An Economical Touch Panel Using SAW Absorption

Surface waves are readily absorbed when a soft object such as a fingertip touches the substrate. This familiar observation is put to use in a touch-sensing display panel to provide readouts of finger location and finger pressure. Reflective array strips placed a long the panel edges s urround the entire panel area. A short pulse launched, say, along the top edge from left to right arrives at the bottom left corner having a long rectangular envelope, w ith each point in time corresponding to a specific vertical path across t he panel. A finger touch causes an amplitude dip whose timing and depth indicate location and finger pressure. Low frequencies (4-10 MHz) make low-cost arrays p ractical. Signal/noise ratio is very high, so the c enter of the dip can be located precisely; r esolution is determined by the associated digital circuits.