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Scientific News  Technology TV, video, audio PLASTIC EYE MIMICS OCTOPUS VISION
PLASTIC EYE MIMICS OCTOPUS VISION
Onion-like layers
create flexible, lightweight lens.
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Thousands of
nanolayers help octopus eyes to focus underwater.
©
Corbis |
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A lens resembling an
octopus eye has been created by US researchers. The sphere consists of hundreds
of thousands of layers of plastic and could revolutionize cameras, telescopes
and spectacles.
Traditional glass lenses use a curved surface to
focus incoming light towards a central point. The stronger the lens, the more
curved its surface must be and therefore the thicker and heavier it is. In
nature, eyes avoid this problem by using materials whose density varies in a
certain way.
Light is bent, or refracted, when it travels
between two substances that have different densities (or refractive indices),
such as air and water. The greater the difference between the two materials, the
more the light is refracted. So a flat object that has a greater refractive
index towards its edges can focus light like a curved lens.
Many biological lenses consist of up to hundreds
of thousands of nanolayers, each of which has a slightly different refractive
index. The layers form a smooth density gradient that helps to focus light.
In human eyes, this lens is made up of about
22,000 layers. But animals that live in water, which has a high refractive index
compared with air, need stronger lenses. The octopus eye, for example, can focus
light five times more strongly than a human eye.
Film stars
Eric Baer of Case Western Reserve University in
Cleveland, Ohio, and his team at the Naval Research Laboratory in Washington DC
set out to mimic the octopus's ability with a synthetic lens.
They created plastic films that were 50
micrometres thick and consisted of roughly 6,000 nanolayers of two different
polymers, either poly (methylmethacrylate) or poly (styreneacrylonitrile). These
polymers have different refractive indices, so by varying the number of polymer
nanolayers in each film, the researchers created 100 films, each of which had a
refractive index that differed from the next by 1%.
When stacked and formed into a sphere, the films
created an eye with a focusing ability equivalent to that of the octopus eye.
Baer is optimistic, however, that as the technique is developed, they will be
able to create even more powerful lenses. "It's possible to create almost
any refractive index," he says.
The researchers described their work last week
at a meeting of the Materials Research Society, in Boston, Massachusetts.
Soft touch
There are several practical advantages to this
type of lens. Glass lenses of a comparable strength would weigh almost four
times as much. And a polymer lens is more flexible: the focus can be tweaked
just by altering a few of the nanolayers.
Eventually the researchers plan to use a softer
plastic that will make it easy to shift the focus of the lens by simply
squeezing it. "You can change the refractive index fast, easily and with
cheap materials," notes biomimetics expert Mehmet Sarikaya, of the
University of Washington in Seattle.
Future applications include lightweight lenses
that can be focused remotely. These could be used for unmanned aerial vehicles
and missile guidance, which will please the research project's sponsor, the
Defense Advanced Research Projects Agency.
But the technology could also benefit human
vision. Baer has already used his nanolayers to make himself a pair of glasses;
they meet his prescription, despite being absolutely flat.
©
2004 ABC
Publishing date: December 24, 2004
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