Sandia ear-plug-sized samplers, with silvery microvalves and solder connectors, seemingly hang poised to sample gases relevant to climate and weather. The prototype devices actually rest on a mirror, reflecting the day’s Albuquerque weather. Image: Randy Montoya
An air sampler the
size of an ear plug is expected to cheaply and easily collect atmospheric
samples to improve computer climate models.
“We now have an
inexpensive tool for collecting pristine vapor samples in the field,” said
Sandia National Laboratories researcher Ron Manginell, lead author of an
article published in Review of Scientific
The novel design employs
a commonly used alloy to house an inexpensive microvalve situated above the
When heated, the
alloy—a kind of solder—melts and flows, blocking the inlet hole. When cooled,
the alloy resolidifies into an impermeable block that seals the gas sample
inside the inert chamber below. Low cost should make widespread distribution of
these sensors possible, while the noncontaminating nature of the design helps
meet stringent technical requirements.
collection is important because uncertainties in fact gathering is one reason
climate models reach a variety of conclusions. Winds may blow gases toward or
away from a sampling site, gas contents at any location may vary by the hour
and by the season, and samples collected by containers in the field may
evaporate or become corrupted before analysis in a distant laboratory. Compounding
the problem are difficulties in widely distributing sensors, which can be
heavy, fragile, and require expensive tending by humans.
phase-change micro-valve sensor is light, cheap, tough, inexpensive to
fabricate, and simple to operate. It takes in gas in seconds through a tiny
hole about the diameter of three human hairs. The hole closes when a tiny,
low-energy hotplate on the canister’s surface melts shut the alloy through
which the hole passes, sealing it.
Because the little
container doesn’t outgas internally, the trapped sample remains uncorrupted
until analyzed in the laboratory. The miniature sensor’s simplicity means it
could travel in unmanned aerial vehicles (UAVs) or as unmonitored cargo in
atmospheric balloons. The poorest countries could afford to play a role in
global climate data collection.
It has so many good
features that one is tempted to ask, Do you want to drive it off the lot now or
accept delivery at home?
Mark Ivey is interested now. He oversees the operation of sounding balloons
that carry sensors skyward for the Department of Energy in Oliktok Point
and Barrow, Alaska. The miniature
blimps, able to sample particles around which cloud droplets form, are tethered
to winches that reel the soaring balloons back in. Getting sensors to Barrow—a
place no highway visits—then into the air and back to a laboratory in the lower
48 makes weight and size a factor.
“Smaller, lighter is
a big deal for us,” Ivey said.
plans to submit an atmospheric sampling proposal this spring to NASA for
something called “ground-truth measurement.” NASA, he said, “has a ton of
satellite data, more than they know what to do with,” but the agency needs to
use data from ground-based or airborne sensors that physically sniff the gases
reported by satellites to calibrate remote instruments.
NASA and the National
Oceanic and Atmospheric Administration (NOAA), who need ground-truth data, have
built systems with flask containers using conventional valves that at open
flasks and then close them at specific altitudes. However, the flasks are big—perhaps
half a liter in size—and heavy, and the valves they require may outgas, ruining
the measurements, Manginell said.
when the material used for the container releases a gas of its own,
contaminating the atmospheric gas trapped in the flask.
The Sandia system “would have 100 of these devices in a package that has a macrovalve on top,”
said Manginell. An altimeter sends an electrical pulse that opens the
macrovalve to fill the package with air. A small pump builds up pressure,
filling the tiny cylinders. “You’d use personal-computer (PC) processors that
you can put on a circuit board to operate the miniature system,” he said.
The balloons would
have global positioning locators on them. The low weight would make them
suitable for balloon and UAV applications. The tiny containers are built of
alumina tubing, cheap and more inert than glass.
Data collected by the
tiny cylinders also could be used to confirm satellite images of airborne
industrial effluents, essential for monitoring cap-and-trade deals.
But not all potential
uses are in the upper atmosphere. Geoscientists drill boreholes for oil and to
understand how the Earth formed. “It’s hard to build a mass spectrometer to go
down a 2-in diameter borehole,” Manginell said. “We’ve proposed instead to use
our miniature samplers outfitted with microvalves to take samples that can be
transported pristinely back to the surface and then examined in a lab.”
In medicine, volatile
compounds that people and animals emit are indicative of disease states and
stress. “Point-of-care medicine, instead of taking a blood sample, could sample
a person’s breath,” Manginell said. “Alcohol gives a gross signal but
infections have a high volatile content as well.” The bacteria that give cows
tuberculosis produce a characteristic signature, for example.
“It would take a
miniature pump the size of the last joint of your thumb to collect a sample,”
Manginell said. “One can perform on-the-spot detection, but also capture a
sample in the miniature chamber to send back to the lab for gold-standard
tests.” E coli and anthrax also have
volatile signatures, he said.
The detector also
could be used by the military to collect and analyze gases on the battlefield.
“We’ve spent a lot of
time over the past 15 years doing field analysis for customers: Microchemlab
work for the military and General Electric, and developing handheld gas
detectors. This is just another tool in the toolbox,” Manginell said. “But we
were pretty happy that this work proved to be broadly cost effective.”
The work, featured in
the paper, “A Materials Investigation of a Phase-Change Micro-Valve for
Greenhouse Gas Collection and Other Potential Applications,” is a
“This is a little
different from what we’ve done in the past,” Manginell said. “The widespread
collection of greenhouse gases has to be extremely cheap. So we collected
people who have done soldering, brazing, and thick-film metallization on
ceramics that’s scalable to high-volume production. Some did analytical
chemistry to figure out if we were contaminating the sample. Others found the
perfect solder mix.”
Curt Mowry said, “I made sure the solder didn’t contribute any carbon dioxide
to the sample that was collected, because then you have a stinky measurement.”
More certainty in
data collection is good because of the uncertainties in climate predictions,
majority of the data seems to point to the fact that there’s warming, but how
do you attribute that: Is it natural variation or manmade influence?” he said. “Distributions of our capsules would greatly improve the accuracy of field
measurements. You’d have a platform that would be ubiquitous, on planes, UAVs,
balloons in countries that can’t ordinarily afford to do these things. In India, it’s
hard to make those measurements when you’re concerned with putting food on the
table. But for legislation or policy decisions on, say, cap and trade, it’s
important to make those measurements accurately.”
Funding came from
Sandia’s Laboratory Directed Research and Development (LDRD) program, Manginell
“We thought we could
do a more ubiquitous job of sensing than anything currently available,” he
testing of the device, Manginell’s work, like science, is never finished.
“What we need to
build next is a normally closed version of the valve that opens when we want it
to,” he said. A presealed container would eliminate another possible source of
contamination in transit.