UBC Theses and Dissertations
Development and validation of dry electrodes for mobile EEG measurements Luu, Cidnee
Electroencephalography (EEG) is a common neuroimaging technique used in clinical, research, and consumer technology due to its non-invasiveness, high time resolution, and sensitivity. Traditional EEG systems consist of wet electrodes and a desktop amplifier for measuring brain activity. While this system provides high signal quality in lab settings, it limits real-world EEG use, such as for ambulatory EEG monitoring, or EEG measurements during exercise. This is due to the training and set up time required for wet electrode application and the bulky, wired traditional amplifier. While some wearable EEG devices exist on the market, EEG measurements during motion requires further signal quality validation to confirm clinical or research utility due to motion artifacts. The objectives of this thesis are to develop custom dry flexible electrodes with improved usability for wearable systems and to compare signal quality of the custom dry electrodes with traditional wet electrodes in mobile measurements. We have developed comb-shaped, dry electrodes for measuring scalp EEG. This electrode incorporates embedded silver thread for a novel yet simple to fabricate design, which allows for a flexible electrode providing impedances similar or lower to those in literature. Participants were instrumented with an EEG cap containing gold cup, gel, and dry electrodes for brain activity measurement as well as an inertial measurement unit (IMU) mouthguard for head kinematics measurements. Data were collected from 8 participants, and during nearly all trials, dry electrodes showed worse signal correlation with gold cup electrodes compared with gel electrodes. For motion artifact characterization, EEG-IMU coherence was found to be higher for dry electrodes in low motion scenarios (e.g., walking), but similar between the 3 electrode types for high motion scenarios (e.g., jumping). This indicates that dry electrodes may be more prone to motion artifacts at lower levels of activity, but with large enough activity all 3 types of electrodes could be equally affected. In summary, we developed custom flexible dry electrodes with improved usability for wearable systems. However, we showed that dry electrode signal quality may be substantially affected by motion artifacts, and wet electrodes may be more suitable for measurements during motion.
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