e., E1??0). Consequently, D1??0, B1??0, and H1??0. Hence, for this case,
the boundary conditions become
^n E2 ?? 0, (13:5)
^n D2 ?? rs, (13:6)
^n H2 ?? Js, (13:7)
^n B2 ?? 0: (13:8)
Since ^n is the unit normal vector to the boundary, the expressions can be further written
in terms of the corresponding tangential and normal components (denoted with subscripts
??????t??™??™ and ??????n,??™??™ respectively) to
E2t ?? 0, (13:9)
D2n ?? rs, (13:10)
H2t ?? Js, (13:11)
B2n ?? 0: (13:12)
From here, it can be seen that for oscillating ?¬?elds there are only perpendicular (normal)
components of the electric ?¬?eld at the surface of a perfect electric conductor. There are no
250 RFID Handbook: Applications, Technology, Security, and Privacy
tangential components of the electric ?¬?eld directly next to a perfect electric conductor. On
the other hand, there are only tangential components of the magnetic ?¬?eld directly next to a
perfect electric conductor. There are no normal components of the magnetic ?¬?eld to the
surface of a perfect electric conductor. Hence, not all components of electromagnetic ?¬?elds
are available near a perfect electric conductor.
There are actually no perfect electric conductors in reality, but since metal has a high
conductivity, it is quali?¬?ed to be close enough as a perfect electric conductor. Figure 13.
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