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”
Banned by the FCC in 3, 2, 1 ….
Censored by the NSA… now!
Door kicked in by FBI… soon
FCC: inhibiting innovation since 1934…
“Banned by the FCC in 3, 2, 1 ….”
FCC encourages a tuned antenna.
+1 for that insight. FCC is all about limiting your transmission to your spectrum allocation. Better tuned antennas == less Out-of-band emissions for your radio.
But what if the changeability means they dont’ have the paperwork for it since they expect a defined frequency response.
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.
My old Ford had an adjustable antenna. When you out the keys in the ignition a small motor would extend the telescopic antenna, then retract it when you parked.
That’s the first thing I thought of. Surely a spool of wire, a contact and a stepper motor could extrude and retract the wire as required.
But you still have the whole spool connected to the antenna, wouldn’t this alter the behaviour of the antenna?
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.
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.
@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.
The spool would be an inductive coil, that changes as you unwind it. This loading coil would also change the effective electrical length.
Or a tape measure with a servo.
That’s pretty much what the SteppIR company does with their ham radio antennas. They use something more like a perforated tape measure instead of a wire, but its basically the idea of spooling a metallic element in and out using a stepper motor to adjust the length. A basic description is here:
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 :)
Two types of antennas already like that:
Yagi – http://www.steppir.com/
Vertical – http://www.diamondantenna.net/sd3301.html
That wasn’t for tuning, that was for keeping kids from ripping them off the car. I had one too by the way…
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.
This is really cool
“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!
+1 for thinking the same thing.
Me, too. I was thinking T-1000 the whole way until they got to ‘mercury’. “Mercury?! Oh, yeah, I suppose…”
It’s only about room temperature…..but awesome idea anyhow!
Now all we need is to make one of these big enough to replace a SteppIR antenna…
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.
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.
> 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.
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?”)
All antennas eat lotta ground.
Those talking about pumping a conductor into a tube to adjust it’s length… Who says the conductor MUST be metal? OK, now I gotta build a salt water antenna….
I’ve seen a saltwater antenna on some tech show years ago now ( innovation may be?) it was a float with a pump, look like a water fountain it was cool.
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.
You can use something like the trombone slide to vary the length. Same concept as the instrument, but at much higher frequency on the surface on the conductor.
There are also MEMS based switching capacitors for tuning antenna for mobile application.
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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