Fingerprint sensor technology currently used in smartphones produces a two-dimensional image of a finger's surface, which can be spoofed fairly easily with a printed image of the fingerprint.
The newly developed ultrasonic sensor eliminates that risk by imaging the ridges and valleys of the fingerprint's surface, and the tissue beneath, in three dimensions.
"Using passwords for smartphones was a big security problem, so we anticipated that a biometric solution was ahead," said David A Horsley, a professor of mechanical and aerospace engineering at the University of California, Davis.

"Ultrasound images are collected in the same way that medical ultrasound is conducted," said Horsley.
"Transducers on the chip's surface emit a pulse of ultrasound, and these same transducers receive echoes returning from the ridges and valleys of your fingerprint's surface," he said.