Electric heating – Microwave heating – With specific generator
Reexamination Certificate
2002-11-25
2004-07-06
Campbell, Thor (Department: 3742)
Electric heating
Microwave heating
With specific generator
C219S702000, C315S039510
Reexamination Certificate
active
06759639
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of Korean Application No. 2002-44453, filed Jul. 27, 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 to a magnetron for microwave ovens, and more particularly, to strip rings of a magnetron having predetermined geometrical configurations to increase the efficiency of the magnetron.
2. Description of the Related Art
Generally, a magnetron includes an anode, and a cathode which discharges thermions. The thermions are spirally moved by an electromagnetic force to reach the anode. At this time, a spinning electron pole is generated around the cathode by the thermions and an induced current is generated in an oscillation circuit of the anode, so as to continuously stimulate an oscillation. The oscillation frequency of the magnetron is generally determined by the oscillation circuit, and has high efficiency and high output power.
The above-described magnetron is widely used as parts of home appliances, including a microwave oven, as well as parts of industrial applications, such as a high-frequency heating apparatus, a particle accelerator and a radar system.
FIGS. 1
to
3
show the construction of a conventional magnetron.
As shown in
FIG. 1
, the magnetron includes a positive polar cylinder
101
made of, for example, an oxygen free copper pipe, and a plurality of vanes
102
which are disposed in the positive polar cylinder
101
and constitute a positive polar section along with the positive polar cylinder
101
. The vanes
102
are radially arranged at regular intervals to form a cavity resonator. An antenna
103
is connected to one of the vanes
102
to induce harmonics to the outside.
Referring to
FIG. 2
, a large-diameter strip ring
104
and a small-diameter strip ring
105
are 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. Rectangular vane channels
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 vanes
102
to be disposed in an upside-down manner.
According to the above-described construction, each opposite pair of vanes
102
and the positive polar cylinder
101
constitute a certain inductive-capacitive (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 radial inside ends of the vanes
102
and the filament
106
. A top shield
108
and a bottom shield
109
are attached to a top and bottom of the filament
106
, respectively. A center lead
110
is fixedly welded to a bottom of the top shield
108
while passing through a through hole of the bottom shield
109
and the filament
106
. A side lead
111
is welded to a bottom of the bottom shield
109
. The center lead
110
and the side lead
111
are connected to terminals of an external power source (not shown), so as to form 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 the 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
. A reference numeral
116
designates cooling fins which 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
.
Referring to
FIG. 3
, with reference to
FIG. 1
, as power is applied to the filament
106
from an external power source (not shown), the filament
106
is heated by an operational current supplied to the filament
106
, and thermions are emitted from the filament
106
. A thermion group
301
is produced in the activating space
107
by the emitted thermions. The thermion group
301
alternately imparts a potential difference to each neighboring pair of vanes
102
while being in contact with front ends of the vanes
102
, being rotated by the influence of a magnetic field formed in the activating space
107
and being moved from one state “i” to the other state “f.” Accordingly, harmonics corresponding to a rotation speed of the thermion group
301
are generated by the oscillation of the LC resonant circuit formed by the vanes
102
and the positive polar cylinder
101
, and are transmitted to the outside through the antenna
103
.
Generally, a frequency is calculated by the equation:
f
=
1
2
π
LC
where L is an inductance and C is a capacitance. The values of the variables of the equation are determined by the geometrical configurations of circuit elements. Accordingly, the configurations of the vanes
102
constituting a part of the LC resonant circuit are principal factors that determine the frequency of the harmonics.
An oscillation frequency of a magnetron for microwave ovens is fixed to a frequency of 2,450 MHz. Since the magnetron for the microwave ovens has a fixed frequency, the magnetron has to be precisely adjusted to the frequency of 2,450 MHz during a production thereof. Although the magnetron has a fixed frequency, the oscillation frequency of the magnetron varies in a range from about ±10 to about ±15 MHz around a central frequency by the variation of a load under actual operational conditions.
Although, in practice, the magnetron generates a variety of frequencies, a single prominent frequency is specified by a frequency measuring process, and referred to as the oscillation frequency of the magnetron. To set the oscillation frequency of the magnetron in the positive polar cylinder
101
, the large-diameter strip ring
104
and the small-diameter strip ring
105
, as well as the vanes
102
, play principal roles. That is, electric phases of the large-diameter and small-diameter strip rings
104
and
105
, which alternately connect the alternately arranged vanes
102
to allow each set of vanes
102
to have the same potential, are changed as electric phases of the vanes
102
are changed. The large- and small-diameter strip rings
104
and
105
oscillate while experiencing the alternate change of the electric phases. A certain amount of electrostatic capacity exists between the large-diameter and small-diameter strip rings
104
and
105
facing each other, and a certain electric oscillation is generated therebetween, generating an unwanted frequency called a parasitic frequency.
Accordingly, a minute frequency is set using the large- and small-diameter strip rings
104
and
105
. The shapes and sizes of the large- and small-diameter strip rings
104
and
105
, which are fixedly mounted in the magnetron, determine an electrostatic capacity between the large-diameter and small-diameter strip rings
104
and
105
, and a frequency related to the electrostatic capacity is generated. Hence, the magnetron is designed to adjust its frequency by controlling the shapes and sizes of the large-diameter and small-diameter strip rings
104
and
105
, and is required to have an entirely symmetrical configuration. Generally, the change of the frequency of the magnetron changes a Q value that determines the efficiency of the magnetron, and accordingly, changes the efficiency of the magnetron.
In the conventional magnetron, the large-diameter strip ring
104
has a geographical configuration of an inside diameter of 17.2 mm, an outside diameter of 18.6 mm, a thickness of 0.7 mm and a height of 1.5 mm, while the small-diamete
Rayskiy Boris V.
Shon Jong-Chull
Campbell Thor
Samsung Electronics Co,. Ltd.
Staas & Halsey , LLP
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