Metamaterial with a twist

While most elastic materials distort when under pressure, the metamaterial of the Karlsruhe Institute of Technology and others, twists. This unusual property is down to the special structure of this material.

Although metamaterial was originally designed to create the weirdest effects with light refraction, the material, built up of microstructures, also turns out to have extraordinary mechanical properties.

Engineers from the Karlsruhe Institute for Technology and the French National Centre for Scientific Research have now developed an elastic material that rotates if you press it down: the motion in one direction is converted to rotation perpendicular to the first (read the press release on the metamaterial). That's impossible with traditional elastic material.

CIRCLE IN THE CUBE

The extraordinary property is down to the structure of the microcells from which the material is constructed. They are open structures in which the ribs do not run from top to bottom, but transition into a circle (see figure). Pressing the rib down results in a torsional force on the circle that causes the bottom of the microcell to rotate.

The microcells are made of elastic plastic using a 3D microprinter, which produces cells of varying sizes, ranging from between 24 µm and 120 µm.

To test the rotation of the material, two pieces of metamaterial were placed on each other: one rotating left and the other right. The resulting total rotation is zero, so that the metamaterials at the top and bottom do not rotate.

Rotation was greatest for large cells, but this material is also the weakest. The opposite is true for small cells. Ultimately, the desired combination between stiffness and twistability determines which cell size is to be selected.

Opening image: the rotating metamaterial with varying cell sizes.