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E-paper: what’s it all about?

12th May 2020
Alex Lynn

Isn't paper a wonderful invention? Really, when you think about it, before paper we had to write our thoughts, dreams and shopping lists on cave walls, then flat stones and eventually slate. In truth, slate has a lot going for it even today; it is almost infinitely reusable, offers excellent contrast and is exceptionally durable.

By Scott Soong, CEO, Pervasive Displays

That kind of makes you wonder why paper took off in such a big way, but only for about a microsecond. Paper is, of course, superior to slate in many other ways; it is manufactured, rather than mined, which tells you it is more reproducible. Paper is also very recyclable, not to mention light, portable and cheap. In terms of data density, slate is superbly inferior to paper; you would need a lot of very heavy slate to record a fraction of what even a small amount of paper can carry.

But paper has many disadvantages, too. For one thing, it is highly perishable; sodden paper is not much use unless it's arts and crafts day. And while it can be recycled, it is not so easy to reuse, at least not for the same purpose. Today's newspaper is tomorrow's… well, you get the idea. All of which begs the question, what will take the place of paper in the future? Well, the future is already here, because e-paper is an established technology that does what all good inventions do; exactly the same thing, only better.

Not to be confused with other forms of electronic display technologies, e-paper has one very important feature that it shares with its predecessors. It retains its information when you're not looking at it. In simple terms, everything that has come before it has been reader-agnostic. A cave wall doesn't rely on anything except incidental light for it to 'be'. The same goes for flat stones, slate and even conventional paper.

Many other forms of writing surfaces are the same. Graffiti on a tree in a forest will still exist, even if there is nobody there to read it. Electronic displays also exhibit a disregard for an audience, but they do need one thing that others don't, power. Remove the power and almost every type of electronic display will cease to operate. In this respect, e-paper is very much in the cave/rock/slate category.

The reason for that is because the underlying technology used in e-paper is predominantly bistable. Electronic engineers may understand that but for those that do not, it means it has no default state; it can rest in either of two states. This differs from a powered device which will revert to a default – normally 'off' – state when power is removed. The relevance here is that e-paper behaves much more like paper than it does an electronic display, however because it is an electronic display it offers many benefits that paper simply cannot.

Top of the list of those benefits is its ability to be updated, just like more conventional displays. This means the information presented on the screen (yes, let's go with 'screen' to keep things simple) is not static; it can be updated like almost every other type of electronic display. However, because it is also pseudo-permanent, any updates will remain on the screen even when power is removed. 

Disruptive technology tends to define its own applications and the same is applicable here. Yes, it is true that e-paper is displacing conventional signage in areas such as shelf labelling (for what are, hopefully, fairly obvious reasons), but the extent to which e-paper can be used is only beginning to be realised.

We live in an age where almost everything is now 'smart'. That means different things to different people, but let's assume it means the 'thing' in question has some way of acquiring information about its condition or its surroundings and sharing that information with the wider world. These devices are typically low power (smart) sensors or actuators and are often required to operate for many hundreds of hours on a single primary cell. The benefits of adding a bistable display to a low power smart device are numerous; user guides or other operator information can be displayed, a bar code or QR code could be provided to guide people to a website for more information, status reports can be accessed, the list goes on.

Outside of these emerging applications, e-paper can be used in almost the same way regular displays can be used, even as an input device. Touch-sensitive layers can be added to e-paper displays to provide a user interface, which adds a whole new dimension. And while most e-paper displays are monochrome, they can also be made with a third colour, such as red or yellow, allowing more vibrant and eye-catching images or text to be displayed.

When it comes to technology, people are uniquely well equipped to exploit it. No other species is quite so inventive or resourceful. The potential for e-paper to fuel that inventiveness and resourcefulness is truly exciting and Pervasive Displays is pleased to be its enabler.

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