Currently, almost all powered prosthetic hands utilize electrodes that detect the user's muscle impulses and convert them into hand movements. A new system which is in development, however, should reportedly work better by utilizing ultrasound.
The technology is being developed by the European Union SOMA project, which involves seven research groups from five countries.
At the heart of the current version of the system is a bracelet that is worn around the forearm. Instead of incorporating electrodes, it utilizes an array of ultrasonic transducers which send dozens of ultrasound pulses per second into the underlying muscle tissue.
By analyzing how long it takes those pulses to be reflected back up to their originating transducers, it's possible to ascertain the thickness of individual muscle strands. If any of those strands are contracting, they will be thicker than they would be if relaxed.
In this way, it's possible to determine which muscle strands are being consciously contracted by the wearer at any one moment. Those readings are presently relayed to a computer where they're analyzed in real time by AI-based software, which in turn relays corresponding movement commands to a prosthetic hand.
"The ultrasonic-based control acts with greater sensitivity and accuracy than would be possible with electrodes," said Dr. Marc Fournelle of Germany's Fraunhofer Institute for Biomedical Engineering, one of the project partners. "The sensors are able to detect varying degrees of freedom such as flexing, extending or rotating."
Plans call for the bracelet to ultimately be replaced with a miniaturized transducer array built into the cuff of the prosthesis itself. Likewise, readings could be transmitted via Bluetooth to an app on the user's smartphone, which would in turn wirelessly transmit commands to the hand.
What's more, the fingers of the hand may one day incorporate pressure sensors that will transmit a sense of touch back to nerves in the user's arm stump. Those signals will be relayed via electrodes, which will stimulate the nerves to produce a tactile sensation in the brain.
Source: Fraunhofer