All of
those results may be derived from the statement in words of the basic laws given earlier.
What we can deduce from those laws, without taking into account the properties on any
materials involved, is that the tangential component of E is continuous across any boundary;
the normal component of B is continuous across such a boundary; the normal component
of D may be discontinuous across a boundary, with a discontinuity being equal to
any conduction charge density rvc per unit area on the surface; and the tangential component
of H may be discontinuous across a boundary, with the discontinuity being equal to
in magnitude and at right angles in direction to a surface current density ?¬‚owing on the
surface.
FIGURE 12.1
Electric ?¬?eld near a conducting surface.
Charge
Conducting surface
Electric field
FIGURE 12.2
Oscillating magnetic ?¬?eld near a conducting
surface. Conducting plane
Current
Magnetic field
234 RFID Handbook: Applications, Technology, Security, and Privacy
When we take into account the restrictions imposed by the properties of the materials
which may exist on one or other side of the boundary, we may further conclude that the
electric ?¬?eld is continuous across the boundary for all materials and time variations; that
there are no electric ?¬?elds or ?¬‚uxes, or time-varying magnetic ?¬?eld or ?¬‚ux densities inside a
good conductor; that a surface current density can exist only on the surface of a perfect
conductor; and that time-varying charge density cannot exist on the surface of a
perfect insulator although a static surface charge density can.
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