Resistive and capacitive strain sensors based on customized compliant electrode: Comparison and their wearable applications

The demand for stretchable strain sensors has increased exponentially due to their ideal interaction with the human body. However, developing stretchable strain sensors with balanced properties such as a low Young’s modulus, easy fabrication, low cost, large deformation, and fast response time remains a challenge. In this study, we simultaneously prepared two high-performance types of stretchable strain sensors (resistive and capacitive sensors) based on customized compliant electrode. The electrode was developed by embedding multi-walled carbon nanotubes (MCNTs) into plasticized polyvinyl chloride (PVC) using the solvent casting method. The resistive strain sensor was fabricated by the compliant electrode and 3 M 4905 tapes in a sandwich structure. The capacitive sensor was obtained after simple stacking steps based on the preparation of resistive sensor. Then, the performance of the resistive and capacitive sensors was investigated, compared and discussed. The results show that both resistive and capacitive sensors have good static and dynamic performance. The two types of sensors have maximum tensile strain of more than 100 %, low Young's modulus less than 200 kPa, and fast response time less than 140 ms. The linearity of capacitive sensor is better than that of resistive sensor. The repeatability of capacitive sensor is better than that of resistive sensor during a long period. The resistive sensor has higher sensitivity (1.16) than the capacitive sensor (0.44), and has better signal anti-interference capability. Finally, the developed resistive and capacitive sensor were used to monitor the motion status of human joints and the motion angle of human joint, respectively, resulting in accurate sensing of human movement.