They’ve been in science fiction books for many years, but now they are finally practical models. Microwave scanners are coming to an airport near you!
Using a 3mm microwave, the equipment builds up a three dimensional map of the space in front of it. Different objects return the beam at different fequencies, so you can tell what things are made of. This is a pretty cool gadget, although it does seem slightly pervy because cloth has almost no microwave return signal so look like they’re naked. Actually, that alone is probably enough to ensure that it goes on the market eventually, because any technology that can be applied to pornographic use has ever failed to sell. Now all they need to do is work out how to make the technology tie in to Star Trek and they won’t be able to keep them on the shelves.
More about the scanner here.