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Engineers Develop Tunable Windows

Tuesday, March 29, 2016

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A new technology could make window blinds and drapes obsolete.

Researchers at Harvard’s John A. Paulson School of Engineering and Applied Science have developed a technique that quickly changes the opacity of a window. A mere flick of a switch is all that’s needed to turn windows from clear to cloudy, or any gradation of opacity in between.

The research for the technology, called tunable windows, is detailed in the journal Optics Letters.

Tunable windows aren’t new, but the researchers claim they have developed a way to reduce costs and improve the efficiency of the technology.

Harvard SEAS

The technology uses geometry to adjust a window’s transparency.

According to the researchers, most previous tunable window technologies relied on electromechanical reactions that were expensive to manufacture. The new technology, developed by David Clarke, the Extended Tarr Family Professor of Materials at Harvard, and Samuel Shian, a postdoctoral fellow, uses geometry to adjust a window’s transparency.

New Coating Technology

Harvard’s version of a tunable window is constructed from a sheet of plastic or glass that is placed between transparent and soft elastomers, and then sprayed with a coating of silver nanowires too small to scatter light. When electric voltage is applied, the nanowires are energized to move toward each other, squeezing and deforming the elastomers.

Since the nanowires are unevenly distributed across the surface, the elastomer deforms unevenly. This causes light to scatter, turning the glass opaque in less than a second.

Windows
David Clarke/Harvard SEAS

The engineers say the technology is scalable for large architectural projects.

Shian compares the technology to a frozen pond.

“If the frozen pond is smooth, you can see through the ice,” he said. “But if the ice is heavily scratched, you can’t see through.” 

The roughness of the elastomer surface depends on the voltage: a higher voltage yields a window that is lightly clouded, while less voltage will create a more opaque window.

Reduced Costs

Most current tunable window technologies use vacuum deposition to coat glass. This expensive and painstaking process deposits molecules layer by layer, according to the researchers.

In contrast, the technology developed at Harvard can be sprayed or peeled onto the elastomer. According to the researchers, this makes the technology scalable for large architectural projects.

“Because this is a physical phenomenon rather than based on a chemical reaction,” Clarke said, “it is a simpler and potentially cheaper way to achieve commercial tunable windows.”

Clarke and Shian will next work on incorporating thinner elastomers, requiring lower voltages, which are better suited for standard electronic supplies.

   

Tagged categories: Building science; Coating chemistry; Glass coatings; Nanotechnology; Research and development; Windows

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