Flexible CNT/silicon piezo-resistive strain sensors geometrical influences on sensitivity for human motion detection

Developing flexible, extremely sensitive strain sensors with a broad operating range is critical for applications such as healthcare, human motion, human–machine interface, and robotics. The COMSOL Multiphysics Finite Element Modeling software has been used to simulate serpentine geometry CNT-silicon-based flexible piezo-resistive (PZR) strain sensors with various sensor line thicknesses (LT), line widths (LW), pitches (P), and structures (Str whereby Str1 is P in the x-direction, and Str2 is P in the y-direction). Their effect on mechanical and piezo-resistive characteristics for strain ranging from 0 to 100% has been studied. The responses of the proposed modeled sensors have been simulated and analyzed in terms of numerous variables, including maximum displacement, von Mises stress, and sensor sensitivity. The simulation study concluded that for the Str1 structure, the PZR strain sensor with P (0.5 mm), LT (0.5 mm), and LW (1.5 mm) had the highest sensitivity (GF 120.50), while the PZR strain sensor with P (0.5 mm), LT (0.5 mm), and LW (1.5 mm) had the lowest sensitivity (GF 48.99). It is also found that the sensitivity of the Str1 PZR strain sensors rises when LW increases while P and LT decrease. Furthermore, the PZR strain sensor with P (0.5 mm), LT (0.5 mm), and LW (1 mm) of structure Str2 has the highest sensitivity (GF 165.95), and the PZR strain sensor with P (1.5 mm), LT (0.5 mm) and LW (0.5 mm) showed the lowest sensitivity (GF 161.62) among all the Str2 sensors, and it is revealed that the sensitivity increases with the decrease of P and LT while the effect of LT is not apparent. As a result, the modeled sensor can be employed as a highly sensitive PZR strain sensor with an excellent capability to monitor a wide range of human motions over the range of 0–100% strain.