# Bio-Inspired Mechano-Sensor Based on the Deformation of Slit Wake
## 3 Results and Discussion
Among the many parameters, the density of the crack has a great influence on the  
Figure 1: The bio-inspired coupling design of slit-based mechano-sensor composed of FUCMSS and substrate with controlled slit. (**a**) Finite-element simulation analysis of the substrate with controllable slit. (**b**) The schematic of the slit-based mechano-sensor. (**c**) The manufactured slit-based sensor sample. (**d**) The bending deformation of FUCMSS covering slit wake. (**e**) The connection–disconnection process of nanoscale cracks with the bending deformation of the FUCMSS. sensitivity of the FUCMSS. In our research, the density of the nanoscale crack was adjusted by changing the radius of the slender rod in Figure 2a. The result indicates that cracks can only be produced when the radius of slender rod is less than 1 mm. With the further decrease in slender-rod radius, the crack density increased significantly. Meanwhile, there was a significant positive correlation between the sensitivity of the FUCMSS and the crack density. Here, the metal slender rod with radius of 0.5 mm was chosen in our research. The dense crack patterns were formed on the Au layer, and the density of crack was about 200/700 \(\upmu\)m\({}^{2}\). The performance of the FUCMSS including sensitivity, mechanical stability, and response time were researched in detail. Figure 3a shows the sensing performance of the FUCMSS that was fabricated using different radii of the slender rod. The result indicates that the sensitivity of the FUCMSS to dynamic mechanical signals can be significantly improved by decreasing the bending curvature radius. Figure 3b shows the dynamic \(\Delta R/R_{0}\) response curve of the FUCMSS under different peak strains. The result indicates the variation in resistance of the FUCMSS for different peak strains, in sharp contrast to the original sample without cracks (purple curve). Under different strains, the current-voltage (I-V) curves of the crack-based sample and crack-free bare film are shown in Figure 3c. The strain-sensitive film with microcracks showed a stable increase in electric current with the increase in strain. Therefore, the FUCMSS, which can even sensitively detect a change of 0.1% strain, showed excellent strain-sensing performance. Hysteresis is also one of the important indicators of the strain sensor. As can be seen from Figure 3d, the response time of the FUCMSS was about 93 ms during the mechanical-signal-loading stage, while 112 ms was required to return to the initial state during the unloading process. In addition, the durability of the FUCMSS was also tested. Figure 3e indicates that the resistance value of the sample was relatively stable during the 0-10,000 cycles of alternating load. There was no significant performance degradation. Figure 3f shows the relative resistance of the tensile and release cycles after eight cycles with the change in the strain curve. The sensing curves of the tensile and release cycles in the 1 st, 10 th, 100 th, 500 th, 1000 th, 2000 th and 5000 th tensile and release cycles were consistent, indicating that the strain sensor has good monotonicity and long-term stability before failure. In summary, the FUCMSS shows excellent sensitivity, repeatability and tensile durability. Figure 2: Fabrication of the crack-based flexible strain sensor. (**a**) The home-made instrument for manufacturing nanoscale crack on flexible PET substrate. (**b**) The crack-based strain sensor. (**c**) The nanoscale crack array on the flexible substrate. (**d**) Local enlarged image taken from (**c**) denoted by green square. The FUCMSS covering the slit wake bends with the open and close of slit. Therefore, to understand the relationship between the different types of bending deformation of the PET substrate and the change in resistance of the Au layer is crucial for optimizing the design of the slit-based mechano-sensor. When compressive stress is applied to the FUCMSS, there will be two different forms of bending deformation: concave bending and convex bending (Figure 4a).