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Interaction of Extremely Low–Frequency Electromagnetic Fields
4.5.2 ELF Magnetic Field
During the 1970s, after the development of ELF electric field dosimetric technologies,
the calculations focused on induced currents and electric fields in simple spheroidal and
prolate human and animal models exposed to ELF magnetic fields by analytical method
(Spiegel 1977b; Hart 1992b). Spiegel (1977b) calculated the induced current densities
and power absorbed by a prolate spheroid model representing a man when exposed to
ELF magnetic fields of transmission lines. Using commercially available spreadsheet
software running a FDM, Hart, Evely, and Finch (1993) presented the calculation for
electric fields and current density distributions induced in an irregularly shaped inhomogeneous model by ELF magnetic fields.
4.5.2.1 Coupling with Simple and Analytical Models
In the past, it was not clear whether observed biological effects were due to magnetic
fields or induced currents inside the test sample. Applying experimental dosimetry, a
circular dish system (petri dish) was used to clarify whether observed biological effects
were caused directly by magnetic fields or by induced currents. If the results are similar
across the petri dish, effects are due to magnetic field, whereas if the results vary across
the cross-section of the petri dish, effects are due to induced currents. Subsequently, calculations of induced currents and induced electric fields for several dish systems, including one using an annular ring, have been published (Misakian 1991; Misakian et al.
1993). Polk (1986) examined the effects of DC and ELF magnetic fields on the motion
and distribution of counterions on surfaces of cylindrical biological cells.
As far as experimental dosimetry is concerned, there are many reports on measuring magnetically induced electric fields. Experimental dosimetry for measurement of
induced electric fields proves difficult due to the need of physical probes in the complex
biological tissues. It entails interactions in term of electromagnetic interference between
the physical probe and exposure to magnetic fields. Miller and coworkers published
a series of papers on experimental dosimetry using a miniaturized physical probe to
measure internal electric fields in conductive rat and human models, chicken eggs, and
anesthetized rats (Miller 1991a,b, 1994, 1996; Miller and Creim 1997; Robertson-De
Mers and Miller 1992). They designed and built a miniaturized electric field probe to
provide data on fields induced by 60 Hz magnetic fields in saline–agar models of a rat
and a human. The probe consisted of 200-μm-diameter silver wires forming Ag-AgCl
electrodes imbedded in a 17-gauge hypodermic needle. The voltage across the probe
electrodes was measured with a lock-in amplifier. The measurement results of this probing agreed roughly with numerical calculations based on the simple cylindrical case.
In the subsequent investigation, the electric fields induced in an egg by a 60 Hz magnetic field at 1 mT were measured. As a result, different conductivities of the yolk and
egg modified the induced electric fields. In order to provide data on the electric fields
induced in an actual rat by a 60 Hz magnetic field exposure, Miller and coworkers measured the induced electric fields related to 60 Hz magnetic fields at 1 mT with a miniaturized electric field probe at 2-mm resolution using rat carcasses. The probe scans
were made at three positions in the abdomen for axial, frontal, and lateral exposure. The
scanning results showed significant differences from the theoretical calculation based
Interaction of Extremely Low–Frequency Electromagnetic Fields
4.5.2 ELF Magnetic Field
During the 1970s, after the development of ELF electric field dosimetric technologies,
the calculations focused on induced currents and electric fields in simple spheroidal and
prolate human and animal models exposed to ELF magnetic fields by analytical method
(Spiegel 1977b; Hart 1992b). Spiegel (1977b) calculated the induced current densities
and power absorbed by a prolate spheroid model representing a man when exposed to
ELF magnetic fields of transmission lines. Using commercially available spreadsheet
software running a FDM, Hart, Evely, and Finch (1993) presented the calculation for
electric fields and current density distributions induced in an irregularly shaped inhomogeneous model by ELF magnetic fields.
4.5.2.1 Coupling with Simple and Analytical Models
In the past, it was not clear whether observed biological effects were due to magnetic
fields or induced currents inside the test sample. Applying experimental dosimetry, a
circular dish system (petri dish) was used to clarify whether observed biological effects
were caused directly by magnetic fields or by induced currents. If the results are similar
across the petri dish, effects are due to magnetic field, whereas if the results vary across
the cross-section of the petri dish, effects are due to induced currents. Subsequently, calculations of induced currents and induced electric fields for several dish systems, including one using an annular ring, have been published (Misakian 1991; Misakian et al.
1993). Polk (1986) examined the effects of DC and ELF magnetic fields on the motion
and distribution of counterions on surfaces of cylindrical biological cells.
As far as experimental dosimetry is concerned, there are many reports on measuring magnetically induced electric fields. Experimental dosimetry for measurement of
induced electric fields proves difficult due to the need of physical probes in the complex
biological tissues. It entails interactions in term of electromagnetic interference between
the physical probe and exposure to magnetic fields. Miller and coworkers published
a series of papers on experimental dosimetry using a miniaturized physical probe to
measure internal electric fields in conductive rat and human models, chicken eggs, and
anesthetized rats (Miller 1991a,b, 1994, 1996; Miller and Creim 1997; Robertson-De
Mers and Miller 1992). They designed and built a miniaturized electric field probe to
provide data on fields induced by 60 Hz magnetic fields in saline–agar models of a rat
and a human. The probe consisted of 200-μm-diameter silver wires forming Ag-AgCl
electrodes imbedded in a 17-gauge hypodermic needle. The voltage across the probe
electrodes was measured with a lock-in amplifier. The measurement results of this probing agreed roughly with numerical calculations based on the simple cylindrical case.
In the subsequent investigation, the electric fields induced in an egg by a 60 Hz magnetic field at 1 mT were measured. As a result, different conductivities of the yolk and
egg modified the induced electric fields. In order to provide data on the electric fields
induced in an actual rat by a 60 Hz magnetic field exposure, Miller and coworkers measured the induced electric fields related to 60 Hz magnetic fields at 1 mT with a miniaturized electric field probe at 2-mm resolution using rat carcasses. The probe scans
were made at three positions in the abdomen for axial, frontal, and lateral exposure. The
scanning results showed significant differences from the theoretical calculation based