Electrical engineers at the University of Delaware developed their version of smart glass technology. It starts opaque but turns transparent when filled with index-matching fluid, as shown in the bottom portion of this pane. Credit: University of Delaware

The next wave of “smart” glass features better light reflection and absorption, without a higher price tag.

A team from the University of Delaware has created “smart glass” panels that cost a fraction of other similar technologies and can switch between allowing light in and blocking it out. This innovation could pave the way for eco-friendly windows, windshields, roof panels and buildings that can absorb light and heat in the winter and reflect it away during the summer.

The smart glass is made with two sheets of plastic that contain tiny cube-shaped structures, separated by a thin cavity. The structures embedded into the plastic make the material retroreflective.

The chamber is filled with methyl salicylate—an inexpensive wintergreen extract that has optical properties that match the optical properties of the plastic. This is the same wintergreen extract that is an active ingredient in some over-the-counter pain relief creams.

Combining the plastic with the methyl salicylate enables light to pass through the system to become transparent in a process called refractive index matching.

The researchers relied on the total internal reflection of one-dimensional structures layered perpendicularly instead of cubes. The glass is highly reflective at up to a 60-degree angle of incidence.

"It performed better than we thought it would based on our theoretical understanding," Keith Goossen, an associate professor of electrical and computer engineering at the University of Delaware, said in a statement.

While smart glass already exists, the new method could make panels at nearly a tenth of the cost of current models. The new glass is also more transparent in its transparent state and more reflective in its reflective state than current models.

The new smart glass can switch between states up to 1,000 times without degrading.

The prototypes, which are capable of modulating visible light transmittance from 8-to-85 percent, were made using a 3D printer, but Goosen said the new technology could eventually be manufactured at a high volume and low cost using injection molding.

The researchers are now testing the system over a wide range of temperatures to see how it performs. They are particularly looking at testing the systems between 3 degrees and 16 degrees Fahrenheit, the temperature that could cause the fluid to freeze.

Commercially available smart glass relies on electric stimuli to modulate the glass from a transparent to a translucent mode of operation. However, the current market technologies, such as electrochromic, polymer dispersed liquid crystal, and suspended particle devices are expensive and suffer from solar absorption, poor transmittance modulation, and in some cases, continuous power consumption.

Goossen shared his latest smart glass prototype on March 5 in a keynote address at the SPIE Smart Materials and Nondestructive Evaluation
for Energy Systems IV conference in Denver.
The study was published in Optics Express.