1.3 Touch Cover Effect

A thicker touch cover increases the distance between the user’s fingertip and the sensor electrode. This causes reduced capacitance between the user and the sensor electrode and a proportional decrease in touch sensitivity.

This can be compensated by increasing the size of the electrode. A thicker cover also has the effect of diffusing the electric field formed between the fingertip and electrode and thus a larger electrode can effectively increase the contact area.

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

All sensor types must be wide enough to extend beyond the dimensions of a touch contact by at least the thickness of the touch cover on both inside and outside. See the examples below:
  • 1 mm touch cover/8 mm contact: recommended width = 10 mm
  • 3 mm touch cover/8 mm contact: recommended width = 14 mm
  • 6 mm touch cover/8 mm contact: recommended width = 20 mm

For an interpolation sensor (slider, wheel, surface with flower pattern), the diffusion of the electric fields results in an extended crossover area between adjacent electrodes and improved accuracy in the reported contact position.