The invisible keyhole
Hard times for burglars and tank crackers: Empa researchers have developed an invisible "keyhole" made of printed, transparent electronics. Only insiders know where to enter the access code.
InkAt first glance, Empa researcher Evgeniia Gilshtein's idea seems inconspicuous - or more precisely: invisible. What initially looks like a simple transparent film actually conceals a whole new level of security. This is because invisible buttons are printed on the transparent carrier material, the position of which is only known to insiders. Such circuits can be connected to a door lock as an access code, for example. If the buttons on the polymer film are touched with a finger in a defined sequence, the door lock can be opened.
The conductive ink can be applied to the surface using an inkjet printer, for example. "Of course, we don't use ordinary office printers for this, but the highly specialized equipment of Empa's Coating Competence Center," says Evgeniia Ghilshtein.
Elegant detour
The sensor surfaces are invisible to the human eye and can be placed in suitable locations, such as above the door hinge of the first prototype.
To make the metal-containing nanoparticle ink more transparent and conductive than conventional products, the researchers used an elegant detour in the production process: After the circuits were printed on the carrier film, the film was dyed blue in a next step.
Since the blue color, unlike a transparent film, can absorb light, this now enables the ink to be "burned in" on the substrate by means of high-energy light irradiation. Not only does the blue color disappear, the "secret ink" made of indium tin oxide also becomes invisible in the same step. "The result is printed circuits that have significantly higher conductivity than previous solutions," says the Empa researcher.
Source: Empa
