Dr. Lawrence Ives is an N.C. State University alumnus and collaborator as well as president and founder of Calabazas Creek Research, a California-based company involved in research for the Department of Defense. Here, Ives explains some of the technology behind the full-body scanners used in airport security. Answers have been edited.
Q: How do full-body scanners work?
Full-body scanners illuminate the body with radiation that reflects off the body rather than penetrating through it. The two technologies used are either backscatter X-rays or millimeter-wave radiation, and both look at an image made from the reflected energy of the scans. Millimeter indicates the wavelength of the radiation; one millimeter is about 4/100 of an inch. The size of features that can be detected depends on the wavelength, so the smaller the wavelength, the smaller the object one can see. Millimeter waves are convenient because the radiation can pass through non-metallic materials, such as clothes and cardboard boxes. But they cannot pass through water.
Q: What kind of things can they detect?
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The scanners can detect metallic objects, plastics and some chemicals.
Q: How are those full-body scanners different from the X-rays used to examine carry-on luggage?
These X-ray devices use high-energy radiation designed to pass through objects to a detector on the opposite side. The wavelength is much smaller and can pass through body tissue.
Q: How does the type and amount of radiation in these scanners compare to other types people regularly encounter - like cell phone radiation, radio and microwaves?
Millimeter-waves have photon energies [much] less than X-rays. The power of the transmitter generating the millimeter-wave radiation is probably comparable to that in a cell phone, though I don't know the detailed specifications of the millimeter-wave source. One can think of a millimeter-wave scanner as a flashlight that can see through clothes. The amount of energy impacting the body is more comparable to a flashlight than to a traditional X-ray source.
Q: Do these systems have health risks?
I'm not aware of any studies indicating that radiation at these power levels has health risks. Since they cannot pass through water, the radiation does not penetrate through the skin, or moisture in the eyes. The energy levels are so low that there is no heating of tissue or other materials.
Q: What kind of work have you done using microwaves for safety and security applications?
Our company develops RF [radio frequency] sources from very low frequencies up to frequencies comparable to the millimeter-wave scanners. The applications we address include defense systems, high-energy physics research, communications and industrial heating. We are not directly involved in the lower power systems used in body scanners.