a signal generated by crossing of the object over at least part of the grid structure. 

The grid structure may itself be the at least one electrode, or one of the electrodes in embodiments where there is more than one. Accordingly, as the object (such as a finger of a user) is slid over the surface of the substrate, the grid structure or an electrode that is in contact with, or in electrical communication with, the sensor may be used to measure a time-dependent signal that is produced by the sliding motion, and one or more parameters of the time-dependent signal may be used to infer the position and direction of motion of the object relative to the substrate. The parameters may include, for example, the number of peaks, their relative positions, their relative amplitudes, or other parameters derived from the shapes of the peaks. 

As used herein, a "grid" means a regular or irregular set of lines that are joined to form a mesh or net extending in two dimensions along a surface. The lines may be straight or curved. Portions of the grid may be modulated according to the spacing between the lines, their thickness, and/or the angles at which they are disposed relative to lines of other portions of the grid. 

Figure 1 shows, in schematic form, a first embodiment of a triboelectric sensor 10. The triboelectric sensor 10 is adapted to detect 2D motion (also referred to herein as a 2D sensor). Sensor 10 may be in the form of a patch or pad, and may form part of a triboelectric control system as shown in Figures 1(a) and 3, the control system also including a further sensor 12 that is adapted to detect I D motion (also referred to herein as a I D sensor). The I D sensor 12 may also be a triboelectric sensor. 

As shown in Figure 1(b), the triboelectric sensor 10 includes a substrate 20 on which are disposed two pairs of electrodes El, E3 and E2, E4 respectively. I n some embodiments, the electrodes E1-E4 may be embedded in the substrate 20. 

Electrodes El and E3 are respectively located at opposite sides 10a and 10c of the substrate 20. Likewise, electrodes E2 and E4 are respectively located at 

