Cleardrop technology, developed and patented as part of a partnership between the start-up VISION and researchers at the IEMN, is based on the use of surface acoustic waves to clean all types of contamination (droplets, solid particles, snow, frost, mud) from optical surfaces.

Physically, ‘nano-earthquakes’ are generated by piezoelectric actuators on the surface of a substrate. These vibrations, known as Rayleigh waves, have a very low amplitude (in the picometre or nanometre range) and a very high frequency (several million vibrations per second), making them invisible to the naked eye. Their energy remains localised on the surface, allowing very efficient transmission to any liquid or solid inclusions present.

In the case of liquid inclusions, the waves propagate inside the droplet at an angle determined by Snell’s law. This radiation generates (i) an internal flow called ‘streaming’ and (ii) a force known as ‘acoustic radiation force’, which together contribute to asymmetrically deforming the droplet and inducing its displacement in the direction of wave propagation. In the case of solid particles, these are accelerated by the elliptical deformation of the surface, causing the particles to jump in the opposite direction to the wave propagation. The solid particles therefore move in the opposite direction to the propagation of the waves.

Thanks to these mechanisms, it is possible to clean any type of inclusion present on an optical surface in less than a second. Cleardrop’s work has consisted of making this technology, initially developed in the laboratory on piezoelectric substrates, functional on all types of optical surfaces.

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More informations :

Contact : michael.baudoin@univ-lille.fr