Before revision:  An analytical channel model for the new mechanism is developed to explore the fundamentals of metamaterial enhanced MI communication in various underground environments. The effects of important system and environmental factors are quantitatively captured, including the operating frequency, bandwidth, and parameters of metamaterial antennas, as well as permittivity, permeability, and conductivity of underground medium .
After revision:  An analytical channel model for the new mechanism is developed to explore the fundamentals of the M^2I mechanism, in the aspects of communication range and channel capacity, and the susceptibility to various hostile and complex environments .