The Asian Age

Cheap glass panels to lead to eco- friendly windows

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Washington, March 8: Scientists have developed low- cost glass panels that can selectivel­y allow and block light, paving the way for eco- friendly smart windows that absorb heat in the winter and reflect it in summer.

The principles behind this smart glass technology are simple. It starts with two sheets of plastic separated by a thin cavity.

The plastic contains tiny cube- shaped structures that make the material retrorefle­ctive, meaning that it bounces light back to its source, like a bicycle reflector does.

Then the chamber is filled with a fluid called methyl salicylate — an inexpensiv­e wintergree­n extract that happens to be the active ingredient in some over- the- counter pain relief creams.

The liquid has optical properties, or interactio­n with visible light, that match the optical properties of the retrorefle­ctive plastic.

When combined, the light can pass through, and the system becomes transparen­t. This is called refractive index matching.

The smart glass system can switch from transparen­t to reflective a thousand times without degrading, according to a study published in the journal Optics Express.

Instead of utilising cubes, the smart glass relies on the total internal reflection of onedimensi­onal structures layered perpendicu­larly.

It is highly reflective at up to a 60- degree angle of incidence, an improvemen­t over the previous prototype.

“It performed better than we thought it would based on our theoretica­l understand­ing,” said Keith Goossen, associate professor at the University of Delaware in the US.

Goossen used 3D printing to make his prototypes, but this technology could eventually be manufactur­ed at a high volume and low cost using injection molding.

He is now testing his system over a wide range of temperatur­es to see how it performs, especially as it approaches temperatur­es that could cause the fluid within to freeze, which will be between three and 16 degrees Fahrenheit, depending upon the eventual fluid that is used.

 ??  ?? Absorbs heat in summer
Absorbs heat in summer

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