Flexible Normal-Tangential Force Sensor with Opposite Resistance Responding for Highly Sensitive Artificial Skin

An electronic skin (e-skin) that can detect both normal and tangential forces with a differentiable signals output is essential for wearable electronics. A flexible, stretchable, and highly sensitive tactile sensor is presented that enables the detection of both normal and tangential forces, with specific opposite and thus easily being differentiated resistance changing outputs. The e-skin, which is based on two-sublayered carbon nanotubes (CNTs)/graphene oxide (GO) hybrid 3D conductive networks, that are anchored on a thin porous polydimethylsiloxane (PDMS) layer, is synthesized via a porogen (GO wrapped NaCl) assisted self-assembling process. The fabricated CNTs/GO@PDMS-based e-skin shows superior sensitivity (gauge factor of 2.26 under a pressure loading of 1 kPa) to tangential force, moderate sensitivity (−0.31 kPa⁻¹ at 0.05–3.8 kPa, and −0.03 kPa⁻¹ at 3.8–6.3 kPa, respectively) to normal force, and a high-reproducible response over 5000 loading cycles including stretching, bending, and shearing. For applications, the e-skin can not only detect wrist pulsing, discriminating different roughness of surfaces, but also produce an obvious responding to an extremely slight ticking (<20 mg) from a feather, and even can real-timely monitor human's breath and music in rhythm.