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Following this introduction, the next section will consider the behavior of electromagnetic
waves near metallic surfaces. This will be then followed by a section on the effects of
metallic surfaces on RFID tag antennas. Finally, the chapter will present a few examples
of passive UHF RFID tags suitable for attaching to metallic structures.
13.2 Electromagnetic Waves near Metallic Surfaces
For a boundary that lies between two media in space with medium 1 characterized by
dielectric permittivity ?«1, magnetic permeability m1, and electric conductivity s1, and
medium 2 characterized by ?«2, m2, and s2, the electromagnetic boundary conditions for a
general case can be expressed (in vector form for time varying ?¬?elds) as follow:
^n (E2 E1) ?? 0, (13:1)
^n (D2 D1) ?? rs, (13:2)
^n (H2 H1) ?? Js, (13:3)
^n (B2 B1) ?? 0, (13:4)
where
^n is the unit normal vector to the boundary directed from medium 1 to medium 2
E and H are the electric and magnetic ?¬?elds, respectively
D and B are the electric and magnetic ?¬‚ux densities, respectively
rs and Js are the surface charge density and surface current density, respectively, that
may exist at the boundary
If medium 1 is a metallic medium and we assume as a practical approximation that it is a
perfect electric conductor with in?¬?nite conductivity (s1!1), there will be no electric ?¬?eld
in this medium (i.
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