Highly Porous Platinum Electrodes for Dry Ear-EEG Measurements

Abstract

The interest in dry electroencephalography (EEG) electrodes has increased in recent years, especially as everyday suitability earplugs for measuring drowsiness or focus of auditory attention. However, the challenge is still the need for a good electrode material, which is reliable and can be easily processed for highly personalized applications. Laser processing, as used here, is a fast and very precise method to produce personalized electrode configurations that meet the high requirements of in-ear EEG electrodes. The arrangement of the electrodes on the flexible and compressible mats allows an exact alignment to the ear mold and contributes to high wearing comfort, as no edges or metal protrusions are present. For better transmission properties, an adapted coating process for surface enlargement of platinum electrodes is used, which can be controlled precisely. The resulting porous platinum-copper alloy is chemically very stable, shows no exposed copper residues, and enlarges the effective surface area by 40. In a proof-of-principle experiment, these porous platinum electrodes could be used to measure the Berger effect in a dry state using just one ear of a test person. Their signal-to-noise ratio and the frequency transfer function is comparable to gel-based silver/silver chloride electrodes.

Miniaturization for wearable EEG systems: recording hardware and data processing

“…In order to solve these problems, methods to increase the effective surface area while reducing the geometrical dimension of the entire electrode have been proposed. Surface roughening techniques by utilizing nanoporous platinum, platinum black electro-patterning, Ag-TiN coating, and nano-patterning based on pillar or arch shapes are developed to measure EEG precisely when using extreme small electrodes [ 36 – 38 ]. Such electrodes are actively manufactured in various bio-potential measurement fields and are expected to get more increasing interest in wearable ultra-small EEG measurement.…”

Recent advances in recording and modulation technologies for next-generation neural interfaces

“…Although there are some drawbacks such as a limited number of electrodes and reduced signal amplitude, several works have demonstrated its feasibility as a facile and unobtrusive neural interface ( Figure 4 B) ( Hoon Lee et al., 2014 ; Kidmose et al., 2013 ; Lee et al., 2018a ). Moreover, it was also demonstrated that the signal quality of this dry electrode was comparable to the conventional EEG system using conductive gels owing to the close contact between the devices and sweat/hair-free surfaces ( Eickenscheidt et al., 2020 ; Kappel et al., 2019 ; Looney et al., 2012 ).…”

Advanced Electrode Technologies for Noninvasive Brain–Computer Interfaces

“…Without the requirements of skin preparation and conducting gel, this electrode can provide a lower and stable surface impedance, which is suitable for long-term EEG measurements (Figure c). Eickenscheidt et al reported a highly porous flexible platinum electrode fabricated via fast laser-aided manufacturing process and electrodeposition (Figure d) . As a flexible electrode, the porous platinum showed good properties, especially in the relevant frequency range from 0.1 to 500 Hz, illuminating a potential application possibility for in-ear EEG (Figure e).…”