When someone talks about a ''touchscreen'' they are most likely referring to their smartphone, iPad or tablet computer. Their glossy screens are called capacitive panels and usually consist of a thin glass insulator coated with a transparent conductor such as indium tin oxide.
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The human body is also an electrical conductor, so when you touch the screen, you create a slight but measurable change in current. The location of the change can be determined using a variety of techniques and is sent to the device controller to be actioned.
The main limitation of a capacitive touchscreen is that it cannot be used when wearing gloves or similar insulating material.
Several years ago, the marketing department of the company I was working for in America wanted to introduce touchscreen interfaces for our software, forgetting that it was often used in steel production plants and that it is difficult to accurately point wearing asbestos gauntlets.
Smart screen manufacturers are developing thinner and more accurate touchscreens, including some that eliminate a layer by building the capacitors inside the display itself. This type of touchscreen provides a more direct contact with the content displayed, allowing for far more subtle gestures and taps to be recorded and processed.
Another common touchscreen is used for terminals often found in bars or restaurants. These are called resistive panels and comprise two transparent, electrically resistive layers separated by a thin space. When pressure is applied by a fingertip or stylus, the two layers touch to form a circuit and, by rapidly switching between each layer, the position of the touch can be determined.
■ Response by Richard Tuft, freelance technology writer
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