Metasurfaces make ultrasounds do the twist

Engineering

Acoustic metasurfaces are very thin materials capable of shaping sound wavefronts. A team of researchers from the CNRS, Bordeaux INP and the University of Bordeaux1 have developed a new generation of these surfaces which can deviate, focus and even ‘twist’ ultrasound waves, using a porous, silicone-based elastomer which is more flexible and easier to shape than existing metasurfaces. Because the speed of sound slows significantly in relation to the porosity of these materials, wave propagation speed gradients can be created by modifying porosity locally. These porous metasurfaces also function in water and across a wide bandwidth. Flat, simple to use and cost-effective, these acoustic lenses create new possibilities in medical imaging by focusing ultrasounds. They can also generate acoustic vortex beams which act like ‘tweezers’ and can be used to manipulate small objects such as biological cells remotely. These findings appear in the 11 January 2019 edition of Nature Communications.

metasurfaces used by the researchers
Metasurfaces used by researchers act as flat acoustic lenses for ultrasound waves generator (on the left of the picture). In the centre, the metasurface is divided into concentric circles, the porosity of which increases from the outside in to generate a spherical wavefront. On the right, the metasurface is divided into several quarters of the same size, with porosity increasing in a clock-wise manner. The resulting wavefront is helical in shape.
© Thomas Brunet

 

  • 1. Institut de mécanique d’ingénierie de Bordeaux (CNRS/University of Bordeaux/Bordeaux INP/Arts and Métiers ParisTech) and the Centre de Recherche Paul Pascal (CNRS/University of Bordeaux)
Bibliography

Flat acoustics with soft gradient-index metasurfaces. Yabin Jin, Raj Kumar, Olivier Poncelet, Olivier Mondain-Monval & Thomas Brunet. Nature Communications, January 11, 2019. DOI : 10.1038/s41467-018-07990-5

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