Modelling RF losses in touchscreens

Touch-sensitive displays (touchscreens) are commonly incorporated into today´s hand-held wireless products because they offer increased screen area and a more natural interface over mechanical switches. The touch-sensing element itself often consists of layers of flexible plastic or glass coated with thin films of Indium-Tin Oxide (ITO) which is both electrically conductive and highly optically transparent. During the development of a wireless product containing such a display, it was observed that the presence of these conducting films caused substantial RF losses which degraded radiated performance. In this paper the effects observed are described, the mechanism for this loss explained, a technique for modelling the effects using ANSYS HFSS is demonstrated and the chosen solution presented.