嗯，這種造成特定波長熱輻射的方法真高明！波長8-13微米的電磁波（屬於光譜中的紅外線光），稱為「大氣窗」，因為大氣層的分子是不會與其發生熱交換反應的，所以對於這種特定波長的紅外線光，大氣層等於是透明的，可以將物體的熱以輻射方式與外太空的極低溫進行交換而帶走。
這些研究人員新發明的塑膠薄膜，會透過上面塗佈的特殊奈米玻璃珠結構，對於入射光線進行多重反射、折射與繞射，增強其能發出波長約3-20微米紅外線的能力，而獲得降溫的效果。
量產的成本跟高級鍍金隔熱遮陽膠膜差不多，其製作方法跟汽車／建築玻璃用的隔熱防曬膜也差不多，若不鍍銀的話，其製造成本會更低。理論值是能降溫40度，而這次實際試製的成果已經能降溫十度，就已經有市場價值了，例如將這個半透明的膠膜包覆在整輛車的鋼板之上，車窗玻璃部分還是貼一般透明的隔熱防曬膠膜，即使在室外的大太陽下曝曬，就還是能保持車內溫度不上升。
「2014年，史丹佛大學電機工程教授范善輝（音譯，Shanhui Fan）的團隊，使用半導體製程的鍍膜技術，創造出一種含有二氧化矽（玻璃）和二氧化鉿（Hafnium dioxide）的薄膜。當時他們發明的薄膜可以反射幾乎所有的光，而且能同時輻射出很多中紅外線，使得他們的薄膜產品可以將接觸物品的表面冷卻多達5℃。不過他們的發明得要使用無塵室來製作，所以成本超高，無法大規模量產。
當科羅拉多大學的材料科學家尹曉波（音譯，Xiaobo Yin）看到這個發明的論文時，他注意到范善輝團隊的設計是讓紅外線能在薄膜內部來回跳動，最終輻射出更多紅外線，這就像吉他的音箱一樣，聲波在裡面不斷反彈共振，而讓吉他的樂音變得更大聲。尹曉波的團隊計算出，如果在薄膜內放入直徑大約 8 微米（比紅血球稍大）的玻璃珠的話，能讓中紅外線輻射量大增。
他們的製作方式是，將玻璃粉與一種透明塑料原料（聚甲基戊烯, TPX）混合，然後把它們製成 300 毫米寬的薄膜，並且在其中一面塗銀，讓它具有像鏡子一樣的反射效果。如果把這個薄膜攤開來，底層的銀幾乎可以反射所有的可見光，所以就算在大太陽下曬，也不太會吸收能量。同時，薄膜也會吸收它所接觸的物體的熱量，並以中紅外線將能量輻射出去，所以這些熱能完全不會被空氣吸收，能一直傳到外太空而消散。」
原始論文在這裡，請自己設法下載。他們也都是先申請了專利，才發表這論文的。
Natural Communications
DOI: 10.1038/ncomms13729
DOI: 10.1038/ncomms13729
Received 9 Jun 2016 | Accepted 28 Oct 2016 | Published 13 Dec 2016
Radiative cooling to deep sub-freezing temperatures through a 24-h day–night cycle
Zhen Chen1,*, Linxiao Zhu2,*, Aaswath Raman1 & Shanhui Fan1
Radiative cooling technology utilizes the atmospheric transparency window (8–13 mm) to passively dissipate heat from Earth into outer space (3 K). This technology has attracted broad interests from both fundamental sciences and real world applications, ranging from
passive building cooling, renewable energy harvesting and passive refrigeration in arid regions. However, the temperature reduction experimentally demonstrated, thus far, has been relatively modest. Here we theoretically show that ultra-large temperature reduction for as much as 60 C from ambient is achievable by using a selective thermal emitter and by eliminating parasitic thermal load, and experimentally demonstrate a temperature reduction that far exceeds previous works. In a populous area at sea level, we have achieved an average temperature reduction of 37 C from the ambient air temperature through a 24-h day–night cycle, with a maximal reduction of 42 C that occurs when the experimental set-up enclosing the emitter is exposed to peak solar irradiance.
passive building cooling, renewable energy harvesting and passive refrigeration in arid regions. However, the temperature reduction experimentally demonstrated, thus far, has been relatively modest. Here we theoretically show that ultra-large temperature reduction for as much as 60 C from ambient is achievable by using a selective thermal emitter and by eliminating parasitic thermal load, and experimentally demonstrate a temperature reduction that far exceeds previous works. In a populous area at sea level, we have achieved an average temperature reduction of 37 C from the ambient air temperature through a 24-h day–night cycle, with a maximal reduction of 42 C that occurs when the experimental set-up enclosing the emitter is exposed to peak solar irradiance.
