Design and Evaluate Semi-dry Watermill-like EEG Electrodes

Jui-Bang Lu, Yu Tsao, Yu Te Wang

Abstract: Semi-dry electrodes act as the middle ground between wet and dry electrodes as they not only have similar contact features (equivalent circuit) with Ag/AgCl-based wet electrodes but also carry the conduct material in their cavity or sponge (e.g. absorb saline water) for long-term brain-computer interface(BCI) applications. However, the trade off between hair-layer penetration and dose control of conductive material is challenging e.g. two electrodes might be bridged when the headset continuously presses or squeezes the reservoir and electrolyte flows on the scalp. The goal of this study is to design, prototype, and evaluate watermill-like electroencephalogram (EEG) electrodes that aim to simultaneously overcome two issues: hair-layer penetration and dose control of conductive material. Two electrode profiles, straight and spiral, were 3D printed, coated and evaluated with participants’ EEGs. Without any help from skilled technicians, the self-wearing mechanical design allows users to wear and acquire their EEGs in few minutes. In addition, the refillable reservoir enable the possibility for long-term BCI applications. The results show that the proposed electrodes can read neural activities on the hair-covered area. Furthermore, straight profile electrodes outperform the spiral profile in the steady-state visually evoked potential (SSVEP) response. In sum, the watermill-like EEG electrodes can shorten the preparation time as well as the dose control of conductive material for naive users. The results suggest the proposed electrodes might open opportunities for BCI users to develop real-world BCI applications in the future.