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Interaction of Extremely Low–Frequency Electromagnetic Fields
comparison between the induced current densities in the spherical conductive model
of parallel electric and magnetic fields and that of orthogonal fields, they suggested that
the total induced current densities were affected by the relationship between the magnitude and the phase difference of the mutually orthogonal electric and magnetic fields.
The second calculation using grounded and ungrounded homogeneous prolate spheroid
human models exposed to concurrent 60 Hz vertical, 1 kV/m electric fields and horizontal 1- to 5-μT magnetic fields with different phase angle between them was made. The
horizontal magnetic fields had important effects on the total induced current distributions. This distribution varied with the phase difference. Closing to the grounded condition, the contribution of the horizontal magnetic fields tended to decrease.
Dimbylow (2005) developed a female voxel model named NAOMI with a 2-mm resolution. He applied the NAOMI model to the calculations of induced current densities and
electric fields due to exposure to ELF magnetic and electric field. He also pointed out
that the induced electric field averaged over a volume of 1 mm 3 in nerve tissue might
be a more appropriate dose quantity for effects. An expert group from HPA (former
NRPB) proposed that the restriction of the induced electric field to less than 100 mV/m is
adequate to protect most adult population and that sensitive individuals should be adequately protected at lower induced electric fields, possibly about a factor of 5 lower, i.e.,
20 mV/m (McKinlay et al. 2004). The induced electric field around 100 mV/m has been
identified for its effects on the nervous system. In Dimbylow’s study, comparisons were
made between induced electric fields from the NAOMI model and those described in the
NRPB Document. A hybrid voxel-mathematical model with a resolution of 2 mm was
developed as a pregnant female model (Dimbylow 2006). Mathematical models with fetus
developing at the 8th, 13th, 26th, and 38th week of gestation were converted into voxels
and combined with NAOMI. This hybrid voxel-mathematical model was used to calculate
the electric fields and induced current densities when exposed to ELF EMF. Using the
originally developed pregnant female model named SILVY, Cech, Leitgeb, and Pediaditis
(2007, 2008) calculated the current densities in a pregnant woman model induced by
simultaneous 50 Hz homogeneous electric and magnetic fields. The SILVY model was
based on MRI and CT images of a pregnant woman in the 30th week of gestation. This
was an anatomical voxel model of an 89-kg woman. The electric current density distributions with this pregnant model were calculated, and the results were compared with basic
restriction recommended by ICNIRP guidelines. In the case of homogeneous electric and
magnetic field exposures, both fields induced the electric current densities and resultant
values were superimposed by vectorial addition. Under worst case conditions of simultaneous exposure, the basic restrictions exceeded ICNIRP guidelines within the CNS of the
mother. However, the basic restrictions are not exceeded in sole field exposure. In addition, the induced current densities within the fetus do not comply with basic restrictions.
In more realistic conditions, Xue, Wood, and Dovan (2004) calculated the induced
current densities in the fetus of pregnant workers in 50-Hz high magnetic field exposures. In this case, the body model consisted of a cylinder and an ellipsoid with two
outer layers. The hemispherically capped cylinder was used to model the trunk of a
pregnant woman and the ellipsoid was used to model a fetus. Two layers were amniotic
fluid and placenta. In the calculation, four different exposure scenarios were modeled
including a worse case: the body of the pregnant woman was at a distance of 30 cm from