Photonics Spectra - March 2011

“Liquid pistons” advance
camera lenses

TROY, N. Y. – A few unassuming drops of liquid locked in a very precise game of “follow the leader” could one day be found in mobile phone cameras, medical imaging equipment, implantable drug-delivery devices – possibly even implantable eye lenses.

Researchers at Rensselaer Polytechnic Institute have developed liquid pistons with oscillating droplets of ferrofluid that precisely displace a surrounding liquid. Saturated with metal nanoparticles, the ferrofluid droplets can be used to pump small volumes of liquid when pulsated and can function as liquid lenses that constantly move, bringing objects into and out of focus.

The liquid pistons are highly tunable, scalable and – because they lack any solid moving parts – suffer no wear and tear. As such, the researchers believe that they could be exploited to create a host of devices, ranging from microdisplacement pumps and liquid switches to adaptive lenses and advanced drug-delivery systems. The scientists’ work appears in Lab on a Chip, Vol. 11, pp. 393-397 (2011).

Researchers at Rensselaer Polytechnic Institute have developed liquid pistons composed of droplets of nanoparticle-infused ferrofluids, which function as liquid lenses that vibrate at high speeds and move in and out of focus as they change shape. The pistons could enable a new generation of mobile phone cameras, medical imaging equipment, implantable drug-delivery devices and, possibly, implantable eye lenses. Courtesy of Amir Hirsa, RPI.

Situated in a chamber filled
with water, the piston is com-
posed of two ferrofluid droplets
placed on a substrate approxi-
mately the size of a piece of
chewing gum. Its substrate fea-
tures two holes, each hosting one
droplet. Using an electromagnet,
Acting as a liquid resonator, the
droplets can move the surrounding liquid
back and forth to act as a pump. As the
droplets move, the shift in volume can dis-
place from the chamber an equal volume
of the surrounding liquid. This discovery
could be integrated into an implantable
device that could accurately release tiny,
timed doses of drugs into a patient’s body,
the scientists report.

Passing light through the droplets, when vibrating, transforms the device into a miniature camera lens. As the droplets vibrate, their shape changes, acting as a camera focus. The images are then captured electronically, and software is used to edit out any unfocused frames, leaving only clear, focused video.

Providing a lighter alternative to camera lenses, the liquid devices also could be used for homeland security applications and, possibly, replacement eye lenses that can be fine-tuned using high-powered magnets.