Design of High-Density Electrodes for EEG Acquisition

In a 256-channel electrode cap for electroencephalogram (EEG) acquisition, the inter-space between adjacent electrodes is around 20mm. Theoretical and experimental evidence predict that improving the density of electrode can get more information from the added electrodes. 10mm or less center distance, corresponding to 1000 electrodes on a full head EEG cap, might be a more proper density to current EEG analysis methods. To develop high-density electrode array with center distance equal or less than 10mm, one must make sure that the adjacent electrodes are electrical isolated. It is difficult to avoid short circuit when common wet electrodes are used to build high-density electrode array. The contact area (about 28mm² with diameter of 6mm) and gelling method make short circuit easily happen. To provide more isolation space between adjacent electrodes, the contact area of the proposed electrode should be less than 8mm². To restrict the diffusion of the electrolyte, a customized hydrogel is used to replace the conventional gel. Compared with common wet electrode and gel, preliminary tests indicate that the high-density hydrogel-Ag/AgCl electrodes perform well at the impedance, isolation, as well as data quality in EEG acquisition.