Hierarchical Metamaterials for Multispectral Camouflage of Infrared and Microwaves

Abstract

Camouflage is an emerging application of metamaterials owing to their exotic electromagnetic radiative properties. Based on the use of a selective emitter and an absorber as the metamaterials, most reported articles have suggested the use of single‐band camouflage, however, multispectral camouflage is a challenging issue owing to a difference of several orders of magnitude in the unit cell structure. Herein, hierarchical metamaterials (HMMs) for multispectral signal control when dissipating the absorbed energy of microwaves through the selective emission of infrared (IR) waves from the unit cell structure of the HMM are demonstrated. Integrating an IR selective emitter (IRE) with a microwave selective absorber, multispectral signal control with the large‐sized unit cell structures of up to 10 cm are realized. With an IRE, the emissive power from the HMM toward 5–8 µm is 1570% higher than the Au surface, which is preventing the occurrence of thermal instability. Furthermore, we determine that the signature levels of targeted IR waves (8–12 µm) and microwaves (2.5–3.8 cm) are reduced by up to 95% and 99%, respectively, when applying the HMM.

High-temperature infrared camouflage with efficient thermal management

“…To control the surface emittance, nanostructure-based surfaces (e.g., metasurfaces 3,8 and metallic-dielectric nanowires 9 ) or films (metal 10 , semiconductor 11,12 , and multilayer films [13][14][15][16][17] ) are demonstrated with low-surface emittance over the whole IR range, and yet the radiative heat transfer is blocked, causing severe heat instability 18 . Wavelength-selective emitters [19][20][21][22][23][24][25] with radiative cooling [26][27][28][29][30][31] in the non-atmospheric window (5-8 μm) 18,20,32 are adopted to mitigate the heat instability without influencing the IR camouflage. However, they cannot operate at high temperature (<523 K) 18,20,32 .…”

“…Wavelength-selective emitters [19][20][21][22][23][24][25] with radiative cooling [26][27][28][29][30][31] in the non-atmospheric window (5-8 μm) 18,20,32 are adopted to mitigate the heat instability without influencing the IR camouflage. However, they cannot operate at high temperature (<523 K) 18,20,32 . To control the surface temperature, thermal insulators 33 , phasechange materials 33 , and transformation thermotics [34][35][36][37] have been proposed.…”

Multispectral camouflage for infrared, visible, lasers and microwave with radiative cooling

“…However, a combination of advanced detectors operating in different wavelength bands developed in recent years entails for a compatible camou age among different spectral bands, i.e. multispectral camou age 15,16 .…”

“…However, radiative heat transfer is blocked in traditional MIR camou age with broadband low emittance, introducing heat instability 31,32 . In addition, camou age against active detection systems including microwave and lidar further aggravates the heat instability due to absorbed microwave/laser energy 16 . To mitigate the severe heat instability and reduce surface temperature, high emittance is required in the MIR non-atmospheric window 5-8 μm for radiative cooling 16,27,[33][34][35][36][37] .…”

“…In addition, camou age against active detection systems including microwave and lidar further aggravates the heat instability due to absorbed microwave/laser energy 16 . To mitigate the severe heat instability and reduce surface temperature, high emittance is required in the MIR non-atmospheric window 5-8 μm for radiative cooling 16,27,[33][34][35][36][37] . Although the MIR compatible multispectral camou age including visible 22,34,38 , microwave 16,[39][40][41] , or laser 25,26,42 bands have been demonstrated, there is no existing material that simultaneously satis es all the aforementioned requirements.…”