Wrinkled metamaterials for controlling light and sound propagation

January 28, 2014

In the top pair of images, sound waves (blue and yellow bands) passing through a flat layered material are only minimally affected. In the lower images, when sound goes through a wrinkled layered material, certain frequencies of sound are blocked and filtered out by the material. (Credit: Felice Frankel)

MIT researchers have developed flexible, layered metamaterials textured with nanoscale wrinkles that could provide a new way to control the distribution of sound or light signals, such as changing the materials’ color or making it optically or acoustically invisible.

The technology could be used for nondestructive testing of materials, new medical diagnostic tools, and sound suppression in a certain volume (location) in space rather than just a single spot, as in current noise-canceling headphones, for example.

The materials can be made through a layer-by-layer deposition process that can be controlled with high precision. The materials can then be flexibly tuned for specific frequencies in real time by changing the deformation.

The process allows the thickness of each layer to be determined to within a fraction of a wavelength of light. The material is then compressed, creating within it a series of precise wrinkles whose spacing can cause scattering of selected frequencies of sound or light.

Better ultrasound diagnosis

For example, current diagnostic techniques for certain cancers involve painful and invasive procedures. In principle, ultrasound could provide the same information noninvasively, but today’s ultrasound systems lack sufficient resolution. The new work with wrinkled materials could lead to more precise control of these ultrasound waves, and thus to systems with better resolution, says MIT postdoc Stephan Rudykh.

Rudykh is co-author  of a Physical Review Letters paper with Mary Boyce, a former professor of mechanical engineering at MIT who is now dean of the Fu Foundation School of Engineering and Applied Science at Columbia University.

The technology is being patented, and the researchers are already in discussions with companies about possible commercialization, Rudykh says.

The research was supported by the U.S. Army Research Office through the MIT Institute for Soldier Nanotechnologies.

Abstract of Physical Review Letters paper

The ability to control wave propagation in highly deformable layered media with elastic instability-induced wrinkling of interfacial layers is presented. The onset of a wrinkling instability in initially straight interfacial layers occurs when a critical compressive strain is achieved. Further compression beyond the critical strain leads to an increase in the wrinkle amplitude of the interfacial layer. This, in turn, gives rise to the formation of a system of periodic scatterers, which reflect and interfere with wave propagation. We demonstrate that the topology of wrinkling interfacial layers can be controlled by deformation and used to produce band-gaps in wave propagation and, hence, to selectively filter frequencies. Remarkably, the mechanism of frequency filtering is effective even for composites with similar or identical densities, such as polymer-polymer composites. Since the microstructure change is reversible, the mechanism can be used for tuning and controlling wave propagation by deformation.