Changyong Cao, MSU

Smokey the Bear admonished that only you can prevent forest fires, but what if Smokey had some high-tech backup?

A team of scientists at Michigan State University has developed a remote forest fire detector and alarm system powered by nothing but the movement of the trees in the wind.

As detailed in their new study published in the journal Advanced Functional Materials, the battery-free device generates electrical power by harvesting energy from the sporadic movement of the tree branches from which it hangs.

Believed to be the first of its kind, the device, which is the size of a soup can and costs just $20 to produce would likely be much cheaper than manned patrols searching from fire watch towers, and more reliable than satellite monitoring which may be hindered by weather or fire smoke.

“The self-powered sensing system could continuously monitor the fire and environmental conditions without requiring maintenance after deployment,” said lead author Changyong Cao, a mechanical engineer who directs the Laboratory of Soft Machines and Electronics at MSU.

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.

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The traditional forest fire detection methods—satellite monitoring, ground patrols, and watch towers—are highly labor intensive, expensive, and somewhat inefficient.

Current 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,” said Yaokun Pang, co-author and postdoc associate at Cao’s lab.

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TENG technology–short for multilayered cylindrical triboelectric nanogenerator—converts external mechanical energy, such as the movement of a tree branch, into electricity.

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 stores its sporadically generated electrical current 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.

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“At a very low vibration frequency, the MC-TENG can efficiently generate electricity to charge the attached supercapacitor in less than three minutes,” Cao said.

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.

Cao and the study’s co-authors hope to field test a production device to monitor forest environmental conditions and test scenarios, making use of materials that mimic a real fire. The team also aims to add additional functionality, allowing the device to be adapted for the weather and environmental conditions where it is deployed.

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