Dry and Noncontact EEG Sensors for Mobile Brain–Computer Interfaces

TLDR

Dry and noncontact EEG electrodes, which do not require gel or direct scalp contact, are seen as a key enabler for practical, real‑world brain‑computer interface platforms. This study aims to compare the performance of wet electrodes with dry and noncontact electrodes in a steady‑state visual evoked potential BCI paradigm. The authors design a dry contact electrode with fingered posts and active buffering, and a noncontact capacitive electrode with a custom high‑impedance analog front‑end. Offline and online tests on ten subjects show that both dry and noncontact electrodes can acquire small‑amplitude SSVEP signals, with the noncontact sensor achieving a 19 bits/min ITR at 100 % accuracy—comparable to wet electrodes—and suggest these sensors are viable for mobile BCI and general EEG.

Abstract

Dry and noncontact electroencephalographic (EEG) electrodes, which do not require gel or even direct scalp coupling, have been considered as an enabler of practical, real-world, brain-computer interface (BCI) platforms. This study compares wet electrodes to dry and through hair, noncontact electrodes within a steady state visual evoked potential (SSVEP) BCI paradigm. The construction of a dry contact electrode, featuring fingered contact posts and active buffering circuitry is presented. Additionally, the development of a new, noncontact, capacitive electrode that utilizes a custom integrated, high-impedance analog front-end is introduced. Offline tests on 10 subjects characterize the signal quality from the different electrodes and demonstrate that acquisition of small amplitude, SSVEP signals is possible, even through hair using the new integrated noncontact sensor. Online BCI experiments demonstrate that the information transfer rate (ITR) with the dry electrodes is comparable to that of wet electrodes, completely without the need for gel or other conductive media. In addition, data from the noncontact electrode, operating on the top of hair, show a maximum ITR in excess of 19 bits/min at 100% accuracy (versus 29.2 bits/min for wet electrodes and 34.4 bits/min for dry electrodes), a level that has never been demonstrated before. The results of these experiments show that both dry and noncontact electrodes, with further development, may become a viable tool for both future mobile BCI and general EEG applications.