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What is smart glass;explain?

“Electric glass” may sound like the name of a ’70s rock band, but it’s becoming a 21st-century reality. The operative term is “smart glass,” and its applications are as varied as the uses of glass itself. Through this technology, glass can turn from transparent to opaque, control the passage of heat and light and convert itself from two-way to one-way, all at the behest of the user.

Smart glass, EGlass, or switchable glass, also called smart windows or switchable windows in its application to windows or skylights, refers to electrically switchable glass or glazing which changes light transmission properties when voltage is applied. In basic terms, smart glass operates by using electric voltage to affect the alignment of microscopic particles within the glass. In the case of electrochromic devices, these particles align or disperse to change between translucence and transparency as soon as an initial electrical impulse is introduced. After that, the conversion takes place on its own with no additional electricity needed. Another electrical application will then reverse the process.

The change takes anywhere from seconds to several minutes to take place, beginning at the edges of the glass and moving inward. In its “resting” state without electric current, some smart glass presents an opaque appearance. Other types are reflective.

Applications for smart glass include building windows, doors and skylights; automobile, boat and aircraft windows; appliance windows, computer screens and cell phone screens. Its use in home and residential windows can all but eliminate the need for blinds or shades, and it fits in with the “green movement” by helping with interior heating and cooling.

Some aspects of the technology feel comfortably familiar. The knob or sliding control used in some electrical “smart windows” is much like that long used to lower or increase the intensity of a light. Meanwhile, a related “passive” smart glass technology works in much the same way as sunglasses that darken in response to a light stimulus. As with many innovative products, however, smart glass is pricey on the front end — as much as 400 percent costlier than standard glass. This has proved a barrier to companies raising high-rise structures with hundreds of windows. It can be argued, however, that the energy-saving qualities of smart glass can pay for that differential over its lifetime. Research is also being done into retrofitting standard windows to incorporate smart glass technology.

“Smart glass” and “switchable glazing” are generic terms that refer to all types of passive and active systems. Photochromic and thermochromic glazing, which are light- and heat-sensitive, respectively, are considered passive, because they do not require electricity. Those transitional sunglasses are smart, but passive. Active-control or electrochromic systems offer more options, but must be hard-wired to a power source.

Active technologies are the focus of most of the current research. Electrochromic windows are generally considered to be the most suitable chromogenic technology for energy control in buildings. They reduce or block light transmission and alter transparency in response to environmental signals, such as glare, sunlight, or temperature. The change from transparent to tinted is achieved when a small electrical current is applied to the window. The window returns to transparent when the voltage is turned off. Light transmittance during operation varies from 5 to 80 percent. Once the change in tint is initiated, the electrochromic glazing does not need constant current to maintain the tinting. In addition, the film can be tuned to block certain wavelengths, such as solar (heat) energy.

Electrochromic windows are made up of several extremely thin plies. Darkening occurs when hydrogen or lithium ions from an ion-storage layer are transmitted through an ion-conducting layer, which, when a voltage is applied, hurls the ions into an electrochromic layer typically made of tungsten oxide. The ions cause this layer to absorb visible light, thus darkening the window’s glass. The thin plies are sandwiched between two sheets of a transparent conducting oxide material. Finally, all the layers are encased between two layers of glass. (Gasochromic windows are similar to electrochromic, but rely on diluted hydrogen in the cavity of the insulated window unit to effect color change.) The main advantage of electrochromic windows is that they typically require low-voltage power, remain transparent across their switching range, and can be modulated to any intermediate state between clear and fully darkened.

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