JPH0142588B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a radio wave seal for a high frequency heater. This is especially effective when applied to devices such as microwave ovens that have doors that can be opened and closed. Configuration of conventional examples and their problems Many radio wave seal devices have been proposed, and the ones that are practically used are those shown in Figures 1 and 2.
There is a "Chiyoke method" shown in the figure. Furthermore, there is also a prior art technique that takes measures against radio wave propagation in the longitudinal direction of the chiyoke groove C of this "chiyoke method." However, these have a chiyoke groove, and the effective depth from the chiyoke groove opening C ₁ to the chiyoke groove end C ₂ is one-fourth of the frequency of the radio wave used.
It is characterized by its wavelength. In other words, the characteristic impedance of the chiyoke groove C is
When the depth of the Zo groove is l and the terminal ends are short-circuited,
The impedance Zin at the chiyoke groove opening is Zin
=jZo tan(2πl/λo). However, λo is the free space wavelength, and the Chi-Yoke method is based on the principle that |Zin|=Zo tan(π/2)=∞ is achieved by selecting the groove depth l to be λo/4. When the chiyoke groove C is filled with a dielectric material (nonpermittivity εr), the radio wave wavelength λ' is compressed to λ'=λo/ _√v . In this case, the groove depth l' becomes short as l'≒l/ _√v . However, l′≒
There is no difference in setting it to λ'/4. Therefore, in the chi-yoke method, the chi-yoke groove C
Since the depth l cannot be made substantially smaller than a quarter wavelength, there is a limit to miniaturization. OBJECTS OF THE INVENTION The present invention is similar to the Chi-Yoke method in that it uses a groove for radio wave sealing, but is called a small groove to distinguish it from the Chi-Yoke groove. The object of the present invention is to commercially implement an openable/closable door in which the depth of the small groove is substantially smaller than a quarter wavelength. Structure of the Invention The principle by which the width and depth of the small groove can be made substantially smaller than one-fourth of the wavelength used will be explained below. Miniaturization can be achieved by changing the characteristic impedance of the small groove in the depth direction of the groove. The limiting conditions are that the characteristic impedance of the aperture of the small groove is smaller than the characteristic impedance of the end of the groove, and that both the width and depth of the groove are smaller than one quarter of the effective radio wavelength. The characteristic impedance will be explained below using FIGS. 3 and 4. FIG. 3 is a perspective view of a parallel line, where the line width is a, the line gap is b, and the dielectric constant of the dielectric medium is ε _v . As is well known, the characteristic impedance Z _p in this case is Therefore, the characteristic impedance Z _p can be made small by widening the line width a, narrowing the line gap b, and increasing the relative dielectric constant ε _v .
FIG. 4 shows an example of the structure of the door. In this case door 1
A groove 5 having a groove width b is formed by wall surfaces 2 and 3 extending in the x direction and a conductive line group 4 having a width a and a pitch p. In this case, the conductor line group 4 acts on the wall surface corresponding to the ground plane as a radio wave propagation system, but the characteristic impedance of each line
Z _p is Therefore, almost the same relationship as in the case of parallel lines is maintained. FIG. 5 shows examples (a), (b), and (c) in which the impedance of the small groove is changed by 2, 3, and n. The section of the characteristic impedance Zio has a length li, the impedance seen from the impedance change point to the groove end side is Zi, and the impedance seen from the groove opening part to the groove end side is Zin _o . Specifically, in case (a) where the groove is divided into two, Z ₂ = jZ ₂₀ tanβl ₂ = jx ₂ or less β is β = 2π/λ _p (b) Z ₃ = jZ ₃₀ tanβl ₃ Z ₂ = Z ₂₀ Z ₃ +jZ ₂₀ tanβl ₂ /Z ₂₀ +jZ ₃ tanβl _{2 ≡jx 3} Zin ₃ =Z 10 Z ₂ +jZ ₁₀ tanβl ₁ /Z ₁₀ +jZ ₂ tanβl _1However , in the case of (Z ₁₀ <Z ₂₀ <Z ₃₀ ) (c) Zn＝jZno tanβl _o Zn−1 = Z(n−1)o
Zn+jZ(n-1)otanβl(n-1)/Z(n-1)o
+jZn tanβl(n-1) ... ...However, (Z ₁₀ <Z ₂₀ <Z ₃₀ ) Z ₂ =Z ₂₀ Z ₃ +jZ ₂₀ tanβl ₂ /Z ₂₀ +jZ ₂ tanβl ₂ ≡jXn Zin _o =Z ₁₀ Z ₂ +jZ ₁₀ tanβl ₁ /Z ₁₀ +jZ ₂ tanβl ₁ . Therefore, the impedance seen from the small groove hole is n
_{In the case of discrete characteristic impedances of _ _ _ _ _} The above formula is valid if Z ₁₀ xn tanβl ₁ are equal |
Zin _o ｜ means that it can be made into ∞. i.e. Z ₁₀
It can be seen that =xn tanβl ₁ is a requirement for increasing the impedance at the groove opening. In the example of λo=122.4mm (=2450MHz) λo/4=30.8mm, the condition of Z ₁₀ ≒ x _o tanβl ₁ is satisfied for the case of two discontinuities in figure a and three discontinuities in figure b. l ₁ , l ₂ ,
(l ₃ ), l total combination of opening characteristic impedance Z ₁₀ and termination characteristic impedance Z ₂₀ or
If the ratio of Z ₃₀ is calculated as 1:2, it will be as follows.

【table】

【table】

[Table] This result means the following. (1) Characteristic impedance Z ₁₀ < Z ₂₀ or Z ₁₀ < Z ₂₀
By setting <Z ₃₀ , the groove depth l (total) can be made smaller than a quarter wavelength. (2) The dimensional compression ratio of the depth of the groove is almost determined by the opening characteristic impedance Z ₁₀ and the end characteristic impedance Z _op , and is hardly influenced by the number of changes n in the characteristic impedance. The above explanation is for the case where Z ₂₀ /Z ₁₀ = Z ₃₀ /Z ₁₀ = 2, but Fig. 6 shows the case where the ratio of dimensions l ₁ and l ₂ is changed from 1 to 5 in the case of two divisions. The graph shows the relationship between the characteristic impedance ratio and the compression ratio at which the depth of the small groove is reduced in size relative to the depth of the chiyoke groove. If you carefully select the characteristic impedance, you can improve the
This graph shows that it can be reduced to less than one-fold. Figure 7 plots the absolute value of the characteristic impedance of the aperture using dimension l ₂ as a parameter when dimension l ₁ is 12 mm, and shows that the maximum value is obtained when dimension l ₂ is 24 mm and 25 mm. There is. Figure 8 shows the measured values of radio wave leakage. This result also
The _l2 dimension shows a minimum value between 23.5 mm and 24.5 mm, which means that: (1) Increasing the absolute value of the impedance of the small groove opening reduces the amount of radio wave leakage. (2) For the groove depth dimensions (l ₁ , l ₂ ) that increase the aperture impedance of small grooves, the calculated values and actual measurements must match accurately. (3) It is possible to reliably reduce the size compared to the depth of the chiyoke groove. When a product (microwave oven) was implemented according to the above principle, a large amount of radio waves leaked from the hinge section, which serves as the fulcrum for opening and closing the door. As shown in Fig. 9, the hinge side, which is the fulcrum for opening and closing the door, is equipped with an x
It was necessary to shorten the outer wall surface 2 extending in the direction. Here, the reason why radio wave leakage increases when the outer wall surface 2 provided on the door body 1 and extending in the x direction is lowered than the conductive line group 4 can be estimated as follows. A small groove composed of a conductor path group 4, an outer wall surface 2 provided on the door body 1 extending in the x direction, and a bottom surface 3 provided on the door body 1 extending in the x direction is formed on the outer wall surface 2.
The height becomes l', which is the same as if the door body 1 became shallower. However, since the characteristic impedance is adjusted by the height of the conductor line group 4, the small groove at the height of the outer wall surface 2 does not have a sealing effect. Moreover, conductor line group 4
It consists of an inner wall surface 6 provided on the door body 1 extending in the x direction, a bottom surface 3 provided on the door body 1 extending in the x direction, and an adjustment plate 7 for adjusting the characteristic impedance of the small groove 5'. There is a possibility that the sealing effect of the small groove 5' may be adversely affected. Therefore, the characteristic impedance can be adjusted to that of a small groove of height l' in the outer wall surface 2, but in this case, since the door body 1 becomes shallow, the characteristic impedance needs to be increased. Specifically, the question is whether the line gap b ₁ should be made smaller or b ₂ should be made larger. By reducing the line gap b ₁ , the characteristic impedance can be adjusted and the radio wave leakage prevention effect can be achieved, but the accuracy is quite strict and the door body 1
It is very susceptible to the accuracy when welding the conductor line group 4 to the conductor line group 4, the deformation of the conductor line group 4 itself, etc., and a stable sealing effect cannot be obtained. Furthermore, by increasing _b2 , the effect of preventing radio wave leakage can be obtained and a relatively stable sealing effect can be obtained, but the most important feature of this radio wave sealing device, which is compactness, is lost. Therefore, in order to achieve product implementation of a radio wave seal in which the depth of the small groove is substantially smaller than a quarter wavelength, the radio wave seal device of the present invention positions the fulcrum for opening and closing the door at the same position as the outer wall surface of the door body. Alternatively, it is placed outside the door body, and the outer wall surface of the door body is configured to be higher than the conductor path group. With this configuration, the theoretical dimensions of the first small groove and the second small groove can be obtained, and a radio wave sealing effect can be exhibited. DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 10 is a perspective view of the main parts of a radio wave sealing device according to an embodiment of the present invention, and FIG.
The figure is a sectional view of the main parts of a radio wave sealing device according to an embodiment of the present invention. As shown in FIGS. 10 and 11, 1 is a door body, 2 is an outer wall surface provided on the door body 1 and extends in the x direction, 3 is a bottom surface provided on the door body 1 and extends in the x direction, and 4 is a bottom surface provided on the door body 1 that extends in the x direction. conductor line group,
5 and 5' are small grooves, 6 is an inner wall surface provided in the door body 1 and extends in the x direction, 7 is an adjustment plate for adjusting the characteristic impedance of the small groove 5', 8 is a radio wave leakage path, and 9 is a door The center of the hinge, which serves as a fulcrum when the main body 1 is opened and closed, is a resin cover 10. An adjustment plate 8 is welded to the door body 1 for adjusting the characteristic impedance of the conductor path group 4 and the small groove 5'.
An outer wall surface 3 provided on the door body 1 and extending in the x direction
are at the same height all around and are higher than the conductor line group 4. The center 9 of the hinge, which is the fulcrum for opening and closing the door, is set so that the door body 1 can be opened and closed smoothly.
An outer wall surface 3 provided on the door body 1 and extending in the x direction
It is supported on the outside. The operation of the radio wave seal device configured as described above will be described below. First, the radio waves scattered in the heating chamber pass through the radio wave leakage path 8 and extend in the x direction through an adjustment plate 7 provided in the door body 1 and an adjustment plate 7 for adjusting the characteristic impedance of the conductor line group 4 and the small groove 5'. A small groove 5' consisting of an inner wall surface 6 and a bottom surface 3 provided in the door body 1 and extending in the x direction.
is attenuated by The radio waves that cannot be attenuated are then
It is damped again by a small groove 5 composed of a group of conducting paths 4, an outer wall surface 2 provided on the door body 1 extending in the x direction, and a bottom surface 3 provided on the door body 1 extending in the x direction. Almost no radio waves leak. As for the hinge side, which is the fulcrum for opening and closing the door, by supporting the fulcrum 9 outside the outer wall surface 2, as shown in FIG. 12, the outer wall surface 2 can be made higher than the conductor path group 4. Therefore, the sealing effect of the small groove 5 made up of the outer wall surface 2, the bottom surface 3, and the conductive path group 4 can be sufficiently exhibited. Effects of the Invention As described above, according to this embodiment, the outer wall surface provided on the door body 1 extending in the x direction is made higher than the conductor path group, and the fulcrum for opening and closing the door is provided outside the outer wall surface, thereby stabilizing the door. A compact sealing effect can be obtained, and a compact structure for preventing leakage of radio waves can be provided.

[Brief explanation of drawings]

Figures 1 and 2 are cross-sectional views for explaining the conventional chi-yoke groove system, Figure 3 is a diagram for explaining the principle of the present invention, and Figure 4 is an example of a groove configuration using the modified parallel line. 5 to 8 are diagrams for explaining the principle of the present invention, Figure 9 is a diagram for explaining problems when implementing the principle of the present invention, and Figure 10 is a diagram for explaining the principle of the present invention. A perspective view of a main part of a door body showing one embodiment of the invention, FIG. 11 is a sectional view of a main part showing the same embodiment,
FIGS. 12A and 12B are a sectional view of the same essential parts and a front view of the conductor line group. 1... Door body, 2, 3, 6... Wall surface, 4...
Conductor line group, 5, 5'...Small groove, 7...Adjustment plate,
8... Radio wave leakage path, 9... Fulcrum, 10... Resin cover.

Claims (1)

[Scope of Claims] 1. One or more small grooves having a groove opening surrounded by a group of groove walls and a short-circuit end are provided in the openable/closable door of the high-frequency heater, and the grooves are periodically cut in the longitudinal direction. The line group is configured such that the groove width at the groove opening is smaller than the groove width at the short-circuit termination part, and the conductor width at the groove opening is larger than the conductor width at the short-circuit termination part. A radio wave sealing device having a structure in which the width and depth of the groove are substantially smaller than one-fourth of the wavelength used, and the outer wall surface extending in the X direction provided on the door body is higher than the conductor line group. . 2. The radio wave sealing device according to claim 1, wherein the fulcrum for opening and closing the door is supported outside the outer wall of the door.