Radio frequency currents induced in the human body for medium-frequency/high-frequency broadcast antennas

Radio frequency currents in the human body, induced by high-frequency and medium-frequency high-power broadcast antennas, were studied theoretically and experimentally. An analytical formula was derived to calculate the foot currents in a grounded semispheroidal model of the human body. The model agrees within 30% with the results given by the standard formula presented by Gandhi on the basis of measurements with humans. Near 100 kHz, the model predicts a decrease of 14% of the current dissipated in the human body, which is due to the beta relaxation of the cells. The effect of the body and foot-contact impedances were studied with the aid of a simplified equivalent circuit which showed that the body impedance does not considerably affect the foot current below 10 MHz. The normalized foot currents measured in front of the broadcast antennas were within 30% agreement of the currents calculated with the Gandhi formula from the electric fields measured at a height of 1 m. The foot currents are induced by vertical electric fields for both medium-frequency and high-frequency antennas in spite of a strong horizontal component in the latter case. The distance at which the occupational exposure limit of 200 mA was exceeded in the worst (maximum coupling) case was 50 m for the high-frequency antenna and < 14 m for the medium-frequency antenna. In the latter case, the radio frequency shocks resulting from touching ungrounded metallic bodies impose a practical limit to about 40 m.