Electrowetting by Jordan Richman for Today in Science

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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Harvard Researchers Create High Performance Optical Nanowires

Jordan Richman, 2/25/04
Using a $20 Bunsen burner and some silica optical fiber (little pieces of glass), Dr. Limin Tong, a visiting professor at Harvard from China, describes in a recent paper published in the December 18 issue of the journal Nature, how he was able to make a 50 nanometer, high performance light transmitting nanowire. First he heats the fiber and draws it out to a 1 micron wide wire. He then winds the wire around a the tip of a heated sapphire needle. Since sapphire is such a good conductor of heat, its heat softens the glass fiber evenly as Dr. Tong draws out the fiber down the shaft of the sapphire needle.
"If you pull fast, it is very thin," said Dr. Tong. He found that if he pulled more slowly he could produce a thicker wire.
Dr. Eric Mazur who led the Harvard optical nanowire research team pointed out that while much thinner nanowires have been produced in the past by other scientists none of them had the even diameters or smoothness exhibited by Dr. Tong's nanowires. The sidewall of the earlier wires were rough and there were unwanted variations in their width. The wires produced by Tong and Mazur are very smooth and offer much less optical loss for either visible and infrared light.
"These wires show surface smoothness at the atomic level, along with uniformity of diameter," Dr. Mazur said.
Even though Tong's and Mazur's optical nanowires are much thinner than even the wavelengths of their transported light, they are still able to guide a light beam with a high degree of accuracy and a minimum of optical signal loss. When light passes through a conventional fiber optic it flows through it like water in a garden hose. Nanowires do not hold the light. They act instead like guide rails for light waves which are much wider than the nanowires. The light surrounds the tiny nanowire as evanescent waves. "Evanescent coupling" occurs when two of the wires touch. Unlike fiber optics where the light is fixed within the filament, coupling causes an exchange of light waves when two of the wires touch. Larger evanescent fields can be produced by varying combinations of nanowires which may applied for the production of smaller and more effective sensor technology. For many sensor devices, especially in medicine, size is of critical importance. Sensors could detect many toxins, for example, at once and with greater precision and accuracy with these new smaller diameter nanowires packed into the same area of a sensor.
Despite their width of only 50 nanometers, these new nanowires are still barely visible since they have a 2 centimeter length. They are able to curl into tiny light conducting loops with remarkable tensile strength. They are as much as five times stronger than spider silk. Their resiliency and flexibility, along with their beadlike structure, have been cited as qualities that may make them play a role in the manufacture of new electronic chips that use on and off optical signals. Reducing the size of the nanowires diameter to less than 50 nanometers probably would not increase their effectiveness in transporting light waves, but the flexibility of Tong/Mazur nanowires introduces many new options in modern electronic engineering. The nanowires can be tied into tiny knots making the alignment of optical components much easier to accomplish.
"It's like the old TV's, where we used to have flexible wires to go from one board to another, " said Dr. Richard Osgood, a professor of electrical engineering and applied physics at Columbia University. "You don't have to get everything exactly aligned to close things."
Dr. Mazur points out that these nanowires are not the same as conventional fiber optic cables that circumnavigate the globe but could be used for distances that range at about an inch. They would be useful for devices that use fiber optics and light signals as low-loss interfaces which would provide further compact design and speed for those processors. Fiber optic cables, which are about the size of a human hair, combine phone messages and then have to separate them. The combiners are called multiplexers and the signal separators are demultiplexers. The new nanowires may one day become part of these processing modes in telecommunications.
End
Notes for Amy Perry
1) Tong, Mazur, and Osgood quotes are all from the NYT's clipping you sent. There is an inked in date at the bottom of the clipping: NYT G8 1/29/04 and the authors E-mail: Eisenberg:nytimes.com (Anne Eisenberg)
For the lead illustration I recommend the one showing Tong's fabrication of his nanowire using the sapphire taper and Bunsen burner since it is not the smallness of the width that was his innovation but the refinement of the nanowires smoothness of surface and and even diameter that he accomplished with his Bunsen burner and sapphire needle.
Showing the nanowire on top of a human hair and the nanowire tied as a knot making a loop are other illustrations that could be used.

ALLERGY

Pollens are the most common cause of Allergy leading to allergic rhinitis. The popular name for rhinitis, "hay fever,"
a term used since the 1830s, is inaccurate.
The condition is not caused by hay nor does it lead to fever. Every season throughout the world, pollens from grasses, trees, and weeds produce the allergic reactions of sneezing, runnynose, swollen nasal tissues, headaches, blocked sinuses, and watery, irritated eyes.
Of the 46 million allergy sufferers in the
United States, about 25 million have rhinitis.
Dust and the house dust mite represent another major source of allergens. While the mite itself is too large to be inhaled, its faeces is about the size of pollen grains and can lead to allergic rhinitis. Other types of allergy can be traced to the fur ofanimals and pets, food, drugs, insect bites, and skin contact with chemical substances or odors.

In the United States there are about 12 million people who are allergic to these substances. In some cases an allergic reaction to an insect sting or drug reaction can cause sudden death, or a serious asthma attack can be brought on by seasonal rhinitis or some other irritating substance.
In the United States there are about 9 million cases of asthma, a disease which is related to allergy.

Jordan P. Richman, Ph.D.


Encyclopedia of Science, Gale Research

The Rosetta Mission by Jordan Richman, Ph.D.

The Rosetta Mission



Launched on March 2, 2004, from Kourou, French Guiana, by the European Space Agency (ESA), a spacecraft designed to fulfill the goals of the Rosetta Mission is set to send a lander to hitch a ride on a comet ten years later (2014). It will study the comet for two years before it launches its lander. Then in 2014 it releases its 220-pound lander, called Philae, which will ride the comet for a year as it travels past Jupiter and flies by the sun.


In the first phase of the project, in order to overcome the effects of gravity, it will circle Earth and Mars three times in March 2005, November 2007, and November 2009. From 2008 to 2009 it will begin to pass through two asteroid belts where it will study the asteroids, Steins and Lutetia. From 2011 to 2013 it begins to reach its maximum orbit, 540 million miles from the sun, and then shuts down its engines. In this phase it studies the comet's coma (the principal part of most comets consisting of a diffuse cloud of gas and dust which surrounds the nucleus) until November 2014 when it delivers its lander.


The technique used to land Philae on the comet Chury and keep it in place for its perilous ride on a comet's back is remarkable. As soon as it touches down, two harpoons will anchor the probe to the surface. A self-adjusting landing gear will then keep it upright even if it is on a slope. The lander's feet will then drill into the ground. All these manuevers are designed to help the lander deal with the low gravity found on comets.


The International Rosetta Mission was approved in November 1993 by ESA. Originally it was set to meet Comet 46p/Wirtanen but after a delay in the launch time it was reset to meet comet 67p/ Churyumo-Gerasimenko (Chury). Studying the two asteroids is also one of Rosetta mission's secondary objectives. It will gather images of these rocks and learn more about their composition, subsurface temperature, and surrounding gas and dust.


The mission takes its name from the Rosetta Stone which was used to decipher Egyptian Hieroglyphics. Just as this stone helped to teach Egyptologists more about ancient Egyptian history, so the Rosetta Mission's probe should help astronomers decipher the history of the solar system as well as the underlying forces that govern planetary systems in relation to their stars.


The lander is called "Philae" after the obelisk that helped decode the Rosetta Stones . If the Rosetta Mission succeeds it will be:


the first to land on a comet;


the first to fly to Jupiter on solar power alone;


the first to fly alongside a comet and orbit its nucleus;


the first to analyze a comet's composition from its surface;


and the first to see a comet transform from a rock to a hot ball of gas and dust.


In February 1999, NASA launched a spacecraft named Stardust which gathered information from comet Wild 2. Since Stardust's launch it has traveled 4 billion kilometers (2.5 billion miles), looping through the inner solar system three times before arriving at Wild 2. It swung by Earth in January 2001 and in November 2002 came close to the asteroid Annefrank, as a kind of test run for its encounter with Wild 2. It then took pictures while scientists studied and modified its orbit.






Then on January 2, 2004, the Stardust spacecraft flew by Comet Wild 2 scooping up grains of dust and ice from the comet's tail. It came within 230 kilometers (143 miles) of the comet's 5.5-kilometer-wide (3.4-mile-wide) core, the closest approach ever to a comet by a spacecraft.If its mission is successful, the craft will return with the first sample ever taken directly from a comet.


Stardust also captured 72 detailed pictures of Wild 2's core, about one every ten seconds, as it swung by. The pictures showed dust and gas venting from various cracks and openings in the core, forming a tail, as in most comets. But the photographs also revealed Wild 2's surface to be strewn with craters, pockmarks and sinkholes. Scientists were shocked by the varied terrain, which was far different from the surface of the comets Halley and Borrelly pictured by othe spacecraft.


As comets approach the Sun they heat up and begin to boil, leaving a trail of dust, ice and other particles in their wake. Stardust flew through this, scooping some of these particles from behind its heavy shields with an outstretched net shaped like a tennis-racket. About an ounce of material was caught in a compound called aerogel, a spongy silicon. Stardust is due to drop these samples back to Earth by parachute in January 2006. The heat-protected package should land near an air force base in the Utah desert.


Scientists are eager to study this material. Comets are assumed to have formed at the outer edges of the solar system and, except when their orbits have brought them close to the Sun, to have remained frozen since then. They assume the dust Stardust captured has remained unchanged since our solar system formed 4.6 billion years ago. Studying this dust could reveal conditions during that period. Some scientists think a torrent of comets may have seeded Earth with water and organic molecules essential to the planet's evolution in its first 500 million years.


Other than moon rocks, this will be the first material from outer space that scientists have brought back for study. Meteorites from Mars and more distant reaches of the solar system have landed on Earth, but they all passed through Earth's atmosphere, heating up so much that their chemical composition could have been changed


Stardust is the fifth spacecraft to have met up with a comet. In 1985, the International Cometary Explorer zoomed by Comet Giacobini-Zimmer, and one year later, the Giotto and Vega spacecraft had their rendevous with Comet Halley.


The comet Chury will have Philae on it until it becomes a fireball. It reaches its perihelion (the nearest distance of a comet's orbit to the sun) in October 2015. Rosetta monitors the comet with its hitchhiker until the mission ends in December of 2015.


Jordan P. Richman, Ph.D.


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