Fabrication and static/dynamic strain sensing performances of CNT microstructure skeleton/PVDF membrane dual mode sandwich flexible sensor

The complexity of engineering structure and strain signal makes the current sensors for structural health monitoring (SHM) face challenges such as high stiffness, poor sensing performance, and insufficient robustness. The development of dual-mode sensor with synchronous sensing of static and dynamic complex strain signals is an effective strategy to solve the problem of complex strain signal sensing and structural monitoring. In this paper, the carbon nanotubes (CNTs) porous ablation skeleton was prepared by microwave ablation method as the piezoresistive layer, and the polyvinylidene fluoride (PVDF) film was prepared by tape casting method. After polarization transformation, it served as the piezoelectric layer. Then polydimethylsiloxane (PDMS) elastomer was introduced to package the piezoresistive/piezoelectric dual-mode sandwich flexible sensor (PREFS). The strain sensitivity, linearity, stability and other sensor performance of PREFS under static/dynamic load were tested respectively. The results show that the assembly thickness of PREFS is only 2.2 mm and the flexibility is good (the bending angle can reach 180°). The piezoresistive layer of PREFS has high sensitivity (GF=259.69%/mV), high linearity (R²=0.997) and low hysteresis (γ_R=6.67%); The sensitivity of the piezoelectric layer is GF=0.038 mV/N, the linearity R²=0.953, and the frequency response is only 9.4 ms. At the same time, PREFS can sensitively sense the finger 0-90° bending and static/dynamic strain amplitude 0-1720 με loading and unloading.