Researchers at Rensselaer Polytechnic Institute (RPI) have created an adaptive liquid lens that captures 250 pictures per second. Because these lenses are simply powered by water and sound, they need less energy to operate than competing technologies. According to the project leader, 'The lens is easy to manipulate, with very little energy, and it's almost always in focus -- no matter how close or far away it is from an object.' In fact, this new technique'could lead to smarter and lighter cameras in everything from cell phones and automobiles to autonomous robots and miniature spy planes.' Read more...
You can see on the left how this new technique works. This new process used "for creating liquid lenses with water and sound could enable a new generation of low cost, lightweight, energy efficient cameras. This series of time-lapse photos shows how the lens, made up of two droplets of water vibrating at a high speed, changes shape and, in turn, moves in and out of focus. The time between frames is four milliseconds." (Credit: Carlos Lopez, RPI) Here is a link to a larger version of this picture.
This development of this new technique has been led by Amir Hirsa, professor and associate department head for graduate studies in the Department of Mechanical, Aerospace and Nuclear Engineering at Rensselaer. Here are two links to his official web page and to his personal home page. Hirsa worked with Carlos Lopez, who earned his doctorate at Rensselaer and now works for Intel Corp.’s research and development lab in Mexico.
So how the researchers built these lenses? "The lens is made up of a pair of water droplets, which vibrate back and forth upon exposure to a high-frequency sound, and in turn change the focus of the lens. By using imaging software to automatically capture in-focus frames and discard any out of focus frames, the researchers can create streaming images from lightweight, low-cost, high-fidelity miniature cameras."
Here are additional details. "Hirsa said a key feature of his new technique is that the water stays in constant, unchanging contact with the surface, thus requiring less energy to manipulate. To do this, his new method couples two droplets of water through a cylindrical hole. When exposed to certain frequencies of sound, the device exploits inertia and water's natural surface tension and becomes an oscillator, or something akin to a small pendulum: the water droplets resonate back and forth with great speed and a spring-like force. Researchers can control the rate of these oscillations by exposing the droplets to different sound frequencies."
In fact, this doesn't look like a camera lens. But wait a minute... "By passing light through these droplets, the device is transformed into a miniature camera lens. As the water droplets move back and forth through the cylinder, the lens moves in and out of focus, depending on how close it is to the object. The images are captured electronically, and software can be used to automatically edit out any unfocused frames, leaving the user with a stream of clear, focused video. 'The great benefit of this new device is that you can create a new optical system from a liquid lens and a small speaker,' Hirsa said. 'No one has done this before.' The size of the droplets is the key to how fast they oscillate. Hirsa said that with small enough apertures and properly selected liquid volumes, he should be able to create a lens that oscillates as fast as 100,000 times per second -- and still be able to effectively capture those images.
In "Liquid Lenses Promise Picture-Perfect Phone Cam Photos," Larry Greenemeier provides additional details about the future of this new manufacturing process. (Scientific American, September 29, 2008) Here is a short excerpt. "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." [Please read a previous post, "Liquid Lenses For Camera Phones" (December 2, 2004) for additional details.]
For more information, this research work has been published in Nature Photonics under the title "Fast focusing using a pinned-contact oscillating liquid lens" (Volume 2, Number 10, Pages 610-613, October 2008). Here is the abstract. "Liquid lenses are attractive for applications in adaptive optics requiring a fast response. In conventional designs focusing time is limited by liquid inertia and the time it takes for transients in lens shape to subside. As a result, operation is confined to after the oscillations have dampened. Here we demonstrate a harmonically driven liquid lens with an oscillating focal length, which can capture any image plane in a given range by grabbing the image 'in sync' with the oscillations. By oscillating the lens, the task of changing the focal length is effectively transformed from a mechanical manipulation to the electronic timing of image capture, which can be achieved much more quickly. High-fidelity imaging is demonstrated at 100 Hz for a millimetre-scale liquid lens, which is driven at resonance and features pinned contact lines. Theoretical predictions show that a significantly faster response is possible with scaled-down lenses."
This article also made the cover story of the October 2008 issue of Nature Photonics. The scientific journal also carries an interview with Amir Hirsa. If you're not a journal subscriber, please note that an access to the article will cost you $18 while reading the interview will cost you $32. Sometimes, I'm wondering what kind of logic leads to these -- somewhat -- strange pricings.
Sources: Rensselaer Polytechnic Institute news release, September 22, 2008; and various websites
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