incl
s
Q
BК
tg
Q
=
,
(6)
By analyzing them we can conclude that the ratio of these signals can be invariant
both to the size of the gap, and to the geometry of the aperture of the node, the
unevenness (nonplanality) of the object at the place of its interaction with the field in
the aperture. However, the expressions (5, 6) are approximate, since are based on the
theory of small perturbations.
Using the approximate expressions (5, 6), it is not difficult to show that from the
fundamental signals ΔQ
s
/Q
s
and Δf/f it is possible to form a signal that is not affected
by these interfering factors and uniquely depends on tgδ, which is important in the
microwave dielcometry of the object parameter
0
0
К(
1)
(
1)
incl
S
S
S
S
S
S
incl
S
S
КQtg
Qf
N
Qtg
Qf
=
−−
,
(7)
where Q
0
is the unloaded initial quality factor of the RMT.
More complete ideas about the behavior of such a combined signal are given by
exact numerical studies, some of which are presented in Fig. 6.
a)
b)
Figure 6. Invariance of the combined signal to the gap (a) and the tip radius for a
spherical and conical shape of the point (b)
Thus, with the help of this invariant relation, it is possible to transform a three-
parameter problem into a two-parameter problem by first selecting the correct range of
gaps and solving the inverse problem with respect to tgδ at each scan point.
CONCLUSION
Scanning microwave microscopy in its near-field version is still a fairly young
field of engineering for a physical and technological experiment. Accumulated
achievements in its development allow us to hope for greater future success when used
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