Two-Wired Active Spring-Loaded Dry Electrodes for EEG Measurements.

Seungchan Lee,Kiseon Kim,Anil Kumar,Younghak Shin,Heung-No Lee

doi:10.3390/s19204572

Seungchan Lee, Kiseon Kim + Show 3 more

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https://doi.org/10.3390/s19204572

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Abstract

Dry contact electrode-based EEG acquisition is one of the easiest ways to obtain neural information from the human brain, providing many advantages such as rapid installation, and enhanced wearability. However, high contact impedance due to insufficient electrical coupling at the electrode-scalp interface still remains a critical issue. In this paper, a two-wired active dry electrode system is proposed by combining finger-shaped spring-loaded probes and active buffer circuits. The shrinkable probes and bootstrap topology-based buffer circuitry provide reliable electrical coupling with an uneven and hairy scalp and effective input impedance conversion along with low input capacitance. Through analysis of the equivalent circuit model, the proposed electrode was carefully designed by employing off-the-shelf discrete components and a low-noise zero-drift amplifier. Several electrical evaluations such as noise spectral density measurements and input capacitance estimation were performed together with simple experiments for alpha rhythm detection. The experimental results showed that the proposed electrode is capable of clear detection for the alpha rhythm activation, with excellent electrical characteristics such as low-noise of 1.131 μVRMS and 32.3% reduction of input capacitance.

Highlights

During the last few decades, dry contact electrode-based electroencephalogram (EEG)acquisition [1] is one of the easiest ways to obtain neural information from the human brain in real time
In a complementary analysis for a sum of the difference between the paired noise spectral densities, we found that the proposed design produces more noise by 2.0433 nV Hz on average than the 3-wired counterpart. This extra noise leads to a small difference between the estimated RMS noise voltages (i.e., 1.131 μVRMS with the proposed 2-wired topology vs. 1.017 μVRMS with the 3-wired counterpart)
These spectral comparisons clearly visualize the maximized spectral differences evoked near the 10 Hz, which belong to the alpha rhythm

Summary

Introduction

Acquisition [1] is one of the easiest ways to obtain neural information from the human brain in real time This type of electrode is rapidly replacing conventional wet electrodes, which have been used in a variety of applications such as patient monitoring of neurological disorders [2], brain–computer interfaces [3], and biofeedback [4]. Dry electrodes are integrated into portable commercial devices with wearable technologies to provide personal services such as healthcare and home diagnostics to improve the quality of life. These electrodes are designed to eliminate the need for electrolytic gels, which makes the installation process simple with a short setup time and prevents an increase in impedance due to drying of gels. The impedance characteristics and the physical contact capability of the electrode device have become crucial design considerations for practical electrolyte-free EEG measurements

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