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US-12618002-B2 - Passive thermal switch coating and a method relating thereto

US12618002B2US 12618002 B2US12618002 B2US 12618002B2US-12618002-B2

Abstract

A passive thermal switch coating can include: a first thermochromic oxide layer; a layer of an infrared-transparent dielectric material; and a second thermochromic oxide layer. The infrared-transparent dielectric material can be disposed between the first thermochromic oxide layer and the second thermochromic oxide layer. The thermal switch coating can also include a substrate, and the second thermochromic oxide layer can be disposed on the substrate.

Inventors

  • Ken Araki
  • Richard Z. Zhang

Assignees

  • UNIVERSITY OF NORTH TEXAS

Dates

Publication Date
20260505
Application Date
20230708

Claims (20)

  1. 1 . A passive thermal switch coating comprising: a first thermochromic oxide layer formed as a periodic nanowire array from VO 2 ; a layer of an infrared-transparent dielectric material; and a second thermochromic oxide layer, wherein the infrared-transparent dielectric material is disposed between the first thermochromic oxide layer and the second thermochromic oxide layer.
  2. 2 . The passive thermal switch coating of claim 1 , further comprising: a substrate, wherein the second thermochromic oxide layer is disposed on the substrate.
  3. 3 . The passive thermal switch coating of claim 1 , further comprising: a second layer of an infrared-transparent dielectric material disposed on the first thermochromic oxide layer, wherein the first thermochromic oxide layer is disposed between the layer of the infrared-transparent dielectric material and the second layer of the infrared-transparent dielectric material.
  4. 4 . The passive thermal switch coating of claim 3 , wherein the layer of the infrared-transparent dielectric material and the second layer of the infrared-transparent dielectric material are formed from a same infrared-transparent dielectric material.
  5. 5 . The passive thermal switch coating of claim 3 , wherein the layer of the infrared-transparent dielectric material and the second layer of the infrared-transparent dielectric material are formed from different infrared-transparent dielectric materials.
  6. 6 . The passive thermal switch coating of claim 1 , wherein the nanowire array forms a grating.
  7. 7 . The passive thermal switch coating of claim 1 , wherein the second thermochromic oxide layer is formed from VO 2 .
  8. 8 . The passive thermal switch coating of claim 1 , wherein the infrared-transparent dielectric material comprises BaF 2 , MgF 2 , KBr, or any combination thereof.
  9. 9 . The passive thermal switch coating of claim 1 , wherein the passive thermal switch coating is configured to have a variable thermal emissivity between about 0.8 and about 0.2 based on a change in temperature of the passive thermal switch coating.
  10. 10 . The passive thermal switch coating of claim 1 , wherein the passive thermal switch coating is configured to have a change in a thermal emissivity of at least 0.5 based on a change in temperature.
  11. 11 . A method of providing the passive thermal switch coating of claim 1 , the method comprising: disposing the first thermochromic oxide layer; disposing the layer of the infrared-transparent dielectric material; and disposing the second thermochromic oxide layer to form the passive thermal switch coating, wherein the infrared-transparent dielectric material is disposed between the first thermochromic oxide layer and the second thermochromic oxide layer.
  12. 12 . The method of claim 11 , further comprising: disposing a substrate, wherein the second thermochromic oxide layer is disposed on the substrate.
  13. 13 . The method of claim 11 , further comprising: disposing a second layer of an infrared-transparent dielectric material disposed on the first thermochromic oxide layer, wherein the first thermochromic oxide layer is disposed between the layer of the infrared-transparent dielectric material and the second layer of the infrared-transparent dielectric material.
  14. 14 . The method of claim 13 , wherein the layer of the infrared-transparent dielectric material and the second layer of the infrared-transparent dielectric material are formed from a same infrared-transparent dielectric material.
  15. 15 . The method of claim 13 , wherein the layer of the infrared-transparent dielectric material and the second layer of the infrared-transparent dielectric material are formed from different infrared-transparent dielectric materials.
  16. 16 . The method of claim 13 , further comprising: disposing a high contrast grating formed on the second layer of the infrared-transparent dielectric material on a side of the second layer of the infrared-transparent dielectric material opposite the first thermochromic oxide layer.
  17. 17 . The method of claim 11 , wherein the first thermochromic oxide layer or the second thermochromic oxide layer is formed from VO 2 .
  18. 18 . The method of claim 11 , wherein the infrared-transparent dielectric material comprises BaF 2 , MgF 2 , KBr, or any combination thereof.
  19. 19 . The method of claim 11 , wherein the coating varies a thermal emissivity between about 0.8 and about 0.2 based on a change in temperature of the passive thermal switch coating.
  20. 20 . The passive thermal switch coating of claim 1 , wherein the nanowire array comprises nanowires having a thickness between 50 nanometers (nm) and 150 nm.

Description

CROSS-REFERENCES TO RELATED APPLICATIONS This application claims the benefit of U.S. Provisional Application No. 63/359,365, filed on Jul. 8, 2022, and entitled “Switchable Emission Coating Comprising Thermochormic Oxide Multilayers and Reflecting High-Contrast Grating,” which is incorporated herein by reference in its entirety for all purposes. BACKGROUND Optical properties of thin films can be manipulated by introducing multilayered nanopatterns or periodic nanoelements that interface with electromagnetic waves from the visible to infrared. Various types of engineered nanoscale coatings include sub-diffraction plasmonic gratings, ultra-high reflection high contrast gratings, traditional diffraction gratings, and simple multilayers such as Fabry-Perot quarter-wave layers. Among those considered, nanoscale metasurfaces are potentially useful in photovoltaic device improvement and thermal emission regulation. SUMMARY In some embodiments, a passive thermal switch coating comprises: a first thermochromic oxide layer; a layer of an infrared-transparent dielectric material; and a second thermochromic oxide layer, wherein the infrared-transparent dielectric material is disposed between the first thermochromic oxide layer and the second thermochromic oxide layer. In some embodiments, a method of providing a passive thermal switch coating comprises: disposing a first thermochromic oxide layer; disposing a layer of an infrared-transparent dielectric material; and disposing a second thermochromic oxide layer, wherein the infrared-transparent dielectric material is disposed between the first thermochromic oxide layer and the second thermochromic oxide layer. In some embodiments, insulator-to-metal temperature phase transition vanadium dioxide (VO2) can enable radiative property switching in the mid- to far-infrared wavelengths. With computational optimization of grating arrangement and layer thickness parameters, identification of a monolithic high-performance turn-down thermal emittance coating can be no more than 2 μm thick, consisting of a VO2 sub-wavelength nanowire grating array on an index-matched Fabry-Perot dielectric thin film on an additional absorbing VO2 sublayer. The working principles of this optimized VO2 structure are its gradient refractive index allowing high through-coating transmittance in the cold state, and its near-unity emissivity from semi-metal-insulator-metal plasmonic coupling in the hot state. This anisotropic patterned structure also considers performance over polarized incident light. A survey of other Fabry-Perot cavity materials with refractive index matching points to higher turn-down performances given an optimal VO2 nanowire volume filling ratio. With 24-hour solar and environmental analysis in comparison to other VO2 metasurfaces and multilayers, this coating enables responsive passive radiative cooling at high temperatures exceeding transition. This nano- and micro-patterned coating can potentially impact self-cooling of the solar cells, batteries, and electrical devices where risk presents at high temperatures. In some embodiments, thermochromic and thermo-radiative cooling metasurfaces can require broadband high reflection in visible-to-near infrared region to block the direct sunlight. The sunlight absorption can be prevented by implementing the structure that creates high contrast in refractive index using Si and Ge. The near-wavelength high contrast grating and prism array provides less solar absorption, but full transparency in mid-infrared region. Similar electromagnetic field responses are observed for both structures to enhance reflectance greater than 0.99. Simultaneous VIS-NIR reflection and MIR transparency may be achieved. In some embodiments, passive infrared emittance switching can be achieved with a metal-to-insulating phase transition material vanadium dioxide (VO2), but its non-transitioning bandgap results in high absorptance in the visible wavelength range. To achieve a half-order reduction of absorptance in the visible to near-infrared region, integrated dielectric photonic metasurface structures can be designed on monolithic VO2 coatings. This combination of nano- and/or micro-patterned dielectric diffractive and resonant gratings with a multilayer VO2 structure can preserve the terrestrial thermal wavelength emission switching capabilities. A periodic microscale diffractive prism array can be demonstrated by comparing the reflectance provided by either infrared-transparent germanium (Ge) or silicon (Si). Despite the advantage of total internal reflection in the broad near-infrared region, some bandgap absorption limits the performance in the visible wavelengths. A better theoretical means to reflect broadband light via waveguide-like Fabry-Pérot resonance are near-wavelength 1D and 2D High Contrast Grating (HCG) high-index metasurface structures surrounded by a low-index host medium. This HCG metasurface may allow broadband high-quality reflection within the