Propagation of EM Signals in Underground Mines

This report is a comprehensive summary of the results of the propagation measurements program conducted for the Bureau of Mines. Data were gathered in the medium frequency (MF) range from a cross sample of six mines representative of the industry having typical wireless requirements. From the data that were gathered, a logical method of data reduction is presented that culminates in a set of average attenuation characteristics for all mines visited. These characteristics define a typical MF wireless system when the communication range requirements are known. Direct through-the-earth propagation and the range enhancement mechanism due to coupling on-and-off conductors are evaluated and related to the planning of a typical wireless MF communications system.