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Liquid lens achieves proper focus with aid of microfluidic pistons

Posted: 17 Jan 2011 ?? ?Print Version ?Bookmark and Share

Keywords:liquid lens? electromagnetic liquid lens? microfluidic pistons?

While immersion lithography now uses liquid lenses to improve resolution, air droplets still need to be manually adjusted to achieve proper focus. Keen on addressing this challenge, Rensselaer Polytechnic Institute (RPI) has developed a liquid lens with a focal length that can be electrically adjusted with tiny microfluidic pistons with no moving parts. According to the company, this electromagnetic liquid lens could benefit all types of precision imaging applications including immersion lithography, implantable retinas and ultra-low power cameras on cell phones.

RPI's technique, developed by professor Amir Hirsa, uses fluids saturated with iron nanoparticles. By carefully oscillating a ferro-fluidic droplet with a magnetic field, the fluids inside can be pumped up-and-down like a piston, allowing the focal length of a lens to be adjusted using even less energy than MEMS does. Because the fields that are generated use alternating currents, the lens is constantly cycling between its closest and furthest focal lengths. But the researchers say that software algorithms can easily eliminate any out-of-focus frames. In demonstrations, the researchers were able to capture in-focus 30fps videos as a proof of concept.

The demonstration set-up housed an opaque ferro-fluidic droplet�the piston�in one hole drilled next to another holding the transparent lens droplet in a solid substrate separating two sealed chambers filled with water. Electromagnetic pulses then forced the piston droplet to vibrate up and down in its hole. Magnetic, capillary and inertial forces combined to cause the second droplet�the lens�to follow the movement of the piston droplet, setting it to oscillating between its maximum and minimum focal lengths.

Hirsa's collaborators on the project included MIT Lincoln Lab researcher Bernard Malouin, Michael Vogel, a private research consultant, RPI doctoral candidate Joseph Olles, and former post-doctoral researcher Lili Cheng, now at General Electric Global Research. Funding was provided by the Defense Advanced Research Projects Agency.

R. Colin Johnson
EE Times

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