable manner via a reconfigurable origami-based metamaterial. For this purpose, the Miura-ori sheet is applied to load the meta-atoms with cross-shaped resistive films. Accordingly, the wide-angle absorption characteristics of the origami absorber change drastically by adjusting the folded states. In contrast with the conventional 2-D and 3-D absorbers, the 3-D origami absorber state has four normal vectors. Thus, it provides an excellent approach to prevent the deterioration of absorption in a wide-angle range. When the folding angle $\theta =35$ °, the origami absorber exhibits an ultrawideband absorption of 1.44–40 GHz and wide-angle absorption up to 70°. As a proof-of-concept, a prototype that can shift the folding angle from 0° to 90° was fabricated. The absorption performances in the two folding states of fixed folding angles are numerically simulated and experimentally verified in the microwave regime. We believe that the better coverage incident-angle characteristics of the proposed reconfigurable origami-based absorber at specific folding state broaden its applications in various fields, such as EM pollution, radar technology, and EM invisibility.

A broadband tunable metematerial absorber is proposed and demonstrated. As demonstrated in waveguide, the absorber consists of eight U-shaped ferrite particles and a metallic ground plane. These U-shaped ferrites directly act as resonators, and when the incident electromagnetic wave and applied magnetic field are simultaneously acting on the Ushaped ferrite particles, U-shaped ferrites can produce ferromagnetic resonance (FMR). Absorption frequency of the allferrite absorber can be tuned by the applied magnetic field and the saturation magnetization. Simulation results show absorption above 70% in the frequency range from 8.55 GHz to 10 GHz under applied magnetic field with 0 H =2700 Oe. By analysis, we find that the magnetic loss and dielectric loss lead to broadband absorption. The experiment test agrees well with the simulation results under different applied magnetic fields. This work provides an alternative route to realize tunable perfect absorbers with all-ferrite structures. With the artificial design of ferrite materials, the broadband tunable absorber can be designed and well serve in high power environment.

In this paper, we present the design, fabrication and characterization of a dual band tunable metamaterial absorber (MMA), which can be tuned by the applied magnetic field and modulated by the permittivity of its components. The MMA consists of a periodic array of cuboid ferrites and a metal ground plane. Unlike other MMAs, the proposed MMA avoids utilizing resonant metallic parts, and only employ ferrites as resonators, making fabrication easy and tuning more convenient. When the incident electromagnetic wave and applied magnetic field act on the ferrites simultaneously, cuboid ferrites can produce ferromagnetic resonance. Modulated by its permittivity, the proposed MMA deduces a dual band perfect absorption. The experiment test agrees well with the simulation results and shows two distinct absorption peaks of 99.9% at 9.14 GHz and 97% at 9.48 GHz, respectively. Further investigation shows that the interval of the two distinct absorption peaks can be enlarged by increasing the permittivity of the ferrite, which clearly shows how absorptivity is influenced by its dielectric properties. This work provides an alternative route to realize tunable perfect absorbers with all-ferrite structures. With the artificial design of ferrite materials, the tunable perfect absorbers can be designed freely and are well served in a high power environment.

In order to achieve compatibility stealth for the infrared radar, a multifunctional coating for achieving both radar stealth through polarization conversion and infrared emission reduction at high temperature was skillfully designed in this paper. The multifunctional coating consists of three layers, from outside to inside, followed by the metasurface, the high-temperature resistant dielectric and the metal background. The radar stealth at microwave frequency was mainly generated from polarization conversion excitation through the unsymmetrical metasurface structure. Infrared emission reduction is attributed to the reflection of the metasurface with a high filling ration. By the simulation, radar stealth with an efficiency of 90% could be achieved in the low-frequency band of 5.2-7.8 GHz, and the infrared emission of the multifunctional coating could be as low as 0.22. Furthermore, the experimental results at different temperatures demonstrated that the theoretical design is effective. The measured reflection in the 5-9 GHz frequency band is below -8 dB and lower as the frequency increases, indicating more than 84% polarization conversion is achieved. A low emission performance is also validated, with the mean emissivity as low as 0.25. Because of the excellent multispectral compatibility, the multifunctional coating may find applications in multispectral stealth technology.