Function-oriented Knowledge Base \ Electronic paper \ Improve image quality of paper-like display
Twisting balls provide fast response of flat panel display
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Introduction Image forming in a panel electrophoretic display
is based upon the electrophoretic movement of color pigment
particles in a dielectric liquid layer enclosed between two
electrodes, one of which is transparent. The image also persists
after electric potentials have been removed. In an addressable-matrix
electrode panel, one coordinate potential is supplied to a
conducting line of a trough structure containing colored particles
of electrophoretic ink of a given polarity in the dielectric
liquid. At the same time, another coordinate potential is
supplied to the upper transparent conductor. Each pixel of
the panel is visible through the transparent conductor with
natural lighting. Due to the action of an electric field between
the electrodes, the electrophoretic particles migrate towards
one of the conductors, thereby creating a colored image. However,
the migration of an electrophoretic particle through the layer
width is relatively slow. As a result, the display state also
changes slowly. It is necessary to provide a fast response
in a flat panel display to control the potential during the
image change.
Description Rotating twisting balls may be used instead
of the linear migration of particles to provide a fast response
in a flat panel display. Each twisting ball particle is located
inside a spherical cavity in a transparent support material.
The diameter of the spherical cavities is a little larger
than the twisting particle diameter, so that the particle
has rotational freedom without translation freedom. The gap
between the twisting particles and the cavity wall is filled
with an optically transparent dielectric liquid. The twisting
particles exhibit electrical anisotropy due to hemispherical
surface coatings of different Zeta potentials and their distribution
in the dielectric liquid volume. The particles also have the
optical anisotropy of these hemispheres. The optical anisotropy
manifests itself in the difference in the hemispheric surface
coatings, either in their color or their other optical properties.
An external electric field causes the particles to rotate
in accordance with their optical anisotropy. Because the particle
rotation can be performed more rapidly than the linear movement
of its mass, the display response as a whole becomes faster.
Thus, twisting the balls provides a fast response in the flat
panel display.
Additional information The size of two-color balls may range from 0.05
millimeters to 0.5 millimeters. The response of a two-color
ball (180 degree rotation) to the applied electric field is
a threshold. Until a threshold voltage is reached, the ball
remains stationary.
