State of the Art of Non-Invasive Electrode Materials for Brain–Computer Interface
Abstract
:1. Introduction
2. EEG Electrodes
2.1. Principle of EEG Acquisition
2.2. Wet Electrodes
2.3. Dry Electrodes
2.3.1. MEMS Dry Electrodes
2.3.2. Non-Contacted Electrodes
2.3.3. Common-Contact Dry Electrodes
2.4. Semi-Dry Electrodes
3. Evaluation Methods for EEG Electrodes
3.1. Evaluation of Chemical Characteristics
3.2. Simulation of Actual Application Scenarios
3.2.1. Antioxidant Performance
3.2.2. Sweat Resistance
3.2.3. Moisture Retention
3.2.4. Structural Stability
3.3. Electrochemical Performance
3.3.1. Impedance
3.3.2. Electrode Polarization and Electrochemical Noise
3.4. Mechanical Performance
3.5. Biocompatibility
3.6. Operation Difficulty and Comfort
4. Challenges for EEG Electrodes and Expectations
Author Contributions
Funding
Acknowledgments
Conflicts of Interest
References
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Electrode Type | Materials (Structure) | Contact Impedance | Correlation | Ref. |
---|---|---|---|---|
MEMS electrodes | Ti/Pt @ Si substrate | — | 83~86% | [70] |
Ti/Ag @ Si substrate | 12.5 kΩ~20 kΩ (@ 10 hz) | 91.63% (@ forehead) | [72] | |
Au/SU-8 @ Ti substrate | 40 kΩ (@ 10 hz on the inner forearm) | — | [74] | |
Cu | 1.9 kΩ (@ 50 kHz on the inner forearm) | — | [75] | |
IrO | Lower than Ag/AgCl wet electrode | — | [78] | |
Ag flakes in silicone | — | 97.85% | [79] | |
Ag @ flexible polyimide organic layer | 3 kΩ (@ Fp1) and 2.7 kΩ (@ Cz) | — | [80] | |
Non-contacted electrodes | A layer of 30 μm polyimide, 30 nm titanium, 10 μm Cu, 30 μm Ni and 100 nm Au | — | 91% (eye closed) and 83% (eyes open) | [86] |
Cu | — | 92.05% | [88] | |
Cu | — | — | [87] | |
Common-contact electrode | BeCu plungers coated with Au | 9 kΩ (@ forehead) 16 kΩ (@ hariy sites) | 95.26% (@ forehead) and 91.47% (@ hairy sites) | [66] |
Spring probes coated with a platinum nanoporous layer | 11.5 ± 4.9 kΩ | 81.79~96.77% | [91] | |
PU multpin coated with TiN | 65~76 kΩ (@ Fp2) | — | [92] | |
Fingered PLA plastic coated with Ag | 3 kΩ (@ 10 hz) | 86.2~99.5% | [93] | |
Bristles made of Ag/AgCl | 5~10 kΩ | — | [94] | |
Bristles coated with Ag | 80 kΩ | — | [95] | |
Pin-shaped PDMS embedded with carbon fiber and coated with Au | 13 kΩ~417 kΩ (Average 133 kΩ) | >90% at most of the frequencies | [96] | |
Reverse-curve arch made of 92.5% Ag and 7.5%Cu | 70 kΩ (@ forehead) and 125 kΩ (@ hairy sites) | — | [97] | |
Fingered EPDM embedded with carbon fiber stainless steel fiber and CNT (finger-shaped) | — | 90% | [99] | |
Ti/TiN | About 250 kΩ | — | [53] | |
PU foam coated with Ni/Cu | 7 kΩ~15 kΩ (0.5 Hz~1000 Hz on the forehead) | 95.56% (@ forehead) | [17] | |
TYPE I: A yarn containing 78% polyamide and 22% elastomer and plated with 99% pure silver TYPE II: 15% nylon, 30% silver plated conductive fibers, 20% Spandex and 35% polypropylene. | — | 82~88% | [100] | |
PU foam with electrically conductive taffeta fabric and Ni/Cu coating | 9 kΩ (@ forehead) and 16 kΩ (@ hairy sites) | 96.14% (@ forehead) and 90.12% (@ hairy sites) | [102] | |
PU foam coated with PANI | — | — | [104] | |
Ag/AgCl screen printed on a sweat-absorbable sponge layer | 2325 ± 1025 Ω (wet skin) and 36,366 ± 17,286 Ω (dry skin) | 90.8 ± 6.2% (dry skin) 96.2 ± 3.2% (wet skin) | [105] | |
Semi-dry electrodes | PAAm hydrogel containing NaCl | 17.4 kΩ | 93.65% (@ F10) and 95.64% (@ Pz). | [65] |
Thermoset PU foam coated with an Ag/AgCl chemically deposited layer | — | 61~94% | [109] | |
Plungers made of Al2O3 porous ceramic | 22.2 ± 8.5 kΩ | 93.8 ± 3.7% | [110] | |
Silver nanoparticles distributed in PDMS matrix | 18.18 ± 7.51 kΩ (@ Fpz) and 23.89 ± 7.44 kΩ (@ Oz) | 90.65~94.25% | [111] | |
Nylon coated with carbon | 15 kΩ | 90.89% at FCz, 92.61% at Cz and 92.62% at Pz | [112] | |
PU foam | 25 kΩ to 8 kΩ (@ 10 Hz) from 0.3 N to 10 N | — | [113] | |
Porous Ti | 2.4 kΩ on forehead 10 hz | 95.55% (semi-dry) and 90.18% (dry) | [114] | |
Melamine foam coated with Ag nanowires | <10 kΩ | — | [115] | |
A solid-gel electrode containing CMC sodium salt, calcium chloride dihydrate, glycerol, and pure water. | From 3 to 25 kΩ (typically 10 kΩ) | — | [116] |
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Yuan, H.; Li, Y.; Yang, J.; Li, H.; Yang, Q.; Guo, C.; Zhu, S.; Shu, X. State of the Art of Non-Invasive Electrode Materials for Brain–Computer Interface. Micromachines 2021, 12, 1521. https://doi.org/10.3390/mi12121521
Yuan H, Li Y, Yang J, Li H, Yang Q, Guo C, Zhu S, Shu X. State of the Art of Non-Invasive Electrode Materials for Brain–Computer Interface. Micromachines. 2021; 12(12):1521. https://doi.org/10.3390/mi12121521
Chicago/Turabian StyleYuan, Haowen, Yao Li, Junjun Yang, Hongjie Li, Qinya Yang, Cuiping Guo, Shenmin Zhu, and Xiaokang Shu. 2021. "State of the Art of Non-Invasive Electrode Materials for Brain–Computer Interface" Micromachines 12, no. 12: 1521. https://doi.org/10.3390/mi12121521