Scientists in Michigan have developed a forest fire alarm system. It can not only monitor when a fire begins but also call for help. This battery-free device hangs in a tree and gains all the energy it needs from the natural swinging of branches. Such a sensor (传感器) could watch the woods for a decade without humans' attention.
"For forest fire monitoring, you don't need high amounts of energy," says Cao Changyong, an engineer at Michigan State University, who 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, Cao says, "to produce enough energy."
There's an obvious need for fast monitoring of faraway forests. Every year, fires burn millions of acres in the United States. Early findings also can save lives. Right now, forest fires are found from satellites or fire towers. Neither, Cao says, is as fast or low-cost as tree-hanging sensors would be.
Cao's group faced some challenges in creating its new sensors. For example, these have to produce enough power to check the forest and send out a signal and that power source has to be used for longer time. To deal with the problems, they decided to change mechanical motion (机械运动) into electricity. The device to do this is known as a TENG short for triboelectric nanogenerator. Scientists have explored TENGS as one way to gain energy from the natural world, including harvesting energy from effects on tabletops, falling rain-even keyboards. The new TENG for forest use produces a current (电流) when a tree branch swings. That current is small, yet enough to power a thermometer (温度计) to monitor the temperature changes signaling fire.
Cao says his team's new model has not yet been tested over long time periods in the real world, but the device is ready. All he needs now is the money to build more of them.