Linear flexible capacitive sensor with double helix structure based on multi-needle water-bath electrospinning technology

Capacitive flexible sensors stand out due to their advantages of simple structure, strong adaptability and low power consumption, and become the mainstream technology for the preparation of wearable flexible devices. In this study, polyamide 6 (PA6) nanofibers were coated on the surface of a silver-coated nylon (SCN) core yarn using a novel multi-needle water-bath electrospinning method. The SCN/PA6 nanofiber core-spun yarns were prepared, and linear flexible capacitive sensors with a double helix structure (double helix structure capacitive sensors, DHSCSs) were produced by winding two nanofiber core-spun yarns in parallel, with different winding densities, on elastic rubber strings. We then characterized the nanofiber core-spun yarn, analyzed its sensing performance, and explored an application in human motion monitoring. Our results confirm that a nanofiber coating with a complete structure can be formed on the surface of the SCN core yarn by multi-needle water-bath electrospinning. The nanofiber diameter was in the 80–100 nm range, which provides a soft and deformable dielectric layer for the sensor. The capacitance of the DHSCSs gradually decreased with an increase in strain. When the strain was small, it exhibited good linearity (R ² > 0.99) and sensitivity (gauge factor of ∼4). With an increase in strain, the linearity and sensitivity of the DHSCSs gradually decreased. The capacitances of the DHSCSs were stable under extended duration cyclic stretching, and their repeatability and stability were good. At different tensile speeds, the sensing performance of the DHSCSs did not change, and the capacitance change was not affected by the tensile speed. The higher winding density of the sensor made it more sensitive. The DHSCS could monitor intermittent and continuous knee bending and walking, effectively monitoring human motion in real time. This sensor has the potential for application in flexible wearable human motion, health monitoring, and other fields.