Capacitor Strain Sensor for Enhancing Feedback to Patients Recovering From a Stroke

Embedded sensors in footwear are of interest for providing feedback on mobility and gait. The most sensitive location is within the sole, requiring development of new materials that have the required functional and mechanical properties. We are developing capacitive strain sensors. The performance of such sensorsis dictated by two fundamental materials properties: dielectric constant (ε) and hardness. The sensitivity is improved by a high dielectric constant and low hardness. This paper describes a novel material that combines a composite elastomeric polymer and single wall carbon nanotubes (SWCNTs). The optimum SWCNT loading in a polyurethane with 80A shore hardness was determined to be 0.1 vol% which delivered a high SNR and maintained its mechanical properties (hardness). Data collected from a shoe strain sensor array of this material can be used for automatic recognition of postures and activities, for characterization of extremity use, and to provide behavioral enhancing feedback to patients recovering from a stroke.