X-ray: Paperless paper

Whatever happened to the paperless office or, indeed, the paperless world? Perhaps it's closer than we think.

It's interesting to muse that, since PCs became ubiquitous, we've gone from transferring the letters on our pages to the letters on our screens and – pretty soon – back again. The concept of electronic paper isn't new, but it is growing as a technology. And while PCs didn't bring us the paperless age they apparently promised (if anything we use more paper now than we did in the past) the advent of electronic paper may do what PCs didn't, and replace paper as a printed (or should we say rendered) medium.

It's all rather cool, of course, but the viability of e-paper is dependent on a wealth of factors, not the least of which is production cost. So just where are we at the moment with this wonderful technology, and how does it work its magic?

Particles and pixels
There are currently a number of methods to produce electronic paper, but the two most prominent include E-ink and Xerox Parc's 'Gyricon'.
Each uses a similar principle, but implement it differently.
E-ink specialises in a method known as electrophoresis that works by rearranging pigment particles via an electrical charge. In the case of E-ink millions of microcapsules (aka pixels), no larger than the width of a human hair, are arranged in a honeycomb structure and sandwiched between two electrodes to form a thin electronic paper film. Each capsule contains a clear liquid suspending both negatively-charged black carbon particles and positively charged white titanium dioxide particles. When a charge is applied, one set of particles is attracted to the visible surface while the other is attracted to the backplane. With E-ink's method it's possible to not only generate black and white states using this for each capsule, but also gradients by applying mixed charges.

Positively and negatively charged titanium dioxide and carbon particles switch sides when a charge is applied.

Currently, the response time for particles switching sides is around 250ms, but with enough voltage can be as fast as 50ms. However rate of change isn't what's important when it comes to electronic ink – afterall, unless there were embedded video (entirely possible) in your e-news paper you're going to be looking at static text and images. What is important, however, is power and longevity.

Unlike LCD screens, E-ink film has no backlight and instead reflects ambient light much like paper does. And, once a charge is applied, it's possible for the capsules to retain their state for years. Both of these features make it possible to, in literal terms, create a viable electronic alternative to paper, with one important difference: the pages can refresh themselves to contain entirely different information.

Xerox Parc's Gyricon solution is similar but instead of using charged particles, tiny bichromal hemisphere (black on one side, white on the other) beads float in oil and are free to rotate depending on an applied charge. Somewhat like an Etch-A-Sketch, Gyricon paper can be fed into a printer which can erase and render a new image – so it's not unlike feeding paper into a printer as you do now, except you have a single piece of paper that can be re-used thousands of times.

The boffins at Xerox Parc envisage spin-off applications like an electronic hand-held 'wand' that can paint an image across electronic paper as it's waved over the surface and, in reverse, read an image from the paper: aka a scanner, copier, and printer all-in-one in the palm of your hand.

It's this kind of thinking that makes you realise that while the impetus for these technologies may have been flexible, electronic, displays the future could hold a wide range of spin-off technologies.

For now both solutions provide other beneifts apart from the obvious – compared to current LCD displays they have a much wider viewing angle, require power only to change their contents but not to display them, produce a truly 'solid' image that doesn't need to be refreshed and is easy on the eyes, and can be eminently flexible (allowing for some innovative devices – like a small notepad reader that can be 'unrolled' from a tube like a scroll).

About the only thing lacking from electronic paper at the moment is good color reproduction, something that's being worked on for the future, and will likely employ color filtered capsules for red, green, and blue that work much like LCD pixels to create color.