A Thermal Radiation Modulation Platform by Emissivity Engineering with Graded Metal–Insulator Transition

Abstract

Thermal radiation from a black body increases with the fourth power of absolute temperature (T4), an effect known as the Stefan–Boltzmann law. Typical materials radiate heat at a portion of this limit, where the portion, called integrated emissivity (εint), is insensitive to temperature (|dεint/dT| ≈ 10−4 °C–1). The resultant radiance bound by the T4 law limits the ability to regulate radiative heat. Here, an unusual material platform is shown in which εint can be engineered to decrease in an arbitrary manner near room temperature (|dεint/dT| ≈ 8 × 10−3 °C–1), enabling unprecedented manipulation of infrared radiation. As an example, εint is programmed to vary with temperature as the inverse of T4, precisely counteracting the T4 dependence; hence, thermal radiance from the surface becomes temperature‐independent, allowing the fabrication of flexible and power‐free infrared camouflage with unique advantage in performance stability. The structure is based on thin films of tungsten‐doped vanadium dioxide where the tungsten fraction is judiciously graded across a thickness less than the skin depth of electromagnetic screening.

Ultrathin Titanium Carbide (MXene) Films for High‐Temperature Thermal Camouflage

“…[6] Reducing the surface temperature and regulating the surface IR emissivity of an object are two main approaches to realize thermal camouflage. [7] Based on these strategies, various materials and systems, such as phase-change materials (PCMs), [2,8] thermal insulation materials, [9][10][11] metal film/coatings, [12][13][14] metasurfaces, [15][16][17][18][19] and several other methods, [20][21][22][23][24][25][26][27] have been developed to date. However, the following problems remain.…”

Wafer-scale freestanding vanadium dioxide film

“…In the temperature ( T thermocouple ) range from 25° to 63°C, the temperature difference between T butterfly and T thermocouple is less than 7°C, and there is an abrupt increase to 27.6°C when the T thermocouple is at 68.3°C. The reflectance of M-phase VO 2 is higher than that of the I-phase VO 2 in the mid-IR region and thus absorbed fewer IR photons ( 36 ). According to Kirchhoff’s law of radiation, the thermal radiation of the M-phase VO 2 decreases because of lower IR absorption.…”

Millikelvin-resolved ambient thermography

“…The function of TIS builds on the well-known MIT ( 13 ) of the strongly correlated electron material W x V 1− x O 2 at the temperature T MIT ≈ 67°C − 24°C· x ·100, which can be conveniently tuned from 67° to −100°C by varying the composition x ( 14 , 15 ). In the insulating (I) state, the material is basically transparent to IR in the 8- to 14 μm wavelength range ( 16 , 17 ), and incoming IR radiation will penetrate through the top two layers with negligible absorption and reflected by the Ag mirror, as shown in Fig.…”