The ratio is only dependent on the touch point position, i.e., x, if l and h remain constant. More importantly, the ratio is independent of the amount of charge, which enables the sensor 10 or the sensor 12 to be used for stable and reliable position sensing even under different contact force and relative humidity. The relationship between I and E can be obtained using the same procedure. Since the raised portions 22h, 22v of the grid structure 22 are of substantially the same height above surface 20a, the distance h is constant. For simulation purposes, h is set to 1.5 mm, and Figure 1(f) shows the resulting simulated V V I and V$_{E}$ I E of the four-electrode sensor 10, as a function of charge location. The results show good monotonicity, which is especially important for accurate inference of the location of touching. Similarly to the 2D sensor 10, the I D sensor 12 may be used to detect the position of a user’s finger according to the ratio of the electrode potentials, VE / VE , in accordance with the principle outlined above. For example, if the ends of the substrate 24 are attached to the wrist and finger of a user as shown at A in Figure 1(a), the user may extend his or her finger to change the length of the sensor 12 which corresponds to a defined position along an axis, while tapping at a point on the surface of substrate 24 that does not change relative to the user’s wrist, to thereby change the ratio of potentials. The electrodes E1-E4 and - 2’ may be attached to the surfaces of their respective substrates 20 and 24. Alternatively, they may be embedded in the substrates 20 and 24. For example, HPE electrodes may be wrapped in silicone rubber during fabrication of the sensor 10 or the sensor 12. When the finger is contacted with the silicone rubber of the substrate 20 or 24, contact electrification occurs at the interface due to the different electron affinities of the