Editor’s note: In a Q & A format, researcher Vikram Iyer, Ph.D., University of Washington, shares the accomplishments and possibilities of a tiny, new device that could offer just the right textiles a surprising opportunity. His work, he says,“takes an interdisciplinary approach to connect ideas between different engineering domains and biology to build end-to-end wireless systems that push the boundaries of technology with particular focus on size, weight, and power. This includes wireless robots and sensors small enough to ride on the back of live insects like beetles and bumblebees.”
Q: I’m quoting from the University’s press release, just to begin: “[These] small robotic devices can change how they move through the air by “snapping” into a folded position during their descent. When these “microfliers” are dropped from a drone, they use a Miura-origami fold to switch from tumbling and dispersing outward through the air, to dropping straight to the ground.” Aside from the origami technique itself, what sort of “aha moment” sent you in this direction?
A. The idea of microfliers, battery-free sensing devices that can fly in the wind mimicking leaves and seeds, but also control their descent, has been a longstanding vision in both the scientific community and popular culture. Despite decades of work since proposals of “smart dust” and advances in specific technologies toward this vision, researchers have faced many challenges in developing fully functional microfliers that harvest ambient energy like sunlight and use it to control their descent.
This is because devices like motors that provide lift and control for drones are large and heavy, and even small insect-inspired wings require more energy to flap than small solar cells can harvest. As a result, prior designs have been large or lacked onboard control. In this work we take a different approach with the key idea of using the unique properties of origami structures.
While prototyping and exploring the properties of origami, we discovered that a small change in shape can have a dramatic effect on their falling behavior switching from a tumbling descent that disperses outward to a straight down, stable descent. Building on this observation we designed a miniaturized robotic flier that can harvest solar energy to power an onboard actuator to change its shape in mid-air and alter its descent. These fliers open up a new design space for robotic, shape-changing fliers, and they create a new aerial platform for wireless sensing.
Q: The beauty of fibrous substrates or films is that they’re so ubiquitous and varied. They can also be engineered to offer the performance capabilities necessary for particular applications. From your viewpoint, what would be the advantage of working with a textile product, if it were possible to find or engineer one that meets your criteria?
There are lots of advantages to using textiles to build these kinds of devices. In addition to being thin and light, which enables miniaturization, a key advantage is that they’re flexible. This is what allows us to create our foldable origami circuit. Patterns of origami folds can even be used to give that material new kinds of properties, such as the ability to store energy like a spring and snap between two folded shapes, as we show in this work. We also use textile and thin film materials in other projects to make things like hinges for small robots. This allows us to pattern flat, 2D structures and fold them like a popup book to create 3D robot parts.
Some of the properties we care about here are the thickness and density for weight, stiffness for the origami properties, robustness to repeated bending cycles when making hinges, and processing temperature to do things like lamination.
Q: What triggers the shapes? Is this a response to environmental changes? A timing mechanism? Or is the shape shifting controlled by whoever launches the devices?
All of the above! To enable deployments of many devices at a time, each flier is individually programmable and can switch its state from a tumbling descent, where it spreads outward, to a more stable, straight downward fall at a specific altitude, time, or upon receiving a radio signal.
The pressure sensors on our microfliers serve the dual purpose of both taking sensor measurements and also detecting altitude. We also have a tiny computer chip onboard with a timer we can program with delays, and a radio receiver so we can send commands from the drone or the ground. This way even when multiple fliers are dropped from a drone at once, we can vary how the fliers spread as they fly. Deploying multiple fliers at a time allows us to automatically disperse a network of sensors in the air.
Q: You said in a 2022 article released by the University of Washington that “our long-term vision is to develop new materials and methods that help us generate a production cycle for electronics in which all the materials and components can either be recycled and reused or degraded and regenerated through the natural biological cycle.” There has been an explosion of research into more sustainable materials in almost every facet of the industrial fabrics world. Can you speculate on what might be possible? How can either a fibrous material or cellulosic film figure into a solution for that? Could a natural fiber-based material be coated in some way, or does this just add too much weight? There must be many considerations, so feel free to break this down.
Textiles made of cellulose and other natural fibers are a great way to make our fliers more sustainable. For example, if you’ve ever folded origami before you’ve probably done that with paper which intuitively shows this should be possible.
My group has a separate theme of work on creating sustainable electronics and computing devices where we’ve developed methods to pattern circuits onto materials made of natural fibers. Going forward we hope to combine these two technologies. Making a device like this biodegradable, though, presents a trade-off: you want to make sure it’s robust enough to last for your sensing application, but you don’t want it to be around forever.
One potential approach here is to combine biodegradable textiles with things like coatings that will protect them for a period of time. This is a similar idea to how certain pills that do controlled drug release work where they slowly dissolve over some time period. By combining this with biodegradable solar cells and transistors in the future, we could create a completely biodegradable flying sensor.
Q: How else might this device, or some variation of the technology, be used?
The focus on this work was creating robotic sensors that could fly in the wind, but the individual techniques we developed could be used for a variety of applications. For example, origami can be used to create compact folded structures that expand out to become much larger. This technique has been used to help deploy structures for satellites.
The low-power electronics also has lots of applications to things like wearable sensors for health or fitness tracking that can operate on small amounts of harvested energy. In this work we also take it a step further and show that we can even enable mechanical motion with small amounts of harvested power.
Q: Could you talk about the material used a bit more, and the potential for using a more traditional textile?
A: The specific material we used was a thin polyimide film, DuPont Pyralux AC121200E coated with copper to pattern the circuit traces on it (12 um thick polyimide, 12 um copper). We could certainly use other materials as well, for example something like paper would likely work.
In terms of using other traditional textiles this may be possible, as well. I think the main questions would be density to make sure the fliers are still light weight (that’s the nice thing about the thin polymer films) and also whether you could produce folds that hold their shape.
We’d have to try it, but my guess is that something like pure cotton fabric, even stretched across the carbon fiber root structure wouldn’t work because the joints wouldn’t stay creased so it would be hard to create the origami behavior. I’m guessing different weaves or blends might work well, though.
I think this could be pretty interesting to folks in the broader textile community, both from the perspective of using origami to enable unique capabilities and this idea of making textile base- fliers, as well as future potential for doing things like making these out of recyclable and biodegradable materials.
Janet Preus is senior editor of Textile Technology Source. She can be reached at email@example.com.
Vikram Iyer, is assistant professor in the Paul G. Allen School of Computer Science & Engineering., University of Washington, co-director of the CS for Environment Initiative and co-senior author of the research team’s findings, which were published in Science Robotics, September 2023.