A liquid antenna can be better adjusted to listen to various frequencies than a rigid structure

Liquid antenna could revolutionise gadget design

Researchers have created a liquid metal antenna that can be tuned to listen to various frequencies by applying electrical voltage.

While positive voltage causes the liquid metal to expand, negative voltage makes it contract. If a small amount of liquid metal is placed inside a capillary, applying a small positive voltage causes the metal to flow into the capillary, while applying a small negative voltage causes the metal to withdraw. Such elongation and shortening of the liquid metal filament changes the antenna’s operating frequencies.

The researchers from North Carolina State University (NCSU) described the experiment in the latest issue of the Journal of Applied Physics.

Liquid electronics have interested researchers for many years, but there have been too many drawbacks previously to fully develop the technology.

"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," explained Jacob Adams, co-author of the study and an assistant professor in the Department of Electrical and Computer Engineering at NCSU.

Although antenna properties can be reconfigured to some extent by using solid conductors with electronic switches, the liquid metal approach greatly increases the range over which the antenna's operating frequency can be tuned. "Our antenna prototype using liquid metal can tune over a range of at least two times greater than systems using electronic switches," Adams said.

The researchers hope the device could find its way into many possible applications, including mobile phones.

"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. "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 trade-offs."

Tuneable antennas could be miniaturised and adapted to correct for near-field loading problems, for example.

According to Adams, liquid metal systems provide a larger range of tuning than conventional reconfigurable antennas and the same approach can be applied to other components such as tuneable filters.

The researchers will now focus on improving the efficiency and speed of the antenna reconfiguration. Eventually, they hope, it will be possible to gain greater control over the shape of the liquid metal, possible creating two-dimensional capillaries and surfaces of nearly any desired antenna shape.

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