How Millimeter Wave Scanners Work


Other Applications of Millimeter Wave Technology

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.

Author's Note: How Millimeter Wave Scanners Work

Given the long pedigree of millimeter waves and the advances they've enabled in medicine, astronomy and meteorology, I'm surprised so few people have praised mmw scanners as a practical, lifesaving tool. Personally, I'm willing to let the machines look under my clothes as long as they catch the would-be terrorist trying to board the same plane.

Related Articles

Sources

  • Brown, Stuart F. "Weapons Revealed." Scientific American. April 2008.
  • Burns, Bob. "Which is it: Millimeter Wave or Backscatter?" The TSA Blog. May 27, 2008. (Oct. 30, 2012) http://blog.tsa.gov/2008/05/which-is-it-millimeter-wave-or.html
  • Choi, Charles Q. "Yes We Scan: Have Post-9/11 Airport Screening Technologies Made Us Safer?" Scientific American. Sept. 6, 2011. (Oct. 30, 2012) http://www.scientificamerican.com/article.cfm?id=have-new-airport-screening-technologies-inspired-by-9-11-made-us-safer
  • Grabell, Michael. "TSA Removes X-Ray Body Scanners From Major Airports." ProPublica. Oct. 19, 2012. (Oct. 30, 2012) http://www.propublica.org/article/tsa-removes-x-ray-body-scanners-from-major-airports
  • Grabell, Michael and Christian Salewski. "Sweating Bullets: Body Scanners Can See Perspiration as a Potential Weapon." ProPublica. Dec. 19, 2011. (Oct. 30, 2012) http://www.propublica.org/article/sweating-bullets-body-scanners-can-see-perspiration-as-a-potential-weapon
  • Groeger, Lena. "Scanning the Scanners: A Side-by-Side Comparison." ProPublica. Dec. 28, 2011. (Oct. 30, 2012) http://www.propublica.org/special/scanning-the-scanners-a-side-by-side-comparison
  • Hasler, Joe P. "The Truth About TSA Airport Scanning." Popular Mechanics. Nov. 18, 2010. (Oct. 30, 2012) http://www.popularmechanics.com/technology/aviation/safety/the-truth-about-tsa-airport-scanning
  • Knox, Richard. "Scientists Question Safety of New Airport Scanners." NPR. May 17, 2010. (Oct. 30, 2012) http://www.npr.org/templates/story/story.php?storyId=126833083
  • L-3 Communications. "ProVision Advanced Imaging Technology." (Oct. 30, 2012) http://www.sds.l-3com.com/advancedimaging/provision.htm
  • McCullagh, Declan. "Feds admit storing checkpoint body scan images." CNET. Aug. 4, 2010. (Nov. 27, 2012) http://news.cnet.com/8301-31921_3-20012583-281.html
  • Moseman, Andrew. "What's the Real Radiation Risk of the TSA's Full Body X-Ray Scans?" Discover Magazine. Nov. 17, 2010. (Oct. 30, 2012) http://blogs.discovermagazine.com/80beats/2010/11/17/whats-the-real-radiation-risk-of-the-tsas-full-body-x-ray-scans/
  • Paddock, Catharine. "Radiation Risk From Full-Body Airport Scanners Very Low, New Analysis." Medical News Today. March 29, 2011. (Oct. 30, 2012) http://www.medicalnewstoday.com/articles/220470.php
  • Paur, Jason. "Questions Linger on Safety of Airport Body Scanners." Wired. Dec. 22, 2011. (Oct. 30, 2012) http://www.wired.com/autopia/2011/12/questions-linger-on-safety-of-airport-body-scanners/
  • Rabin, Roni Caryn. "X-Ray Scans at Airports Leave Lingering Worries." The New York Times. Aug. 6, 2012. (Oct. 30, 2012) http://well.blogs.nytimes.com/2012/08/06/x-ray-scans-at-airports-leave-lingering-worries/
  • Transportation Security Administration (TSA). "Advanced Imaging Technology: AIT: How It Works." Oct. 24, 2012. (Oct. 30, 2012) http://www.tsa.gov/ait-how-it-works
  • Winter, Michael. "TSA replaces X-ray scanners at some major airports." USA Today. Oct. 19, 2012. (Oct. 30, 2012) http://www.usatoday.com/story/news/ondeadline/2012/10/19/tsa-x-ray-scanners-replaced-millimeter-wave-airports/1644937/

More to Explore