The science of touch

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Published:
07 Jun 2017
Duration:
16 min read
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1301 words
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Tech
From the Archive (Jun, 2016): We don’t usually think about the science behind touchscreen technology. But the science is fascinating
Today, touchscreens have been implemented to such an extent that we don’t even think about the science behind the technology. But the science is fascinating nonetheless

Driven by consumer demand, touchscreens have turned into a necessity that has influenced the aesthetics of devices as well. Consider older feature phones and their variations in design, like Motorola’s famous Razr phones, which flaunted thin metallic designs or even the various Walkman phones marketed by Sony Ericsson that came in a plethora of innovative designs. Modern phones, because they’re dependent on a flat surface panel for input, have identical aesthetics designed around huge displays flanked by an earpiece, cameras and sensors on top and the home button, navigation keys or a speaker grill at the bottom. Touchscreens have also influenced how humans interact with devices. Because the touchscreen mechanism can be so easily incorporated in creating intuitive controls, it has replaced many of the earlier input modes—such as trackballs, mice and keyboards in a lot of devices. Touchscreen controls are so intuitive that a toddler can grasp the concept of touch and swipe much faster than the input methods of a traditional computer. And the ease of use it allows has meant that ATMs and vending machines have also started using touch interfaces.

Because the touchscreen mechanism can be so easily incorporated in creating intuitive controls, it has replaced many of the earlier input modes

Today, touchscreens have been implemented to such an extent that we don’t even think about the science behind the technology. Touchscreens started appearing in devices in the late 1960s, and over the years, the technology has developed significantly. Three types of touchscreens are popularly used in modern devices these days: infrared, resistive and capacitive. An infrared touchscreen unit uses light, while resistive and capacitive units work with electricity and are not baked into their device’s display. The latter two have a conductive grid laid out on a thin piece of glass that is usually coated with indium tin oxide, which is preferred for its electrical conductivity as well as its transparency. Resistive and capacitive units detect electrical interference within the electric grid and pin-point the location on X, Y coordinates. Although they make use of electrical interference, the science behind how these two technologies work is rather different.


Resistive

Resistive touchscreen mechanisms make use of two layers: the conductive layer that houses the conductive grid and a resistive surface that sits atop the conductive layer. This technology works with any kind of smooth surface because it is an analog system,with moving parts, that makes use of electronic resistance. The resistive layer is flexible, and when a finger applies pressure on the topmost layer, the layer flexes and disrupts the flow of current on the conductive layer below. Because the conductive material is laid out as a grid, the controller chip, which is paired with the resistive device, can easily identify where the electrical disruption is taking place. After identifying the analog coordinates on the grid, the Analog to Digital Converter (ADC), found within the controller chip, sends out the digital coordinates that the rest of the digital components on your device can understand. Although this analog approach to touch has been superseded by solid state capacitive technology, some modern-day devices still use resistive touchscreens. Mostly because these touchscreens work with almost any smooth surface and are not limited by the electro conductivity that drives capacitive technology. While resistive technology is still being used in modern Nintendo Gameboy Consoles and a few consumer devices, it has almost disappeared from the smartphone industry. This is primarily because it can’t detect more than one touch point at a time and also because the technology requires various layers that refract light and reflect it back quite aggressively.

Capacitive

While resistive technology relies on electronic resistance, capacitive technology is based on electrical capacitance. This means that the technology works with an electrically charged field, which causes a voltage dip when a conductive material comes in contact with it. Electrical charge is passed through a conductive material, and without anywhere to go, the electricity forms a field of electric charge that conductive material, like the human skin, steal a small charge from, thus completing the circuit. This causes a dip in voltage in the area where the human interaction occurred. The circuit board on the touch device detects this abnormality and maps the location of this interference and sends a digital X, Y coordinate to the device. The device in turn understands these coordinates as input.


More and more devices are adopting capacitive touchscreen technology today because it is capable of detecting multiple touch points—since distortions on different parts of the field are mapped in parallel. Furthermore, it doesn’t use resistive layers, which add to the bulk of the device, helping producers of devices to trim excess fat from them, and thus allowing for lighter and thinner constructions. Capacitive touchscreens are also precise and receptive, which makes navigating through complex touch-based interfaces a breeze. The only drawback of capacitive touchscreens is that they need conductive surfaces to work (this is why your phone does not react to wollen gloves and fingernails).

Infrared

Infrared touch technology is not widely known because it’s mostly not used in personal electronic devices. This technology uses infrared lasers on two edges of the touch device—such as an ATM or a vending machine—to create a grid and cameras of the other two sides to map the flow of light. Once you interact with the display, your finger blocks off certain portions of the light rays; the cameras map this disruption and send the X, Y coordinates back to the device. Because of their rudimentary technology, these types of touchscreens are not as precise—since the lag times between touch inputs and displays are significant. But because of their cheap production cost, ATM machines and vending machines use this technology on their simplified interfaces.

Although the different touch surfaces use different designs, they all accomplish the same thing: making your devices easier for you to use. Today, owing to touch technology, smartphones are smart, custom user-interfaces can be tailored by apps, and modern devices like tablets, touch-based laptops and screens are so easy to use. Although we’re more keyed into the glitz and glamour of software like Android and iOS, the science behind the unseen hardware that makes touch technology possible paints a fascinating picture on its own.