Researchers have accomplished the feat of developing a reconfigurable liquid metal antenna that is controlled by voltage alone, potentially opening up new doors in the field of liquid metal electronics.
Advances in liquid metal devices have been slow-moving because these types of innovations have always required external pumps that are difficult to integrate into electronic systems, the American Institute of Physics reported. To remedy this, researchers determined that by placing an electrical potential across the interface between the liquid metal and an electrolyte, the liquid metal could be spread by applying a positive charge or retracted by applying a negative one.
"Using a liquid metal -- such as eutectic gallium and indium--that can change its shape allows us to modify antenna properties more dramatically than is possible with a fixed conductor," said Jacob Adams, coauthor and an assistant professor in the Department of Electrical and Computer Engineering at NCSU.
The team created the incredible tunable antenna using electrochemical reactions to "shorten and elongate" a filament of liquid metal, changing the operation frequency. The application of a small amount of positive voltage causes the metal to flow into the capillary, while negative voltage makes it retract outward.
"[The positive voltage] electrochemically deposits an oxide on the surface of the metal that lowers the surface tension, while a negative potential removes the oxide to increase the surface tension," Adams said. "[The advance makes it possible to] remove or regenerate enough of the 'oxide skin' with an applied voltage to make the liquid metal flow into or out of the capillary. We call this 'electrochemically controlled capillarity,' which is much like an electrochemical pump for the liquid metal."
The resulting prototype can tune over range that is at least two times greater than systems using electronic switches, allowing for a range of potential benefits for new mobile devices.
"Mobile device sizes are continuing to shrink and the burgeoning Internet of Things will likely create an enormous demand for small wireless systems," Adams said. "And as the number of services that a device must be capable of supporting grows, so too will the number of frequency bands over which the antenna and RF front-end must operate. This combination will create a real antenna design challenge for mobile systems because antenna size and operating bandwidth tend to be conflicting tradeoffs."
Tunable antennas on the other hand can be miniaturized and may help solve near-field loading problems, such as the iPhone 4's tendency to drop calls when held from the bottom.
The findings were published in a recent edition of the Journal of Applied Physics.
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