Electric lamp and discharge devices: systems – Combined load device or load device temperature modifying... – Distributed parameter resonator-type magnetron
Reexamination Certificate
1998-06-16
2002-08-20
Lee, Benny T. (Department: 2817)
Electric lamp and discharge devices: systems
Combined load device or load device temperature modifying...
Distributed parameter resonator-type magnetron
C315S039530
Reexamination Certificate
active
06437511
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetron, and particularly relates to a magnetron in which the structure of the choke is altered such that when designing the choke, the design allowance range is expanded so as to realize the optimum efficiency. Thus the unnecessary harmonic waves are more inhibited, and the coupling of the output part is improved due to the impedance of the choke, thereby doubling the output and efficiency.
2. Description of the Related Art
As shown in
FIGS. 1 and 2
, the conventional magnetron includes: a filament like cathode
1
disposed at the center of the interior; a cylindrical metal anode
2
installed around the cathode
1
to form an interaction space
3
; a plurality of vanes
9
installed in a radiative form around the cathode
1
, with one end each of the vanes
9
being fixed to the inside of the anode
2
; an antenna feeder
11
with one end of it electrically connected to the vanes
9
to transmit electronic energy; permanent magnets
6
and
7
respectively attached to an upper yoke
4
and a lower yoke
5
, for forming a closed magnetic circuit to supply magnetic fluxes to the interaction space
3
as shown in
FIG. 1
; a magnetic pole
8
for forming a magnetic circuit path; an anode seal
18
for serving as a magnetic circuit path and as a body support; and first and second chokes
20
and
21
for inhibiting the harmonic waves coming through the anode seal
18
as shown in FIG.
1
.
In
FIG. 1
, reference code
10
indicates cooling fins,
12
indicates a ventilating tube,
13
indicates an antenna ceramic,
14
indicates an antenna cap,
15
indicates a choke coil for preventing the reverse flow of the harmonic waves toward the power source,
16
indicates a high voltage capacitor,
17
indicates a filter box for removing the unnecessary radiations coming along the supply line, and
19
indicates a filament seal.
The conventional magnetron for microwave ovens constituted as above will be described as to its operations referring to
FIGS. 1
to
3
.
First, the magnetic fields of the permanent magnets
6
and
7
form a closed magnetic circuit along the upper and lower yokes
4
and
5
and the magnetic poles
8
, so that a magnetic field is formed within the interaction space
3
between the cathode
1
and the anode
2
.
Then power is supplied to the cathode
1
, so that an electric field is formed in the interaction space
3
. Then owing to the interaction between the electric field and the magnetic field, the cathode
1
discharges thermionic electrons.
Then the thermionic electrons perform cycloid movements within the interaction space
3
, i.e., within the plurality of resonance cavities which are formed by the plurality of the vanes
9
. Thus a high frequency energy (hereinafter, referred to as “microwaves”) which is an electron energy is generated. These microwaves are transmitted to the vanes
9
, and then are supplied into the cavity of the microwave oven through the antenna feeder
11
.
Under this condition, for example, microwaves of 2450 MHz are generated in the resonance cavities. Besides the fundamental waves, harmonic components having a frequency of integer multiple of that of the fundamental waves are generated simultaneously.
If these harmonic components together with the fundamental waves are supplied into the cavity of the microwave oven, then the shielding of the waves becomes much more difficult because the wavelengths of the harmonic waves are much shorter, with the result that the waves escape to the outside.
Even if the leaked harmonic waves are very weak, they cause serious harm to the human body. Further, they may interfere with the wireless communication. Therefore, in order to inhibit the leakage of the harmonic waves, a filter consisting of a coil and a capacitor is installed at the input side, and at the same time, first and second chokes
20
and
21
which take the form of a metal cylinder are coupled to the interior of the anode seal
18
of the output side.
The structures of the first and second chokes
20
and
21
are as shown in FIG.
3
. The first and second chokes
20
and
21
are installed above and below respectively within the anode seal
18
. The first choke
20
includes: a cylindrical body
20
a
for allowing the antenna feeder to pass through; and a flange part
20
b
extending from the bottom of the cylindrical body
20
a
toward the anode seal
18
.
The second choke
21
includes: a cylindrical body
21
a
for allowing the antenna feeder to pass through; and a flange part
21
b
extending from the bottom of the cylindrical body
21
a
toward the anode seal
18
.
The first and second chokes
20
and
21
are designed in the following manner. That is, if it is assumed that the wavelength of the harmonic waves to be removed is &lgr;, then &lgr;/4 is adopted as the basic dimension. Then by considering the flanging capacitance, the heights of the chokes are made slightly smaller than ¼ of the wavelength of the harmonic waves. In this case, however, the external conditions other than the choke height are not matched. As a result, an accurate design becomes difficult, and its application also becomes difficult. Therefore, the capability of inhibiting the harmonic components was limited.
Meanwhile, in order to assemble the first and second chokes
20
and
21
to the output part of the magnetron, there was employed a jig
22
which consists of a multi-stepped guide rod
22
a
and a base
22
b
for supporting the guide rod
22
a.
By using this jig
22
, the first and second chokes
20
and
21
are assembled in the following manner. That is, the second choke
21
is fitted to the guide rod
22
a
, and then the first choke
20
is fitted to it, in such a manner that the first and second chokes
20
and
21
should maintain a proper gap between them. In this state, a brazing is carried out to fix them to the anode seal
18
.
This will be described in further detail. That is, the second choke
21
is positioned such that its flange part
21
b
should be disposed below. In this state, the cylindrical body
21
a
is fitted to the guide rod
22
a
until the second choke
21
is engaged to a second engaging step
22
c
of the guide rod
22
a
, so as to make the second choke
21
secured. Then the flange part
20
b
of the first choke
20
is positioned so as for it to be disposed below, and then the cylindrical body
20
a
of the first choke
20
is fitted to the guide rod
22
a
until it is engaged to a first engaging step
22
d
. Thus a gap is maintained between the first and second chokes
20
and
21
.
Then in order to fix the first and second chokes
20
and
21
, brazing stocks are inserted into the anode seal
18
. Then they are passed through a high temperature hydrogen brazing furnace. Thus the brazing stocks are melted, and the respective parts are fixed.
Therefore, in the fixing method using the jig
22
, the inside diameter of the cylindrical body
20
a
of the first choke
20
should be necessarily smaller than the inside diameter of the cylindrical body
21
a
of the second choke
21
, if the assembling is to be possible. Thus a limit is imposed on designing the inside diameter which decisively affects the damping of fifth harmonic waves. Consequently, the fifth harmonic wave damping is lowered.
That is, the design should be such that the inside diameter of the first choke
20
should be smaller than that of the second choke
21
. Therefore, when designing it by considering the surrounding conditions and the inside diameters of the chokes, the design allowance cannot but be limited.
Particularly, the heights of the chokes should be reduced by considering the flanging capacitance based on experiments, and therefore, an accurate decision of the choke dimensions becomes difficult, with the result that there is a limit in improving the damping of the leakage of the harmonic waves.
SUMMARY OF THE INVENTION
The present invention is intended to overcome the above described disadvantages of the conventional art.
Therefore it is an ob
Lee Benny T.
LG Electronics Inc.
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