Magnetic signal transmission (MST) is an effective method for transmitting information underground by radio to allow efficient drilling work. This paper shows that the transmission media of MST are an electromagnetic wave and a domain wall. Experiments showed that the propagation time for MST signals becomes longer as the distance between the transmitting and receiving coils increases. The propagation time for magnetic signals is also affected by the rod material, the frequency, and the current. MST signals have a velocity of 2653.4 [m/s] when ƒ=200 [Hz], It=0.25 [A], χ= 1 [m] and the rod material is SPCC. The cause of the variance of the propagation time of MST signals was confirmed by impulse response.
