Numerical Analysis of Induced Current in Human Head Exposed to Nonuniform Magnetic Field Including Harmonics

In this paper, induced currents in an anatomical head model exposed to a non-uniform ELF magnetic field (B-field) including harmonics are numerically calculated, and are discussed based on the basic restriction established by International Commission on Non-Ionizing Radiation Protection (ICNIRP). A casual hair dryer of 100V and 1.2kW is chosen as a typical source of the non-uniform B-field including both the fundamental and second harmonic components. The B-field distribution around the hair dryer is estimated by using the 3-orthogonal magnetic dipole moments, which are derived from a couple of measured values around it. The high-resolution human head model used is constructed based on the MRI images of a real human, and consists of six kinds of tissues (bone, brain, eyeballs, muscle, skin and blood). So-called impedance method is used for the numerical calculation of the induced current. The numerical results show that the maximum values of the induced current of 17µA/m², for the 60Hz component, which is about 1/120 of the ICNIRP basic restriction appear in the muscle near the eyeball when the hair dryer is used from the side of the head model, and the averaged current in the eyeballs that have the highest conductivity is the highest among the six tissues. It is also demonstrated that the induced current due to the 120Hz B-field becomes comparable to the 60Hz current although the magnitude of the 120Hz B-field is much smaller than that of the 60Hz B-field.