Annular Micro-Needle Array as a Minimally Invasive Flexible Dry Electrode for on-Hair EEG Recording

This paper reports a novel dry electrode based on micro-needle array (MNA) and flexible polyimide substrate with annular shape, which is compatible for recording electroencephalogram (EEG) signal on hairy scalp. Owing to the ring-structure that allows hairs to be threaded through and be pressed on the back side, micro-needles on the “loop” can directly touch the scalp. The micro-needles with spiky tips, based on polyimide as well, are able to penetrate the outermost stratum corneum layer of skin to realize low-impedance contact with minimal invasiveness. The modification layer of biocompatible conducting polymer PEDOT:PSS on electrode surface makes the contact impedance significantly decrease. Compared with commercial and clinical wet electrode, no conductive gel is required for annular MNA electrode thus the electrode density and user-friendliness are expected to be improved. Furthermore, a portable EEG acquisition and processing module is developed to achieve on site signal analysis.