JP3165342B2 - Magnetron - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetron used for a high frequency heating device such as a microwave oven. In particular, it relates to an improvement in the anode of a cavity resonator driven at a low voltage.

[0002]

2. Description of the Related Art A magnetron is one of the crossed field devices in which a DC magnetic field and a DC electric field are perpendicular to each other in a working space in an electron tube, and is characterized by a high efficiency of about 70%.

FIG. 5 is a configuration diagram of a conventional cylindrical magnetron. A plurality of vanes 62 are radially formed on the cylindrical anode 61 toward the center, and this constitutes a cavity resonator. The cathode 63 is arranged on the central axis of the cylindrical anode 61, and the working space is between the cathode and the vane. At both upper and lower ends of the anode 61, hole pieces 64 for forming a uniform magnetic field in the working space are attached in close contact with a magnet 66 having a yoke 65. The anode 61
A radiator plate 67 for dissipating heat generated by the anode loss is disposed between the heat sink and the yoke. Anode loss occurs when electrons emitted from the cathode are accelerated by the anode voltage and collide with the anode.

[0004] The magnetron currently used for high frequency heating equipment such as a microwave oven is mainly of a cylindrical type, but there is also a flat type magnetron. FIG. 6 is a cross-sectional view of a conventional flat-type magnetron, and FIG. 7 is a perspective view thereof. A plurality of vanes 12 are provided on the flat plate-shaped anode 11.
3. It is formed perpendicular to the sole part 14, and this constitutes a cavity resonator. The cathode 13 is a flat anode 11
Is located at the lower left end of the box, and between the sole and the vane is the working space. On both side surfaces of the anode, hole pieces 24 for forming a uniform magnetic field in the working space are attached in close contact with a magnet 26 having a yoke 25. Also, yoke 2
5 is a radiator plate 1 for releasing heat generated by anode loss.
7 are arranged.

In this configuration, the inside of the anode is evacuated, a magnetic field is applied to the working space by the magnet 26, and the anode 1
1. When a voltage is applied between the sole 14 and the vane 12 from the power input unit 18, electrons jump from the cathode toward the vane. The jumped-out electrons move rightward in FIG. 6 while performing cycloidal motion in the working space similarly to the cylindrical magnetron by the magnetic field received from the magnet 26. From the electrons, energy is given to the cavity resonator, a high-frequency electric field is generated, and is extracted from the microwave output unit 19 as a microwave.

In the conventional magnetron, the operating voltage is 4 KV, and a transformer is required for driving with a household power supply voltage of 100 V. In order to drive this directly with a household power supply voltage of 100 V without using a transformer, it is necessary to lower the intensity of the applied magnetic field or to reduce the pitch of the anode vanes. When the magnetic field intensity is reduced, the oscillation efficiency is remarkably reduced. Therefore, in practice, it is necessary to cope only with a fine pitch.
However, when changing the operating voltage 4KV to 100V,
The pitch of the vanes is about 15% of the current level, and there is a problem that the oscillation becomes unstable due to the problems of processing accuracy, strength, and heat resistance. In view of this, as shown in FIG. 8, a magnetron has been proposed in which a dielectric 73 is packed between vanes 72 of a conventional cylindrical magnetron anode 71 to increase the capacitance and thereby reduce the voltage. (JP 6
2-272423). This utilizes the fact that the resonance frequency of the anode decreases in inverse proportion to the square of the rate of increase of the capacitance between the vanes. That is, the same resonance frequency is obtained by absorbing the increase in capacitance due to the dielectric material by reducing the size of the vane. This will make the magnetron smaller and lighter,
By inserting a dielectric between the vanes, mechanical strength and heat resistance are increased, and oscillation is stabilized.

In the case of a magnetron using a split anode, oscillations in various modes occur depending on the number of splits. Among them, the mode actually used is called a π mode in which the phase shift between adjacent resonators is equal to π radian, and has the strongest interaction. However, in the oscillation of the magnetron, if the oscillation frequencies of the π mode and other modes are close to each other, even if the operating conditions slightly change, a jump from the π mode to another mode (mode-jumping) occurs, As a result, the oscillation frequency and the output change suddenly. Therefore, it is necessary to make the coupling between the resonators dense so that the resonance frequency of each mode is separated as much as possible.

Therefore, in the conventional magnetron, modes are separated by an equalizing ring system or a Tachibana-shaped system. In the equalizing ring system, every other anode vane is connected by a conductor. This forces the potential of every other anode to oscillate in the same phase. Therefore, the mode in which oscillation is possible can be limited to the π mode and the 0 mode (all the anode vanes vibrate in the same phase). On the other hand, the Tachibana-shaped method separates modes without using an equalizing ring. In this, large and small resonators are alternately arranged. These two types of resonators have a large difference in their individual resonance frequencies, and the resonance frequency in the π mode has an intermediate value.

In order to stably oscillate the magnetron with a high vacuum inside, there is a technique of maintaining a vacuum using a getter material. The getter material is a chemically active material, and is used as a means for reducing the pressure in the vacuum vessel by its chemical adsorption. There are two types of getter materials: evaporable and non-evaporable. In the evaporative type, a fresh and active getter surface is generated by continuously or intermittently supplying a getter material as a simple substance or an alloy from an evaporation source as necessary to a predetermined exhaust surface, and exhaust is performed by surface chemisorption. . Examples of the evaporable getter material include Ta, Ti, Mo, and Zr. On the other hand, in the non-evaporation type, a getter surface is prepared in advance, and a gas chemically adsorbed on the surface of the getter surface heated to a high temperature is diffused into the getter material to activate the getter surface and perform exhaust. As the non-evaporable getter material, Zr-Al alloy,
There is a Zr-V-Fe alloy or the like.

[0010]

As described above, when driving at a low voltage, the pitch of the vanes must be reduced to increase the number of anodes, which makes the processing difficult. For example, when the operating voltage is changed from 4 KV to 100 V, the pitch of the vanes is about 15% of the current value. For example, in a flat-type magnetron, in order to oscillate at a frequency of 2.45 GHz used for high-frequency heating, the cavity resonator has a vane pitch of 0.3 mm and a groove width of 0.1 mm to 0.1 mm.
5mm, groove depth is about 30mm. In general, for such processing, a multi-wire saw is used, and a piano wire wound between rollers having pitches is moved while applying a solution (lapping liquid) in which abrasive grains are dispersed to perform grooving and cutting. 0.3mm at processing pitch, 120 at cutting margin
Processing of about μm is possible. Therefore, it is difficult to process the anode of the cavity resonator, and problems occur in accuracy and strength.

Further, as disclosed in Japanese Patent Application Laid-Open No. 62-272423, when a dielectric is inserted between vanes to separate the oscillation modes of the equalizing ring system and the Tachibana-shaped system, the following problem occurs. I will. In the case of the pressure equalizing ring system, if the number of divisions of the anode is large, various modes are close to each other even if the pressure equalizing ring is attached, and the mode separation cannot be sufficiently performed. On the other hand, in the case of the Tachibana-shaped method, the mode can be separated even if the number of divisions of the anode is considerably large, but it is necessary to change the size of the anode alternately, and the processing is troublesome.

In particular, in the case of a flat-type magnetron, since the number of divisions of the anode is large, even if an equalizing ring is provided, various modes are close to each other and mode separation cannot be performed sufficiently. On the other hand, in the case of the Tachibana-shaped method, mode separation can be performed even when the number of divisions of the anode is considerably large. In the case of a flat-type magnetron, it is difficult to increase the distance between the vanes because the size of the anode is increased. That is, large and small resonators are alternately formed with two types of groove depths. However, it is difficult to form a groove deeply with a small pitch, which causes a decrease in yield. In addition, since the structure of the vane becomes asymmetric, the vane may be deformed by heat.

In addition, when the number of divisions of the anode is large, it is difficult to obtain sufficient conductance in the exhaust system, so that it takes a long time to exhaust, and it is difficult to exhaust to a high vacuum. In order to maintain a high vacuum, it is necessary to apply a getter material inside the magnetron. However, in the case of a non-evaporable getter, the required amount is determined by the ratio to the internal surface area. However, when the number of divisions of the anode is large, the surface area becomes extremely large with respect to the internal volume, so that the ratio of the area to which the getter material can be applied becomes small with respect to the entire surface area, and the sufficient effect cannot be exhibited.

The present invention provides a magnetron capable of separating oscillation modes with a simple structure, facilitating machining of an anode of a cavity resonator, and improving mechanical strength and heat resistance. It is to be. Another object of the present invention is to provide a magnetron capable of improving the conductance of an exhaust system and easily maintaining a high vacuum state.

[0015]

In order to solve the above-mentioned problems, the present invention provides an anode of a cavity resonator comprising two kinds of dielectrics having a relative dielectric constant of more than 1 and different values between a plurality of vanes. A magnetron having a structure in which the magnetrons are inserted alternately. In this magnetron, it is preferable that a non-evaporable getter material is applied to the surface of the cavity resonator.

[0016]

[Function] By alternately inserting two kinds of dielectrics having relative dielectric constants greater than 1 and different values, even if the vanes have substantially the same size, the same oscillation mode separation effect as that of the Tachibana shape can be obtained. be able to. Therefore, the structure of the anode of the cavity resonator is simplified, processing is facilitated, and processing accuracy is improved. In addition, since the shape of the anode having the vanes is also symmetrical and the dielectric is inserted between the vanes, deformation due to heat hardly occurs. In selecting a material for the dielectric, it is necessary to select a material having a relative dielectric constant greater than 1 in a frequency band of 2.5 GHz. Further, a material which does not have anisotropy with respect to the dielectric constant and is stable even at an internal temperature of about 300 ° C. during magnetron operation is desirable. Furthermore, the larger the difference between the dielectric constants of the two types of dielectrics, the larger the difference between the respective resonance frequencies and the greater the effect of mode separation.

Further, since the dielectric having a relative dielectric constant greater than 1 is filled between the vanes, the conductance of the exhaust system is improved, and the area where the non-evaporable getter material can be applied to the entire surface area of the cavity resonator is improved. Can be improved (10 to 30 times), so that the inside of the magnetron can be easily maintained at a high vacuum.

[0018]

FIG. 1 is a sectional view showing an embodiment of a flat type magnetron according to the present invention. This plate magnetron has an operating voltage of 100V. Since the basic structure is the same as that of FIG. 6 shown in the prior art, the same portions are denoted by the same reference numerals and description thereof will be omitted. This embodiment is characterized in that two kinds of dielectrics having relative dielectric constants greater than 1 and different values are alternately inserted between the plurality of vanes 12 of the anode 11. These two types of dielectrics have a relative dielectric constant of 1 in a frequency band of 2.5 GHz.
You need to choose something larger. Further, it has no anisotropy with respect to the dielectric constant, and has an internal temperature of 3 during magnetron operation.
A material that is stable even at around 00 ° C. is desirable. Therefore, as the two kinds of dielectrics, for example, a Pyrex glass (relative dielectric constant: 4.84) plate 21 and a soda glass (relative dielectric constant: 7.5) plate 22 of the same size are used.

Now, the anode of the cavity resonator is assembled as follows. A vane 12, a Pyrex glass plate 13, and a soda glass plate 14 made of an oxygen-free copper plate processed to a thickness of 0.15 mm, a width of 12 mm, and a length of 11 mm are sequentially laminated and joined. This is spotted with oxygen-free copper block 10 and spot weld 16
To form the anode 11.

Inserting a dielectric between the vanes 12 increases the capacitance of the equivalent circuit of the cavity resonator. The resonance frequency of a cavity resonator is inversely proportional to the 1/2 power of the rate of increase of its capacitance. The same resonance frequency is obtained by absorbing the increase in capacitance due to the dielectric by reducing the size of the vane. Therefore, if a material having a relative permittivity of four times is packed in the cavity, the necessary groove depth can be reduced to half. For this reason, processing is facilitated and the groove depth is reduced, so that the size and weight can be reduced.

Further, by alternately inserting two types of dielectrics having relative dielectric constants greater than 1 and different values, the capacitance between vanes is different, and the resonance frequency is accordingly greatly different. Therefore, even if the gap size between the vanes in which the dielectric is inserted is the same, the same oscillation mode separation effect as that of the Tachibana shape can be obtained.

In this way, since the dielectric is inserted between the vanes, the mechanical strength is increased, and the gap between the vanes into which the dielectric is inserted can be substantially constant, so that the processing is simple and the thermal deformation is strong. Therefore, the oscillation modes can be effectively separated, and the oscillation output can be improved.

An experiment was conducted to compare this embodiment with a flat-type magnetron in which one type of dielectric was inserted between vanes.
The latter flat magnetron has a thickness of 0.15 mm and a width of 12 mm.
Oxygen-free copper plate 32 and soda glass plate 33 with a length of 11 mm
Are alternately laminated and joined to the oxygen-free copper block 31 by spot welding to produce an anode (FIG. 2). While measuring with a spectrum analyzer, an oscillation frequency of 2.45 GHz used for high-frequency heating was output. At this time, the anode voltage was 100 V, the distance between the anode and the sole was 0.5 mm, and the magnetic field strength was 1360 Gauss. The oscillating output of the planar magnetron of this embodiment is 78 W, and the oscillating output of the planar magnetron in which one kind of dielectric is inserted between the vanes is 11 W.
W. That is, by alternately inserting two types of dielectrics between the vanes, rather than inserting one type of dielectric,
It was confirmed that the oscillation output was improved about seven times.

Next, an experiment was conducted to compare the oscillating output with a flat magnetron having a Tachibana anode. The anode part has a groove width of 0.15 mm and a pitch of 0.3 mm in the oxygen-free copper block 41.
It was fabricated by alternately slitting with a groove depth of 30 mm and 14 mm using a multi-wire saw (FIG. 3). The wire diameter is 130 μm, the abrasive is GC1000, and the cutting speed is 100 μm / min. This anode was incorporated into a flat-type magnetron, and the oscillation output at 2.45 GHz was measured with a spectrum analyzer.
The oscillation output was measured at a distance between the soles of 0.5 mm and a magnetic field strength of 1360 Gauss. The result was 81 W, and it was confirmed that the anode according to the present example can obtain the same oscillation output as the Tachibana type anode.

FIG. 4 is a sectional view showing a flat-type magnetron according to the present invention in which a non-evaporable getter material is applied. The non-evaporable getter 23 is applied to the surface of a cavity in which two different dielectrics are alternately placed. The non-evaporable getter is, for example, 70% Zr-24.6% V-5.4.
% Fe alloy, which was applied to a thickness of 50 μm. The initial activation of this non-evaporable getter material is 450
Perform for 15 minutes.

Since a dielectric is inserted between the vanes and there is no gap between the vanes, the conductance of the exhaust system is improved and the vacuum can be easily made. Further, since the surface area of the anode decreases and the ratio of the application area of the getter material to the total surface area increases, the getter material works more effectively. Furthermore, since the internal temperature of 400 ° C. during the operation of the magnetron becomes the activation temperature of the non-evaporable getter material, the activation process is performed each time the magnetron is operated, so that the getter effect can be maintained for a long time. A high vacuum can be maintained for a long time without requiring any special operation.

An experiment was conducted to compare this anode with the Tachibana-shaped anode shown in FIG. The non-evaporable getter 23 was applied to the surface of the cavity in which the anode of the Tachibana-shaped configuration shown in FIG. 3 was incorporated, as in FIG. Non-evaporable getter is 70% Z
r-24.6% V-5.4% Fe alloy,
It was applied to a thickness of 0 μm. As a result, the ultimate vacuum degree was greatly improved to 4.5 × 10 ⁻⁵ Pa, compared with the ultimate vacuum degree of 6.5 × 10 ⁻⁴ Pa when the Tachibana-shaped anode was used. As a result, it was confirmed that an upward effect was obtained.

[0028]

As described above, according to the present invention, since two kinds of dielectrics having relative dielectric constants greater than 1 and different values are alternately inserted between a plurality of vanes, the dimensions of the vanes are substantially the same. As a result, the processing of the split anode of the magnetron becomes easy, and the oscillation mode can be effectively separated. The structure of the vane is also symmetrical, and since the space between the vanes is not a cavity, deformation of the vane due to heat can be prevented. In addition, the size of the anode is reduced, so that the size of the magnetron can be reduced.

Further, since a dielectric was inserted between the vanes,
The ratio of the surface area to which the non-evaporable getter can be applied to the surface area inside the magnetron is increased, and the conductance is improved by eliminating grooves, making it easier to maintain a high vacuum inside and enabling the oscillation to be stabilized. . Also, since the internal temperature of 400 ° C. during the operation of the magnetron becomes the activation temperature of the non-evaporable getter (70% Zr-24.6% V-5.4% Fe alloy), the activation process is performed every time the magnetron is operated. As a result, the getter effect can be maintained for a long time, so that a high vacuum can be maintained for a long time without requiring any special operation.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of a flat-type magnetron according to the present invention.

FIG. 2 is an enlarged cross-sectional view of a conventional flat magnetron anode in which one kind of dielectric is packed between vanes.

FIG. 3 is an enlarged cross-sectional view of an anode of a conventional flat-plate type magnetron using a Tachibana-shaped method.

FIG. 4 is a cross-sectional view showing a flat-type magnetron according to the present invention in which a non-evaporable getter material is applied.

FIG. 5 is a sectional view showing a conventional cylindrical magnetron.

FIG. 6 is a cross-sectional view showing a conventional flat-type magnetron.

FIG. 7 is a sectional view showing a conventional flat-type magnetron.

FIG. 8 is a perspective view showing a conventional cylindrical magnetron anode in which a high dielectric is packed between vanes.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Anode 12 Bain 21, 22 Dielectric

Claims (2)

(57) [Claims] 1. A magnetron, wherein an anode of a cavity resonator has a structure in which two kinds of dielectrics having different relative dielectric constants greater than 1 and having different values are alternately inserted between a plurality of vanes. 2. The magnetron according to claim 1, wherein a non-evaporable getter material is applied to a surface of the cavity resonator.