Scanning mania

After all the commotion about the full body scans performed at Schiphol Airport in the aftermath of the failed terrorist attack on an airplane bound for Detroit last Christmas, the latest news is that the Dutch police also want to use the millimeter wave technique to scan people at – for instance – malls and football stadiums.

Instead of projecting beams of radio frequency energy in the millimeter wave spectrum onto people’s bodies and measuring the energy reflected back, as is being done at the airport, the police intend to use passive scanners which measure the millimeter waves that are reflected from people naturally. Enough of these waves, emitted by everyday objects around us, pass through clothing and are reflected by the skin.

The ministry of Internal Affairs provided half a million euro to develop such a millimeter wave scanning device that is portable and thus can be used at any location. Did the terrorist attack give political momentum to unleash millimeter wave scanning technology on society?

Professor Ben Ale, lecturer in safety science at the faculty of Technology, Policy and Management, thinks the attack has certainly speeded up the deployment. Due to European rules concerning privacy protection, Schiphol Airport previously wasn’t allowed to use the fifteen scanners they had. The emerging pictures from the machines of naked grey people were deemed improper. Software has now speedily been adjusted so that on top of a neutral doll only yellow spots appear on body parts where the scanner detects something suspicious. The next step in the procedure is then a targeted search.
According to optics researcher dr. Paul Planken (faculty of Applied Sciences), you need quite a large mirror to detect the millimeter waves reflected by people. He thinks this is the reason why there is no portable scanner as of yet. Assuming the scanner uses waves of 30 gigahertz, like the ones at the airport, Planken’s rough calculations reveal that in order to scan people from a distance of 10 meters you would need a mirror with a diameter of no less than a meter. “And this would result in images with a resolution of just 5 to 10 centimeters”, Planken says. “Anything smaller will be very blurry or invisible.”

If you raise the wave frequency, the resolution increases linearly. Or put differently, you can obtain the same resolution with a smaller mirror. But there are limitations. For one, the equipment needed to analyze the received waves becomes more expensive. And above 1 terahertz or so, the waves that, until then would go right through clothes, will be scattered and filtered by the clothes and thus not reach the skin or the detector.
Professor Ale is a bit skeptical about the development of scanners and putting two-billion passengers a year through them. He argues that security should be more focused on the 50,000 names on the flight blacklist and on the couple of dozens lads who are likely to try to ruin a party.