Microwave heating cavities and applicators - Microwave-Assisted Concrete Technology: Production, Demolition and Recycling - page 218

60

55

β × 35 cm

50

β × 30 cm

45

40 β × 25 cm

35

30

25

20

15

10

5

0

0.5 0.7 0.9 1.5

β Cavity's Physical Dimension Factor

1.1 1.3 1.7 1.9 2.1 2.3 2.5

Figure 6.18 Variation in the number of possible resonant modes with the size of a cav-
ity for a rectangular cavity at a microwave frequency of 2.45 GHz. (From
Mehdizadeh, M., Microwave/RF Applicators and Probes for Material Heating,
Sensing, and Plasma Generation: A Design Guide. Norwich, NY: William
Andrew, 2009. With permission.)

cavities are usually studied using empirical probing measurement methods
and numerical methods [7]. A variety of commercial numerical simulation
packages based on inite-element or inite-difference time domain methods
are available to perform cavity studies to investigate the performance of
alternative cavity designs for a certain application. One of the major capa-
bilities of state-of-the-art electromagnetic field analysis software such as
COMSOL is their multiphysics capability, which allows coupling of various
analysis, including electromagnetic, thermodynamic, and structural analy-
ses to study the behaviour of particular materials subjected to microwaves
in a multimode cavity [8,9]. Various examples of modeling performed using
such software packages were presented in Chapters 2 to 4 to illustrate the
capabilities of the various microwave-assisted methods introduced.

6.4.1.2 Improving the heating uniformity
in multimode cavities
As discussed, one of the major challenges in designing multimode cavities
for material processing is improving the field uniformity in the cavity. The
variations in the field intensity because of the modal configuration lead to
temperature nonuniformity in the load placed in the cavity. However, besides
the modal configuration, the temperature distribution in the load heated in
a multimode cavity is also affected by a number of other parameters. One