Investigation into the origin of the noise of surface electrodes

Abstract

In the recording of biomedical signals, a significant noise component is introduced by the electrode. The magnitude of this noise is considerably higher than the equivalent thermal noise from the electrode impedance. As the noise in surface electrodes limits the resolution of biopotential recordings, it is important to understand its origin. It was found that the noise mainly originates in the electrolyte-skin interface and that it is highly dependent on the electrode gel used and the skin properties of the test subject. Depending on skin treatment, magnitudes between 1 and 20 microVrms were measured among subjects. When the metal-electrolyte interface was allowed time to stabilise, electrodes of different metals measured face to face all showed a negligibly small noise magnitude (< 1 microVrms). In pre-gelled electrodes, where the metal-electrolyte interface has stabilised, no difference in noise properties was found between Ag-AgCl electrodes and other metals when measured on the skin. In subjects at rest, the contribution of EMG signals to the total noise level was shown to be negligibly small compared with the noise contribution of the electrolyte-skin interface. The magnitude of the noise of electrodes appeared to be inversely proportional to the square root of the area of the electrode on the skin.

Dry-Contact and Noncontact Biopotential Electrodes: Methodological Review

“…Interestingly, the only electrode type with consistently higher observed noise than the predicted thermal noise from the skin-electrode coupling noise model are the wet-contact Ag/AgCl electrodes at lower frequencies. Elevated -like low-frequency drifts of the Ag/AgCl offset (half potential mismatch) voltage were confirmed in extended (1-hour) recordings and are consistent with observations in Huigen et al [4].…”

“…It is well known that the noise level, while strongly correlated with skin impedance, far exceeds the amount predicted by thermal noise at low frequencies [4]. It has been theorized that the redox reaction at the electrode accounts for the characteristic with wet Ag/AgCl electrodes [4].…”

“…The standard Ag/AgCl electrode has been well-characterized and studied over many decades [3]- [5]. Most of its properties are well understood [6], and sufficient empirical data exists for mechanism that are not, such as low-frequency noise and drift [4]. Nevertheless, with proper preparation, the signal is excellent.…”

Baseline Adaptive Wavelet Thresholding Technique for sEMG Denoising

“…The baseline is the combination of the two noise sources originated in the electronics of the amplification system (thermal noise) and at the skin-electrode interface (electrochemical noise), respectively [9], [10].…”

Towards Noise-Enhanced Augmented Cognition

“…In particular: the half-cell potential, the long term stability and the contact noise. The latter is known to be a function of electrode contact area [25], which is decreasing with the move to fingered electrodes. To begin to evaluate the impact of this, the remainder of this paper investigates the effect of excess recording noise on a workload monitoring Augmented Cognition task.…”