Design of a wireless and fully flexible insole using a highly sensitive pressure sensor for gait event detection

Gait event detection is a requirement for clinical diagnosis and control strategies for power exoskeletons and rehabilitation robots. Smart insoles are widely used in gait research as they are easy to wear. However, current sensor insoles still have some problems, such as being easily affected by temperature, low sensor sensitivity and discomfort while wearing. To solve these problems, in this work we developed a fully flexible insole based on a high-sensitivity capacitive sensor. High sensitivity was achieved by preparing the dielectric material with a porous structure and full flexibility was obtained by using customized compliant electrodes. The porous structure was produced by mixing xylitol with silicone rubber and the compliant electrode was manufactured by mixing conductive carbon nanotubes into plasticized polyvinyl chloride. The mechanical and sensing properties of the sensor were studied. The results show that our sensor has high sensitivity, a good dynamic response, a fast response time (about 80 ms), a large pressure detection range (0–500 kPa), good durability (>1000 cycles) and is little influenced by temperature. We integrated the sensors into the self-made flexible silicone insole. A wireless data transmission measurement module was developed for ease of use. Finally, we found that the prepared sensor insole is able to detect gait events.