<<<------- I'm a Radio Engineer.
Originally Posted by
motorguy
... maybe someone with real expertise in the field could enlighten us as to what is being used and where, and how we can recognize which is which in our local airport...
Yes, there are two technologies, and yes, a lot of people are confused.
One is millimeter-wave (MMW) radio frequency. The frequency band (according to papers on the FCC website from the manufacturer) is 24.5 - 30 GHz; the wavelength is therefore about 10 mm (0.4"). Higher frequency than cell phones, but well below Terahertz and infrared. (There were some prototype systems at ~100 GHz (still not quite THz) that I've referred to in earlier posts.)
The other is x-ray (also called backscatter x-ray, or sometimes just backscatter or BSKX). So yes, ionizing radiation.
You can tell what's where from the link Friendly Skies posted (which Friendly Skies maintains^^). And you can tell them apart at the airport by looking at the type of machine. The MMW is a round booth with glass doors, while the x-ray is two large rectangular boxes that the
victim suspected Bad Guy stands between.