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The demand for flexible and wearable electronic devices with excellent stretchability and sensitivity is increasing, especially for human motion detection. In this work, a simple, low-cost and convenient strategy has been employed to fabricate flexible strain sensor with a composite of carbon black and silver nanoparticles as sensing materials and thermoplastic polyurethane as matrix. The strain sensors thus prepared possesses high stretchability and good sensitivity (gauge factor of 21.12 at 100% tensile strain), excellent static (almost constant resistance variation under 50% strain for 600 s) and dynamic (100 cycles) stability. Compared with bare carbon black-based strain sensor, carbon black/silver nanoparticles composite-based strain sensor shows ~18 times improvement in sensitivity at 100% strain. In addition, we discuss the sensing mechanisms using the disconnection mechanism and tunneling effect which results in high sensitivity of the strain sensor. Due to its good strain-sensing performance, the developed strain sensor is promising in detecting various degrees of human motions such as finger bending, wrist rotation and elbow flexion.

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