Fabrication and performance assessment of a new dry in-ear EEG sensor for brain monitoring

Bioelectrodes are commonly utilized for sensing electrical signals from the electrochemical activity of excitable cells, recording ionic currents from the body, and translating them into detectable electrical signals. Conventional scalp EEG electrodes, nonetheless, are subject to practical drawbacks such as discomfort, high preparation times, and incompatibility with daily wear. To overcome these issues, the present study proposes a new wearable in-ear EEG sensor produced through silver conductive fabric, designed particularly for EEG signal recording from the ear canal area with enhanced flexibility and comfort. Simultaneous EEG recordings were taken from the proposed in-ear sensor in the external auditory meatus and standard scalp electrodes (wet Ag/AgCl electrodes at occipital O2 and temporal T6 locations, referenced to linked mastoids) in 15 healthy adults (average age: 22.2 ± 3.5 years, 8 males) during standardized neurophysiological paradigms: resting-state eyes-open/eyes-closed conditions, steady-state visual evoked potentials (SSVEP, 12 Hz), and auditory steady-state responses (ASSR, 40 Hz, 55 Hz, 70 Hz). Quantitative comparisons revealed that the alpha modulation ratio recorded by the in-ear sensor was lower than that of occipital scalp electrodes ( r = 0.642, p < 10 −4 , temporal; r = 0.272, p < 10 − 4 , occipital). For the SSVEP task, the in-ear sensor signal amplitude was similarly attenuated compared to other electrodes, reflecting the expected signal decay due to the ear canal recording location. In contrast, the in-ear sensor signals were extremely like temporal scalp recordings, particularly for ASSR tasks. The in-ear and temporal signals were found to have a high relationship ( r = 0.264, p < 10 −4 ). These results indicate that the proposed in-ear EEG sensors successfully record cortical activity near the temporal areas, opening possibilities for comfortable, non-intrusive EEG monitoring and wearable devices.