Fully printed non-contact touch sensors based on GCN/PDMS composites: enabling over-the-bottom detection, 3D recognition, and wireless transmission

As a result of the swift progress in intelligent bionics, electronic skin has become a crucial element in bionic robots, allowing them to react to different external stimuli promptly. The combination of wearable touch sensors and IoT technology forms the essential foundation for attaining the versatile functionality of electronic skin. Nevertheless, the majority of current touch sensors depend on deformations of the capacitive layer caused by pressure, which leads to alterations in capacitance values. Regrettably, despite their potential, sensors of this nature are frequently constrained in practical applications due to their relatively uniform sensing capabilities. This study introduces a novel approach involving the incorporation of graphitic carbon nitride (GCN) into polydimethylsiloxane (PDMS) at a low concentration. Remarkably, this combination of two materials with higher dielectric constants surprisingly results in the formation of composite films with lower dielectric constants, contrary to the anticipated outcomes. Unlike traditional capacitive sensors, our non-contact touch sensors rely on electric field interference between the object and the edge of the sensor, an effect enhanced by the use of low dielectric constant GCN/PDMS film. As a result, we have fabricated touch sensor grids using an array configuration of dispensing printing techniques, with distances between the finger and the device ranging from 5 to 100 mm, enabling fast response as well as ultra-low-limit detection of contact. These sensors showed excellent resolution in recognising the 3D shape of objects and accurately detecting positional motion, and enabled real-time monitoring of the array data with signal transmission over a 4 G network. In summary, our proposed approach for the fabrication of low dielectric constant thin films, as applied in non-contact touch sensors, introduces novel avenues for the advancement of electronic skin technology.