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 ΔR/R0 of 0.024 under stretching up to 140% after 1,000 times. When the strain-insensitive 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 (∼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 (ΔC/C0) 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.