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Are airport body scanners dangerous?

05 Jul 2013  | Steve Taranovich

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The TSA claims that it was privacy concerns—not radiation—that resulted in the agency cancelling its contract with Rapiscan Systems in January. Rapiscan, unlike the maker of the millimeter-wave machines (L-3 Communications Security & Detection Systems) was unable to meet TSA's deadline to develop software to convert the nude-like images produced by their machines into stick-like figures, the agency has said.

In spite of criticism by some groups, I think the TSA has done a pretty good job at our airports——they're not perfect, but what group is? Their record speaks for itself.

The move to all millimeter wave scanners: How they work
Millimeter waves, being similar to our cell phones (by the way, millimeter waves are at 92GHz vs. less than 10GHz for cell phone RF)

These millimeter wave body scanning machines emit a special type of microwave signal, not X-ray. Two rotating transmitters produce the waves as a passenger stands hands over the head and very still inside the machine. The energy passes through clothing, bounces off the person's skin—as well as any potential threats—and then returns to two receivers, which send images, front and back, to an operator station.

Since the wavelengths of millimeter waves are between 1 to 10 mm, they are large relative to natural and synthetic fibres, but they tend to pass through most materials, such as clothing, making them an ideal candidate for scanning technologies.

Millimeter wave scanners produce their waves with a series of small, disc-like transmitters stacked on one another like vertebrae in a spine. A single machine contains two of these stacks, each surrounded by a curved protective low-loss dielectric shell known as a "radome", connected by a bar that pivots around a central point. The job of the "radome" is to protect the antenna while not affecting its electrical performance. The thickness of this dielectric material is on the order of the antenna wavelength.

Each transmitter emits a pulse of energy, which travels as a wave to a person standing in the machine, passes through the person's clothes, reflects off the person's skin or concealed solid and liquid objects and then travels back, where the transmitter, now acting like a receiver, detects the signal. Because there are several transmitter/receiver discs stacked vertically and because these stacks rotate around the person, the device can form a complete picture, from head to toe and front to back.

Figure 1: L-3 Communications Security & Detection Systems makes three types of millimeter wave people scanners (Image courtesy of L-3 Communications).

The software then interprets the data and displays an image on an operator screen. It creates a 3-D, black-and-white, whole-body silhouette of the person. Another key feature in the system is known as "automated target recognition" (ATR), which is software that detects threats and highlights in the image. ATR technology is able to detect metals, liquids, plastics, gels, powders and ceramics, and most impressive is the ability to detect standard and homemade explosives, drugs and money!

Some millimeter wave scanners do not have this type of software, so they form images that reveal a person's unique topography, but in a way that looks like a crudely formed graphite prototype—- you can see some physical features, but not with the same detail X-ray backscatter scanners do (Passengers and the TSA do not want this!). A millimeter wave scanner with this software produces a generic outline of a person – everyone looks the same (The 'stick figure" that the TSA was looking for!) – and highlights areas that may require additional screening.

Millimeter wave scanners do not function like a metal detector though. They see through clothing to look for metallic and nonmetallic objects (Plastic guns, explosives in your underwear and knives, for example). Although this equipment is capable of storing images, they are deleted automatically as soon as the remote security officer completes his or her inspection. This needs to be strongly monitored by the TSA and the US government.

The EU ATOM Project1
One unique radar/millimeter wave sensor technique proposed in Europe is the ATOM project (Airport detection and Tracking Of dangerous Materials by passive and active sensors arrays). The system operates in an FM-CW mode, which guarantees the highest possible average power. A monolithic microwave integrated circuit of the 94GHz radar module includes a varactor tuned VCO with injection port, very compact transmit and receive amplifiers and a single-ended resistive mixer.

Figure 2: The ATOM project will provide a new airport security concept (Image courtesy of Fraunhofer Institute for High Frequency Physics and Radar Techniques1).

Figure 3: The ATOM millimeter wave front end contains a complete and effective RF architecture (Image courtesy of Fraunhofer Institute for High Frequency Physics and Radar Techniques2).

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