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Nanogenerator provides continuous power by harvesting energy from the environmen
Posted on Thursday, April 05, 2007 @ 21:58:06 UTC by vlad
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 Close-up image shows a prototype direct-current nanogenerator
fabricated by Georgia Tech researchers using an array of zinc oxide
nanowires. Credit: Georgia Tech Photo: Gary Meek
Researchers have demonstrated a prototype nanometer-scale generator
that produces continuous direct-current electricity by harvesting
mechanical energy from such environmental sources as ultrasonic waves,
mechanical vibration or blood flow.
Based on arrays of vertically-aligned zinc oxide nanowires that move
inside a novel “zig-zag” plate electrode, the nanogenerators could
provide a new way to power nanoscale devices without batteries or other
external power sources.
“This is a major step toward a portable, adaptable and
cost-effective technology for powering nanoscale devices,” said Zhong
Lin Wang, Regents’ Professor in the School of Materials Science and
Engineering at the Georgia Institute of Technology. “There has been a
lot of interest in making nanodevices, but we have tended not to think
about how to power them. Our nanogenerator allows us to harvest or
recycle energy from many sources to power these devices.”
Details of the nanogenerator will be reported in the April 6 issue of
the journal Science. The research was sponsored by the Defense Advanced
Research Projects Agency (DARPA), the National Science Foundation
(NSF), and the Emory-Georgia Tech Center of Cancer Nanotechnology
Excellence.
The nanogenerators take advantage of the unique coupled
piezoelectric and semiconducting properties of zinc oxide
nanostructures, which produce small electrical charges when they are
flexed.
Fabrication begins with growing an array of vertically-aligned
nanowires approximately a half-micron apart on gallium arsenide,
sapphire or a flexible polymer substrate. A layer of zinc oxide is
grown on top of substrate to collect the current. The researchers also
fabricate silicon “zig-zag” electrodes, which contain thousands of
nanometer-scale tips made conductive by a platinum coating.
The electrode is then lowered on top of the nanowire array, leaving
just enough space so that a significant number of the nanowires are
free to flex within the gaps created by the tips. Moved by mechanical
energy such as waves or vibration, the nanowires periodically contact
the tips, transferring their electrical charges. By capturing the tiny
amounts of current produced by hundreds of nanowires kept in motion,
the generators produce a direct current output in the nano-Ampere
range.
Wang and his group members Xudong Wang, Jinhui Song and Jin Liu
expect that with optimization, their nanogenerator could produce as
much as 4 watts per cubic centimeter – based on a calculation for a
single nanowire. That would be enough to power a broad range of
nanometer-scale defense, environmental and biomedical applications,
including biosensors implanted in the body, environmental monitors –
and even nanoscale robots.
Nearly a year ago, in the April 14, 2006 issue of the journal Science,
Wang’s research team announced the concept behind the nanogenerators.
At that time, the nanogenerator could harvest power from just one
nanowire at a time by dragging the tip of an atomic force microscope
(AFM) over it. Made of platinum-coated silicon, the tip served as a
Schottky barrier, helping accumulate and preserve the electrical charge
as the nanowire flexed – and ensuring that the current flowed in one
direction.
With its multiple conducting tips similar to those of an AFM, the
new zig-zag electrode serves as a Schottky barrier to hundreds or
thousands of wires simultaneously, harvesting energy from the nanowire
arrays.
“Producing the top electrode as a single assembly sets the stage
for scaling up this technology,” Wang said. “We can now see the steps
involved in moving forward to a device that can power real
nanometer-scale applications.”
Before that happens, additional development will be needed to
optimize current production. For instance, though nanowires in the
arrays can be grown to approximately the same length – about one micron
– there is some variation. Wires that are too short cannot touch the
electrode to produce current, while wires that are too long cannot flex
to produce electrical charge.
“We need to be able to better control the growth, density and
uniformity of the wires,” Wang said. “We believe we can make as many as
millions or even billions of nanowires produce current simultaneously.
That will allow us to optimize operation of the nanogenerator.”
In their lab, the researchers aimed an ultrasound source at their
nanogenerator to measure current output over slightly more than an
hour. Though there is some fluctuation in output, the current flow was
continuous as long as the ultrasonic generator was operating, Wang
said.
To rule out other sources of the current measured, the researchers
substituted carbon nanotubes – which are not piezoelectric – for the
zinc oxide nanowires, and used a top electrode that was flat. In both
cases, the resulting devices did not produce current.
Providing power for nanometer-scale devices has long been a
challenge. Batteries and other traditional sources are too large, and
tend to negate the size advantages of nanodevices. And since batteries
contain toxic materials such as lithium and cadmium, they cannot be
implanted into the body as part of biomedical applications.
Because zinc oxide is non-toxic and compatible with the body, the
new nanogenerators could be integrated into implantable biomedical
devices to wirelessly measure blood flow and blood pressure within the
body. And they could also find more ordinary applications.
“If you had a device like this in your shoes when you walked, you
would be able to generate your own small current to power small
electronics,” Wang noted. “Anything that makes the nanowires move
within the generator can be used for generating power. Very little
force is required to move them.”
Source: Georgia Institute of Technology
Via: http://www.physorg.com/news95001943.html
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Re: Nanogenerator provides continuous power by harvesting energy from the environmen (Score: 1)
by nanotech on Friday, April 06, 2007 @ 08:37:51 UTC
(User Info | Send a Message) | This is phenomenal and excellent! Amazing! A number of the posters here on this forum have predicted that serious energy-related technology will come from nanotechnology/engineering. This is true. I also think that many real world ZPE devices will be based on molecular and micro engineering.
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