While our bodies are pretty amazing, their dynamic nature makes integrating circuits into our clothing a frustrating process. Squaring up against this challenge, a team of researchers from North Carolina State University have hit upon a potential boon for wearable electronics: silver nanowires capable of being printed on flexible, stretchy substrates.
It helps that the properties of silver nanowires lend themselves to the needs of wearable circuits — flexible and springy in their own right — but are not without complications. Silver nanowires tend to clog print nozzles during printing, so the research team enlarged the nozzle and suspended the nanowires in a water-soluble solvent, dramatically cutting the chance of clogging. Normally this would have a negative impact on precision, but the team employed electrostatic force to draw the ink to the desired location and maintain print resolution. Once printed, the solvent is rinsed away and the wearable circuit is ready for use.
By controlling print parameters — such as ink viscosity and concentration — the team are able to print on a wide variety of materials. Successful prototypes thus far include a glove with an integrated heating circuit and an electrocardiograph electrode, but otherwise the size of the printer is the only factor limiting the scale of the print. Until this technique becomes more widely available, interested parties might have to put their stock into more homebrew methods.
Business cards are stuck somewhere between antiquity and convenience. On one hand, we have very convenient paperless solutions for contact swapping including Bluetooth, NFC, and just saying, “Hey, put your number into my phone, please.” On the other hand, holding something from another person is a more personal and memorable exchange. I would liken this to the difference between an eBook and a paperback. One is supremely convenient while the other is tactile. There’s a reason business cards have survived longer than the Rolodex.
Protocols and culture surrounding the exchange of cards are meant to make yourself memorable and a card which is easy to associate with you can work long after you’ve given your card away. This may seem moot if you are assigned cards when you start a new job, but personal business cards are invaluable for meeting people outside of work and you are the one to decide how wild or creative to make them.
Here’s some interesting work shared by [Ben Kromhout] and [Lukas Lambrichts] on making flexible 3D prints, but not by using flexible filament. After seeing a project where a sheet of plywood was rendered pliable by cutting a pattern out of it – essentially turning the material into a giant kerf bend – they got interested in whether one could 3D print such a thing directly.
The original project used plywood and a laser cutter and went through many iterations before settling on a rectangular spiral pattern. The results were striking, but the details regarding why the chosen pattern was best were unclear. [Ben] and [Lukas] were interested not just in whether a 3D printer could be used to get a similar result, but also wanted to find out what factors separated success from failure when doing so.
After converting the original project’s rectangular spiral pattern into a 3D model, a quick proof-of-concept showed that three things influenced the flexibility of the end result: the scale of the pattern, the size of the open spaces, and the thickness of the print itself. Early results indicated that the size of the open spaces between the solid elements of the pattern was one of the most important factors; the larger the spacing the better the flexibility. A smaller and denser pattern also helps flexibility, but when 3D printing there is a limit to how small features can be made. If the scale of the pattern is reduced too much, open spaces tend to bridge which is counter-productive.
Kerf bending with laser-cut materials gets some clever results, and it’s interesting to see evidence that the method could cross over to 3D printing, at least in concept.
Whether it’s wheels, tracks, feet, or even a roly-poly body like BB-8, most robots have to deal with an essential problem: dirt and grit can get into the moving bits and cause problems. Some researchers from UCSD have come up with a clever way around this: pneumatically actuated soft-legged robots that adapt to rough terrain.
At a top speed of 20 mm per second, [Michael Tolley]’s squishy little robot won’t set any land speed records. But for applications like search and rescue or placing sensors in inhospitable or inaccessible locations, slow and steady might just win the race. The quadrupedal robot’s running gear can be completely 3D-printed on any commercial printer capable of using a soft filament. The legs each contain three parallel air chambers within a bellowed outer skin; alternating how the chambers are inflated controls how they move. The soft legs adapt to unstructured terrain and are completely sealed, eliminating intrusion problems. The video below shows how the bot gets around just fine over rocks and sand.
The legs remind us a little of our [Joshua Vazquez]’s tentacle mechanism, but with fewer parts. Right now, the soft robot is tethered to its air supply, but the team is working on a miniaturized pump to make the whole thing mobile. At which point we bet it’ll even be able to swim.
Electronic components are getting smaller and smaller, but the printed circuit boards we usually mount them on haven’t changed much. Stiff glass-epoxy boards can be a limiting factor in designing for environments where flexibility is a requirement, but a new elastic substrate with stretchable conductive traces might be a game changer for wearable and even implantable circuits.
Researchers at the Center for Neuroprosthetics at the École Polytechnique Fédérale de Lausanne are in the business of engineering the interface between electronics and the human nervous system, and so have to overcome the mismatch between the hardware and wetware. To that end, [Prof. Dr. Stéphanie P. Lacour]’s lab has developed a way to apply a liquid metal to polymer substrates, with the resulting traces capable of stretching up to four times in length without cracking or breaking. They describe the metal as a partially liquid and partially solid alloy of gallium, with a gold added to prevent the alloy from beading up on the substrate. The applications are endless – wearable circuits, sensors, implantable electrostimulation, even microactuators.
University of Wisconsin-Madison is doing some really cool stuff with phototransistors. This is one of those developments that will subtly improve all our devices. Phototransistors are ubiquitous in our lives. It’s near impossible to walk anywhere without one collecting some of your photons.
The first obvious advantage of a flexible grid of phototransistors is the ability to fit the sensor array to any desired shape. For example, in a digital camera the optics are designed to focus a “round” picture on a flat sensor. If we had a curved surface, we could capture more light without having to choose between discarding light, compensating with software, or suffering the various optical distortions.
Another advantage of the University’s new manufacturing approach is the “flip-transfer” construction method they came up with. They propound that their method produces a vastly more sensitive device. The sensing silicon sits on the front of the assembly without any obstructing material in front; also the metal substrate it was built on before flipping is reflective; also increasing the sensitivity.
All in all very cool, and we can’t wait for phone cameras, with super flat lenses, infinite focus, have no low light capture issues, and all the other cool stuff coming out of the labs these days.
Still working with PCBs in 2D? Not [Yoav]. With some clever twists on the way we fab PCBs, he’s managed to create a state-aware foldable circuit board that responds to different configurations.
From his paper [PDF warning], [Yoav] discusses two techniques for developing foldable circuits that may be used repeatedly. The first method involves printing the circuit onto a flexible circuit board material and then bound front-and-back between two sheets of acrylic. Valid folded edges are distinguished by the edges of individual acrylic pieces. The second method involves laying out circuits manually via conductive copper tape and then exposing pads to determine an open or closed state.
Reconfigurable foldable objects may open the door for many creative avenues; in the video (after the break), [Yoav] demonstrates the project’s state-awareness with a simple onscreen rendering that echoes its physical counterpart.
While these circuits are fabbed from a custom solution, not FR1 or FR4, don’t let that note hold your imagination back. In fact, If you’re interested with using PCB FR4 as a structural element, check out [Voja’s] comprehensive guide on the subject.