shortly anyone on the globe can selectively download books from a library of millions,” he says. However, even with the promise of so much content, potential buyers may put off purchasing e-readers until the displays can support desktop-quality color in devices that do not cost as much as a tablet PC.
Kars-Michiel Lenssen and his team at Philips Research in Eindhoven, Netherlands, are working to solve this problem. Lenssen, who is director and principal scientist at Philips Research, started the color e-paper project several years ago with the goal of making low-power, color e-paper brighter than is currently possible. “We believed that electronic paper would enable new applications, but we also realized that bright colors would be required for a really broad market acceptance in the future,” Lenssen says. “That’s why Philips decided to start a dedicated research project on this topic.”
Philips’ technology, called in-plane electrophoretics, is different from E Ink’s electrophoresis technique. With the electrophoresis technique, used in the Kindle and other popular e-readers, an electric field controls titanium dioxide particles that are suspended in capsules. By applying an electric current, the particles can be forced to the top of the capsules. When the particles are near the display’s surface, the display appears white because light is reflected or scattered. When the particles are farther away from the surface, the display appears dark because light is
absorbed. By selectively making certain areas light or dark, fonts and images can be rendered on the display.
Lenssen’s in-plane electrophoretics technique, in contrast, relies on two particle-filled capsules for each pixel, one containing yellow and cyan, the other magenta and black. By controlling voltages, the colored particles either spread across the pixel or move out of sight altogether, making it possible to render different colors by controlling the number of colored particles shown. To create white, the particles simply shift to reveal the white substrate beneath the capsules. With in-plane electrophoretics research now maturing, Lenssen and his team are exploring several applications for the technology, with the next step being to bring the technology to production in real-world products.
Lenssen says he is looking beyond e-readers as the primary application. “We think there is more potential, particularly when bright color e-paper will be available,” he says. “For example, replacing printed paper signs in retail with electronic paper could save a lot of money not only on printing costs, but also on distribution costs and labor costs for installing and replacing signs.”
Besides display-type applications, such as e-readers and digital signage, Lenssen says there are many other opportunities for in-plane electrophoretics, such as digital surfaces on which color could be changed electronically.
Such surfaces, which Lenssen calls “digital paint,” could be used, for example, as electronic skins for consumer devices. Instead of physically exchanging a device’s skin with one of a different color, a user could electronically choose his or her preferred color for each occasion.
“Our e-paper technology could also enable patterns that appear on the electronic skin of a device like a kind of electronic tattoo,” he says. “ Chameleons and cuttlefish are inspiring examples from nature in this respect.”
Another approach to the problem of low-power, high-quality color in e-paper comes from the Novel Devices Lab at the University of Cincinnati. The technology, called electrofluidic display, uses voltage to manipulate colored inks in much the same way that print heads operate in color printers. Jason Heikenfeld, a professor of electrical engineering at the University of Cincinnati and head of the Novel Devices Lab, formed Gamma Dynamics LLC earlier this year to create products based on his electrofluidic display technology. He and his colleagues are considering a wide range of applications, from e-readers to e-windows to tunable casings for electronic devices. “One challenge,” he says, “is picking a first target application out of so many opportunities.”
Heikenfeld says the Kindle and other e-readers have created a tip-
Jason heikenfeld, head of the novel Devices Lab at the university of cincinnati, is working on electrofluidic display technology based on a process involving pigment dispersion.
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