(Figure 4(d)), and eight-direction designs 108, 110 with varying electrode width and number (Figure 4(e), (f)). Generally, the grating structures may differ from each other in one or more of: the number of grating elements, the widths of the grating elements, and the sequence of the grating elements. At least some of the grating elements may be non-rectilinear, for example arcuate as in the sensors 104, 106 and 108, in which the grating elements radiate outwards from the centre of the respective sensors. I n some embodiments, a contact pad 120 may be provided as part of electrode 100, 102 or 104, to facilitate connection of the electrode 100, 102 or 104 to an external circuit. Figure 5 shows a four-direction device 200 according to an example embodiment for 2D motion sensing and control. Specifically, as shown in Figures 5(a),(b),(c), the device 200 comprises a connected Al electrode grid 202 fabricated on a PET substrate 204 and having a dielectric PTFE thin film covering layer 206 on top. The electrode grid 202 includes different grating structures 211 to 214 for the respective directions indicated by arrows 1 to 4 . The electrode grid 202 may have a contact pad portion 220. The grating structures 211 to 214 differ in their number of grid lines. For example, grating structure 212 comprises 2 grid lines, whereas grating structure 214 comprises 4 grid lines. The operation mechanism of device 200 is based on the contact electrification and electrostatic induction between the surface of the PTFE covering 206 and an active sliding object such as a human finger. I n operation, after coming into contact with each other, the surface of the PTFE covering 206 becomes negatively charged and the finger becomes positively charged. Then, when the finger is sliding in a particular direction across (i.e., sliding in and out of) one grating structure e.g. 211 of the electrode grid 202 with a constant speed, the positive charges on the finger balance the negative charges on the surface of the PTFE covering 206, inducing electric potential difference and thereby an output signal in the external circuit. Therefore, an output signal with a characteristic number/structure of peaks is generated when the finger slides across the corresponding grating structure of the electrode pattern. Three different sliding