Creative use of noise brings bio-inspired
electronic improvement
Researchers at Osaka University have developed a single-
walled carbon
nanotube device that can detect below-
threshold signals through the use of
stochastic resonance
SUMMARY
Researchers are working to exploit stochastic resonance to
enhance signal transmission for a new generation of devices, using
single-walled carbon nanotubes. They created a summing network SR device that
detects subthreshold signals, fabricated to include a self-noise component.
This is a rendering of what the
Osaka University research team's SR device entails.
Credit: Megumi Akai-Kasaya
In conventional electronics, a great
deal of effort is devoted to eliminating stochastic resonance (SR) -- the
annoying hiss that generally hinders the detection of weak signals and degrades
overall device performance. But, what if there were a way to exploit this
effect to enhance signal transmission for a new generation of devices, such as
bio-inspired sensors and computing processors whose design is based on the
neural networks of the brain?
Researchers at Osaka University in
Japan are working to achieve just that, using single-walled carbon nanotubes
(SWNTs). They created a summing network SR device that detects subthreshold
signals, fabricated to include a self-noise component. The researchers report
their findings this week in the journal Applied Physics Letters, from
AIP Publishing.
"The functional capabilities of
our network SR device, which relies on dense nanomaterials and exploits
intrinsic spontaneous noise at room temperature, offer a glimpse of future
bio-inspired electronic devices," said Megumi Akai-Kasaya, assistant
professor at Osaka University.
Researchers have known over the last
few decades that some animals use SR to enhance the transmission or detection
of signals below the detection threshold. Paddle fish living in muddy rivers,
for example, can detect, and thus feed on, the nearest plankton only when there
is background electrical noise coming from another plankton mass. The
background noise is used to amplify the signals of the nearby plankton.
Crayfish also use SR, which is part of the mechanical noise in water, to detect
subtle movements of predators.
There is also evidence that the
human brain uses SR in visual processing. Undetectable light signals to the
right eye become detectable through the addition of noise to the left eye. More
recently, researchers have discovered that adding random noise such as SR, in
the right way, to electronic devices can increase the detectability of signals
and the transmission efficiency of information.
There are two basic requirements for
developing an SR-based electronic device: a signal detection threshold and the
presence of additional noise. To satisfy these requirements in their SWNT
device, the research team created a SWNT network in which up to 300 carbon
nanotubes were aligned parallel to each other between chromium electrodes,
which increased the signal detection ability.
They functionalized the SWNTs with
phosphomolybdic acid (PMo12) molecules, which can firmly adsorb on graphite
materials, before drying the device on a hotplate at 150 degrees Celsius under
atmospheric pressure. The adsorption of the PMo12 molecules on the SWNTs
generated additional noise.
"SWNTs can be generators of
spontaneous noise, owing to their high sensitivity to external surface
perturbation," Akai-Kasaya said. "What we found is that the
introduction of an extra disruptor -- molecular adsorption, and particularly
with the adsorption of PMo12 -- generated a large and tunable type of
electrical noise in addition to common environmental noise."
The group tested 10 different
molecules adsorbed in the SWNTs as noise generators and found that the
SWNT/PMo12 combination was more than twice as effective as the other SWNT
functionalized combinations.
"SWNTs offer a promising route
to realizing a small-size summing network SR device that utilizes molecular
thermal fluctuation as the noise source." Akai-Kasaya said.
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