Tap Tap Tap – Engineering a Touchscreen Device

By Simon Jones

Modern Life is Good

Twenty years ago (that’s 1994), people would scarcely be able to imagine that in the near future we would all be armed with small portable devices, capable of transferring sound, images and information across the world in real time. Whether we like our technologically progeric world or not, we can still marvel in the technological wonders that make it all happen.


Someone using a touchscreen phone. I wish my hands were that pretty. [Public Domain]

 And today, I want to examine how touch screen technology in phones, laptops and tablet computers works.

The touchscreen works like so: We use our fingers to provide our phone (or other device) with a set of 2 dimensional co-ordinates which can then be processed as an input. Effectively, the computer can work out where on the screen you press and what should be on the screen at that time, and through the magic of programming the two can be matched up to provide some kind of fun or functionality.

It’s all abσut the Sigma

Touchscreens have existed in various forms for a while. However modern touchscreen devices rely on our fingers being a reliable electrical conductor. Our bodies have a fairly rigid level of conductivity (a value we call sigma and write as σ in physics) which is able to disrupt an electrical charge on the phone’s screen. Because the charge is spread out across a grid, any disruptions can be located with co-ordinates and fed back to the computer.

So that’s the science, but how do engineers work it into our lives? Firstly, we can think about the materials engineers who make the touch sensitive layer work reliably with the same capacitance as our fingers, using an alloy of two elements: Indium and Tin. What I find fascinating about materials engineering is that, once you (or the team of people you work with) have created a material such as this, and so long as your material is very good at the job it’s meant to do, then people want it. People will pay money to have your material, and that can be very rewarding for engineers. Touchscreens are a fantastic example of this, the technology has only been commercially available for around 7 years, yet many of us have decided we want this material in our lives.

Engineers also have to think about making the touchscreen work for everyone. It’s hard to believe sometimes, but people are different. They have different kinds of skin; some have tough old wartorn fingers and other fingers are soft and squidgy. The touchscreen device needs to be discerning enough to encompass all the small differences in finger conductivity, while still providing accurate sensitivity. Compromising on these two factors is important for these material engineers.

Who Needs Fingers..?

Which leads to my final point; what if we don’t want to use our fingers at all? Many of us will have experienced the frustration of wearing gloves in winter and trying to write a text message with a touchscreen… it doesn’t work.

Gloves have a different conductivity value to skin and the capacitance screen isn’t able to recognise this. This problem calls for a designed solution. One such solution is a glove with a conducting wire in the index finger, which effectively works in the same way as a finger. These types of gloves and other touch screen accessories are being pumped out these days like hot cakes. We live in a modern golden age, that much is apparent.


Image: science made simple CC-BY-NC

But why stop at gloves? When we were testing out science demos for our latest food themed banana show, we discovered that an unpeeled banana works just as well as any finger or stylus for activating touch screen devices. This actually works, and is sure to intrigue a few passers by.

We’re always looking to inspire the next generation of materials engineers and electrical engineers, and this is something we discuss in our Tomorrow’s Engineers and IET funded shows. We’re excited to say we’ll be rolling out more of these in the 2014/15 academic year!



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Curriculum Links – engineering a touch screen

Key Stage 3 Physics, England:

  • Differences in resistance between conducting and insulating components (quantitative)

Key Stage 3 Physics, Wales:

  • The behaviour of current in electrical circuits
  • How familiar devices/machines work by using electricity, light, sound and other energy transfers

We have a wide variety of engineering shows for primary, secondary and family audiences.

We also work in partnership with Tomorrow’s Engineers to inspire the next generation of engineers!


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