In a new study, a team of Michigan State University scientists designed and fabricated a remote forest fire detection and alarm system powered by nothing but the movement of the trees in the wind. The device, known as MC-TENG — short for multilayered cylindrical triboelectric nanogenerator — generates electrical power by harvesting energy from the sporadic movement of the tree branches from which it hangs.

MSU's Changyong Cao directs the Laboratory for Soft Machines and Electronics. (Photo courtesy of MSU)

“The self-powered sensing system could continuously monitor fire and environmental conditions without requiring maintenance after deployment,” said Professor Changyong Cao.

For Cao and his team, the tragic forest fires in recent years across the American West, Brazil, and Australia were driving forces behind this new technology. Cao believes that early and quick response to forest fires will make the task of extinguishing them easier, significantly reducing the damage and loss of property and life.

Traditional forest fire detection methods include satellite monitoring, ground patrols, and watch towers, which have high labor and financial costs, yet low efficiency. Currently remote sensor technologies are becoming more common, but primarily rely on battery technology for power. Although solar cells have been widely used for portable electronics or self-powered systems, it is challenging to install these in a forest because of the shading or covering of lush foliage. TENG technology converts external mechanical energy — such as the movement of a tree branch — into electricity by way of the triboelectric effect, a phenomenon where certain materials become electrically charged after they separate from a second material with which they were previously in contact.

The simplest version of the TENG device consists of two cylindrical sleeves of unique material that fit within one another. The core sleeve is anchored from above while the bottom sleeve is free to slide up and down and move side to side, constrained only by an elastic connective band or spring. As the two sleeves move out of sync, the intermittent loss of contact generates electricity. The MC-TENG are equipped with several hierarchical triboelectric layers, increasing the electrical output. It stores its sporadically generated electrical charge in a carbon-nanotube-based micro-supercapacitor. The researchers selected this technology for its rapid charge and discharge times, allowing the device to adequately charge with only short but sustained gusts of wind.

At a very low vibration frequency, the MC-TENG can efficiently generate electricity to charge the attached supercapacitor in less than three minutes. The researchers outfitted the initial prototype with both carbon monoxide (CO) and temperature sensors. The addition of a temperature sensor was intended to reduce the likelihood of a false positive carbon dioxide reading.

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This article first appeared in the September, 2020 issue of Sensor Technology Magazine.

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