The potential to communication with miners trapped underground was realised in the 1920's, when simple investigations of underground reception of Long Wave commercial stations were made. At the level of radio technology then, it was not possible to build a practical system. The most important research and results were obtained during the 1970's and 1980's. Since then the interest in EM wave propagation through rock and underground tunnels has declined. However, new technologies demonstrated some drawbacks, for example in obtaining a stable predictable and directional RFID reading and collision warning in VHF and UHF spectrum. The paper presents results of a few successful application of VLF technology that are being implemented in South Africa and Germany in order to provide effective collision warning and RFID.
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