Tiny battery-free device floats in the air like dandelion seeds

Wireless sensors can monitor how temperature, humidity or other environmental conditions vary over large areas of land, such as fields or forests.

These tools can provide unique insights for a variety of applications, including digital agriculture and climate change monitoring. One problem, however, is that it is currently time-consuming and costly to physically place hundreds of sensors over a large area.

Inspired by how dandelions use the wind to distribute their seeds, a team from the University of Washington has developed a tiny sensor-carrying device that can be blown by the wind as it falls toward the ground. The system is about 30 times heavier than 1 milligram of dandelion seed, but can still travel up to 100 meters in moderate wind, about the length of a football field, from where it was released by the drone. Once on the ground, the device, which can hold at least four sensors, uses solar panels to power its onboard electronics and can share sensor data from up to 60 meters away.

The team published these results on 16 March Nature,

“We show you can use off-the-shelf components to make small things. Our prototype shows you can use a drone to drop thousands of devices in a single drop. They’re all Air will move a little differently, and basically you can build a 1,000-device network with this one drop,” said senior author Shyam Golkota, a UW professor in the Paul G. Allen School of Computer Science and Engineering. “This is surprising and transformative for the field of sensor deployment, as it can take months to manually deploy so many sensors right now.”

Since the devices have electronics on board, it is challenging to make the entire system as light as an actual dandelion seed. The first step was to develop a shape that would allow the system to take its own time to fall to the ground so that it could be tossed out of the air. The researchers tested 75 designs to determine what would be the smallest “terminal velocity” or what would be the maximum speed of the device when it fell through the air.

Lead author Vikram Iyer said, “The way dandelion seed structures work is that they have a central point and these tiny bristles stick out to slow their fall. We’ve created the basis for our structures.” It took 2D projection to make the design.” UW Assistant Professor at the Allen School. “As we added weight, our bristles began to bend inward. We added a ring structure to make it more rigid and take up more area to help slow it down.”

To keep things light, the team used solar panels instead of bulky batteries to power the electronics. The equipment landed with solar panels facing up 95% of the time. Their shape and structure allow them to flip and fall in a consistently upright orientation, similar to a dandelion seed.

However, without a battery, the system cannot store the charge, which means that after the sun goes down, the sensors stop working. And then when the sun rises the next morning, little energy is needed to get the system started.

“The challenge is that most chips will get a little bit more power for a short period of time when you first turn them on,” Iyer said. “They’ll check to make sure everything is working properly before executing the code you’ve written. This happens when you even turn on your phone or laptop, but of course their Have a battery.”

The team designed the electronics to include a capacitor, a device that can store some charge overnight.

“Then we have this little circuit that will measure how much energy we have accumulated and, once the sun rises and more energy comes in, it will trigger the rest of the system to turn on as it senses that it is over some threshold.” up,” Iyer said.

These instruments use backscatter, a method that involves sending information by reflecting the transmitted signals, so that sensor data can be sent back to researchers wirelessly. Instruments carrying sensors that measure temperature, humidity, pressure and light send data until sunset when they are turned off. Data collection resumed when the devices returned themselves the next morning.

To measure how far the devices would travel in the air, the researchers dropped them from different heights, either by hand or by drones on campus. One trick to stretch the devices from a droplet point, the researchers said, is to slightly vary their shape so that they can be carried by wind in a different way.

“It’s mimicking biology, where the variation is really a feature rather than a bug,” said co-author Thomas Daniell, a UW professor of biology. “Plants can’t guarantee that next year is going to be good where they grew up this year, so they have few seeds that can go far to hedge their bets.”

Another advantage of a battery-free system is that there’s nothing on the device that will run out of juice—the device will continue to run until it’s physically broken. One drawback of this is that the electronics will be scattered throughout the ecosystem of interest. Researchers are studying how to make these systems more biodegradable.

“It’s just the first step, which is why it’s so exciting,” Iyer said. “There are many other directions we can take right now – such as developing large-scale deployments, creating devices that can change shape as they fall, or even add some more mobility so that equipment can move around once on the ground. Get closer to what we’re curious about.”

Hans Gainsbauer, who completed this research as a UW graduate in electrical and computer engineering and is now an engineer at Gridware, is also a co-author.