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

Abstract

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 (R2 > 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.

Flexible Strain Sensors for Walking Gait Monitoring

“…Some researchers have made innovative designs on flat plate structures to enhance the performance of capacitive strain sensors to monitor knee activity more effectively. Han X. et al [61] used a novel multi-needle water bath electrostatic spinning method to coat polyamide 6 (PA6) nanofibers on the surface of silver-plated nylon (thiocyanate) core yarn. SCN/PA6 nanofiber corespun yarns were prepared, and linear flexible capacitive sensors with double helix structures (Dual helix structure of linear flexible capacitive sensors, DHSCSs) were prepared by putting two different elastic rubber wires.…”

Electrospun Micro/Nanofiber-Based Biomechanical Sensors

“…Electrospun yarn and textile have been applied in the development of flexible biomechanical sensors recently. , Yarns and textiles are attractive options as carriers for flexible electronics because of the high flexibility, good abrasion resistance, and superior conformability, which are usually achieved by means of special electrospinning devices or equipment. − Tang et al prepared highly ductile CNT/TPU composite nanofibers with elongation at break up to 476% by evenly dispersing CNT into a flexible TPU matrix through a multineedle water-bath electrospinning device. In this study, a conductive yarn (CTY) is developed from processing nanofibers via a twisted collection device, which is further prepared as a smart sports bandage.…”

Electric field simulation of multi-needle water bath electrospinning and the structural properties of SCN/PAN micro/nanofiber composite yarns

“…The water bath twisting yarn method has a high utilization rate of nanofibers, but it needs to rely on the continuous flow of the water bath and the formation of a whirlpool to complete the wrapping of nanofibers on the surface of the core yarn; therefore, its controllability is poor. In our previous work, we designed an improved water bath electrospinning method to fabricate micro/nanofiber composite yarns that do not require continuous flow and the formation of a whirlpool [14][15][16][17]. By using rotation and continuous movement of the core yarn, nanofibers sprayed on the surface of the water bath were rolled on the surface of the core yarn, and various kinds of micro/nanofiber composite yarns with skin-core structures were successfully prepared.…”

“…In our previous study, micro/nanofiber composite yarns were prepared by electrospinning on the surface of silvercoated nylon (SCN) coated with polyamide 6 (PA6) nanofibers, and were used to develop the one-dimensional doublehelix flexible capacitance sensor [14], in which SCN served as the electrode and the PA6 nanofibers served as an insulating dielectric layer. The structure of the dielectric layer, such as thickness and porosity, has an impact on the performance of the capacitance sensor [27,28], but the nanofiber structure was not analyzed in this work.…”