With this material, the working group led by Professor Martin Wegener at KIT’s Institute of Applied Physics (APH) has overcome a limitation of metamaterials. Lead author Dr. Yi Chen compares this to human communication and an effect known from the “game of telephone”: When people communicate through a chain of intermediaries, the message the last person receives can be completely different than if the first and last people had spoken directly to each other. According to Chen, this principle also applies to metamaterials. “The material we designed has special structures (red in the illustration). With these structures, individual components no longer only ‘communicate’ via their neighbors with components further away, now they can also communicate directly with all other components of the material.” Chen said.

Experiments on 3D printed microscopic samples

“These structures give the material fascinating properties such as unusual stretching properties,” says co-author Ke Wang, also from APH. The team was able to demonstrate this with micron-sized samples of the material, which they produced using 3D laser printing technology and examined with a camera-equipped microscope. Their analysis showed that a one-dimensional (1D) beam stretched in an irregular manner when pulled from one end.

Unlike an object like a rubber band, which stretches evenly when pulled, the metamaterial actually exhibited compression in some places, with some short sections stretching more than longer sections despite the same force being applied throughout. “This unusual behavior of localized stretching and compression is impossible in conventional materials,” said Jonathan Schneider of APH, another co-author. “Now we will investigate this in two-dimensional (planar) and three-dimensional materials.”

The metamaterial is extremely sensitive to loads, which can be a potentially useful property. Depending on the point where the force is applied in the material, completely different stretching reactions can occur even at relatively distant points. According to the researchers, reactions in conventional materials are only observed directly at the point where force is applied, while only weak or negligible effects can be identified at distant locations in the material. A material with this sensitivity could be valuable for engineering applications where large-scale forces need to be measured, such as to monitor building deformations or in biological research to characterize forces in cells.

This research was supported by KIT’s 3D Matter Made to Order (3DMM2O) Cluster of Excellence and Heidelberg University.