2.3 Touch Cover Effects

A thicker touch cover increases the distance between the user’s fingertip and the sensor electrodes and has the effect of diffusing the electric field formed between them. There is a reduction in touch contact capacitance, but this can be compensated by increasing the size of the electrode and the amount of interdigitation.

For maximum sensitivity, each sensor must be designed to extend beyond the touch contact by at least the thickness of the touch cover.

In the case of a 1 mm touch cover thickness, the smallest touch button or the narrowest slider/wheel must be $(8mm+(2\times 1mm)=10mm$.

For a 3 mm cover, this is increased to $(mm+(2\times 3mm)=14mm$.

In an interpolated sensor (slider, wheel or surface), a thicker cover benefits from an extended crossover area between adjacent electrodes and thus improved accuracy in the reported contact position.

For flooded X sensors, a thicker cover leads to a more pronounced reduction in sensitivity. It is recommended not to use a touch cover thicker than the X-Y layer separation.