BACKGROUND OF THE INVENTION
(1) Field of the Invention
[0001] The present invention relates to a plate-type magnetron applied to high-frequency
heating devices such as microwave ovens etc., in particular, relating to a multi-purpose
plate-type magnetron which efficiently provides microwaves having a desired power
and frequency.
(2) Description of the Prior Art
[0002] A magnetron is a crossed-field device in which magnetic fields and electric fields
are produced orthogonally to each other in the interaction space of an electron tube,
and the oscillation modes are of two types, namely, the A-type oscillation and the
B-type oscillation.
[0003] Microwave Magnetrons - Massachusetts Institute of Technology Radiation laboratory
Series 6, edited by George B Collins, published by McGraw-Hill Book Company Inc, 1948,
Chapter 19 "Typical Magnetrons" p. 759 etc, especially pp. 766-769, is an example
of a prior art document describing a magnetron.
[0004] The A-type oscillation depends only on the magnetic field strength, and is produced
by periodic rotating movement of electrons caused by the magnetic field. Because the
wavelength of this oscillation is little affected by cavity resonators as external
circuits, unlike the B-type oscillation mode (described later), it is determined only
by the magnetic field and can be represented by the following relation:
![](https://data.epo.org/publication-server/image?imagePath=2002/19/DOC/EPNWB1/EP98301106NWB1/imgb0001)
where λ is the oscillation wavelength, H is the magnetic field strength and α is
2πmc/e. Here, m is the mass of electron and e is the charge of an electron, hence
the constant α is theoretically 10,650, but empirically, has a value from 10,000 to
13,000.
[0005] In this A-type oscillation, there are two kinds of electron orbits, one gaining energy
from the alternating electric field and the other giving up energy to the alternating
electric field, and it is necessary to remove the electrons in the former orbits.
[0006] Referring next to Fig.1, the B-type oscillation will be described.
[0007] Fig.1 is a diagram showing a conventional cylinder type magnetron configuration.
As shown in this figure, a cylindrical anode 21 has a plurality of vanes 22 extending
radially toward its center, forming cavity resonators. A cathode 23 is provided on
the central axis of the cylindrical anode thus defining the interaction space between
cathode 23 and vanes 22.
[0008] Provided on the top and bottom ends of anode 21 are pole pieces 24, each being attached
in close contact with a magnet 26 having a yoke 25. Provided between anode 21 and
yoke 25 are radiating plates 27 for releasing heat generated by anode dissipation.
This anode dissipation will arise when the electrons emitted from cathode 23 and accelerated
by the anode voltage collide with anode 21.
[0009] A pair of electrodes (end hats) 30 are provided across, or at right angles with the
direction of the magnetic field, sandwiching this interaction space. A negative voltage
is applied to these end hats 30, so that the electrons are confined within the interaction
space.
[0010] In this arrangement, the space inside the anode 21 is decompressed to a vacuum. When,
with a magnetic field formed in the interaction space by magnets 26, a high voltage
is applied to cathode 23 and vanes 22 using a power supply input portion 28, electrons
are emitted from cathode 23 toward vane 22.
[0011] The thus emitted electrons travel under the influence of the magnetic field from
magnets 26 toward vanes 22 following a spiral or cycloidal path. As a result, these
electrons give up energy to the cavity resonators, generating high-frequency electric
fields, which are output as microwaves through a microwave output portion 29.
[0012] As the electron source of the magnetron, a thermionic cathode is predominantly used
at present. A thermionic cathode is a cathode in which thermionic emission provides
the source of electrons. Thermionic emission is the mechanism for emitting electrons
over the potential barrier at the material surface by heating the material up to a
temperature from 1500 to 2500°K so as to impart energy equal to or greater than the
work function of the material to the free electrons in the conduction band. Thermionic
cathode is formed of a pure metal, or a metallic oxide, etc., but currently, a sintered
type which is obtained by mixing a Ba compound (5BaO·2Al
2O
3·CaO etc.) and a W powder and press-sintering the mixture, an impregnation type which
is obtained by impregnating Ba compound in a molten state into porous W, are mainly
used. Either of these has a high emission density of electrons and additionally has
advantages that gases are emitted less during evacuation and it can be reactivated
if it is exposed to the air because of the effect of barium aluminates used.
[0013] Another type of electron source is a cold cathode. A cold cathode is a cathode which
emits electrons based on field emission, instead of thermionic emission. Field emission
is a method of electron emission wherein a high electric field is applied at and in
proximity to the material surface to lower the potential barrier at the surface so
as to emit electrons, using the tunnel effect. This cathode is called a cold cathode
since it does not need to be heated, unlike the thermionic cathode. The current-voltage
characteristics can be approximated by the
Fowler-Nodeheim formula. Fig.2 shows a sectional view of the configuration of a cold cathode. Emitter
portions 90 made up of a metal or semiconductor such as Si etc. are made to have a
pointed structure so as to form a high voltage gradient therearound and are covered
with a metallic film forming a gate 70 with an insulating layer 80 such as SiO
2 film in between. When a voltage is applied to gate 70, a strong electric field is
generated at the pointed ends of the emitter, thereby causing emission of electrons.
The cold cathode has advantages over the thermionic cathode in that the operating
temperature is lower than that of the thermionic cathode and a high current density
can be obtained by providing them in an arrayed form.
[0014] The prevailing type of magnetrons currently used in high-frequency heating appliances
such as microwave ovens are of a cylindrical type. But there are some which use a
plate-type magnetron. Figs.3 and 4 are sectional and perspective views respectively,
showing a plate-type magnetron employing a cold cathode, similar to that shown in,
for example, EP-A-0 694 948.
[0015] A plate-type anode 41 shown in Fig.3 has a number of vanes 42 which are provided
on and perpendicularly to a cathode 43 and a sole portion 51, defining cavity resonators.
Here, sole portion 51 is at equi-potential with cathode 43, but indicates the portion
which will not contribute to emission of electrons unlike the cathode 43. Cathode
43 is arranged in the lower left portion of anode 41. The space between anode 41 and
sole 51-vanes 42 forms an interaction space. A pole piece for forming a uniform magnetic
field in the interaction space is attached to the magnet of the yoke, on either side
of anode 41. This yoke has radiating plates 47 for releasing heat generated due to
anode dissipation.
[0016] In this configuration, the space inside the anode 41 is decompressed to a vacuum.
When, with a magnetic field formed in the interaction space by magnets 46, voltages
are applied between gate 60 and sole 51-vanes 42 and between anode 41 and sole 51-vanes
42 from the power supply input portion, electrons are emitted from cathode 43 toward
vanes 42, as illustrated using Fig.2.
[0017] The thus emitted electrons travels under the influence of the magnetic field from
magnets 46 towards the right in Fig.2, in the interaction space, following a cycloidal
path in a similar manner as in a cylindrical magnetron. During travel these electrons
give up energy to the cavity resonators, generating high-frequency electric fields,
which are output as microwaves through a microwave output portion 49.
[0018] In the case of a magnetron using anode segments, it is possible to cause various
modes of operation depending upon the number of the segments . The mode mainly used
in the B-type oscillation called π-mode, in which the phase difference between successive
resonators is π radian and the interaction therebetween is the strongest.
[0019] However, in the oscillations of a magnetron, if there is another mode which has an
oscillating frequency close to that in this π-mode, mode jumping from the π-mode to
the other mode occurs triggered by a slight change in the operating conditions. As
a result, the oscillating frequency and output power change abruptly. Therefore, it
is necessary to make resonant frequencies of modes as discreet as possible by making
the couplings between the resonators compact as close as possible.
[0020] In conventional magnetrons, alternate anode segments and vanes are connected through
a conductor forming an equalized ring, so as to separate one mode from another. Since
this equalized ring forces the alternate anode segments to have an oscillation of
voltage in phase, it is possible to limit the possible modes of oscillation to the
π-mode and 0-mode (in which all the anode segments and vanes oscillate in phase).
[0021] In this way, conventional magnetrons are constructed such that the application of
a fixed magnetic field to the interaction space by the magnets attached to the yoke
is used to generate microwaves having a fixed frequency and fixed output power. Accordingly,
the output power and frequency obtained could not be varied in accordance with its
usage.
[0022] Since magnetrons have extremely useful characteristics, i.e., very high oscillation
efficiency, high power and low cost, there is a demand that magnetrons be applied
to a variety of technical fields other than microwave ovens. Accordingly, there has
been an important theme of how a multi-purpose magnetron can be realized which can
be applied to these broadened fields, such as commutations, radar, electronic devices
etc.
SUMMARY OF THE INVENTION
[0023] It is desirable to solve the above problems and provide a plate-type magnetron which
can be used for multiple purposes and can efficiently produce microwaves having a
desired power and frequency.
[0024] The present invention provides a plate-type magnetron as set out in claim 1.
[0025] Preferred features of the invention are set out in claims 2 to 4.
[0026] The invention also provides a plate-type magnetron as set out in claim 5.
[0027] In the above way, the output power can be varied in accordance with change in the
potential of the electrodes while the frequency can be varied in accordance with the
distance between the magnets. Further, when a positive voltage is applied to the electrodes,
it is possible to remove the electrons, which can disturb the oscillation, from the
interaction space.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028]
Fig.1 is a constructional view showing a conventional cylindrical magnetron;
Fig.2 is a sectional view showing the configuration of a conventional cold cathode;
Fig.3 is a sectional view showing a conventional plate-type magnetron;
Fig.4 is a perspective view showing a conventional plate-type magnetron; and
Fig.5 is a sectional view showing a plate-type magnetron in accordance with an embodiment
of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0029] The embodiment of the invention will hereinafter be described with reference to the
accompanying drawings. Fig.5 is a sectional view showing a plate-type magnetron in
accordance with an embodiment of the present invention. As shown in Fig.5, this plate-type
magnetron is composed of an anode 11, vanes 12, a cathode 13, pole pieces 14, a yoke
15, magnets 16 and end hats 20.
[0030] The space sandwiched between anode 11 and cathode 13, which are arranged vertically,
defines an interaction space 18. Provided on both sides in the horizontal direction
of interaction space 18 are a pair of electrodes or end hats 20 facing each other,
to which positive and negative potentials are applied. A pair of pole pieces 14 for
generating a required magnetic field in interaction space 18 are arranged facing each
other, on the outer sides of end hats 20. A pair of magnets 16 are provided on the
outer sides of pole pieces 14. Magnets 16 have a yoke 15, which is disposed in contact
with anode 11. The elements which contribute to forming the magnetic field in interaction
space 18 are magnets 16, pole pieces 14 and yoke 15, which are magnetically coupled
with one another. These elements are called, as a whole, a magnetic portion.
[0031] Here, magnets 16 are of a ferrite type and are affixed to the side walls of the housing.
Since yoke 15 also serves as a radiating plate for releasing heat generated from anode
dissipation, it is made of a galvanized iron material.
[0032] In this plate-type magnetron, the gap of the magnetic portion (the gap-distance in
the magnetic portion) affecting the magnetic field strength in interaction space 18
can be varied by providing pole pieces 14 and yoke 15 in the form of bellows so that
a variation of 20 mm in the gap-distance in the magnetic portion can be achieved.
Magnets 16 can also be moved with the change in this distance.
[0033] Anode 11 is one which is produced by the fabrication method of a plate-type magnetron
anode disclosed in Japanese Patent Application Laid-Open Hei 8 No.315,742.
[0034] Next, the operation scheme of this plate-type magnetron will be described.
[0035] First, the gap-distance in the magnetic portion is set as desired by operating the
bellows of pole pieces 14 and yoke 15 so that a desired magnetic field is formed in
interaction space 18. When a voltage is applied in a similar manner as described for
the conventional magnetron with reference to Fig.3, electrons are emitted from cathode
13 and travel in interaction space 18 under the influence of this magnetic field,
following a cycloidal path. As a result, these electrons give up energy to the cavity
resonators, generating high-frequency electric fields. Accordingly, microwaves having
a frequency and output power associated with the distance between the magnets or the
adjusted amount of pole pieces 14 and yoke 15 will be extracted.
[0036] In the plate-type magnetron shown in Fig.5, a positive or negative voltage can be
selectively applied to end hats 20, and magnets 16 are adapted to move and so the
yoke length and the pole-piece length can be varied so as to provide microwaves having
a desired output power and frequency. In other words, this plate-type magnetron is
constructed such that the electrons which will disturb the oscillation are removed
from the interaction space by the application of a positive voltage to end hats 20
and this voltage is changed so as to control the output power.
[0037] Magnets 16 are adapted to be movable and bellows-like pole pieces 14 and yoke 15
are adjusted to change the yoke length and the pole piece length, whereby the gap-distance
in the magnetic portion is altered, thus controlling the frequency.
[0038] Illustratively, when the anode voltage is set at 100 V, the anode-sole distance set
at 0.5 mm, the magnetic field strength set at 1,360 Gauss (the distance between the
magnets set at 30 mm), the end hats set a voltage of -10V, then an emission current
of 2.1A flows and an output power of oscillation of 160 W (2.5 GHz) can be obtained.
[0039] When the magnetic field strength is altered to 1,090 Gauss, microwaves having a frequency
of 3.1 to 5.1 GHz with an output power of oscillation of 3 to 7 W can be obtained.
Additionally, when a voltage of +10 V is applied to end hats 20, microwaves having
a frequency 3.1 to 5.1 GHz with an output power of oscillation of 10 to 20 W, about
the three times of the output power under the former conditions, can be produced.
[0040] As described above, in accordance with the invention of claim 1, since the magnetic
portion can be constructed so as to vary the magnetic field strength generated in
the interaction space, it is possible to alter the oscillating frequency by changing
the magnetic field strength. In particular, the magnets, the length of the pole pieces,
and the yoke length can be adjusted so as to alter the magnetic field strength in
accordance with the gap-distance in the magnetic portion, thus making it possible
to change the frequency.
[0041] In accordance with the invention of claim 5, since electrodes which can be applied
with a positive or negative voltage are provided, when a positive voltage is applied
to these electrodes, it is possible to remove the electrons which will disturb the
oscillation, from the interaction space.
[0042] Although an embodiment using a cold cathode has been described, it is also possible
to use a thermionic cathode.
1. A plate-type magnetron comprising:
a cathode (13) for emitting electrons;
an anode (11) having a plurality of vanes (12) arranged at regular intervals thereon;
a magnetic portion (14, 15, 16) for producing a uniform magnetic field in an interaction
space sandwiched between the cathode (13) and the anode (11); and
a pair of electrodes (20) arranged facing each other, perpendicularly to the uniform
magnetic field, on sides of the interaction space,
wherein the magnetic portion (14, 15, 16) is adjustable to vary the magnetic field
strength produced in the interaction space.
2. The plate-type magnetron according to claim 1, wherein the magnetic portion comprises:
a yoke (15), a pair of pole pieces (14) arranged facing each other on sides of the
interaction space; and a pair of magnets (16) which each are attached to a respective
pole piece (14) and are set in close contact with the yoke (15) to form a magnetic
coupling, wherein the magnets (16) are adapted to be movable.
3. The plate-type magnetron according to claim 1, wherein the magnetic portion comprises:
a yoke (15), a pair of pole pieces (14) arranged facing each other on sides of the
interaction space; and a pair of magnets (16) which each are attached to a respective
pole piece (14) and are set in close contact with the yoke (15) to form a magnetic
coupling, and the pole pieces (14) can be varied in length.
4. The plate-type magnetron according to claim 1, wherein the magnetic portion comprises
a yoke (15), a pair of pole pieces (14) arranged facing each other on sides of the
interaction space; and a pair of magnets (16) which each are attached to a respective
pole piece (14) and are set in close contact with the yoke (15) to form a magnetic
coupling, and the yoke (15) can be varied in length.
5. A plate-type magnetron comprising:
a cathode (13) for emitting electrons;
an anode (11) having a plurality of vanes (12) arranged at regular intervals thereon;
a magnetic portion producing a uniform magnetic field in an interaction space sandwiched
between the cathode (13) and the anode (11); and
a pair of electrodes (20) arranged facing each other, perpendicularly to the uniform
magnetic field, on sides of the interaction space,
wherein a positive or negative voltage can be selectively applied to the electrodes
(20).
1. Plattenförmiges Magnetron mit:
- einer Kathode (13) zum Emittieren von Elektronen;
- einer Anode (11) mit einer Anzahl von Flügeln (12), die mit regelmäßigen Intervallen
an ihr angebracht sind;
- einem magnetischen Abschnitt (14, 15, 16) zum Erzeugen eines gleichmäßigen Magnetfelds
in einem zwischen der Kathode (13) und der Anode (11) eingebetteten Wechselwirkungsraum;
und
- einem Paar von Elektroden (20), die einander zugewandt rechtwinklig zum gleichmäßigen
Magnetfeld an den Seiten des Wechselwirkungsraums angeordnet sind, wobei der magnetische
Abschnitt (14, 15, 16) einstellbar ist, um die im Wechselwirkungsraum erzeugte Magnetfeldstärke
zu variieren.
2. Plattenförmiges Magnetron nach Anspruch 1, bei dem der magnetische Abschnitt Folgendes
aufweist: ein Joch (15), ein Paar Polstücke (14), die einander zugewandt an Seiten
des Wechselwirkungsraums angeordnet sind; und ein Paar Magnete (16), die jeweils an
einem jeweiligen Polstück (14) befestigt sind und in engen Kontakt mit dem Joch (15)
gebracht sind, um eine magnetische Kopplung zu bilden, wobei die Magnete (16) beweglich
angeordnet sind.
3. Plattenförmiges Magnetron nach Anspruch 1, bei dem der magnetische Abschnitt Folgendes
aufweist: ein Joch (15), ein Paar Polstücke (14), die einander zugewandt an Seiten
des Wechselwirkungsraums angeordnet sind; und ein Paar Magnete (16), die jeweils an
einem jeweiligen Polstück (14) befestigt sind und in engen Kontakt mit dem Joch (15)
gebracht sind, um eine magnetische Kopplung zu bilden, wobei die Länge der Polstücke
(14) variiert werden kann.
4. Plattenförmiges Magnetron nach Anspruch 1, bei dem der magnetische Abschnitt Folgendes
aufweist: ein Joch (15), ein Paar Polstücke (14), die einander zugewandt an Seiten
des Wechselwirkungsraums angeordnet sind; und ein Paar Magnete (16), die jeweils an
einem jeweiligen Polstück (14) befestigt sind und in engen Kontakt mit dem Joch (15)
gebracht sind, um eine magnetische Kopplung zu bilden, wobei die Länge des Jochs (15)
variiert werden kann.
5. Plattenförmiges Magnetron mit:
- einer Kathode (13) zum Emittieren von Elektronen;
- einer Anode (11) mit einer Anzahl von Flügeln (12), die mit regelmäßigen Intervallen
an ihr angebracht sind;
- einem magnetischen Abschnitt (14, 15, 16) zum Erzeugen eines gleichmäßigen Magnetfelds
in einem zwischen der Kathode (13) und der Anode (11) eingebetteten Wechselwirkungsraum;
und
- einem Paar von Elektroden (20), die einander zugewandt rechtwinklig zum gleichmäßigen
Magnetfeld an den Seiten des Wechselwirkungsraums angeordnet sind, wobei an die Elektroden
(20) wahlweise eine positive oder eine negative Spannung angelegt werden kann.
1. Magnétron à plaques comprenant :
une cathode (13) destinée à émettre des électrons ;
une anode (11) munie d'une pluralité d'ailettes (12) disposées à intervalles réguliers
;
une partie magnétique (14, 15, 16) destinée à produire un champ magnétique uniforme
dans un espace d'interaction interposé entre la cathode (13) et l'anode (11) ; et
une paire d'électrodes (20) disposées l'une en face de l'autre, perpendiculairement
au champ magnétique uniforme, sur les côtés de l'espace d'interaction, dans lequel
la partie magnétique (14, 15, 16) est ajustable pour faire varier la puissance du
champ magnétique produite dans l'espace d'interaction.
2. Magnétron à plaques selon la revendication 1 dans lequel la partie magnétique comprend
: une culasse (15), une paire d'éléments polaires (14) disposés l'un en face de l'autre
sur les côtés de l'espace d'interaction ; et une paire d'aimants (16) fixés l'un et
l'autre à un élément polaire respectif (14) et placés en contact étroit avec la culasse
(15) afin de former un couplage magnétique, dans lequel les aimants sont adaptés à
être déplacés.
3. Magnétron selon la revendication 1, dans lequel la partie magnétique comprend : une
culasse (15), une paire d'éléments polaires (14) disposés l'un en face de l'autre
sur les côtés de l'espace d'interaction ; et une paire d'aimants (16) fixés l'un et
l'autre à un élément polaire respectif (14) et placés en contact étroit avec la culasse
(15) afin de former un couplage magnétique, et la longueur des éléments polaires (14)
est susceptible de varier.
4. Magnétron selon la revendication 1, dans lequel la partie magnétique comprend : une
culasse (15), une paire d'éléments polaires (14) disposés l'un en face de l'autre
sur les côtés de l'espace d'interaction ; et une paire d'aimants (16) fixés l'un et
l'autre à un élément polaire respectif (14) et placés en contact étroit avec la culasse
(15) afin de former un couplage magnétique, et la longueur de la culasse (15) est
susceptible de varier.
5. Magnétron à plaques comprenant :
une cathode (13) destinée à émettre des électrons ;
une anode (11) munie d'une pluralité d'ailettes (12) disposées à intervalles réguliers
;
une partie magnétique destinée à produire un champ magnétique uniforme dans un espace
d'interaction interposé entre la cathode (13) et l'anode (11) ; et
une paire d'électrodes (20) disposées l'une face à l'autre, perpendiculairement au
champ magnétique uniforme, sur les côtés de l'espace d'interaction, dans lequel il
est possible d'appliquer sélectivement une tension positive ou négative aux électrodes
(20).