Optimal design of electrodes for functional electrical stimulation applications to single layer isotropic tissues

Abstract

Purpose – The purpose of this paper is to investigate the design of skin surface electrodes for functional electrical stimulation using an isotropic single layered model of the skin and underlying tissue. A concentric ring electrode geometry was analysed and compared with a conventional configuration, specifically to localise and maximise the activation at depth and minimise the peak current density at the skin surface. Design/methodology/approach – The mathematical formulation determines the spatial electric potential distribution in the tissue, using the solution to the Laplace equation in the lower half space subject to boundary conditions given by the complete electrode model and appropriate asymptotic decay. Hence, it is shown that the electric potential satisfies a weakly singular Fredholm integral equation of the second kind which is then solved numerically in MATLAB for a novel concentric ring electrode configuration and the conventional two disk side-by-side electrode configuration. Findings – In both models, the electrode geometry can be optimised to obtain a higher activation and lower maximum current density. The concentric ring electrode configuration, however, provides improved performance over the traditional two disk side-by-side electrode configuration. Research limitations/implications – In this study, only a single layer of medium was investigated. A comparison with multilayer tissue models and in vivo validation of numerical simulations are required. Originality/value – The developed mathematical approaches and simulations revealed the parameters that influence nerve activation and facilitated the theoretical comparison of the two electrode configurations. The concentric ring configuration potentially may have significant clinical advantages.