Characterization and Validation of Flexible Dry Electrodes for Wearable Integration

Abstract

When long-term biosignal monitoring is required via surface electrodes, the use of conventional silver/silver chloride (Ag/AgCl) gelled electrodes may not be the best solution, as the gel in the electrodes tends to dry out over time. In this work, the electrical behaviour and performance of dry electrodes for biopotential monitoring was assessed. Three materials were investigated and compared against the gold-standard Ag/AgCl gelled electrodes. To characterize their electrical behaviour, the impedance response over the frequency was evaluated, as well as its signal to noise ratio. The electrodes' performance was evaluated by integrating them in a proven electrocardiogram (ECG) acquisition setup where an ECG signal was acquired simultaneously with a set of dry electrodes and a set of standard Ag/AgCl gelled electrodes as reference. The obtained results were morphologically compared using the Normalised Root Mean Squared Error (nRMSE) and the Cosine Similarity (CS). The findings of this work suggest that the use of dry electrodes for biopotential monitoring is a suitable replacement for the conventional Ag/AgCl gelled electrodes. The signal obtained with dry electrodes is comparable to the one obtained with the gold standard, with the advantage that these do not require the use of gel and can be easily integrated into fabric to facilitate their use in long-term monitoring scenarios.

Keywords: carbon; dry electrodes; electrocardiogram; graphene; silver; wearables.

Figure 1

On the (top), from (left) to (right): electrodes’ dimensions in mm and silver electrode. On the (bottom), from (left) to (right): carbon and graphene.

Figure 2

Impedance measurement circuit.

Figure 3

Electrodes’ placement.

Figure 4

Impedance Response.

Figure 5

Artifacts present during a regular acquisition.

Figure 6

Beat-by-beat comparison.