Design of Flexible Dry CNT/PDMS Electrodes for In-ear EEG

Abstract

In-ear EEG is a discreet and convenient method for monitoring EEG by placing the electrodes in the ear canal. This enables everyday monitoring outside of clinical environments in contrast to generally used scalp EEG with wet electrodes. This thesis proposes and describes the design of novel flexible dry CNT/PDMS electrodes with short pins, long pins, and a snake pattern. These dry electrodes make use of microstructures to improve electrode-skin impedance (ESI) by enlarging the effective contact area. In the composite fabrication process, SEM is used to optimize CNT dispersion which plays a significant role in the impedance of the material. The performance of the proposed dry electrodes is evaluated in comparison to conventionally used wet Ag/AgCl electrodes. Electrode impedance measurements show the superior performance of CNT/PDMS electrodes with microstructures with lower aspect ratios. This is confirmed by ESI measurements, which show a 49 % improvement at 10 Hz for the electrode with short pins compared to the electrode with long pins, and a further 53 % improvement for electrodes with the snake pattern. This makes the latter comparable to wet electrodes. Moreover, normalization by the projected surface area shows significantly lower ESI at low frequencies for dry CNT/PDMS electrodes with a snake pattern compared to wet electrodes. ESI of the dry electrode at 10 Hz is 30 kΩ cm2, one order of magnitude lower than for wet electrodes. At 1 kHz the ESI is 9.9 kΩ cm2, which is comparable to wet electrodes. Finally, ASSR tests show comparable suitability of dry CNT/PDMS electrodes and wet electrodes for in-ear EEG monitoring, suggesting that the proposed dry CNT/PDMS electrodes are a viable solution for in-ear EEG applications.