Towards conductive-gel-free electrodes: Understanding the wet electrode, semi-dry electrode and dry electrode-skin interface impedance using electrochemical impedance spectroscopy fitting

• Published in: Sensors and actuators. B, Chemical Vol. 277; pp. 250 - 260
• Main Authors: Li, Guangli, Wang, Sizhe, Duan, Yanwen Y.
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 20.12.2018; Elsevier Science Ltd
• Subjects: Abrasion; Circuits; Dry electrode; Electrochemical impedance spectroscopy; Electrode-Skin impedance; Electrodes; Equivalent circuit; Semi-dry electrode; Sensors; Signal quality; Spectrum analysis; Wet electrode; Wet electrode; Dry electrode; Semi-dry electrode; Equivalent circuit; Electrode-Skin impedance; Electrochemical impedance spectroscopy
• ISSN: 0925-4005; 1873-3077
• DOI: 10.1016/j.snb.2018.08.155

•Equivalent circuit models for three typical EEG electrodes were proposed.•Area-normalized impedance was used throughout the whole analysis.•Impedance fitting with mild pressure and skin abrasion conditions were investigated.•Inspiration for development of novel conductive-gel-free electrodes was discussed. The electrode-scalp impedance of six subjects is studied by electrochemical impedance spectroscopy using three representative electrodes, namely wet electrodes, semi-dry electrodes, and dry electrodes. With the analysis of proposed equivalent models and area-normalized impedance (kΩ cm2), the specific electrode double layer resistances are 530 Ω cm2 for all electrodes, their specific contact resistances Res are 80 Ω cm2, 114 Ω cm2 and 20,077 Ω cm2, and their specific skin resistances Rs are 867 Ω cm2, 1730 Ω cm2 and 46,145 Ω cm2 for these three representative electrodes respectively. When pressure was applied on dry electrodes, Res reduced by 47% and Rs reduced by 81%. When pressure was applied on semi-dry electrodes, Rs reduced by 50% (Res is not applicable for semi-dry electrodes). After application of scalp abrasion for dry electrodes, Res reduced by 36% and Rs reduced by 82%. After application of scalp abrasion for semi-dry electrodes, Rs reduced by 64%. Seeking novel interface materials may break through the bottleneck for dry electrodes development in terms of integrated materials, mechanical support and electronic circuitry, while semi-dry electrodes have much development space to meet a balance of quick setup, comfortable wear, and satisfactory signal quality in many medical and out-clinic applications.