JPS61208776A - 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.

In conventional technology high frequency heating equipment, the fundamental wave is 2.45GH1±5
When set to 0 MHz, it has been confirmed that the following harmonics are generated. However, not all harmonics are large.

2nd harmonic 4.90H-g±100MHz
3rd harmonic 7.35 GHz±15oMuz
4th harmonic 9.8 GHz±200MHz 5th harmonic 12.25 GH1±250MH! 6th harmonic 14.7 GHz±300MHz 7th
Harmonics: 17.15 GHz ± 350 MHz Of the above, the 5th harmonic is in the broadcast frequency band 11.7 to 12.7 GHz of direct broadcast satellite (DBS), which is received individually in each home.
This may cause actual damage such as horizontal stripes appearing on the TV image. In addition, it is expected that other harmonics will overlap the frequency band of some wireless devices in the future and cause actual damage.

The main means for preventing harmonic leakage in high frequency heating equipment are as follows.

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

(Smell) A harmonic choke is provided in the output antenna section of the high frequency oscillator.

(3) A harmonic filter is provided in the waveguide connecting 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 (8) 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 symmetrically in one plane 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 cutoff wavelength λC that is longer than the free space wavelength λ0, and a channel wavelength λg corresponding to this λC. Therefore, in the case of continuous plate-shaped ribs as in the above publication, it is necessary to select the height, thickness, and pitch of the ribs for each harmonic transmission mode, so the higher the harmonic order, the more complex the structure becomes. Ta.

The problem that the invention aims 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 problem: In the rectangular waveguide that connects the heating chamber and the harmonic oscillator, a fishbone-shaped metal plate with a plurality of slits cut to attenuate the TEmo mode of the harmonic is inserted into the TE+s of the fundamental wave. The configuration 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 1gm6 mode and harmonics.

Operation With this configuration, a sufficient attenuation effect is 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.

Figure 8! A filter 4 for harmonic attenuation is inserted into a rectangular waveguide 6 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 the heating frequency, that is, the free space wave modulus of the fundamental wave.
-<A<λo, B(-), TE, - mode propagates with respect to λ and length λ0, respectively.In this rectangular waveguide 6, there is a free space of harmonics. Wavelength λO
A fishbone-shaped metal plate 7 with a plurality of slots 6 cut in the high-frequency energy transmission direction (two directions) having a depth D of about 7 is cut into a fishbone-shaped metal plate 7 with a depth D of about 7 or less of the harmonic free space wavelength λ. P and arranged in the long side direction (π direction).

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 that is less than one of the free space wavelength λO of the harmonic with respect to the E plane 8 in the rectangular waveguide, and has two ends at 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 1'5 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. moreover.

The fishbone-shaped metal plate 7 and the support body 10 are integrally molded by die-casting made of a good conductor such as aluminum or zinc.

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 3. In the Zyz coordinate shown in FIG. 1, the number of maximum electric field points in the long side direction (two directions) of the rectangular waveguide 3 is m (m =
1.2.5. ...).

The number of maximum electric field points in the short side direction (y direction) is defined as n(n
= 1.2.3. -), TEMfi mode, TEM.

It is well known that there is a mode, TEon mode, and when similarly viewed in terms of the number of maximum magnetic field points, there are TM, I mode, TM town mode, and TM+a mode. In the present invention, modes other than the TEN-0 mode are cut off by the support 10 for at least one of the harmonics 1, 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 y direction, so the harmonics The wave is y
There is a maximum electric field point in the direction (, m TEmo modes in the Z direction enter the mode, and other modes are cut off. There is a gap at the joint between the support 10 and the 8 surfaces 9 of the rectangular waveguide 6. If there is, the harmonic TEoyx mode will enter the filter 4, so it is necessary to make it as close as possible to the filter 4. Also, if the support 10 is a dielectric material, for example, a fishbone-shaped metal plate 1 as shown in FIG. It is assumed that the electromagnetic field that has passed through the dielectric enters between the Zs, and the ratio of the electromagnetic field that enters into the slot 6 decreases, resulting in less harmonic attenuation. It has been experimentally confirmed that the harmonic damping effect of the plate 7 is so small that it is not practical as a filter.If the support body 10 is made of metal as in the present invention, the support body 10 will be able to connect the high frequency oscillator 1 to the filter 4.
In addition to the mode regulating effect of limiting the harmonic components entering the TEmo mode, the electromagnetic field is controlled by the slot line formed between the 8 surfaces 8 of the square tube 6 and the fishbone-shaped metal plate 7 as shown below. There is a channel restriction effect that forces the radio wave to propagate along the path.

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 fishbone-shaped metal plate 7
The slot 6 is omitted, and 14 is an image of the fishbone-shaped metal plate 7. Considering the image 14, the radio wave path between the fishbone-shaped metal plate 7 and the eight surfaces 8 of the rectangular waveguide 3 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 λ0
It is. In such a slot line, supports 10 and 8
In order to introduce most of the TEmo mode that has passed through the gap between the fishbone-shaped metal plates 7 and 8, the gap size G between the fishbone-shaped metal plates 7 and 8 must be It is necessary that the gap size Q between the shaped metal plates z (see FIG. 2) be smaller. Also, considering the continuity of the surface current between the surfaces of the support 10 and the fishbone 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, as is well known, the slot line can be considered in place of a microstrip line which is dual to this line. Therefore, the radio wave path between the fishbone-shaped metal plate 7, which is provided with a plurality of slots 6 with a depth D of about -000 mm, and the surface 8 is equivalent to a microstrip line having a strip conductor as shown in FIG. it is conceivable that. The microstrip line shown in FIG. 7 is one in which a plurality of microstrip lines are provided on the main line 15 at a pitch including negative branch lines, and is known as a band rejection filter. By letting λO be the free space wavelength of the harmonics, it acts as a band rejection filter for the harmonics.

Next, the relationship between the pitch P of the fishbone metal plate 7, the depth of the slot 6, the pitch Ps, and the free space wavelength λ0 of the harmonic wave will be summarized. As the pitch P of the fishbone metal plate 7, T of the harmonic wave passing through the gap GXA between the support 10 and the H surface 8
E. , TE26, TE,. ,... If the fishbone metal plate 7 is set to correspond to the position of the maximum electric field in all modes, the input end of each slot line will have the maximum electric field, and the electromagnetic field will flow into the slot line. This makes it easier for the electromagnetic field to enter the slot 6, increasing the proportion of the electromagnetic field that enters the slot 6, and allowing it to fully function as a band rejection filter. The gap between the fishbone-shaped metal plates Z is the gap G between the support 10 and the H surface 8.
The mode with the shortest cutoff wavelength λC among the TE light modes of the harmonics passing through XA is the highest order mode. As for the maximum value of the pitch P, when the cutoff wave of the highest mode is large, the harmonic electromagnetic field easily enters the gap between the fishbone-shaped metal plates Z, and the harmonics entering the slot 6 This is because the proportion of the electromagnetic field decreases, and the function as a band rejection filter is impaired.

This is the - value when the numerical value of m that satisfies two people is maximized, and at this time, λC is closest to λ0. By the way, A
=: In the rectangular waveguide 6 of 80H, the fundamental wave is 2.450H
2, the maximum value of the pitch P of the TERno mode of the fifth harmonic may be considered to be approximately - of the free space wavelength λ0 of the harmonic. The depth D and pitch Ps of the slot 6 (see FIG. 5) are determined by the distance between the fishbone metal plate 7 and the H surface 8.
Assuming that the gap between the two lines is a slot line, this slot line is dual to the microstrip line, and considering the conditions for the microstrip line to act as a band-stop filter, both dimensions are harmonics. The free space wavelength λ is the function of the free space wavelength λ. However, the electromagnetic field distribution near the entrance of the slot B changes depending on the relative dimensions such as the gap size G and the slot width W between the fishbone metal plate 7 and the H surface 8, so the slot depth D and the slot width change. The reason why λOtch Ps is set as - of harmonics is as a rough guide.

The taper 16 provided at both ends of the fishbone metal plate 70 is as follows.

The high frequency energy transmitted in the rectangular waveguide 3 is divided into two parts, upper and lower, to prevent sparks between the fishbone metal plate 7 and the H surface 8, and to prevent reflections due to the insertion of the filter 4. It is intended to reduce

Since the fishbone-shaped metal plate 7 and the support body 10 are integrally molded, there is no incomplete contact at the joint between the two parts 7 and 10.
Loss due to high frequency current is small, and insertion loss of the filter 4 is reduced.

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

The gap GXA't-TE, which is divided into upper and lower parts by the taber 13, and is between the support 10 and the H 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 H surface 8. For example, the fundamental wave is 2.450HK
The depth D of the slot 8 is two dimensions away from the fifth harmonic, and the fifth harmonic passes through the filter 4 portion with almost no attenuation.

As described in detail, 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 in the long side direction (two directions) of the rectangular waveguide. The fishbone-shaped metal plates arranged in a row are supported by a metal support, and the support and the fishbone-shaped metal plates are integrally molded to reduce loss due to high-frequency current, resulting in low insertion loss and a simple structure. Therefore, the dimensions of the rectangular waveguide in the axial direction (two directions) can be shortened, and a high-frequency heating device equipped with a compact and cost-effective filter can be provided.

[Brief explanation of drawings]

FIG. 1 is a perspective view of a main part of a filter placed in a rectangular waveguide of a high-frequency heating device according to an embodiment of the present invention. Figure 2 is a cross-sectional view of the same filter at plane 27, Figure 6 is a perspective view of the vicinity of the screw attachment part of the same filter, and Figure 4 is a fish bone assuming that the support is made of a dielectric material. Fig. 5 is an enlarged view of the fishbone-shaped metal plate in the yz plane, and Fig. 6 is a cross-sectional view showing an example of the electromagnetic field distribution in the vicinity of the rectangular waveguide. FIG. 7 is a principle diagram of the same microstrip line type band-stop filter, and FIG. 8 is a cross-sectional view of essential parts showing an embodiment of the high-frequency heating device of the present invention. . 1...High frequency oscillator, 2...Heating chamber. 3... Rectangular waveguide, 4... Filter. 6...Slot, 7...Fish bone shaped metal plate. 8...H side, 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) that maintains a gap with respect to the surface (8) and has both ends joined to the E surface (9), and shaped metal plate (
7) and a support body (10) are integrally molded.