Thermochromic VO2-based smart radiator devices with ultralow refractive index cavities for increased performance

Design of highly reflective film for smart radiation device

“…Wang et al reported a Ag/HfO 2 /VO 2 three-layer SRD which realized a ∆𝜀 of 0.55 [12]. Beaini et al studied the effect of individual layers on the SRD performance, and achieved a large ∆𝜀 0.66 by selecting BaF 2 as the optical medium layer [13]. However, those works did not involve the investigation on solar absorption (𝐴 ).…”

Passive radiative temperature regulator: Principles and absorption-emission manipulation

“…For instance, Fig. 1(a) gives the extinction coefficients of VO2, which is a typical phase-changing material with a moderate and tunable transition point close to room temperature [41]. For instance, Wang et al have demonstrated that the IMT temperature of as-prepared VO2 can be decreased from 58°C to 5°C as the tungsten doping concentration increased from 0 wt% to 3 wt% [42].…”

“…To accomplish this, as shown in Fig. 6(a), a sandwich configuration of VO2(20 nm)/ZnSe(1000 nm)/Ag(200 nm) is employed according to our optimization based on the experimental refractive index data from [41,[45][46][47], which can form an F-P cavity as the VO2 layer turns into the metallic phase [48]. The physical principle is the same as the switching component of VO2/MgF2/W proposed by Ono et al [33].…”

“…6(b), the parasitic absorption is too high in both the insulator (αsolar = 0.32) and metal states (αsolar = 0.44), which fails to satisfy the requirement of RTRs on parasitic absorption ratio (i.e., αsolar < 0.13). The strong parasitic absorption of the sandwich configuration is reasonable due to the F-P resonances in the visible and the large absorption coefficient of VO2 [41,[49][50][51], which is also a well-known open technical challenge in the field of smart windows. Based on the experimental material data of VO2 [37], the configuration of RTRs proposed by [26] is revisited, which proves that the structure without solar shielding could not function as an ideal RTRs efficiently, mainly due to the high parasitic absorption of VO2 layers.…”

Thermochromism Frequency-Selective Emitter for Infrared Stealth Application

“…Moreover, since the infrared radiation intensity of the environment vary dynamically because of temperature, moisture, and solar intensity, infrared materials capable of emissivity modulation or the adaptive infrared stealth materials have aroused research interest in recent years. − Vanadium dioxide (VO 2 ) is one of the promising thermochromic materials for emissivity engineering applications. − Below the transition temperature ( T c ), VO 2 is in the insulating state and exhibits high infrared transmission. Above T c , VO 2 is in the metallic state and has high reflection efficiency in the infrared region. − In recent years, many efforts have been focused on improving the thermochromic effect of VO 2 for infrared stealth and radiative cooling through doping, − structural design, − and process optimization. , Liu et al , prepared the W-doped VO 2 thin films by the sol–gel method for adaptive infrared stealth. The emissivity of pure VO 2 varies between 0.9 and 0.25 as the temperature changes, while the phase transition temperature and the emissivity modulation range would decrease with the doping of W. Numan et al proposed a layered stack of a-Si:H/SiO 2 /VO 2 on the flexible Al sheet, which shows a high emission-switching Δε of 0.39 with the potential applications as smart radiation devices.…”