Thermal camouflaging metamaterials

A Novel Strategy in Electromagnetic Wave Absorbing and Shielding Materials Design: Multi-Responsive Field Effect

Broadband multispectral compatible absorbers for radar, infrared and visible stealth application

Thermal radiation control has attracted increasing attention in a wide range of field, including infrared detection, radiative cooling, thermal management, and thermal camouflage. Previously reported thermal emitters for thermal camouflage presented disadvantages of lacking either tunability or thermal stability. In this paper, we propose a tunable thermal emitter consisting of metal-insulator-metal (MIM) plasmonic metamaterial based on phase-change material Ge2Sb2Te5 (GST) to realize tunable control of thermal radiation in wavelength ranges from 3 μm to 14 μm. Meanwhile, the proposed thermal emitter possesses near unity emissivity at the wavelength of 6.3 μm to increase radiation heat dissipation, maintaining the thermal stability of the system. The underlying mechanism relies on fundamental magnetic resonance and the interaction between the high-order magnetic resonance and anti-reflection resonance. When the environmental background is blackbody, the tunable emitter maintains signal reduction rates greater than 80% in middle-IR and longer-IR regions from 450 K to 800 K and from room temperature to 800 K, respectively. The dependences of thermal camouflage on crystallization fraction of GST, incident angles and polarization angles have been investigated in detail. In addition, the thermal emitter can continuously realize thermal camouflage for various background temperatures and environmental background in atmospheric window in the range of 3-5 μm.

https://www.mdpi.com/2079-4991/11/2/260/pdf

Tunable Thermal Camouflage Based on GST Plasmonic Metamaterial

The size and ability of a target to reflect radar energy can be summarized into a single term, σ, known as the radar cross-section, which has units of m2. This unit shows, that the radar cross section is an area. If absolutely all of the incident radar energy on the target were reflected equally in all directions, then the radar cross section would be equal to the target's crosssectional area as seen by the transmitter. In practice, some energy is absorbed and the reflected energy is not distributed equally in all directions. Therefore, the radar cross-section is quite difficult to estimate and is normally determined by measurement.

Radar Cross Section

In this paper, an optically transparent coding metasurface structure based on indium tin oxide (ITO) thin films with simultaneously low infrared (IR) emissivity and microwave scattering reduction is proposed. To this end, two ITO coding elements which can reflect 0° and 180° phase responses are firstly designed. Based on these two elements, four coding sequences with different scattering patterns are designed. Three of them can realize anomalous reflections and the fourth can realize random diffusion of normal incident electromagnetic (EM) waves. A prototype of the random diffusion coding metasurface was fabricated and measured. The experimental results show that for normal incident EM waves, at least 10dB backward scattering reduction from 3.8GHz to 6.8GHz can be achieved, and the structure is polarization insensitive. The averaged transmittance of visible light through the coding metasurface reaches up to 72.2%. In addition, due to the high occupation ratio of ITO on the outside of the coding metasurface, a low IR emissivity of about 0.275 is obtained. Good consistency between the experiment and simulation results convincingly verifies the coding metasurface. Due to its multispectral compatibility, the proposed coding metasurface may find potential applications in multi-spectral stealth, camouflage, etc.

Optically transparent coding metasurface with simultaneously low infrared emissivity and microwave scattering reduction

An optically transparent broadband metamaterial absorber for radar-infrared bi-stealth

A visible-light-transparent camouflage-compatible flexible metasurface for infrared-radar stealth applications

Multi-spectral functional metasurface simultaneously with visible transparency, low infrared emissivity and wideband microwave absorption

Optically transparent metamaterials with the performance of infrared radar compatible stealth have been designed and manufactured on the basis of the continuous in-depth research on single-band stealth technology. In this paper, metamaterials are designed through theoretical calculations and modeling simulations. The designed structure can achieve higher than 90% broadband (8.7-32 GHz) absorption at wide-angle (45 degrees), emissivity of 0.3 in infrared atmospheric window, and optical transparency. In addition, the material can be bent, which greatly expands its application scenarios. The experimental results are consistent with the theoretical calculation and simulation results.

Changhui Tian

Papers

Optically transparent coding metasurface with simultaneously low infrared emissivity and microwave scattering reduction

An optically transparent broadband metamaterial absorber for radar-infrared bi-stealth

A visible-light-transparent camouflage-compatible flexible metasurface for infrared-radar stealth applications

Multi-spectral functional metasurface simultaneously with visible transparency, low infrared emissivity and wideband microwave absorption

Ultra-wideband flexible transparent metamaterial with wide-angle microwave absorption and low infrared emissivity.