Flexible materials to manipulate sound and light

Flexible, layered materials textured with nanoscale wrinkles could be used to control the wavelengths and distribution of waves of sound and light. Researchers at the Massachusetts Institute of Technology (MIT) in the US say the technique could have numerous applications from non-destructive testing (NDT) to sound suppression.

While materials' properties are known to affect the propagation of light and sound, in most cases these are fixed. However, MIT's wrinkled layered materials have changing properties that enable an element of 'tuning' to a material that filters out specific colours of light or frequencies of sound.

"These effects are highly tuneable, reversible, and controllable," says MIT researcher, Stephan Rudykh. "For example, we could change the colour of the material, or potentially make it optically or acoustically invisible."

The materials are made using a layer-by-layer deposition process, which is precisely controlled to allow 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 that cause scattering of selected frequencies of either sound or light waves. These effects can even work in materials where the alternating layers have almost identical densities.

Rudykh says: "We can use polymers with very similar densities and still get the effect. How waves propagate through a material, or not, depends on the microstructure, which we can control.
"If you know you want to control a particular range of frequencies, you can design it that way."

MIT's work with wrinkled materials could lead to more precise control of ultrasound waves to produce better imaging resolution potentially meaning more effective, and less invasive, diagnosis of cancer. It could also be used for sound cloaking, an advanced form of noise cancellation.

The technology is now being patented, and the researchers are already in discussions with companies about commercialisation.

Justin Cunningham

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