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05 Sep 2003
Electrochromic motorcycle visors developed in Sweden may help prevent road accidents.
A team from Uppsala University and the firm Chromogenics Sweden AB have developed a flexible electrochromic foil and integrated it into the visor of a motorcycle helmet. The result is a visor that the rider can electronically switch between dark and transparent states.
Applying a voltage of about 1V to the initially transparent visor causes it to darken in a matter of seconds. When the voltage is turned off, the visor keeps its properties, while applying a reverse voltage makes it revert to its natural lightly tinted state.
In essence, the construction of the visor is similar to a thin-film battery. Smart optically-active materials and a transparent ion-conducting laminate are sandwiched between two thin polyester foils.
Both polyester foils are coated with a transparent indium-tin oxide layer that acts as an electrode and allows a voltage to be applied. In addition, one foil is coated with a top layer of porous tungsten oxide and the other porous nickel oxide.
The coated foils act as the battery’s anode and cathode while the laminate serves as its electrolyte. When the battery is being “charged” the optical absorption of the filling between the foils changes, causing the visor to darken.
According to Claes Granqvist, a member of the research team, measurements with visible light at 550 nm show that the transmittance of the visor can go from 20% to 42% in just 6 seconds. The darkening process takes slightly longer.
“Helmets with dark visors are often used by motorcycle riders but these may be dangerous when riding after sunset or going from full daylight into a tunnel,” Granqvist told Optics.org. “Of course, it is possible for the rider to stop and mount another transparent visor but this is inconvenient. A solution is a visor that brightens at the push of a button or by a voice command.”
Chromogenics Sweden AB is now looking for financial partners in order to set up a production line for making the smart visors.
Author
Oliver Graydon is editor of Optics.org and Opto & Laser Europe magazine.
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