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The Big Five Touch Technologies
Most touch screen systems have a sensor unit that is attached to a display unit. The sensor works with a controller
and a software device driver to sense a touch, determine its location and transmit the information to the computer's
operating system. Touch screen sensors use one of five technologies, each exhibiting with attributes that make it best suited to
specific applications.
Resistive¡¶TOP
Resistive touch screens have a flexible top layer and a rigid bottom layer separated by insulating dots,
with the inside surface of each layer coated with a transparent metal oxide.
Pressing the flexible top sheet creates electrical contact between the resistive layers, essentially closing a switch in the circuit.
The control electronics alternate voltage between the layers to get x then y touch coordinates.
Capacitive¡¶TOP
Capacitive touch screens are curved or flat glass overlays coated with a transparent metal oxide on the top surface.
A bare finger or conductive stylus draws current from each corner of the electric field, creating a voltage drop that is measured
to determine touch location.
Near Field Imaging¡¶TOP
Field Imaging touch screens consist of two laminated glass sheets with a patterned coating of transparent metal oxide between.
An AC signal is applied to the patterned conductive coating, creating an electrostatic field on the surface of the screen.
Acoustic Wave¡¶TOP
Acoustic wave touch screens use transducers mounted at the edge of a glass overlay to emit ultrasonic sound waves along two sides. These
waves are reflected across the glass and received by sensors. A finger or other soft tipped stylus absorbs some of the acoustic energy and
the controller measures the amplitude change of the wave to determine touch location.
Infrared¡¶TOP
Infrared touch screens are based on light-beam interruption technology. Instead of an overlay on the surface, a frame surrounds the display.
The frame has light sources, or light emitting diodes (LED) on one side and light detectors on the opposite side, creating an optical grid
across the screen. When an object touches the screen, the invisible light beam is interrupted, causing a drop in the signal received by the
photosensors.
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