Very-low-frequency (VLF) radio is being combined with digital audio compression to carry voice and text for several miles through the Earth, as well as through steel and concrete.
The technique holds promise for security and rescue teams, underground miners, and emergency-response personnel. Two-way VLF underground radio (in the 3 to 30-kHz range) was originally developed by the U.S. DoE, but is being commercialized by Vital Alert Technologies, Cleveland, with help from engineers at Los Alamos National Laboratory. According to Vital Alert, "this technology is the 'real' solution to radio failures that plagued warning and rescue operations during disaster and extreme environmental situations." The wireless network will be secure, work underground and in ocean environments as well as in urban centers, and could be used to track and locate specific transmitters.