Mechanical Evaluation for Dry Electrode Tip Geometry in Scalp Electroencephalography Measurements

In electroencephalography (EEG) with dry electrodes, a tradeoff between signal stability and user comfort is a critical barrier to long-term, wearable applications. While various approaches exist, the mechanical impact of electrode tip geometry has not been adequately quantified. Moreover, while existing evaluations utilize subjective feedback, which is an indispensable metric for assessing user comfort, quantitative, mechanics-based analyses that complement these findings have not yet been commonly established. The current study aimed to evaluate the mechanical influence of different electrode tip geometries under both vertical and tilted contact conditions. Finite element analysis was conducted using strain energy density (SED), a mechanical index known to correlate with neural impulse activity, as a quantitative indicator of the mechanical influence of tip geometry on the skin. Six types of electrode tip geometries, ranging from flat to hemispherical, were defined based on the ratio of fillet radius to prong radius. These geometries were analyzed under inclination angles from 0 deg to 5 deg, and their peak SED values were compared. Building on these initial trends, an iterative search algorithm was employed to identify the geometry ratio that tends to minimize peak SED across extended inclination angles up to 15 deg, evaluated as a design boundary. The findings indicate that intermediate fillet geometries tend to reduce peak SED under inclined conditions. While hemispherical tips appear favorable at inclination angles beyond 15 deg, intermediate geometries may offer improved load distribution within the inclination range of 0 deg to 10 deg evaluated in this study.