Materials for Dry Electrodes for the Electroencephalography: Advances, Challenges, Perspectives

Electroencephalography (EEG) is extensively applied in brain cognition, clinical diagnosis, and artificial intelligence through detecting and analyzing the human brain biopotential. The Ag/AgCl combined with a conductive gel is the most widely used electrode in EEG. However, pre-preparation before testing is time-consuming and complicated. The dried gel has to be cleaned from hair after testing, otherwise discomforting the subjects. Therefore, it is strongly desired to develop a dry electrode to ease the test process and comfort the subjects. However, the high electrode–skin contact impedance weakens the intensity of biopotential signals. The materials with the features of high conductivity, good biocompatibility, and ease to obtain are more favorable for the dry EEG electrodes. This review provides state-of-the-art materials for the dry electrode for the EEG with respect to the material preparation, and their electrical and electroencephalographical properties. Challenges and perspectives related to the material preparation, cost, and applications are also discussed.