If you think polyimide-based flexible PCBs are cool, wait until you get a load of what polymerized liquid metal networks can do.
Seems like [CNLohr] has some pretty cool friends, and he recently spent some time with a couple of them who are working with poly LMNs and finding out what they’re good for. Poly LMNs use a liquid metal composed of indium and gallium that can be sprayed onto a substrate through a laser-cut stencil. This results in traces that show the opposite of expected behavior; where most conductors increase in resistance when stretched, pol LMNs stay just as conductive no matter how much they’re stretched.
The video below shows [CNLohr]’s experiments with the stuff. He brought a couple of traditional PCB-based MCU circuits, which interface easily with the poly LMN traces on a thick tape substrate. Once activated by stretching, which forms the networks between the liquid metal globules, the traces act much like copper traces. Attaching SMD components is as simple as sticking them to the tape — no soldering required. The circuits remain impressively stretchy without any apparent effect on their electrical properties — a characteristic that should prove interesting for wearables circuits, biological sensors, and a host of real-world applications.
While poly LMNs aren’t exactly ready for the market yet, they don’t seem terribly difficult to make, requiring little in the way of exotic materials or specialized lab equipment. We’d love to see someone like [Ben Krasnow] pick this up and run with it — it seems right up his alley.
How many times does it survive being stretched? If it lasts it might be a good position sensor in a body suit or glove.
There was a chart in the video @4:17 that highlighted a 10,000 stress cycle
In one of the graph for resistance, it’s been tested up to 8000 times (so I guess it wasn’t failing meanwhile).
weird flex, but ok
This is how you get truly comfortable wearables.
I can see this being a great option for synthetic on a robot hand. I was working on a layered skin a few years back. I used that easy peal rubbery glue that’s usually used for magazine inserts and spam from your bank. It has the nice ability to self heal when cut and it’s more or less transparent. I used a reflective sheet, followed by a black liquid jelly, then a layer of the glue, embedded a load of smd LEDs and sensors into it and then I sealed it up with clingfilm. I coated the LEDs in black nail varnish then made a pinprick hole in the top to narrow the beam, I did similar with the sensors but left the top un painted. I considered a tinfoil layer to sense “pain” but touch seemed like enough. Upon prodding the surface the black jelly was displaced and the light would be able to reach the sensors proportionate to the depth of the prodding, position was read by reading the sensors as a matrix and resolution was increased by only turning on some of the LEDs at any one time, in the end I opted for some analogue switch ICs, a couple of decoders to select them and counters to drive them. I had issues with creasing so I added some of those little plastic bathroom tile separator crosses. This is where a 3D printer might have come in handy at the time, printing aa semi flexible shell would have been an easier option.
Cutting a long story short, it didn’t go to plan, it was too heavy, time consuming to build on a large enough scale and the output wasn’t all that consistent, but it was a fun experiment, I might even revisit it one day.
that gives a whole new meaning to the term flexible circuit.
I would be suggesting painting PCBs with the stuff accept activation requires mechanical strain to be added to the material. Obviously a bit more difficult with inflexible substrates. :D Then their would be the cost. Indium is more common than silver but still not exactly cheap. Copper is more common (and conductive), it is unlikely they could (or would want to) use copper as it tends to be extremely toxic at those sizes. (Then their is the thermal properties of copper.)
is that just Alien tape with the liquid metal solder stuff (VHB and LMS)?? Damn, I can make this at home…
Can’t wait to see your results.