New Security Scanner Sees Through Clothes, But With Modesty

March 27, 2007

A new sensor technology under development promises to give security screeners a peek through clothing without revealing the naked details, a scientist says.

The sensor may prove a more acceptable way to detect concealed weapons than the controversial backscatter x-ray technology the U.S. Department of Homeland Security started testing last month at the international airport in Phoenix, Arizona.

The backscatter machines bounce low-intensity x-ray beams off skin to create black-and-white images that render clothing transparent. Concealed weapons like ceramic knives and pistols are completely revealed.

But so are intimate body parts.

In U.S. congressional testimony last year, the American Civil Liberties Union called the backscatter technology a "tremendous invasion of privacy" that could reveal personal details like evidence of a mastectomy or genital size.

The less invasive technology creates images from the heat waves people naturally emit. Since concealed objects such as guns and knives appear cooler than body temperature, they show up in contrasting colors. (Related story: "Heat-Detecting Sensor May be Able to Detect Lying" [January 2, 2002].)

"This method does not reveal the body surface shapes like backscatter x-rays or visual light," Panu Helistö, chief research scientist at the VTT Technical Research Centre in Finland, explained in an email.

"Intimate parts of the body are not clearly visible," he said. "It is also difficult, if not impossible, to recognize the person from such a body temperature map."

Helistö described the technology earlier this month at a meeting of the American Physical Society in Denver, Colorado.

Passive Imaging

Instead of bouncing x-rays off an object to create an image, the sensor Helistö described simply absorbs natural thermal radiation.

The device is sensitive to terahertz frequencies—electromagnetic radiation from between the infrared spectrum and radio spectrum.

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