Skin in the Game: A Tunable Interface-Quality Sensor for Human-Coupled Accessories

The value and effectiveness of human-coupled accessories, such as personal protective equipment (PPE), shoes, prosthetics, and wearable devices, are linked to the interface quality with the user's skin. Poor interface quality can lead to injuries or reduce the user experience. Prior research has focused primarily on sensing contact pressures to monitor interface quality, but these methods cannot detect air gaps originating from poor fitting. In this letter, we demonstrate a capacitive method to sense both contact pressures as well as air gaps to enable comprehensive interface-quality monitoring. We do this by adding the skin as an active electrode to the capacitive sensor model and through careful design of the composite dielectric between the accessory and the skin. Our sensor is easy to manufacture with completely commercial materials and processes. We provide results showing our sensor's performance in air-gap and contact pressure sensing. We also demonstrate its performance when integrated into an insole for shoe-fit and gait sensing.