Natural propagation of electromagnetic waves in tunnels

An experimental study of the electromagnetic wave propagation in various tunnels at frequencies between 1 MHz and 1000 MHz is presented. The results provide a better understanding of various propagation mechanisms in underground galleries. The analysis shows the existence of a cutoff frequency, and enables one to distinguish three different ranges of frequency characterized by three different modes of propagation. Experimental verification was made in road and mine tunnels of various shapes and sizes. The results show a strong correlation between the propagation characteristics and the transverse dimensions of the tunnel.