How Does Smart Glass Work?
Although the smart glass industry likes to use the word glass, most of the time the actual smart part is made by using a substrate made of various plastic films. The smart substrate contains multiple layers with a separator between them. Each layer is made from different material and each manufacturer has their own secret sauce, but typically lithium cobalt oxide is used on one layer and polycrystalline tungsten oxide on the other. Lithium ions are then injected into one of the layers where they settle in. The layers are then sandwiched between two or more glass panes to create the final window unit. The lithium ions remain in either of the layers until a voltage is applied. When a voltage is present, the ions will migrate to the opposite layer where they will once again settle in and remain, even after the voltage is removed. Depending on the layer the lithium ions are in they will combine with the layer to either reflect light (opaque or semi-translucent) or allow light to pass through (transparent). It’s not an all or nothing system. Leave the voltage applied for a short time will allow a limited number of ions to travel between the two layers. The more ions on one side the higher percentage of opacity or transparency is achieved.
Types of Smart Glass
There are different kinds being manufactured, but here are some common ones that you might run across. Electrochromic – With electrochromic glass, its normal state is opaque, but when an electrical charge is applied to the smart window, the glass changes state moving from semi-translucent to fully transparent. PDLC (Polymer-Dispersed Liquid-Crystal devices)- This method replaces the ions used in an Electrochromic glass with liquid crystal that is dissolved in a polymer. The liquid polymer is applied to plastic substrates and allowed to cure. The substrate is sandwiched between two or more glass layers to form the finished window unit. In use, the liquid crystals behave much like those in an LCD display, with no voltage present the crystals are randomly arranged to block the passage of light. Apply a voltage and the crystals align allowing light to pass through. Nanocrystal- This technology uses a thin layer of nanocrystals usually made up of indium tin oxide applied to a plastic film. The finished layer is encapsulated between two or more panes of glass. Nanocrystal-based windows main advantage is that they can effectively block both heat (infrared) as well as visible light making them a good candidate when you need to fully block light or control heat gain.
Smart Glass Usage
The various types of smart glass find usage in many categories. The most common remains as part of home exterior windows where they serve to enhance or replace the use of blinds and curtains to control privacy. Smart glass also finds usage in homes that have large banks of windows facing south. Using a product like nanocrystal windows can reduce the heat gain in the summer and allow the heat gain in the winter. Other interesting usages around the home can be found in shower glass, allowing the shower to be seen when not in use, and blocked from view when using the shower. Aviation, marine, and auto manufacturers are all making use of smart glass to employ dynamically controlled window tinting. This can be used to reduce reflections onto to display surfaces, or to help reduce glare coming into the cockpit. If you have been flying in any of the latest Boeing Dreamliners, you may notice the window has no pull-down shade, instead the glass becomes opaque at a touch of a control. Another use in cars is to control transparency and tint of sun/moonroofs.
