Tech Briefs Magazine - June 2021 - ST-28

Tech Briefs
To track the changes in the cavity's resonant
wavelength with high sensitivity, a stable
single- frequency laser is locked to the
cavity. The researchers have also employed
an optical frequency comb - a device that
can be used as a ruler to measure the wavelength
of light - to measure the cavity
length with high accuracy. The markings
of the ruler (the teeth of the comb) can be
thought of as a series of lasers with equally
spaced wavelengths. When the proof mass
moves during a period of acceleration,
either shortening or lengthening the cavity,
the intensity of the reflected light
changes as the wavelengths associated with
the comb's teeth move in and out of resonance
with the cavity.
Accurately converting the displacement
of the proof mass into an acceleration
is a critical step that has been problematic
in most existing optomechanical
accelerometers. However, the team's
new design ensures that the dynamic
relationship between the displacement
of the proof mass and the acceleration is
simple and easy to model through first
principles of physics. In short, the proof
mass and supporting beams are
designed so that they behave like a simple
spring, or harmonic oscillator, that
vibrates at a single frequency in the
operating range of the accelerometer.
This simple dynamic response
enabled the scientists to achieve low
measurement uncertainty over a wide
range of acceleration frequencies - 1
kilohertz to 20 kilohertz - without ever
having to calibrate the device. This feature
is unique because all commercial
accelerometers have to be calibrated,
which is time-consuming and expensive.
Since the publication of their study, the
researchers have made several improvements
that should decrease their
device's uncertainty to nearly 1%.
Capable of sensing displacements of
the proof mass that are less than one
hundred-thousandth the diameter of a
hydrogen atom, the optomechanical
accelerometer detects accelerations as
tiny as 32 billionths of g, where g is the
acceleration due to Earth's gravity.
That's a greater sensitivity than all
accelerometers now on the market with
similar size and bandwidth.
With further improvements, the NIST
optomechanical accelerometer could be
used as a portable, high-accuracy reference
device to calibrate other
accelerometers without having to bring
them into a laboratory.
For more information, contact Jason J.
Gorman at jason.gorman@nist.gov.
Sensors Eliminate Sparking Risk in Hydrogen Vehicles
Hydrogen vehicles can refuel much more quickly and go farther without refueling than
today's electric vehicles. But one of the final hurdles to hydrogen power is securing a
safe method for detecting hydrogen leaks.
University of Georgia, Athens, GA
ydrogen as a clean, renewable alternative
to fossil fuels is part of a sustainable-energy
future, and very much already
here. However, lingering concerns
about flammability have limited the
widespread use of hydrogen as a power
source for electric vehicles. Previous advances
have minimized the risk, but new
research from the University of Georgia
now puts that risk in the rearview mirror.
Hydrogen vehicles can refuel much
more quickly and go farther without refueling
than today's electric vehicles, which
use battery power. But one of the final
hurdles to hydrogen power is securing a
safe method for detecting hydrogen leaks.
A new study documents an inexpensive,
spark-free, optical-based hydrogen
sensor that is more sensitive - and
faster - than previous models.
" Right now, most commercial hydrogen
sensors detect the change of an electronic
signal in active materials upon
interaction with hydrogen gas, which can
potentially induce hydrogen gas ignition
by electrical sparking, " said Tho Nguyen,
associate professor. " Our spark-free optical-based
hydrogen sensors detect the
presence of hydrogen without electronics,
making the process much safer. "
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Cov
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Hydrogen as a clean, renewable alternative to
fossil fuels is a part of a sustainable-energy
future, and very much already here. (Image
courtesy of UGA Franklin College of Arts and
Sciences.)
Hydrogen power has many more
applications than just powering electric
vehicles, so flammability-mitigating technologies
are critical. Robust sensors for
hydrogen leak detection and concentration
control are important in all stages
of the hydrogen-based economy, including
production, distribution, storage,
and utilization in petroleum processing
and production, fertilizer, metallurgical
applications, electronics, environmental
sciences, and in health and safety-related
fields.
The three key problems associated
with hydrogen sensors are response
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ToC
time, sensitivity, and cost. Current mainstream
technology for H2 optical sensors
requires an expensive monochromator
to record a spectrum, followed by
analyzing a spectral shift comparison.
" With our intensity-based optical nano
sensors, we go from detection of hydrogen
at around 100 parts-per-million to 2
parts-per-million, at a cost of a few dollars
for a sensing chip, " Tho said. " Our
response time of 0.8 seconds is 20% faster
than the best available optical device
reported in the literature right now. "
The new optical device relies on the
nanofabrication of a nanosphere template
covered with a Palladium Cobalt
alloy layer. Any hydrogen present is
quickly absorbed, then detected by an
LED. A silicon detector records the
intensity of the light transmitted.
All metals tend to absorb hydrogen
but finding the suitable elements with a
right balance in the alloy and engineering
the nanostructure to amplify subtle
changes in light transmission after
hydrogen absorption enabled them to
set a new benchmark for how fast and
sensitive these sensors can be.
For more information, contact Alan
Flurry aflurry@uga.edu.
Sensor Technology, June 2021
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Tech Briefs Magazine - June 2021

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