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. 2023 May 2;23(9):4453.
doi: 10.3390/s23094453.

Development of Low-Contact-Impedance Dry Electrodes for Electroencephalogram Signal Acquisition

Ramona B Damalerio  1 , Ruiqi Lim  1 , Yuan Gao  1 , Tan-Tan Zhang  1 , Ming-Yuan Cheng  1
Affiliations

Development of Low-Contact-Impedance Dry Electrodes for Electroencephalogram Signal Acquisition

Ramona B Damalerio et al. Sensors (Basel). .

Abstract

Dry electroencephalogram (EEG) systems have a short set-up time and require limited skin preparation. However, they tend to require strong electrode-to-skin contact. In this study, dry EEG electrodes with low contact impedance (<150 kΩ) were fabricated by partially embedding a polyimide flexible printed circuit board (FPCB) in polydimethylsiloxane and then casting them in a sensor mold with six symmetrical legs or bumps. Silver-silver chloride paste was used at the exposed tip of each leg or bump that must touch the skin. The use of an FPCB enabled the fabricated electrodes to maintain steady impedance. Two types of dry electrodes were fabricated: flat-disk electrodes for skin with limited hair and multilegged electrodes for common use and for areas with thick hair. Impedance testing was conducted with and without a custom head cap according to the standard 10-20 electrode arrangement. The experimental results indicated that the fabricated electrodes exhibited impedance values between 65 and 120 kΩ. The brain wave patterns acquired with these electrodes were comparable to those acquired using conventional wet electrodes. The fabricated EEG electrodes passed the primary skin irritation tests based on the ISO 10993-10:2010 protocol and the cytotoxicity tests based on the ISO 10993-5:2009 protocol.

Keywords: dry electroencephalogram (EEG) electrodes; flexible printed circuit board (FPCB); low-impedance electrodes; polydimethylsiloxane (PDMS).

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Conflict of interest statement

The authors have no conflict of interest to declare.

Figures

Figure 1
Figure 1
Designed dry electroencephalogram (EEG) electrode and its corresponding snap connector in the designed dry EEG head cap (not drawn to scale). The exploded view shows the configuration of the designed electrode, which consists of a rigid metal snap connector, partially embedded polyimide flexible printed circuit board (FPCB), polydimethylsiloxane, and tips coated with Ag–AgCl.
Figure 2
Figure 2
Design of the proposed dry EEG head cap: (a) shielded EEG cables attached with Velcro and fastened at the inner side of the cap. (b) Electrode arrangement (the 10–20 arrangement) and channels (Fp1, Fp2, F3, F4, C3, C4, P3, P4, O1, and O2) of the proposed head cap.
Figure 3
Figure 3
Photos of the mold tools and FPCB. (a,b) Mold tool of electrode design A. Each mold tool consists of a top and bottom mold, and FPCB which consists of a gold layer over a copper layer.
Figure 4
Figure 4
Photograph of the fabricated dry EEG electrodes. Design A is a normal electrode intended for use on hairy parts of the head, and design B is intended for use on portions of the head with limited hair. All electrode legs and bumps are coated with Ag–AgCl through dipping.
Figure 5
Figure 5
Photo of the fabricated dry head caps. The (a) 10-channel configuration and (b) nine-channel configuration follow the standard 10–20 electrode arrangement. Both one-piece structures can be integrated with EEG cables and allow the repositioning of dry EEG electrodes.
Figure 6
Figure 6
Photographs of (a) the Nihon Kohden junction box with EEG cables plugged into the target electrode locations. (b) Impedance values shown on the display of the Nihon Kohden EEG system.
Figure 7
Figure 7
Photograph of the display screen of the NuAmps amplifier when measuring the impedance of flat-disk electrodes. The value of the measured impedance is indicated by the color scale to the right. All the electrodes for which values are displayed in magenta were not connected.
Figure 8
Figure 8
Brain signals recorded by using Nihon Kohden system: signals obtained when using (a) the full wet electrode system under the eyes closed condition, (b) the full dry electrode system under the eyes closed condition, (c) the full wet electrode system under the eyes open condition, (d) the full dry electrode system under the eyes open condition.
Figure 9
Figure 9
Photographs of the setup comprising a mobile application (app) and a flexible circuitry board. (a) Two flat-disk electrodes placed at Fp1 and Fp2. The flexible circuitry is placed as close as possible to these electrodes, (b) wet reference electrode placed behind the ear, and (c) mobile app used to read EEG signals through 1000× gain amplification.
Figure 10
Figure 10
(a) EEG signal acquired before filtering, (b) after filtering within a bandwidth of 8–12 Hz, and (c) signal zoomed-in to a period of 13–15 s from (b).
Figure 11
Figure 11
Photographs of cytotoxicity result (a) test sample, (b) positive control.
See this image and copyright information in PMC

References

    1. Sharma M., Tiwari J., Acharya U. Automatic Sleep-Stage Scoring in Healthy and Sleep Disorder Patients Using Optimal Wavelet Filter Bank Technique with EEG Signals. Int. J. Environ. Res. Public Health. 2021;18:3087. doi: 10.3390/ijerph18063087. - DOI - PMC - PubMed
    1. Baud M., Schindler K., Rao V. Under-sampling in epilepsy: Limitations of conventional EEG. Clin. Neurophysiol. Pract. 2021;6:41–49. doi: 10.1016/j.cnp.2020.12.002. - DOI - PMC - PubMed
    1. Sánchez-Reyes L.-M., Rodríguez-Reséndiz J., Avecilla-Ramírez G., García-Gomar M.-L., Robles-Ocampo J.-B. Impact of EEG Parameters Detecting Dementia Diseases: A Systematic Review. IEEE Access. 2021;9:78060–78074. doi: 10.1109/ACCESS.2021.3083519. - DOI
    1. Torres-Simon L., Doval S., Nebreda A., Linas S.J., Marsh E., Maestu F. Understanding brain function in vascular cognitive impairment and dementia with EEG and MEG: A systematic review. NeuroImage Clin. 2022;35:103040. doi: 10.1016/j.nicl.2022.103040. - DOI - PMC - PubMed
    1. Carrasco-Gómez M., Keijzer H., Ruijter B., Bruña R., Tjepkema-Cloostermans M., Hofmeijer J., van Putten M. EEG functional connectivity contributes to outcome prediction of postanoxic coma. Clin. Neurophysiol. 2021;132:1312–1320. doi: 10.1016/j.clinph.2021.02.011. - DOI - PubMed

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