Ultrasonic Fingerprint Readers Can Unlock Phones Even When Your Fingers are Gross and Sweaty

Experts say ultrasound fingerprint sensors are harder to hack

Frettie via Wikimedia Commons (CC BY-SA 3.0)

Press a fingertip to a smartphone nowadays and the device unlocks when it recognizes the skin's characteristic whorls and loops — either by measuring the pattern of different voltages generated by ridges and valley or by analyzing an image. But both methods can be rendered useless by dirty, sweaty or greasy fingers. Now, researchers are experimenting with a new way of reading human digits: ultrasound fingerprint sensors. Boer Deng reports for Nature:

When a user puts his or her finger to the print-reading chip, an ultrasonic pulse bounces against it. The chip is coated with a layer of aluminum nitride, which can convert mechanical stress to electric energy or vice versa.

When the ultrasonic pulse bounces back off the fingerprint, ridges and valleys return different patterns of stress, which can then be converted into electrical signals. By measuring the bounce from the ultrasound for longer period of time, the scanner can also sense the depth of the ridges and valleys.

This additional data gleaned from ultrasound pulses means that the system is also more secure than technology currently in use. “If you can sense deeper characteristics, not just the shape, of a fingerprint, you can better tell the difference between what’s real or not,” Rob Rowe, vice president of development at security-technology firm HID Biometrics told Deng. 

The UC Davis researchers wrote up their technology in Applied Physics Letters. They say that the system is easier to manufacture that previous ultrasound fingerprint systems, so they hope it could eventually end up on many people’s smartphones and computers in the future. Already, at least one company has a different ultrasound sensor ready to go. 

If they succeed, wet and dirty fingers won’t foil the smartphone any more — plus it will be harder to copy someone’s fingerprints to hack into their devices.

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