A Concentric Ring Microneedle Electrode With Low Contact Impedance for Close Sources Laplacian EEG Recording

Microneedle electrodes are a promising solution to the long-term collection of high-quality electroencephalography (EEG) signals without skin preparation. However, conventional microneedle electrodes still suffer from poor spatial resolution due to the volume conduction effect, which results in signal aliasing from adjacent electrodes and interference from remote sources.

Here, we introduce the design, fabrication, and application of an iridium oxide (IrO_x) concentric ring microneedle electrode (CRME) for surface Laplacian EEG (SLEEG) signals recording. The fabrication of a concentric ring structure with microneedles distributed on every ring is realized through high-precision 3D printing, replica molding, laser cutting, and sputtering technology, which can improve spatial resolution.

The contact impedance density of the IrO_x CRME reduces by about 13 times compared to a common-used AgCl dry electrode and is lower than that of a standard wet electrode. Meanwhile, the IrO_x CRME can acquire signals with a higher signal-noise ratio (SNR) and lower background noise. Besides, the mutual information between signals from adjacent IrO_x CRMEs is lower than that from traditional microneedle electrodes (reduced from 0.8-0.9 to 0.1-0.2). The signal tests on the forehead reveal that the proposed electrodes can overcome the interference and are sensitive to close frontal lobe theta wave sources.

The IrO_x CRME shows low contact impedance, high SNR, and selectivity to close sources.

This work improves traditional microneedle electrodes with combining concentric ring structure and can potentially promote the detection of the theta wave benefiting applications such as the monitoring of fatigue and stress.