In recent years, with the rapid development of flexible electronic technology, flexible wearable sensor devices for monitoring human motion have attracted widespread attention from both academia and industry. Among them, flexible pressure sensors play an important role in monitoring physiological health signals such as pulse, blood pressure, respiration, etc. Fabric based pressure sensors have become an ideal choice for the development of smart wearable electronic products due to their excellent flexibility and breathability. However, currently most fabric based pressure sensors are difficult to accurately monitor pressure signals in the presence of strain interference, which limits their further applications.
In recent years, with the rapid development of flexible electronic technology, flexible wearable sensor devices for monitoring human motion have attracted widespread attention from both academia and industry. Among them, flexible pressure sensors play an important role in monitoring physiological health signals such as pulse, blood pressure, respiration, etc. Fabric based pressure sensors have become an ideal choice for the development of smart wearable electronic products due to their excellent flexibility and breathability. However, currently most fabric based pressure sensors are difficult to accurately monitor pressure signals in the presence of strain interference, which limits their further applications.
Recently, the teams of Associate Professor Wang Bin and Professor Zhang Xiuqin from Beijing Institute of Fashion Technology have prepared a conjugated electrospun core-shell conductive nanofiber yarn to address the aforementioned issues, and woven it into a sensing fabric with a unique knitted ribbed structure. The design of the core-shell structure yarn effectively improves the sensitivity of pressure sensing, and the unique woven interlocking structure leaves room for extension (tensile resistance) of the conductive path. The synergistic effect of the two makes the sensor highly sensitive to pressure but insensitive to tension, exhibiting excellent resistance to tensile interference pressure sensing performance even under 100% tension. This NYPS-R2 × 2 sensor has a high sensitivity of up to 101.03 kPa − 1, a detection limit as low as 0.14 Pa, and a response/recovery time of approximately 36/54 ms. It has demonstrated excellent resolution and stability in 1000 pressure cycle tests, as well as excellent resistance to tensile interference.
Researchers prepared NYs nanofiber yarns using conjugate electrospinning technology. The conductive yarn passes through the center of the conical nozzle and wraps around the collection drum, while TPU nanofibers are sprayed from two high-pressure nozzles and form Taylor cones, ultimately adhering to the conductive yarn to form a stable shell structure. Subsequently, these yarns are woven into fabrics with different structures using a knitting machine, giving them excellent breathability and moisture permeability. Two pieces of fabric are stacked to form a capacitive pressure sensor NYPS-R2 × 2, where the conductive core layer serves as the upper and lower electrode layers, the yarn shell layer, and the middle air layer together form the dielectric layer, thus obtaining a "sandwich" structure of a micro capacitive sensor with high sensitivity and resistance to strain interference.
By comparing the morphology of the fabric before and after 100% stretching through the schematic diagram, it is shown that even under extreme stretching, the conductive path remains unchanged. The strain capacitance change rate curve proves the insensitivity of the sensor to strain. During the stretching process of the fabric, there will be rotation and slippage between the yarns, but it will not affect the dielectric constant and electrode spacing. The calculation results show that the strain interference factor (SIF) is only 8%, which is much lower than the capacitance change rate caused by pressure, proving that NYPS-R2 × 2 has excellent resistance to strain interference.
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