Smoke detectors are everywhere, but still thousands of people die in
fires annually. Fire gas detectors, which detect carbon monoxide and
nitrogen oxide, identify fires at an early stage. Thanks to a new
measurement principle developed by Fraunhofer researchers, these costly
sensors will soon be inexpensive and ready for the mass market.
As the stars twinkle in the sky high above the house, people lie
sleeping in their beds. It's just an ordinary night -- and yet, on this
night, the slumberers' lives are at stake: A cable is smoldering away
and poisonous carbon monoxide spreads unnoticed through the room. The
smoke detector doesn't sound the alarm because it responds only to
smoke, which is not always produced in a smoldering fire. In short, the
room's occupants are in great danger.
Reliably detects carbon monoxideGas sensors could wake people in time and save their lives. Researchers
at the Fraunhofer Institute for Physical Measurement Techniques IPM in
Freiburg have developed just such a sensor. It recognizes a fire not by
its smoke but by the carbon monoxide it emits. Nitrogen dioxide, which
is produced a little later in the course of the fire, also triggers the
alarm. Even the tiniest amounts of these gases suffice. "The sensors are
extremely sensitive, so they respond very early in the fire's
development. After all, every second counts," explains Dr. Carolin
Pannek, a researcher at the IPM.
Life-saving carbon-monoxide sensors of this kind are already available
today, but they are too expensive for the mass market. Furthermore, they
require maintenance and use a lot of electricity. Commercially
available semiconductor gas sensors are cheaper, but can't distinguish
between different gases. That's not the case with the new sensor type
created by the IPM researchers. "Ours responds only to carbon monoxide
and nitrogen dioxide -- it ignores other gases. By using roll-to-roll
processing, we can produce the sensors very inexpensively, making it
affordable for consumers," confirms Pannek.
This is primarily thanks to the dyes at the core of the sensor. Just as a
lock opens only with a specific key, each dye responds only to a
specific gas. Thus the sensor contains one dye for carbon monoxide and
another for nitrogen dioxide. It works by having a small LED shine blue
light into a waveguide coated with a polymer into which the dyes have
been mixed. The light travels in a zigzag path to the other end of the
waveguide, where it meets up with a detector. If the air in the room is
normal, the coating glows purple -- which means it absorbs only a small
amount of blue light and lets most of the blue light reach the detector.
If however there is carbon monoxide in the air, the dye glows yellow.
The yellow dye absorbs more blue light -- so the overall amount of light
reaching the detector is lower. Below a given threshold value this
trips the alarm. To detect nitrogen oxide, the researchers include a
second waveguide coated with another dye.
Costs slightly more than a smoke detector
The researchers were careful to ensure that the sensor could be
manufactured cost-effectively in bulk -- after all, no one wants to dig
much deeper in their pocket than they would for a conventional smoke
detector, even though gas sensors offer significantly more protection.
"When mass produced, the sensors will cost about the same as smoke
detectors -- and significantly less than the fire gas detectors
currently available," Panneck believes.
To make their fire gas sensors, the researchers use the same components
found in smoke detectors and supplement them with the optical
waveguides. The electronics determine the threshold at which the sensor
should sound the alarm. To manufacture these components, the researchers
have worked together with an industry partner to develop a roll-to-roll
process similar to newspaper printing that is capable of printing
15,000 measurement systems on a continuous roll. The process is both
suitable for mass production and cost effective. But it will certainly
take a few years for the gas sensors to become as ubiquitous in living
and bedrooms as smoke detectors are now.
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