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BY LIA
UNRAU
Rice News Staff
September 23, 1999
Research associate David Lancaster carefully packed up
his engineering equipment in a few overnight delivery
boxes last week and shipped it off to Colorado, where
atmosphere experts will push it to its limits.
Lancaster's creation, Rice's second version of an air
quality sensor, can detect trace gases and monitor the
slightest changes in air quality in real-time.
Built by Rice researchers Frank Tittel, professor of
electrical and computer engineering, Lancaster and Dirk
Richter, a graduate student, the new gas sensor boasts
new features over previous models. It is
tougher--vibrations don't faze it--and it measures gases
with high precision--it can measure gases in extremely
small quantities, down to sub-parts-per-billion levels,
or
less than one part-per-billion. The improvements over
the previous sensor stem from using a different type of
pump laser system in the form of fiber coupled diode
lasers and amplifiers.
The group will publish their results in an upcoming issue
of Applied Physics B.
"This system is much more stable and robust,"
Lancaster
says. "We want to make it suitable for industrial
and field
use, and we're getting closer to that goal."
Because the new sensor system is hard-wired through
fiber, and does not use optics, which are highly
sensitive
to movement and collect dust, it is not sensitive to
vibration, and the sensor continues to work, even though
it may be moving, or the temperature may change.
"We can use this for long-term autonomous
operation,"
Tittel says. "We are aiming for the type of
reliability you
get with a laptop computer--you want it to work for
several years."
Last week, Lancaster shipped his system to the National
Center for Atmospheric Research (NCAR) in Boulder,
Colo., where researchers study atmospheric chemistry.
They hope to be able to use this sensor or a similar
version to study trace gases, such as formaldehyde
plumes at different temperatures and heights in the
atmosphere. Currently NCAR uses a large aircraft to fly
their own sensor, a bulky, cryogenically-cooled system at
30,000 feet to detect and quantify trace gases in
different
parts of the country. If used, the smaller,
lighter-weight
Rice system would offer significant cost savings and
convenience.
The current Rice sensor can measure more than 12 trace
gases to date, and the researchers plan to use their
sensor
for the detection and control of ammonia, hydrochloric
and hydrafluoric acid, which are critical process gases
in
the semiconductor industry.
Because this version of the sensor uses fiber coupled
diode lasers to measure the concentration of a particular
gas, the lasers do not need to be realigned, as is the
case
of the previous system, which used convention optics.
This allows the new sensor to run on its own for an
extended period of time. Because the lasers and other
components stay aligned, and are not sensitive to
temperature change, such a sensor can be used for
numerous field applications without affecting its ability
to measure gas concentration in demanding
environmental conditions.