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What is it?

What is it?

How touch screens work

Eduardo CesarTouch screen technology builds sensors into the screen and has software programs to interpret the user’s commands. The most popular devices use three technologies: resistive, capacitive and acoustic. With the resistive screens, one uses a sort of pen (stylus). The screen works with the help of two thin superimposed transparent plates that do not touch, allowing a small electric current to run between them. When one touches a given point on the screen with one’s finger or with a stylus, the plates touch, causing a change in the electrical field that is picked up by the device. The coordinates of this spot are then recorded and associated with a given command.

The capacitive screens have a thin layer of a material that can store electrical potential, such as indium tin oxide. As the human body conducts electricity, when one touches the device with one’s finger, a distortion of the screen’s electrostatic field occurs. This is perceived as a change in the storage capacity of the point that was touched, whose coordinates are recorded by the system. Contrary to resistive screens, which work on pressure, capacitive screens do not allow the user to wear gloves or any other conducting material.

In acoustic screens, ultrasonic waves are employed. They cross the screen’s surface and when the screen is touched, a part of the electromagnetic wave is absorbed and the oscillation change enables the recording of the coordinates at the point that was touched.

Farid Nourani, from the Institute of Geosciences and Exact Sciences of Unesp at Rio Claro