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Touch Screen IDs Users via Fingerprints

A touch screen that reads fingerprints could make the technology more useful.
July 17, 2013

Tabletop computers have not exactly taken the world by storm, as some predicted they would. While a few have appeared in shops, bars, and hotels, it’s not hard to understand why devices that until recently cost more than $8,000 have failed to gain wider adoption.

touch screen fingerprint reader
Who’s who: This tabletop computer can identify users each time they touch it.

But prices are falling, with one model from SmartTech now selling for $1,499, and new innovations could increase their appeal. Christian Holz and Patrick Baudisch of the Hasso Plattner Institute in Potsdam, Germany, have developed Fiberio, the first touch-controlled tabletop computer that can identify multiple users from their fingerprints each time they interact with it.

Holz says this has the potential to make large touch tabletops more useful, and while the system could not currently be used in smaller mobile devices, he and his colleagues are currently investigating ways to adapt it for them.

Entering usernames, passwords, and pins is generally seen as sufficient security for desktops and mobile devices, but things become much more complicated when computers are used by multiple users, especially simultaneously.

“Keeping track of who is doing what is a key element for collaborative interactive systems,” says Holz. “We have now created a touch screen that accomplishes this unobtrusively for every touch users make. Incorporating the ability to do this securely and seamlessly opens up a wide range of new applications.”

A hospital bedside device based on Fiberio, for example, could let patients see a basic version of their medical records, while nurses could request medications and doctors could make amendments to records, and authorize new drugs. Business employees could use multi-user computers to authorize invoice payments, or to make trades up to varying individual limits. Withdrawing money from ATMs would be a lot quicker if customers could simply touch on-screen buttons marked $20, $50, or $100.

Touch tabletops that allow children to learn collaboratively already exist, but the progress of individual students could be more precisely monitored and feedback better tailored if teachers could track individual contributions precisely.

Human computer interaction researchers have been working on this problem for years. The key challenge has been producing a screen that can simultaneously scatter light outward to display an image while reflecting it downward with sufficient contrast to produce a fingerprint scan.

Several existing tabletops use a “diffused illumination” set-up to track the position of fingers. Images are beamed from a projector below a piece of frosted glass or a plastic screen which scatters the light so it can be seen from all directions. Infrared light is also shone onto the screen from below so that when objects including fingers touch the surface, a camera identifies where this occurs thanks to the greater reflection of infrared light.

Fiberio adapts this system by using a three-millimeter-thick fiber optic plate made up of 40 million fibers that run perpendicular to the surface as the screen. The light that makes up the projected image is scattered as it travels through the optical fibers, before being emitted to the viewer.

The ends of these fibers are highly reflective, which means that as infrared light exits the screen, some is reflected back to the camera below. However, when it exits into skin from a finger, less reflection occurs and these areas show up darker. This provides sufficient contrast between the ridges and valleys of fingerprints at a resolution greater than 500 dots per inch—the minimum recommended by the FBI for reliable identification of fingerprints.

In an evaluation of the prototype, 10 volunteers touched the screen with their right index, middle, and ring fingers, five times each. Details of points at which fingerprint ridges split or ended were recorded. Each of the 150 fingerprints was then compared with the remaining 149. While in two cases not enough detail was recorded to find a match, the remaining cases were correctly matched.

The current version of Fiberio could not be incorporated into mobile devices because it uses a camera, and cameras have to be a certain minimum distance from the objects they are imaging. The team is investigating the use of alternative components.

“People assume that tabletop systems should be able to do fingerprint recognition, but it is technically difficult to do,” says Andy Wilson, who leads the natural interaction research group at Microsoft Research in Redmond, Washington, and who worked on the original Microsoft Surface, a 30-inch touch tabletop launched in 2007 (see “Your Coffee Table as a Computer”). “Christian has demonstrated it through a series of technical innovations which I think are terrific, so he deserves a lot of credit,” he says.

Asked about adapting Fiberio for smaller devices, Wilson says: “That’s the $64,000 question. I don’t know offhand, but there are people doing some interesting work to find ways to break the rules with regards to field of view and depth of field, such as using arrays of small lenses; perhaps another solution might be to take many cameras and gang them up together.”

Details of Fiberio are due to be presented at the ACM Symposium on User Interface Software and Technology in St. Andrews, Scotland, in October.

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