Current density and electric field analysis of microelectrodes using finite element modeling

Geometrically and electrically accurate finite element models of microelectrodes used in microstimulation of the central nervous system were created to examine the current density along the surface of the electrode as well as the electric field generated within the tissue medium. Sharp tipped microelectrodes (tip radius=15 μm; cone angle=10°) were examined with electrode surface areas that ranged from 250-1000 μm². Analysis of these models showed that the current density was concentrated at the tip of the microelectrode, and increasing the surface area of the electrode has little effect on reducing the peak current density. The models also showed that as the surface area of the microelectrode was increased, the gradient of the electric field within the tissue decreased, and the modeling of the electric field generated by a sharp tipped microelectrode by a theoretical point source electrode was valid only for distances greater than 20 μm from the electrode tip. The results of this study have important implications for electrochemical reactions at the electrode surface, and for modeling of neural excitation with metal microelectrodes