Touch Screens Have Totally Changed The Way We Use Mobile Phones. But How Does Wiping Your Finger On A Glass Screen Make Things Happen Inside Your Phone?




Don't be fooled by the mild-mannered glass surface; you're poking your finger fair smack into an electric field or two when you swipe your phone. (Source: iStockphoto)

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Touch screens on phones and tablets really have the X factor. Being able to text, phone or film something just by swiping your finger on glass almost makes up for all those other failed sci-fi promises of the 60s.
But considering how futuristic touch screens seem, they rely on a bit of physics that's almost as old as Newton — capacitance — and the fact that your finger is three parts salty water.
If you stick your finger on a regular piece of glass, the most you can hope for is a smudge.
But if there's an electric field on the other side of the glass, some serious rearranging of electric charges goes on in the glass, in your finger and in the field itself. (Read more about electric fields).
And if there are dozens of small electric fields forming and disappearing in a grid formation on the other side of your glass screen, your phone can not only tell when a finger is touching it, it can pinpoint exactly where on the screen that finger is. Here's how.

Journey to the centre of the smartphone

The touch detection part of a smartphone is in the top part of the phone, above the LCD screen and the battery and circuits.
It's made up of two sheets of glass and a bunch of wires that are so skinny they're see-through. The top sheet of glass is the one you touch — it's mostly for protection and to keep your finger away from the business end of things, which happen on the layer of glass below. This second layer has got the skinny wires running over both sides: across it on one side, and up and down on the other. Together they make up a grid pattern.

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