Electrode Coating Microstructure for EDA Sensor Skin Contact
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Solution Overview
Problem
Existing electrodermal activity (EDA) sensors face challenges in maintaining close, conformal contact with the skin due to varying skin ridge spacings and the saturation of electrodes over time, particularly in applications where skin contact is brief or the measurement location changes.
Innovation Solution
An electrode assembly with a substrate and separate electrodes covered by an electrically conductive coating featuring a microstructure of unit cells, where the unit cells are formed from a material with a specific hardness and are spaced apart with gaps filled by a conductive material of lower hardness, allowing for conformal contact with the skin and enhanced conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If hydrogel or wetting mechanism is used to increase contact area, then electrical contact is improved, but electrode saturation occurs over time reducing effectiveness
Solution Approach 1:
The coating is segmented into discrete unit cells (e.g., domes, hemispheres, or pyramids) spaced apart from each other, rather than using a continuous hydrogel layer. Each unit cell independently contacts the skin, providing multiple contact points that prevent saturation while maintaining electrical conductivity.
Solution Approach 2:
The unit cells are formed from a conductive material with specific local properties (higher hardness) while the gaps between them are filled with a softer conductive material (lower hardness). This creates localized regions of different hardness to optimize both structural integrity and conformal contact with skin irregularities.
2Area of stationary object
If continuous coating is used to ensure skin contact, then contact area is increased, but adaptability to varying skin ridge spacings is reduced
Solution Approach 1:
The coating is divided into multiple discrete unit cells that can independently deform and conform to skin surface irregularities. This segmentation allows the coating to adapt to varying skin ridge spacings while collectively providing sufficient total contact area through the combined effect of multiple unit cells.
Solution Approach 2:
The unit cells are designed to be mechanically compliant and capable of deforming under skin contact pressure. This dynamic response allows each unit cell to adjust its shape and position to match the underlying skin topography, ensuring conformal contact across diverse skin surfaces.
3Reliability
If unit cells are placed close together to increase contact area, then electrical conductivity is improved, but manufacturing precision becomes more difficult
Solution Approach 1:
Rather than requiring perfect continuous coverage, the design uses discrete unit cells with gaps between them. This partial coverage approach is sufficient to achieve the required electrical conductivity while significantly easing manufacturing constraints, as the gaps reduce the precision requirements for unit cell placement and formation.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The electrode assembly effectively reduces contact resistance by conforming to the skin's surface irregularities, enhancing electrical conductivity and maintaining effective contact even with varying skin conditions and repeated use.
Implementation Method 1
The electrode assembly effectively reduces contact resistance by conforming to the skin's surface irregularities, enhancing electrical conductivity
Data Source
AI summary
An electrode assembly structured for use in detecting electrodermal activity (EDA) includes a substrate, at least two separate electrodes affixed to the substrate, and a separate electrically-conductive coating covering each electrode. Each coating includes a base portion and a plurality of unit cells extending from the base portion. The unit cells combine to form a microstructure on an outer surface of the coating. Dimensions and spatial arrangements of the unit cells can be controlled to provide controlled variations along a contour defined by the microstructures, so that the contour conforms to ridges in the skin surfaces of multiple users. This increases electrical conductivity between the skin surfaces and the conductive coating, thereby enhancing electrical contact between the user and the electrodes covered by the coating.