1. Introduction - 2. Development
- 3. Applications - 4. Links & more
5. Liquid metal Elastic Stretchable wire - 6. Practical issues
a. Adjustable Yagi b.
My first example is the adjustable Yagi in the diagram on the right. The red represents the conductors, the black the air tubing, blue the tubing for the liquid metal, and the liquid metal is gray. This would allow you to tune the elements within a band to give you wider gain bandwidth.
If you had the yagi elements on an adjustable track, you could perhaps make the whole yagi cover several bands! The liquid metal sections could be made long enough to change bands and the element spacing adjusted mechanically. Nothing says that you could not put the liquid metal's tubing at an angle to make the whole element straighter. (I have not investigated angles yet.)
An easy application for a Liquid Metal Antenna element is to be the
driven element in a corner reflector. By adjusting the length of
the LM-Antenna and spacing to the corner reflector, you can have very wide
tuning bandwidth and gain. I might try this variation on my house
with a rotator.
"Combo" LM-Antenna 2 meter, 222, 440, with 6 meter fixed extension
My prototype can adjust as a 1/4 wave grounded element between 2m, 222,
to 440 or connect with at contact at the upper end for a 6m extension.
Air Driven Liquid Metal Switches (or "Relays")
Switching parts of an antenna array without wires can have advantages. For example, you could have a pneumatically driven 1/4 wave antenna at one frequency that is air switchable with 1/4 wavelength phasing section(s) for collinear Super-J or Extended Super-J operation on a higher frequency. Make the type of antenna you want by switching sections of it the way you want with pneumatics!
It may be cheaper and easier to use liquid metal switches, or relays, in many applications. Why buy an expensive high frequency coax switch when you can do it with an inexpensive air driven Liquid Metal Switch? Instead of a transformer to power a relay, you need an aquarium air compressor for pressurized air. Air tubing can also be as cheap, or cheaper, than wire. Lightening should be less of an issue also. (You don't need lightening protection on pneumatic air lines...)
Liquid Metal could also be moved with liquids, though I thought hydraulic operation was more messy. The liquid metal tended to form droplets with some fluids. (Mercury may be vary dangerous with hydraulics because it is more toxic when combined with organic compounds. It is another reason to avoid mercury as a liquid metal and use Galinstan or another Gallium based liquid metal.)
Note that "do it yourself" pneumatics is much cheaper than industrial
pneumatic devices. For example, you could use a cheap plastic medicine
syringe as a pneumatic cylinder. An aquarium air pump and valve will
push it. Two syringes back to back give you two way operation.
How about 5/8 wave 2 meter, 222, 440, and 1/4 wave 6 meter mobile?
With tubing long enough for 1/4 wave of liquid metal at 6 meters, you
could add switchable matching coils for 5/8 wave on 2 meters, 222, and
440 Mhz. To make it more interesting, you could switch the coils
in and out using pressure driven liquid metal switches.
Adjustable length or switchable polarization Helical Antennas?
Tubing could be spiraled and used for an adjustable length Helical Antenna.
You could have two opposite polarizations on the same frame, and use suction
to draw out liquid metal for one or the other polarization. (Some
type of valve could be used to select separate pressure driven polarizations.)
Liquid Metal Coils?
Another possibility is to make coils with liquid metal that you push in enough for the number of turns that you want. Coil tapping and switching could also take place with liquid metal.
Connecting with Constant Impedance from Coax
|This is a "biggie" for those who want the greatest bandwidth. The diagram
on the left is a cross section of keeping the impedance constant up to,
and including, the liquid metal storage chamber. The red is solid
metal, blue the non-metalic chamber and tubing, gray the liquid metal,
and black is the input for pressurized air.
I borrowed this idea from the "Super Dummy" RF load documented in the 1990 ARRL Handbook, page 34-22. The diameter from the outside of the coax is expanded in proportion to the inside being expanded, keeping the impedance constant. A more gradual transformation than the diagram would be better.
Because the diameter of the opening containing the container would set the maximum useable frequency, making the container narrower would be better for higher frequencies. You could do that by making the container longer down below the groundplane. For that matter, the center of your coax could be a tube supplying the liquid metal to the antenna. Somewhere you still must store it and respect the impedance. (A way to store it outside the coax would be to have it pass through a "liquid coil" choke to an outside container that would be RF free. The input contact would be on the coax side of the choke.)
You can calculate the diameters using the feedline.exe program from VE3SQB's website ve3sqb.com. The hardline part of the program gives you the necessary diameters for the impedance. I have found all of his antenna design and other programs very useful. Here is the link to his website:
The height of the liquid metal is proportional to the air pressure pushing it up. An electronic air pressure gauge and automatic regulator would be ideal. Industrial regulators and gauges are another possibility.
You can make your own gauge using a duplicate of the Liquid Mental Antenna for use as a gauge. If you substituted water, it will rise further in response to the pressure. Water may be more useful as a gauge for tuning the tips of a Yagi or other fine adjustment.
With a single element SWR is useful. However, with a multiple
element antenna like a beam you need to tune each element to resonance.
An alternate to measuring the pressure in a muli-element situation could
be to use fiber optics for measuring the height directly. Unfortunately
fiber optics are not cheap. Still, could you do any better with solid adjustable
elements and electro-mechanical positioning?
What are the endless possibilities of making the liquid
metal go where you want it for that "ultimate mega antenna"?
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