Rensselaer Polytechnic has developed a liquid lens that reduces focussing from precision movement to software processing.

"The lens is easy to manipulate, with very little energy, and it's almost always in focus - no matter how close or far away it is from an object," said project leader Professor Amir Hirsa. "There is no need for high voltages or other exotic activation mechanisms, which means this lens may be used and integrated into any number of different applications and devices."

The lens is two coupled droplets of water in a cylindrical hole.

By choosing the right frequency, the droplets can be resonated by acoustic vibrations. "Researchers can control the rate of these oscillations by exposing the droplets to different sound frequencies," said the university.

The lens focuses at different distances as the water droplets move back and forth through the cylinder so it effectively scans through the depth of field each cycle of sound wave.

The images are captured electronically, with software editing out any unfocused frames, said Rensselaer, leaving the user with a stream of clear, focused video.

"The great benefit of this new device is that you can create a new optical system from a liquid lens and a small speaker," Hirsa said. "No one has done this before."

The size of the droplets is the key to how fast they oscillate - the prototype captures 250 pictures per second. Hirsa said that with small enough apertures and properly selected liquid volumes, he should be able to create a lens that oscillates at 100kHz, and still be able to effectively capture images.

Most current methods for focussing liquid lenses, said Rensselaer, involve changing the size and shape of the area where the liquid contacts a surface. "This takes both time and valuable energy."

Hirsa said a key feature of his technique is that the water stays in constant, unchanging contact with the surface, thus requiring less energy to manipulate.

He anticipates interest in his device from phone manufacturers, and also envisions small, lightweight, liquid lens cameras being integrated into micro air vehicles.

Results of the study are to be detailed in the paper "Fast focusing using a pinned-contact oscillating liquid lens" in the journal Nature Photonics.

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