UNCLAIMED TERRITORY. “Terahertz frequencies, or submillimeter wavelengths, which exist between microwave frequencies and infrared wavelengths can be metaphorically termed “unclaimed territory” where almost no devices exist. Because there are limits to propagating the terahertz band through the atmosphere, the commercial sector has remained uninvolved with such technological development.”
https://en.m.wikipedia.org/wiki/Terahertz_metamaterials