Researchers from the University of Washington (UW) have developed a sensor-carrying device that can be blown by the wind as it tumbles toward the ground, like a dandelion.
While the sensors are about 30 times as heavy as a 1 mg dandelion seed, they can still travel up to 100 m in a moderate breeze after being released by a drone. Researchers said the battery-free, wireless sensors could be used to monitor how temperature, humidity and other environmental conditions vary across farms or forests.
When these sensor-carrying devices land, solar panels power onboard electronics and can share sensor data up to 60 m away. The devices can hold at least four sensors for multiple monitoring.
"We show that you can use off-the-shelf components to create tiny things,” said Shyam Gollakota, a professor in the Paul G. Allen School of Computer Science & Engineering. “Our prototype suggests that you could use a drone to release thousands of these devices in a single drop. 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. This is amazing and transformational for the field of deploying sensors, because right now it could take months to manually deploy this many sensors."
Device shape
Because of the electronics integrated into the devices, it was challenging for the system to be as light as an actual dandelion seed.
UW engineers developed a shape that would allow the system to take its time falling to the ground that could be tossed around by a breeze. Researchers tested 75 designs to find the one with the smallest terminal velocity, or the maximum speed a device would have as it fell through the air.
"The way dandelion seed structures work is that they have a central point and these little bristles sticking out to slow down their fall,” said Vikram Iyer, a UW assistant professor in the Allen School. “We took a 2D projection of that to create the base design for our structures. As we added weight, our bristles started to bend inwards. We added a ring structure to make it more stiff and take up more area to help slow it down."
Instead of a battery, engineers used solar panels to power the electronics. When tested, the devices landed with the solar panels facing upright 95% of the time. The shape and structure allow them to flip over and fall in a consistently upright orientation like a dandelion seed.
While the system can’t store a charge, and when the sun goes down, the sensors stop working.
"The challenge is that most chips will draw slightly more power for a short time when you first turn them on," Iyer said. "They'll check to make sure everything is working properly before they start executing the code that you wrote. This happens when you turn on your phone or your laptop, too, but of course they have a battery."
How it gathers data
To allow the device to store some charge overnight, the electronics includes a capacitor. These devices use backscatter, a method that involves sending information by reflecting transmitted signals to wireless send sensor data back to the researchers.
Data carrying sensors can send data until sunset when they turn off. Data collection resumed when the devices turn themselves back on the next morning.
Another benefit of the battery-free system is there’s nothing on the device will run out of juice and will keep going until it physically breaks down. And while a drawback is that electronics will be scattered across the ecosystem of interest, researchers are studying how to make these systems more biodegradable.
"This is just the first step, which is why it's so exciting," Iyer said. "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."
The full research can be found in the journal Nature.
