Smart Glass - Related Areas of Technology

Related Areas of Technology

The expression smart glass can be interpreted in a wider sense to include also glazings that change light transmission properties in response to an environmental signal such as light or temperature.

• Different types of glazing can show a variety of chromic phenomena, that is, based on photochemical effects the glazing changes its light transmission properties in response to an environmental signal such as light (photochromism), temperature (thermochromism), or voltage (electrochromism).
• Liquid crystals, when they are in a thermotropic state, can change light transmission properties in response to temperature.
• Recent advances in electrochromic materials have led to the discovery that transition metal hydride electrochromics create a reflective face instead of an absorbent face. These materials have the same idea, but go about the problem in a different way by switching between a transparent state when they are off to a reflective state when a voltage is applied. Switchable mirrors were originally developed by Tom Richardson and Jonathan Slack of Berkeley Lab’s Environmental Energy Technologies Division. They used rare earth metals and created the first metal-hydride switchable mirrors. Low emittance coatings reject unwanted thermal heat due to solar infrared21. These mirrors have become common place in cars’ rearview mirrors in order to block the glare of following vehicles. An optically absorbing electrochromic color reduces the reflection intensity. These mirrors must be fully transformed to a reflective state as muted reflection must persist in the darkened state. Originally a metal, they are converted into a transparent hydride by injecting hydrogen in a gas or liquid phase. It then switches to a reflective state.
• Various metals have been investigated. Thin Mg-Ni films have low visible transmittance and are reflective. When they are exposed to H₂ gas or reduced by an alkaline electrolyte, they become transparent. This transition is attributed to the formation of magnesium nickel hydride, Mg₂NiH₄. Films were created by cosputtering from separate targets of Ni and Mg to facilitate variations in composition. Single-target d.c. magnetron sputtering could be used eventually which would be relatively simple compared to deposition of electrochromic oxides, making them more affordable. Lawrence Berkeley National Laboratory determined that new transition metals were cheaper and less reactive, but contained the same qualities, thus further reducing the cost.

• Tungsten-doped Vanadium dioxide VO₂ coating reflects infrared light when the temperature rises over 29 degrees Celsius, to block out sunlight transmission through windows at high ambient temperatures.

These types of glazings cannot be controlled manually. In contrast, all electrically switched smart windows can be made to automatically adapt their light transmission properties in response to temperature or brightness by integration with a thermometer or photosensor, respectively

The topic of smart windows in a further sense includes LED Embedded Films which may be switched on at reduced light intensity. The process of laminating these LED embedded films between glass will allow the production of Transparent LED embedded glasses. As most glass companies are not skilled in mounting LEDs (Light Emitting Diodes) onto metallized glass, the LEDs are located on a separate transparent conductive polymeric interlayer that may be laminated by any glass lamination unit.

Production technologies

Smart glass is produced by means of lamination of two or more glass or polycarbonate sheets.