Two permanent magnets are tracked with magnetic field sensors. MIT engineers have devised an algorithm for high-speed tracking of any number of magnets, with significant implications for augmented reality and prosthesis control.
©2019 IEEE Sensors Journal. Photograph by Jimmy Day courtesy of MIT.
Researchers at the Massachusetts Institute of Technology (MIT) Media Lab have devised an algorithm that promises to vastly improve the simultaneous tracking of any number of magnets, which they say has significant implications for prostheses, augmented reality, robotics, and other fields.
Graduate student Cameron Taylor, lead researcher on the project in the Media Lab’s Biomechatronics group, said the algorithm dramatically reduces the time it takes for sensors to determine the positions and orientations of magnets embedded in the body, wood, ceramics, and other materials.
“I’ve been dreaming for years about a minimally invasive approach to controlling prostheses, and magnets offer that potential,” said Hugh Herr, PhD, professor of media arts and sciences at MIT and head of the Biomechatronics group. “But previous techniques were too slow to track tissue movement in real time at high bandwidth.”
Prostheses have relied on electromyography to interpret messages from a user’s peripheral nervous system, and electrodes attached to the skin adjacent to muscles measure impulses delivered by the brain to activate them. But the ability of electrodes to sense signals that change over time, as well as to estimate the length and speed of muscle movement, is limited, and wearing the devices can be uncomfortable.
As scientists studied how to use magnets, which can be embedded in the body indefinitely, to control high-speed robotics, they found it took computers too long to determine precisely where the magnets were and initiate a reaction.
“The software needs to guess at where the magnets are, and in what orientation,” Taylor said. “It checks how good its guess is given the magnetic field it sees, and when it’s wrong, it guesses again and again until it homes in on the location.”
The Biomechatronics group researchers developed an improved method of tracking magnets, including enhanced reflexive control of prostheses and exoskeletons, simplified magnetic levitation, and improved interactions with augmented and virtual reality devices, which extends magnet tracking technology to new high-speed applications. Disturbance from the Earth’s magnetic field also had to be accounted for, and traditional methods of eliminating that interference weren’t practical for the compact, mobile system needed for prostheses. The team was able to program the software to search for the Earth’s magnetic field as if it is simply another magnetic signal.
In comparison to state-of-the-art magnet tracking systems, the new algorithm increased maximum bandwidths by 336 percent, 525 percent, 635 percent, and 773 percent when used to simultaneously track one, two, three, and four magnets, respectively.
“This is the first time a team has demonstrated this technique for real-time tracking of several permanent magnets at once,” Taylor said.
“All kinds of technology exists to implant into the nervous system or muscles for controlling mechatronics, but typically there is a wire across the skin boundary or electronics embedded inside the body to do transmission,” Herr said. “The beauty of this approach is that you’re injecting small passive magnetic beads into the body, and all the technology stays outside the body.”
The group has applied for a patent on its algorithm and its method for using magnets to track muscle movement. It is also working with the U.S. Food and Drug Administration on guidance for the transition of high-speed, broad bandwidth magnetic tracking into the clinical realm.
“I think it’s possible we would begin human testing as soon as next year,” Herr said. “This isn’t something that’s ten years out at all.”
“Low-Latency Tracking of Multiple Permanent Magnets,” was published by in the December issue of IEEE Sensors Journal.
