Helically Wrapped CNT-Based Yarn Strain Sensor for Multi-Modal Human Motion Sensing

Monitoring human body movement and position is a key research area in bioelectronic interfaces and wearable electronics. Current wearable human motion sensors rely on core-sheath or coiled yarn which detect bending and stretching via resistance change. However, there remains a challenge in developing sensors capable of detecting complex and multiple deformations, including tensile and torsional deformation of human joints. In this study, we developed a helically wrapped carbon nanotube (CNT)-based yarn strain sensors which can detect both tensile and torsional strains. A well-aligned and conductive CNT sheet was helically wrapped around the elastomeric polymer core at a specific angle to prepare the yarn strain sensor. The helically wrapped CNT effectively detects multiple deformations by leveraging the normal and shear components of both tensile and torsional strains. When mechanical deformation was applied, the shear strain to the CNT induced changes in the wrapping angle, providing mechanical stretchability to the yarn sensor. Simultaneously, normal strain to the CNT sheet deformed the connectivity within the individual bundles, causing the reversible resistance changes. This innovative design offers a practical solution for multi-modal sensing, making it highly promising for applications, including smart wearable devices, personalized healthcare and bio-integrated devices.