Function-oriented Knowledge Base \ Electronic paper \ Improve image quality of paper-like display
Microstructure with reflective corona enhances image contrast of gyricon display
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Introduction In a monolayer gyricon display with a maximal
packing density of bichromal twisting balls, the balls are
placed directly in a dielectric fluid. The balls and the dielectric
fluid are sandwiched between two electrode substrates. A gyricon
display with a closely packed monolayer exhibits light reflectance
that surpasses that of a multi-layer display. The primary
problem of a monolayer gyricon display with closely packed
balls is that the balls can not be packed together to completely
fill the area of the display due to the interstices between
them. In addition, regardless of which microstructure is used
and how the balls are packed, the balls often can not exactly
rotate to the precise orientation with the desired color facing
the viewer. The unfilled spaces between the balls and the
incomplete rotation of the balls result in each ball being
surrounded by a peripheral area. Instead of useful color information,
this peripheral area actually reflects the color of the substrate
that is typically dark. The dark peripheral area decreases
the contrast. It is necessary to enhance the image contrast
of a gyricon display.
Description Using a reflective corona around each particle
to enhance the image contrast of a gyricon display is proposed.
A plurality of open cavities is provided in an elastomer layer.
The periphery near the cavity openings is metallized, thereby
forming reflective coronas. The cavities are filled with bichromal
balls and a dielectric liquid and are covered at the top with
an electrode substrate. An ambient light ray incident upon
the display is reflected from a portion of the white hemisphere
of a ball. The light ray is then reflected by the reflective
corona surface and travels to the viewer. The light is reflected
from a surface that is larger than the particle due to the
reflective corona. Thus, the reflective corona around the
particle creates the appearance of a surface area of a particle
that is larger than the actual surface area of the particle.
The peripheral area that lacks color information disappears,
so the pixel brightness is increased. This enhances the image
contrast.
Additional information At certain incident angles of light, the reflective
corona may be formed by using the principle of total internal
reflection, when the reflecting surface represents an interface
of two different materials, even if the interface is not made
of a material highly reflective in the ordinary sense. Optical
lenses may also be utilized to form enlarged images for each
bichromal ball particle. In such an arrangement, light from
the surface of the particle is projected onto the peripheral
area through refraction instead of reflection. The reflective
corona may be formed for twisting bichromal particles of various
shapes (for example, cylindrical particles).
