1. Introduction - 2. Development - 3. Applications - 4. Links & more
5. Liquid metal Elastic Stretchable wire - 6. Practical issues

Also, see my article on eHam.net.
 

Why make a Liquid Metal Elastic Stretchable Wire?

The basic advantage of using liquid metal is that the RF can be kept in a straight line for the best (and predictable) velocity factor, inductance, and impedance.  Putting the non-toxic liquid metal into a stretchable elastic rubber tube gives you RF performance!  It eliminates the problem of the non-toxic liquid metal sticking, because it is ok to stick in this application.  You can also use it in almost any position, with certain limitations.

Above is an animated diagram of a stretchable elastic liquid metal wire being stretched out, then "springing" back.  In the diagram red is the solid wire, the gray is liquid metal, and the rubber tube is black.

Another application of this idea is to put a balloon inside a balloon, with liquid metal in between the balloons.  Then when you inflate the inner balloon the liquid metal forms a thin shell.  This gives you an air pressure adjustable antenna element.
 
 

Where did the idea come from?

The one annoyance with my first Liquid Metal Antenna efforts is that the liquid metal was being pushed up vertical.  Gravity made going downwards or horizontal seemingly impractical.  When I thought about using plastic telescopic sections or similar, the ideal of a rubber balloon came to me.  A stretchable tube seemed the ideal shape.  You might even be able to pump the liquid metal into the stretchable elastic tube!  Another possibility was to use a rubber strip or sheet coated with liquid metal, you could stretch it the way that you wanted.

You end up with a good and predictable surface for RF currents as long as the liquid metal flowed smoothly along the surface.  Stretchable products with wire woven in them are unlikely to be very useful or predictable with RF.

I did a search on Google for "elastic stretchable wire" and came up with only 3 hits, none relating to this application.  Changing to "stretchable elastic wire" on Goggle came up with 0 hits.  You can find "elastic wire" on Google, but "elastic" does not have to be stretchable.  The elastic only wire does not have the amazing stretch properties of the Liquid Metal Elastic Stretchable Wire.
 
 

Development of the Elastic Stretchable Wire and Balloon

Considering the problems with the liquid metal sticking, I thought that I could simply coat a rubber band, add contacts, and go.  That damn liquid metal did not want to stick!  It would stick when you did not want it to.  Though I knew that I could get it to stick eventually, I went straight to testing a rubber tube.

Below is a picture of the first and second Liquid Metal Stretchable Elastic Wires.  The red tubing ^*  was all I had at home, so I made a short sample.  The solid copper wire is duct taped to the ends, this was just a prototype after all.

Putting a balloon inside a balloon was easy.  When I put the liquid metal between the layers of balloon there were some air bubbles.  So when the inner balloon was inflated, you can see some spots without any liquid metal.  Most of it still had a good layer of liquid metal inside.  The cat approved it.

Applications of Liquid Metal Elastic Stretchable Wire:

Because of the RF properties, it can be stretched into adjustable length antenna elements.  You could connect short sections together to create longer stretchable wires.

Another application is to pump liquid metal into the stretchable elastic tubing using methods discussed in the Liquid Metal Antenna development and applications.

Other than antenna uses, this stretchable elastic wire may be useful for it's other properties.  It gets thinner when stretched, so it's resistance will go up for the entire length.  You could use it for a "stretch meter" or similar application.

Elastic Stretch Yagi  (I will provide photos when I finish one.)

Making it work - development concerns

1. Solid protective tubing:  It may be best to stretch the liquid metal wires inside a shielded plastic tubing.  If the rubber tube were to break then you can keep the liquid metal, which is not cheap.
2. Oil for protection from oxygen:  I do not know how well the rubber will protect the liquid metal from forming oxide (or "rusting"), so using the stretchable wire within oil may help.  Another possibility is if you could make multiple layer tubing with oil or some other protective substance in the outer layer.
3. Preventing air bubbles in the tubing:  My first attempt lost contact when fully stretched.  I thought that the tube was fully filled, but there was still some air inside.  Longer contacts at the ends may help keep contact if smaller bubbles can not be avoided.
4. Sealing the ends:  Duct tape was a quick solution for testing.  I will try the rubber dip that you buy in hardware stores to see if it works well.  Other materials may also work.
5. Pumping in Liquid Metal to lengthen the tubing:  I am not sure of the best methods for this application.  Putting the tubing in a sealed oil filled tube may help keep the tubing from expanding and make it lengthen instead.  Other methods of confinement may also help.
6. Elastic Stretchable Strip or Sheet:  I will try to make the liquid metal stick, and protect it with oil or a cover sheet.  I can see more applications but it has been harder to work with.  Another method is stretching out a flattened balloon with the liquid metal inside it.
7. Balloon within a balloon:  See the picture above.  This may be one of the easiest ways to get a thin layer of liquid metal as it is pressed by the inner balloon against the outer balloon.
8. Also: check out my concerns for Liquid Metal Antenna development.

Conclusion

I stopped working on the other Liquid Metal Antenna experiments while I investigated these ideas.  With so many possible uses and tests for the liquid metal I need to recycle between experiments or buy more.  The liquid metal that I do have may be slightly contaminated with who knows what by now, but it still seems to be working ok.

I will be dividing my time now between using the Liquid Metal Wire and the other Liquid Metal Antenna experiments.  I have health concerns to be taking care of also, so do not expect new and constant discoveries.  I am hopeful that other people, like you, will look into experimenting with theses ideas.
 

Links & more

Liquid Metal Antenna group on Yahoo!

See the Main page of Ham Domain.com - or - About me on  hamdomain.com

I give this information freely, without concern of profit or reward, because I believe in compassion.  I wish the world did also.

© Copyright 2016 - Michael John Lake - Make copies for personal use only.

* Red Tubing:  The red tubing is actually from a no. 14 FR catheter that I was unable to use or return.  SCI patients would understand.