Inspired by how dandelions use the wind to distribute their seeds, researchers have developed a tiny sensor-carrying device that can be blown by the wind as it tumbles toward the ground.

Wireless sensors can monitor how temperature, humidity, or other environmental conditions vary across large swaths of land, such as farms or forests.

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

The new sensor is about 30 times as heavy as a 1 milligram dandelion seed but can still travel up to 100 meters in a moderate breeze, about the length of a football field, from where it was released by a 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 up to 60 meters away.

“We show that you can use off-the-shelf components to create tiny things. 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,” says senior author Shyam Gollakota, professor in the Paul G. Allen School of Computer Science & Engineering at the University of Washington.

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

Because the devices have electronics on board, it’s challenging to make the whole system as light as an actual dandelion seed. The first step was to develop a shape that would allow the system to take its time falling to the ground so that it could be tossed around by a breeze. The researchers tested 75 designs to determine what would lead to 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. We took a 2D projection of that to create the base design for our structures,” says Vikram Iyer, an assistant professor in the Allen School and lead author of the paper.

“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.”

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

Without a battery, however, the system can’t store a charge, which means that after the sun goes down, the sensors stop working. And then when the sun comes up the next morning, the system needs a bit of energy to get started.

“The challenge is that most chips will draw slightly more power for a short time when you first turn them on,” Iyer says. “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.”

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

“Then 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 says.

These devices use backscatter, a method that involves sending information by reflecting transmitted signals, to wirelessly send sensor data back to the researchers. Devices carrying sensors—measuring temperature, humidity, pressure, and light—sent data until sunset when they turned off. Data collection resumed when the devices turned themselves back on the next morning.

To measure how far the devices would travel in the wind, the researchers dropped them from different heights, either by hand or by drone on campus. One trick to spread out the devices from a single drop point, the researchers say, is to vary their shapes slightly so they are carried by the breeze differently.

“This is mimicking biology, where variation is actually a feature, rather than a bug,” says coauthor Thomas Daniel, 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.”

Another benefit of the battery-free system is that there’s nothing on the device that will run out of juice—the device will keep going until it physically breaks down. One drawback to this is that electronics will be scattered across the ecosystem of interest. The researchers are studying how to make these systems more biodegradable.

“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.”

The paper appears in Nature.

Hans Gaensbauer, who completed this research as a UW undergraduate majoring in electrical and computer engineering and is now an engineer at Gridware, is also a coauthor. The Moore Inventor Fellow award, the National Science Foundation, and a grant from the US Air Force Office of Scientific Research funded the work.

Source: University of Washington

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The wind rushing through skyscrapers can make it difficult to operate small drones in urban areas. So why do pigeons have so little trouble?

With their sights set on unlocking the secrets of birds’ smooth sailing, researchers developed a new 3D method for recording the shape of birds’ wings during flight.

“We’re trying to figure out how birds are capable of flying so well in these complex, turbulent environments and a lot of that comes from how they deform the shape of their wings, left versus right, to adjust to gusts quickly,” says David Lentink, an assistant professor of mechanical engineering at Stanford University.

Birds morph their wings through an incredible range of shapes, but until now we’ve known little about the angle, twist, and asymmetries of each wing beat.

Grid and ‘barcode’

After seven years of development, researchers may have figured out how to more closely observe birds’ morphing skills: They’ve created a new way of automatically recording wing shape that works at high speeds and results in high-definition 3D reconstructions.

This bird’s flight through lasers could improve drones

Current techniques for recording animals in motion often rely on tracking markers attached to the animal or features of the animal like stripes or spots, an approach that can’t directly or automatically reconstruct an entire wing surface at high resolution. Other methods, which use patterned light, are easier to automate but are too slow to record bird flight.

As reported in the Journal of Experimental Biology, the new method builds on previous structured-light techniques, but automatically resolves body shape changes at high speed and in high resolution.

“The great thing about this system is it’s the first fully automated, high-speed reconstruction of birds in the world,” says Marc Deetjen, a graduate student in the Lentink lab and senior author of the paper.

The group’s setup consists of a video camera synced with a projector that projects two overlapping patterns of light. The first layer is a dense grid which, by covering much of the surface of the bird, gives the researchers a high resolution image. The second is a set of unequally spaced lines, like a barcode, projected perpendicular to the first. The irregular second pattern assures that no two areas of the light field look alike. When the bird flies through these patterns, its body acts like a projector screen and the straight lines of light deform based on the bird’s shape.

An algorithm that Deetjen developed matches the deformed pattern on the bird that the camera captures with the original projected pattern. It then produces a detailed 3D reconstruction of how the bird moves through the light field.

Go, Gary, go!

To test their technique, researchers trained Gary, a four-year-old parrotlet, to fly from one perch to another, with the light grid projected onto it as it took off. Gary’s light coloring allowed the camera to capture a clear light pattern, like a near-white projector screen. For this paper, the group only recorded the top surface of the bird, but multiple cameras could create a full-body reconstruction in the future.

Tricked-out ‘treadmill’ for birds could lead to better drones

The researchers intended this as a simple test of their system but ended up with an insight so unexpected and intriguing, they thought it was a mistake.

A scientist who studies flying snakes in Borneo might want to give the technique a try.

After recording a portion of four of Gary’s downstrokes, they computed the bird’s effective aerodynamic angle of attack—how much the wing flips backward—and found it was consistently between 55 degrees and 75 degrees in the first downstroke and 45 degrees and 60 degrees in the second.

Most airplanes stall when the angle of attack reaches about 15 degrees because even this angle can create drag so significant that the airflow becomes separated from the wing, resulting in reduced lift. The researchers concluded that the bird is actually supporting its body weight using drag oriented upward. In addition, the lift it generates is rotated forward so it functions as thrust.

“They’re actually able to generate more total force on lift-off,” Deetjen says. “That enables them to not only push up and overcome gravity but to accelerate forward.”

Details like this could bring us closer to replicating the efficient and acute takeoff of birds in small flying machines, like drones. For their next step, the researchers are planning to apply this technique in a specialized bird wind tunnel to investigate the many mysteries of bird flight in turbulence.

Although the team tested the technique on bird flight, it could be applied to many forms of movement. For example, it could show what happens to a car’s shape during a simulated crash. Lentink has also been talking with a scientist who studies flying snakes in Borneo who might want to give the technique a try.

“This is a technique that goes all the way from animal locomotion to direct applications in engineering, where things deform fast,” he says. “We only need to create one frame and then we can reconstruct the shape in 3D. This technique, in principle, does not have a speed limit.”

Source: Stanford University

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