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.

39 thoughts on “Liquid Metal Changes Shape To Tune Antenna

  1. I have seen back in the 80’s a glass thin rod with mercury used this way as well, add pressure to make the antenna longer. Except it was for far lower frequencies, 400mhz they used a servo on a diaphragm to adjust the mercury column and had an analog feedback loop that auto tuned the antenna for 1:1.

        1. I imagine it would, but in a predictable way. Maybe caging it would help?

          This liquid metal method has the excess metal sitting around, albeit in a more compact storage.

          1. i’m pretty sure antennae work based off of surface area. not positive, but when i was reading about stealing wifi a couple years back i’m pretty sure that’s what it amounted to.

          2. @Sparhawk817 pretty sure antennas are all about shape, not only about surface :D No, really, you can study this kind of stuff, and a big fat piece of sheet metal won’t have nearly the same amount of radiation efficiency than a appriately formed antenna with a tiny tiny fraction of the area.

    1. Maybe this is the joke you were going for, but that feature was only so that the antenna didn’t get broken off by environmental hazards or vandals. Not tuning.

      Now, if the antenna also moved up and down 1.3mm every time you clicked 0.2MHz on the tuner, then we’d be talking :)

  2. I saw something like this at Dayton Hamvention about 10 years ago. It was a long tube with some sort of conductive liquid inside. The level was raised, lowered by some sort of pump. This was much larger, a couple yards or so if I remember right and several inches thick as it was for HF bands.

  3. “The first thing that pops into our head when we think of liquid metal is a silvery blob of mercury”

    Wow, really? That’s number two here. How can you not first think of Terminator? Especially with ‘changes shape’ in the title!

  4. That CNC controlled syringe deposition method is very interesting in itself. Does anyone know if this metal (gallium?) would remain in shape while being encapsulated in epoxy?

    I’m imagining a clear epoxy (or acrylic) cube with a highly tuned fractal antenna “growing” through it.

    1. The video showed what looked like a yagi inside a clear, soft, plastic or rubber like substance. A two process print system, with liquid metal in one print head and a bath of epoxy to lower it into and harden with UV, might work. Hard part, I could think, would be linking the metal and insuring that it stays connected as you add Z height to it.

  5. > What works at one frequency is suboptimal at another, so an adjustable antenna would be a key component of a multi-band device.

    Um, no. Nonononono.

    Let’s analyze this like we have the slightest of ideas what we’re talking about:

    > What works at one frequency is suboptimal at another,

    True; we shouldn’t forget that a half wavelength dipole might work as 1.5 wavelength dipole too, and so on, but that’s the short version of “a system optimized for A will not inherently work well on B, especially when optimization for A and B would modify the same system variable”.

    > so an adjustable antenna would

    “would”? what’s not adjustable about the tuned antennas of all radios of the early to late 20th century…

    > it all boils down to a conductor whose length resonates

    … because an antenna technically is nothing more than an impedance matcher from free space impedance to line impedance, tuning circuits must be viewed as part of an antenna. So it’s not only the length that resonates, it’s also intentionally added capacitance/reactance (so-called electrically short antennas, tuned antennas), and all kind of parasitics.

    > be a key component of a multi-band device.

    Have a look at your transistor radio. It’s multi-band. Ok, it has two antennas, but it’s still a multi-band device.

    Now, your mobile phone has but one antenna for (standard/MHz) LTE/UMTS800, UMTS/GSM850, UMTS/GSM900, LTE1750, UMTS/GSM1800, GSM1900, UMTS2100, LTE/WIFI2500, WIFI5000

    So that’s a fucking wide bandwidth. And you get that with a single antenna, because antenna designers are smart and can combine shapes so that antennas work well for a set of frequencies (which is probably what cell phone designers aim for, because working bad outside these is good for signal quality), or over a range (like vivaldi antennas, logpers etc).

    Electrical engineers have had a definition for an antenna that’s wideband for around eight decades now: An antenna is wideband if the range of frequencies it receives well (at least half as good as its best frequency) is in the same ballpark as its smallest good frequency.

    1. Do remember to account for feedline loss. Not really an issue in cellphones. :-) Also allow for excess ohm’s law loss if your elements are oversized. Ground interaction gets interesting. And radiation patterns may get a little strange – cloudwarmers got the name from somewhere. Radiation pattern is a bit of a non-starter on cellphones, sure. Still, sure – the 160-190 KHz band requires some ugly compromises, and sometimes some “creative” interpretation of the rules. It works, sort of.

      (When I looked at your username, I though “Ham from Alaska, but too many characters?”)

  6. Might have to do something similar with a satellite antenna… I figure that with the appropriate gearing attached to the azimuth drive motor, I could get the dish to automatically compensate for the Doppler effect.

    Might also be possible to fill a small plastic cylinder with the liquid metal with a contact at one end with a small hole drilled in the other side so that an insulated wire could be inserted. You’d tune the antenna by inserting and extracting the incoming wire.

  7. Can anyone find information on the speed at which this can adjust frequencies? There are very specific applications in experimental physics that require a waveguide that can move at relativistic speeds and I wonder if this could be modified into such a device.

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