Interferential Current Stimulation for Non-Invasive Somatotopic Sensory Feedback for Upper-Limb Prosthesis: Simulation Results using a Computable Human Phantom

The addition of sensory feedback to upper-limb prostheses has been shown to improve several aspects of the user experience. In an attempt to create an intuitive sensory feedback method, transcutaneous electrical stimulation of the stump has been used to elicit referred sensation in the phantom hand by stimulating the underlying nerves. However, the sensation at the electrodes is always reported due to the stimulation of mechanoreceptors. This work investigates the use of interferential stimulation (the superposition of two kilohertz-frequency stimulation currents to form a low-frequency envelope stimulation waveform) to produce focused and selective stimulation that reduces the sensation at the electrodes. A computable human arm phantom model was used to analyse the electric fields created by interferential stimulation against those created by low-frequency stimulation. The results support the assumption that interferential stimulation could result in reduced sensation at the electrode. However, they did not show benefits in terms of penetration at the frequency range considered. In fact, the results suggest that slightly higher currents may be required.