Calculation of electric fields and currents induced in a millimeter-resolution human model at 60 Hz using the FDTD method with a novel time-to-frequency-domain conversion

The finite-difference time-domain (FDTD) method has previously been used to calculate induced currents in anatomically based models of the human body at frequencies ranging from 20 to 915 MHz and resolutions down to 1.31 cm. Calculations at lower frequencies and higher resolutions have been precluded by the huge number of time steps which would be needed to run these simulations in the traditional way. This paper describes a new method used to overcome this problem and calculate the induced currents in a MRI-based 6-mm-resolution human model at 60 Hz. A new algorithm based on solving two equations with two unknowns is used for calculating magnitude and phase from the CW FDTD simulation. This allows magnitude and phase calculations to be made as soon as steady-state is reached, which is within a fraction of a cycle. For incident electric fields of 10 kV/m, local induced current densities above 16 mA/m/sup 2/ have been calculated in the torso, with even higher values up to 45 mA/m/sup 2/ for the legs. These are considerably higher than the 4 or even 10 mA/m/sup 2/ that have been suggested in the safety guidelines.