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. 2014 Dec 10;14(12):23758-80.
doi: 10.3390/s141223758.

Soft, comfortable polymer dry electrodes for high quality ECG and EEG recording

Yun-Hsuan Chen  1 , Maaike Op de Beeck  2 , Luc Vanderheyden  3 , Evelien Carrette  4 , Vojkan Mihajlović  5 , Kris Vanstreels  6 , Bernard Grundlehner  7 , Stefanie Gadeyne  8 , Paul Boon  9 , Chris Van Hoof  10
Affiliations

Soft, comfortable polymer dry electrodes for high quality ECG and EEG recording

Yun-Hsuan Chen et al. Sensors (Basel). .

Abstract

Conventional gel electrodes are widely used for biopotential measurements, despite important drawbacks such as skin irritation, long set-up time and uncomfortable removal. Recently introduced dry electrodes with rigid metal pins overcome most of these problems; however, their rigidity causes discomfort and pain. This paper presents dry electrodes offering high user comfort, since they are fabricated from EPDM rubber containing various additives for optimum conductivity, flexibility and ease of fabrication. The electrode impedance is measured on phantoms and human skin. After optimization of the polymer composition, the skin-electrode impedance is only ~10 times larger than that of gel electrodes. Therefore, these electrodes are directly capable of recording strong biopotential signals such as ECG while for low-amplitude signals such as EEG, the electrodes need to be coupled with an active circuit. EEG recordings using active polymer electrodes connected to a clinical EEG system show very promising results: alpha waves can be clearly observed when subjects close their eyes, and correlation and coherence analyses reveal high similarity between dry and gel electrode signals. Moreover, all subjects reported that our polymer electrodes did not cause discomfort. Hence, the polymer-based dry electrodes are promising alternatives to either rigid dry electrodes or conventional gel electrodes.

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Figures

Figure 1.
Figure 1.
(a) Pin-shaped and (b) cylinder-shaped conductive polymer dry electrodes.
Figure 2.
Figure 2.
Schematic of the three-electrode set up for impedance measurement by the IVIUM potentiostat.
Figure 3.
Figure 3.
(a) Conductive polymer dry electrode connects with gel removed wet electrode; (b) A pair of wet and dry electrode; (c) Electrode locations for ECG measurements.
Figure 4.
Figure 4.
(a) Schematic of active circuit; (b) PCB of the active circuit; (c) Polymer electrode attached to the backside of the PCB; (d) The terminal board which can accept up to 16 channels of active electrodes.
Figure 5.
Figure 5.
(a) Wet and dry electrodes were mounted on the scalp by elastic bands; (b) Electrode location of dry electrode recording; (c) Electrode location of reference recording.
Figure 6.
Figure 6.
Normalized impedance at 10 Hz signal frequency of conductive polymer electrodes with various carbon content (a) of materials themselves, on phantoms and on human skin; (b) on forearm skin of four different subjects (S1–S4).
Figure 7.
Figure 7.
(a) Hardness and (b) elastic modulus of polymer cylinders with various carbon content.
Figure 8.
Figure 8.
Load-displacement curves of pin-shaped electrodes containing various carbon content.
Figure 9.
Figure 9.
(a) Filtered ECG signals acquired by conductive polymer dry electrodes and by conventional wet electrodes; (b) Electrode locations using wet and dry electrodes; (c) Electrode locations using all wet electrodes; (d) Filtered ECG signals using all wet electrodes.
Figure 10.
Figure 10.
(a) Filtered EEG signals; (b) EEG spectrum of wet and dry electrodes when the eyes of subject were open and closed.
Figure 11.
Figure 11.
(a) Filtered EEG signals; (b) EEG spectrum; (c) Averaged correlation of reference recording when the eyes of subject were open and closed.
Figure 12.
Figure 12.
(a) Correlation when subject's eyes open and closed; (b) Coherence when subject's eyes closed; (c) SNR of each electrode of the wet gel electrodes (reference) and dry electrode recordings. The average value from three test segments of each recording condition is shown. The error bars indicate the best and worst result of the three segments.
Figure 13.
Figure 13.
Skin irritation experiment for short term use of polymer electrodes (a) electrode with pins of 2 mm length; (b) Skin condition before and (c, d) after contact with short pin electrode.
Figure 14.
Figure 14.
Skin irritation experiment for short term use of polymer electrodes (a) electrode with pins of 5 mm length; (b) Skin condition before and (c, d) after contact with long pin electrode.
Figure 15.
Figure 15.
Skin condition after coin-shaped electrode/skin contact for 6 days.
Figure 16.
Figure 16.
Skin condition (a) after 10 h of electrode/skin contact; (b) after 35 h of electrode/skin contact; (c) 4 h after the electrode was removed.
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