JPS6024554B2 - Door seal device for high frequency heating equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a door seal device for preventing leakage of radio waves from a door portion of a high frequency heating device.

In the prior art, door seals are constructed using a combination of three components: a choke structure metal contact, and ferrite rubber as a radio wave absorbing material. Here, the ferrite rubber absorbs and attenuates radio waves that cannot be prevented from leaking by the choke structure and metal contact, and without it, it is not possible to reliably reduce the leakage level below the legal regulation value.

Furthermore, if there is insufficient metal contact, the leakage level may exceed the legal regulation value even if ferrite rubber is attached. In other words, the choke structure does not contribute much to preventing radio wave leakage.

FIG. 1 shows the basic structure of the choke structure provided in the door part used in the prior art. 1 is the door front plate forming the choke groove 8, and 2 is the choke groove 8 formed in the high-frequency heating chamber 7. The door rear plate 3, which protrudes from the side and closes off an open surface 5, is an open flange.

In this structure, the width of the choke groove 8, that is, the distance from the surface 6 of the choke groove 8 to the open surface 5 is set to approximately 0/4 when the wavelength of the radio wave used is set as 0, so that the surface 4 is closed by the conductor wall. It is equivalent to .
However, this principle only holds true when the radio waves are incident perpendicularly to the longitudinal direction of the choke groove, and when the radio waves are incident obliquely, the wavelength seen in the groove width direction is, for example, 45 degrees. The choke effect disappears.

Further, since the obliquely incident radio wave is expressed as the sum of a perpendicularly incident component and a parallel incident component with respect to the longitudinal direction of the groove, it can be said that there is a choke effect on the former, but not on the latter. On the other hand, in high-frequency heating devices such as microwave ovens,
The direction of incidence of radio waves is a function of location, and if a turntable or the like is used to prevent uneven heating, it is also a function of time.

Therefore, preventing leakage of components incident parallel to the longitudinal direction of the choke groove provides a more complete leakage prevention mechanism. The drawback of the conventional technology is that it does not take this point into account, and therefore requires expensive radio wave absorbing materials such as ferrite rubber. Furthermore, in the prior art, a door sealing device such as a choke structure is incorporated into the door structure itself as shown in FIG. 1, which increases the thickness of the door portion. In order to reduce the thickness, reduce the external dimensions of the high-frequency heater, and make it highly functional, it is necessary to incorporate a door seal structure on the oven flange side. The purpose of the present invention is to eliminate the above-mentioned drawbacks of the prior art, to reduce the cost by removing the ferrite rubber, and to achieve a lower cost than the prior art.
It is an object of the present invention to provide a safer door seal device having a leakage prevention effect greater than MB, and to provide a door that is thinner than conventional ones.

By arranging metal or a dielectric with a high permittivity in an appropriate periodic structure in the groove of the oven flange, a slow-wave line with a phase velocity smaller than the speed of light can be constructed in the longitudinal direction of the groove, and the groove forms a closed loop. Therefore, it becomes a bandpass filter.

Now, when a lotus wave line is realized in the longitudinal direction of the groove, the phase constant in the direction perpendicular to the longitudinal direction of the groove is attenuated to a pure imaginary number, that is, IJ active, so the energy of the wave incident parallel to the longitudinal direction of the groove is It is trapped in the periodic structure and does not leak to the outside. Next, consider means for preventing leakage of waves incident perpendicularly to the longitudinal direction of the groove.

A conductor post with a diameter of about ^/8 (^ is the wavelength of the radio wave used) is placed in a normally used rectangular waveguide parallel to the E plane with one end
If it is fixed on one side and the other end is placed at a distance of 1/4 degree from the H side, when viewed from the input end, the plane that includes the center line of the post and is perpendicular to the tube axis is a radio shorting plane, i.e. It looks equivalent to replacing that surface with a conductive plate, and the incident energy is completely reflected. If we expand this idea and widen the waveguide width (width at the sun's surface) sufficiently, we can arrange multiple conductor posts as described above on a plane perpendicular to the tube axis, and the same aircraft's performance will be achieved. A short-circuit surface can be created on this surface. In addition, when the conductor post is hollowed out in the direction of the pipe axis and a hole is raised, even if the width of the hole is about 1/8, if the thickness of the hole is 1/19,
When a radio wave passes through the hole, a reactive attenuation of about 13% is obtained, which is equivalent to having no hole in terms of radio waves. Based on the above idea, by installing a metal plate bent into a wave shape in the longitudinal direction of the groove of the oven flange, a periodic structure is formed in the longitudinal direction of the groove to prevent leakage of incident waves parallel to the longitudinal direction of the groove. In addition, for incident waves perpendicular to the longitudinal direction of the groove, a radio wave short-circuit surface is formed at the position of the metal plate bent into a corrugated shape, so it is possible to completely reflect the incident wave toward the heating chamber side. Become. FIG. 2 shows a cross section of the door and heating chamber of the high-frequency heater. The oven flange 3 has an oven flange groove 40 having an opening □ facing the door part.

FIG. 3 is an explanatory diagram for explaining the radio wave effect when a corrugated metal plate is installed in the groove 40, and the groove 40 of the oven flange portion is provided in the oven flange 3 on the wall surface of the heating chamber 7. The width 12 of the opening □ of this groove 40 is selected to be smaller than the width 13 of the heating chamber wall surface facing the door, and the oven flange 3 and the door rear plate 2 constitute a radio wave passage 19 in the form of a parallel plate line. Oven flange groove 401
A corrugated metal plate 10 as shown in FIG. 4 is installed here. Further, a choke cover 9 made of a dielectric material is attached to the closed part of the groove 40 to prevent dirt from entering and protect the structure inside the groove 40. Next, the effect will be explained in detail.

First, the function of the corrugated metal plate 10 forming the main part of the present invention will be explained. FIG. 5 shows a corrugated metal plate 10 installed between the door rear plate 2 and the groove bottom surface 41. A corrugated metal plate 10 coordinate system is introduced, where the longitudinal direction of the corrugated metal plate 10 is the Z direction, the height direction is the x direction, and the direction perpendicular to the longitudinal direction is the y direction. In FIG. 5, when a plane wave having an electric field component in the x direction is incident in the Z direction, since the corrugated metal plate 10 has a periodic structure, the period of the radio wave propagating on this structure is the same as that of the structure. corresponds to an integer multiple of the period of . (In FIG. 5, the period of the radio wave is shown as twice the period of the corrugated metal plate 10). Here, the period P of the corrugated metal plate 10 is twice the bending length 15 (FIG. 4) of the corrugated metal plate 10. At this time, if the radio wave propagates so that the phase difference between the adjacent peaks 20 of the corrugated metal plate 10 is 1800 as shown in FIG. 5b, the wavelength input z in the Z direction becomes the input z
= Becomes Sha. For example, when P=in o/4 (in o is the wavelength in free space), in, z=in. /2,Z
The phase velocity Vz in the direction is Vz=Co/2. C here
Since o is the speed of light and the phase velocity of a plane wave propagating in a normal parallel plate line is Co, the phase velocity in the Z direction of the wave becomes 1/2 of that in the optical direction due to the periodic structure of the corrugated metal plate. In other words, a slow wave circuit can be realized. Now, (2/
^. )2=8×28y28z2, where 8×, 6y, az are phase constants, for example, 8z is a phase constant in the Z direction, defined as 3z=2/inz,
Bamboo is Pi. In the structure shown in FIG. 5, the electric field components of the radio waves incident through the radio wave paths 19 with small intervals are considered to be uniformly distributed in the x direction, so 8x
= 0, (2 digits/in.) 2=8y20 (2 digits/＾＾z
) becomes 2. One piece included. = 2 input z, so 8y must be a pure imaginary number. That is, 3y=-jay. Here, i is an imaginary unit and 8y' is a real number. This 8y
If we use
8yy=e-8y'y=e-zo Write 12 bamboo y.

This equation means that waves are reactively attenuated and do not propagate in the y direction, that is, energy is stored in the y direction as well, but its density decreases exponentially. For example, enter in the y direction. When moving away from the corrugated metal plate 10 by /4, the energy density decreases by about 2. To summarize the above, Z
It can be said that when a plane wave is incident from a direction, it propagates in the Z direction as a wave with a lower velocity than in free space, and does not propagate in the y direction, only being attenuated. The above has been a description of the effect of the corrugated metal plate 10 on waves that are incident parallel to the longitudinal direction of the groove.Next, the effect on waves that are incident perpendicularly will be explained. As is well known in the field of microwave engineering, as shown in FIG.
When placed perpendicular to the plane 23 and parallel to the E plane 22, its transmission characteristics are, for example, 2 over a wide frequency band as shown in Figure 6b.
You can get more attenuation than World B.

Figure 6b shows the width of the prism 24 being 2 for the frequency 254 and the M ratio.
This is a case where the depth 26 of the prism 24 is selected to be I/16, and the gap between the prism 24 and the H surface 23 of the waveguide 21 is selected to be I/40. The reason why such a blocking characteristic is obtained is that the energy of the electric field stored in the gap between the conductor post 24 and the H-plane 23 of the waveguide and the current flowing on the surface of the conductor post 24 cause the electric current to flow around the conductor post 24. The energy of the stored magnetic field corresponds to capacitance and inductance in an electric circuit, and these form a series resonant circuit, which exhibits a cutoff characteristic as shown in FIG. 6b around a certain frequency.

Further, even if the square pillar is hollowed out according to the hollowed-out hole 25 and a metal tube-shaped body is installed in place of the square pillar, the transmission characteristics shown in FIG. 6b will hardly change.

The reason is that the width of the metal tube is 1/8 and the depth is 1/1.
6, the coupling of radio waves at the entrance and exit of the metallic body is approximately 11X and 4X, which is equivalent to blocking the entrance and exit of a hole with a metal plate. Also, when only the depth is reduced to /64, the above combination is approximately Ichiku B
It becomes so large that it can no longer be regarded as a conductor post, and the transmission characteristics as shown in FIG. 6b cannot be obtained. Now, when considering a wave that is incident perpendicularly to the longitudinal direction of the groove 40 of the open flange portion, if the width of the H-plane 23 of the waveguide is made sufficiently wide in FIG. 6a, it is sufficient to consider, for example, about 4 waves.

In this case, if a plurality of metal tube-shaped bodies are arranged periodically in a direction perpendicular to the tube, the transmission characteristics as shown in FIG. 6b can be similarly obtained. This structure is a corrugated metal plate 10 shown in FIG. 5a.
This is similar to installing the groove 40 in the oven flange in the longitudinal direction. From the above, it can be seen that neither waves incident parallel to the longitudinal direction of the groove 40 of the oven flange nor waves incident perpendicularly to the longitudinal direction of the groove 40 of the oven flange portion leak from the corrugated metal plate 1 to the outside.

Note that in the above explanation, waves have been divided into vertically incident waves and parallelly incident waves, but since the door seal device of the present invention does not contain nonlinear soot materials such as ferrite rubber, the principle of superposition is established. However, thinking separately does not involve even the slightest approximation. Next, appropriate structural dimensions in the present invention will be described.

FIG. 7 shows the leakage power density from the high-frequency heating device door section with respect to the width 14 of the corrugated metal plate 10, and as the width becomes smaller, the leakage power increases. The reason for this is, as generally stated, that as the width 14 of the corrugated metal plate becomes smaller, the blocking effect becomes smaller for waves that are incident perpendicularly to the longitudinal direction of the groove 40 of the oven flange portion. Therefore, as a matter of course, a structure in which the wire is bent has almost no blocking effect. Therefore, the width of the corrugated metal plate is
30 or more is required. However, the data in FIG. 7 is for a gap between the radio wave paths 19 of ^/120. Next, the distance 11 between the corrugated metal plate and the twill outer peripheral wall will be explained.

As already explained, a slow wave line can be realized in the longitudinal direction of the groove 40 of the oven flange by installing the wave-shaped metal plate 10 in the groove 4 of the oven flange. However, this cannot be achieved unconditionally across all frequency bands.
A slow-wave line is formed only in a specific frequency band, and in frequency bands outside of this, the line becomes attenuated, and waves do not propagate in the longitudinal direction of the groove 8, but propagate perpendicularly to the longitudinal direction, causing leakage. Observed as radio waves. When the corrugated metal plate 10 is installed in the waveguide as shown in FIG. 8a and the transmission characteristics are examined, the results are as shown in FIG. 8b. In the same figure, a slow wave circuit is realized in a frequency band where the amount of attenuation is comparable to that of the old one, and as mentioned above, only at this time, waves propagating perpendicular to the axis of the waveguide are actively attenuated by 1''. . As can be seen from Figure 8b, for example, the frequency of the radio waves used is 245 M.
If it is z, it needs to be 1:12 skin, that is, 1 is included/10 or less. When the distance 17 between the corrugated metal plate 10 and the groove opening on the side of the heating chamber 7 becomes smaller, lines of electric force will cross between the two. In other words, the wave incident on the corrugated metal plate is no longer a plane wave, but has an electric field component in the direction perpendicular to the height direction of the corrugated metal plate.
The radio wave blocking effect of the corrugated metal plate 10 is reduced.
FIG. 9 shows the leakage power density with respect to the distance 17 between the corrugated metal plate 10 and the groove opening on the heating chamber 7 side. It can be seen that the distance 17 is necessary for the entry/1 place closing.

By providing the door seal structure on the oven flange side in this way, not only can a predetermined door seal performance be achieved, but also the door itself has an opening/closing function, a heating chamber see-through function, and forms a parallel plate track 19 together with the oven flange 3. Since it only needs to have a function, we can expect its thickness to be significantly thinner than before.

Next, an embodiment of the present invention in which the door thickness is reduced will be described with reference to FIG. 10. In FIG. 10, a corrugated metal plate 10 is installed in a groove 40' of the open flange portion, and a cover 9 made of dielectric material is provided at the opening of the groove 40.
is attached. In this example, in addition to the oven flange 3 formed on the surface facing the door, a heating chamber wall extension 43 is formed, and the former faces the metal transparent plate that allows the inside of the heating chamber T to be seen through, and the radio wave passage 19 The latter faces the door rear plate 2 and forms a radio wave passage 30. The reason why the radio wave passage 30 is provided also on the outer periphery of the door in this way is as follows. As already explained, in FIG. 5, the wave traveling from the Z direction travels as a slow wave in the Z direction, and undergoes reactive attenuation in the y direction at a rate of 2 per input/4.
By providing the radio wave path 30, the leakage power density can be reduced, for example, by the radio wave path 3 having a length of /6 in a household microwave oven.
By adding 0, it can be lowered by 7 groups. In the structure shown in FIG. 10, the effective transparent part is located in the heating chamber 7.
There is an effect that can be made equal to the opening of .

As described above, by incorporating the door seal structure into the oven flange side, the thickness of the door can be reduced compared to the conventional technology, as shown in FIG. Since the radio wave path is formed in the form of a flat plate line, the effective transparent part of the door finder can be made equal to the entrance part of the heating chamber 7.

Conventionally, even when a choke structure, metal contact, and ferrite rubber as a radio wave absorbing material were used in combination, radio wave leakage of, for example, 0.1 mW/ground occurred even when the door was sealed, but the structure of the present invention According to , even if the ferrite rubber is removed and the operating frequency is 245 MHz, even if the gap in the radio wave path 19 is one sail, the power output is 0.01 mW.
/ Can be ground leakage power, low cost and 1B
The above safety improvements were achieved.

Furthermore, by incorporating the door seal structure into the oven flange side, the thickness of the door can be made smaller than in the prior art, and the depth of the heating chamber can be increased for the same external depth of the high-frequency heater.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view of a choke structure that is a conventional door sealing device, Fig. 2 is a longitudinal sectional view of a high-frequency heater having a groove on the heating chamber wall, and Fig. 3 is a schematic diagram of the door sealing function.
Fig. 4 is a perspective view of an embodiment of the corrugated metal plate used in the present invention, and Fig. 5 is a diagram illustrating the radio wave action of the corrugated metal plate, in which a is a cross-sectional view and b is a cross-sectional view of the corrugated metal plate. Figure 6 is a diagram showing the relationship between the period and the period of radio waves. Figure 6 is a diagram explaining the radio wave action of a corrugated metal plate, with a post set up inside a waveguide. A diagram showing the relationship between quantities,
Fig. 7 is a diagram showing the relationship between the width of the corrugated metal plate and the leakage power density, and Fig. 8 is a diagram showing the relationship between the corrugated metal plate and the side wall with respect to the slow wave action of the corrugated metal plate. FIG. 9 is a diagram showing the relationship between the leakage power density and the distance between the corrugated metal plate and the groove entrance on the heating chamber side, and FIG. 10 is a diagram showing the relationship between frequency and attenuation. It is a sectional view of an example. 1...Door front plate, 2...Door rear plate, 3
...Oven flange (heating chamber wall), 4...
...Short circuit surface, 5...Open surface, 6...Short circuit surface, 10...Corrugated metal plate, 19...
・Radio wave passage, 40...Groove in the oven flange. Fig. 1 Fig. 3 Fig. 4 Fig. 5 Fig. 6 Fig. 2 Fig. 7

Claims (1)

[Claims] 1 In order to prevent radio wave leakage from the area around the door of the high-frequency heating device, a groove is installed on the oven flange side facing the door, and a corrugated metal plate with a width of approximately 1/30 wavelength or more of the radio wave used is used. The microwave oven is bent with a bending length of approximately less than 1/2 wavelength and installed in the longitudinal direction of the groove, and a parallel plate line-shaped radio wave path is formed by the metal transparent plate that allows the heating chamber to be seen through and the oven flange. A door seal device for a high frequency heating device, which is characterized by: