Researchers turn to liquid metals for agile electronics Published Feb. 8, 2017 By Marisa Alia-Novobilski Air Force Research Laboratory WRIGHT-PATTERSON AIR FORCE BASE, Ohio – Self-healing electronics, antennas that can change shape and function with the flick of a switch and clothing woven with conductive threads able to electrically connect devices may seem like science fiction fodder. But, for scientists at the Air Force Research Laboratory, these concepts are much closer to reality. A collaborative, multi-disciplinary team of AFRL researchers recently demonstrated that non-toxic liquid metals are capable of creating multi-functional, reconfigurable electronics and flexible power connections for non-traditional electronics, with potential applications in a number of Air Force mission and other domains. “This is changing the paradigm of how we think about electronic materials for applications,” said Dr. Christopher Tabor, a research scientist in the Nanoelectronics Branch of AFRL’s Materials and Manufacturing Directorate, who received his doctoral degree from Georgia Tech. “We looked at liquid metals from a multi-faceted, application driven perspective, and our joint efforts were a great success.” Tabor and his team demonstrated that liquid metal alloys could be flowed through channels embedded in structural aerospace components, creating physically reconfigurable electronic material able to change antenna and electrical circuit characteristics, virtually on demand. “Essentially, we showed that you can rewire a system for a new mission set. By flowing liquid metals through channels in a system, you can change the frequency and function by simply removing the metal and patterning it in a new place,” said Tabor. “This can add multiple functions to a single platform, ultimately enhancing mission capabilities.” Tabor and a team of scientists from across AFRL, that included Drs. Jeff Baur and Michael Durstock of the Materials and Manufacturing Directorate as well Dr. Michelle Champion from the AFRL Sensors Directorate and Dave Zeppettella from the Aerospace Systems Directorate, demonstrated that non-toxic, conductive Gallium Liquid Metal Alloys could be flowed through channels embedded into an airframe to behave as radio frequency antennas. Unlike traditional, solid antennas that are only operable within a specific frequency range based on their size and location, the liquid metal antennas can be reconfigured within the airframe to operate at new frequency ranges and provide additional operational directivity. Whereas multiple radio frequency systems may impact the size, weight and power available to an aircraft, liquid metals enable increased functionality without adding additional material to a platform. “Liquid metals enable more function without the additional equipment,” Tabor said. “We’re trying to design electronics on the front-end, not to compete with what’s already out there, but to complement these technologies. The potential for low-cost, attritable aircraft application—those aircraft that we don’t need to operate over millions of lifecycles—is great, as it gives you a wider range of possibilities for a mission, with the ability to shift, if needed.” Though Tabor and his team have demonstrated that the liquid metal antennas are mission capable in the laboratory setting, they are still in the process of maturing the technology for transition to the warfighter. The biggest challenges include precise control of the interfaces between the liquid metals and other traditional electronic systems and the residue left when the liquid metals are removed from one channel and flowed into another, which can cause interference. They are also working with industry partners to develop packaging for the material to make sure it works in application platforms that may have traditional electronic systems on board. “We’re looking at this from multiple perspectives,” said Tabor. At the same time Tabor’s research team is moving liquid metals forward in the aerospace electronics domain, a tandem effort is underway within the flexible electronic materials research team, exploring the potential for liquid metals to power flexible electronic devices such as human performance monitoring sensors and wearable devices. “If you take traditional copper wires and place them on a stretchable material, like a rubber band, the copper wires may break or disconnect,” said Tabor. “Instead, if you make channel systems and fill them with liquid metal, the channels change sizes and the liquids fill them. For electronics that bend and crease, stretch or compress, liquids allow you to maintain stretch-ability and conductivity.” AFRL researchers are also looking at a new project to use liquid metals for self-healing electronics. By transforming liquid metals into microscopic nanoparticles, failure points on traditional electronic circuits can be repaired, without a need for replacement. “Nanoparticles have the potential to be sprinkled over failure points and adhere to the locations where a break needs repair, essentially ‘healing’ a junction,” Tabor said. “We are working to engineer those small nanoparticles with different surfaces so they can work in predictable ways.” In the end, exploration of new material systems for novel approaches to traditional electronics are expanding the potential application space, with a tremendous impact on warfighter needs. “Liquid metals open up new possibilities, impacting the technologies of today and the future,” said Tabor. Dr. Christopher Tabor and his team’s research in liquid metal reconfigurable antennas will be on display during DoD Lab Days at the Pentagon in Washington, D.C., May 17, 2017. It is one of thirteen Air Force Research Laboratory technologies that will be showcased during the public event.