Dr. Alexander Stoppa, Managing Engineer
If you imagine a sectional view through a modern HMI, several layers lie one behind the other in the direction of the user’s gaze. First the cover glass, then the ITO sensor, which detects the position of the finger(s), then the display.
In school, we learned in physical optics that reflections always occur at the contact surfaces of materials with different optical densities. This is exactly the case in our mental cross-section through the HMI. If you simply place the individual layers one behind the other, there is air in between. Disturbing reflections occur at the contact surfaces of glass and air, which impair perfect readability.
To prevent this, all the gaps are filled with a synthetic material in a clean-room environment. This filler material has the same optical properties as glass. Thus, a ‘pile of panes with air in between’ becomes a single pane with constant optical density. The density jumps at the glass/air transitions are eliminated – and with them the disturbing reflections.