Researchers at Rensselear Polytechnic Institute have developed "liquid pistons" that could be suited to a variety of applications. Using electromagnets the liquid pistons, which are highly tunable, scalable and have no solid moving parts, can function as pumps for lab-on-a-chip systems or could be used for adaptive lenses in future mobile phone cameras and implantable lenses.

The device consists of two drops of ferrofluid liquid, which are saturated with metal nanoparticles, situated in two holes in a substrate about the size of a piece of chewing gum. The entire device is situated in a chamber filled with water and pulses from an electromagnet are used to make one of the droplets – the driver – vibrate back and forth.

Get things pumpin'

This vibration, through a combination of magnetic, capillary and inertial forces, causes the second droplet to vibrate in an inverted pattern to the first, thereby creating a piston that resonates back and forth with great speed and a spring-like force. By exposing the driver ferrofluid droplet to different magnetic fields, the researchers are able to finely control the strength and speed of these vibrations.

This piston motion allows the droplets to act as a liquid resonator, capable of moving the surrounding liquid back and forth from one chamber to another. Also, by displacing an equal volume of the surrounding liquid from the chamber, the liquid piston also acts as a pump.

The research team, led by Rensselaer Professor Amir H. Hirsa, is confident this new discovery can be exploited to create a host of new devices such as micro displacement pumps, liquid switches and advanced drug delivery systems.

Liquid lenses

The researchers also discovered that, because the droplets shape is always changing as they vibrate, they could be transformed into a miniature camera lens by passing light through them. As the droplets move back and forth, the lens automatically changes its focal length.

The team says that by capturing the images electronically and using software to edit out any unfocused frames, it is possible to produce a stream of clear, focused video. So far the speed and quality of the video the researchers have captured from these liquid lenses has surpassed 30 Hz.

The researchers say that aside from camera lenses, the technology could even hold the key to replacement eye lenses that can be fine-tuned using only high-powered magnets.

While such liquid lenses promise lighter camera lenses that require only a fraction of the energy demanded by today’s digital cameras, Philips unveiled a liquid lens back in 2004 and we’re still waiting for the technology to appear on consumer devices. Although Samsung’s patent filing for a liquid zoom lens last year could hint that the liquid lens is a technology that is soon to realize its potential.

The Rensselaer team’s research is detailed in a paper published online by the journal Lab on a Chip.

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