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Electromagnetic Fields in Biological Systems
exposure to electric fields generated by a transmission line (Deno 1977). Deno (1977)
presented induced currents in an anatomically detailed human model and developed a
simple measuring technique for the external surface electric fields on the human body
and human body model standing under the transmission lines. The human body was
assumed to act as a conductor at 50/60 Hz. It means that the objects like humans and
animals perturb electric fields in the vicinity of the transmission lines. This distortion
has the enhancement effect of the electric fields in the context of the object’s outer surface
and the attenuation effect of the electric fields inside the object. The charge distributions
and electric fields on the surface of the object are used for assessing the currents and the
electric fields inside the body. Deno (1977) also showed that the short-circuit currents
(current to ground) induced in the human body are proportional to the square of height
of the mannequin model. If the human body is 1.8 m in height and stands on the ground
under the vertical electric fields, short-circuit currents are about 17.5 μA/(kV/m). From
the field measurement, Deno (1979) estimated the current densities induced in various
parts of the grounded human body under uniform electric fields. The main conclusions
are (1) current densities inside the 1.78-m-tall human body standing in an unperturbed
electric field of 1 kV/m are in the range of 0.427 to 3.55 mA/m 2 and (2) the electric fields
on the surface are enhanced compared with the unperturbed electric fields and this
enhancement factor is 18.3 at the top of the head.
The first approach to the numerical estimation of internal electric fields and current
densities in humans was taken using simple models such as spheres and prolate and
oblate ellipsoids. The results of these investigations have been reviewed (Kaune and
Phillips 1985). Actual measurements have been performed for the short-circuit currents
in animal and human models exposed to uniform electric fields. It is worth noting that
between 1970 and 1980, many analytical methods addressed experimental and numerical dosimetries through specific simple geometrical models.
As for experimental dosimetry, measurements were limited for only short-circuit
currents through body cross-sections (Kaune and Forsyth 1985; Kaune, Kistler, and
Miller 1987). Kaune and Forsythe (1985) measured current densities in a homogeneous
mannequin model standing on the ground, which was subject to a vertical 60 Hz, 10 kV/m
electric fields. For comparison, researchers evaluated the measured current densities
induced in a homogeneous human model on the ground versus the measured current
densities induced in a grounded hemispheroidal model. The comparison between these
two models was positive. It means that the dosimetric evaluation of induced fields and
current densities in the human body depends on mathematical modeling. Then, Kaune,
Kistler, and Miller (1987) extrapolated the data associated with grounding to the one
related to ungrounded exposure conditions.
A number of analytical studies have been reported using a dielectric spherical model.
The geometric shapes of many living things such as humans and animals (rat, mice, and
baboons) do not represent spherical shapes. Researchers considered ELF electric fields
coupling to prolate and oblate dielectric spheroidal models. Researchers used simplistic
human models such as prolate dielectric spheroidal objects (Lattarulo and Mastronardi
1981; Shiau and Valentino 1981), circular cylinders (Kaune and McCreary 1985), and simplified body-like shapes in further analysis (Spiegel 1981; Chen, Chuang, and Lin 1986;
Dimbylow 1987). Shiau and Valentino (1981) studied the coupling between ELF electric