Liquid-Metal Antennas Lengthen or Shorten on Electronic Command

A significant drawback slowing the advance of liquid metal electronics devices is that they tend to require external pumps that can't be easily integrated into electronic systems. A team of North Carolina State University researchers set out to create a reconfigurable liquid metal antenna controlled by voltage only. They did so by using electrochemical reactions to shorten and elongate a filament of liquid metal and change the antenna's operating frequency. Applying a small positive voltage causes the metal to flow into a capillary, while applying a small negative voltage makes the metal withdraw from the capillary. 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. Many potential applications await within the realm of mobile devices.

Transcript

00:00:00 you can imagine this device could tune over a much wider bandwidth could replace multiple antennas or replace multi-resonant antennas i'd like to share with you a little bit of our work on liquid metal antennas so mercury is the most familiar liquid metal that people think about and unfortunately mercury is toxic so by process of elimination we've been

00:00:26 working with gallium and alloys of gallium which are also liquid at room temperature unlike mercury it the surface of it oxidizes and forms a skin and that allows us to control the shape of the metal when i saw that as a antenna engineer i immediately thought well if we can harness this

00:00:47 there's a lot we can do very first thing we did was simply inject the metal using a syringe it's really extremely simple and the end result is you get wires and also antennas or any sort of metallic structures that have mechanical properties defined by the encasing material so

00:01:06 if you were to inject it into a rubber band like material you would end up with a rubber band conductor in the case of our printing work the metal comes out of the syringe it immediately reacts with air to form this oxide skin and as we move the syringe along the surface

00:01:25 the oxide sticks to the substrate and also stabilizes the structures mechanically so we can print them into lines and or spirals for example and they hold their shape because they're essentially stuck inside of a little bag and the bag in this case is the oxide skin and so the essence of our work is

00:01:47 actually controlling the surface tension without the oxide the metal assumes a very large surface tension and wants to beat up and we've developed a way to lower the surface tension substantially so that we can let other forces take over in essence that's what we're harnessing in

00:02:04 collaboration with professor adams is we're switching back and forth between a state of high surface tension and a state of low surface tension so we went initially from a relatively low frequency around 700 megahertz or so and then probed then instructed the antenna to tune to about 1.2 gigahertz and so the antenna will withdraw from

00:02:23 the channel uh relatively quickly uh because we are actually applying uh reductive bias and that bias removes the oxide skin along with the presence of the naoh and causes the surface tension to increase as we near that frequency we change the bias to an oxidative bias so that it will cause the oxide skin to regrow and then that will cause

00:02:48 it to hold its position you can imagine this device could could tune over a much wider bandwidth could replace multiple antennas or replace multiple multi-resonant antennas that are on on a mobile device and allow you to cover more bands