JPS61208778A - 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 Industrial Application) The present invention relates to an improvement in a harmonic leakage prevention structure of a high frequency heating device.

(Prior Art) - In a high-frequency heating device, when the fundamental wave is set to 2.45 GHz to 50 MHz, it has been confirmed that the following harmonics are generated. However, not all harmonics are large.

2nd harmonic 4.9 GHz±100MHz 3rd
Harmonics 7.35 GHz ± 150 MHz 4th harmonic 9.8 GHz ± 200 MHz 5th harmonic
12.25GHz±250MHz 6th harmonic 14.
7GHz±300MHz 7th harmonic 17.15GH
z±350MHz Of the above, the 5th harmonic is broadcast frequency band 11 of direct broadcast satellite (DBS) which is received individually in each home.
7 to 12.7 GHz, and may cause actual damage such as horizontal stripes on TV images. 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 harmonic leakage prevention means for high frequency heating equipment 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 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) Fully inject radio wave attenuation material into joints such as waveguides and heating chambers.

(6) In addition to the fundamental wave choke, a harmonic choke or a harmonic absorber is provided on the seal portion 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. 17891/1989 proposes that a filter structure having a plurality of ribs arranged symmetrically on two planes is provided in a rectangular waveguide corresponding 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 a continuous plate-shaped lip as in the above publication, the height and thickness of the lip are determined for each harmonic transmission mode.

Because it is necessary to select the pitch, the higher the harmonic order, the more complex the structure.

(Problem to be solved by the invention) Conventional waveguide filters for preventing harmonic leakage.

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

The disadvantage is that it is 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 therein to attenuate the TEmo mode of the harmonic is used to generate the fundamental wave. It is configured to be supported so as to secure a gap with the H plane by a metal support that cuts off modes other than the TE10 mode and the harmonic TEmo mode.

(Function) 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.

(Embodiment) Nine embodiments of the present invention will be described below with reference to the configuration and operation 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 completely 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 heated object.

The configuration of the filter 4 is shown in FIGS. 1-6. In these figures, the long side dimension A of the rectangular waveguide 3 and the short side molten body are fan
On the right side of Shumegorei, <A<λO, B (2) for Hakusan Shimonbocho λO of x Daigo, and the TE10 mode is propagated.This rectangular conduction Inside the wave tube 6, there are a plurality of slots 6 having a depth D of approximately 1 of the free space wavelength λO of the harmonics, and a fishbone-shaped metal plate 7 cut in the direction (two directions) of transmitting high frequency energy. Spatial wavelength λ0
They are arranged in the long side direction (x direction) at a pitch P of about 7 or less. The entrance of the slot B faces the H plane (wide plane) 8 within the rectangular waveguide. The fishbone-shaped metal plate 7 has a harmonic free space wavelength λ0 of 7 for the 8 surfaces 8 of the rectangular waveguide 3.
It is supported by a metal support 10 which maintains the following gap size G and is joined to the fE plane (narrow side) 9 at both ends. A screw attachment part 12 with a hole for screwing a screw 11 into the support body 10 is provided at the junction with the 8th surface 9 of the rectangular waveguide 6. When joining the surface 9, the screw 11 is not exposed to the space inside the rectangular waveguide 3. Both ends of the fishbone-shaped metal plate 7 are provided with tapers 13 to reduce the reflection of the fundamental wave and to equally divide the high frequency energy into two parts, the upper and lower parts of the rectangular waveguide filter.

Next, the operation of the embodiment of the above configuration will be explained.

When the 2nd to 7th harmonics are mixed in the rectangular waveguide 6 that is the passband for the fundamental wave, there are many higher-order modes for each harmonic in the rectangular waveguide 3. exists. In the xyz coordinates shown in FIG. 1, the number fm of maximum electric field points in the long side direction (x direction) of the rectangular waveguide 3 (m=
1, 2. 3e...).

The number of maximum electric field points in the short side direction (x direction) fn (n=
1.2.3z・ ), T Emnmo )
'.

There are TEmo mode and TEon mode, and when viewed similarly in terms of the number of maximum magnetic field points, TMmn+ mode,
It is well known that the TMmlT M 1 n mode exists. In the present invention, at least one of the harmonics 2, for example, the 5th harmonic, is T E
m.

This mode cuts off modes other than the 5TEmo mode and further attenuates the 5TEmo mode by the fishbone metal plate 7.
The action will be explained in detail below.

In FIG. 2, the air gap between the support 10 and the 8 surfaces 8 of the rectangular waveguide 6 is defined by the free space wavelength λ of the harmonic in the X direction.
The dimension G is kept below the value of O.

With respect to the X direction, the A dimension is larger than the free space wavelength λ0 of the fundamental wave, which is 7, so harmonics have no electric field maximum point in the X direction with respect to this gap GxA, and m Enter as TEmo mode.

Other modes are cut off.

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

In addition, when the support body 10 is a dielectric material, the electromagnetic field transmitted through the dielectric material enters between the fishbone-shaped metal plates Z as shown in FIG. 4, and the ratio of the electromagnetic field entering the slot 6 is It is presumed that this will reduce the attenuation of harmonics. Under such conditions, the harmonic damping effect by the fishbone metal plate 7 is small.

It has been experimentally confirmed that it is not practical as a filter.

When the support body 10 is made of metal as in the present invention.

In addition to the mode regulating function of limiting the harmonic component tl-TEmO mode that enters the filter 4 from the high-frequency oscillator 1, the support 10 also controls the electromagnetic field through the rectangular waveguide 3 as described below.
There is a channel restriction effect that forces the radio wave to propagate along the slot line formed between the 8 faces 8 and the fishbone-shaped metal plate 7.

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 Figure 5.

The entire 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 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 within the slot line is the free space wavelength λ0. In order to introduce most of the T Emo mode sound 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).

Also, 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 8th surface 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 has a plurality of slots 6 with a depth D of about 1, and the surface 8 is as follows:
It is considered to be equivalent to a microstrip line with IJ tube conductor gold as shown in Figure 7.

The microstrip line in Figure 7 is connected to the main line 15 by 2-0.
A plurality of branch lines are provided at a pitch of 't7, and are known as band rejection filters. By setting λ0 to be the free space wavelength of the harmonics, it acts as a band rejection filter for the harmonics.

Next, we will summarize the relationship between the pitch P of the fishbone-shaped metal plate 7, the depth of the slot 6, and the pitch PS and the free space wavelength λO of the harmonic.

As the pitch P of the fishbone-shaped metal plate 7, TE10°TE2 of the harmonics passing through the gap GxA between the support 10 and the 14th surface 8
0. TE30. ...If the fishbone-shaped metal plate 7 is set to correspond to the position of the maximum electric field in all modes, 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 gap between the fishbone metal plates 7 is the gap between the support 10 and the surface 8 G This is a higher mode. The maximum value of the pitch P is a dimension corresponding to the cutoff wavelength λC of the highest mode. This is because when the pitch P is larger than the cutoff wavelength λC of the harmonic TEmo mode, the harmonic electromagnetic field easily enters the gap between the fishbone-shaped metal plates 7 and enters the slot 6. This is because the proportion of the electromagnetic field containing harmonics decreases, and the function as a band rejection filter is impaired. The highest order cutoff wavelength λC of the TEmo mode is λc=”), lot-satisfaction A The value of when the amount of gold is also increased, and in this case, λC is closest to λO. By the way, A
In the rectangular waveguide 6 of 280 m, the fundamental wave is 2.45 GHz.
Then, the highest mI of the fifth harmonic TEmO mode is
I'i+, and l at this time is 13.311IIIλ
0, - is 12.2 mm, and l and l are close values. Therefore, as the maximum value of pitch P.

It may be considered to be about 7 of the free space wavelength λO of the harmonic.

The depth D and pitch PS (see FIG. 5) of the slot 6 are determined by considering the gap between the fishbone metal plate 7 and the surface 8 as a slot line, and this slot line is dual to the microstrip line. Considering the conditions for the microstrip line to function as a full band rejection filter, both dimensions are 2 of the free space wavelength λO of the harmonic. However, the electromagnetic field distribution near the entrance of the slot 6 changes depending on the relative dimensions such as the gap size G between the fishbone metal plate 7 and the surface 8 and the slot width W, so the slot depth D and the slot pitch vary. The PS value of 7 harmonics is used as a rough guide.

Tapers 13 are provided at both ends of the fishbone-shaped metal plate 7.

The high frequency energy transmitted through the rectangular waveguide 3 is divided into two halves, upper and lower, to prevent sparks between the fishbone metal plates 7 and 8, and to prevent reflections caused by the insertion of the filter 4t. There is something to reduce it.

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

The gap GXA'jiTE10 is divided into upper and lower halves by the taper 13, and is between the support 10 and the 8 surfaces 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, the fundamental wave? 2.45GHz
If the depth Di of the slot 8 is set to about 6.1 min, which is ■ of the free space wavelength λ0 of the fifth harmonic, for blocking the fifth harmonic, then for the fundamental wave, ■ is 3Q, 6+m, which is two dimensions. They are far apart and pass through the filter 4 portion with almost no attenuation.

(Effects of the Invention) As explained above, according to the present invention, the high frequency energy generated from the high frequency oscillator is transmitted to the end of the fishbone-shaped metal plate disposed in the long side direction (x direction) inside the rectangular waveguide. The taper provided divides the metal plate into two parts near the H-plane above and below, and the slot provided on the side facing the H-plane of the fishbone-shaped metal plate allows
Since at least one harmonic mixed in the above-mentioned high-frequency energy is blocked, there is no generation of sparks, and the dimensions of the rectangular waveguide in the axial direction (two directions) can be shortened, making it compact and cost-effective. A high frequency heating device including a filter can be provided.

[Brief explanation of drawings]

FIG. 1 is a perspective view of a main part of a filter 4 placed in a rectangular waveguide 3 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 xy 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 the same yz
FIG. 6 is an enlarged view of the fishbone-shaped metal plate 7 in the plane, and FIG. 8 is a principle diagram of the same microstrip line type band rejection filter, and FIG. 8 is a sectional view of essential parts showing an embodiment of the high frequency heating device of the present invention.

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) High frequency energy is applied to both ends of the upper and lower H planes (8
) A high-frequency heating device characterized in that a taper (13) that divides the area into equal parts is provided in the vicinity.