The computing power of the smartphones in our pockets has often drawn comparisons to computing machines of the mid-20th century, which themselves were powerful for their time. Our access to such potent technology owes itself to advances in electronics, signalling, and fabrication – but its ultimate ubiquity owes itself to a human-machine interface that has become so intuitive as to make smartphones an extension of our arms: the touchscreen.
What is a touchscreen?
A touchscreen is a surface that combines two functions: to receive inputs for a computer (say, tapping on an app) and to display the output (launching the app). Aside from smartphones, touchscreens are also found today on ATM machines, various household appliances (including TVs and refrigerators), e-readers, billing systems, and electronic voting machines.
By many accounts, the touchscreen was invented by an engineer named E.A. Johnson at the Royal Radar Establishment in Malvern, U.K., in 1965. In two papers he published in 1965 and 1967, Johnson set out the specifics of his invention – a capacitive device that could register being touched by a finger. In the 1967 paper, he wrote:
“The idea of the Touch Display was conceived at R.R.E. in an attempt to overcome the limitations in man-machine communications …. It was originally put forward in the context of an Air Traffic Control Data-processing System for which it has clear application, but it is felt that the arrangement has much wider application…”
The next major invention on this front was the resistive touchscreen in 1970, attributed to G. Samuel Hurst, then at the University of Kentucky. These two inventions, but the latter in particular, gave way to a stream of innovation. For example, in 1982, Nimish Mehta at the University of Toronto developed a touchscreen that could sense two touches at the same time (i.e. multitouch). In 1983, the American artist Myron Krueger reported a way to capture different hand gestures as actions on a screen. Bob Boie at Bell Labs built on Mehta’s work to develop the first transparent (capacitive) multitouch interface in 1984.
While touchscreens also came to be adapted for computer terminals that non-experts could use to interact with the machine from the early 1970s, touchscreens started to become commonplace in everyday-use with a portable email-capable device that IBM and BellSouth launched in 1993, called Simon, followed by Apple’s Newton, the Palm Pilot PDA, and other PDAs (short for personal digital assistants). In the early 2000s, engineers lead the way with wall-sized touchscreens that multiple people could interact with, even remotely; devices that could render ‘normal’ computers capable of sensing touch and gestures; early touchpads that used multitouch to bring finger movements into the virtual realm; plus various improvements to the way touchscreens worked.
Vis-a-vis consumer electronics, there were two big breakthroughs in 2007: the release of the LG Prada and the Apple iPhone, which were the first phones with touchscreens.
How do touchscreens work?
The two most common types of touchscreens are capacitive and resistive; there are other techniques as well. Of these, capacitive touchscreens are used in smartphones and other portable ‘information appliances’.
Such a touchscreen consists of a surface with a grid of capacitors. A capacitor is an electronic device that consists of two plates parallel to each other, with an air gap in between, and each plate connected to the circuit. The plates store electric charge. When a finger touches the surface, an imperceptible amount of charge from a capacitor nearby flows through the wires into the finger, distorting the electric field at that point. Sensors located at the edges of the screen locate this distortion and relay it to a signal-processor to determine where the finger has touched. (This is why some touchscreens can’t sense touch if the user is wearing gloves.)
A more involved architecture, called the projected capacitive method, is used in smartphones with the mutual capacitance architecture. Here, there are two conducting layers. Each layer consists of strips of conducting material: in one, the strips run left to right, and in the other from top to bottom. When two strips cross over each other, they form a capacitor, and the chances in its capacitance are used to measure where a finger has touched the screen. This scheme is amenable to detecting multiple simultaneous touches.
Instead of capacitors, a resistive touchscreen uses resistance. That is, there are two sheets, both conductors, separated by a small gap. When a finger touches one sheet, it moves it at that point to touch the underlying sheet, allowing a current to pass there. Again, sensors pick up on this distortion from a grid of wires attached to one of the two sheets and, using a processor, determine the point of touch. Other touchscreen technologies are based on optical inputs and acoustic waves, among others.
Between 2007 and 2013, capacitive touchscreens overtook resistive touchscreens in the consumer electronics market. Resistive touchscreens are cheaper to make and require less power to operate. But according to a review published in the journal Sensors in July 2021, capacitive touchscreens have better image clarity, sensitivity, and durability.
What next for touchscreens?
While touchscreen technology has advanced rapidly, innovation continues to this day, given the advent of smartwatches and their small screens; machine-learning approaches that can extract more and more information from noisy inputs; and the integration of more and more sensors into smartphones themselves.
Ultimately, what E.A. Johnson wanted was a way to ease “man-machine interactions”, not a way to have haptic interactions with machines per se. In this sense, the machines around us virtually have a long way to go until, like in the Iron Man films, they’re extensions of ourselves.
- A touchscreen is a surface that combines two functions: to receive inputs for a computer (say, tapping on an app) and to display the output (launching the app).
- The two most common types of touchscreens are capacitive and resistive; there are other techniques as well. Of these, capacitive touchscreens are used in smartphones and other portable ‘information appliances’.
- Between 2007 and 2013, capacitive touchscreens overtook resistive touchscreens in the consumer electronics market. Resistive touchscreens are cheaper to make and require less power to operate.
