Science News for Students - Spring 2021

Trees power this alarm system for remote forest fires Swaying branches are all that’s needed to power these temperature sensors Scientists in Michigan have developed a forest- fire alarm system. It not only can detect when a blaze begins but also call for help. This battery- free device dangles like an ornament from a tree and harvests all the energy it needs from the natural swaying of branches. Such a sensor could watch the woods for a decade without human attention. “It’s a great idea,” says engineer Chris Knight in Newcastle, Australia. He works at CSIRO, Australia’s national research agency. He didn’t contribute to the newwork but he knows about wildfire sensors. Changyong Cao led the team behind the new device. It recharges itself about every 10 minutes with just enough power to take a measurement. That’s plenty of time “to generate sufficient energy,” says this engineer at Michigan State University, in East Lansing. If it detects a fire, the sensor signals a device up By Stephen Ornes

to a mile away. That hub can relay an alarm. It can collect such data from tens or even hundreds of sensors, Cao says. Right now, forest fires are spotted from satel- lites or fire towers. Neither, Cao notes, is as fast or low-cost as tree-hanging sensors would be. The newdevices turn mechanical motion into static electricity. To do this, they use a pair of nested cylinders, one inside another. Each is coatedwith a copper film. The bottom is made of a similar batch of nested cylinders. But these are coatedwith a material called PTFE (which coats many nonstick frying pans). The top and bottom slide into each other, then the package is hung from a tree branch. The bot- tom cylinder hangs from a rubber band attached to the upper part. When a tree branch sways, the top and bottom cylinders move together and apart. This causes the PTFE and copper to exchange electric charges, producing a current. That current is small, yet easily enough to power a thermometer to detect the temperature changes signaling a fire. Cao’s team described its new device August 7, 2020 in Advanced Functional Materials . “A system like this is a great idea,” says Knight. And, he adds, “You don’t need that many of them to get a whiff of smoke and send off an alarm.” × Once they become blazing infernos, wildfires are easy to spot. The trick to controlling fires is to catch them as they’re just entering a forested area. New tree sensors can do this. And the only energy they need to power them is wind mov- ing through tree branches.

This shows a series of sensors (grey cylinders) hanging from a tree. An actual sensor (in blue-gloved hand below) created enough power to light this LED outline of Michigan State’s symbol, the Spartan.

YELANTSEVV/ISTOCK/GETTY IMAGES PLUS; CHANGYONG CAO

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