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Electromagnetic Fields in Biological Systems
by using a semianalytical solution method. In this study, the model was a biological
trimedium spherical structure composed of tissues, their membranes, and extra tissues. The results showed that both change in the thickness and electric properties of
bimembrane and the difference in the conductivities significantly affected the current
passing through the membrane, which resulted in the induced currents.
4.5.3 Extremely Low–Frequency Electromagnetic Field
It is possible to treat exposure to electric and magnetic fields separately in the ELF
region. If a human stands near and/or under a transmission line, the magnetic fields
generate electric fields and electric currents within the human body. The magnitudes
of the induced electric fields and the current densities are proportional to the radius of
the loop, the electrical conductivity of the tissue, and the rate of change and magnitude
of the magnetic flux density. The electric fields generated from the transmission line are
vertically polarized, and the current flows in the body from the head, through the torso,
to the feet. The EMF at the ELF region has a quasistatic nature, and exposure to electric
and magnetic fields is considered separately. In the case of simultaneous exposure to
ELF EMF, the induced electrical quantities can be superimposed (Olsen 1996). Exposure
to ELF EMF results in no temperature rise and no power absorption inside the body.
Table 4.5 shows the examples of the calculated and measured current densities in
simple and anatomical voxel human models exposed to EMF.
Spiegel (1976) calculated the ELF EMF coupling to homogeneous spherical models of
human and animals. He suggested that spherical dielectric models of humans or animals could be expected to provide the degree of the right order of magnitude of induced
currents, induced electric fields, and power absorption inside models from exposure to
the proposed Navy’s Sanguine antenna and extra high voltage (EHV)/ultra high voltage
(UHV) transmission lines. As an analytical solution, the induced electric fields inside a
dielectric sphere are the summation of the quasistatic solution by electric and magnetic
fields. The results showed, based on the validity of the spherical models, that neither
the Sanguine antenna nor the EHV/UHV transmission lines produced body current or
body heat levels to interfere with normal biological function of the human body.
Hart and Marino (1982) published a paper on the calculation of electric and magnetic
couplings to a homogeneous, grounded hemiellipsoid model exposed to a high-voltage
transmission line. They mentioned that the coupling depends strongly on the conductivity and shape of the model. The calculation of induced electric fields and current
densities was conducted for a live-line worker exposed to ELF EMF generated by highvoltage transmission line. This is the scenario for occupational exposure, and basically
is nonuniform exposure fields.
Using the FEM, Hoang et al. (2009) computed the induced currents in a heterogeneous human body model exposed to both the electric and magnetic fields generated
by a three-phase transmission line. A human body model (named ZOL) composed of
17 different tissues was built by using the segmented data of the Visible Human Project.
Furse and Gandhi (1998) used the FDTD method at 10 MHz utilizing the conductivities
corresponding to 60 Hz to calculate the electric fields and currents induced in the 6-mm
version of the Utah model and scaled to 60 Hz.