1 THE HEATING PRINCIPLE OF
MICROWAYE
Microwave is one kind of radio wave whose
wavelength
is
very
short,
frequency is
very
high. Therefore, it is
called
ultrahigh
frequency electromagnetic wave. Microwave can heat food mainly result in the
mutual
affect
of
the food in the microwave
field
and the microwave
field
itself.
Under the affect of microwave field, the thermal
effect
mechanism produced
from
the mutual affect of the
microwave and the food includes
two
aspects. One is Dielectric
loss
of polar molecule; the other is
conductive
loss
of ion.
Usually, food is constituted of organism (plant and animal). The organism is formed by
all
kinds of polar water
molecule,
polar protein molecule, and all
sorts
of saltion. The center of gravity of the positive and negative charge
in the molecule is not coinciding. In normal condition, the molecule is in irregular order due to its thermal action,
thus
the food do not appear polarity.
(FIG.
1-la).
Under the action of outer electric
field,
the positive end of the
polar molecule trend to the negative electric field, the negative end of polar molecule trend to the positive electric
field, and somewhat arrange in order through the direction of the electric field (FIG.
1-1
c). This phenomenon
usually is called
"TORGUE
POLARITY". When the outer electric field
apply
for the opposite
polarity,
the polar
molecule then arrange an opposite direction order accordingly (FIG.
1-1
b).
If
the direction of the outer electric field
changed repeatedly, the polar molecule
would
repeatedly sway accordingly. During the swaying, it is
understanding that the polar molecule would produce heat due to somewhat similar friction
among
them.
When
the electric field is applied for ultrahigh frequent microwave field from the outside, its direction would change tens
billion
times
per second, so do the molecule. This kind of molecule swaying producing similar frictional heat from
the
interference
and błock of the action strength among the molecule, and changed to microscopic microwave
heating.
Microwave
heating not
only
concerned the naturę of the matter
itself,
but
also
closely connected with the
electric strength and frequency. When the frequency is Iow, the molecule swaying
ratę
and the acute degree of
the mutual friction among the molecule is Iow, and would produce much heat. When the frequency is too high, as
the swing of the polar molecule is with rotating
inertia,
it
madę
the swing do not in
linę
with the changing rhythm
of the electric field because of the friction
drąg,
thus, actually
Iowed
the polar molecule swaying speed. The
friction dragging degree is concerning about the magnelectric wave frequency, polar molecule shape, and the
matter's
sticky degree. To different
matter's
molecule, there is different special frequency
żonę.
Those absorbing
microwave energy from this
żonę
arę
most capable to turn microwave energy to heat energy.
(a)
(b)
(c)
Fig.
1-1
Apart
from the above said
action,
there is another action which is electric ion under the action of
microwave
field,
act fiercely accompanied with the acceleration of electric field. The positive ion transfer to the negative polarity of
the field
while
the negative ion does opposite. Accompanying with the changing electric field, the electric ion
hanging accordingly. During the transferring, heat produced with the crash among the ion. This kind of action
takes the
main
effect to those microwaves heating of high salt molecule.
No matter it is the polar molecule swaying or the ion transferring, they both
arę
turning the microwave energy
which the heating matter got from the microwave field to heat energy. From the analysis of theory, we can draw
such
a conclusion that the power which a unit of volume matter absorbed from the microwave field as the
following formuła:
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