With exoskeletons, people with paraplegia could move their arms, hands and maybe even legs again in the future. Thoughts alone should be enough to control the numerous electric motors, artificial muscles and joints. In principle, brain-computer interfaces could be implanted for this purpose, but the risks of such an intervention would be extremely high. Alternatively, sensors attached to the outer skull record controlling brain waves. However, the accuracy of such electro-encephalography (EEG) signals is not sufficient for precise exoskeleton motor functions. Neuromagnetic fields generated by brain waves would be more suitable. The extremely sensitive sensors required for this are now being developed as part of the “NeuroQ” project – funded with almost nine million euros by the Federal Ministry of Research (BMBF).
“Magnetic fields penetrate the skin and skull undistorted and thus provide significantly clearer signals than electric fields, since these are greatly weakened on the way from the source to the sensor. Magneto-encephalography (MEG) has significant advantages over electro-encephalography (EEG) , but is only rarely used due to technical hurdles,” says project manager Jan Jeske from the Fraunhofer Institute for Applied Solid State Physics IAF in Freiburg. He wants to overcome these hurdles together with his partners – the Charité in Berlin, the University of Stuttgart and several companies.
Diamonds for the hand prosthesis
Even today, the smallest magnetic fields can be measured with great accuracy. However, the SQUID sensors (Superconducting Quantum Interference Devices) used for this must be cooled to at least minus 200 degrees Celsius because of the integrated superconductors. This cooling makes it impossible to develop a wearable sensor cap for paralyzed patients. The solution to this problem is said to lie in diamond-based quantum sensors. These quantum magnetometers could be integrated into a sensor cap and thus enable paralyzed people to control a prosthetic hand much more precisely than has been the case up to now.
These quantum sensors use small defects in the crystal structure of a diamond, so-called nitrogen vacancy centers (NV / nitrogen-vacancy centers). The defects give the diamond unique electromagnetic properties. Today, diamond quantum magnetometers are the only highly sensitive magnetometers that work at room temperature without deep refrigeration. They can even be used to determine the exact orientation of a magnetic field. Thanks to this level of accuracy, an exoskeleton could be controlled using the magnetic fields induced by the brain waves. The researchers led by Jan Jeske now have until 2027 as part of “NeuroQ” to develop the first prototypes for such an interface from the brain to the computer or to the prosthesis.
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