Highly Sensitive Flexible/Stretchable Smart Insole Pressure Sensor with Multi-walled Carbon Nanotubes and Polydimethylsiloxane Double-layer Composites

Abstract

To realize a pressure sensor capable of detecting human motions and gait disease for a smart insole system, highly flexible/stretchable and electrical sensing materials are required. In addition, the impact parameters of pressure sensors such as high linearity and sensitivity and a wide range of dynamic pressure are needed to accurately detect external pressure stimuli during the operation. Recent researches have demonstrated a low-cost wearable sensing insole by using scalable and deformable conductive materials. However, although the sensors are suitable to wearable insole system due to scalable and deformable properties, there still are the lack of stretchability and sensor's performances such as high sensitivity, hysteresis, linearity, and fast response time to obtain an accurate and reliable data. Here, a double-layer multi-walled carbon nanotubes/polydimethylsiloxane (MWCNT/PDMS) pressure sensor with a gap gradient is fabricated by stacking two different composites consisting of 6 and 7 wt% compositions of MWCNTs for top and bottom layers, respectively. Due to the stacked double-layer configuration with different concentrations, the pressure sensor shows high linear sensitivity (~700 kPa) and a pressure range of 0-2 MPa, providing extensively potential applications in monitoring human motions. Moreover, the sensor attached to a shoe insole not only can classify user's motion states for walking, running, and jumping but also exhibited stability for long-term use.