3
Coupling of Electromagnetic Fields into Biological Systems
opening of conductance pores and into molecular mechanisms that underlie biological
effects. The technological breakthrough at millimeter-wave (mmW) and terahertz frequencies has stimulated new applications not only in biology and medicine but also in
environmental studies, material science, telecommunication, and security screening in
the form of whole-body image scans. Besides their primary intended roles, these fields
and waves produce other effects that may influence the vital activities of a biological
system. The changes produced depend on many physical and biological factors. They
may or may not be grossly apparent and observable soon after exposure of the living
organism.
The biological effects of electromagnetic fields and waves have been a subject of scientific research since the discovery of electromagnetic radiation and its first use in therapeutic applications more than 100 years ago. Since then, our knowledge regarding its
effects on health has increased tremendously. Nevertheless, they have become the focus
of much attention because of the expansion and distribution of electric power at 50 and
60 Hz in the extremely-low-frequency (ELF) spectrum (between 3 Hz and 3 kHz) and
because of the accelerated use of RF radiation (300 MHz–6 GHz and beyond) in wireless
communication in recent decades. A notable reason for the increased attention on the
subject is the uncertainty and lack of understanding of the mechanism of interaction
of electromagnetic fields and waves with biological systems. Although ELF fields and
RF radiation are all part of the same known electromagnetic spectrum, the mode of
coupling into biological tissues and mechanism of interaction can be quite different for
the two. This chapter discusses the coupling of electromagnetic fields and waves into
biological systems. Clearly, regardless of the mechanism of interaction fields must be
coupled into the system and energy must be transferred, absorbed, or deposited in the
biological system in order for the system to respond in some manner. Thus, to gain a
greater knowledge of biological responses, the electric, magnetic, or electromagnetic
field that is effective in exerting its influence must be quantified and correlated with the
observed effect.
This chapter is intended to provide a common understanding of essential interactions and field coupling phenomena to facilitate better appreciation and understanding
of their importance in research on biological effects and in scientific, industrial, and
medical applications. For further information, the reader is referred to the book series
on Advances in Electromagnetic Fields in Living Systems edited by Lin (1994, 2009).
1.2 Physical Laws Governing
Electromagnetic Phenomena
Electromagnetic phenomena consist of electric and magnetic fields that change with
space and time. Their spatial variation is dictated by the electromagnetic properties
of the material medium, that is, electrical permittivity and magnetic permeability.
The physical interactions of electromagnetic fields with biological systems are defined
by laws describing their characteristics and behavior in biological systems and other
material media. These mathematical expressions are commonly known as Maxwell’s
equations (Maxwell 1904). Maxwell’s equations are laws that define the relationship
Coupling of Electromagnetic Fields into Biological Systems
opening of conductance pores and into molecular mechanisms that underlie biological
effects. The technological breakthrough at millimeter-wave (mmW) and terahertz frequencies has stimulated new applications not only in biology and medicine but also in
environmental studies, material science, telecommunication, and security screening in
the form of whole-body image scans. Besides their primary intended roles, these fields
and waves produce other effects that may influence the vital activities of a biological
system. The changes produced depend on many physical and biological factors. They
may or may not be grossly apparent and observable soon after exposure of the living
organism.
The biological effects of electromagnetic fields and waves have been a subject of scientific research since the discovery of electromagnetic radiation and its first use in therapeutic applications more than 100 years ago. Since then, our knowledge regarding its
effects on health has increased tremendously. Nevertheless, they have become the focus
of much attention because of the expansion and distribution of electric power at 50 and
60 Hz in the extremely-low-frequency (ELF) spectrum (between 3 Hz and 3 kHz) and
because of the accelerated use of RF radiation (300 MHz–6 GHz and beyond) in wireless
communication in recent decades. A notable reason for the increased attention on the
subject is the uncertainty and lack of understanding of the mechanism of interaction
of electromagnetic fields and waves with biological systems. Although ELF fields and
RF radiation are all part of the same known electromagnetic spectrum, the mode of
coupling into biological tissues and mechanism of interaction can be quite different for
the two. This chapter discusses the coupling of electromagnetic fields and waves into
biological systems. Clearly, regardless of the mechanism of interaction fields must be
coupled into the system and energy must be transferred, absorbed, or deposited in the
biological system in order for the system to respond in some manner. Thus, to gain a
greater knowledge of biological responses, the electric, magnetic, or electromagnetic
field that is effective in exerting its influence must be quantified and correlated with the
observed effect.
This chapter is intended to provide a common understanding of essential interactions and field coupling phenomena to facilitate better appreciation and understanding
of their importance in research on biological effects and in scientific, industrial, and
medical applications. For further information, the reader is referred to the book series
on Advances in Electromagnetic Fields in Living Systems edited by Lin (1994, 2009).
1.2 Physical Laws Governing
Electromagnetic Phenomena
Electromagnetic phenomena consist of electric and magnetic fields that change with
space and time. Their spatial variation is dictated by the electromagnetic properties
of the material medium, that is, electrical permittivity and magnetic permeability.
The physical interactions of electromagnetic fields with biological systems are defined
by laws describing their characteristics and behavior in biological systems and other
material media. These mathematical expressions are commonly known as Maxwell’s
equations (Maxwell 1904). Maxwell’s equations are laws that define the relationship