Making waves Magnetic shape-shifting surface can move stuff without grasping it A ferromagnetic elastomer sheet can bulge and bend under magnetic influences. Jacek Krywko Dec 27, 2024 8:45 am | 6 Story textSizeSmallStandardLargeWidth *StandardWideLinksStandardOrange* Subscribers only Learn moreWhen you want to move an object from one place to another, you usually grab it with your hands or a robotic arm. But what if you want to move something you cannot touch without damaging or disrupting it, like a droplet of liquid? A solution proposed by a team of scientists at the North Carolina State University is a metamaterial that can change shape in response to magnetic fields.This material had to be easily deformable to change shape, yet at the same time stiff enough to bear loads. That seemed contradictoryhow do you make something that is stiff and deformable at once? says Jie Yin, a mechanical metamaterials researcher at NC State. His team did it with ferromagnetic elastomers, kirigami cuts, balloons, and magnets.Refreshable Braille displayThere is not much research on using magnets to manipulate non-magnetic objects. It is very, very hard, says Yinding Chi, another NC State researcher and lead author of the study. The idea Chi and his colleagues came up with could be compared to a refreshable Braille display. They imagined a surface dotted with domes that could rise, turn, or depress on demand, allowing it to dynamically form relief-like images or move in a pattern similar to waves in the ocean. Objects would then move on these surfaces like they were carried by waves. This way, you can move various objects without using grippers, Yin says.The first step needed for manufacturing elastic domes was to use disks made with a ferromagnetic elastomer, a blend of standard flexible elastomeric material and magnetic particles. These disks, 5 millimeters in diameter and 265 microns thick, were then placed over an inflatable membrane, inflated like a balloon to form a dome, magnetized, and returned to their original flat state.After this process, those disks would bulge or depress in response to a magnetic field. There were a few problems with this design, though.The first issue was that continuous disks didnt dome up high enough. When bulging in a mangetic field, they peaked at just barely over one millimeter. The second problem was the relatively low stiffness of the material the disks were made of, which limited what they could lift. As a result, the disks couldnt move anything, even when exposed to strong magnetic fields.Cut and stretchChis team tried solving this problem by cutting the disks with a laser cutter in a kirigami-like pattern.Kirigami, a variation of origami, is a Japanese art of cutting and folding paper to form intricate three-dimensional shapes that stand up from the page. Chis team expected that introducing kirigami-like cuts to their ferromagnetic elastomer disks would increase the height of the dome.Disks with orthogonal cuts 1.5 millimeters long and 250 microns wide could reach 4 millimeters when exposed to the magnetic field, more than twice as high as domes without them. They could even rotate by up to a degree.But there was a problem.Introducing cuts should significantly reduce Youngs modulus, a measure of how robust the material is under stress. To calculate the structural stiffness of a spherical shell, like a dome, you multiply its Youngs modulus by the square of its thickness and divide it by the shells radius. On paper, a kirigami dome should have been four times less stiff than a standard one and thereby worse at carrying loads. But it was way better.Magnetic magicThe reason why these predictions were off was that the equations did not take into account the magnetic fields. We found that certain ratios of the cuts width and length, the cuts size, enable us to achieve a material that is highly compliant but also has very high stiffness when a magnetic field is applied, Yin says.A kirigami design where the cuts length-to-width ratio was six was way more responsive to magnets, and that, in turn, enhanced an effect known as magnetically induced stiffening. With no magnets around, the kirigami disk was way more compliant than one without cuts. But when a magnetic field was applied, it became more than 1.8 times stiffer.Overall, the kirigami dome could lift an object weighing 43.1 grams (28 times its own weight) to a height of 2.5 millimeters and hold it there. To test what this technology could do, Yins team built a 55 array of domes actuated by movable permanent magnetic pillars placed underneath that could move left or right, or spin. The array could precisely move droplets, potato chips, a leaf, and even a small wooden plank. It could also rotate a petri dish.Next-gen hapticsThe team thinks one possible application for this technology is precise transport and mixing of very tiny amounts of fluids in research laboratories. But there is another, arguably more exciting option. Chis shape-shifting surface is very fast; it reacts to changes in the magnetic field in under 2 milliseconds, which is a response time rivaling gaming monitors.This, according to the team, makes it possible to use in haptic feedback controllers. Super-fast, magnetically actuated shape-shifting surfaces could emulate the sense of touch, texture, and feel of the objects you interact with wearing your VR goggles. Im new to haptics, but considering you can change the stiffness of our surfaces by modulating the magnetic field, this should enable us to recreate different haptic perceptions, Yin says.Before that becomes a reality, there is one more limitation the team must overcome.If you compared Yins shape-shifting surface to a display where each dome stands for a single pixel, the resolution of this display would be very low. So, there is the question how small can you make those domes, Yin says. He suggested that, with advanced manufacturing techniques, it is possible to miniaturize the domes down to around 10 microns in diameter. The challenge is how we do the actuation at such scalesthat is something we focus on today. We try to pave the way but there is much more to do, Chi adds.Science Advances, 2024. DOI: https://doi.org/10.1126/sciadv.adr8421Jacek KrywkoAssociate WriterJacek KrywkoAssociate Writer Jacek Krywko is a freelance science and technology writer who covers space exploration, artificial intelligence research, computer science, and all sorts of engineering wizardry. 6 Comments