Ju-Hee So, North Carolina State University

FROM radios and mobiles phones to wireless-networking gear and satellite-navigation devices, antennas are everywhere. Yet, despite their ubiquity, they are delicate pieces of equipment. Civilians, for the most part, take them for granted, but the armed forces know just how easily an antenna can be destroyed in a war zone—with potentially catastrophic consequences. Now, a technology that allows antennas to bend fluidly and “self heal” as they get whacked around in the chaos of war could make using them a great deal easier.

Antennas transmit signals by using an oscillating electrical current in a length of conductive material to generate electromagnetic radiation, such as radio waves. When receiving they do the opposite, transforming electromagnetic radiation passing through the conductive material into electrical current.

The most common conductive material used is copper. This, however, has a tendency to snap with only a small amount of punishment. Michael Dickey, an engineer at North Carolina State University, therefore wondered if a more resilient alternative might be found.

Dr Dickey put together a team of electrical and chemical engineers and, together, they started looking at metals and metal alloys that are soft at room temperature. The best mix they came up with was an alloy of gallium and indium. This had all the electrical properties that antennas need to function, but was much more flexible than its copper equivalent. Indeed, it was more than just flexible. At room temperature it was actually liquid, and thus flowed when deformed, rather than breaking.

The result, as they report in Advanced Functional Materials, is an antenna that can be housed in variety of covers, appropriate to different uses. Rigid casings will make the antenna more solid and rubber ones will allow it to stretch like an elastic band.

Moreover, when a liquid antenna is housed in an elastic material it can be tuned in a novel way. For good reception, the length of an antenna needs to correspond with the wavelength of the radiation it is receiving. This matching of antenna-length to wavelength is the process known as “tuning”. A traditional antenna does not actually change length, however. Instead, external circuitry is used to change its effective length. One of Dr Dickey's rubber-coated antennas, though, can be tuned by stretching the antenna itself.

Besides being useful in the military applications that stimulated the project, Dr Dickey thinks this flexibility might be exploited to make stress-detectors for civil-engineering projects such as dams and bridges. If lots of flexible antennas attached to small radio sets were placed inside a bridge, they would expand or contract along with the bridge and so would constantly retune themselves. Engineers monitoring the bridge would just need to scan them with radio waves to see which wavelength they responded to, in order to find out what was going on.