end is movable and subjected to tensile stress (Figure 19(a)). When knocking a point with constant distance to El’ on the patch 12, a voltage ratio of the two electrodes (i i E ) can be obtained, through Figure 1(e) and Equation 3. Then the patch 12 may be stretched to a certain distance, and the voltage ratio decreases when the same point is knocked at a constant distance relative to the El’ position. The ratio further decreases with increasing stretch length. Based on this phenomenon, the stretch length of the E2’ end can be measured by knocking a fixed point relative to El’. That is to say, the stretch displacement and stretch velocity/acceleration of the E2’ end with fixed knocking frequency can be measured. The I D sensor 12 exhibits stretchable capability as shown in Figure 19(a). I n an experiment, three different sizes of the patch 12 were investigated in terms of their output voltage ratios. The ratio change as a function of change of stretch percentage of the two electrode ( ’, E2’) voltages is shown in Figure 19(b). It can be seen that with the same percentage of stretching, the voltage ratio is basically the same, indicating that the width and thickness of the patch does not affect the output value during stretching. I n terms of displacement and velocity detection, the resolution of stretch displacement was determined. The relationships of the error bars of E2’/E1’ to the stretch displacement corresponding to different initial lengths are shown in Figure 19(c). The resolution gradually decreases with the increase of stretch length. In addition, the longer the initial length, the faster the resolution decreases. It can be seen that when the stretch displacement is less than 25 mm, the resolution of the three patches is ~ 5 mm. When the stretch length exceeds 25 mm, the resolution is greater than 5mm. Therefore, a patch with a shorter initial length is calibrated in terms of the stretch curve in advance, for later application. Figure 19(d) shows the curves of the voltage ratios with time under a stretch speed of 5 mm/s. The I D sensor 12 can be stretched to as long as 500%, and the stretchability depends on the type, thickness and curing extent of the silicone rubber. To check the reliability and long-term stability of the device 12, a reliability test was conducted on the I D sensor 12 as shown in Figure 24 and a long-term stability test was conducted as shown in Figure 25. Similar to the 2D sensor 10,