Search for a Suitable Numerical Model for Electrical Stimulation: from the Electric Double Layer to Electrokinetics, Confrontation with Impedance Measurements
Electrical Stimulation is widely used today for Deep Brain Stimulation treatments and retinal prostheses. The Electrical Double Layer formed at the interface between the electrode surface and the extracellular medium is considered thru the linear Helmholtz model and the nonlinear more realistic modified Poisson Boltzmann model. These different models, solved using COMSOL Multiphysics, are compared with experiments: impedance spectra are measured using a Medtronic 3389 DBS electrode immersed in a NaCl 137mM solution. Impedance measurements and calculations clearly show that the EDL cannot be neglected for frequencies lower than the kHz. The full temporal Electrokinetics equation is in better agreement than the complex one. Advantages and shortcomings of each studied model are summarized to conclude about the best choice one has to make when modeling electrical stimulation.