One of the limitations of modern digital technology is the need for us to use an interface to communicate with our computers. Many of our current interfaces have come to feel quite natural, such as the mouse and keyboard. Others are tailored for a very specific task, such as the joystick. However, the most immediately intuitive interface is the touch screen. Utilizing a tactile interface is something that anyone can do with little instruction.

The touch screen has been around for a surprisingly long time, going as far back as the 1970s. Most modern touch screen technology was made possible by the invention of the capacitor. A capacitor consists of two layers of conductive material separated by a layer of non-conductive material. The purpose of a capacitor is to store an electrical charge.

Fast Fact: Thunderstorms are gigantic capacitors, with the clouds and the earth making up the two layers of conductive material and the air in-between isolating them. This capacitor builds up a massive amount of charge and eventually releases it in a form we all recognize, lightning!

In older touch screens, the entire screen is one capacitor. The pressure of a finger or a stylus pushes the two layers of conductive material closer together, which changes the amount of charge at the point of contact. This is measurable and allows the device to calculate the position the user has touched.

Fast Fact: A capacitor works in a way similar to a water tower. As water runs through a system, the water tower fills up. If the water source is disconnected, then the water tower will continue, briefly, to supply the system with water. A capacitor stores and releases electrical charge in a similar way.

Many modern devices, notably the iPhone and the recently unveiled Playstation Portable 2, use a slightly different system that allows for multiple touches to be detected simultaneously. If you have used an iPhone in the past, you may have noticed that the device only responds to your bare finger, not a stylus or a glove. Instead of the entire screen being one capacitor, there is one half of a capacitor embedded at every point along the screen. The second half of the capacitor is you. Placing your finger on the screen completes a capacitor, which again produces an effect that is measured by the device. The obvious advantage is that you can touch the screen in multiple places and complete multiple capacitors, which is what allows for “multi-touch” input.

Fast Fact: The first multi-touch interface was developed at the University of Toronto and used a camera to detect the shadow of fingers on the back of a frosted glass screen.

These days touch screens are being used everywhere, from your car's GPS, mall information kiosks, and even in restaurants! Next time you use a tablet or a smart phone, think about all of the science which underlies that device!

Learn More!

Learn more about how the iPhone works

Learn more about how capacitors work

See some cool videos of the research being done by theUniversity of Toronto’s Input Research Group

Article first published March 3, 2011.

Peter Kublik

Peter is a freelance science writer from Calgary, Alberta. He has been granted several exciting opportunities to share his passion for science outreach and education in the media, most recently during a four month media fellowship with CBC Radio's Calgary morning show, the Eyeopener. Outside of the lab he is an amateur photographer, an avid outdoorsman, and an enthusiastic technophile.

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