Flower Power: Floating Sensors Inspired By Dandelions

IRA FLATOW: This is Science Friday. I’m Ira Flatow.

When was the last time you thought about dandelion seeds? Maybe as a kid, you would blow a dandelion stem until that white puff ball broke apart, and the pieces floated into the sky. Well, those floating dandelion seeds inspired engineers at the University of Washington to design a new ultralight sensor. It’s solar powered. It weighs just 30 milligrams. The goal is to use these sensors to do things like, well, track temperature fluctuations and survey crops.

Joining me now is Vikram Iyer, Assistant Professor in the Paul G. Allen School of Computer Science and Engineering, University of Washington, in Seattle. He’s the lead author of a study recently published in the journal Nature, all about these tiny pieces of dandelion-inspired tech.

Welcome to Science Friday.

VIKRAM IYER: Hey, Ira. Thanks so much for inviting me.

IRA FLATOW: Nice to have you. To start off, what are these floating sensors used for? What’s the problem that they were created to solve?

VIKRAM IYER: If we think about a lot of these scenarios that people are talking about in smart agriculture, where we’d like to make measurements of environmental conditions across farms, or if we want to evaluate changing climates, and we want to measure temperature, humidity fluctuations across large areas, this is something that’s very difficult to do right now. Because if you want to make measurements across a large geographic area, that requires actually going out and placing individual sensors at many different locations. And this can be really time consuming and expensive.

IRA FLATOW: And you were able to shrink down sensors to be the size of these little tiny seeds that come out of a dandelion?

VIKRAM IYER: Yeah, exactly. So our motivation here was to address this problem of being able to disperse a large number of sensors automatically over a large area. We looked at dandelion seeds for inspiration. Because if we think about it, these little plants, they can’t even move, but they’ve evolved to spread their seeds over large areas, sometimes distances of up to a kilometer.

And so, by looking at these plants for inspiration, we decided to try to make these sensors as small and light as possible, to be able to automatically disperse them in the wind.

IRA FLATOW: That’s cool. So do they have a battery in them, a tiny little battery?

VIKRAM IYER: Yeah. One of the things that we had to do here to really cut down on the size and weight is we actually don’t have a battery in these devices at all. Instead, what we have is we have these small solar panels. And so our device, after it’s deployed, it harvests power from sunlight, and it can use that to do its sensing operations and communicate data wirelessly.

IRA FLATOW: All right, the geek in me wants to know, what they are made out of, how they’re manufactured, how you disperse them.

VIKRAM IYER: Yeah, great questions. So the way that we actually make these things is, basically, by using this laser cutter that can pattern really small features. We start with this really thin sheet of a plastic material. And we put that in our laser cutter, and we can cut all kinds of really fine patterns. And the cool thing about this technique is we can easily change that pattern to vary the amount of time that this is in the air and how far these little sensors are going to disperse.

We can actually imitate how– there’s some natural variation in individual seeds, where some of them will travel shorter distances, some of them will travel farther, to be able to get good coverage over an area. After we cut these little patterns, we can also use the same technique to pattern little wires to make circuits, and then attach our electronic components onto them to make our full wireless sensor.

IRA FLATOW: And so how do the sensors float through the air? Do you have to shoot them at a certain level? Do they use air currents? Tell me what’s going on there.

VIKRAM IYER: We design our devices to have what’s called a really low terminal velocity. So think if you drop these from a certain height, they’re going to fall to the ground very slowly. And the lower that we can get that number, the more opportunity it has to stay up in the air, and the more opportunity it has for the wind to carry it to longer distances.

The way that we actually deploy these is– we show experiments where we drop them from a drone. So if we drop them from a drone from, say, 20 meters– about five, six stories in the air– we saw that, in a moderate breeze, they can fly for up to distances of 100 meters.

IRA FLATOW: And how do they keep those little solar panels turned toward the sun all the time? I would imagine you would have to do that.

VIKRAM IYER: That’s actually one of the other features that we leverage in our design by looking at dandelion seeds for inspiration. If you look at a dandelion seed, and you drop it upside down, you’ll notice, what happens is, it actually flips over in midair and it always lands in the same upright orientation. And so by mimicking this sort of structure, we can make our devices also flip over in mid-air, even if they’re dropped upside down, and make sure that they always land in the same upright orientation, with the solar cells facing the sun.

IRA FLATOW: And so how long do they last? How long do they send back usable information? What’s their life expectancy?

VIKRAM IYER: So these devices could in theory last forever, right? They don’t have any kind of battery that limits their lifetime. And they can harvest energy from solar power. So as long as they’re outside– they can actually start up even after sunset, on the start of a new day, when the sun comes out, and start transmitting information.

IRA FLATOW: OK, so you’ve got your launch of these seed-like devices. They fall down. How do they get the data transmitted back to you?

VIKRAM IYER: We use this technique called backscatter communication to really reduce both the size and the power of our wireless transmissions. And the idea here is that we’re communicating using reflections.

So compared to a typical radio, like the Bluetooth or Wi-Fi that you have in your phone, those devices are generating a radio signal that goes out into space, which requires both a lot more energy and larger components and circuitry to actually generate that. What we’re doing here is, if you think of those systems, like normal Bluetooth or Wi-Fi as like a flashlight that you’re turning on and off to communicate, say, a Morse code-style message, what we’re doing here instead is we can outsource that flashlight onto another device. And then, our really small dandelion sensor, you can think of that as just a mirror that’s changing its angle a little bit to either reflect or not reflect that light.

And so by doing this decoupling with all of the power-expensive components onto another device, we can make these really, really small devices communicate data wirelessly. And the way that we actually implement that is with a little antenna that’s connected to a switch that toggles between two states, one that’s very reflective, one that’s not.

IRA FLATOW: Let’s talk about the different uses you could make of this technology. You mentioned about going out, let’s say, looking at the temperature or the humidity of crops in the field. Could you use it to understand crowds of people or traffic or stuff like that? Or what else could you do with it?

VIKRAM IYER: Yeah, there are certainly lots of applications that you could explore with this. As we mentioned, environmental monitoring is one of the first things that comes to mind, where we might want to measure things like temperature or humidity, pressure, across a large area. But we could also think of examples like we showed that we can put a little magnetometer on this device that can detect a passing car, for example.

We could also think of future applications, where we have these little wireless transmitters, right? Can we use that to immediately deploy a large network of connected devices in a place where the wireless infrastructure has been knocked out, for example?

The other cool thing about the way that we built this device is it uses a general purpose computing platform that can allow lots of other researchers to build upon this work and adapt it to different applications.

To expand a little more on that, compared to having to design a custom silicon chip from the ground up, our devices are programmable. So pretty much anyone with a computer science, computer engineering-type degree, can easily modify and reprogram the design for new applications.

IRA FLATOW: I know in your research you said that the goal is for a drone to be able to drop, what, 1,000 of these sensors at once? But what happens to the sensors once they’re all out there in nature? I imagine it would be a challenge to go collect 1,000 tiny sensors once they’ve been scattered.

VIKRAM IYER: Yeah, that’s definitely a great question, and something that we’ve been thinking a lot about. One thing to think about in the context of the e-waste problem itself is these devices are pretty small, and they actually don’t have a battery, right? So compared to all the phones and laptops that get thrown out, they’re fairly small by volume, right?

But I think when we talk about these examples, like environmental monitoring in these remote, hard to reach places that I talked about, our motivating applications, I think it’s really important to try to find ways to make these devices more sustainable going forward.

For example, we’re thinking about ways to make these devices out of biodegradable materials. For example, rather than like the thin plastic films that we use right now, we could easily make these out of, say, paper, a material that could biodegrade. And I think, in the long term, it’d be really cool to build these devices where we could drop them out for some kind of sensing application, and design them so that, after a period of time, when we know they’re going to be used, they’ll just degrade naturally.

IRA FLATOW: That’s interesting. What’s next for this technology? Is this part of a larger project? I know you work in a laboratory that talks about sensors and robots.

VIKRAM IYER: Yeah, that’s a great question. So really, this is one part of our broader vision on creating what we call the internet of bio-inspired and biological things. And if we think about it, there’s this pretty big gap between biological systems and the capabilities of current, say, Internet of Things, and other embedded little sensing devices, because most of these are pretty big and heavy, and they can’t move around.

And so instead, what we’ve been thinking about is, can we create these tiny, battery-free wireless devices that can actually move around? For example, float in the air like these dandelion seeds. Or can we make these little sensors that are small enough to be able to put on live insects? For example, like bees, beetles. And we’ve even used this sort of technology to track the murder Hornets that you might have heard about, that were found a couple of years back in Washington state.

And we can also build on these same technologies by adding– integrating things like actuators, to build insect-scale robots as well.

IRA FLATOW: I’m fascinated about the insect-size robotics lab. Can you actually create an artificial insect with a sensor on it?

VIKRAM IYER: Yeah. So that’s actually something that we’re working out, kind of as a next step for this work where, rather than having to deploy these devices from a drone, could we actually have them fly around themselves to different locations to take these measurements? We could think of lots of scenarios where this could be useful for, say, in disaster-type scenarios, where you, again, don’t have infrastructure. You could think of the example of, say, these little robots flying around to go locate a gas leak, or something like that.

And the other cool thing that we can do with this technology is, once we have these little sensing and computing platforms of this small size, we can also study the behavior of lots of animals, like small birds, where there really aren’t good tools to be able to do this.

IRA FLATOW: That’s fascinating. Thank you very much for taking the time to be with us today.

VIKRAM IYER: Yeah, it was great talking to you.

IRA FLATOW: Vikram Iyer, Assistant Professor in the Paul G. Allen School of Computer Science and Engineering at the University of Washington, based in Seattle.

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