How Does Touch Screen Technology Work?

If you’re old enough to remember 1990, that’s the year MC Hammer released his signature, Grammy-nominated song “U Can’t Touch This.” Hammer may have looked great rapping in parachute pants but he wasn’t that great at prognosticating. Within 15 years people were indeed touching it . . . and they were about to touch it a whole lot more after 2007, once Apple released its groundbreaking iPhone, the first handheld device ever shipped with a multi-touch display. Today, the appetite for high-quality interactive displays has spawned a massive industry with sales by 2018 expected to reach $31.9 billion. Though the display-user interface is now ubiquitous and so intuitive that even infants seem to know how to swipe left and right, we sometimes forget how truly revolutionary and disruptive this technology was when it was introduced.

Touch-device shipment and revenue will continue to rise year over year, peaking in 2019, according to market-data insight firm IHS DisplaySearch. Some touchscreens employ pressure sensors to detect contact, while some use visible or infrared light, and still others use sound waves. The broad range of environments and conditions under which the displays are deployed has required designers and manufacturers to get creative. Let’s take a look at some of the different types of touch technology, how they function, and what their advantages are in terms of reliability, durability, accuracy, size, number of touch points and, of course, cost.

Resistive Touch Screen

Resistive touchscreens are the most common and cost effective. Applications best suited to this pressure-sensitive technology are industrial, human-machine interfaces with zero tolerance for error. Because the surface responds only to direct pressure, it means users are less likely to register a false touch. The display functions well in high-traffic or rugged environments where there’s moisture or even debris, and it can independently work as LCD advertising player. And you can use it with gloves or a stylus, which makes it perfect for mining, petroleum, manufacturing, construction, and laboratory applications. Note the two types of resistive touchscreens: soft and hard surface. The soft display bears a flexible top layer of plastic ITO (indium tin oxide) film affixed over a layer of glass. In between is a crosshatch of electrode sensors that form a grid of X- and Y-axis touch points. The hard-surface display is similar but for a grid that’s sandwiched between two panes of glass, usually bezeled around the perimeter. It’s a cost-efficient technology but there are some downsides, too. Number one, the grid is an analog technology that drifts, requiring periodic recalibration. Second, the ITO film can wear and crack over time. And, finally, the screen can be difficult to read under bright light, where the image quality suffers.

Projected Capacitive Touch Screen

Unlike resistive touch, which relies on pressure, projected capacitive touch screens rely on shifting electrical charges instead of moving parts. If you’ve ever worn socks on carpeting in winter then touched a metal object and gotten a shock, you’ve experienced electrical capacitance. PCAP technology involves two conductive layers that create an electrostatic field, which transfers energy when contacted. One of the key benefits is its ability to process multiple touch points simultaneously. Another great thing is, by eliminating the layers of film and glass PCAP offers near-perfect optical clarity and performance. It’s one of the main reason so many smart phones use it. It tends to be more expensive than resistive touch but its optical clarity, power efficiency and aesthetics have made it the go-to technology for tablets and phones. Because its images are accurate and contrast ratios high, it’s also popular in medical imaging and other industries where an onscreen blotch or defect could lead to catastrophic results. An optional ‘optical bonding’ feature recommended by Premio, which eliminates air and moisture between the layers, makes for an even clearer and more rugged display that withstands shocks and vibrations. A downside is PCAP’s susceptibility to ‘noise’ generated by electromagnetic interference (EMI). Because the display must be finely calibrated to ignore nearby EMI noise, users have to operate PCAP with a finger rather than fingernail, gloved finger or stylus.

Surface Acoustic Wave Touch Screen

Surface acoustic wave (SAW) touch technology uses a transducer to record the absorption of ultrasonic waves transmitted across the display’s surface. Superior clarity and resolution make SAW ideal for in-door applications that require precision image quality as in devices used for research and monitoring. The technology primarily is used with smaller touchscreens of up to 32 inches. Other suitable in-door uses include ATMs and information kiosks, such as self service kiosk. Key advantages include high-durability glass, superior optical clarity, and broader activation capabilities using finger, gloved-finger or soft-tip stylus. Vulnerabilities include moving liquids or condensation that produces false touches, solid stains that cause non-responsiveness until cleaned, and less-robust drag and draw capabilities.