Electrowetting Creates the Miniature Liquid Lens
It is easy to miniaturize cellphones and hand-held computers that have built-in cameras, but to get these cameras to focus and zoom requires tiny moving parts that are costly and wear out quickly from friction. As a result of this cost factor, most miniature cameras have a fixed-focus glass or plastic lens. A new experimental liquid lens, however, can change its shape and thereby its focus through the low cost of a very small electronic charge. Instead of numerous small parts, all it needs is a tiny battery to produce a near zero charge to change its focal length.
Electrowetting is the process whereby the liquid lens changes the curvature of its surface to form a flexible lens.
A lens is a device, usually made of glass or plastic, for either concentrating or diverging rays of light. It is usually formed from a piece of shaped glass or plastic, but other substances have been used to form lenses. Magnifying glasses, eyeglasses, contact lenses, microscopes, telescopes and cameras are just some of the many objects that require the use of lenses.
The lens has two curved surfaces. The type of curvature of its surfaces will determine the kind of jobs it does. Like a prism, a lens works by refracting or bending the light that passes through it.
Lens are classified by the curvature of these two surfaces. A convex lens bulges out from its center, A concave lens bulges inward towards its center. A flat surface is caled a plano lens. If the curvatures of both surfaces are equal it is a meniscus lens
The kind of lens used determines the distance necessary to bring the object into focus. That distance is called its focal length which is determined its refractive index.
The value of the focal length f for a particular lens can be calculated from a lensmaker's equation.
The focal length f is positive for converging lenses (convex), negative for diverging lenses (concave), and infinite for meniscus lenses. The value 1/f is known as the power of the lens. Since meniscus lenses are equal on both surfaces they neither magnify nor diminish the object.
Philips Research has developed a liquid lens for a miniature camera through the use of a process known as electrowetting, that is the passing of an electric current over the surface of two fluid bodies.
As an experimental laboratory process, electrowetting (applying an electrical current to fluid surfaces) has been studied as a curiosity for about forty years. Even before formal experiments were conducted on electrowetting, scientists were concerned about what happens when two opposite forces such as electricity and water were combined. People are warned not to go swimming when it is raining because lightning hitting the water could electrocute them. Benjamin Franklin discovered electricity with his kite and key but took precautions to avoid the rain when he made those tests. He chose a cloudy, not rainy day. The major effect of water on an electric current is to short circuit it, but that problem is overcome in electrowetting experiments mainly by using very small amounts of fluids in mixtures.
Electrowetting is a process that controls the way a nonmixable fluid mixture changes its surface tension. The effect of passing an electric current across the surface of a fluid mixture that contains a water solvent fluid at one end and a hydrophobic fluid (non-water combing fluid) that has difficulty mixing with water at the other end, like oil, is to change the surface tension where the two fluids meet (its meniscus) from convex to concave.
This effect takes place because the electric current reduces the hydrophobia (water aversion) of the nonwater mixing fluid. The surface tension of the meniscus (point where the two fluids meet, changes from convex, plano, to concave thus altering the focal length of the object. The miniature camera can now zoom in and out of objects.
[Without the electrical charge, the surface of the liquid would always be a fixed convex curve. When the charge is applied through the electrodes, however, the reduced surface tension forces the droplet lens to undergo quick changes from a convex to a flat and to a concave lens depending on the amount of current which is passed through the fluids.]
The above bracketed lines could be the text for a captioned diagram.)
[Amy: Here if possible there are several diagrams showing the two tubes of Philips' FluidFocus lens with the fluids in them to explain how the electric current changes the shape of the fluid lens.]
Philips liquid lens takes up hardly any electric battery power. It is extremely fast in switching its focus to a wide range of focal lengths. The durability of the lens is also very high. Philips tested it over a million operations without any loss of its optical power. It is shock resistant and can operate over a wide temperature range. The absence of moving mechanical parts eliminates friction and cost consuming wear and tear problems that smaller cameras have.
It will be interesting for the commercial future of the liquid lens to see the outcome of the patent claims made by another company, Varioptics, against Philips' decision to present its liquid lens. Varioptics contests Philips' development of the liquid lens by announcing its international patents on a single-element focusing lens. They claim that since the 1940s their optical engineers have been working on a lens that could focus without moving parts and that they already hold patents for a liquid lens that changes it shape from convex to concave using the process of electrowetting.
Electrowetting is also being used to develop a new video display technology. Using what is called "electronic paper" the process of electrowetting (applying electrical charges to fluid surfaces) can be used to form a video display that may some day be used for computer video monitors. As in the case of using electrowetting for the liquid lens, Royal Philips Electronics is at the forefront of using electrowetting for developing electronic paper.
The liquid lens may only be a year or so away from the market, but the idea of electronic paper video displays is believed to be at least five years from a usable product form.
Even so, Peter Kurstjens, general manager of Electronic Ink Displays at Philips points out that, "while the amount of information that we digitally process ever increases, more printers are sold each year. This contrast goes to show we still prefer reading from paper rather than from electronic displays,"
Printing and paper distribution are the mostly costly parts of information distribution. If it were as easy to read monitor displays as it is to read a paper book the cost savings of information retrieval could be enormous. Reading from a video display is difficult because it reflects light unlike paper's absorption of light. Despite all the technological hurdles ahead of e-paper, (electronic paper) large companies see the economical potential of e-paper displays.
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It is easy to miniaturize cellphones and hand-held computers that have built-in cameras, but to get these cameras to focus and zoom requires tiny moving parts that are costly and wear out quickly from friction. As a result of this cost factor, most miniature cameras have a fixed-focus glass or plastic lens. A new experimental liquid lens, however, can change its shape and thereby its focus through the low cost of a very small electronic charge. Instead of numerous small parts, all it needs is a tiny battery to produce a near zero charge to change its focal length.
Electrowetting is the process whereby the liquid lens changes the curvature of its surface to form a flexible lens.
A lens is a device, usually made of glass or plastic, for either concentrating or diverging rays of light. It is usually formed from a piece of shaped glass or plastic, but other substances have been used to form lenses. Magnifying glasses, eyeglasses, contact lenses, microscopes, telescopes and cameras are just some of the many objects that require the use of lenses.
The lens has two curved surfaces. The type of curvature of its surfaces will determine the kind of jobs it does. Like a prism, a lens works by refracting or bending the light that passes through it.
Lens are classified by the curvature of these two surfaces. A convex lens bulges out from its center, A concave lens bulges inward towards its center. A flat surface is caled a plano lens. If the curvatures of both surfaces are equal it is a meniscus lens
The kind of lens used determines the distance necessary to bring the object into focus. That distance is called its focal length which is determined its refractive index.
The value of the focal length f for a particular lens can be calculated from a lensmaker's equation.
The focal length f is positive for converging lenses (convex), negative for diverging lenses (concave), and infinite for meniscus lenses. The value 1/f is known as the power of the lens. Since meniscus lenses are equal on both surfaces they neither magnify nor diminish the object.
Philips Research has developed a liquid lens for a miniature camera through the use of a process known as electrowetting, that is the passing of an electric current over the surface of two fluid bodies.
As an experimental laboratory process, electrowetting (applying an electrical current to fluid surfaces) has been studied as a curiosity for about forty years. Even before formal experiments were conducted on electrowetting, scientists were concerned about what happens when two opposite forces such as electricity and water were combined. People are warned not to go swimming when it is raining because lightning hitting the water could electrocute them. Benjamin Franklin discovered electricity with his kite and key but took precautions to avoid the rain when he made those tests. He chose a cloudy, not rainy day. The major effect of water on an electric current is to short circuit it, but that problem is overcome in electrowetting experiments mainly by using very small amounts of fluids in mixtures.
Electrowetting is a process that controls the way a nonmixable fluid mixture changes its surface tension. The effect of passing an electric current across the surface of a fluid mixture that contains a water solvent fluid at one end and a hydrophobic fluid (non-water combing fluid) that has difficulty mixing with water at the other end, like oil, is to change the surface tension where the two fluids meet (its meniscus) from convex to concave.
This effect takes place because the electric current reduces the hydrophobia (water aversion) of the nonwater mixing fluid. The surface tension of the meniscus (point where the two fluids meet, changes from convex, plano, to concave thus altering the focal length of the object. The miniature camera can now zoom in and out of objects.
[Without the electrical charge, the surface of the liquid would always be a fixed convex curve. When the charge is applied through the electrodes, however, the reduced surface tension forces the droplet lens to undergo quick changes from a convex to a flat and to a concave lens depending on the amount of current which is passed through the fluids.]
The above bracketed lines could be the text for a captioned diagram.)
[Amy: Here if possible there are several diagrams showing the two tubes of Philips' FluidFocus lens with the fluids in them to explain how the electric current changes the shape of the fluid lens.]
Philips liquid lens takes up hardly any electric battery power. It is extremely fast in switching its focus to a wide range of focal lengths. The durability of the lens is also very high. Philips tested it over a million operations without any loss of its optical power. It is shock resistant and can operate over a wide temperature range. The absence of moving mechanical parts eliminates friction and cost consuming wear and tear problems that smaller cameras have.
It will be interesting for the commercial future of the liquid lens to see the outcome of the patent claims made by another company, Varioptics, against Philips' decision to present its liquid lens. Varioptics contests Philips' development of the liquid lens by announcing its international patents on a single-element focusing lens. They claim that since the 1940s their optical engineers have been working on a lens that could focus without moving parts and that they already hold patents for a liquid lens that changes it shape from convex to concave using the process of electrowetting.
Electrowetting is also being used to develop a new video display technology. Using what is called "electronic paper" the process of electrowetting (applying electrical charges to fluid surfaces) can be used to form a video display that may some day be used for computer video monitors. As in the case of using electrowetting for the liquid lens, Royal Philips Electronics is at the forefront of using electrowetting for developing electronic paper.
The liquid lens may only be a year or so away from the market, but the idea of electronic paper video displays is believed to be at least five years from a usable product form.
Even so, Peter Kurstjens, general manager of Electronic Ink Displays at Philips points out that, "while the amount of information that we digitally process ever increases, more printers are sold each year. This contrast goes to show we still prefer reading from paper rather than from electronic displays,"
Printing and paper distribution are the mostly costly parts of information distribution. If it were as easy to read monitor displays as it is to read a paper book the cost savings of information retrieval could be enormous. Reading from a video display is difficult because it reflects light unlike paper's absorption of light. Despite all the technological hurdles ahead of e-paper, (electronic paper) large companies see the economical potential of e-paper displays.
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