News | Oct 8, 2019
Forget smartwatches, wearable electronics is going to mean all our clothing
US Air Force Research Lab has developed liquid metal inks, a foundational material design strategy for manufacturing flexible, stretchable electronics
The day we ditch our smartwatches for sensor- or camera-embedded smart clothing powered by our own steps could be coming soon.
The Air Force Research Laboratory announced Sunday that it has overcome a significant hurdle in manufacturing stretchable electronic textiles embedded with conductive substrates by developing polymerized liquid metal networks that autonomously change their physical structure.
“This response to stretching is the exact opposite of what you would expect,” said Dr. Christopher Tabor, AFRL lead research scientist on the project. “Typically a material will increase in resistance as it is stretched simply because the current has to pass through more material. Experimenting with these liquid-metal systems and seeing the opposite response was completely unexpected and frankly unbelievable until we understood what was going on.”
Textiles and tech companies will almost certainly be interested as fitness trackers mature into a medical device and consumer tech market. Earlier this month, the U.S. Patent & Trademark Office revealed Apple’s latest patent application for a fabric-based stretchable band embedded with electronics.
The Air Force’s flexible materials and processes team is developing backbone technology that enables the wiring of smart clothing that can maintain performance in all positions. The researchers started with individual particles of liquid metal enclosed in a shell, sort of like a tiny water balloon. Each particle is then chemically chained to the next through polymerization.
As the connected liquid metal particles are strained, the particles tear open and liquid metal spills out. Connections form to give the system both conductivity and inherent stretchability. During each stretching cycle after the first, the conductivity increases and returns back to normal. Testing has been limited to a finger so far, but no fatigue was detected after 10,000 cycles, and the Air Force believes the material could be integrated into a long-sleeve garment that could transfer power through the shirt, across the body, in a way that bending an elbow or rotating a shoulder won’t degrade the power transferred.
“The discovery of Polymerized Liquid Metal Networks is ideal for stretchable power delivery, sensing and circuitry,” said Capt. Carl Thrasher, AFRL Materials and Manufacturing Directorate research chemist. “Human interfacing systems will be able to operate continuously, weigh less and deliver more power with this technology.”
“We think this is really exciting for a multitude of applications,” he said. “This is something that isn’t available on the market today so we are really excited to introduce this to the world and spread the word.”
TechLink, as the Air Force’s national partnership intermediary for technology transfer, can navigate businesses to R&D partnerships with the Air Force Research Laboratory via patent license agreements and cooperative research and development agreements. TechLink’s staff are in constant contact with dozens of Department of Defense labs and continuously evaluate their inventions for commercial potential, which allows them to help private companies leverage the U.S. military’s substantial investment in basic and applied R&D.
For example, the Air Force was granted U.S. Patent 10,428,234 on October 1 for the metal inks developed by Dr. Tabor and his colleagues for manufacturing conductive substrates using direct-write or inkjet printing techniques. (Tabor’s research also earned the Air Force U.S. Patent 10,129,975 last fall.)
With TechLink’s no-cost assistance, U.S. companies can evaluate the technologies, obtain a license, and use it to manufacture new products.
And there’s more.
Click here to browse more of the Materials & Manufacturing Directorate’s available technologies, like the semi-transparent photovoltaic cells that the Air Force is making using an inexpensive material called inorganic-organic hybrid perovskite.