A Ben-Gurion graduate who is on post at MIT has discovered a new way to affect wave propagation

Tuning the wavelength, optical, elastic or acoustic, can mask or change the color of physical materials

A graduate of Ben Gurion University of the Negev, Dr. Stefan Roddick, discovered a new way to manipulate wave propagation to change the properties of physical materials on demand.

Roddick, who is in his postdoctoral studies at MIT, received his doctorate in mechanical engineering from Ben-Gurion University of the Negev in 2012, in the laboratory of Prof. Gal de Botton. The discovery was recently published in the peer-reviewed journal Physical Review Letters.

Waves (optical, elastic or acoustic) propagate in different ways in different materials. The different scattering creates effects such as different colors, transparency and sound absorption or even more 'exotic' effects, such as acoustic and optical camouflage. Traditionally, once these structures have been created in nature or manufactured in a laboratory, it is difficult to change these properties.

Dr. Roddick and his laboratory team focus their research on ways to change the propagation of waves and thereby influence the properties of the given material according to demand. The research examines the most convenient way for the manufacturer to influence the properties of a given material. Because recent advances in "layer-by-layer" production make it possible to produce complex materials with sub-wavelength resolution of the layers' thickness. This resolution makes it possible to create structures to change the spread of visible light.

"In some ways, these layered structures are very simple and in others they are not simple at all. For example, when the material is compressed, the stiffer phase collapses (due to so-called elastic instability) and forms the crumpled shapes of rigid layers. In this way we create an orderly structure on a very small scale. These complex micro-structures serve as a system that disperses and interferes with the propagation of the waves," Dr. Roddick explains. Indeed, this controlled microstructure is significantly richer than simple straight layers and these materials create interesting effects. In particular, we can actively filter out unwanted frequencies of elastic waves, and this phenomenon can be used to design noise-cancelling materials.

These effects are very available for tuning, reversible and controlled - and as a result of the properties of the material they can be changed proactively. For example, the researchers could change the material's color, or perhaps even become optically or acoustically invisible.

In addition, the present study is an important step towards understanding wave propagation in a soft environment, which may potentially improve non-invasive diagnostic techniques in biomedical applications. Nature sometimes designs materials that are not completely stable, and wrinkled and collapsing forms are very common in biological tissues. This is the reason why it is extremely important to understand the properties of these soft materials, which are so easy to change their shape.