Smart windows that reduce energy consumption

Windows that can change colours depending on humidity — and without the need for electricity — are being developed by researchers.

A joint research team from Pohang University of Science & Technology (POSTECH) and Korea Advanced Institute of Science and Technology (KAIST) successfully developed a variable colour filter using a metal–hydrogel–metal resonator structure, and combined it with solar cells to make a self-powering humidity sensor.

The research team found that when the chitosan hydrogel is made into the metal–hydrogel–metal structure, the resonance wavelength of light transmitted changes in real time depending on the humidity of the environment. This is because the chitosan hydrogel repeats expansion and contraction as the humidity changes around it.

Using this mechanism, the team developed a humidity sensor that can convert light’s energy into electricity by combining a solar battery with a water variable wavelength filter made of metal–hydrogel–metal structured metamaterial that changes resonance wavelength depending on the external humidity.

The design principle is to overlap the filter’s resonance wavelength with the wavelength where the absorption of the solar cells changes rapidly. This filter is designed to change the amount of light absorption of solar cells depending on the amount of moisture, and to lead to electric changes that ultimately detect the surrounding humidity.

Unlike conventional optical humidity sensors, these newly developed ones work regardless of the type of light, whether it be natural, LED or indoor. Not only does it function without external power, it can also predict humidity according to the filter’s colour.

“This technology is a sensing technology that can be used in places like nuclear power reactors where people and electricity cannot reach,” said Professor Junsuk Rho, who led the research.

“It will create even greater synergy if combined with IoT technology such as humidity sensors that activate or smart windows that change colours according to the level of external humidity.”

Image credit: ©stock.adobe.com/au/silvae