Tech Briefs Magazine - June 2021 - ST-30

Tech Briefs
New Sensor Paves Way to Low-Cost Sensitive Methane
Measurements
Recent advances could make it feasible to deploy networks of methane sensors to detect
this greenhouse gas at large facilities.
The Optical Society (OSA), Washington, DC
esearchers have developed a new
sensor that could allow practical and
low-cost detection of low concentrations
of methane gas. Measuring methane
emissions and leaks is important to a
variety of industries because the gas contributes
to global warming and air pollution.
Agricultural
and waste industries emit
significant amounts of methane, which
is also critical for the oil and gas industry
for both environmental and economic
reasons because natural gas is mainly
composed of methane.
Researchers from Princeton
University and the U.S. Naval Research
Laboratory have demonstrated their
new gas sensor, which uses an interband
cascade light emitting device (ICLED)
to detect methane concentrations as low
as 0.1 parts per million. ICLEDs are a
new type of higher-power LED that
emits light at mid-infrared. The
researchers hope that this will eventually
open the door to low-cost, accurate and
sensitive methane measurements. The
sensors could be used to better understand
methane emissions from livestock
and dairy farms and to enable more
accurate and pervasive monitoring of
the climate crisis.
Laser-based sensors are currently the
gold standard for methane detection,
but they cost between $10,000 and
$100,000 each. A sensor network that
detects leaks across a landfill, petrochemical
facility, wastewater treatment
plant, or farm would be prohibitively
expensive to implement using laserbased
sensors.
Although methane sensing has been
demonstrated with mid-IR LEDs, performance
has been limited by the low
light intensities generated by available
devices. To substantially improve the
sensitivity and develop a practical system
for monitoring methane, the
researchers used a new ICLED developed
at the U.S. Naval Research
Laboratory.
The ICLEDs they developed emit
roughly ten times more power than commercially
available mid-IR LEDs had
30
Cov
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Researchers have developed a new sensor that uses an interband cascade light emitting device
(ICLED) and could allow practical and low-cost detection of low concentrations of methane.
(Credit: Sameer A. Khan/Fotobuddy)
generated and could potentially be
mass-produced. According to the
researchers, this could enable ICLEDbased
sensors that cost less than $100
per sensor.
To measure methane, the new sensor
measures infrared light transmitted
through clean air with no methane and
compares that with transmission
through air that contains methane. To
boost sensitivity, the researchers sent the
infrared light from the high-power
ICLED through a one-meter-long hollow-core
fiber containing an air sample.
The inside of the fiber is coated with silver,
which causes the light to reflect off
its surfaces as it travels down the fiber to
the photodetector at the other end. This
allows the light to interact with additional
molecules of methane in the air
resulting in higher absorption of the
light.
To test the new sensor, the researchers
flowed known concentrations of
methane into the hollow core fiber and
compared the infrared transmission of
the samples with state-of-the-art laserbased
sensors. The ICLED sensor was
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able to detect concentrations as low as
0.1 parts per million while showing
excellent agreement with both calibrated
standards and the laser-based sensor.
According to the researchers, this
level of precision is sufficient to monitor
emissions near sources of methane pollution.
An array of these sensors could
be installed to measure methane emissions
at large facilities, allowing operators
to detect leaks and mitigate them
affordably and quickly.
The researchers plan to improve the
design of the sensor to make it practical
for long-term field measurements by
investigating ways to increase the
mechanical stability of the hollow-core
fiber. They will also study how extreme
weather conditions and changes in
ambient humidity and temperature
might affect the system. Because most
greenhouse gases, and many other
chemicals, can be identified by using
mid-IR light, the methane sensor could
also be adapted to detect other important
gases.
For more information, contact
mediarelations@osa.org.
Sensor Technology, June 2021

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Tech Briefs Magazine - June 2021

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