4.2 Source and Vortex Interpretation
We remain ?¬?rmly committed to the source and vortex interpretation (Cole, 2002) of those
equations. In that interpretation, the earlier equations stated that the electric ?¬?eld vector E
can have vortices caused by changing magnetic ?¬‚ux; the magnetic ?¬?eld H can have vortices
caused by conduction or displacement currents; the electric ?¬‚ux density D can have sources
caused by conduction charge density; and the magnetic ?¬‚ux density vector B can have no
sources.
Electromagnetic Coupling in RFID 233
In linear media, some of the statements about D and B can be extended to E and H, but
when nonuniform ?¬?elds and boundaries are considered, it can be shown that E, D, and H
can have both sources and vortices, but B is alone in that it can have no sources.
Figures 12.1 and 12.2 provide archetypical illustrations of the source nature of the
electrostatic ?¬?eld and the vortex nature of a magnetodynamic ?¬?eld, as well as illustrations
of two of the most important boundary conditions which apply when any electric ?¬?eld E or
a magnetodynamic ?¬?eld H approaches a conducting surface.
12.4.3 Boundary Conditions
We have already given simpli?¬?ed illustrations for the most important cases of sinusoidal
electric and magnetic ?¬?elds occurring adjacent to conductors.
A full statement of the electromagnetic boundary conditions is provided later.
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