JPS6331918B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a radio wave sealing device for a high frequency heating device. A heating device such as a microwave oven has a door that can be opened and closed, and radio waves from the heating chamber leak into space through a gap between the main body and the door. The amount of radio wave leakage must be kept within standard values in terms of human safety.

As a conventional technique, there is a chiyoke system as shown in the attached document, "Microwave and Millimeter Wave Circuits" by Koguchi, Maruzen, pp. 334-337. In this method, in order to reduce the impedance seen from the main radio wave action space to the mechanical coupling gap, a quarter-wavelength radio wave region (hereinafter referred to as a chiyok cavity) with one end short-circuited is placed in the gap. ), and the distance from the gap start point (the boundary between the gap and the main radio wave action space is called the gap start point) to the cavity is selected to be a dimension equivalent to a quarter wavelength.

Representative patents for radio wave seals based on the Chi-Yoke method include US Pat. No. 3,182,164. Furthermore, in the Chi-Yoke method, there is an example in which a periodic structure is arranged in the longitudinal direction of the Chi-Yoke cavity in order to solve the problem of radio wave propagation in the longitudinal direction of the Chi-Yoke cavity.

Additionally, some have been loaded with dielectric material to reduce the geometric dimensions of the cavity.

The Chiyoke method is an excellent method that has been put into practical use in most of the current microwave ovens. However, as is clear from the above explanation, both the dimension from the gap start point to the Chi-Yoke cavity and the dimension of the Chi-Yoke cavity are set to 1/4 wavelength, that is, the dimension from the gap start point to the Chi-Yoke cavity short-circuit part is set to 2 In principle, it is necessary to reduce the wavelength to 1/2, and there is a limit in terms of compactness.

The present invention aims to provide a compact radio wave sealing device, and its structure is characterized in that parallel line transmission lines having T-branches are periodically arranged in the gap between the mechanical joints.

In the present invention, since the parallel line transmission lines are periodically arranged, radio wave propagation in the direction of the periodic arrangement can be prevented. In addition, the parallel line transmission line has T on the voltage plane (hereinafter referred to as the E plane).
Since it takes a branch configuration, one of the three basic characteristics of a T-branch circuit, which is well known to those skilled in the art, is that by appropriately shorting one of the three ports that a T-branch has, the remaining two ports can be short-circuited. By taking advantage of the fact that power transmission between the lines can be eliminated, leakage components into space can be eliminated in the direction of parallel line travel.

Furthermore, the value of the radio wave leakage amount is not based on the qualitative concept of simply reducing the impedance from the gap starting point, but by using a quantitative analysis method that considers both the resistance and reactance components of impedance, it is possible to calculate the value of the actual measured value. By comparing this with the calculated value from analysis, it was found that in the configuration of the present invention, it is possible to reduce the amount of radio wave leakage by making the dimension from the gap start point to the T-branch smaller than 1/4 wavelength. As a result, we have realized a radio wave sealing device with excellent radio wave sealing performance and a compact configuration.

Before going into detailed explanation, a conventional example will be explained with reference to FIGS. 1 and 2. Figure 1 shows an example of applying the Chi-Yoke method to the coupling part of the waveguide. In order to prevent wave leakage from the waveguide, which is the main radio wave action space, part C is short-circuited and the length is 4 minutes from part B. The dimension of the transmission line from the gap starting point A part to the part B is set to 1/4 wavelength. If the transmission path from part B to the external space can be made into a minute gap as shown in the figure, it will function as an ideal radio wave sealing device.

FIG. 2 is an example in which the Chi-Yoke method is applied to a high-frequency heating device as seen in US Pat. No. 3,182,164. In the figure, radio waves from the heating chamber 1 leak to the outside between the main body wall 2, the sealing plate 3 constituting the door, and the chiyoke wall group 4. By making the dimension up to the hole 6 and the dimension from the aperture 6 to the short-circuit surface 7 each a quarter wavelength, the amount of leakage waves can be reduced.

In the present invention, a parallel line transmission line is used in the radio wave seal part, but the division of the transmission line is DD
Griegetal“Microstrip−ANew Transmission
Techrique for the Kiromegacyle Range”
Proceedengs of The IRE Dec.1952, p. 1644~
Details on page 1646 etc.

Furthermore, there is a prior art technique in which simple parallel line transmission lines are periodically arranged.

Examples of the present invention are shown in FIGS. 3-4. The structural features are that parallel line transmission lines with T-branches are arranged periodically in the x direction, and that the dimension from the gap start point to the T-branch is smaller than a quarter wavelength. In FIG. 3, radio waves from the heating chamber 8 leak into a space 15 through a gap formed by a door section consisting of a main body wall 9, a sealing plate 10, and a door wall surface 11. In this region, a T-branch is formed which has an aperture 13 whose end 14 is short-circuited at a portion closer than 1/4 wavelength from the gap starting point 12. The illustrated embodiment shows an example in which a dielectric material 16 having a relative permittivity of greater than 1 is loaded in the T-branch. Parallel transmission lines 17a, b, c, and d constitute a transmission path with the main body wall 9 as a ground plane. FIG. 4 shows a perspective view of the main part of FIG. 3. (The dielectric 16 is omitted.) In the case of 2450MHz, the quarter wavelength is approximately 30.6 mm, but in the example, each dimension is L ₁ = 10 mm, L ₂ = 32 mm (when the relative permittivity is half 1) L ₃ =5~10mm parallel line width 10mm,
Parallel lines are arranged at a pitch of 15 to 20 mm in the X direction.
According to experiments, in the above example, when the dimension L ₁ is set to about 1/4 wavelength and when it is set to 10 mm, which is shorter than that, the amount of radio wave leakage is about 2 to 3 times smaller in the former case than in the latter case.
It was confirmed that this relationship was maintained even when the gap between the main body and the door was increased from a close contact state to 4 mm.

The above-mentioned results of the configuration of the present invention, which cannot be explained by the idea of the York system, can generally be quantitatively explained by considering the following.

FIG. 5 shows an equivalent circuit diagram for explaining the general concept. Terminal a-a corresponds to the gap starting point. The idea is that when the impedance seen from the starting point of the clearance to the heating chamber side is Z (=R+jX), the amount of radio wave leakage is proportional to R・Z ⁻ / ₀ /R・Z ⁻ / ₀ + R ² + X ² . When this concept is applied to the embodiment, the result will be as shown in FIG. 6. That is, when the impedance seen from the line end to the external space is Z _L and the reactance due to the T-branch configuration is Z ₁ , Z ₂ , Z ₃ , Z ₄ , Z ₅ ,
The impedance Z seen from the terminal a-a to the left side, which is equivalent to the gap starting point, can be calculated. That is Z=
The amount of radio wave leakage can be quantitatively calculated based on the form R+jX. FIG. 7 shows the correspondence between analytically calculated values and actually measured values using such an analytical method.

Figure 7 shows that the tendency of the measured values of radio wave leakage can be explained almost with the calculated values, and also that the amount of radio wave leakage is 30.6mm, which is equivalent to a quarter wavelength, for the T-branch dimension _L2 .
A lower leakage amount is recommended for a longer length of 32 mm, but the results can also be analyzed and explained.

The results shown in FIG. 7 can be qualitatively explained using FIG. 6 as follows. That is, at the T branch in FIG. 6, the combined value of the reactance components (Z ₃ , Z ₄ , Z ₅ ) due to the branch structure and the short-circuited line reactance at a distance L ₂ from terminals dd is obtained from the transmission line L ₁ . It controls the transmission amount to the transmission line L ₂ section, and the radio wave sealing effect is increased from the transmission line L ₁ section to the transmission line L ₃ by increasing the above T-branch reactance composite value.
A necessary condition is to reduce the amount of transmission to the parts. In the case of Fig. 7, this can be realized by setting the dimension _L2 to 32 mm.

In addition ^{, the} overall impedance Z (=R ⁺ _j By adjusting L ₁ , it is possible to reduce the amount of leakage in the dimension L ₂ =32 mm.

This can be achieved by making the value of the dimension L ₁ as smaller as possible than a quarter wavelength.

If this way of thinking about the amount of radio wave leakage is applied to the configuration of the present invention, it will be shown that the dimension L ₁ from the gap start point to the T-junction is better to be shorter than a quarter wavelength, and the above results can be explained analytically. Specifically, Figure 7 shows an example of the correspondence between experimental values and calculated values based on this theory.
This is the result obtained when L ₁ is 12 mm. This is 2450M
This shows that it is possible to sufficiently prevent radio wave leakage even if the _L1 dimension is made extremely shorter than approximately 30 mm, which corresponds to a quarter wavelength of Hz.

Therefore, if the configuration of the present invention is adopted, the dimension in the Y direction is almost the same as that of the chiyoke system, but the dimension in the Z direction can be shortened, and a compact radio wave sealing device can be realized.

As explained above, according to the present invention, the following effects can be expected.

A compact radio wave seal device can be realized.

Compared to the one described in Japanese Patent Publication No. 51-34580, there is only one T-branch line, and only one dielectric is required for loading the dielectric.

Can be designed quantitatively and analytically.

Even if the gap between the main body and the door becomes large, the amount of radio wave leakage can be kept low.

By loading a dielectric material with a relative permittivity of more than 1 into the T-branch, the geometrical dimension in the y direction can also be reduced.

Note that in the above explanation, the word dimension does not refer to a geometric dimension, but a radio wave phase dimension, so geometric dimension compression due to dielectric loading is
It is within the scope of the present invention to apply it to ₁ part of L and ₃ parts of L.

[Brief explanation of the drawing]

1 and 2 are explanatory diagrams of conventional examples, in which FIG. 1 shows the case where it is applied to a waveguide and FIG. 2 shows the case where it is applied to a heater. Third
The figure is a sectional view showing an embodiment of the present invention, and FIG.
5 and 6 are explanatory diagrams for quantitatively explaining the concept of the present invention, and FIG. 7 is an illustrative diagram of analytically calculated values and actual measured values of the amount of radio wave leakage in the configuration of the present invention. . 9... Body wall surface, 10... Sealing plate, 11... Door wall surface, 12... Clearance starting point, 13... T branch opening, 14... Short circuit termination, 17... Parallel line transmission line.

Claims (1)

[Claims] 1. The heating chamber opening has a door that can be opened and closed, and either the main body or the door has a T-branched part with a short-circuited end in the direction (z direction) orthogonal to the direction around the heating chamber opening (x direction). Parallel transmission line in peripheral direction (x
A radio wave sealing device that is periodically arranged in a direction (direction) and has a configuration in which the dimension from the gap start point to the T-branch opening is smaller than a quarter wavelength.