Magnetic field induced currents in a human head from use of portable appliances

The induced currents in a model of the human head resulting from use of small hand-held appliances were computed. The source of the induced currents, i.e. the alternating (60 Hz) magnetic field was modelled as a magnetic dipole. The limits of applicability of this model are given. The model of the human head was obtained by translating MRI data into tissue conductivity data. Computations of the distribution of the induced currents were performed using the impedance method. The induced current density rapidly decreases with the distance from the appliance. The maximum, however, predictably is not at the surface, because of the geometry of the head. For typical appliances, the values of the maximum current densities are high as compared to those induced by a uniform magnetic field. Generalized graphs were obtained for the maximum induced current density normalized to the appliance magnetic moment, as a function of the distance from the appliance. These graphs are given for two representative locations of the appliance with respect to the head.