LIQUID LENS: Researchers at Rensselaer Polytech are developing a liquid lens that uses water, sound and surface tension to adjust the focus.TROY, N.Y.—Despite their ubiquity, cell phones are not known for their ability to take picture-perfect photos. But budding "liquid lens" technology promises to change that by providing phone photogs with the autofocus capabilities lacking in today's cellular optics.
The latest advance in this area comes from Rensselaer Polytechnic Institute, here, where researchers have developed a liquid lens by placing a few drops of water into a cylindrical hole drilled in a Teflon surface and using a small speaker (that plays a high-frequency sound) to provide the resonance needed to move the water back and forth, changing the focus of the lens. Light passing through the droplets transforms them into a mini camera lens, which is capped on both sides with plastic or glass.
The experiment, led by Amir Hirsa, associate chief of graduate studies in the school's Department of Mechanical, Aerospace and Nuclear Engineering, used the liquid lens to capture 250 images per second. "The mass of the system is pushed back and forth as a result of surface tension," Hirsa says. "This adds variable focus capability to lenses that have never had it before." He and a team of researchers have been working on the project since 2004, thanks to a $400,000 grant from the National Science Foundation. The researchers describe their findings in the upcoming issue of the journal Nature Photonics.
Hirsa says the research could pave the way to a more sophisticated liquid lens that could be hooked up to a computer program that would only snap digital pictures of scenes or an object that is in focus (instead of taking a series of images in approximate focus from which a photographer can choose).
The lens is simpler than earlier liquid lens designs that use a combination of water (or some other fluid capable of conducting electricity) and oil as well as an electric charge. By using water, sound and surface tension to adjust the focus, Rensselaer researchers are hoping to develop more efficient and less expensive lenses than those made by Varioptic, S.A., in Lyon, France, although the company has a significant head start: It first demonstrated a lens in 2005 that sandwiches drops of water and oil between glass or plastic, according to PC Magazine.
Varioptic's design uses a small integrated circuit to deliver a low-voltage charge (measured in milliwatts, or thousandths of a watt) to the lens that causes the fluids to change shape. A higher current pulls the drop in on itself, creating a concave effect whereas a lower voltage makes it rounder. There are no moving parts, and the oil, which has to be of even density and temperature, helps keep the drop in shape and in place.
Varioptic earlier this year announced a partnership with Japan's Seiko Instruments USA, Inc., to begin mass producing liquid lenses by the end of 2008. In June Varioptic began working with China's Shenzhen Akkord Electronics Company, Ltd., to make the first 1.3- and 2.0-megapixel liquid lens variable-focus Web cameras. Philips Electronics in the Netherlands and the Institute of Materials Research and Engineering (IMRE) in Singapore have also developed prototype liquid lenses.
Hirsa says his team will seek more NSF funding to study the dynamics of the liquid's movement and find a way to package the lens in devices such as cell phones or Webcams without breaking it or disturbing the droplets. "If you make the inside coated with something water-resistant," he says, "the droplets would simply re-form if they were disrupted."
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