Touch screens utilize electron flow for user experience

Josh Andah Sep 25, 2016

Nine years ago, at a keynote address, an excited Steve Jobs unveiled his company’s latest invention to the world — a black and silver, rectangular, touch-screen phone. That device, called the iPhone, revolutionized the personal computing market. Today, touch-screen technology is indispensable. People use it to check their mail, swipe through holiday photos, scroll past endless selfies on Instagram, and catch Pokémon. But, how does it actually work? How does a glass screen respond to touch and make the device perform?

There are many different types of touch-screens. The technology varies between devices and manufacturers, and many factors ultimately determine which version is chosen. Nevertheless, they all detect the same thing: user stimulus. There are three main types of touch screens: capacitive, resistive, and super acoustic. This article discusses capacitive touch screens, because that is what almost all mainstream smartphones use.

The uppermost surface of a capacitive touch screen is made of an insulating material, such as glass.
This glass surface is coated with a thin layer of a transparent conductor. An electric charge is stored in this conductor, establishing an electrostatic field across the surface. Unlike those in a circuit, the electrons supplied to the screen have nowhere to flow. The difference in this electric potential energy, which makes electrons flow from one location to another, is called electric potential difference. These electrons build up, creating stored charge across the display. When a user touches the screen, the amassed electrons finally have a place to flow to — the finger. The finger reduces the charge at that point on the screen, and so the charge and capacitance — the ratio of charge to potential difference — at that point are reduced to lower than the rest of the screen. These charges are very small, which is why you are not jolted with a shock whenever you interact with your phone, which would be extremely inconvenient and detract from the user’s experience.Circuits along the edges of the touch screen detect these minute differences in capacitance and pinpoint their locations in xy coordinates. The information is sent to a processor, which interprets the user’s touch as a specific command.

Touch screens specifically work with fingers and skin because the human body conducts electricity, which is why when your phone is in your pocket the touch screen is not reacting to your every movement. In addition, as you have probably noticed, it is much more difficult to use your phone with gloves on. The fabrics gloves are made of are usually insulators, so they draw no charge off the screen and no touch is detected. However, special gloves are sold with material to help conduct electricity.

Touch screens provide numerous benefits to the producer and the consumer. Most noticeably, they eliminate the need for buttons. Buttons are easily damaged or jammed, and they reduce the waterproof capabilities of a device.
Fewer buttons allow more space for large displays, which are crucial aspects of the user experience. Most importantly, touch screens allow users to interact naturally with the user interface (think pinch-to-zoom, swiping, scrolling, and 3D Touch), improving device usability drastically.

Touch technology has come a long way since 2007, and is continuously evolving. Today, researchers at Carnegie Mellon are developing EM-Sense, a technology that lets a user’s smartwatch know what object they are touching or holding, which could create a new era of context aware apps. The Future Interfaces Group (FIG) of the Human-Computer Interactions Institute has developed SkinTrack. SkinTrack turns the arm into an extended touch screen and allows the user to use the human body as a touch screen. In the future, as science aims to make human and machine interaction more natural, touch screens will require minimum screen ‘touch.’ It could be replaced by gesture tracking, voice recognition, etc., evident by Google ATAP’s Project Soli, which uses a miniature radar system, built into a smartwatch to track touchless gestures.

Touch screen technology has changed the way we interact with technology for the better, and continues to define and enrich the interaction of people and machines. But most importantly, the next time you pull out your phone and swipe to unlock, you’ll know how it all works.