Clip from the opening post/link in this thread:
Those who have experimented with electric field transmitters like those above have probably discovered that they only work well when the antenna is free and clear and there is little solid matter between the transmitter and receiver. The electric field is easily "shorted out" by even slightly conductive materials. In contrast, this loop transmitter generates a magnetic field that can cut right through the thickest walls.
Just to note that electromagnetic radiation (a radio wave) ALWAYS includes both a magnetic and an electric field. Neither one can exist without the other. In the far field, they always have the same relationship to each other -- no matter what geometric form of antenna (vertical monopole, loop etc) produced that radiation.
Most consumer-grade, indoor AM broadcast band receivers use a horizontally oriented loopstick antenna, which responds only to the magnetic field of the radio wave. Those receivers have no problem receiving the radiation from the vertical monopole radiators of AM radio stations (licensed or unlicensed), because the magnetic field is oriented +/-90 physical degrees from the electric field, AND they are using only the magnetic field for such reception.