NC State Researchers Show Magnets Can Transform Random Metamaterial Snapping Into Ordered Sequences
A team led by North Carolina State University has demonstrated that magnetizing patterned elastic polymer sheets turns their chaotic snapping behavior into repeatable, sequential unfolding, boosting kinetic energy absorption by 30 percent.
Researchers at North Carolina State University have demonstrated that magnetizing elastic polymer sheets with geometric cut patterns can transform their random snapping behavior into controlled, sequential unfolding. The finding, published March 20 in Science Advances, opens potential applications in shock absorption, reconfigurable robotics, and biomedical devices.
The study was led by Haoze Sun, a Ph.D. student at NC State, and Jie Yin, a professor of mechanical and aerospace engineering, with collaborators from Syracuse University and the Helmholtz-Zentrum Dresden-Rossendorf laboratory in Germany.
From Chaos to Order
Metamaterials are engineered structures whose properties arise from their physical architecture rather than their chemical composition. In this case, the researchers cut T-shaped patterns into polymer sheets, creating a material that extends into a mesh-like form when pulled. Without magnetization, all the cuts pop open simultaneously in an unpredictable manner.
When the team incorporated magnetic materials into the sheets and magnetized them, the behavior changed fundamentally. Instead of snapping open all at once, the rows opened one at a time. According to Yin, this sequential action occurs because the magnetic force tries to hold the pieces of the sheet together while gravity pulls them apart, creating a tug-of-war that forces the rows to open in sequence rather than simultaneously.
The researchers also found that small, unavoidable defects in each individual sheet determined the specific order in which rows snapped open. Because those defects remain constant, the sequence is repeatable for any given sheet.
Achieving 90 Percent Repeatability
To further reduce randomness, the team paired two magnetized sheets back-to-back with their magnetic fields oriented to repel each other. This configuration produced ordered top-to-bottom snapping 90 percent of the time, a marked improvement over the essentially random behavior observed in unmagnetized samples.
Yin noted that the team can “drastically reduce randomness in that behavior by aligning these metamaterials properly,” pointing to the potential for engineering highly predictable mechanical responses into soft materials.
Energy Absorption Gains
Beyond controlling the sequence of deformation, the magnetized metamaterials demonstrated a practical advantage in energy dissipation. The team found that magnetized sheets absorbed 30 percent more kinetic energy than their unmagnetized counterparts. In a demonstration, a ball dropped onto unmagnetized material bounced off, while the same ball came to rest on the magnetized version.
The amount of energy absorbed can be tuned by adjusting the strength of the internal magnetic attraction. Stronger magnetism enables the metamaterial to absorb more energy, offering a degree of control that could prove valuable in designing adaptive protective equipment or impact-dampening systems.
Potential Applications
The researchers identified several areas where magnetically controlled sequential snapping could find use. In wave propagation, the ordered unfolding could serve as a mechanism for guiding mechanical waves through a structure in a predetermined direction. In soft robotics, programmable deformation sequences could enable more sophisticated locomotion or manipulation strategies. Biomedical applications, such as devices that need to deploy in a controlled sequence inside the body, represent another potential direction.
The study was co-authored by Yinding Chi and Haitao Qing, both NC State Ph.D. graduates now at the University of Pennsylvania and UC Berkeley respectively; Gabriel Alkuino and Teng Zhang of Syracuse University; and Yevhen Zabila and Denys Makarov of Helmholtz-Zentrum Dresden-Rossendorf. The work was funded by the National Science Foundation, the European Union’s REGO project, and the European Research Council.