MEMS-Based Flexible Wearable Tri-Polar Concentric Ring Electrode Array With Self-Adhesive Graphene Gel for EEG Monitoring

Electroencephalography (EEG) is widely used to study brain activity and diagnose brain diseases due to its low cost and non-invasiveness. EEG has an excellent temporal resolution, but it does not provide good spatial resolution. The blurring effects of the head volume conductor are considered to be the main reason for the low spatial resolution. Concentric ring electrodes have been shown to provide significantly better spatial resolution than conventional electrodes which usually used silver or gold as contact conductors with the scalp. However, the metallic interfaces have high impedance. Herein, we designed a tri-polar concentric ring electrode (TCRE) array to precisely analyze the EEG signal and report a flexible self-adhesive graphene gel to reduce contact impedance. The electrodes are made of flexible material and are comfortable to wear. The electrode-scalp contact impedance was reduced to below 10 $\text{k}\Omega $ at 10 Hz and the EEG signal of alpha oscillations was successfully recorded. The average coherence between the original signals recorded by TCRE and the commercial Ag/AgCl gel electrode reached 0.913. The TCRE also shows significantly less mutual information between positions than the disk electrodes, showing high spatial resolution.