Underlying Technology
Presently, there are two core technologies that make up the ìinkî of ePaper or smart paper: Bichromal Beads and Electrowetting.
The first and more simplistic approach
is that of using tiny
bichromal (two colors) plastic beads, each just 0.03-0.10 millimeters in
diameter.Ý Each bead is white on one
side, black on the other.Ý
Source:Ý Gyriconmedia.com Website
These beads are encapsulated in a layer of transparent
molten silicone rubber.Ý The molten
silicone is then cooled on flat slabs and cut into sheets; next the rubber is
soaked in oil, which it soaks up voraciously. ÝAs it absorbs the oil, the sheets expand and oil-filled pockets
form around the beads, which can then float and rotate freely.Ý Each bead is then given an electric charge
that is slightly greater on one side than on the other.Ý Finally, this composite is laminated between
two layers of protective plastic film.
Source:Ý Gyriconmedia.com Website
When an electric field is applied to the surface of the
sheet, the beads rotate in the area receiving the current to present a
particular colored side to the viewer. Partial rotation can be used to create
shades of grey.Ý This image remains
static until new voltage patterns are applied.
ÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝ 
Example of ActuationÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝ Actual Film of Excited Bichromal Bead
This technology was originally development by Xeroxís Palo
Alto Research Centre (PARC) and is presently marketed by Gyricon Media Inc. as
Smart Paper.
ìInkî via Polymer LEDs
The second method of creating the display is similar but
has a few fundamental differences.Ý It
uses the principal of electrophoresis, the movement imparted by an electric
field to charged particles that are suspended in a liquid.Ý The ink is made up of millions of tiny
ëswitchableí polymer microcapsules suspended in liquid.
Each transparent microcapsule contains hundreds of
positively charged, sub-micron spheres of white titanium dioxide and negatively
charged black particles suspended in a clear liquid carrier medium.Ý The microcapsules are about 100 microns wide; about 100,000 of them
would fit in a square inch.
These capsules are printed between thin,
flexible electrodes. When the electrode has a positive charge, the negatively
charged particles are attracted to the top of the capsules where they become
visible, producing a white area on a page. At the same time, an opposite
electric field pulls the black particles to the bottom of the microcapsules
where they are hidden. By reversing this process, the black particles appear at
the top of the capsule, making the surface appear dark in that area.
The next step of course to make the display color instead of simply black & white.Ý Making a system that works in color requires that a colored filter is laid across the top of the monochrome display, as is done with todayís LCDs.Ý The filter makes each pixel appear as red, green or blue when the pixel below it is white.Ý When the pixel is black, the filter above essentially reflects no light so no color is seen in that area.
The diagram below illustrates the principle of using positive and negative charges to attract or repel dark or light capsules.
Source:Ý E-Ink Website
To finalize this and create a display this film of ìinkî must ultimately be laminated to a layer of circuitry or connected to an electronic driver device such as that of an active matrix display.Ý This electronic driver will process the image to be presented and create the appropriate positive and negative charges to cause the image to appear on the e-paper display.
Source:Ý E-Ink Website
The finished product can be assembled into a wide variety of products.Ý One example of an application of this technology is an e-book using e-paper as shown in the photo below.
Photo
courtesy of Philips Electronics & E-Ink Website
Another example would be the electronic sign shown below, which communicates wirelessly with a PC to receive itís messages for display.
Source:Ý Gyriconmedia.com Website
