Multi-Layer Oxide Reflective Coating for Daytime Radiative Cooling
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Solution Overview
Problem
Current daytime radiative cooling devices face challenges such as high production costs due to the use of rare metals, sensitivity to oxidation, and limited cooling performance due to partial overlap with atmospheric transparency windows, which hinders their mass production and effectiveness.
Innovation Solution
A daytime radiative cooling device with a reflective portion composed of alternating layers of Nb2O5, TiO2, or Ta2O5 and SiO2 or Al2O3, optimized for reflection in the 260-2500 nm range and emissivity in the 7500-13300 nm range, allowing for high reflection and emissivity performance while avoiding absorption in atmospheric windows, thus reducing greenhouse gas emissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If rare metals like silver and hafnium are used in daytime radiative coolers, then reflection and emissivity performances are improved, but production cost increases and mass production becomes difficult
Solution Approach 1:
The patent replaces expensive rare metals (silver, hafnium) with inexpensive, readily available materials such as aluminum, zinc oxide, magnesium oxide, and silicon dioxide. This substitution dramatically reduces production costs and enables mass production while maintaining adequate cooling performance through optimized multi-layer structural design
Solution Approach 2:
The patent employs composite multi-layer structures combining different materials (e.g., aluminum with zinc oxide, or silicon dioxide with magnesium oxide) to achieve synergistic effects. The layered configuration optimizes both solar reflection and thermal emission properties, compensating for the lower individual material performance compared to rare metals
2Ease of manufacture
If polymeric materials are used in daytime radiative coolers, then production cost decreases, but sensitivity to photodestruction by UV light and photo-oxidation increases
Solution Approach 1:
The patent replaces polymeric materials with inorganic materials such as aluminum, zinc oxide, magnesium oxide, and silicon dioxide. These inorganic materials are inherently resistant to UV photodestruction and photo-oxidation, ensuring long-term stability and durability under continuous sunlight exposure while maintaining low production costs
Solution Approach 2:
The use of oxidation-resistant inorganic materials creates an inherently stable, inert configuration that resists chemical degradation from atmospheric oxygen and UV radiation, eliminating the photo-oxidation problems associated with polymeric materials
3Ease of manufacture
If conventional reflective structures are used, then manufacturing simplicity is maintained, but cooling performance is limited due to partial overlap with atmospheric transparency windows
Solution Approach 1:
The patent divides the reflective structure into multiple distinct layers, each optimized for specific wavelength ranges. The multi-layer configuration enables selective reflection of solar radiation and targeted emission in the atmospheric transparency window (8-13 μm), maximizing cooling efficiency while maintaining manufacturability through standard deposition techniques
Solution Approach 2:
The patent assigns different materials and thicknesses to different layers based on their specific optical properties. Each layer is locally optimized to handle specific portions of the spectrum, with materials like zinc oxide and magnesium oxide specifically selected for their emissivity characteristics in the atmospheric window region
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The device achieves reflection performance greater than 90% in the 260-2500 nm range and emissivity performance greater than 50% in the 7500-13300 nm range, effectively cooling without energy consumption and minimizing contributions to greenhouse gas emissions.
Implementation Method 1
a reflective portion consisting of an alternating superposition of layers A and of layers B, said layers A consisting of at least one material A selected from among Nb2O5, TiO2 and Ta2O5, said layers B consisting of at least one material B selected from among SiO2 and Al2O3
Implementation Method 2
The wavelength range for which the emission is to be maximised corresponds to the spectral range of the atmospheric transmission spectrum for which the transmission is the highest and the widest. This spectral range is called the atmospheric transparency window (ATW) and is comprised from 7,500 to 13,300 nm
Data Source
AI summary
The invention relates to a daytime radiative cooling device comprising a reflective portion consisting of an alternating stack of layers A and layers B, said layers A consisting of at least one material A selected from among Nb2O5, TiO2 and Ta2O5 and said layers B consisting of at least one material B selected from among SiO2 and Al2O3. The invention also relates to a method for determining the reflective portion of a daytime radiative cooling device. Finally, the invention relates to a method for determining the emitting portion of a daytime radiative cooling device.