Prostheses: New Sensors Improve Control through Thoughts

JKU researchers in Linz have developed a new type of sensor that greatly increases prosthetic quality.

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Dr. Theresa Roland (Institute of Biomedical Mechatronics, JKU Linz, dept. head: Prof. Werner Baumgartner) explained the system by example of an arm amputation: "Nowadays, prostheses can be controlled by thoughts providing there is muscle tissue. The patients can control the arm by using their thoughts." These thoughts are actually just an electrical signal in the brain transmitted by nerve fibers to muscle fibers. This electrical impulse can be measured on the surface of the skin.

Patients Work Up a Sweat
Although these kinds of mind-controlled prostheses have been around for quite some time, they have their pitfalls. Previous sensors could only work with a sealing layer. However, the level of sweat must also be regulated. One particular problem is that conductive sensors have to be pressed firmly against the skin. This can lead to unpleasant pressure points and problems for people who have circulatory disorders in general.

Interference by Mobile Phones
The new JKU development: capacitive sensors. This means flexible sensors made out of insulating and conductive materials. They can also be made of textile materials sewn into clothing and are therefore particularly comfortable to wear. Above all, however, they are more fail-safe.

Each slip and vibration tends to trigger malfunctions in conventional sensors, which in turn activate the prosthesis. The JKU sensors are far less sensitive. Dr. Roland explained: "They adapt better to the skin, which reduces malfunctions. Above all, however, we have developed a relatively simple algorithm and our sensors can distinguish between thought signals and interference impulses."

What sounds like a small advantage has a big effect. "All in all, this brings a significant improvement in the way prosthesis work as it is only activated when the muscles actually contract." Otherwise, a mobile phone activated in close proximity could cause the prosthesis to move.

The new sensors were developed in cooperation with Otto Bock Healthcare Products Ltd. Vienna and funded by the Linz Center of Mechatronics. The project was presented to experts in the journal "Sensors".

Next, Dr. Roland wants to integrate artificial intelligence. Neural networks will further improve the distinction between interference and useful signals.