A look at the touch screen technologies on the market
Three touch screen technologies are in wide use today.
In 2007 the iPhone arrived and changed both the phone world and touch technology profoundly. Once merely one option among several, the touch screen has now become indispensable in devices, above all in smartphones.
Today, owning a touch screen device is no longer difficult. Have you ever been curious about their history? Do you know how many touch screen technologies there are? Let us walk through the history and the two common touch technologies of today.
A look back at the history
The father of touch screen technology is Dr Samuel Hurst. In 1971 he was working at the University of Kentucky Research Foundation, where he had to read a very large volume of student graduation papers. To save time he designed a touch sensor that he
called the "Elograph" (electronic graphics) — an invention that let him enter data faster. The company Elographics (today Elo TouchSystems) was born alongside it. The device was unlike today's touch technologies, but it was a major step towards the modern touch screen.
Three years later, in 1974, he designed the first transparent touch screen; in 1977 Elographics invented and patented the 5-wire technology that is still extremely common today.
Types of touch technology
Fundamentally, the hundreds of types of touch screens in use today rely on two main technologies: capacitive touch and resistive touch. A third technology, infrared touch, is good but less widely used; this article covers it as well.
Resistive touch
Before 2007, when the iPhone arrived and changed the smartphone world completely, this was the most common touch technology in the world. Almost every touch phone of the time used it. If you were lucky enough to own a PDA or a Windows Mobile device with a touch screen, it was most likely a resistive one. The technology is still used today in inexpensive devices.
Its greatest strengths are that it is easy to make and cheap. But the resistive touch screen has one fatal weakness that has made it steadily less popular: it scratches easily, and scratches degrade touch quality badly.
Resistive screens come in three main variants: 4-wire, 5-wire and 8-wire; in practice the 5-wire type is the most widely used. Later, three-layer resistive screens raised the touch lifetime enormously — 35 million clicks against 1 million for the traditional two-layer technology.
The principle is simple: two conductive layers and a sensing layer separated by spacer dots. In operation a current passes through the screen, the layers interact and the position that was "touched" is determined. The screen can therefore be touched with anything at all, but it only registers a single touch point.
So the resistive touch screen has:
Strengths: low cost, easy to manufacture, can be touched with anything (a stylus, a fingertip, a key and so on).
Weaknesses: scratches easily, and scratches reduce touch quality. Low durability, single touch point only, and a dimmer display.
Capacitive touch
This is the technology used in almost every touch screen today, above all in smartphones. If you own a multi-touch screen such as the one on an iPhone or a Galaxy, you are using capacitive touch. Apple and the iPhone are credited with introducing multi-touch capacitive technology to the world.
Capacitive screens come in two main kinds: single touch and multi-touch. A capacitive screen has a single layer (an electrical grid) protected by a conductive coating (usually indium tin oxide) and no spacer layer. Four electrodes at the four corners determine where the user touched.
The distinctive trait of a capacitive screen is that only certain objects can operate it — a human finger, for example. Capacitive screens support multi-touch and give better brightness. Their lifetime is also very high, around 225 million clicks.
The capacitive touch screen has:
Strengths: multi-touch, high durability, brightness and sensitivity. Hard to scratch.
Weaknesses: high cost, and not everything can be used to touch it.
Infrared touch
A less widely used kind of touch is infrared. As the name says, this technology is based on infrared beams. Infrared touch screens come in two kinds: thermal and optical. Thermal sensing works from a change in temperature and optical sensing from a change in light — infrared can "sense" both.
Infrared touch technology is less common than the others because it is the most expensive kind of touch. Manufacturers therefore rarely use it for mass production.
Its sensors sit above and around the screen and emit beams that form an infrared grid. When we touch the screen the grid is "broken", which locates the touch point. The lightest touch is therefore enough to register. The weakness of this screen is that it works less accurately in very bright light or at very low temperatures.
In practice, good as it is, infrared touch is little used because it costs too much to make. It is reserved for work that demands high accuracy and extreme sensitivity.
So the infrared touch screen has:
Strengths: extremely sensitive, can be touched with anything. Resistant to scratches and dust.
Weaknesses: high cost. In some conditions, such as strong light, touch quality drops; modern coded-scanning techniques suppress background interference effectively and keep sensitivity high even in bright light, but they also add to the cost.
Source: GenK