Millimeter wave scanners have caused a stir, but similar waves surround us every day and help us do things we now take for granted. For example, your cell phone relies on millimeter wave technology to send and receive data and calls. That smartphone activity occurs by way of communication satellites, which receive microwave signals from ground stations and then direct them, as downlink transmissions, to multiple destinations. Remember that electromagnetic waves come in a range of wavelengths. They also come in a range of frequencies, which is a measure of how many wave crests pass a certain point every second. Microwaves used in satellite communications are super-high frequency, or SHF, waves in the range of 3 gigahertz to 30 gigahertz (GHz).
NEXRAD, or next-generation weather radar, also uses waves in the 3 GHz range to help meteorologists make weather forecasts. NEXRAD relies on the Doppler effect to calculate the position and speed of rain, snow and weather fronts. First, a radar unit emits a pulse of energy, which travels through the air until it encounters an object, such as a raindrop. Then the unit listens for an echo -- energy reflected back to it from the object. By sending a constant stream of pulses and listening for echoes, the system is able to create a color-coded picture of the weather in a particular area.
Astronomers take advantage of extremely high frequency (EHF) waves in the range of 30 to 300 GHz to study the formation of stars and galaxies millions of light-years from Earth. Instead of traditional telescopes that sense light, these scientists use radio telescopes to "see" energy with millimeter and submillimeter wavelengths. Because structures on the ground can interfere with these waves, radio telescopes are usually placed at very high locations. For example, the Combined Array for Research in Millimeter-wave Astronomy (CARMA) encompasses 23 radio dishes in the Inyo Mountains near Big Pine, Calif.
So, millimeter waves are well-understood and quite common in a number of applications we regularly use. Even the microwave oven in your kitchen zaps food with a form of energy from this narrow band of the electromagnetic spectrum. Its adoption in airport security is a natural -- and harmless -- extension of the technology, especially when you consider the type of disaster it's trying to prevent. As of November 2012, the TSA has installed hundreds of mmw scanners at airports across the U.S. And internationally, they are being used in airports and mass-transit systems in several countries, including Canada, the Netherlands, Italy, Australia and the United Kingdom.