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Using a commercial printer and some silver ink, researchers from Florida State University have found a novel way of producing motion sensors en masse. The low-profile sensors support new applications in wearable electronics, structural health monitoring, and, perhaps soon enough, microrobotics.

Lead researcher and doctoral candidate Joshua DeGraff assembled the technology from buckypaper — razor-thin, flexible sheets of durable carbon nanotubes.

DeGraff handles a buckypaper sensor. (Image Credit: Florida State)

In addition to a strip of seven micron-thin buckypaper, the sensor features silver ink electrodes printed from a common, commercially available EPSON Stylus C88+ ink-jet printer.

Degraff, along with Richard Liang, professor and director of Florida State's High-Performance Materials Institute, spoke with Tech Briefs about how the manufacturing method offers an important benefit for emerging technologies like wearables and robotics: scalability.

Tech Briefs: What are the characteristics of buckypaper?

Dr. Richard Liang: Buckypaper is a carbon-molecule thin film, about 10-15 microns in width. All the carbon nanotubes work in tandem together. The material is extremely lightweight: 5 grams per square meter. By adjusting the contact between the carbon nanotubes, you achieve a wider range of conductivity and sensitivity.

Tech Briefs: How is the buckypaper sensor made?

Joshua DeGraff: We use the printer and silver ink to print patterned electrodes on low-profile plastic substrates. Then, we position our buckypaper films on the printed circuit and laminate it. Lamination holds everything in place and protects the components. We then crimp on low-profile electrical contacts for easy connection. I’m able to print out maybe 100 sensors at a time, and I can make them pretty fast.

Tech Briefs: What is the sensing element?

DeGraff: The buckypaper is the sensing element. It’s very sensitive — about eight times more sensitive than commercial sensors that are usually just made out of metallic prints. Its function is to provide the change in resistance and conductivity. The whole point of this is to have a low-profile sensor that’s scalable, so we can print these in large quantities in continuous fashion.

Dr. Liang: If you want a wearable sensor for everybody, scalability and affordability is key. If somebody wants to cover the whole human body with sensors, we can do it in a very affordable way. We don’t need a very expensive 3D printing machine. We don’t need to use very special conducting ink. You can make 100 sensors a day; that’s a very unique scalability.

Tech Briefs: What applications do you envision right away? What applications do you envision in the future?

DeGraff: Right away, I see the sensors in wearable technology. We were able to integrate our sensors into gloves. The sensors detect very small finger movements, and also large bending movements.

I also see the sensors in structural health monitoring soon. The sensors can basically detect “invisible” deformations and microstrains that we can’t see with the naked eye. They’re affordable, and we can use them to create sensor arrays. We’re doing more lifecycle tests, especially with structural health monitoring with carbon-fiber composites. Down the road, when we figure out how to integrate the sensor with the artificial muscles, we may see them in microrobotics and soft robotic systems.

Tech Briefs: Has buckypaper been used before as a sensor material? Is this a novel approach?

DeGraff: They’ve been used in other sensors, but the problem is the way they are commercialized and manufactured. You want it to be a scalable process. You also want to have the mechanical properties, so you can have a highly sensitive sensor. We have a mixture of both here, and that’s why we have such a high gauge factor [how much resistance value changes as a material is strained or bent]. We can print out lots of sensors at a time, and we can even tailor them to different applications.

Tech Briefs: What’s most exciting to you about this sensor?

DeGraff: I like the fact that it has a wider range of applications, and we can help people out in their daily lives, and not in just one sector, like aerospace. When it comes to wearable technology, athletes can track how intense their workouts are.

You can count your steps. You can have bed sheets that can tell, by your movements, how well you’re sleeping. You can help people who have carpal tunnel syndrome, who are going through treatment, and who need to know how well their self-rehabilitation is going. It can go from there to the structural health monitoring and the detecting of vibrations in buildings.

Tech Briefs: Do you have any advice for fellow engineers and sensor researchers?

DeGraff: If you have an idea and you have the materials, just try it. Instead of wondering whether or not it will work out, or reading if somebody else did it before, take the initiative; try things out yourself and see how it works out for you.

What do you think? Will scalable motion sensors improve adoption of wearables? Share your thoughts below.

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