# Simultaneous Sensing of Touch and Pressure by Using Highly Elastic e-Fabrics
## 3 Experimental
### Results and Discussion  
#### 3.2.1 Characterization of the e-Fabric Skin  
Figure 4 shows scanning electron microscope (SEM) images of the standard spacer fabric with the magnified view showing the initial yarns, and the printed yarns with SWCNTs/silver at different steps of the process proposed. The diameter of the single PET yarn is about 10 \(\upmu\)m and appears loosely twisted with ample free space between the microfibers, as shown in Figure 4a,d. SWCNT particles could be observed in the form of thin printings, which stuck randomly onto the PET/SP yarns with a 50% printing area (Figure 4b,e). Otherwise, the silver conductive layer was printed onto CNTs-PET/SP yarns with a 95% printing area, as shown in Figure 4c,f. Figure 3: (a) Structure of the capacitive pressure sensor layer, (b) real picture, (c) working principle of the capacitive pressure sensor layer, and (d) working principle at the sensing point. In order to analyze the electrical response of the proposed multi-structure sensor (capacitive pressure sensor layer), we developed an experimental setup in order to test sensor data using a customized universal testing machine (UTM machine, South Korea), as shown in Figure 5a. Figure 5b shows the sensitivity (S) of the capacitive pressure sensor under applied pressure levels from 0 to 100 kPa. The sensitivity of the pressure sensor can be expressed as S = \(\Delta\)C/C\({}_{0}\)/P, where \(\Delta\)C represents the change in capacitance (C-C\({}_{0}\)), C\({}_{0}\) is the initial capacitance with no pressure, and P represents the pressure load. There are two slopes based on 60 kPa. The pressure sensitivity is \(93.3\times 10^{-4}\) kPa\({}^{-1}\) at 60 kPa and \(205\times 10^{-4}\) kPa\({}^{-1}\) at 100 kPa. This value depends on the level of pressure. Otherwise, Figure 5c,d show the relative change in the capacitance and compression distance under pressure from 0 to 1000 kPa. These results demonstrate a large working range of the sensors under high pressure (up to 1000 kPa). At the 1000 kPa pressure level, the output signals of the sensing points were still below the saturation point. However, the sensitivity values of the sensors reduced at this level. From the relative change in the capacitance under pressure levels, it is clear that this structure ensures the sensitivity and the working range of the sensors. Besides, Figure 5e also shows the breathable ability of this structure that is impermeable to water and permeable to air. Figure S2 (Supplementary Materials) demonstrates the test method for determining the breathability of the sensors. The sample was kept on the hand for 5 h. This skin area was not itchy or discolored when compared to the skin area nearby. Response/recovery time are important parameters for evaluating the performance of the sensor in the dynamic application. The viscoelastic nature of the PET yarns of the spacer fabric is the main reason for a delay time. Figure 5f shows a fast response/recovery time of 6 ms at 100 kPa. Due to the fast self-recovery process of the PET connections, our sensors demonstrate the rapid recovery of the electrical property and ensures the performance of the device during high pressure or a lot of working cycles. This advantage is mainly caused by the excellent elastic properties of the PET/SP spacer fabric, especially the release-ability of PET connections between two parallel-plate electrodes of the capacitive pressure sensor points. Response/recovery times and breathable ability become important when the skin-like sensor is used in dynamic applications such as human-machine interfaces [45], soft wearable robotics applications [46], and healthcare [47].