Invisible” Aircraft © Jupiterimages Corp

“Invisible” Aircraft © Jupiterimages Corp. To be stealthy is to move about in ways that go undetected. Skillful spies are stealthy. So is the F-117 stealth fighter plane. © Jupiterimages Corp. It’s all but invisible to radar. presented by Science a-z a division of Learning A-Z

Radar antennae send out bursts of radio waves that are reflected back by the objects they hit. The antenna measures the time it takes for the reflection to return. That tells how far away the object is and how big it is. In wartime, that information could get By Ron Fridell a plane and its pilot shot down. In the Harry Potter® books, Only a fictional character like Two factors make the F-117 stealthy. One is shape. Most aircraft Harry covers himself with a Harry can do it, for now. have a rounded profile that radar can easily detect. But the F-117 magic cloak that makes him But that may soon change! has flat surfaces and sharp edges that bounce radar waves out disappear when he needs to Scientists at two U.S. and away at sharp angles. get out of a tricky situation. universities have engineered © iStockphoto.com/Dale Robins The other factor is covering. Most planes are made of metals Wouldn’t it be fun to be able to coverings that make small that reflect radio waves. But the F-117 is covered in a material choose when to be visible? objects seem to disappear. that absorbs radio waves instead of reflecting them. Together, How did they accomplish this the F-117’s shape and covering only reflect about as much radar astonishing feat? The key is as a hummingbird. light waves. We see things because they reflect and absorb visible light, which travels in waves that can Radar is an acronym, bend. That’s why a straw a word formed from in a glass of water Christopher Nolan, George Cairns the first letter or letters appears to zigzag; © iStockphoto.com/Luminis,

of several words. Jozsef Szasaz-Fabian the light waves bend © iStockphoto.com/ Radar = as they pass from RAdio the air to the water. Detection And Illustration by Judy Martin Ranging See Invisibility on page 2

Continued from page 1 Write About This! The scientists wanted to bend visible light away and route it around an object the way Casey Jones Illustration by water in a stream flows around Light a stone. Then the object would neither absorb nor reflect light. © iStockphoto.com/Tony Tremblay/Rest It would not cast a shadow With the new covering, light either. The object would be bends around an object like water invisible to human eyes. around a rock in a stream.

To reach their goal, they So far, these scientists have engineered microscopic metal managed to weave together strands that bend light waves only very small coverings. away, then wove them into What do they want to do now? Suppose we had unlimited supplies of coverings that coverings that look like nets. Their next goal is to produce make things invisible. Let’s say the coverings could be When they place one of these coverings big enough to cloak a made of cloth, paper, or paint. What practical uses could coverings over a small object, person—just like Harry Potter’s they be put to? One scientist thought of coating an ugly the object vanishes from sight. cloak of invisibility. factory building that blocked a beautiful view of distant Observers can see only what’s mountains. Think of three or more uses and make a list. behind the object, as if they Then put your thoughts into writing. were looking right through it.

see you. © Jupiterimages Corp. Doctor: I can’t see him © Shizuo Kambayashi/AP Images This coat uses a camera to project now. Bring in the image behind it onto the front. the next patient. But an invisibility cloak could look Scientist Jie Yao demonstrates like this. the invisibility material.