Today, 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 (ITO).

The human body is also an electrical conductor. When you touch the screen you create a slight but measurable change in electrical 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 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, with some being made that eliminate a layer by building the capacitors inside the display itself. This type of touchscreen gives more direct contact with the content displayed, allowing for far subtler gestures and taps to be recorded and processed.

The second most common touchscreens are 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. The top layer has a special resistive coating on the underside and conductive connections along its sides. The lower layer has the coating on the topside and connections along the top and bottom edges.

A voltage is applied to one layer, and sensed by the other. 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. These screens are favoured by restaurants because they tolerate moisture and contaminants and are considerably less expensive.

Capacitive touchscreens were first described in articles in the mid-1960s and a transparent version was developed by engineers at CERN in the early 1970s. A resistive touch screen was developed in America and patented in 1975 but not produced until 1982.

Response: Richard Tuft, freelance technology writer

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