Material built from gears
A specifically designed collection of gears is soft on one end and rigid on the other. These are robust properties of the system that hold even in the presence of manufacturing imperfections. This emerging research area may lead to new ways of designing geared devices like satellite trackers or watches. Publication in Physical Review X.
Image you have two connected gear wheels. If you turn one clockwise, the other will turn counterclockwise. Now what if you connect another gear to both of them, to form a circle? The system will get stuck. Leiden physicists Anne Meeussen and Jayson Paulose now have developed a complex structure of gears that is stuck in one place, but loose in another. If you consider the whole structure as a new (meta)material, it is rigid on one end and soft on the other.
In the video below, this remarkable mechanism seems like magic, but the researchers have actually devised it from mathematics. ‘The beauty of this principle is that it’s a robust system,’ says group leader Prof. Vincenzo Vitelli. ‘We can decide which parts are soft or rigid, and the mechanism keeps working even if the gears are imperfect. This property is often called topological robustness.’
Because the rigidity properties are inherent to the system, manufacturers can use the theory to build mechanical devices like watches using cheaper components, while preserving performance. Vitelli: ‘This may be best applicable to tracking devices, like satellite trackers that are based on geared mechanisms’.
The theory is inspired by electronic topological insulators, which earned the 2016 Physics Nobel Prize. Those are insulators on the inside, but conduct electricity on their surface. And even if they have imperfections, the current will keep flowing. Instead of electronic properties, Vitelli’s group addresses rigidity. His systems are rigid in selected places and soft in others, irrespective of imperfections.
Anne S. Meeussen, Jayson Paulose, and Vincenzo Vitelli, 'Geared Topological Metamaterials with Tunable Mechanical Stability', Physical Review X