Jason Barnes lost one of his hands after an accident at work in 2012. Now, five years later, a new prosthesis developed at the Georgia Tech College of Design allows Barnes, a musician, to play the piano again with both hands.

The feat is made possible by an ultrasonic sensor fitted into the device. While Barnes lost his hand and most of his forearm, the muscles that controlled his fingers are still there. Many existing prostheses employ an electromyogram (EMG) to pick up on muscle movements and move the artificial fingers in response.

There's just one problem: EMG sensors lack the accuracy needed for the sort of fine motor control you'd need to, say, play the piano. That's where ultrasound, the technology doctors uses to look at babies in the womb, makes a difference.

Coupling the ultrasound sensor with machine learning allows for a much more precise reading. The prosthetic can pick up on simultaneous finger movements and even the amount of intended force. 

There's a great deal more detail on how the team at Georgia Tech is working with Barnes to improve their research right here. There's also a similar project underway at the University of Utah, but with a slightly different focus: This one aims to restore actual feeling to amputees via prostheses.