The metamaterials offer methodology and infinite possibilities for ultra-broadband microwave absorption (MA). However, maintaining stable broadband MA under extreme high-temperature environments remains one of the most cutting-edge challenges. Herein, we report a RuO ₂ /glass resistive material for the fabrication of microwave-absorbing metasurfaces. Based on tunneling effect, an ultra-low temperature coefficient of resistance was achieved in RuO ₂ /glass, resulting in temperature-insensitivity of its electrical properties, thereby ensuring stability of MA properties of metasurfaces against temperature. Furthermore, using low-dielectric alumina aerogel composites and Al ₂ O _3f /Al ₂ O ₃ ceramic composites as dielectric spacer layer, we propose the multifunctional composites integrated with MA, thermal insulation and load-bearing (MTL). The MTL integrated composites show an impressive broadband (2~12 GHz) MA performance that is ultra-robust against temperature variations (25~1000 °C), thermal shock (50 cycles at 25~1000 °C), incidence angle (±45°) and polarization. Additionally, the integrated composites also demonstrate a long-term thermal insulation ability and a high compressive modulus (6.58 MPa). This advancement provides insights for developing MA materials that can work in extreme multi-field environments.

A transparent and tunable metamaterial absorber with simultaneously low infrared (IR) emissivity is proposed in this Letter. The designed structure consists of an infrared shielding layer (IRSL), a radar absorber layer (RAL), and an air/water dielectric layer with an indium-tin-oxide (ITO) backplane. Both the IRSL and RAL are made of ITO films and polyethylene terephthalate substrates, so the absorber exhibits optical transparency. By changing the thickness of the water layer, the 90% absorption band can be converted from 7.6–12.5 to 12.8–18.2 GHz. The absorber is polarization insensitive and stable at wide incidence angles. The IR emission value of IRSL is 0.24. Both numerical simulations and experimental measurements demonstrated the good performance of the proposed structure, indicating its great potential applications in multi-spectrum compatible stealth.

An optically transparent chessboard metasurface is proposed to achieve wideband radar cross section (RCS) reduction in this paper. The metasurface is a single-layer sandwich structure composed of indium-tin-oxide (ITO) square patches with different sizes and surface resistances, polyethylene terephthalate (PET) substrate, and ITO backplane from the top downwards. Based on optimized multielement phase cancellation (OMEPC) to select the sizes and surface resistances of ITO patches, the proposed metasurface can achieve the 10 dB RCS reduction from 10.1 to 26.4 GHz with a relative bandwidth of 89% under normal incidence. The total thickness of the metasurface is 2 mm, which makes it highly flexible. When there is a slight cylindrical curvature on the metasurface and the curvature angle is less than 30°, an approximate 10 dB RCS reduction can still be achieved in the frequency range of 10-25 GHz under normal incidence. When the oblique incidence angle is less than 45°, the proposed metasurface also exhibits nearly 10 dB RCS reduction at the specular direction in the frequency range of 10-25 GHz. Finally, a sample is fabricated and measured, and the experimental results are in good agreement with the simulation results.

This paper proposed a single-layer checkerboard metasurface with simultaneous wideband radar cross-section (RCS) reduction characteristics and low infrared (IR) emissivity. The metasurface consists of an indium tin oxide (ITO)-patterned film, a polyethylene terephthalate (PET) substrate and an ITO backplane from the top downwards, with a total ultra-thin thickness of 1.6 mm. This design also allows the metasurface to have good optical transparency and flexibility. Based on phase cancellation and absorption, the metasurface can achieve a wideband RCS reduction of 10 dB from 10.6 to 19.4 GHz under normal incidence. When the metasurface is slightly cylindrically curved, an RCS reduction of approximately 10 dB can still be achieved from 11 to 19 GHz. The polarization and angular stability of the metasurface have also been verified. The filling rate of the top ITO-patterned film is 0.81, which makes the metasurface have a low theoretical IR emissivity of 0.24. Both simulation and experimental results have verified the excellent characteristics of the proposed checkerboard metasurface, demonstrating its great potential application in radar–IR bi-stealth.

A transparent metamaterial absorber (MMA) with both tunable absorption bandwidth and low infrared (IR) emissivity is proposed in this paper. The MMA is hierarchical, which consists of an infrared shielding layer (IRSL), two radar-absorption layers (RALs), an air/water layer, and an indium–tin–oxide (ITO) backplane from the top downwards. The IRSL and the RALs are made of ITO patterns etched on polyethylene terephthalate (PET) substrates. By changing the thickness of the water, the 90% absorption bandwidth can be tuned from 6.4–11.3 GHz to 12.7–20.6 GHz, while retaining good polarization and angular stability. An equivalent circuit model (ECM) is present, to reveal the physical mechanism of absorption. The proposed MMA has a low theoretical IR emissivity of about 0.24. A sample was fabricated and measured, and the experimental results are consistent with the simulation results, showing its potential applications in stealth glass and multifunctional radome.

In this letter, a novel active frequency-selective surface (AFSS) with a wide reconfigurable operation band is proposed. Based on the switchability of p-i-n diodes and the flexibility of biasing strategies, the proposed AFSS can be controlled to operate in four modes: dual-polarized ultrawideband shielding, TE- or TM-polarized wave selection, and dual-polarized bandpass filtering. The advancement of the proposed AFSS lies in its third-order wideband switchable frequency responses and the simple, one-layer bias design with no extra feeding network. The symmetric structure of the proposed AFSS makes it polarization-insensitive and polarization-independently controllable. Simulation results illustrate that the proposed AFSS achieves a wideband high transmittance (|S21| ≥ -0.5 dB) window covering 7.78-12.50 GHz with a fractional bandwidth of 46.55% for TE-polarization and 7.84-12.52 GHz (45.97%) for TM-polarization under normal incidence in bandpass filtering or corresponding polarization selection modes. In the shielding mode, the proposed AFSS can achieve an ultrawide stopband from 0 GHz to 20 GHz under normal incidence. A prototype of the proposed AFSS has been fabricated and measured. The measurement results are in high consistency with the simulation ones.