Dry-Contact and Noncontact Biopotential Electrodes: Methodological Review

Abstract

Abstract-Recent demand and interest in wireless, mobile-based healthcare has driven significant interest towards developing alternative biopotential electrodes for patient physiological monitoring. The conventional wet adhesive Ag/AgCl electrodes used almost universally in clinical applications today provide an excellent signal but are cumbersome and irritating for mobile use. While electrodes that operate without gels, adhesives and even skin contact have been known for many decades, they have yet to achieve any acceptance for medical use. In addition, detailed knowledge and comparisons between different electrodes are not well known in the literature. In this paper, we explore the use of dry/noncontact electrodes for clinical use by first explaining the electrical models for dry, insulated and noncontact electrodes and show the performance limits, along with measured data. The theory and data show that the common practice of minimizing electrode resistance may not always be necessary and actually lead to increased noise depending on coupling capacitance. Theoretical analysis is followed by an extensive review of the latest dry electrode developments in the literature. The paper concludes with highlighting some of the novel systems that dry electrode technology has enabled for cardiac and neural monitoring followed by a discussion of the current challenges and a roadmap going forward.

The surface Laplacian technique in EEG: Theory and methods

“…The discussion currents generated by the scalp-electrode interface are beyond the scope of this paper, and the readers are referred to (Metting van Rijn et al, 1990Huigen et al, 2002;Chi et al, 2010) 6 Here the attentive reader may argue that (12) may not be well-defined on the surface of the scalp because of its discontinuous boundary conditions. First of all, it is important to point out that the Laplacian is related through the right hand side of (12) to a physically measurable quantity, and therefore always defined at a point.…”

A comparative study of electrical potential sensors and Ag/AgCl electrodes for characterising spontaneous and event related electroencephalagram signals

“…When using conventional gel electrodes a connection between the scalp and metal conductor is achieved through the application of an electrolyte solution. The electrical properties of this interface, known as a half-cell potential, are governed by the electrochemical reactions between the two layers (Chi, 2010). The electrochemical reactions produce fluctuations in the metal-electrolyte potential that can cause an increase in noise levels of up to 10uV peak-to-peak for Ag/AgCl electrodes (Geddes, 1972).…”

“…Dry conducting electrodes, consisting of a benign metal (such as stainless steel) with no electrolyte between electrode and skin, provide a more user friendly approach, with the electrodes making resistive contact directly with the skin (Chi, Jung, & Cauwenberghs, 2010). This overcomes some of the problems caused by the wet gel electrodes, but introduces additional variables: the variation in contact resistance due to perspiration, skin creams etc.…”

“…and their susceptibility to movement artefacts. For these reasons dry conducting electrodes tend to produce noisier signal measurements than wet electrodes (Chi et al, 2010). However, a clinical comparison of concurrent measurements with wet and dry EEG electrodes concludes that there is a high degree of correlation between the signals obtained from both types of electrodes.…”

Towards Noise-Enhanced Augmented Cognition

“…As a result, in recent years there has been a huge amount of research dedicated to improving the EEG unit and the overall recording experience. [1]- [6] represent a small selection of such papers.…”