3-D electrical model of a neuroprosthesis stimulator based on the concept of stimulus router system

Lost sensory or motor functions can be restored using electrical neural prostheses (NP), which include surface NPs, implanted or subcutaneous NPs and the more recent Stimulus Router System (SRS). The latter type of NP outperforms the other types in its selective excitation and least invasiveness. In each case, the achieved performance depends on a multitude of design factors among which the electrical excitation waveform shape, frequency, duration of pulses, configuration of electrodes, number of intervals, thermal conditions and electrode material. To investigate the effects of these parameters on the distribution of electric current inside biological tissues, numerical modeling can be employed as a powerful computational method. In this work, a 3-D electrical model is proposed to simulate the distribution of electric potentials and currents in the adult human forearm for an SRS NP. At the frequency of 50 Hz and for a 5 mA square waveform current source, results of our simulation show that the ratio of the current flowing inside the implanted conductor to the current applied to the cathodal electrode (capture ratio) is approximately equal to 2.02%. This value is close to the experimentally reported result for the SRS, 1.9%, giving an absolute error of 0.12% and relative error of 6.3%.