Energy Bands
Piezoelectricity
Superconductivity
Techniques of Application of Electromagnetic Fields
Summary
References
Introduction
The electrical properties and processes exhibited by biological tissue are of interest because of
the insights that knowledge of them may provide concerning the way the body regulates its myriad
processes, and because they may help explain the effects produced by applied electromagnetic energy.
It is perhaps teleological to suggest that some electrical properties of tissue must have physiological
significance simply because they are there. On the other hand, nature does not frequently endow living
things with useless characteristics and it is especially important to explore those electrical properties
that do not readily fit into present orthodox concepts.
The following brief discussion of the electrical characteristics of tissue provides a framework
for understanding the studies that are described in later chapters. For a more comprehensive treatment,
the reader should consult the original literature.
Energy Bands
The electronic conductivity of a material is determined by the properties of its constituent atoms
or molecules, and by the manner in which they are arranged in the lattice (1). Conductivity can be
described in terms of a solid-state model that relates electronic processes to valance and conduction
energy bands. The valance band consists of electrons that, because they have relatively low energy, are
associated with individual atoms or molecules: the conduction band contains more energetic electrons
that are free to move throughout the material in response to applied electromagnetic energy.
The number and mobility of conduction electrons determines the electronic conductivity of a
material. If the valance and conduction bands are separated by a small gap, then, at typical
temperatures, thermal activity will deplete the valance band and populate the conduction band; such a
material is a conductor. If the bands are widely separated in energy, the conduction band will be vacant
and the material will be an insulator. A semiconductor is a material whose band structure falls between
that of a conductor and an insulator-it can be an insulator at one temperature and a conductor at a
higher temperature. Semiconductors can contain impurity atoms whose energy states lie within the gap
between the valance and conduction bands; such impurities strongly affect conductivity by donating or
accepting electrons.
An important consequence of the existence of energy bands is that they permit electronic
processes in one region of a material to affect not only the immediate area, but also the entire structure.
Szent-Gyorgyi proposed that common energy levels existed over relatively large dimensions in
biological structures, possibly with the cell wall itself as the boundary (2). Evans and Gergely (Szent-
Gyorgyi's student) calculated the band gap in hydrogen-bonded models of biopolymers and showed
that it would be so large that the biopolymers would behave electrically as insulators (3).
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