Next I want to consider the impact of returning the current to two flanking electrodes rather than to the distant ground/return electrode used in the previous simulations. The edge to edge separation between the stimulating cathode and the flanking anodes is 3 mm. This configuration is defined as a tripolar electrode configuration, shown in the upper left.
A -1.479 V stimulus applied to this electrode configuration produces a Jth pattern for the 10 µm axons and for the 20 µm axons. At 2Jth the boundary is as indicated for the 10 µm axons and for the 20 µm axons all fiber in the fascicle are activated at 2Jth. To see the effect of constraining the current into the upper portion of the cuff, by adding the flanking return electrodes, take note of the results shown for the monopolar configuration.
RR Chintalacharuvu, DA Ksienski, JT Mortimer, Annual Int Conf of the IEEE Engr in Med and Biol Vol 13, No 2 1991, pp 0912-13
Rekha R. Chintalacharuvu, A Numerical Analysis of the Electric Field Generated by the Nerve Cuff Electrode, MS thesis, 1991 Case Western Reserve University