Magnetron for microwave ovens

Details Magnetron for microwave ovens Magnetron for microwave ovens

2002-11-29

2004-02-17

Wong, Don (Department: 2821)

Electric lamp and discharge devices: systems

Combined load device or load device temperature modifying...

Distributed parameter resonator-type magnetron

C315S039630

Reexamination Certificate

active

06693378

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATION
This application claims the benefit of Korea Application No. 2002-46167, filed Aug. 5, 2002, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a magnetron for microwave ovens, and more particularly, to a vane of a magnetron for microwave ovens.
2. Description of the Related Art
Generally, a magnetron is constructed to have an anode and a cathode such that thermions are discharged from the cathode and spirally moved to the anode by electromagnetic force. A spinning electron pole is generated around the cathode by the thermions and current is induced in an oscillation circuit of the anode, so that oscillation is continuously stimulated. An oscillation frequency of the magnetron is generally determined by the oscillation circuit, and has high efficiency and high output power. The magnetron is widely used in home appliances, such as microwave ovens, as well as in industrial applications, such as high-frequency heating apparatuses, particle accelerators and radar systems.
The general construction and operation of the above-described magnetron are briefly described with reference to
FIGS. 1 through 3
.
As shown in
FIG. 1
, the magnetron generally includes a positive polar cylinder
101
made of an oxygen free copper pipe or the like, a plurality of vanes
102
disposed in the positive polar cylinder
101
to constitute a positive polar section along with the positive polar cylinder
101
and radially arranged at regular intervals to form a cavity resonator, and an antenna
103
connected to one of the vanes
102
to induce harmonics to an outside. The magnetron also includes a large-diameter strip ring
104
and a small-diameter strip ring
105
disposed on upper and lower portions of the vanes
102
, respectively, to alternately and electrically connect the vanes
102
so that the vanes
102
alternately have the same electric potential as shown in FIG.
2
.
Rectangular depressions
202
are formed in the vanes
102
, respectively, to allow the strip rings
104
and
105
to alternately and electrically connect the vanes
102
, and cause each opposite pair of the vanes
102
to be disposed in an inverted manner. According to the above-described construction, each of the pair of opposite vanes
102
and the positive polar cylinder
101
constitute a certain LC resonant circuit. Additionally, a filament
106
in a form of a coil spring is disposed in an axial center portion of the positive polar cylinder
101
, and an activating space
107
is provided between radially inside ends of the vanes
102
and the filament
106
. An upper shield
108
and a lower shield
109
are attached to a top and bottom of the filament
106
, respectively. A center lead
110
is welded to a bottom of the upper shield
108
while being passed through a through hole of the lower shield
109
and the filament
106
. A side lead
111
is welded to a bottom of the lower shield
109
. The center lead
110
and the side lead
111
are connected to terminals of an external power source (not shown), and therefore, forms a closed circuit in the magnetron.
An upper permanent magnet
112
and a lower permanent magnet
113
are provided to apply a magnetic field to the activating space
107
with opposite magnetic poles of the upper and lower permanent magnets
112
and
113
facing each other. An upper pole piece
117
and a lower pole piece
118
are provided to induce rotating magnetic flux generated by the permanent magnets
112
and
113
into the activating space
107
. The above-described elements are enclosed in an upper yoke
114
and a lower yoke
115
. Cooling fins
116
connect the positive polar cylinder
101
to the lower yoke
115
, and radiate heat generated in the positive polar cylinder
101
to the outside through the lower yoke
115
.
According to the above-described construction of the magnetron, when power is applied to the filament
106
from the external power source, the filament
106
is heated by operational current supplied to the filament
106
, the thermions are emitted from the filament
106
, and a group of thermions
301
are produced in the activating space
107
by the emitted thermions as shown in FIG.
3
. The group of thermions
301
alternately imparts potential difference to each neighboring pair of the vanes
102
while being in contact with front ends of the vanes
102
, being rotated by influence of the magnetic field formed in the activating space
107
, and being moved from one state “i” to another state “i”. Accordingly, harmonics corresponding to a rotation speed of the thermion group
301
are generated by oscillation of the LC resonant circuit formed by the vanes
102
and the positive polar cylinder
101
, and transmitted to the outside through the antenna
103
.
Generally, frequency is calculated by an equation
f
=1/2
&pgr;{square root over (LC)},
where L is an inductance and C is a capacitance. Values of the variables of the above equation are determined by geometrical configurations of circuit elements. Thus, the configurations of the vanes
102
constituting part of the LC resonant circuit are principal factors in determining the frequency of harmonics.
In the magnetron having the above-described construction and operation, noise of a considerably wide band considered as unwanted electromagnetic waves is generated. The noise may induce malfunction in other devices. Thus, a reduction in the noise is an important technical issue that has been researched for a long time. In this regard, the geometrical configuration of the vane, which is one of factors that determine a frequency of electromagnetic waves generated in the magnetron, is an important technical issue relative to the generation of noise.
Conventional vanes constituting parts of the magnetron are constructed as shown in FIG.
4
. The shortcomings of the conventional vanes are described with reference to FIG.
4
. As shown in
FIG. 4
, a pair of neighboring vanes is illustrated as being opposite to each other for convenience of explanation.
As shown in
FIG. 3
, the depressions
202
are formed to allow the strip rings to be disposed therein. In
FIG. 4
, the depressions
202
are constructed to have rectangular shapes. After the thermions arrive at sections “a,” “b” and “c” of the front side of a vane
102
, the thermions arriving at the section “a” are moved to the section “c” of the front side of another neighboring vane
102
because of the inverted relationship of the pair of neighboring vanes
202
. As the thermions arrive at the front side of the vane
102
, a potential difference is generated between the pair of neighboring vanes
102
and, current (that is, the flow of thermions) is supplied to the filament
106
. The thermions arriving at the sections “a” and “c” are moved to the sections “c” and “a” of the front side of the neighboring vane
102
along roundabout paths due to a hindrance effect of the depressions
202
, thus resulting in delaying the arrival of the thermions at the section “b” of the front side of the neighboring vane
102
in comparison with the arrival of the sections “a” and “c”.
In
FIG. 4
, arrows L
1
, L
2
and L
3
represent distances along which the thermions travel from one of the vanes
102
to the neighboring vane
102
. The thermions at the sections “a” and “c” travel along the same distance at the same time. A main frequency of the magnetron is generally determined by the sections “b” of the vanes
102
. Therefore, the delays in the thermions reaching the sections “a” and “b” of the neighboring vane
102
cause noise in all the frequencies of the magnetron.
SUMMARY OF THE INVENTION
Accordingly, it is an aspect of the present invention to provide a magnetron for microwave ovens to reduce high frequency noise caused by a difference between velocities of thermions flowing through vanes of the magnetron, thus optimizing frequency of microwaves emitted from the magnetron.
A

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