JPS61208784A - High frequency heater - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an improvement in the harmonic leakage prevention structure of a high frequency heating device.

Conventional technology In high frequency heating equipment, the fundamental wave is 2.45 GHz ± 5
When set to 0 MHz, it has been confirmed that the following harmonics are generated. However, not all harmonics are large.

2nd harmonic 4.9 GHz±100 MHz 3rd
Harmonics 7.35 GHz ± 150 MHz 4th harmonic 9.8 GHz ± 200 MHz 5th harmonic
12.25GHz±250MHz 6th harmonic 14
．． 7 GHz:l:300 MHz 7th harmonic 1
7.15GHz f 350MH2 Among the above, the 5th harmonic overlaps with the broadcasting frequency band 11.7-12.7GHz of Direct Broadcasting Satellite (L)BS, which is received individually in each home.Wrinkles such as horizontal stripes appearing on TV images. There is a risk of causing actual harm. Furthermore, it is expected that other harmonics will overlap and cause actual damage to the frequency bands of some wireless devices in the future.

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m twist? kB 'km 肚, l-L l-y J- are as follows.

(1) A harmonic filter is provided on the input side of the high frequency oscillator 9, for example, a magnetron.

(2) Install a harmonic choke in the output antenna section of the high frequency oscillator.

(3) A harmonic filter is installed in the waveguide that connects the high-frequency oscillator and the heating chamber.

(4) Air intake holes in the heating chamber and the outer box that houses the heating chamber.

Adjust hole diameter, pitch, etc. of exhaust holes, etc.

(5) Fill the joints of waveguides, heating chambers, etc. with radio wave attenuating material.

(6) In addition to the fundamental wave choke, a harmonic choke or harmonic absorber is installed in the seal part of the door that opens and closes the opening of the heating chamber.

If the harmonic leakage prevention effect in item (3) above is sufficient.

By simply adding the means in item (1) above, other means become unnecessary, which is advantageous in terms of cost.

Japanese Patent Publication No. 52-17891 proposes that a filter structure having a plurality of lips arranged 9-sided symmetrically is provided in a rectangular waveguide, which corresponds to item (3) above. According to this publication, the rib is in the shape of a continuous plate that is perpendicular to the tube axis direction of the rectangular waveguide. A fundamental wave waveguide has a plurality of transmission modes for harmonics, and the higher the order of the harmonics, the more transmission modes can be transmitted. It is known that each harmonic transmission mode has its own unique cutoff wavelength λ· longer than the free space wavelength circle, and a guide wavelength λg corresponding to this λ·. Therefore, in the case of continuous plate-like ribs as in the above publication, it is necessary to select the height, thickness, and pinch of the ribs for each harmonic transmission mode.The higher the harmonic order, the more complex the structure becomes. Ta.

The problem that the invention seeks to solve Conventional waveguide filters for preventing harmonic leakage.

The higher the harmonic order, the more complex the structure.

This was disadvantageous in terms of cost.

Means for Solving the Problems In the rectangular waveguide connecting the heating chamber and the harmonic oscillator, a fishbone-shaped metal plate with a plurality of slits cut therein to attenuate the TEmo mode of the harmonics is used to The structure is such that it is supported so as to secure a gap with the H plane by a metal support that cuts off modes other than the TE, o mode, and harmonic TEmo mode.

Operation With this configuration, a sufficient attenuation effect can be exerted on all higher-order modes of at least one harmonic wave attempting to propagate from the rectangular waveguide toward the heating chamber.

EXAMPLE Below, the structure and operation of one embodiment of the present invention will be described with reference to the drawings.

As shown in FIG. 8, a filter 4 for attenuating harmonics is inserted into a rectangular waveguide 3 connecting the high frequency oscillator 1 and the heating chamber 2,
The harmonics generated from the high frequency oscillator 1 are prevented from propagating into the heating chamber 2. In the heating chamber 2, a turntable 5, for example, is provided to reduce uneven baking of the object to be heated.

The configuration of the filter 4 is shown in FIGS. 1-3. In these figures, the long side dimension A and the short side dimension B of the rectangular waveguide 3 are −<A<λ・ and B<1−, respectively, with respect to the heating frequency, that is, the free space wavelength λ・of the fundamental wave, and λ .

Therefore, the TE1o mode is propagated.

Inside this rectangular waveguide 6, a fishbone-shaped metal plate 7 is provided with a plurality of slots 6 cut in the high wave energy transmission direction (g direction) and having a depth D of about 1 of the free space wavelength λ of the harmonic. are arranged in the long side direction (two directions) at a pitch P of about 1 or less of the free space wavelength λ· of the harmonic.

The entrance of the slot 6 is the H plane (wide side) of the rectangular waveguide 3.
It is facing 8. The fishbone-shaped metal plate 7 maintains a gap size G under the child plate of the free space wavelength λ of the harmonics with respect to the E plane 8 in the rectangular waveguide, and both ends of the plate 9 are connected to the E plane (narrow side).
It is supported by a metal support 10 joined to 9. A screw attachment part 12 with a hole for screwing a screw 11 into the support body 10 is provided at the joint part with the 8th surface 9 of the rectangular waveguide 3. When the surface 9 is joined, the screw 11 is not exposed to the space inside the rectangular waveguide 6. Both ends of the fish bone shaped metal plate 7 are.

A taper 16 is provided to reduce the reflection of the fundamental wave and to equally divide the high frequency energy into the upper and lower parts of the rectangular waveguide 3.

Next, the operation of the embodiment of the above configuration will be explained. The second to
When seven harmonics are mixed, a large number of higher-order modes exist for each harmonic in the rectangular waveguide 6. In the 2D coordinate shown in FIG. 1, the number of maximum electric field points in the long side direction (X direction) of the rectangular waveguide 6 is expressed as
．． 2.3. ), and the number of maximum electric field points in the short side direction (V direction) is n (n = 1.2.3.-), TEmn mode, TEm.

There is a mode, TEon mode, and when viewed similarly in terms of the number of maximum magnetic field points, there are TMmn mode and TMm1 mode.

It is well known that TM+n mode exists. In the present invention, modes other than the TEmo mode are cut off by the support 10 for at least one of the harmonics 9, for example, the 5th harmonic, and the TEmo mode is further attenuated by the fishbone-shaped metal plate 7. However, the action will be explained in detail below.

In FIG. 2, the gap between the support 10 and the 8 surfaces 8 of the rectangular waveguide 3 has a dimension A that is large for harmonics in the ν direction, so the harmonics The wave is V
The field enters as a TEmo mode with m electric field maximum points in the direction (, g), and other modes are cut off.

If there is a gap between the support 10 and the eight surfaces 9 of the rectangular waveguide 3, harmonic TEon mode will enter the filter 4, so it is necessary to make them as close as possible. Moreover, when the support body 10 is a dielectric material.

For example, as shown in Figure 4, it is assumed that the electromagnetic field that has passed through the dielectric enters between the fishbone-shaped metal plates Z, and the proportion of the electromagnetic field that enters the slot 6 decreases, reducing the attenuation of harmonics. . It has been experimentally confirmed that under such conditions, the harmonic attenuation effect by the fishbone metal plate 7 is so small that it is not practical as a filter.

When the support body 10 is made of metal as in the present invention, the support body 1
In addition to the mode regulation effect of limiting the harmonic components entering the filter 4 from the high frequency oscillator 1 to the TEmo mode, 0 also controls the electromagnetic field by connecting the 8 surfaces 8 of the rectangular waveguide 3 and the fishbone-shaped metal plate as shown below. There is an effect of restricting the radio wave path by forcibly propagating the wave along the slot line formed between the two.

The electromagnetic field that has propagated into the gap between the support 10 and the surface 8, that is, the electromagnetic field concentrated near the H surface 8, is primarily transmitted to the radio wave path between the bone-shaped metal plate 7 and the surface 8. enter. This radio wave path is shown in FIG. 5, and the electromagnetic field distribution in the area surrounded by the dashed line in this figure is shown in FIG. However, in FIG. 6, in order to make the electromagnetic field distribution easier to understand, the slot 6 of the fishbone-shaped metal plate 7 is omitted, and 14 is the slot 6 of the fishbone-shaped metal plate 7.
This is an image of Considering the image 14, the fishbone-shaped metal plate 7
The radio wave path between this and the 8th surface 8 of the rectangular waveguide O can be regarded as a slot line known as a type of microwave transmission line. The wavelength of the electromagnetic field in the slot line is the free space wavelength λ
It is 0. In order to introduce most of the TEmo mode that has passed through the gap between the support 10 and the 8 surfaces 8 into such a slot line.

Based on the principle of boundary conditions between electric field and conductor, fishbone-shaped metal plates 7 and 8
It is necessary that the gap size G with the surface 8 is smaller than the gap size Q between the fishbone-shaped metal plates 7 (see FIG. 2).

Furthermore, considering the continuity of the surface current between the surfaces of the support 10 and the fishbone-shaped metal plate 7 that are opposite to the 8 surfaces 8, as shown in FIG. Preferably, they are on the same plane and electrically conductive. Furthermore, the slot line can be thought of in place of the microstrip line, which has a dual relationship with this line.

As is well known. Therefore, the radio wave path between the fishbone-shaped metal plate 7, which has a plurality of slots 6 with a depth D of about 7, and the 8th surface 8 is equivalent to a microstrip line with a strip conductor as shown in FIG. it is conceivable that. Microstrip line λ in FIG. λ. , ' are provided with a plurality of negative branch lines on the main line 15 at a pitch of T, and are known as band rejection filters. By letting λ0 be the free space wavelength of the harmonic,
It acts as a band rejection filter' for harmonics.

Next, let us summarize the relationship between the pitch P of the fishbone-shaped metal plate 7, the depth of the slot 6, the pitch P, and the free space wavelength λ· of the harmonic.

As the pitch P of the fishbone-shaped metal plate 7, the supporting body 10 and the 8 surfaces 8
TB+o of the harmonics passing through the air gap GxA.

If the fishbone-shaped metal plate 7 is set to correspond to the position of the maximum electric field in all the modes of TE 20 , TE 50 #..., the electric field will be maximum at the input end of each slot line.

It becomes easier for electromagnetic fields to enter the slot line, and slot 6
The ratio of the electromagnetic field that enters the band increases, and the function as a band rejection filter can be fully exerted. The shortest cutoff wavelength λ in the TEmo mode of the harmonics in which the gap between the fishbone metal plates Z passes through the gap GXA between the support 10 and the 8th surface 8
The mode with C is the highest order mode. As for the maximum value of pitch P.

This dimension corresponds to the cutoff wavelength λC of the highest mode. This is the cutoff wavelength λ of the harmonic TEmo mode.
When the pitch P is larger than the end of C, the fishbone metal plate Z
This is because the harmonic electromagnetic field 4: easily enters the dark gap between them, the proportion of the harmonic electromagnetic field entering the slot 6 decreases, and the function as a band rejection filter is impaired. T
The highest cutoff wavelength λ of Emo mode is λ・==2A
＞ , the value of m that satisfies 2o is the largest and the value of the sum included, at this time.

λC is closest to λ0. By the way, A=80
In the rectangular waveguide 3 of mm, the fundamental wave is set to 2.45 GHz.

The highest order m of the TEmo mode of the fifth harmonic is 6, and the maximum value of the pitch P may be considered to be approximately - of the free space wavelength λ of the harmonic. Depth D and pitch P of slot B,
(See Fig. 5), the gap between the fishbone-shaped metal plate 7 and the 8th surface 8 is regarded as a slot line.

This slot line is dual to the microstrip line, and considering the conditions for making the microstrip line act as a band rejection filter.

In both the solid solution method, the free space wavelength λ0 of the harmonic is -.

However, the gap size G between the fishbone-shaped metal plate 7 and the 8th surface 8.

The electromagnetic field distribution near the entrance of the slot 6 changes depending on the relative dimensions such as the slot width W.

λ.

The slot depth D and pinch P are set to 7 harmonics as a rough guide.

Tapers 16 are provided at both ends of the fishbone-shaped metal plate 7.

The high-frequency energy transmitted through the rectangular waveguide 6 is divided into two parts, upper and lower, to prevent sparks between the fishbone-shaped metal plate 7 and the surface 8, and to prevent reflections caused by inserting the filter 4. It is intended to reduce

The fundamental wave generated from the high frequency oscillator 1 is as follows.

The gap GxA is divided into upper and lower halves by the taper 13, and is between the support 10 and the surface 8, respectively.

It passes as a mode and enters the radio wave path in the gap between the fishbone-shaped metal plate 7 and the surface 8. For example, if the fundamental wave is 2.45GHz
The depth D of the slot 8 is the fifth harmonic, which is 9 mm apart, and passes through the filter 4 portion with almost no attenuation.

DETAILED DESCRIPTION OF THE INVENTION According to the present invention, the high frequency energy generated from the high frequency oscillator propagates from the rectangular waveguide toward the heating chamber, but only in the long side directions (two directions) of the rectangular waveguide.
By supporting the fishbone-shaped metal plates lined up on a metal support and setting the dimensions of each part of this support and the fishbone-shaped metal plate,
It is possible to block at least one harmonic mixed in the high frequency energy, the structure is simple, and the dimensions of the rectangular waveguide in the axial direction (two directions) can be shortened,
A high-frequency heating device equipped with a compact and cost-effective filter can be provided.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a main part of a filter 4 placed in a rectangular waveguide 6 of a high-frequency heating device according to an embodiment of the present invention, FIG. 2 is a sectional view of the same filter 4 in the zy plane, and FIG. FIG. 4 is a perspective view of the vicinity of the screw attachment part 12 of the filter 4, and FIG. Figure 5 is i1
An explanatory diagram of the electromagnetic field distribution in the radio wave path between the 8 surfaces 8 of the rectangular waveguide 3 and the fishbone-shaped metal plate 7, FIG. 7 is a diagram of the principle of the same microstrip line type band rejection filter, and FIG. FIG. 1 is a sectional view of a main part of an embodiment of a high-frequency heating device of the present invention. 1...High frequency oscillator, 2...Heating chamber. 6... Rectangular waveguide, 4... Filter. 6...Slot, 7...Fish bone shaped metal plate. 8...E side 9 9...E side. 10...Support.

Claims (1)

[Claims] A high frequency oscillator (1
) Rectangular waveguide (3) that transmits high frequency energy from
a plurality of slots (6) having entrances facing the H-plane (8) of the waveguide (3);
A plurality of fishbone-shaped metal plates (7) cut with
The fishbone-shaped metal plate (7) is supported by a metal support (10) which maintains a gap with respect to the surface (8) and which is joined at both ends to the E surface (9). Assuming that the free space wavelength is λ_■, the following conditions are met: (1) the pitch P of the fishbone-shaped metal plate (7) is λ_■/2 or less; (2) the depth D of the slot (6) is approximately λ_■/4 , (3) the above support (
10) and the H-plane (8) of the rectangular waveguide (3), the high-frequency heating device comprises a filter (4) whose gap size G satisfies λ_■/2 or less.