Unformatted text preview: Chapter 10 Electromagnetic Wave Propagation
in Isotropic Materials Different materials aﬁect the propagation of electromagnetic waves in different and
important ways. Materials can slow the waves, reﬂect them, redirect them, trap them,
attenuate them, and even absorb them. This chapter classiﬁes materials according to their conductivities and permittivities to determine their effects in each case.
August 25, 2009 10.1 Propagation in Dielectric Materials with Purely
Real Permittivities The simplest change we can make from propagation in free space is to consider mate—
rials 1n which the permittivity is a real constant differing from that of a vacuum, 60.
The displacement current in phasor form 1s J— - waE for harmonic oscillations, and
since no and s are purely real, J 1s 90° out of phase with E. This same temporal rela-
tionship exists for a vacuum for which 5 — so and the analysis of the wave equation
is identical, except for 5 replacing so. This leads to k2(w) = w2po€ => k(w) = :l:w,/p.oe As in the vacuum case, the wavenumber k is purely real, since no and s are real
numbers and very little changes in the earlier results. If n is diﬂ'erent from #0 as well, then clearly,
k(w) = :lszue The phase velocity and impedance formulas are, respectively, m/s and 17: thms 1
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- Fall '06