Civil Engineering Reference
In-Depth Information
(a)
(b)
Figure 6.23
(a) Coaxial applicator; (b) strip transmission line.
strip transmission lines (Figure 6.23b). TEM applicators may operate over
a wide frequency range without any lower bound. The upper bound of the
operating frequency range of TEM applicators occurs when the wavelength
reaches or is close to the dimensions of the applicator cross section.
Contrary to TEM applicators, the direction of the field in TE or TM
applicators is not limited to the cross section of the applicator, and electric
and magnetic field components are also present in the direction of propaga-
tion. Unlike TEM applicators, which usually require at least two conduc-
tors, TE and TM applicators can consist of only one conductor, such as a
hollow waveguide. In addition, unlike TEM applicators, there is a lower
limit for frequency at which TE and TM waveguides can operate. This fre-
quency is referred to as the cutoff frequency. The most popular examples of
TE and TM applicators are open-ended waveguides and waveguide horns
(Figure 6.24).
The following reviews some of the basic working principles of open-
ended coaxial applicators with focus on their application in microwave
drilling and open-ended hollow rectangular waveguides with focus on
their application in microwave-assisted selective demolition of concrete dis-
cussed in Chapter 3.
Flared horn
Waveguide
Figure 6.24
Flared horn as an open-ended microwave applicator.
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