Floating sensors to monitor climate change

Floating sensor packages inspired by dandelion seeds can be easily scattered in the wind to help monitor key indicators of climate change, including temperature, humidity, and other environmental conditions, over large areas of farms or forests. By gathering this data, they can also provide valuable information to other applications, such as precision agriculture.

The novelty was developed by a team at the University of Washington and, despite being about 30 times heavier than a 1-milligram dandelion seed, can travel for up to 100 meters in a moderate breeze after being launched by drones. Once on the ground, the package, which can contain more than four sensors, is powered by solar panels and can share up to 60 meters away, according to its creators.

“Our prototype suggests it is possible to use a drone to release thousands of these devices at once. They will be carried by the wind in a slightly different way to basically create a network of a thousand devices,” explains Shyam Gollakota, author and professor at the Paul G. Allen School of Computer Science and Engineering at the University of Washington. “This is amazing and transformative in the area of sensors because it would take months to manually deploy that many such devices,” he adds.

The first step of the research was to develop a shape that would allow the sensor package not to take longer to fall to the ground. Seventy-five designs were tested to find the one that would have the maximum speed for this task. “The dandelion seed structures have a central point and small bristles. We made a 2D projection of it to create our basic design,” explains Vikram Iyer, another author of the invention and an assistant professor at the same institution. “As we added weight, the bristles started to bend inwards. We added a ring structure to make the pack stiffer and occupy a larger area in order to slow down the assembly,” details the researcher.

Solar panels were used to power the electronics. 95% of the time, the packets landed with the solar panels facing upwards. The shape and structure of the packet cause it to consistently rotate and fall in that position, similar to what happens with dandelion seeds.

The system is not designed to store energy. This means that after the sun goes down, the sensors stop working. When the sun comes up again the next morning, the system will use some energy to be restarted. “The set of sensors will check that everything is working properly before they start running code. This also happens when we switch on our mobile phone or laptop. The difference is that they rely on a battery,” explains Iyer. The package includes a capacitor to store some charge overnight.

To send sensor data to the researchers, these devices use the backscatter method, which sends information by reflecting the transmitted signals.

To measure how far the sensors would travel when carried by the wind, the researchers conducted tests, dropping them from different heights, either manually or by drone. “We are mimicking biology, which considers variation a characteristic, not a problem,” commented Thomas Daniel, another author of the invention from a biology professor at the University of Washington. “Plants have no way of guaranteeing whether the place where they grew this year will also be good the next season, so some seeds may travel further to secure their bets,” says the professor.

The researchers are studying how to make the system more biodegradable. “That is just the first step. There are many other avenues we can take, such as developing large-scale solutions, creating devices that can change shape as they fall, or even making them a little more mobile, so they can move when they are on the ground and get closer to areas of interest,” adds Iyer.

The research was funded by the Moore Inventor Fellow award, the National Science Foundation and a grant from the US Air Force Office of Scientific Research. Details of the research were published in Nature on 16 March.