Underground wireless communications using high-temperature superconducting receivers

The authors have developed a method for communicating in underground areas with voice. This system utilizes low-frequency electromagnetic radiation and high-temperature superconducting quantum interference devices (SQUIDs) as receivers. The system is primarily,used to communicate in underground areas using through-the-earth electromagnetic waves. The underground areas are typically mines, but the application is not restricted to that purpose. The communication channel is being used to send, voice that has been digitally compressed. Typical rock masses do not allow conventional radio frequency electromagnetic waves to penetrate significant distances. Here, the authors use carrier frequencies of a few kilohertz that penetrate hundreds of meters into rock masses. They are using low-noise broadband superconducting receivers and have established that the signals propagate several hundred meters with modest power levels. Audio has been successfully received at distances in excess of 100 in through solid rock.