Excellent job. However for purposes of scientific accuracy, I have to point out that the MMW scanners do not use "sound" waves. They use electromagnetic (EM) waves (radiation) just like the backscatter x-ray scanners do. However it is EM radiation of quite a different wavelength: 10–12 mm (millimeters, one-thousandth of a meter) for the L-3 machines, according to what I found online. By way of comparison, cell phones operate at wavelengths approximately 10 times larger (e.g., 12 cm = 120 mm, for 2.5 GHz frequency). I have not been able to find data for the wavelength that the Rapiscan backscatter x-ray scanners operate at, but by definition, x-ray wavelengths range from 0.01–10 nm (nanometers, one-billionth of a meter). But both types of scanners are using electromagnetic radiation.