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Touch-Sensitive Displays: A New Technology Surfaces

Spotlighting a new type of display using proprietary digital cameras and software to determine the contact point of an object on its surface...

by Rich Handley

April 2003

Until now, the interactive display arena has incorporated a number of different technologies categorized as either passive or active touch. The main distinction between the two, of course, is that active touch requires the touch surface to be activated by a special pointer, whereas passive touch does not.

As AI readers know, passive touch displays utilize four separate technology types: analog-resistive, surface acoustive wave, capacitive and infrared LED. With analog-resistive technology, two layers of conductive material are separated by pockets of air or spacers; once touched, the two layers make contact and complete a circuit, communicating the position to a computer. Surface acoustic wave (SAW) technology utilizes transducers to vibrate the edge of a thick pane of glass to produce acoustic waves; touching the surface breaks the waves, sending a signal to the computer.

Capacitive technology, meanwhile, uses a glass sheet with a transparent conductive coating fused to its surface and a low-voltage AC field running across it; a finger touching the surface creates a current telling the computer where the touch has occurred. Finally, infrared LED (light-emitting diode) technology involves transmitters and receivers around the edge of a surface; the computer receives input whenever an object breaks the infrared path.

Active touch displays, on the other hand, use either electromagnetic or laser technology. An EM field operates from a panel behind the display, while a proprietary pen attuned to its frequency disturbs the field, sending the disturbance's location to the computer. Laser technology pinpoints infrared lasers just above the active display area, which continuously scan and track movement of a proprietary bar-coded pen. When the pen intersects the laser beams, the processor determines the position and transfers that data to the computer as mouse activity.