Polymeric foams for flexible and highly sensitive low-pressure capacitive sensors

Flexible low-pressure sensors ( <10 kPa) are required in areas as diverse as blood-pressure monitoring, human–computer interactions, robotics, and object detection. For applications, it is essential that these sensors combine flexibility, high sensitivity, robustness, and low production costs. Previous works involve surface micro-patterning, electronic amplification (OFET), and hydrogels. However, these solutions are limited as they involve complex processes, large bias voltages, large energy consumption, or are sensitive to evaporation. Here, we report a major advance to solve the challenge of scalable, efficient and robust e-skin. We present an unconventional capacitive sensor based on composite foam materials filled with conductive carbon black particles. Owing to the elastic buckling of the foam pores, the sensitivity exceeds 35 kPa−1 for pressure <0.2 kPa. These performances are one order of magnitude higher than the ones previously reported. These materials are low-cost, easy to prepare, and display high capacitance values, which are easy to measure using low-cost electronics. These materials pave the road for the implementation of e-skin in commercialized applications.Highly sensitive foam sensorsHigh sensitivity is a critical feature for flexible pressure sensors and a novel and low-cost emulsion method has been invented to make capacitive sensors with higher sensitivity. A team of CNRS scientists from France led by Prof Annie Colin develops an unconventional approach for flexible and highly sensitive low-pressure capacitive sensors based on carbon black filled foams. They embed the carbon black in Polydimethylsiloxane (PDMS) elastomer using a water-in-oil emulsion method, which achieves a large change of the permittivity associated to large changes in capacitance upon small compression forces. Consequently, the sensitivity exceeds 35 kPa-1, one order of magnitude higher than previous results. The team then demonstrates arterial pressure measurements and in deed the technique can be applied to much wider fields requiring low-cost and low-power consumption.