Scientists have discovered a type of conductor that shifts autonomously under strain and could revolutionise wearables.
The US Air Force Research Laboratory (AFRL) has revealed a new technology that could help overcome some of the biggest challenges when it comes to wearables and strain put on the electronics of these devices. Writing in Advanced Materials, a research team revealed it has developed a liquid metal conductor that can autonomously change its structure when put under such strain.
Typically, electrical conductivity decreases and resistance increases with stretching, but this new technology – dubbed Polymerised Liquid Metal Networks – does the complete opposite. Instead, it can be strained up to 700pc while keeping resistance between these two states virtually the same and still return to their original state.
Wires that can maintain their properties under a range of different conditions could have a significant number of applications, particularly in wearables. For instance, the team suggested that this could be integrated into a long-sleeve garment and used for transferring power through the shirt and across the body in such a way that bending an elbow or rotating a shoulder won’t change the power transferred.
‘Completely unexpected and frankly unbelievable’
“This response to stretching is the exact opposite of what you would expect,” said Dr Christopher Tabor, AFRL lead research scientist on the project. “Experimenting with these liquid metal systems and seeing the opposite response was completely unexpected and frankly unbelievable until we understood what was going on.”
The team also tested the technology in something resembling a heated glove, measuring thermal response with sustained finger movement. This showed a near-constant temperature, unlike current state-of-the-art stretchable heaters that lose substantial thermal power generation when strained due to the resistance changes.
Developing it required the team to start with individual particles of liquid metal enclosed within a shell that closely resembles a water balloon. Each particle is then chemically tethered to the next through polymerisation. As these links in the chain become strained, the particles tear open and liquid metal spills out. Connections form to give the system both conductivity and inherent stretchability.
Importantly, after testing for 10,000 cycles, no sign of fatigue was seen. Lead author of the research, captain Carl Thrasher, added: “Human interfacing systems will be able to operate continuously, weigh less and deliver more power with this technology.”