I want to share with you what I have learned from the thesis work of Rekha Chintalacharuvu. She created a mathematical model of the cuff electrode, one with a single cathodic contact and a return electrode at a large distance away, also called a monopolar electrode configuration and a tripolar electrode configuration, where the flanking contacts are the return electrodes or anodes. The tripolar configuration constrains the current to the cuff and forces the current to be concentrated in the upper portion of the cuff. She also explored the effects of field steering with these two cuff configurations, an anodic current applied simultaneously to a contact 180˚ from the cathodic contact.
Rekha R. Chintalacharuvu, A Numerical Analysis of the Electric Field Generated by the Nerve Cuff Electrode, MS thesis, EE Dept, 1991 Case Western Reserve University
Chintalacharuvu, R.R., D.A. Ksienski, and J.T. Mortimer, "A Numerical Analysis of the Electric Field Gererated by a Nerve Cuff Electrode", IEEE Engineering in Medicine and Biology Society , vol 13, p 912-913, 1991