Stretchable ionic composites for strain-insensitive dual-mode pressure and proximity sensors

Abstract

Simultaneously sensing pressure and proximity allows for the detection of contact pressure and the distance of approaching objects. This dual functionality ensures precise human-machine interactions and real-time adaptive responses to dynamic environments, proving it useful in human-machine interfaces, robots, and wearable devices. In this study, we introduce a highly stretchable and strain-insensitive pressure and proximity sensor capable of maintaining its electrical properties under mechanical deformations, achieved by establishing a continuous conductive pathway through an ionic bridge between conductive fillers. The strain-insensitive and stretchable composite exhibits Delta R/R-0 of 0.024 under stretching up to 140% after 1,000 times. When the straininsensitive composite is combined with a micro-patterned insulating layer, the resulting piezoresistive pressure sensors exhibit uniform pressure sensing capability even under mechanical deformations of tensile strain (similar to 50%) and bending curvature (1.3 cm(-1)). Moreover, our pressure sensor can be functioned as a capacitive-type proximity sensor capable of identifying material, shape, and distance of approaching objects with high sensitivity (capacitance change (Delta C/C-0) of -0.88). As a proof-of-concept demonstration, our dual-mode pressure sensor with a multichannel array enables real-time monitoring of contact/noncontact pressure distribution, including intensity, shape, and proximity regardless of mechanical interference and surface roughness. Our approach to achieving high sensitivity and selectivity for desired contact/noncontact stimuli independent of mechanical interferences offers a novel platform for practical sensor applications.