A window is more than just an opening that you can see through. It can affect the way a building looks, how much energy a building uses-and even how you feel.


Windows affect the way a building looks and how much sunlight gets in during the day.

I. Peterson
Researchers are now working on new technologies to create "smart windows." Unlike normal windows, high-tech smart windows can change from clear to dark and back again with the touch of a button-or even automatically as the outside light changes.

Smart windows have the potential to make the world a cleaner and more comfortable place. Instead of turning on air conditioners, people could simply dim the windows in a building's empty rooms. The rooms would stay cool, and people would save energy and money at the same time.

That's why smart windows are so exciting, says Claes Granqvist. He's a professor of solid-state physics at Uppsala University in Sweden.

Indoor life

If you think that you don't care much about windows, you should think again, Granqvist says.

Most people who live in developed countries spend, on average, 90 percent of their time inside buildings and cars. You might spend even more time than that indoors during the winter if you live in a cold climate.


Being able to see out a window can help cheer you up, even if you're ill.

Imagine then what it would be like if there were no windows. You'd have no idea what's going on outside.

"It took us a long time to figure out what a window really is," Granqvist says. "It's contact with the outside world. You have to have visual contact with the surrounding world to feel well."

So, windows and natural light are important for improving the way people feel when they're stuck indoors.

Yet, windows are the weak link in a building when it comes to energy and temperature control. In the winter, cold air leaks in. When it's hot and sunny, sunlight streams in. All of this sunlight carries lots of heat and energy. And all of this extra heat forces people to turn on their air conditioners.

Producing blasts of cold air, which can feel so refreshing, actually suck up enormous amounts of electricity in buildings around the world. Most electricity comes from coal-burning and nuclear power plants. These energy sources generate carbon dioxide and pollutants or produce radioactive waste. And a growing population demands more energy.


It would be more energy efficient to have buildings without windows, but windows are important for how buildings look and how people feel inside them.

I. Peterson
"It would be very energy efficient to have a house with no windows," Granqvist says, "but we don't want that."

Color changes

Windows have been a major focus of energy research for a long time. Over the years, scientists have come up with a variety of strategies for coating, glazing, and layering windows to make them more energy efficient.

Smart windows go a step further. They belong to a group of technologies described as chromogenic. Chromogenic technologies involve changes of color.


Smart windows use electricity to change from dark to clear and back again.

Courtesy of Claes Granqvist
Electrochromic windows use electricity to change color. For example, a sheet of glass coated with thin layers of chemical compounds such as tungsten oxide works a bit like a battery. Tungsten oxide is clear when an electric charge is applied and dark when the charge is removed. So, applying a voltage determines whether the window looks clear or dark.

One important feature that makes a smart window so smart is that it has a sort of "memory." All it takes is a small jolt of voltage to turn the window from one state to the other. Then, it stays that way. Transitions take anywhere from 10 seconds to a few minutes, depending on the size of the window.

The amount of electricity required to power a smart window is so small, Granqvist says, that it should be possible to run it completely on solar power.

"It takes very, very little energy to change it back and forth," he says. "It's totally insignificant compared with the amount of energy you save from overheating and over-air-conditioning."


It doesn't take much electricity to make certain panes of a smart window darker.

Courtesy of Claes Granqvist
A wireless control system would make it easy to program a building to be dark when no one's there. Or, people could darken an individual window when they're sitting at the computer, or when they're going out of town for a while.

"There's no reason to have transparent windows," Granqvist says, "when there's no one to look through them."

Dark market

Some companies already have test versions of smart windows on the market. Still, the industry faces some major obstacles before the technology becomes truly widespread.

"There's still a ways to go," says Carl Lampert. He's managing director of Star Science, a consulting company in Santa Clara, Calif. "The manufacturing is complicated."

For one thing, smart windows simply haven't been around long enough for people to trust that they'll work well and last for a long time. At this point, making smart windows is also an extremely expensive process, thanks to the complexity of the machines needed to apply coatings.

To turn people on to smart windows, Granqvist wants to start small by selling the technology to people who have special needs. Right now, he's working on motorcycle and ski helmets with facemasks that could easily switch between dark and clear.


This experimental helmet has a facemask that can switch between dark and clear.

Courtesy of Claes Granqvist
Once these products catch on, it's only a matter of time before our office buildings, schools, even houses are full of smart windows. "I think it's definitely going to catch on," Lampert says. "People are really excited about this."

Smart windows could literally change the way we see the world, Granqvist says. It's already happened to him.

"I travel quite a bit all over the world-to Singapore, Hong Kong, China," he says. "When I began working on smart windows, I started to see air-conditioning systems everywhere. Buildings, even nice old buildings, were covered in ugly air-conditioning units."

The development of smart windows could mean that massive air-conditioning systems may no longer be needed. "In the future," Granqvist says, "our buildings may look different."

The blue-green streaks of a swallowtail butterfly's wings are more than just beautiful. They're also a lesson in physics.


The bands of brilliant color on this butterfly's wing are produced from tiny scales on the wing's surface.

Image courtesy of Peter Vukusic/University of Exeter
Swallowtails that belong to a group called Princeps nireus actually have fluorescent wings. This means that when the wings absorb a special type of light, called ultraviolet light (or "black light"), they give off a bright blue-green glow. The glow that they give off has a longer wavelength than the ultraviolet light they absorb.

Physicist Peter Vukusic of Exeter University wanted to figure out why the wings are unusually bright. So, he took a close-up look.

Butterfly wings are covered with hundreds of thousands of colored scales, like tiles covering a roof. The scales are made of cuticle, a material that is similar to human fingernails. Vukusic and his colleagues used highly sensitive microscopes to look at individual scales.


Optical microscope image of a single scale from a butterfly wing.

Image courtesy of Peter Vukusic/University of Exeter
Their pictures show that each scale has three vertical levels. The bottom level is itself split up into three more layers, like an Oreo cookie, with an air space sandwiched between two layers of cuticle. Each layer is about 90 nanometers thick. One nanometer is one-billionth of a meter. A human hair is about 80,000 nanometers wide.

The middle level is a 1.5-micrometer-thick air space, held together by columns of cuticle. One micrometer is one-millionth of a meter, or 1,000 nanometers.

Finally, the top level is made of cuticle arranged in a sort of honeycomb pattern, 2 micrometers thick. The honeycomb holds tiny cylinders of air, measuring 240 nanometers across. The walls of these cylinders hold the pigments that cause the wings to glow, or fluoresce.

The wings seem to achieve their bright glow in two ways, the scientists conclude. First, the pigment-filled cylinders in the top level and the Oreo sandwich in the bottom level cause all of the fluorescence to reflect out of the top of the wing. Second, the bottom level adds even more blue-green light by reflecting sunlight that filters down and hits it.


Peter Vukusic with several different butterflies that have wings covered with special scales that brighten the color.

Image courtesy of Peter Vukusic/University of Exeter
Some electronic devices called light-emitting diodes (LEDs) work in a remarkably similar way. LEDs light up the numbers on clocks and watches and show when appliances are on, among many other jobs.

It's another amazing example of technology imitating nature, whether intended or not.-E. Sohn

You've probably heard of robots. Now, make way for musclebots.

Scientists in California have made tiny walking machines out of heart muscle grown from rat cells. When the muscle contracts, then relaxes, the musclebot takes a step. The entire device is tinier than a comma.

Viewed under a microscope, "they move very fast," says bioengineer Jianzhong Xi of the University of California, Los Angeles (UCLA). "The first time I saw that, it was kind of scary."


A musclebot (bottom left) consists of a bundle of muscle cells attached to a layer of gold, making the device look like a golden arch. This sequence of images shows how a musclebot takes a single step by contracting, then relaxing. The top row shows image

Jianzhong Xi, Jacob J. Schmidt, and Carlo D. Montmagno, UCLA/Nature Materials
Scientists have already used muscle tissue to make machines, but these earlier machines were much larger than the new musclebots. A few years ago, for instance, a team at the Massachusetts Institute of Technology made a palm-sized device, called a biomechatronic fish, which swam by using living muscle tissue taken from frogs' legs.

Adding muscles to a minuscule machine requires a different approach. Instead of using whole tissue, the scientists grew a thin film of heart muscle right on their bot. To do this, they borrowed some methods from the industry that makes chips for computers and other high-tech devices. But these methods can harm cells, so the team also invented some cell-friendly techniques to help do the job.

In the end, the musclebot looks like a golden arch, coated on its inner surface with muscle. Kept alive in a special solution containing glucose, the heart muscle cells beat, causing the bot to scoot along. When the muscle contracts, the arch squeezes together, and the back leg moves forward. When the muscle relaxes, the arch widens, and the front leg moves forward.

Researchers envision a number of applications for the new technology, including musclebots that deliver drugs directly to the cells that need them. They might also be useful for building other tiny machines, converting muscle motion into electric power for microcircuits, or studying muscle tissue.

So far, musclebots can move only in one direction, and they can't be easily turned on and off. Future versions are sure to be more versatile.-E. Sohn

Televisions enhanced with direct internet access and 3D displays will be among the most anticipated products unveiled when the world's biggest annual technology showcase kicks off in Las Vegas on Thursday.

This year could see a revolution in televisions on high street sale as they converge with the web, allowing viewers to watch services such as the BBC's iPlayer and YouTube more conveniently.

Manufacturers including Sony, Panasonic and LG are expected to launch sets with a broad range of new capabilities at the Consumer Electronics Show, including High Definition TV (HDTV) screens with the internet telephony service Skype built in, so people can use their TVs for video chats with friends and family anywhere in the world.

The BBC launched a limited trial last month of the iPlayer on some high definition Freesat boxes - the free-to-air satellite service is increasingly integrated into TVs - and is anticipating even more viewers being online when the next generation of sets emerges.

There is a scramble to profit on the hype surrounding 3D after cinema hits Avatar and Up. A number of companies will be debuting their attempts at high-quality 3D screens. The Discovery Channel could even announce plans to launch a 3D TV channel next year.

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