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Interaction of Extremely Low–Frequency Electromagnetic Fields
field strength around the transmission line. They also estimated the effective number
and position of shield wires to reduce the ground-level field using CSM. Myung, Lee, and
Huh (1998) published a research paper on the calculation of the induced currents in the
human body around and under 765-kV transmission lines. The short-circuit currents in
the body were measured in the range of 0.3 to 6.8 mA. In addition, they calculated and
simulated the electric field distribution by applying their algorithm to the Korean case.
A series of research papers on the application of the FEM to the calculation of induced
current densities inside grounded and ungrounded human models exposed to 60 Hz
electric fields were published in Japan (Chiba et al. 1984; Chiba, Isaka, and Kaune 1998;
Chiba and Isaka 1997, 1998, 1999, 2000, 2004; Isaka et al. 1987; Matsumoto et al. 2004).
They presented the experimental and numerical results of induced currents and induced
electric fields in a highly simplified human body–shaped model. Chiba and coworkers
developed a FEM to estimate the distribution of the current densities in a human model.
In the calculations, they assumed that the human model consisted of a biological organism whose conductivity and permittivity were on the same order as those of human body
tissues. The first model was a cylinder with a hemisphere, and the second one was a modification of the first one, which resembled a human body much more. These axisymmetric
human models were made of wood and insulating material covered with aluminum foil.
They had a maximum diameter of 27 cm and heights ranging from 150 to 180 cm. They
also developed a cylinder plus hemisphere human model with the two tissues having
different conductivities. Based on the simple wooden model, the electric field strength at
the top of the head was 16.0 and 18.3 times higher than the unperturbed electric fields
attributed to the 150- and 180-cm-tall models. The induced current densities depended
on the transverse section areas and the height of the body part above ground but were
independent of conductivities of body tissues. The total induced currents and the induced
current densities matched the experimental results well. The current density distributions
in a human model standing on an insulating plate were also calculated by the FEM (Chiba
and Isaka 2000). Matsumoto et al. (2004) developed a two-step analytical method for the
estimation of the induced current densities in a three-dimensional shape model. Two
steps were involved in the estimation. The first step consisted of the deviation associated
with the induced currents originating from the surface of the human model, measured
through the surface charge method. The second step involved the application of these
values as the boundary values of the FEM, using an isoparametric hexahedral element.
Takuma et al. (1990) developed a three-dimensional method to calculate the induced
currents in human and baboon models using 60 Hz electric fields. Their calculation program was based on CSM. The animal model consisted of several block parts of simple geometric forms such as a sphere, a cylinder, or a cone. The total calculated induced currents in
the baboon model with the postures such as standing upright, positioned on four legs, and
sitting on the floor confirmed prior experimental values very well. Techaumnat, Hamada,
and Takuma (2000) presented the calculation results of electrostatically induced current
in a human model using the Boundary Element Method (BEM). The human model was
put together using second-order curved elements and had five distinct internal organs. The
conductivity of these internal organs had a considerable impact on the induced currents.
Table 4.2 gives the examples of the calculated and measured current densities in simple homogeneous and heterogeneous human models exposed to ELF electric fields.