New Fire-Retardant, Self-Extinguishing Motion Sensor for Use in Extreme Temperatures

Envisage a device that has the ability to withstand even the most extreme fires so that it can automatically alert others when a firefighter becomes immobilized on the job.

The triboelectric nanogenerator can detect when wearers are in danger or disabled because it can sense the difference between walking, running, jumping and stillness. (Image credit: UCLA and McMaster University)

Now, scientists from UCLA, along with coworkers from two other universities, have created the world’s first self-extinguishing, fire-retardant motion sensor and power generator. Resembling the size of a quarter, the novel device can be integrated into clothing or shoes worn by oil drillers, firefighters, or other people who have to work in harsh environments or extreme temperatures.

The results of the study have been reported in the journal, Nano Energy. Richard Kaner, UCLA’s Dr Myung Ki Hong, Endowed Chair in Materials Innovation and a member of the California NanoSystems Institute at UCLA, has led the study.

The innovative self-powered sensor can be considered as a kind of triboelectric nanogenerator. During triboelectric charging, energy is produced from electron exchange when a material rubs up against another—in this case, the ground and the device, or the wearer’s skin or clothing and the device itself. This phenomenon is the same as the one that produces an electric shock when individuals rub their feet on a carpet and then touch a doorknob.

Called FRTENG (abbreviated for fire-retardant triboelectric nanogenerator) by the researchers, the device has the ability to detect when wearers are disabled or in danger because it is capable of perceiving the variation between stillness, walking, jumping, and running.

Different movements create electric signals with different voltages and currents. Those different currents allow us to identify whether and how someone is moving—so the device could be integrated into a firefighter’s shoes, for example, and send a help signal wirelessly in case of an emergency.

Maher El-Kady, Study Co-Author and Assistant Researcher, UCLA.

According to Kaner, who is also a distinguished professor of chemistry and biochemistry, and of materials science and engineering, although triboelectric nanogenerators already exist, they tend to utilize materials like flammable textiles and plastics. Moreover, present-day models cannot tolerate extreme temperatures or fire.

In order to overcome that barrier, the novel sensor device is created from a carbon aerogel invented by the team. The aerogel is stable at high temperatures and is also extremely lightweight (95% of its volume is air), thus making it perfect for utilizing in a fire-retardant device.

The carbon aerogel conducts electricity efficiently and contains materials that are environmentally friendly. Because the aerogel is so light, the wearer wouldn’t even feel the device.

Maher El-Kady, Study Co-Author and Assistant Researcher, UCLA.

In order to create the aerogel, the investigators combined two chemicals—resorcinol and formaldehyde—with graphene oxide sheets and polyacrylonitrile fibers that had a thickness of just a few nanometers—a nanometer is roughly 1/75,000th the width of a human hair, or equivalent to one-billionth of a meter. The ultra-lightweight material is supported by both the nanosheets and nanofibers.

To remove the liquid content, the team subsequently dried the gel and heated it in a compact, hydrogen-filled chamber, leaving behind a lightweight and long-lasting carbon aerogel nanocomposite.

Using triboelectric charging, the carbon aerogel functions as a motion sensor and a power generator. Unlike traditional sensors that rely on batteries for their power, the new device can operate indefinitely without the need for any power sources.

Abdelsalam Ahmed, Study First Author and Visiting Scholar, McMaster University.

To test the fire resistance of the new device, the researchers subjected it to a butane flame for a period of 90 seconds, and they eventually discovered that the device did not spread the fire and, at the same time, it was also self-extinguishing. Even at 200 °C, the structure of the device was maintained and its electrical output continued to be stable.

At such extreme temperatures, a majority of traditional triboelectric devices would lose their performance or may even catch on fire, stated Kaner.

According to El-Kady, the innovative device may also prove handy for space missions—for instance, for tracking the vital signs of astronauts or for producing emergency power. During space flight, the use of other electronic devices is usually prevented by extreme temperatures.

Other co-authors of the study are Mit Muni, a UCLA graduate student; Islam Hassan, Ayman Negm and Ponnambalam Ravi Selvaganapathy of McMaster University; and Amir Masoud Pourrahimi of the University of Chemistry and Technology, Prague.

The study was supported by Nanotech Energy, a company that manufactures graphene oxide, graphene¸ and graphene super batteries and was spun off from UCLA research. El-Kady is the company’s chief technology officer and Kaner is chair of the company’s scientific board.

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