# 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: SEM images of surface under different processing steps, consisting of (**a**) surface of the fabric at 100 \(\upmu\)m before printing, (**b**) surface at 100 \(\upmu\)m after printing SWCNT, (**c**) surface at 100 \(\upmu\)m after printing silver paste, (**d**) surface at 50 \(\upmu\)m before printing, (**e**) surface at 50 \(\upmu\)m after printing SWCNT, and (**f**) surface at 50 \(\upmu\)m after printing silver paste. The working performance of the sensors is evaluated through the stable electrical functionality and mechanical integrity during their loading/unloading cycles (dynamic durability). This is mainly caused by the fatigue and plastic deformation of the PET connections under high pressure, which causes damage to the spacer layers and the sensing nanomaterials (silver breads/SWCNTs). The durability was performed under a lab-customized UTM, and the capacitance was measured every 50 cycles. Attributed to the high elastic recovery performance of the spacer fabric dielectric layer, the sensors show an intact sensitivity and is highly reproducible. Uniform capacitive changes of less than 7% were recorded after 10,000 loading/unloading cycles at 100 kPa, as shown in Figure 6a, as well as less than 10% after 20,000 intensive cycles at 1000 kPa, as shown in Figure 6b. It is worth mentioning that the electric fabric sensor also has high durability to other deformation types. Figure 6c,d demonstrate that the conductivity of two electrode layers is almost constant when stretching from 0 to 20%, bending, and twisting at different angles, which is significant for wearable applications. In real applications, sensors often face high stretches and large deformation (Figure 6e). Figure 7a,b show the effect of environments on the performance of the sensors. The capacitance has a little change in the temperature range from 20 \({}^{\circ}\)C to 30 \({}^{\circ}\)C, as well as in the humidity range from 40% to 60%. With these sensors, the influence of humidity is slightly higher than that of the temperature. This is likely due to the relative permittivity of the air inside the spacer layer changing with the humidity and temperature. In order to decrease the effect of these factors, we suggest decreasing the volume of the air by injecting silicones or encapsulation paste to the spacer layer. However, this method will also decrease the breathability of the sensor, so it needs more experiments. Textile electronics have a major limitation, that is, the electrode materials (CNTs/silvers) will fall out after washing. Figure 7c shows the capacitance of the sensors at 100 kPa after a number of washing times. It is clear that the sensors can still work well after 50 washing times. This advantage is mainly caused by the adhesive ability of silver pastes in order to protect the electrode materials. Hysteresis is the maximum difference between the output values obtained for the same input value. The small hysteresis properties of the fabricated sensors are shown in Figure 7d, and the maximum error is 5%. Figure 5: (**a**) Universal testing machine (UTM), (**b**) relative change in capacitance under pressure from 0 to 100 kPa, (**c**) relative change in the capacitance under pressure from 0 to 1000 kPa, (**d**) relative change in the compression distance under pressure from 0 to 1000 kPa, (**e**) breathable ability, (**f**) response/recovery time, and (change the numerical order of sub-figures). The sensors are evaluated in an overview comparison with other existing works. Our sensors have a sensitivity higher than two studies, (0.283 kPa\({}^{-1}\) at 5 kPa) [26] and (\(121\times 10^{-4}\) kPa\({}^{-1}\) at 100 kPa) [48], and lower than two studies (0.007 kPa\({}^{-1}\) at 5 kPa) [34, 49].