JPS6298591A - Radio 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 Application of the Invention] The present invention relates to a high-frequency heating device for subjecting an object to be heated stored in a heating chamber to irradiation with microwaves for continuous heat treatment. This invention relates to a waveguide filter that removes unnecessary radio waves from the band and prevents them from leaking outside the heating chamber.

[Background of the invention]

Generally, the fundamental frequency assigned to high-frequency heating devices is 2.45 GHz±50 MHz. However, although the level is extremely low from the magnetron,
Frequencies other than the fundamental frequency (unnecessary radio waves) are also generated at the same time. If these unnecessary radio waves leak to the outside of the high-frequency heating device, it will have a serious negative impact on other electronic equipment, so various countermeasures are taken at the design stage of the high-frequency heating device. For example, in Japanese Patent Publications No. 59-16713 and No. 59-16714, Magnet)
A microwave oven has been proposed in which a filter is provided in a waveguide that guides microwaves from an on to a heating chamber to remove unnecessary radio waves. However, the single-child range configured in this way generates unnecessary radio waves that are relatively close to the fundamental frequency.

Although it is effective against noise, no consideration was given to removing harmonics. On the other hand, in recent years, broadcasting satellites have been launched, and television signals can now be transmitted directly from the satellites to homes. However, the assigned frequency of this broadcasting satellite is 11.7 to 12.7 CI (z), whereas the fifth harmonic of a microwave oven is 12.0 to 12.5 GH.
There will be almost complete overlap at z.

Therefore, if the fifth harmonic from the microwave oven leaks, there is a risk that it will have an adverse effect on the satellite television receiver.

As a product that removes such harmonics, the
A wideband filter is proposed in Japanese Patent No. 17891. However, this wideband filter does not take into consideration higher-order modes and has problems such as being relatively expensive.

[Purpose of the invention]

Therefore, the present invention has been made in view of the above-mentioned conventional problems, and its object is to provide a waveguide capable of sufficiently attenuating and eliminating all higher-order modes of at least one harmonic. An object of the present invention is to provide a high frequency heating device equipped with a tube filter.

Another object of the present invention is to provide a high-frequency heating device equipped with a waveguide filter that can be obtained at low cost.

[Summary of the invention]

It is a well-known fact that a large number of modes can be transmitted when the fifth harmonic is transmitted in a waveguide that transmits the fundamental frequency. For example, the fundamental frequency (2,45GHz t50M
The cross-sectional dimensions of the standard waveguide WRJ-2 for transmitting Hz) are 109.22 x 54.61 + 111 T,! However, the fifth harmonic (12.0 to 12.5 GHz) can be transmitted in several tens of modes. Although it is difficult to block microwaves transmitted in such a large number of modes, the present invention separately provides means for blocking the 18m0 mode and means for blocking other modes (Tgmn, Tgnm). In particular, unnecessary radio waves can be effectively removed.

Also, generally speaking, if the mode orders (values of m and n) differ,
The performance of this type of filter deteriorates because the tube wavelengths are different. For example, in the standard waveguide WRJ-2 mentioned above, the 18m0 mode at 1225GHz is TEl, -T
E8. Up to 8 modes can be transmitted, but the channel wavelength is 24.151111°T"80 for TE10, which is significantly different from 50.33 IoI.

Therefore, in the present invention, the in-tube wavelength of the 18m0 mode is kept almost constant regardless of the mode order, thereby improving the ability to eliminate and attenuate unnecessary radio waves.

[Embodiments of the invention]

Next, embodiments of the present invention will be described in detail using the drawings.

FIG. 1 is a sectional view showing an embodiment of a high frequency heating device according to the present invention. In the same figure, a filter 4 for harmonic attenuation is inserted into a waveguide 3 connecting a high frequency oscillator 1 and a heating chamber 2, and the fifth harmonic generated from the antenna 1a of the high frequency oscillator 1 is transmitted to the heating chamber. 2 is prevented from being transmitted inward. Note that 5 is a door through which heated materials are taken in and out of the heating chamber 2.

FIG. 2 is a perspective view showing the configuration of the filter 4 housed within the waveguide 3. FIG. In the same figure (a), the filter 4 is
A plurality of fishbone-shaped metal plates 6 are stacked together at a predetermined interval in a direction perpendicular to the direction in which the fifth harmonic propagates toward the heating chamber 2. fish bone shaped metal plate 6
is the free space wavelength λ of the harmonic on the long side as shown in FIG. A plurality of slots 7 formed with a depth D approximately equal to A tapered part 8 to be divided into equal parts and a spacer 10.11 having a fitting part 9 of a predetermined height formed by drawing and forming in one direction on the flat part on the short side are combined and laminated. It has screw holes 12 and 13 for fixing. The fish-bone metal plates 6 are assembled by fitting the spacers 10.11 to each fish-bone metal plate 6 by fitting their fitting portions 9 into each other, as shown in FIG. 6(e). figure(,)
They are stacked at predetermined intervals as shown in the figure. Further, the assembly of the fishbone-shaped metal plates 6 laminated by VC is shown in FIG. 3 (
As shown in a), a filter 4 is constructed by being fixedly disposed t-g on eight surfaces 3e in the waveguide 3 with screws 14. In this case, since the filter 4 is fixedly disposed approximately at the center of the waveguide 3, the gaps g1 and g1' between the H surface 3h of the S4 waveguide 3 and the fishbone metal plate 6 are approximately equal, and the spacer 10
．． 11 and the gap g2+g2' is also approximately equal. Here, in FIG. 3(a), the left side 8 surface 3C of the waveguide 3 is in contact with the surface including the cheek part 8 of the fishbone-shaped metal plate 6, and the right side 8 surface 3e of the waveguide 3 is in contact with the surface including the cheek part 8. Although the structure in which the fitting portion 9 makes contact has been described, as shown in FIG. 3(b), the structure in which the fitting portion 9 contacts the fishbone-shaped metal plate 6 as shown in FIG. 3(C).

The same effect can be obtained by forming a protrusion 20 as shown in FIG. 3(d) and providing a gap 6a between the fishbone-shaped metal plate 6 and the left side 8 surface 3e of the waveguide 3.

By configuring the filter 4 in this way, (1) The fundamental wave can be transmitted with almost no loss.

(2) Transmission of the fifth harmonic can be almost completely blocked.

Effects can be obtained. Of the above item (2), modes other than TEmo mode (TEmn, TMmn) can be almost completely blocked for the following reason. In other words, modes other than the TEmo mode are always generated on the upper and lower wall surfaces of the waveguide 3, and on the υH surface 3h.
Since it has an electric field component parallel to , it cannot pass through this filter 4. It is possible to pass through gap g2
and g2F are large, and the gaps g, and g21 are the free space wavelength λ of the fifth harmonic. It is a well-known fact that if the value is less than %, the fifth harmonic of the mode having this electric field component cannot pass due to cant-off.

In other words, by selecting an appropriate height for the spacers 10 and 11, transmission in modes other than the TEmo mode can be prevented. In particular, in this actual case, the spacers 10 and 11i/i have a U-shaped cross section as shown in Figure 2, so they have a four-stage blocking structure in the direction of the tube, resulting in high performance. can be obtained.

Next, the reason why the aforementioned fundamental wave can be transmitted with almost no loss and the reason why the TERflo mode of the fifth harmonic can be almost completely blocked will be explained. First, in order to facilitate understanding of the transmission of the fundamental wave, we will introduce Throft 7 and Sube 21.
A filter made of a strong metal plate in which all of the filters 0 and 11 are present will be described, and a comparison will be made later with a fishbone-shaped metal plate 6 provided with these.

Figure 4 is a cross-sectional view from the side showing how the basic unit can transmit data. In the figure, the fundamental wave is traveling from the left to the right of the waveguide 3 that houses the metal plate 21 described above inside. As is well known, the fundamental wave is TE engineering. Considering the mode, the electric field 22 and magnetic field 23 are directed in the directions shown by the arrows, respectively.
is occurring.

When the electromagnetic field reaches the metal plate 21, since the metal plate 21 has a tapered portion 21a at its end, the electromagnetic field is quickly divided into upper and lower parts. In this case, as explained with reference to FIG. 3, the gaps g1 and 1 are approximately equal, so they are equally divided into upper and lower parts. FIG. 5 is a cross-sectional view seen from the magnetron side showing the electromagnetic field after being split. The electric field 22 is divided into a first electric field 22a, a second electric field 22b,
The magnetic field 23 is divided upwardly and downwardly into a first magnetic field 23a and a second magnetic field 23b, respectively. Note that the reason why no electromagnetic field exists between the adjacent metal plates 21 is that the interval G is sufficiently narrower than the cutoff dimension of the fundamental wave. Therefore, the inner wall of the waveguide 3 and the metal plate 21
There are electric fields 22a and 22 shown in the arrow direction in the figure.
b and magnetic fields 23a, 23b are generated. The electric fields 22a and 22b in this portion become zero on the center line 24 because the upwardly divided component and the downwardly divided component are almost equal and opposite in direction. Further, the magnetic fields 25a and 25b in this portion have a shape perpendicular to the plane of the paper.

In the figure, 26 conceptually represents the electric field strength near the top wall of the waveguide 3, and 27 conceptually represents the electric field strength near the right side wall, which is clear from the figure. As shown, the strong electric field ETH is large in the vicinity of the metal plate 21 and becomes smaller and fluctuates between adjacent metal plates 21, but its envelope 28 retains the remains of the original TEIO mode. On the other hand, the electric field strength ETE near the cloth side wall surface is maximum near the upper and lower ends of the metal plate 21,
It is zero on the center line 24. Therefore, center line 2
Equal transmission yc even if partitioned vertically at the edge of the paper along 4
Does not give a shadow "J.And the electromagnetic field is caused by the eight metal plates 21
This transmission line is concentrated on the outside of the center line 24.
This is equivalent to two waveguides with a U-shaped cross section facing each other in the vertical direction. This will become clearer from the explanation of surface current described later.

FIG. 6 is a diagram showing the state of the surface current flowing through the metal plate 21, and is a sectional view seen from the top surface of the waveguide 3, showing the lower half with the tube axis 29 as the boundary. In the figure, the surface current 30 flowing along the edge of the metal plate 21 is perpendicular to the magnetic field 23, flows only in a direction parallel to the tube @29, and the direction of flow is reversed for each procedure length.

FIG. 7 is a diagram showing the surface current flowing to the outside of the metal plate 21 at the end of the eight metal plates, where =l, the surface current 31 shown by the dotted arrow, and the magnetic field 23a shown by the solid line.

23b.

The surface current 30.3 explained in these FIGS. 6 and 7
As is clear from the flow in Figure 1, this is a normal waveguide mode TE process. sb, which is equivalent to two waveguides with U-shaped cross sections facing each other vertically, as explained in FIG. Therefore, this transmission line can transmit the fundamental wave with almost no loss.

Next, the influence of the fishbone-shaped metal plate 6 having the slot 7 and the spacers 10.degree. 11 described above on the fundamental wave will be explained.

As can be seen by comparing FIG. 3 and FIG.
1 (see Figure 2) only affects the transmission of the fundamental wave.

As shown in Fig. 5, the degree of this only affects the strong IF/rx of the electric field near the left and right side walls in the waveguide 3, so it is insignificant compared to the overall energy, and there is only a slight discontinuity. give rise to sex. Discontinuities of this magnitude can be sufficiently matched, but by appropriately selecting the distance between the spacers 10 and 11 shown in FIG. 2, the reflections can be canceled out and automatic matching can be achieved. In addition, slot 7 is provided to remove the fifth harmonic, as will be described later, but its depth -gD and spacing are extremely small for the fundamental wave, and can hardly be ignored. can. However, since the wavelength is somewhat shortened, care must be taken in matching the load impedance.

Next, the reason why transmission of the fifth harmonic in TEm0 mode can be blocked will be explained.

As in the case of the fundamental wave, in order to facilitate understanding, we will explain the metal plate shown in Fig. 2 in which all the slots and spacers 10 and 11 are not present, and later compare it with the fishbone-shaped metal plate 6 provided with these. and explain.

First, the Tglo mode of the fifth harmonic has the same shape as the fundamental wave. The only difference is the shorter wavelength, so it is essentially the same as the electromagnetic field distribution shown in Figure 4. If the wavelength is short, Figure 4 shows the TE10 mode of the first and fifth harmonics. It shows the situation. Similarly, FIGS. 5, 6, and 7 can be considered in the same way. However, in FIG. 5, the distance G between the metal plates 21 is equal to the free space wavelength λ of the fifth harmonic. 5% or less,
Otherwise, the effect cannot be obtained because the component of the magnetic field 22 parallel to the metal plate 21 enters between all the metal plates 210.

Here, as shown in FIG. 5, the fifth harmonic TElo
As described above, when the mode is transmitted, it is equivalent to two waveguides having a U-shaped cross section facing each other with the center line 24 as a boundary, and there is almost no loss. Therefore, in FIG. 4, TE2o from the left side inside the waveguide 3
As the mode progresses, the electromagnetic field divided by the metal plate 21 becomes as shown in the eighth factor. That is, the electric field 22 in the left half is the first electric field 22a and the 20th electric field 22.
The magnetic field 23 is divided into a first magnetic field 23a and a second magnetic field 23b. Similarly, the electric field 22 on the right half is divided into a third electric field 22e and a fourth electric field 22d, and the magnetic field 23 is divided into a third magnetic field 23c and a fourth magnetic field 23d. Then, an electromagnetic field also enters between the metal plates 21 in the center. Therefore, in this case, it is equivalent to four waveguides each having a U-shaped cross section facing each other with the center line 24 as a boundary, and transmission is possible with virtually no loss.

Similarly, FIG. 9 shows the case of TE8o mode, and since the electromagnetic field penetrates between all the metal plates 21, a total of 1
This is equivalent to eight waveguides facing each other with the center line 24 as a boundary. Although not shown in the figure, other ""3Q+TE40+TFl:5o, TE(
Similar results are obtained for lQ+T”70 mode.However, TE8o.

T.E. , TE01 have an even number of eight metal plates 21, so the three odd modes are slightly different from those shown in the figure, but there is essentially no difference. What is important here is that the surface current 30 flowing on the upper and lower edges of the metal plate 21 is parallel to the tube axis 29 in any mode (TEmo) as shown in FIG. Moreover, what is particularly important is that the channel wavelengths are approximately the same in all modes of the fifth harmonic.

Next, using FIG. 10, it will be explained that the wavelengths in the tube are almost equal. In the figure, metal plates 21 and 21'
In a normal waveguide where there is no 18m0 mode, the cant-off wavelength λ. . is expressed by the following equation.

2 people λ=−・・・・・・(1) mm However, A is the lateral dimension of the waveguide 3.

On the other hand, the cant-off wavelength of the TElo mode explained in FIG. 5 is a waveguide with a U-shaped cross section. equal. Therefore, the cutoff wavelength λ of the TEIO mode. □ becomes . However, a and b are the dimensions shown in FIG.

Similarly, the cutoff wavelength λ of TE20 mode. .

From FIG. 8 and FIG. 10, is the cutoff wavelength of the waveguide whose lateral dimension is the point 32-33-36-37-36-134-35. In other words, it becomes. Therefore, the cutoff wavelength λem of the TEmo mode is expressed as λem. Here, in order to compare equations (1) and (4), we set them approximately as follows. Equation (4) becomes It shows what will happen.

As mentioned above, the standard waveguide WRJ-2 (J
In IA standard WR-430), the fifth harmonic TEL o+
Tgs.

In-tube wavelength λ5,o at 12.25GHz of the mode
2g80 are λ2, respectively. = 24.15 units 2g80 = 50.33+al As explained above, according to equation (6), λglO = 24.56 units λgso = 24.89 units, and the combination of λgIO and 2g80 There is almost no difference. In other words, TE engineering. This means that the tube wavelengths of the eight modes from mode to TE8o mode are approximately equal. As will be described later, this is extremely important because only one type of size is required for the structure that blocks transmission of the fifth harmonic. Conventionally, in this type of filter, the wavelength inside the tube differs greatly depending on the mode, so it has rarely been necessary to change the dimensions for each mode. However, in the case of the present invention, the wavelength within the tube remains approximately constant regardless of the mode, so this is not necessary.

As mentioned above, for ease of understanding, the metal plate 21 is shown in FIG. 2 without all the slots 7 and spacers 10 and 11.
We have explained the transmission of the fifth harmonic to the filter structure formed by 29, and the tube wavelength of the 18m0 mode was constant regardless of the mode.

Next, as shown in FIG. 2, slot 7 and Sube!
The effect of the filter 4 formed by the fishbone-shaped metal plate 6 having IT-10 and IT-11 will be explained.

First, when the spacers 10 and 11 shown in FIG. 2 are present, they block the electromagnetic field that enters between the fishbone-shaped metal plates 6, which is not clear compared to FIG. 9, so there is some effect. can be obtained, but this alone is not sufficient. In particular, as described with reference to FIG. 5 regarding transmission of the fundamental wave, the TElo mode of the fifth harmonic can hardly be expected to have a blocking effect with a width of 10.11. Therefore, the main blocking effect on the T-mode of the fifth harmonic is due to the slit 7, which will be explained next.

FIG. 11 is a diagram illustrating the function and effect of the slit 7 provided in the fishbone-shaped metal plate 6.

First, as shown in FIG. It is arranged side by side. Since the surface current 40 described in FIG. 6 flows through the convex portions 7a formed between the slits 7, a surface current 41 in the opposite direction flows through the corresponding wall surface of the waveguide 3. Therefore, this part can be represented by an equivalent circuit using two parallel lines as shown in FIG. 2(b). In the slit portion 7, two tank circuits 42 resonating at a frequency corresponding to the pipe wavelength λ3 are connected in series in parallel.

As for the insertion loss (Loss) of this equivalent circuit, an extremely large blocking effect can be obtained by matching the tube wavelength λ to the fifth harmonic IjL5fo, as shown in FIG. In-tube wavelength λ3
As mentioned above, in the 18m0 mode, it is almost constant regardless of all modes, so the same effect can be obtained in any mode.

FIG. 12 is a diagram illustrating another embodiment of the fishbone-shaped metal plate. In the figure (,), the dimensions of the slit 7 and the convex portion 7a from the inner wall surface of the waveguide 3 are respectively hl and h2 (h2<hl), and the width of the fishbone metal plate is λ. , /4.

The equivalent circuit in this case is as shown in the same figure (b), where the characteristic impedances z0 and 2. Lines with length λg/4 are shown connected alternately. The insertion loss of this equivalent circuit is shown in FIG. 10C, and although the blocking effect at the fifth high frequency 5fo is not as great as in the case of FIG. 11, it has the advantage of providing broadband characteristics. This %i impedance z1
．． Since Z2 is considered to be inversely proportional to the distance h□, h from the wall surface of the waveguide 3, the following relationship holds true. Therefore, the larger the ratio between distance h2 and ho, the stronger the blocking effect.

In this way, although the fishbone-shaped metal plate 6.6' has a large blocking effect on the fifth harmonic 5fo, it has a simple structure and can be realized at an extremely low cost because it only requires punching from a sheet metal.

〔Effect of the invention〕

As explained above, according to the present invention, the fifth harmonic can be effectively removed despite the occurrence of many higher-order modes, and such a four-wave tube filter can be obtained at low cost. An extremely excellent effect can be obtained.

[Brief explanation of drawings]

Fig. 1 is a sectional view of a main part showing an embodiment of a high-frequency heating device according to the present invention, Fig. 2 is a diagram explaining the configuration of a waveguide filter, and Figs. Figure 3 (e
), (d) is a diagram showing a state in which a protrusion is provided on a fishbone-shaped metal plate, and Figures 4 to 9 show the electromagnetic field and surface current of a waveguide filter housed in a waveguide. Figure 10 is a conceptual diagram of how to find the cant-off wavelength.
FIGS. 11 and 12 are schematic diagrams showing the shape of the slot portion and its performance. 1... Magnetron, 1a... Output section, 2...
...Heating chamber, 3...Waveguide, 3e...E surface,
3h...H plane, 4...Waveguide filter, 5
... Door, 6 ... Fishbone-shaped metal plate, 7 ... Slot part, 8 ... Tapered part, 9 ... Fitting part, 1
0.11...Svepe, 12.13...Screw hole, 14...Screw.

Claims (1)

[Claims] In a high-frequency heating device that transmits microwaves emitted from a magnetron output part into a waveguide and radiates them into a heating chamber, a plurality of metal plates each having a plurality of slots at the edges are integrated into the waveguide. The metal plates are engaged by the formed spacers and arranged parallel to each other at regular intervals in a direction perpendicular to the tube axis and the side wall surface to isolate the metal plate from the upper and lower wall surfaces of the waveguide. A high-frequency heating device characterized in that a waveguide filter is configured by being fixed to a waveguide filter.