Over the years, fingerprinting has evolved from an inky mess to pressing fingers on sensor screens to even a few touch-free systems that work at a short distance. Now a company has developed a prototype of a device that can scan fingerprints from up to two meters away, an approach that could prove especially useful at security checkpoints in places like Iraq and Afghanistan.

The device, called AIRprint, is being developed by Advanced Optical Systems (AOS). It detects fingerprints by shining polarized light onto a person's hand and analyzing the reflection using two cameras configured to detect different polarizations.

Joel Burcham, director for projects at the Huntsville, Alabama-based company, says AIRprint could help make authorization more efficient in lots of settings. Instead of punching a keypad code or pressing fingers to a scanner, individuals could simply hold up a hand and walk toward a security door while the device checks their identity. "We're looking at places where the standard methods are a hassle," says Burcham. For instance, AIRprint could be linked to a timecard system, he says, to help avoid a logjam at manufacturing plants at the start or end of the workday.

Slightly smaller than a square tissue box, AIRprint houses two 1.3 megapixel cameras and a source of polarized light. One camera receives horizontally polarized light, while the other receives vertically polarized light. When light hits a finger, the ridges of the fingerprint reflect one polarization of light, while the valleys reflect another. "That's where the real kicker is, because if you look at an image without any polarization, you can kind of see fingerprints, but not really well," says Burcham. By separating the vertical and the horizontal polarization, the device can overlap those images to produce an accurate fingerprint, which is fed to a computer for verification.

The prototype device, which scans a print in 0.1 seconds and processes it in about four seconds, can handle only one finger at a time. Also, the scanned finger must remain at a fixed distance from the device. But by April, Burcham expects to have made significant improvements. By then, he says, the device should be able to scan five fingers at once even if a person is moving toward or away from the cameras, and the processing time ought to have dropped to less than a second.