back to article Boffins build elastic wires with liquid metal

Researchers at North Carolina State University have shown “conductive wires that can be stretched up to eight times their original length while still functioning.” The wires have been tested, and demonstrated in the video below, to work perfectly well as headphone wires. Sound continues to reach the headphones even as the …


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  1. DF118


    "...housed in a very plastic polymer"

    Surely you meant elastic, no? I always thought the two words were antonymic, so a plastic polymer is one which has no capacity for physical deformation.

    Then again I dropped out of chemistry after 2nd year of secondary school.

    1. Graham Dawson Silver badge

      Re: Plastic

      Plastic means flexible and soft. We tend to associate it with hardness because petrochemical "plastics" appear hard in comparison, but they're generally quite malleable.

    2. frank ly

      Re: Plastic/Elastic - Fantastic

      This is why a dictionary is so useful. (Wikipedia too, if you really want to.) :)

    3. naam

      Re: Plastic

      Plastic Deformation is usually (well in my nick of the woods) meant to denote deformation that doesn't return to the original state, whereas elastic deformation does. So you're right that they use the word strangely here, although it's not exactly the antonym of elastic (it's still deformable, after all).

  2. 123465789


    "When the cable is stretched, the resistance increases. " - headphone or network cables with variable resistance? I don't think so.

    1. Anonymous Coward
      Anonymous Coward

      Re: resistance

      The audiophiles won't be impressed.

      1. Anonymous C0ward

        Re: resistance

        So charge $600 for it. They'll bite your hand off.

        1. Christoph

          Re: resistance

          Then release the de-oxygenated super refined crystal aligned gold-iridium-platinum plated version at fifty times the price. (It's actually the identical cable except it's a different colour.)

      2. Kevin McMurtrie Silver badge

        Re: resistance

        Figure out how to make magnetohydrodynamic headphones. I'm sure they'd be technically awful but for audiophile junkies they'd be worth their weight in oxygen-free gold.

    2. Anonymous Coward
      Anonymous Coward

      Re: resistance

      I do think so. Network cable is capable of dealing with lengths from 1m to 100m... so unless the 100m patch cable uses thicker wire, it will have a resistance 100 times that of the 1m cable. Same for headphone cables, which come in widely different lengths, yet seem to work just fine. Perhaps because the resistance of the wire itself is negligible compared to the resistance of other components in series to it?

      1. Poor Coco

        Re: resistance

        It’s not so much resistance as impedance; the cables are designed to have a certain characteristic impedance per unit length (capacitive and inductive effects are present too). If there was a stretchy part in, say, a twisted-pair Ethernet cable, then the twisting rate would vary, as would the conductor spacing (as the insulation stretches it must get thinner to compensate). This would result in a less-than-ideal section for noise resistance… but probably no worse than bunging in a 6-inch shielded patch cable to make up a slight length difference.

        1. ElReg!comments!Pierre


          1. if you are serious about your network you are never 2 inches short. Ideally you should know how to terminate your cables by yourself and you will always have just the right length, otherwise you just have to buy a slightly longer cable.

          2. I agree that the variation in impedance is not going to make a huge difference in the end; but depending on the physical properties of the cable, the constant tension may have desastrous effects. Just watch the cables jump out of the sockets one by one as the plastic jacks weaken over time... physical tension on my Ethernet cables? Not on my watch!

          1. Destroy All Monsters Silver badge

            Re: Network

            Additionally, the kinks in a stretched cable should prove interesting.

    3. harmjschoonhoven

      Re: resistance

      Does anyone remember mercury?

      Fill a rubber tube with mercury and stretch it. Measure the electric resistance and you know the length.

      Used to have some interesting applications in medical research.

  3. Neil Barnes Silver badge

    Resistance is futile

    Strikes me that the volume of the conductor in the cable must remain constant, so if it gets longer, it gets proportionally narrower. Which means, as the researchers point out, that the resistance rises.

    While the resistance isn't specified, it does imply two effects: first the decrease in signal level into any low or medium impedance load (e,g, headphones, and it really isn't going to work for cat-5...) and secondly the power dissipation in the cable itself,and therefore self heating. How friendly is boiling Indium/Gallium vapour to those inadvertently breathing it?

    1. Patrick R

      Re: Resistance is futile

      "Increase" doesn't mean it goes "from zero to something" nor that it suddenly becomes enough to boil metal surely. The end of the world was two days ago, get over it.

      1. Neil Barnes Silver badge

        Re: Resistance is futile

        @Patrick R - 'increase' means it has, like every other non-superconductor, resistance. Irrespective of what that is, there will be a voltage across that resistance if current is flowing through it (i.e. it's not driving an infinite input impedance). If the cross sectional area is reduced - which it must be if the volume remains constant and the length increases - then the resistance, which is proportional to area and inversely proportional to length, will increase.

        When the resistance increases, the power dissipated in the cable (remember P=IV?) will increase also. You might like to consider the case of a fuse blowing: it dies because it can no longer dissipate the power it is required to and it melts - this cable, which is already fluid, will simply heat until it boils. At which point you have a flexible plastic container around hot metal vapour.

        This is electronics 101. While I may have exaggerated for effect, you can guarantee that the amount of metal used will be no more than the makers can get away with, which will render it more, not less, likely to accidental overload.

    2. Vladimir Plouzhnikov

      Re: Resistance is futile + 3rd effect

      The headphones flying off your head, slamming into your hi-fi, overturning your coffee mug and scattering a pile of CDs, papers and stuff all over the room in the process...

      That of course presumes that someone would actually use the stretching effect while ignoring the highly uncomfortable feeling of the phones being constantly tugged by the elastic wire, which brings me back to the question - what is the frikkin' point?

      Also nice to know that if your insulation breaks your wires will leak out, happily seeking out and shorting any bit of electrical equipment that they can find.

      1. Bush_rat

        Re: Resistance is futile + 3rd effect

        Ignoring the statement in the article about possible applications in wearable computing, I could imagine this as a very useful temporary wire. Imagine your setting up a concert, a jack cable snaps and the replacement(which you should have anyway) is missing, whip out your elastic wire which is nice and stretchy, allowing it to fit many uses.

  4. Zobbo
    Thumb Up

    Already solved for headphones

    I bust two sets of bluetooth earbuds by killing the cables, but they do get used daily. Shure have solved this problem anyway - you can replace the cables and plug new ones into the earbuds. Maybe other companies have similar solutions too. I'm sure the stretch-armstrongness has other useful applications though.

    1. Ragarath

      Re: Already solved for headphones

      A I missing something here?

      Why are you plugging cables into "bluetooth" headsets?

      1. Zobbo

        Re: Already solved for headphones

        Because it's quite hard to fit a bluetooth transmitter and power source in an earbud. I haven't seen anyone do it yet.

        1. Ragarath

          Re: Already solved for headphones

          Ah, but in the title, he said headphones. That implies some sort of rigid connecting material in my mind.

          Though I must admit, in his post he does say buds. My post went with headphones you'll note.

        2. Anonymous Coward
          Anonymous Coward

          Re: Already solved for headphones


  5. Anonymous Coward
    Anonymous Coward

    "When the cable is stretched, the resistance increases."


    I love you looooong time.

  6. Simbu

    Xmas cynicism below...

    'Extending' (sorry) the network cable analogy, I expect margin-eeking manufacturers to sell 97cm as a metre if they use this stuff.

  7. Will Godfrey Silver badge

    Never mind headphone cables, if this resistance change is stable and repeatable the stuff might be usable for strain gauges.

  8. Richard Ball

    ...don't want to eat... ...may be toxic...

    Might as well just use mercury and be done with it.

    1. jubtastic1

      Re: ...don't want to eat... ...may be toxic...

      May I suggest Raptors, they are also stretchy, conductive and just as likely to appear in a consumer product as this witches brew.

      1. Destroy All Monsters Silver badge

        Re: ...don't want to eat... ...may be toxic...

        Clever girl!

  9. MrT

    End of an era...

    ... no more 'headphone cable too short' comedy moments. Like in 'My Big Fat Greek Wedding'. Only funnier.

    Did you know 'headphone' is a Greek word though?

    1. Destroy All Monsters Silver badge

      Re: End of an era...

      > Did you know 'headphone' is a Greek word though?

      No, but then I started analyzing the word "headphone" and the image of God pumping God's Words into the brain of a lunatic over the blower started to appear, unbidden.

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  11. Cliff

    Keep well away from aeroplanes

    As I recall gallium makes mercury look woosy when it comes to amalgamating with aluminium to ruin any strength it had. Small scratch and the gallium creeps in, and carries on into the aluminium block which will still look quite unchanged on the surface, yet be quite brittle and crushable under finger pressure!

    1. 123465789

      Re: Keep well away from aeroplanes

      Hmmm... aeroplanes ... brittle and crushable ... "no sir, that's no explosive device in my luggage, just my 100 m headphone cable."

      1. Tim Worstal

        Re: Keep well away from aeroplanes


        And there are very special rules indeed about how to package gallium for transport by plane. The old Russian method used to be a couple of ziploc style plastic bags. Which is fine in cold weather. But mid summer in hot places, well Ga melts at 27 oC. And liquid Ga spilling onto the Al alloy floor of a cargo hold. In theory it should just eat right through.

        There is a story that this happened once: no idea whether it's actually true though.

        1. Neil Barnes Silver badge

          Re: Keep well away from aeroplanes

          @Tim W

          Indeed. Not with Indium - but we've had (at work, where we run electronics way beyond their rated temperatures in high vibration environments) problems with trace contamination of bismuth. Made the chips fall right off the boards...

      2. Bush_rat

        Re: Keep well away from aeroplanes

        "Hmmm... aeroplanes ... brittle and crushable ... "no sir, that's no explosive device in my luggage, just my 100 m headphone cable.""

        My god, you would have nearly a kilometre of stretched cable, what on earth could you possibly do with that much cable!

    2. Anonymous Coward
      Anonymous Coward

      Re: Keep well away from aeroplanes

      IPhone replacement time. Jonny Ive must be working on prototypes even now.

  12. Adam Foxton

    So essentially

    Its useless for headphones if theyll ever be worn near, say, a zip? Or while in an aircraft- take a look at youtube to see what Gallium does to aluminium. Network cable would find itself rendered useless if stretched, too (differing resistive/capacitive properties would really screw with the signal properties). And you couldnt keep a bundle laying around the house because if they got hot you'd end up with heavy metal poisoning.

    I really hope this doesnt catch on...

  13. Anonymous Coward

    Too late?

    I'm guessing that wifi and wireless tech will outpace this soon enough to make it rather pointless. Except for certain specialist uses I guess.

  14. Suricou Raven

    Spiraly wire?

    Havn't telephone handsets been using coiled wire for decades to solve the same problem? Liquid metal wires might have a niche when you need to send high-current over a variable-length pathway within space contraints which prohibit the use of coiled or folded wire, but that is a very small niche. Could make a nifty distance-measuring device in robotics though.

    1. Anonymous Coward
      Anonymous Coward

      Re: Spiraly wire?

      Many years ago I helped develop a coiled audio cable. The problem with it is that it is fine when the things on each end are heavy, but not when they are light. Like ear buds...there must be enough return force to hold the thing together in the return position. What is needed is a constant force spring, but Dr Hooke and Prof Young say it wont work.

  15. Mage Silver badge

    I presume

    That this is safer than Victorian era Rubber tubing and Mercury?

    Lighter too.

    I guess it might be handy to connect something vibrating and moving?

    Speaker voice coil connections?

    Engine mounted electronics

    Cables on a Lift (elevator).

    I can't see it being useful for headphones really.

    1. Anonymous Coward
      Anonymous Coward

      Re: I presume

      Beryllium copper is your friend here.

      1. Uffish

        Re: beryllium copper

        Beryllium copper has good physical properties but nasty biological properties.

        1. Tim Worstal

          Re: beryllium copper

          BeCu, well, after it's been manufactured it's fine. The problem is in the dust (shavings, fines etc) from the manufacturing process(es).

          Be dust causes berylliosis, a nasty version of asbestosis. But Be Cu in something ain't a problem.

  16. Clive Galway
    Thumb Up

    Retractable headphones

    AFAIK, all the major manufacturers stopped making retractable headphones for your phone (The ones that wind up into a little cassette) mainly because the wires and connections inside kept snapping during the strain of winding and unwinding.

    If they could use this tech to solve that issue then I would be a very happy bunny as I loved that form-factor.

  17. Anonymous Coward
    Anonymous Coward

    Re. So essentially

    This little tip is useful, I made up some DIY removal alloy with bismuth and indium, however BiSn works fine when mixed with both tin/lead and slightly less well with tin/copper.

    Best to add a little (30%) indium for that.

    Ch*quik is essentially the same but has some other metals including possibly gallium to make it flow better.

    Liquid metal roll up piano/PC keyboards, now we are talking.

    Lets see someone break THAT! :-)

  18. Anonymous Coward
    Anonymous Coward

    8 times too fat

    If you can stretch this cable 8 * its length without degradation then why not pre-stretch it in the factory and make 8 * as much money (duh!)

    I'm sure these guys (and gals) have come up with something that is groundbreaking in its own way (and all credit to them), one-way stretchy cable isn't it.

  19. slightly-pedantic

    There's already a solution to this...?

    I believe many telephone handset leads still use a special type of wire called "tinsel" where there is a nylon fibre core wrapped in one or more helical windings of copper foil. As you stretch the wire the helix extends to give you a much longer strain before failure- massively reducing cable failures on kinks, bends and stretches.

    It seems to have gone out of fashion I suspect because:

    It has a higher resistance so isn't ideal for low impedance headphones

    It's a complete pain in manufacturing- special insulation displacement connectors are required and it's kind of tricky to solder!

  20. d3rrial

    Fluid dynamics

    Have they tried it vertically?

  21. Anonymous Coward
    Anonymous Coward

    Re. Tinsel

    Wonder if this would work if LEDs were placed inside the cores, with axial connectors?

    They might be prone to shorting out but this is a non issue as the sheer number of them makes a flexible, stretchable light source that would blow OLED out of the water.

    Just have bits of copper like they use with EL wire and sheet, so the segments can be cut up and soldered together.

    Ideal for clothing, safety applications etcetera.

  22. Peddler

    What everyone here is missing...

    Liquid metal! This is a way of distributing Terminators. The rise of the machines has begun.

  23. Stevie


    So, not just mercury in two lengths of plastic sleeving then?

  24. ckaspereli

    clearly the solution is to find a cheap plastic hybrid that is reasonably stretchable - after all if the sole application is to sell endorsements on jerseys worn by pro athletes the price doesn't have to drop too much, right?

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