Uniformity of current density under stimulating electrodes

Abstract

This work examines all the factors that go into designing, simulating, implementing, and experimentally testing high-current bioelectrodes. It reviews previous work on the properties and risks of electrodes used to interface high currents to the human body. It is a self-contained presentation covering all aspects of the design, test, and implementation of high-current stimulating bioelectrodes. Inherent properties derived from theoretical work are pointed out. The tools to design and evaluate electrodes are introduced and discussed. Analytical methods provide insights into inherent characteristics, but lack generality and are often very difficult to use. Numerical methods overcome the difficulties of analytical procedures and are capable of quantitatively evaluating existing electrode designs, or can be used to find a design that is optimal in certain properties and specific applications. Experimental studies have verified and provided knowledge of the mechanisms that can potentially cause damage to the patient. They are also used to test the validity as well as the limitations of numerical models and their predictions, and to point out which aspects of the numerical methods need to be improved. Experimental measurements are in good agreement with the analytical predictions and simulation results. For example, all three approaches pinpoint that the edge effect (the current density at the electrode-body interface increases toward the perimeter of the electrode) is an inherent property of a low-impedance electrode attached to a body of higher resistivity. Also, several optimal stimulating electrode designs to obtain the uniformity of current density under the electrodes are presented.