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.

Highlights

  • Biopotential signals are the result of the electrochemical activity of certain cells of the nervous, muscular or glandular tissue

  • The impedance decreases with the increasing of carbon content

  • It is obvious that the trend of decreasing impedance with increasing carbon content is similar for all substrates

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Summary

Introduction

Biopotential signals are the result of the electrochemical activity of certain cells of the nervous, muscular or glandular tissue. Electrodes can be clamped on the scalp by a cap, requiring shorter setup and removal times, but being uncomfortable to wear To avoid these drawbacks of wet electrodes, various types of dry electrodes have been introduced, as discussed in various publications [11,12,13,14,15,16,17,18,19,20,21,22]. In order to enhance the electrode-skin contact, a tattoo-like epidermal sensor-system was developed for biopotential signal recordings [21] This tattoo-like system consists of dry electrodes in the shape of a stretchable metal mesh on thin silicone which is attached very well to the skin. Regarding pin shaped dry electrodes, full metal electrodes have the lowest impedance but due to their rigidity combined with the pressure essential for good skin contact, they are painful during use [23]. The optimized conductive polymer electrodes were used for ECG and EEG recording, and the obtained biopotential signals were compared to those obtained using conventional wet electrodes, by studying correlation, coherence and signal to noise (SNR) ratios

Shape Designs
Materials
Experimental Section
Mechanical Properties of Various Polymer Compositions
Electrodes Set-Up and Recording System
Signal Analysis
EEG Recording
Recording System and Active Electrodes
Electrodes Locations and EEG Recording
User Comfort and Skin Irritation
Impedance Measurements of Various Polymer Compositions of Bulk Electrodes
ECG Recordings
EEG Recording by Using One Wet and One Dry Electrodes
Reference Recording by Using All Wet Electrodes
Short Term Usage of Polymer Electrodes
Long Term Usage of Polymer Electrodes
Electrode Mounting Systems for EEG Recording
Conclusions
Full Text
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