The dependence of spectral impedance on disc microelectrode radius.

As microelectrodes gain widespread use for electrochemical sensing, biopotential recording, and neural stimulation, it becomes important to understand the dependence of electrochemical impedance on microelectrode size. It has been shown mathematically that a disc electrode, coplanar in an insulating substrate and exposed to a conducting media, exhibits an inhomogeneous current distribution when a potential step is applied. This distribution is known as the primary distribution, and its derivation also yielded an analytic solution for electrical resistance of the conducting media (R(s)), between the disc surface and a distant ground, which is inversely proportional to disk radius [R(s) = 1/(4kappar), where kappa is media conductivity and r is disk radius].