Millimeter Waves and Junk Pictures

With all the attention given to the TSA and the Full-Body airport scanners, I thought it would be interesting to explain some of the technology involved. Currently there are 2 types of full body scanners being used, Millimeter Wave and X-Ray BackScatter.

Let’s begin with the Millimeter Wave scanner, MMW.

So, why do they call it “Millimeter Wave” radar?

The millimeter refers to the wavelength of the energy that is used. Wavelength?? Huh?

To explain wavelength, just think of a jump rope with one end tied to a wall and the other held by a person.

If that person gives the rope a continuous quick up and down motion, you can see the wave go on the rope from the persons hand to the wall.

The distance from one peak of a wave to the next is called the wavelength

So the more “wavelengths” or cycles in a given amount of time, the quicker those wavelengths will pass a given point. This rate or “cycles per second” is called “frequency” and it can be thought of as the quantity of items that pass a point.

Frequency used to be measured in units called obviously…cycles per second. But to honor a scientist, Heinrich Hertz, a few years back they changed the “cycles per second” to the unit “hertz”. Means the same thing.

Now electromagnetic radiation travels in a vacuum at a really, really, fast speed. Precisely measured at 299,792,458 meters per second.

Now suppose someone stated that they have a transmitter that sends out energy at a frequency of 299,792,458 hertz. What do you think the distance traveled in one wavelength would be?

Think about it, you have 299,792,458 cycles and it travels at 299,792,458 meters in one second. So 1 wavelength would be 1 meter.

Notice how the wavelengths get smaller and smaller as the frequencies go up.

Am radio station may have a full wavelength of 240 meters. Since antennas are usually made to be 1/4 of the wavelength, that may mean it needs an antenna of 60 meters. A 1/4 wavelength CB antenna may be about 2.7 meters long.

So in an indirect way, wavelength can be used as a different way of stating the frequency of the energy transmitted.

Here is a picture that shows you the relative wavelengths of several frequencies.

Interesting note is that visible light is just electromagnetic radiation at a narrow wavelength or frequency.

A cheap laser pointer may state a wavelength of 650 nm. This means a wavelength of 650 nanometers or the frequency of an astonishing 450 Terahertz. But our eyes just happen to be able to see that energy so it would be the color red. A simple red laser pointer.

But you can see how the frequency number is getting impossibly large. That’s one reason that it’s easier to say it in wavelength.

Okay, getting back to the TSA body scanners. They are called millimeter wave radar because that’s the range that they operate in. About 5 millimeters so they use a energy of around 60 gigahertz although some scanners work at a lower frequency of around 30 gigahertz.

That is really high up in radio frequency, way beyond cell phones and your free Starbucks WiFi connections.

In fact, until recently it was impossible to have electronic components that could produce radio frequencies that high.

Millimeter Wave radar was only developed in the early 1960’s for the military by Georgia Tech and it was not what you would call portable and cheap.

There are several interesting qualities about frequencies when they get this high…. besides the obvious one of it being impossible to design compact without complete computer simulation.

The transmitted energy is absorbed by oxygen quite rapidly so they cannot transmit very far in air. It’s very narrow and directional and can be designed so that it reflects off organic material with moisture content such as skin, but goes right through materials such as cloth.

When a passenger steps into a scanner booth, a scanning array of transmitter/ antennas sweep across your body from about 2 feet. The received beam that has gone through your clothes and bounced back must be digitally processed before it can even begin to resemble a picture.

But because of the direct reflection and short wavelength, the picture it produces is quite detailed.

The person literally is being viewed naked by a TSA agent. The picture below has the face blurred out and some detail smudged, but make no mistake about it….the process produces a VERY detailed nude picture.

In my opinion, this is where the Millimeter wave scanners have failed and the public relations has been a disaster. There’s no need to have that much nudity detail displayed.

It’s almost like some geeky engineer said…”Look at what I can do”.



Because of the extensive digital processing, you could have just a stick figure being displayed. In fact, Germany has this method in operation already. The digital processing can discern far more detail and patterns to look out for than a slightly higher than minimum wage paid TSA agent.

Hell, even the new XBox Connect on sell for Christmas this year can do facial and pattern recognition beyond what a TSA agent could do. The TSA doesn’t even need to have a body displayed. Let the machine do the scan and make the decision that the person needs to be checked further. Simple red light / green light.

In my opinion, that would be the ideal system that would alleviate a lot of peoples concerns about privacy. Maybe that will be a couple of revisions down the road for the company that makes these scanners.

My hope is that the changes come around quickly because they are just too intrusive right now.

As far as genetic risks from millimeter wave scanners, studies have been done but so far there is no conclusive evidence that millimeter wave scanners cause any DNA or genetic harm.

If any reader can point out a scientific peer reviewed study that does indicate genetic damage, please post a link to the study in comments and this post will be revised with that new information.

The next post will go into the other system, X-RAY BackScatter. This is the system that people are concerned about with the ionizing radiation. Should it be a real concern?

Next post…..X-RAY Back Scatter and Junk Pictures.