Tiny battery-free devices float in the wind like dandelion seeds

Wireless sensors have the potential to revolutionise digital agriculture and climate monitoring, providing practical, real-time information about on-ground conditions across large tracts of land. But despite their potential, they haven’t yet been widely embraced – the time and money required to physically place hundreds of sensors across large areas has stymied their uptake.

Determined to turn this situation around, a team of researchers from the University of Washington (UW), US, has taken inspiration from nature to develop miniature sensor-carrying devices that can be blown by the wind as they tumble toward the ground.

Mimicking the whimsical flight of dandelion seeds – beloved of children everywhere – the tiny devices can travel up to 100 metres in a moderate breeze after being released by a drone.

Publishing their results in Nature, the researchers outline the potential to release thousands of these mini-monitors in a single drop.

“The way dandelion seed structures work is that they have a central point and these little bristles sticking out to slow down their fall,” says lead author Vikram Iyer, an assistant professor at UW’s Paul G Allen School of Computer Science & Engineering. “We took a 2D projection of that to create the base design for our structures.”

“They’ll all be carried by the wind a little differently, and basically you can create a 1,000-device network with this one drop,” adds senior author Dr Shyam Gollakota, also of the Allen School.

“This is amazing and transformational for the field of deploying sensors, because right now it could take months to manually deploy this many sensors.”

Once a device hits the ground, it draws on solar panels to power its on-board electronics to share sensor data over a range of up to 60 metres.

Though essential to operation, these on-board electronics make the devices quite heavy – at least in comparison to a dandelion seed. Overcoming the challenge posed by this weight required some very nifty engineering, with 75 different designs tested before the prime candidate was decided.

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The first step was to remove the need for a heavy battery, replacing it with minute solar panels. Of course, solar panels only work when they can see the sun, so the team also had to design the devices to consistently hit the ground in an upright orientation – a feat that dandelion seeds have long since evolved to achieve.

Without a battery, the charge that each sensor builds up during the day can’t be stored away to see them through the night. This poses a second challenge: as the first rays of sunshine rouse the device into action each morning, the chips housed inside require extra energy to shake off the cobwebs.

“Most chips will draw slightly more power for a short time when you first turn them on,” says Iyer. “They’ll check to make sure everything is working properly before they start executing the code that you wrote.”

To help get the devices over the morning hump the team added a capacitor to their design, allowing a small amount of charge to be stored overnight.

“We’ve got this little circuit that will measure how much energy we’ve stored up and, once the sun is up and there is more energy coming in, it will trigger the rest of the system to turn on because it senses that it’s above some threshold,” Iyer explains.

Interestingly, each tiny device is unique – just as each dandelion seed is unique. The researchers have deliberately incorporated variability into their design so that each is carried by the breeze slightly differently, maximising their spread.

“This is mimicking biology, where variation is actually a feature, rather than a bug,” says co-author Thomas Daniel, a UW professor of biology.

“Plants can’t guarantee that where they grew up this year is going to be good next year, so they have some seeds that can travel farther away to hedge their bets.”

Excited by the enormous potential opened up by this new design, the researchers are keen to keep the momentum going.

“This is just the first step, which is why it’s so exciting,” Iyer says.

“There are so many other directions we can take now — such as developing larger-scale deployments, creating devices that can change shape as they fall, or even adding some more mobility so that the devices can move around once they are on the ground to get closer to an area we’re curious about.”