Flexible Assembled Metamaterials for Infrared and Microwave Camouflage

Abstract

camouflage platform with metamaterials to manipulate electromagnetic energy efficiently is one of the solutions to satisfy the needs in energy, [9,10] military, [11][12][13][14][15] and space applications. [16] Hence, many researchers have developed several camouflage platforms with metamaterials, [17,18] such as metal-dielectric-metal (MDM) structure, [19,20] photonic crystal, [21] multilayers, [22,23] and novel materials [24][25][26][27] to control the electromagnetic energy for breaking the limits of conventional applications. [28,29] There are two camouflage mechanisms: reduction in the reflection or the emission from the target against the detector at the specific wavelength. In reducing the reflected wave from the target such as the microwave, [30,31] metamaterials for microwave camouflage match the impedance with the medium and consume the incident wave through the energy dissipation in the structure, inducing the unity of absorptivity. Otherwise, when the detector measures the emitted wave from the target in the infrared (IR) wave, the emissivity (absorptivity) in the detected band should be zero; it means the unity reflectivity on the surface contrary to the metamaterials for microwave camouflage. These different mechanisms make the multispectral camouflage difficult because camouflage materials should satisfy both the zero and the unity absorptivity in the different spectral regimes in the same structure. Furthermore, blocking the signal from the target can induce energy accumulation based on the energy conservation law, [32] meaning that we also need to consider the energy dissipation through the undetected spectrum to prevent the unwanted energy accumulation in the structure. [33] Therefore, there have been several studies on metamaterials for camouflage with a specific property of the unity absorptivity for microwave [30,31,34] or reflectivity for IR wave. [33,[35][36][37] However, only a few studies of the multispectral metamaterials have been conducted [38,39] since they should solve the issue of size difference depending on the target wavelength. In metamaterials, the operating wavelength is proportional to the unit cell size. This requires that they contain various unitcell sizes in the same structure to cover the multispectral wavelength range such as microwave (O ∼ centimeter) and IR wave (O ≈ micrometer), [40] which makes the fabrication difficult. Light, heat, and waves in electromagnetic energy are the foundation for the advancement of human being. Camouflage materials based on metamaterials are used to excel the performance limits by manipulating the electromagnetic energy. However, multispectral camouflage materials with flexibility are difficult to fabricate because required radiative properties in each spectral regime are different and have largely different scales of the unit cell in a single structure. The authors propose flexible assembled metamaterials (FAM) by assembling the flexible infrared (IR) emitter and flexible microwave absorber. The authors adopt the intermediate layer to a...

A Lightweight, Elastic, and Thermally Insulating Stealth Foam With High Infrared‐Radar Compatibility

“…The decreased radiative energy in the above infrared band may lead to accumulated energy inside the material and thermal instability. [ 47 ] This may cause an increase in the surface temperature of the device, which may render it easily detected by infrared detectors. Therefore, in order to realize infrared stealth, reducing surface temperature of the protected equipment to suppress infrared radiation is another effective method.…”

Multifunctional Green Electromagnetic Interference Shielding Material for the Sub-6-GHz Band

“…35 In 2022, a flexible and opaque bispectrum shielding material was put forward with a wider microwave absorption (>0.9) range (2− 12 GHz) than conventional microwave absorbers and 0.25 IR emissivity. 36 Zhang et al proposed a flexible and transparent material with a 90% absorption range in 7.7−18 GHz, and the emissivity about 0.23. 37 Nowadays, bispectrum (microwave and IR) shielding multifunctional materials, whether based on conventional materials or MMAs, still struggle to satisfy both ultralow IR emissivity, optical transparency, flexibility, g s ≥ 1, and SE R < 3.01 38−42 in the sub-6G band.…”

“…Ref reported an optically transparent but inflexible material with microwave absorption over 90% at 5.8–8.3 GHz and IR emissivity of 0.52 at 8–14 μm . In 2022, a flexible and opaque bispectrum shielding material was put forward with a wider microwave absorption (>0.9) range (2–12 GHz) than conventional microwave absorbers and 0.25 IR emissivity . Zhang et al proposed a flexible and transparent material with a 90% absorption range in 7.7–18 GHz, and the emissivity about 0.23 .…”

Large‐Area and Flexible Plasmonic Metasurface for Laser–Infrared Compatible Camouflage

“…Additionally, it is very important to achieve flexible camouflage material for adapting to the random surface in practical applications. [35][36][37] Conventionally, there are two ways to realize the flexibility: i) using flexible material in each component; [19,36,38] and ii) changing the structure to reduce the mechanical stress. [35,39] However, there still exists much challenge in the fabrication of the flexible material with meticulous structures.…”