Spatial Interpolation

It uses toothed electrodes to interpolate the capacitive change spatially as a finger moves across the sensor. The length of the slider can be increased by stretching the interleaving teeth between segments. It is possible to achieve up to 200mm slider with spatial interpolation method.

The important point to consider while stretching the segments is that the touch surface area of two electrodes at each point along the slider. When moving left to right, there should be a linear decrease in touch area of the left electrode and a corresponding linear increase in area of the right electrode.

The following figure depicts the dimension of Spatially Interpolated sensor design.

Figure 1. Two-layer Long Slider (Spatially Interpolated)

To design a long slider, the number of interleaving teeth between segments can be increased to achieve a maximum width of 4mm between the two consecutive teeth.

Tip of the tooth should not be stretched extremely thin. Thinner the tip of the tooth, lesser will be the touch surface area towards the edge of each segment. This would cause a drop in signal while moving between segments. Minimum tooth width should be around 0.25mm to get the sufficient surface area at the edge of the teeth.

Using a two-layer spatially interpolating electrode array to make much longer slider (more than 200mm) is not advisable. Although it is possible to design longer sliders this way, the complexity involved in such sensor design favors the use of a resistively interpolated slider.