Researchers from the North Carolina State University have discovered a way to turn liquid metal into an antenna, opening up a number of possibilities for the discovery.
In a study published in the Journal of Applied Physics, Jacob Adams and colleagues set out to make a reconfigurable antenna made from liquid metal that can be controlled simply by voltage. Their work drew inspiration from a liquid metal studies carried out by Michael Dickey's team from the NCSU chemical and biomolecular engineering department. Dickey is involved in the current study as well.
According to Dickey's original study, it is possible for liquid metal to change its shape by applying electrical potential between an electrolyte and the liquid metal. By introducing a positive charge, the liquid metal would spread; by adding a negative charge, the liquid metal would contract.
Length and shape are of importance because these determine the critical properties of an antenna, much like radiation pattern and operating frequency. Adams explained that using liquid metals that can change shape allowed the researchers to modify the antenna's properties more extensively compared to what a fixed conductor is capable of.
The researchers shortened and lengthened a liquid metal filament using electrochemical reactions, where a positive voltage caused it to flow into a capillary and a negative voltage made it retract from the capillary. A positive voltage leaves an oxide on the metal's surface, lowering surface tension, while a negative voltage removes said oxide, increasing surface tension.
"We call this 'electrochemically controlled capillarity,' which is much like an electrochemical pump for the liquid metal," said Adams.
While solid conductors can also be used to reconfigure antenna properties, using liquid metals greatly increased the range over which operating frequencies can be altered. According to the researchers, liquid metals offer at least twice more range compared to electronic-switch systems.
This discovery in manipulating liquid metals is seen by researchers as having the most use in mobile devices. With the possibility of manipulating them to almost any size, tunable antennas can be used to address near-field loading problems like the "death grip" issue in the iPhone 4 where calls were dropped when the phone was held at the bottom.
The researchers are already looking into ways on how to improve speed and efficiency in reconfiguring liquid metals. In the future, they hope to be able to better control shape to expand applications.
