Flexible Multi-Modal Capacitive Sensors with Polyurethane Foam Dielectrics for Wearables

We present on the design of highly-sensitive capacitive sensors using conductive textile electrodes and polyurethane (PU) foams as the dielectric layer for wearable sensing applications. Previous works involve complex processes in the fabrication of flexible, stretchable, and composite dielectrics using additional fillers or microstructures. In this work, we demonstrate a simple and cost-effective fabrication technique using polyurethane foam as the dielectric material to form capacitive sensors that are sensitive to stretching, bending and pressure. The magnitude of change in capacitance (10-60%) is increased due to the combined effect of micropores in the dielectric foam and the air gaps at the interface between the textile electrodes and dielectric layer. With the use of microporous PU foam, the change in capacitance under a mechanical load is not only due to the change in the thickness of the dielectric layer but also due to the change in the relative permittivity. Hence the proposed textile capacitive sensors can capture critical information when deployed in different locations on the body demonstrated via a shoe insert, speech detection, breathing and heart rate monitoring.