Researchers at Rensselaer Polytechnic Institute have developed liquid pistons, which can be used to precisely pump small volumes of liquid. Comprising the pistons are droplets of nanoparticle-infused ferrofluids, which can also function as liquid lenses that vibrate at high speeds and move in and out of focus as they change shape. These liquid pistons could enable a new generation of mobile phone cameras, medical imaging equipment, implantable drug delivery devices, and possibly even implantable eye lenses. |
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, and even
implantable eye lenses.
Engineering
researchers at Rensselaer Polytechnic Institute have developed liquid
pistons, in which oscillating droplets of ferrofluid precisely displace a
surrounding liquid. The pulsating motion of the ferrofluid droplets,
which are saturated with metal nanoparticles, can be used to pump small
volumes of liquid. The study also demonstrated how droplets can function
as liquid lenses that constantly move, bringing objects into and out of
focus.
These
liquid pistons are highly tunable, scalable, and — because they lack
any solid moving parts — suffer no wear and tear. 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 ranging from micro
displacement pumps and liquid switches, to adaptive lenses and advanced
drug delivery systems.
“It
is possible to make mechanical pumps that are small enough for use in
lab-on-a-chip applications, but it’s a very complex, expensive
proposition,” said Hirsa, a professor in the Department of Mechanical,
Aerospace, and Nuclear Engineering at Rensselaer. “Our electromagnetic
liquid pistons present a new strategy for tackling the challenge of
microscale liquid pumping. Additionally, we have shown how these pistons
are well-suited for chip-level, fast-acting adaptive liquid lenses.”
Results
of the study are detailed in the paper “Electromagnetic liquid pistons
for capillarity-based pumping,” recently published online by the journal
Lab on a Chip. The paper will be featured on the cover of the journal’s
February 2011 issue, and can be read online at: http://xlink.rsc.org/?DOI=c0lc00397b
Hirsa’s
team developed a liquid piston that is comprised of two ferrofluid
droplets situated on a substrate about the size of a piece of chewing
gum. The substrate has two holes in it, each hosting one of the
droplets. The entire device is situated in a chamber filled with water.
Pulses
from an electromagnet provoke one of the ferrofluid droplets, the
driver, to vibrate back and forth. This vibration, in turn, prompts a
combination of magnetic, capillary, and inertial forces that cause the
second droplet to vibrate in an inverted pattern. The two droplets
create a piston, resonating back and forth with great speed and a
spring-like force. Researchers can finely control the strength and speed
of these vibrations by exposing the driver ferrofluid to different
magnetic fields.
In
this way, the droplets become a liquid resonator, capable of moving the
surrounding liquid back and forth from one chamber to another.
Similarly, the liquid piston can also function as a pump. The shift in
volume, as a droplet moves, can displace from the chamber an equal
volume of the surrounding liquid. Hirsa said he can envision the liquid
piston integrated into an implantable device that very accurately
releases tiny, timed doses of drugs into the body of a patient.
As
the droplets vibrate, their shape is always changing. By passing light
through these droplets, the device is transformed into a miniature
camera lens. As the droplets move back and forth, the lens automatically
changes its focal length, eliminating the usual chore of manually
focusing a camera on a specific object. The images are captured
electronically, so software can be used to edit out any unfocused
frames, leaving the user with a stream of clear, focused video.
The
speed and quality of video captured from these liquid lenses has
surpassed 30 hertz, which is about the quality of a typical computer web
cam. Liquid lenses could mean lighter camera lenses that require only a
fraction of the energy demanded by today’s digital cameras. Along with
handheld and other electronic devices, and homeland security
applications, Hirsa said this technology could even hold the key to
replacement eye lenses that can be fine-tuned using only high-powered
magnets.
“There’s
really a lot we can do with these liquid pistons. It’s an exciting new
technology with great potential, and we’re looking forward to moving the
project even further along,” he said.
Along
with Hirsa, co-authors on the paper are Rensselaer doctoral graduates
Bernard Malouin Jr., now with MIT’s Lincoln Laboratory; and Michael
Vogel, a private research consultant; Rensselaer mechanical engineering
doctoral student Joseph Olles; and former postdoctoral researcher Lili
Cheng, now with General Electric Global Research.
This study was supported with funding from the Defense Advanced Research Projects Agency (DARPA).
For more information on Hirsa’s research at Rensselaer, visit:
- Controlling Light With Sound: New Liquid Camera Lens as Simple as Water and Vibration
- http://news.rpi.edu/update.do?artcenterkey=2783
- Liquid Lenses Promise Picture-Perfect Phone Cam Photos http://www.scientificamerican.com/article.cfm?id=liquid-lens
- Low-Power Liquid Lens
- http://www.technologyreview.com/computing/21449/?a=f
