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Electromagnetic Fields in Biological Systems
4.2.2.1 Coupling through ELF Electric Fields
When considering coupling with ELF electric fields, charges are induced on the body
surface of an organism. The external electric fields may be disturbed. This disturbance depends on the shape, size, and position of the organism in ELF electric fields.
If  the  human body is in vertical ELF electric fields, electric flux lines enter the body
surface perpendicularly and electric currents and electric fields are induced in the conductive human body.
4.2.2.2 Coupling through ELF Magnetic Fields
With regard to coupling of ELF magnetic fields, the magnetic permeability (μ) of humans
and animals is equal to the permeability of free space (μ 0 ), and organisms do not disturb
the magnetic field. However, electric field is induced by magnetic field based on Faraday’s
law. As a result, an electric current is induced in organisms exposed to ELF magnetic
fields. This induced current flows primarily in a circular path that is perpendicular to
the direction of applied ELF magnetic field. In the case of homogeneous materials, the
induced current densities are proportional to the radius of the loop, conductivity, frequency, and magnetic flux density. If the magnetic field is oriented from front to back,
the largest current densities can be obtained in the largest loop (Figure 4.1).
To summarize, there are major differences in the direction and strength of induced
currents inside an organism in relation to ELF electric and magnetic fields. In electric
field, the induction between high voltage of object and organisms causes current flow.
Vertical electric field on the surface of the organisms situated beneath a transmission
line triggers dominant current flow in vertical direction. The current will be greater in a
grounded human body under a transmission line than in an ungrounded one. The electric currents induced by magnetic field form closed loops and are called “eddy currents.”
These eddy currents are zero at the center of the plane perpendicular to the applied
magnetic field and grow larger as distance from the center increases.
4.3 Numerical Dosimetry Approaches
The state-of-the-art method for numerical computation of EMF inside the human and
animal models involves solving the Maxwell equation in anatomical, high-resolution,
realistic models based on magnetic resonance imaging (MRI) and computed tomography (CT). Due to the development of computational resources and techniques, numerical simulations have been successfully applied to problems in the field of electromagnetic
phenomena including bioelectromagnetics.
Frequently used numerical calculation methods for internal dosimetry in the ELF
region are the impedance method (IM) (Orcutt and Gandhi 1988) and scalar potential
finite difference (SPFD) method (Dawson and Stuchly 1996). These methods are applied
to computational human models constructed by voxels (cubic cells). For calculations,
quasistatic approximation is adopted since (1) the conducted current is dominant over
the displacement current for the human exposure to magnetic field of frequencies
below about 10 MHz and (2) the wavelength of the field is long relative to the human
body’s dimension. Additional methods that have been applied to bioelectromagnetic