In this paper, we present modelling of VLF (very low frequency; 3–30 kHz) through-the-Earth (TTE) radio transmissions in four multistory buildings using the finite-difference time-domain (FDTD) method. These structures are generally made of reinforced concrete, whose steel content is the most important control on bulk conductivity. The floors and walls are represented as sheets of a given conductance, based on the fact that electromagnetic geophysical methods will only resolve conductive sheets in terms of their conductance as opposed to both conductivity and thickness. We validate this approach first using synthetic data, and second, by comparison with field data. Conductance models were derived from observed data for a variety of propagation environments, including reinforced concrete, steel floors, and basements, and for transmission into, out of, or within a building. The models were able to account for non-intuitive observations, such as increases in signal strength near the edges of buildings and in localized areas in between buildings. Conductances obtained for the floors and walls could be used as representative values in future forward modelling to assess the viability of, or optimize a TTE radio link in a multistory building.

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Keywords Antennas, Buildings, Conductivity, conductor, FDTD, Finite difference methods, multistory building, Numerical models, Radio transmitters, Through-the-Earth radio, Time-domain analysis, VLF
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Journal IEEE Transactions on Antennas and Propagation
Ralchenko, M. (Maxim), Roper, M. (Mike), Samson, C, & Svilans, M. (Markus). (2017). Near-field VLF electromagnetic signal propagation in multistory buildings. IEEE Transactions on Antennas and Propagation. doi:10.1109/TAP.2017.2783321