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Electromagnetic Fields in Biological Systems
carrying of 500 A (rms) of each conductor. The third scenario was the maintenance
condition in an underground vault. Conductors were separated 5.08 cm on-center, with
one cable pair and bus bar for each conductor. The last scenario was the inspection of
isophase buses of 700-MW generators. In this case, there were 11 conductors. The lower
conductors were located 1.2 m above ground, and the upper conductors were 3 m above
ground. The conductors were 0.9 m apart. Depending on the actual exposure scenarios
and using the proposed simple method for estimation of induced electric fields, the estimated dose for most organs is conservative.
In the computational approach, the human body model was constructed by discretization into small cells, voxels, with body tissue. Each tissue was generally assigned
conductivity and permittivity values of the human tissues. In calculations in the ELF
region, conduction current was considered and displacement currents were neglected
because of the small magnitude of permittivity. Barchanski et al. (2005b) checked these
assumptions using an anatomically realistic human body model, Hugo model, based on
the Visible Human representing a 38-year-old male (187-cm height and 113-kg weight)
in the frequency range of 10 Hz to 1 MHz. The conclusion is, by FIT, that the impact
of displacement currents on the electric fields is independent of model resolution. At
50 Hz, errors are 1% for the averaged electric fields and 2% for the maximum electric
fields. They emphasized that there existed some uncertainties concerning the model
and the dielectric tissue data in the ELF region and the research needed more accurate
measurements.
An interesting calculation of induced currents in rat was done by Wake, Tanaka, and
Taki (2000). They compared the relationship between the induced current densities in
pineal gland and retina of a rat and polarity of magnetic field exposure. Induced currents in two MRI-based numerical rat models with resolutions of up to 0.125 mm 3 were
calculated by the IM. The authors showed that calculated induced current densities in
the whole body were extremely small, <30 μA/m 2 in the whole body and <2 μA/m 2
in the pineal gland and the retina for both linearly and circularly polarized magnetic
fields. Because of the polarization in a vertical plane, both linearly and circularly polarized magnetic fields with the same strength had no significant difference in amplitude
or polarization of induced currents in the pineal gland. However, the magnetic fields
rotating in the horizontal plane produced the most circularly polarized currents both
in the pineal gland and in the retina. Wake et al. (1998) investigated the induced current density distributions in the heterogeneous human head model in magnetophosphenes. Magnetophosphenes is the flickering sensations of light when the human being
is exposed to a changing magnetic field. They applied a magnetic field of 20 Hz, 5 mT to
the center of the retina. The induced current density distributions throughout the head
were calculated. The maximum induced current density was estimated to be 11 mA/m 2
in the retina and the induced electric field was 7.3 × 10 −3 V/m. Electrophosphene is also
the flickering sensations of light when electric currents pass through the eye to induce
currents near the retina. Dosimetric studies for electrophosphenes at ELF electric fields
could be done to estimate the current densities and internal electric fields. The thresholds of electrophosphene in the internal electric field in the retina are 200–220 mV/m.
The induced current density depends on model conductivity (Carstensen et al. 1985;
Lindenblatt and Silny 2002; Taki, Suzuki, and Wake 2003).