Generating Frequency Selective Vibrations in Remote Moving Magnets

Extensive efforts in providing upper limb amputees with sensory feedback have primarily focused on the restoration of tactile capabilities, while challenges in evoking proprioceptive sensations have been poorly addressed. Previously, an human-machine interface (HMI) was proposed based on permanent magnets implanted in residual muscles of an amputee, namely the myokinetic interface, to control robotic limb prostheses. Besides control, implanted magnets offer an unprecedent opportunity to trigger musculotendon proprioceptors via untethered selective vibrations. Herein, the challenge of tracking multiple moving magnets is addressed (e.g., following muscle contractions) while being vibrated by controlled magnetic fields produced by external coils. Results demonstrate the viability of a real-time (RT) system capable of simultaneously tracking and vibrating multiple moving magnets within a three-dimensional workspace. Highly selective torsional vibrations in the frequency span eliciting movement illusions (70, 80, and 90 Hz) are achieved on two moving magnets, with efficiencies above 0.82 (over 80% of spectral power at the desired frequency). Tracking accuracy and precision remain robust to the coil magnetic field, with position median errors below 1.2 mm and median displacement errors below 0.95 mm. This study represents a crucial step towards the development of a bench system to study proprioception in humans. Real-time (RT) magnetic actuation system, able to simultaneously track and vibrate multiple moving magnets. The system tracks multiple permanent magnets at 60 Hz while delivering selective untethered vibrations in the frequency range 70-90 Hz. This is a bench device that can be exploited to study the kinesthetic sense in human amputees with implanted permanent magnets in their residual muscles.image (c) 2024 WILEY-VCH GmbH