Multifunctional integrated metamaterials for radar-infrared-visible compatible multispectral stealth.

Metamaterials offer exciting opportunities for developing multispectral stealth due to their unique electromagnetic properties. However, currently transparent radar-infrared-visible compatible stealth metamaterials typically involve complex hierarchical designs, leading to thickness and transparency limitations. Here, we propose an integrated metamaterial for multispectral stealth with high transparency. Our design features an ITO/dielectric/ITO sandwich structure, with the upper-layer ITO acting as a resonator for broadband microwave absorption while maintaining a high filling ratio to suppress infrared (IR) radiation. Experimental results demonstrate excellent performance, with over 90% microwave absorption in 8-18 GHz, an IR emissivity of approximately 0.36 in 3-14 µm, an average optical transmittance of 74.1% in 380-800 nm, and a thickness of only 2.4 mm. With its multispectral compatibility, the proposed metamaterial has potential applications in stealth and camouflage fields.

High temperature infrared-radar compatible stealthy metamaterial based on an ultrathin high-entropy alloy.

In this work, a high temperature infrared (IR) and radar compatible stealthy metamaterial based on ultrathin high-entropy alloy are proposed. From room temperature to 600°C, the fabricated radar absorption layer (RAL) can have wideband absorption in X-band (8.2-12.4 GHz) with average absorption 78% owing to magnetic resonance and ohmic loss. The ultrathin high-entropy alloy film is further design as infrared shielding layer (ISL) due to low-emissivity property. The ISL and RAL consist of the IR-microwave compatible stealth metamaterial. It can give rise to the strong reduction of both radar wave reflection and infrared thermal emission. Its bandwidth (absorption over 90%) is 2.15 GHz. In the infrared atmosphere window, it can suppress a half of thermal radiation. This is realized by the subtle combination between the RAL and specifically designed ISL that control the infrared emission and microwave absorption. These results show that they are practically very promising for the application of a radar-infrared bi-stealth technology in high temperature environment.

Extremely angle-stable transparent window for TE-polarized waves empowered by anisotropic metasurfaces.

Impedance mismatch generally exists upon interfaces between different media. This is especially true for TE-polarized waves with large incident angles since there is no Brewster effect. As a result, high-efficiency transmission can only be guaranteed within limited incident angle range. It is desirable that transparent windows possess robust angle-stability. In this work, we propose a strategy of realizing transparent windows with extreme angle-stability using anisotropic metasurfaces. Different from traditional isotropic materials, anisotropic metasurfaces require specific three-dimensional permittivity and permeability parameters. Theoretical formulas are derived to realize a highly efficient transmission response without angular dispersion. To validate our design concept, a two-layer cascaded electromagnetic anti-reflector is designed, and it exhibits a characteristic impedance matching for nearly all incidence angles under TE-polarization illumination. As a proof-of-concept, a prototype of extremely angle-stable transparent window is fabricated and measured. Compared with the pure dielectric plate, the reflection coefficients are on average reduced by 40% at 13.5 GHz for TE-polarized waves from 0° to 80°. Therefore, we think, anisotropic cascaded electromagnetic transparent windows are capable of tailoring the electromagnetic parameter tensors as desired, and provide more adjustable degrees of freedom for manipulating electromagnetic wavefronts, which might open up a promising way for electromagnetic antireflection and find applications in radomes, IR windows and others.

Tailoring permittivity using metasurface: a facile way of enhancing extreme-angle transmissions for both TE- and TM-polarizations.

The transmission of electromagnetic (EM) waves through a dielectric plate will be decreased significantly when the incident angle becomes extremely large, regardless of transverse electric (TE)- or transverse magnetic (TM)- polarization. In this regard, we propose a facile way of tailoring the permittivity of the dielectric material using metasurface to enhance the transmissions of both TE- and TM-polarized waves under extremely large incidence angles. Due to parallel or antiparallel electric fields induced by the metasurface, the net electric susceptibility is altered, and hence the effective permittivity can be tailored to improve the impedance matching on the two air-dielectric interfaces, which enhances the wave transmissions significantly under extreme incident angles. As an example, we apply this method to a typical ceramic-matrix composite (CMC) plate. By incorporating orthogonal meta-gratings into the CMC plate, its effective permittivity is reduced for the TE-polarized waves but increased for the TM-polarized waves under the extreme incidence angle, which can reduce the impedance for the TE-polarization and increase the Brewster angle for the TM-polarization. Therefore, the impedance matchings for both TE- and TM-polarizations are improved simultaneously and dual-polarized transmission enhancements are achieved under the extreme angles. Here, the transmission responses have been numerically and investigated using the finite-difference-time-domain (FDTD) method. A proof-of-principle prototype is designed, fabricated, and measured to verify this method. Both numerical simulations and measurement results show that the prototype can operate under extremely large incidence angles θi∈[75°,85°] with significant transmission enhancement for both TE- and TM-polarizations compared to the pure dielectric plate. This work provides a facile way to enhance the transmissions under extreme angles and can be readily extended to terahertz and optical frequencies.