From enhancing virtual reality to controlling tiny scientific samples, dynamic rippling movement manipulates objects magnetically.

In science fiction, magnetism has been used to manipulate all manner of materials without touching them, from flying vehicle suspension to containing spheres of antimatter.

Meanwhile, a seemingly unrelated long-standing design challenge is communication through touch, a key missing technology in accessibility. There has been a growing demand for compact haptic devices that provide touch-based information like a dynamic braille display to allow the visually and hearing impaired to effectively interact with electronics.

Enter a real-life solution to the problem of influencing materials magnetically without touching them, proposed by a team of scientists at the North Carolina State University – a metamaterial that can change shape in response to magnetic fields, dynamically flexible and strong enough to bear loads.

"That seemed contradictory – how do you make something that is stiff and deformable at once?" said Jie Yin, a mechanical metamaterials researcher at North Carolina State. The team's solution features ferromagnetic elastomers, kirigami cuts, tiny balloons, and magnets.

"There is not much research on using magnets to manipulate non-magnetic objects. It is very, very hard," said Yinding Chi, fellow North Carolina State researcher and lead author of the study.

Combining old and new

The solution Chi and his colleagues came up with could be compared to a modern dynamic braille display. They visualized a surface that could form relief-like images or move in a pattern similar to ripples in the ocean. Objects could then be moved across these surfaces like being carried by those waves.

"This way, you can move various objects without using grippers," Yin said.

The key components are disks made with a ferromagnetic elastomer, a blend of standard flexible elastomeric material, and magnetic particles. These five-millimeter disks – a mere 265 microns thick – were then placed over an inflatable membrane, inflated to form a dome, magnetized, and returned to their original flat state. After this process, the disks bulge or depress in response to a magnetic field.

When bulging in a magnetic field, the initial disk design barely cleared one millimeter. The second issue was the relatively low stiffness of the elastomer, which limited the weight it could support.

Chi's team tried solving this problem using kirigami, a variation of Japanese origami, using cutting and folding techniques to form intricate three-dimensional shapes. Chi's team introduced kirigami-like patterns of cuts to their ferromagnetic elastomer disks to increase the height of the dome.

Disks with orthogonal cuts 1.5 millimeters long and 250 microns wide could reach four millimeters when exposed to the magnetic field, more than twice as high as domes without them. They could even rotate by up to one degree.

Basic equations predicted the kirigami dome design being used should have lost four times the stiffness, weakening its ability to carry loads – but the team's equations did not take into account the magnetic fields.

"We found that certain ratios of the cut's width and length, the cut's size, enable us to achieve a material that is highly compliant but also has very high stiffness when a magnetic field is applied," Yin said.

The configuration of the cuts unexpectedly enhanced an effect known as magnetically induced stiffening by more than 1.8 times, lifting 43.1 grams (28 times its own weight) to a stable height of 2.5 millimeters.

Yin's team built a five-by-five array of domes actuated by movable pillars of permanent magnets that could move left or right or spin underneath the metamaterial. The array could precisely move droplets, potato chips, a leaf, and even a small wooden plank. It could also rotate a petri dish.

Next generation haptics

The research team proposes one research application for this technology, which is the precise transport and mixing of very tiny amounts of fluids in laboratories.

However, the project's design history proposes a more widespread solution.

According to the team, the metamaterial reacts to changes in the magnetic field in under two milliseconds, making it potentially useful in haptic feedback controllers to emulate the sense of touch, texture, and feel of virtual objects.

Super-fast, magnetically actuated shape-shifting surfaces could interact with someone wearing virtual reality goggles or working with programs too complex to break down into braille.

"I'm 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 said.

However, there is a final hurdle between this material and its application in access and enhanced reality.

Comparing the metamaterial to a display where each dome stands represents a single pixel, the resolution is far too low to replicate a 72-dpi screen.

"So, there is the question how small can you make those domes," Yin said.

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 scales – that is something we focus on today. We try to pave the way but there is much more to do," Chi concluded.