
27Fundamentals of Wave Propagation
δ
α ωµσ
= ≈
1 2
(2.17)
2.9 Surface Impedance
At high frequency the ow of current is almost entirely conned to a very
thin layer of the surface of the sheet of a conductor. The impedance (Z
s
)
offered by the surface to the ow of current is referred to as surface imped-
ance Z
s
and is given by
Z
j j
R jX
s s s
= = = = +
( )ωµσ
σ
ωµ
σ
η
(2.18)
Where
R X
s s
= =
ωµ
σ2
(2.19a)
In view of Equation 2.17, Equation 2.19a can be written as
R X
s s
= =
1
( )σδ
(2.19b)
2.10 Poynting Theorem
The rst Maxwell’s Equation 2.1a can be manipulated to yield the relation:
( ) ( )E J d
t
H
d
t
E
d E H ds
s
⋅ ⋅
ν ν ν
ν
∂
∂
µ
ν
∂
∂