E-paper display draws on child’s toy

For decades it was one of the most popular children’s toys: an erasable screen on which you can draw or write with a magnetic pen. Now the idea behind the Magna Doodle has been given a new lease of life by scientists in Japan, who have created an electronic-paper version that could be used as a large interactive display for classrooms.

Electronic or e-paper is a type of computer display that mimics the appearance of ordinary paper by reflecting, rather than emitting, light. The roots of the technology are old, but it has seen a resurgence in recent years with e-book readers such as the Amazon Kindle. The Kindle’s display – a type of electrophoretic display – has a mixture of oppositely charged black and white particles sandwiched between transparent and opaque electrodes. A spatially varying voltage between the electrodes then forces some white particles to the transparent electrode and some black, creating an image.

E-paper has proved popular because it is fairly cheap to manufacture and can sustain an image without draining battery power. But most modern e-papers offer little on-screen interactivity, making it is impossible, for instance, to write over the top of an electronic document.

Yusuke Komazaki and colleagues at the University of Tokyo hope to change that. Their technology builds on a type of e-paper display invented in the 1970s, known as a twisting-ball display. The concept is similar to the Kindle’s electrophoretic display, except that instead of two types of particle there is just one. That one type of particle has two distinct hemispheres: one white and positively charged, and one black and negatively charged. To make an image, a voltage simply rotates some of the particles to show their black side rather than their white side.

New twist

The new twist provided by Komazaki and colleagues is to implant one hemisphere of the particles with super-paramagnetic material, allowing the particles to be rotated from white to black by a magnetic field, as well as by an electric field. That means that, like a Magna Doodle, writing on the twisting-ball display simply requires a magnetic pen. Once finished, you can erase your handwriting by applying a voltage to reset the display.

The potential of the new twisting-ball display is greater than that of the Magna Doodle, however. ‘The Magna Doodle is not a display, so it cannot display electronic data such as text and images,’ says Komazaki. ‘In our display, colour can be controlled both electrically and magnetically, so it can display electronic data in addition to handwriting.’

Komazaki admits that the resolution of the display is low, making it better suited to signage and classroom displays than small e-book readers. Unlike the electronic whiteboards already used in classrooms, the twisting-ball display cannot show moving images. Still, Komazaki believes that the simplicity of its design will allow it to be manufactured cheaply.

There may be other hurdles to overcome, however. Peer Fischer, a chemist at the Max-Planck Institute in Stuttgart, Germany, who has also worked on twisting-ball displays, says there is an inherent contrast problem between the white and black hemispheres that the Tokyo group needs to address. Youngwoo Lee at Samsung Electro-Mechanics in South Korea believes the resolution could also be improved upon. Nonetheless, he says, ‘writing on e-paper is already realised but is not widely adapted in industry. Writing is an essential function for paper, and handwriting using a small magnet is an advantage over conventional e-paper’.