Electric lamp and discharge devices: systems – Combined load device or load device temperature modifying... – Distributed parameter resonator-type magnetron
Reexamination Certificate
2000-12-18
2002-12-31
Lee, Benny T. (Department: 2817)
Electric lamp and discharge devices: systems
Combined load device or load device temperature modifying...
Distributed parameter resonator-type magnetron
C315S039510
Reexamination Certificate
active
06501224
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a magnetron used in microwave heating apparatuses such as microwave ovens or in radars.
FIG. 1
is a half sectional view of a magnetron which has been conventionally employed. Numeral
1
denotes an anode shell which is made of oxygen-free steel or the like and which forms a part of a vacuum wall (wall surface of a vacuum vessel) wherein a plurality of vanes
2
are provided at an inner periphery thereof to extend towards the center in a radial manner with every second vane
2
being connected by strap rings
7
,
8
of small-diameter and large-diameter for achieving stabilization of &pgr; mode oscillation. Magnetic pole pieces
9
,
10
, which are also referred to as pole pieces, are respectively provided on both ends of the anode shell
1
for focusing a magnetic field in an interaction space formed between tip ends of the vanes
2
and a filament
3
which is axially provided in a central portion of the anode shell
1
to thus form anode portions.
The filament
3
is a filament obtained by winding, for instance, a thorium tungsten wire in a coil-like manner, and is provided at the central portion of the anode shell
1
in a space which is enclosed by the tip ends of the respective vanes
2
to form a cathode portion. End hats
4
,
5
for supporting the filament
3
are fixedly attached to both ends thereof. Numeral
6
denotes an antenna conductor connected to one of the vanes
2
, and the magnetic pole piece
9
is provided with a hole through which the antenna conductor
6
is pierced.
Numeral
11
denotes a top shell, which is a sealing metal, fixedly attached to the anode shell for pinching the magnetic pole piece
9
, numeral
12
denotes a stem metal, which is a sealing metal, fixedly attached to the anode shell
1
for pinching the magnetic pole piece
10
, the magnetic pole pieces
9
,
10
having a tapered portion having a thickness Tg, numeral
13
denotes an antenna ceramic fixedly attached to the top shell
11
through brazing for supporting an output portion, numeral
14
denotes an output pipe fixedly attached to the antenna ceramic
13
and further connected to the antenna conductor
6
, numeral
15
denotes an antenna cap which is press-fitted into the output pipe
14
, and numeral
16
denotes a stem ceramic fixedly attached to the stem metal
12
for supporting the end hats
4
,
5
.
The above members constitute a vacuum tube, while numerals
17
,
18
denote annular magnets which are respectively disposed above and below the anode shell
1
, numeral
19
denotes a cooling fin fitted and attached to an outer peripheral surface of the anode shell
1
, and numeral
20
denotes a yoke for enclosing the anode shell
1
, the magnets
17
,
18
and the cooling fin
19
. Numeral
21
further denotes a shielding case for enclosing the stem ceramic
16
projecting out from the yoke
20
and for housing therein a choke
22
and a feedthrough capacitor
23
which constitute a filter circuit.
Numeral
24
denotes a gasket which is in close contact with a joint portion of the microwave oven, and numeral
25
denotes a gasket ring press-fitted into the top shell
11
for holding the gasket
24
. In such an arrangement, a cylindrical space formed between the filament
3
and the vanes
2
is called an interaction space wherein thermoelectrons emitted from the filament
3
perform orbiting movements within the interaction space through magnetic force applied in a vertical direction with respect to an electric field to thereby generate microwaves of high-frequency energy. Microwaves which are generated at the anode portion will be transmitted through the antenna conductor
6
and emitted to the exterior from a surface of the antenna cap
15
.
However, a conventional magnetron is designed to prevent magnetic saturation of a magnetic circuit, and since the magnetron attached to a microwave oven will increase in magnetic temperature accompanying an increase in operational time, a central magnetic flux density of the interaction space will be decreased accordingly accompanying the operational time. Thus, oscillating efficiencies would fluctuate to cause unstableness in heating control of food within the microwave oven.
The present invention thus aims to provide a magnetron capable of restricting decreases in magnetic flux density, that is, decreases in oscillating efficiencies owing to increases in magnetic temperature of the magnetron accompanying operation of the microwave oven and capable of achieving substantially constant oscillating efficiencies.
SUMMARY OF THE INVENTION
In accordance with a first aspect of the present invention, there is provided a magnetron comprising an anode portion, a cathode portion provided in a center of the anode portion, a cylindrical interaction space formed of the anode portion and the cathode portion, and iron magnetic pole pieces located at both ends of the interaction space in an tube axis direction thereof, wherein a relationship between a thickness Tg (mm) of a tapered portion of the magnetic pole pieces and a magnetic flux Bg (mT, at 25° C.) of a center of the interaction space is set to satisfy 155<Bg/Tg<165.
In accordance with a second aspect of the present invention, there is provided a magnetron comprising an anode portion, a cathode portion provided in a center of the anode portion, a cylindrical interaction space formed of the anode portion and the cathode portion, and iron magnetic pole pieces located at both ends of the interaction space in an tube axis direction thereof, wherein an outer diameter of the interaction space is not more than a diameter of a central hole of the magnetic pole pieces and wherein a relationship between a thickness Tg (mm) of a tapered portion of the magnetic pole pieces and a magnetic flux Bg (mT, at 25° C.) of a center of the interaction space is set to satisfy 155<Bg/Tg<165.
With this arrangement, it is possible to restrict decreases in magnetic flux density, that is, decreases in oscillating efficiencies due to increases in magnetic temperature of the magnetron accompanying operation of the microwave oven and it is thus possible to obtain a magnetron with substantially constant oscillating efficiencies.
REFERENCES:
patent: 4772823 (1988-09-01), Matsuzaki et al.
patent: 5357168 (1994-10-01), See
patent: 5635798 (1997-06-01), Ogura et al.
patent: 2000-299070 (2000-10-01), None
European Search Report for EP 00127801 dated May 14, 2001.
Patent Abstracts of Japan: 03011526 (Jan. 18, 1991), 05041173 (Feb. 19, 1993), and 62113336 (May 25, 1987).
Hasegawa Setsuo
Miki Kazuki
Nakai Satoshi
Lee Benny T.
Sanyo Electric Co,. Ltd.
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