Abstract
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.
Highlights
The skin is the largest organ of the human body, allowing humans to explore their environment through touch
The emulsion consists of an aqueous solution of carbon black droplets dispersed in a matrix of PDMS and a curing agent
The water-in-oil emulsion loaded with carbon black particles is spread with a stencil that has a depth of 900 μm on a plastic surface with a diameter of 24 mm
Summary
The skin is the largest organ of the human body, allowing humans to explore their environment through touch. The imitation of human skin’s sensory ability via electronics (e-skin) is raising great interest due to its potential for applications, including humanrobot interactions, prosthesis arms with lifelike sense of touch, drivers’ drowsiness detector, and heart monitoring.[1,2,3,4] Recent piezo-resistive materials that emulate tactile sensing via flexible pressure sensors have been reported.[5] Under pressure, changes in material’s electrical resistance are achievable by breaking and reforming percolating pathways. Mannsfeld et al.[7] microstructured a polydimethylsiloxane (PDMS) film to subtly change the permittivity of piezo-capacitive sensors. They reported a sensitivity of 0.55 kPa−1 compared to 0.02 kPa−1 for an unstructured PDMS film. PDMS has a low permittivity, leading to low recorded capacitive signals. It makes the use of electronic amplifications, like OFET, essential to detect very small pressure changes. The conception of sensitive flexible sensors is conditioned by the possibility to develop new materials
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