JPH0142583B2 - - 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. Conventional configurations and their problems Many radio wave sealing devices have been proposed, and one that is in practical use is the "chiyoke system." Furthermore, there is also a prior art that takes measures against radio wave propagation in the longitudinal direction of the chiyoke groove in this "chiyoke method." However, these devices have a chiyoke groove, and the effective depth from the chiyoke groove opening to the chiyoke groove end is required to be one-fourth the wavelength of the radio wave frequency used. Therefore, the size of the seal cannot be made small, which hinders miniaturization of the product. Therefore, in recent years, by changing the characteristic impedance of the groove in the depth direction, a so-called small-groove seal has been developed, which can be made smaller in both the width and depth directions by reducing the wavelength to less than a quarter of the wavelength used. Here, the principle that miniaturization is possible by changing the characteristic impedance of the groove in the depth direction will be explained. In FIG. 1, examples in which the impedance of small grooves is changed by 2, 3, and n are shown at a, b, and c. 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 the case of a where the groove is divided into two, Z ₂ = jZ ₂₀ tanβl ₂ ≡jx ₂ or less β is β = 2π/λo Zin = Z ₁₀ Z ₂ +jZ ₁₀ tanβl ₁ /Z ₁₀ +jZ ₂ tanβl _1However , (Z ₁₀ <Z ₂₀ ) In the case of 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 , (Z ₁₀ <Z ₂₀ <Z ₃₀ ) In case of c Zn=jZno tanβl _o Zn−1 =Z(n−1)o
Zn+jZ(n-1)o tanβl(n-1)/Z(n-1)
o + jZntanβl (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 ≡jX _o 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 discontinuous characteristic impedances _, Zin _o =Z ₁₀ Z ₂ + _{jZ 10} tanβl ₁ /Z ₁₀ +jZ ₂ tanβl ₁ = _{jZ 10} The above formula is valid if Z ₁₀ xntanβl ₁ are equal |
Zin _o ｜ means that it can be made into ∞. i.e. Z ₁₀
It can be seen that =x _o tanβl ₁ is a requirement for increasing the impedance at the groove opening. In the example of λo = 122.4 mm (f = 2450) λo/4 = 30.8 mm, 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. _l1 ,
Combination of l ₂ , (l ₃ ), ltotal with 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. 2 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. This graph shows that if the characteristic impedance is carefully selected, it is possible to create a groove with less than one-tenth of the chiyoke groove. Figure 3 plots the absolute value of the characteristic impedance of the opening 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. . Figure 4 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) The depth dimensions (l ₂ , l ₂ ) of the small grooves that increase the impedance of the openings must be such that the calculated values and actual measurements match accurately. (3) It is possible to reliably reduce the size compared to the depth of the chiyoke groove. As described above, size reduction has become possible by changing the characteristic impedance of the groove. However, unlike the chiyoke groove, it is made smaller than a quarter of the wavelength used, so the thinner and smaller it is, the more accurate the dimensional accuracy is required, but the current press working and welding work cannot achieve dimensional accuracy, so radio waves The leakage prevention performance was significantly degraded. OBJECTS OF THE INVENTION The present invention solves the above-mentioned drawbacks and provides a compact radio wave leakage prevention device with good performance. Structure of the Invention In order to achieve this object, the radio wave sealing device of the present invention is configured by integrating a group of conductive lines and a group of walls. With this configuration, the dimensions required for the radio wave seal are integrally formed by the conductor line group and the wall group, which eliminates dimensional variations due to welding, etc., improves dimensional accuracy, and improves radio wave leakage prevention performance. DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 5 is a sectional view of the door opening/closing side of the radio wave sealing device in one embodiment of the present invention. FIG. 6 is a sectional view of the radio wave seal device on the hinge side in one embodiment of the present invention. In FIG. 5, a door body 1 is provided so as to be openable and closable, facing the opening periphery 4 of the heating chamber 7. Inside the door body 1 is a door inner plate 3.
is provided, and when the door is closed, the door inner plate 3 and the opening peripheral edge 4 are in surface contact with each other. The door opening/closing side of the door body 1 has an inner wall surface 8 extending in the X direction provided on the door body 1 and an X side provided on the door body 1.
The bottom surface 9 extending in the direction, the conductor line group 2 and the door inner plate 3
It has a small groove 11' whose wall surface is integrally formed with a small groove 11 consisting of a small groove 11 and a conductive line group 2. The wall surface integrated with the conductor path group 2 and the outer wall 10 of the door body 1 hold the door key 5. Note that the conductor line group 2 and the door inner plate 3 are welded to the door body 1. In FIG. 6, a door body 1 is provided so as to be openable and closable, facing the peripheral edge 4 of the opening of the heating chamber 7. A door inner plate 3 is provided inside the door body 1, and the door inner plate 3 and the opening periphery 4 are in surface contact with each other when the door is closed. The fulcrum 12 side for opening and closing the door includes an inner wall surface 8 provided on the door body 1 extending in the X direction and a bottom surface 9 provided on the door body 1 extending in the X direction.
A small groove 11 composed of a group of conducting paths 2 and a door inner plate 3, an outer wall surface 10 provided on the door body 1 extending in the X direction, a bottom surface 9 provided on the door main body 1 extending in the X direction, and a conducting path. It has small grooves 11' made up of groups 2. Note that the door inner plate 3 and the conductive path group 2 are welded to the door body 1. The operation of the radio wave seal device configured as described above will be explained below. First, when the door is closed, the leakage of radio waves inside the heating chamber 7 to the outside is attenuated by the surface contact l between the opening periphery 4 and the door inner plate 3. Since the attenuated radio waves are attenuated by the small grooves 11, 11', leakage of radio waves to the outside of the door body 1 can be suppressed even if the dimensional accuracy is somewhat poor. Next, when the door body 1 is partially open, the radio waves cannot be completely blocked, and the radio waves are transmitted to the inner wall surface 8 provided on the door body 1 extending in the X direction and the bottom surface provided on the door body 1 extending in the X direction. 9, the conductor path group 2, and the door inner plate 3. However, this small groove 11 does not have dimensional accuracy because the conductor line group 2 and the door inner plate 3 are welded together, and radio wave leakage is not sufficiently attenuated. The radio waves that have not been completely attenuated enter the small groove 11'. Since the wall surface of this small groove 11' is constituted by the conductor line group 2, the dimensional accuracy is determined by the accuracy of press processing (currently ±0.2). Therefore, by experimenting to determine dimensions that have a large effect of attenuating radio wave leakage, a sufficient sealing effect can be obtained without variation. Here, the wall surface of the small groove 11' on the door opening/closing side is integrally formed with the conductor path group 2, and the small groove 11' on the hinge side
1' is composed of the conductor path group 2, the outer wall surface 10, and the bottom surface 9, and if the configuration on the door opening/closing side is the optimum size for the radio wave seal, the configuration on the hinge side will have the outer diameter due to the aperture of the door body 1. The sealing effect will be lower on the hinge side, where optimal dimensions are difficult to obtain due to waving on the wall and welding misalignment when welding the conductor line group 2 to the door body 1, etc., but as shown in the cross-sectional view of the door half-opened in Figure 7. Door body 1 and opening rim 4
The gap between them is g ₁ ≪ _{g 2} , and since there is always a small gap on the hinge side, radio wave leakage will be reduced by this amount.
As a result, the radio wave leakage value when the door is half open can be set to a value sufficiently lower than the permissible value. Effects of the Invention As described above, according to the present invention, by integrally configuring at least the conductive path group on the door opening/closing side and the wall surface,
It is possible to provide a safe radio wave sealing device with improved dimensional accuracy and less radio wave leakage not only when the door is closed but also when a gap is created between the door body and the periphery of the opening. Furthermore, since the wall surface integrated with the conductor path group is a necessary part to support the door key, the number of parts and the number of processing steps can be reduced, which has a great effect.

[Brief explanation of drawings]

Figures 1 to 4 show the depth and width of the grooves at 4 wavelengths.
Diagram 5 showing the principle of the present invention that can reduce the size to less than 1/2
The figure is a sectional view of the door opening/closing side of a radio wave seal device in an embodiment of the present invention, FIG. 6 is a sectional view of the hinge side in an embodiment of the present invention, and FIG. 7 is a radio wave seal device in an embodiment of the present invention FIG. 3 is a cross-sectional view showing a state in which the door of the device is left half-open. DESCRIPTION OF SYMBOLS 1... Door main body, 2... Conductive line group, 3... Door inner plate, 4... Opening periphery, 5... Door key, 7... Heating chamber, 8... Inner wall surface, 9... Bottom surface,
10...Outer wall surface, 11, 11'...Small groove, 12
...The fulcrum of the hinge.

Claims (1)

[Claims] 1. A door of a high-frequency heater having a door that can be opened and closed is provided with a groove having a groove opening surrounded by a group of groove walls and a short-circuit end, and at least one wall of the group of walls is provided with a groove having a short-circuit end. Consisting of a line group having periodic notches in the longitudinal direction, the groove width of the groove opening is smaller than the groove width of the short-circuit termination part, and the conductor width of the groove opening is larger than the conductor width of the short-circuit termination part. The radio wave sealing device is composed of a group of conductive lines as shown in FIG. 2. The radio wave sealing device according to claim 1, wherein the door key is supported by a groove wall formed integrally with the conductor path group.