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article imageSmart windows can self-illuminate when it rains

By Tim Sandle     Jun 2, 2020 in Science
On a rainy or cloudy day illumination is affected by overcast clouds, especially through windows leading to a need to turn on lights. This is an energy hungry activity. New smart windows may provide a solution.
The idea behind the smart windows is that they have the ability to self-illuminate when the outdoor light levels drop, negating the need to turn on electrical lights within the built environment. Scientists at Pohang University of Science & Technology have created self-powering, color-changing humidity sensors. These sensors provide the basis for smart windows. There are other applications for the sensors as well, including health care and with safety management (such as indicating the presence of adverse environmental conditions).
To develop the technology, scientists worked on a variable color filter fashioned from a metal-hydrogel-metal resonator structure. At the heart of this was a chitosan-based hydrogel. The substance was then combined with solar cells to form a self-powering humidity sensor. The technology behind this was based on nanoscience and optics.
For the creation of smart windows, the final material was transformed into multilayer thin films of metal-dielectric-metal. For the self-illumination to work, the wavelength of transmitted light needs to be controlled based on the thickness and refractive index of the dielectric layer. It is the hydrogel that enables the required wavelength to be achieved.
Commenting on the technology, lead scientist Professor Junsuk Rho said that the technology "will create even greater synergy if combined with IoT technology such as humidity sensors that activate or smart windows that change colors according to the level of external humidity."
A hydrogel is composed of a 3D network structure which can hold up to large volumes of water and is typically manufactured using polyvinyl alcohol. The chitosan is a linear polysaccharide, derived from the shells of crustaceans like shrimps.
The research has been published in the journal Advanced Optical Materials. The research paper is titled "Self‐Powered Humidity Sensor Using Chitosan‐Based Plasmonic Metal–Hydrogel–Metal Filters."
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