What is Terahertz Frequency?
Terahertz frequency is the type of frequency that sits between microwave and infrared, but the wonderful part about this Terahertz frequency is that it is categorized as non ionizing. And what it means is it is totally safe. How safe is safe? Well, way back in 2008, this article from Science Daily, it says this, within the last few years, a number of transport checks above all at airports has been increased considerably.
A worthwhile effort as after all, it concerns the protection of passengers, possibilities for new and safe methods of checking people are offered by Terahertz radiation. So now globally, we are using Terahertz frequency in airports as scanners because it is totally safe.

