Liquid Metal Changes Shape to Tune Antenna

Antennas can range from a few squiggles on a PCB to a gigantic Yagi on a tower. The basic laws of physics must be obeyed, though, and whatever form the antenna takes it all boils down to a conductor whose length resonates at a specific frequency. What works at one frequency is suboptimal at another, so an adjustable antenna would be a key component of a multi-band device. And a shape-shifting liquid metal antenna is just plain cool.

The first thing that pops into our head when we think of liquid metal is a silvery blob of mercury skittering inside the glass vial salvaged out of an old thermostat. The second image is a stern talking-to by the local HazMat team, so it’s probably best that North Carolina State University researchers [Michael Dickey] and [Jacob Adams] opted for gallium alloys for their experiments. Liquid at room temperature, these alloys have the useful property of oxidizing on contact with air and forming a skin. This allows the researchers to essentially extrude a conductor of any shape. What’s more, they can electrically manipulate the oxidative state of the metal and thereby the surface tension, allowing the conductor to change length on command. Bingo – an adjustable length antenna.

Radio frequency circuits aren’t the only application for gallium alloys. We’ve already seen liquid metal 3D printing with them. But we need to be careful, since controlling the surface tension of liquid metals might also bring us one step closer to this.

3D printing with liquid metals


While 3D printers of today are basically limited to plastics and resins, the holy grail of desktop fabrication is printing with metal. While we won’t be printing out steel objects on a desktop printer just yet, [Collin Ladd], [Ju-Hee So], [John Muth], and [Michael D. Dickey] from North Carolina State University are slowly working up to that by printing objects with tiny spheres of liquid metal.

The medium the team is using for their metallic 3D prints is an alloy of 75% gallium and 25% indium. This alloy is liquid at room temperatures, but when exposed to an oxygen atmosphere, a very thin layer of oxide forms on a small metal bead squeezed out of a syringe. Tiny metal sphere by tiny metal sphere, the team can build up metallic objects out of this alloy, stacking the beads into just about any shape imaginable.

In addition to small metal spheres, [Collin] and his team were also able to create free-standing wires that are able to join electrical components. Yes, combined with a pick and place machine, a printer equipped with this technology could make true printed circuit boards.

Even though the team is only working on very small scales with gallium, they do believe this technology could be scaled up to print aluminum. A challenging endeavour, but something that would turn the plastic-squeezing 3D printers of today into something much more like the Star Trek replicators of tomorrow.

Video demo below, or check out [Collin]’s editing room floor and a vimeo channel. Here’s the paper if you’ve got a Wiley subscription.

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