|Microfluidic channels in plastic shaped like dipole to house a metal alloy of gallium and indium that is liquid at room temperature.|
PORTLAND, Ore. With the disappearance of the visible antenna from our wireless portable electronics, antenna designers have turned to flat flexible metallic models. But any solid metal can crack if bent once too often.
Liquid antennas, on the other hand, can conform to any shape without strain, can be bent without fatigue, and will self-heal after being cut. By etching micro-fluidic channels inside a flexible plastic substrate, researchers have demonstrated a novel new liquid technology for conformable, high-reliability antennas.
"The key component in our liquid antenna is gallium, because it's the gallium that oxides and creates a skin which keeps the liquid metal stable inside of the channel," said Michael Dickey, a professor at North Carolina State University who teamed with University of Utah professor Gianluca Lazzi on research into liquid antennas. "Then, by adding indium to the gallium, we make it liquid at room temperature."
Both gallium and indium are expensive metals compared to copper, but Dickey claims that the small size of an antenna used by a portable wireless electronics device would cost only a few cents. In tests where he encased his liquid antennas in microfluidic channels etched in plastic, the antenna could be bent into any shape and even healed itself after being cut.
"Our antennas can stretch, bend, roll, and twist while maintaining constant, consistent electrical conductivity," said Dickey. "And by using lithographic methods, they could be fabricated as easily as conventional copper antennas."
The researchers' prototype had gallium-indium filled microfluidic channels cast on a polydimethylsiloxane substrate. In tests over a frequency range of 1910-to-1990 MHz, the antenna radiated with about the same efficiency as a copper dipoleabout 90 percent.
One novel use of the antenna would be to tune it by stretching the PDMS to a different length, potentially making it an ultra-sensitive strain gauge with less than 0.3 percent accuracy. As a strain gauge, the researchers envision casting the microfluidic channels into flexible silicone shells which could be inserted into the walls of buildings and the supports for bridges while they are being constructed, then checked for strain by safety engineers anytime thereafter.
For military antennas, they could be folded or rolled into any convenient shape that fits into a backpack, then unfolded by the radio operator in-the-field.
Funding for the liquid antenna research was provided by the National Science Foundation.