the influence of humidity and force on I D sensor 12 can be ignored. As shown in Figure 25, there is no significant change of ratios of opposite electrodes after testing under 5000 cycles, which indicates a stable and durable electrical property of the sensor 12. 

As discussed above, the I D sensor 12 and 2D sensor 10 can enable trajectory, displacement and velocity detection. Therefore, the combination of the two patches can achieve 3D signal detection and control. The concept can be applied to the applications of robotics, electronic skins, and automatic control, etc. To evaluate 3D control enabled by the sensors 10 and 12, a robotics control system 30 was developed as shown in Figure 3. Through the control connection between the patches 10, 12 and the robotic manipulator (34, 36), experiments with different sliding speeds were conducted to control the robotic manipulator with different moving speeds. The trajectory tracking ability of the sensors 10, 12 were utilised to control the robotic manipulator to write different letters. Three letters "C","X" and "Q" were selected and written by the robot manipulator on a whiteboard. Figure 20(c) illustrates the voltage curves of four electrodes corresponding to the letter trajectories induced by a fingertip. 

## Example 2 

The energy harvesting performance of a four-direction device 200 from hand tapping (~3 Hz, illustrated in Fig. 26(a)) is shown in Figure 26. When the resistance of the external load varies, a maximum output power of 4.8 mW can be achieved (Figure 26(b)). Figure 26(c) and Figure 26(d) illustrate the output voltage of the device under 100 ΜΩ load (~355 V) and short circuit current (~12 µΑ ), respectively. 

Eight-direction control can, for example, be realised through a device 400 with a single electrode grid 401 (Figure 27(a)) according to an example embodiment, shown in Figure 27. The electrode grid has different interconnected grating structures e.g. 402 along the different respective directions 1 to 8 with grating element width of 8 mm (e.g. grating element 404) and 4 mm (e.g. grating element 406), and spacing of 6 mm (e.g. 408). Grating elements with larger 

