JPS6348159B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a radio wave seal for a high frequency heating device. 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 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 are characterized in that they have a chiyoke groove, and that the effective depth from the chiyoke groove opening to the chiyoke groove end is a quarter wavelength of the frequency of the radio wave used. That is, the characteristic impedance of the chiyoke groove is Zo,
When the depth of the groove is l and the terminal end is short-circuited, the impedance Zin at the opening of the chiyoke groove is in=
jZotan (2πl/λo). However, λo is the free space wavelength, and the Chi-Yoke method is based on the principle that |Zin|=Zotan(π/2)∞ is achieved by selecting the groove depth l as λo/4. When the inside of the chiyoke groove is filled with a dielectric material (relative permittivity εr), the radio wave wavelength λ′ becomes λ′=
Compressed to λo/√. In this case, the groove depth l′ is
It becomes shorter as l′≒l/√. However, l′=l′/4
There is no difference in that. Therefore, in the Chi-Yoke method, the depth of the Chi-Yoke groove cannot be made substantially smaller than a quarter wavelength, and there is a limit to miniaturization. FIGS. 1 and 2 show examples of conventional configurations. 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 invention aims at configuring the depth of the miniature grooves to be substantially less than a quarter wavelength. Structure of the Invention 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 εv. As is well known, the characteristic impedance Zo in this case is

[Formula] (k: constant of proportionality). Therefore, the characteristic impedance Zo is the line width a
To widen the line gap b, to narrow the line gap b,
By increasing the relative dielectric constant εv, it can be reduced to a small value. FIG. 4 shows an example of the structure of the door. In this case, the wall surfaces 2 and 3 extending in the x direction provided on the door 1 and the width a,
A groove 5 having a groove width b is formed by a conductive line group 4 having a pitch p. In this case, the conductor line group 4 acts as a radio wave propagation system against the wall surface corresponding to the ground plane, but the characteristic impedance Zo for each line is

[Formula] (k': constant of proportionality) holds almost the same relationship as in the case of parallel lines. Next, the principle of the present invention will be explained using FIGS. 5 to 8. FIG. 5 shows an example in which impedances of the small grooves are changed by 2, 3, and n 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 case (a) where the groove is divided into two, Z ₂ = jZ ₂₀ tanβl ₂ ≡jx β less than ₂ is β = ² 〓〓 _p In case (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 In the case of (c), Zn=jZnotanβl _o Zn−1=Z(n−1)oZn+jZ(n−1) otanβl(n
-1)...Zn-1=Z(n-1)oZn+jZ(n-1)otanβl(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 ≡jXn becomes. Therefore, the impedance seen from the small groove opening is Zin _o =Z ₁₀ Z ₂ +jZ ₁₀ tanβl ₁ /Z ₁₀ +JZ ₂ tanβl ₁ =jZ ₁₀ xn+Z ₁₀ tanβl ₁ /Z ₁₀ − xntanβl becomes ₁ . 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 =xntanβl ₁ is a requirement for increasing the impedance at the groove opening. In the example of λo = 122.4 mm (f = 2450 MHz) 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. When the combination of l ₁ , l ₂ , (l ₃ ), and ltotal is calculated assuming that the ratio of the opening characteristic impedance Z ₁₀ to the termination characteristic impedance Z ₂₀ or Z ₃₀ is 1:2, the result is as follows.

【table】

【table】

[Table] (Unit: mm)
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. This glove shows that by carefully selecting the characteristic impedance, it is possible to reduce the characteristic impedance to less than one-tenth of that of the chiyoke groove. 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 the small groove, the calculated value and the actual value must match accurately. (3) It is possible to reliably reduce the size compared to the depth of the chiyoke groove. Next, the configuration of the present invention will be explained. The present invention provides a first groove and a second groove having a groove opening and a short-circuit end in at least one of the main body or the door of the microwave oven, and a conductor having cut portions periodically in the longitudinal direction of the groove. The structure is such that the groove is divided into two grooves by a plate, and the width and depth of the groove are substantially smaller than a quarter of the wavelength used.
The structure is characterized in that the ratio of the characteristic impedance of each opening of the groove and the short-circuit termination part is approximately equal to perform radio wave sealing. Description of Embodiment Hereinafter, one embodiment will be described based on the drawings. FIG. 9 is a sectional view of the radio wave seal portion, FIG. 10 is a perspective view of the conductor plate, and FIG. 11 is a perspective view of another modification of the conductor plate. In FIGS. 9 and 10, 1 is a heating chamber, and 2 is a door that covers the opening periphery of the heating chamber 1, and is attached to the main body metal plate 3 of the heating chamber 1 so as to be openable and closable. 4 is a conductor plate with an inverted S-shaped cross section fixed to the door 2 by spot welding, etc., and has two grooves M ₁ and M ₂ between it and both side walls of the door 2, and an opening in the grooves M ₁ and M ₂ . Part width b11, b21 and short-circuit end part width b12, b2
2 and b11, b21<b12, b22, and the dimensional relationship between the conductor width a11 and a12 is a11
> a12, the width b and depth d of the grooves M ₁ and M ₂ are substantially smaller than a quarter of the wavelength used, and b11≒b12, b21≒b22, the first groove M ₁ and the first groove The ratio of the characteristic impedances of the respective openings of the two grooves _M2 and the short-circuit termination portions is made approximately equal to achieve double radio wave sealing. A groove cover 5 covers the openings of the grooves M ₁ and M ₂ . Furthermore, as the door 2 becomes smaller, the dimensions of the opening widths b11 and b21 of the grooves M ₁ and M ₂ inevitably become smaller, making it difficult to fix the conductive plate 4 to the door 2 by spot welding or the like between them. Therefore, by setting the gap c11 between the conductor plate 4 and the conductor width a11 to be at least 5 mm or more, spot welding etc. can be performed between the conductor plate 4 and the conductor width a11. P is the pitch in the conductor width direction. FIG. 11 shows a conductor plate B ₆ which is a modification of the conductor plate 4 in FIG. This has the same effect as 4. Effects of the invention (1) Essentially, the depth of the groove can be made smaller than a quarter wavelength, and the radio wave seal part can be made smaller. (2) Two radio wave seal grooves having almost the same sealing effect can be constructed with one conductor plate, and a more reliable radio wave sealing effect can be obtained by double sealing. (3) A remarkable sealing effect can be obtained with an extremely simple configuration, and a large cost reduction can be achieved. (4) By providing a gap of 5 mm or more between the conductor wires, even if the seal part is downsized, it can be easily fixed using spots on the conductor plate.

[Brief explanation of the drawing]

Figures 1 and 2 are cross-sectional views of main parts showing conventional examples of chiyoke grooves, Figure 3 is a diagram showing parallel lines for explaining the principle of the present invention, and Figure 4 is a diagram for explaining the principle of the present invention. Partial cross-sectional perspective views showing examples of the structure of grooves using modified parallel lines, FIGS. 5a, b, c,
7 and 8 are diagrams for explaining the principle of the present invention, FIG. 9 is a sectional view of the radio wave seal part of a high frequency heating device which is an embodiment of the present invention, and FIG. 10 is a diagram for explaining the principle of the present invention. FIG. 11 is a partially sectional perspective view showing another example of the conductive plate shown in FIG. 10. DESCRIPTION OF SYMBOLS 1...Heating chamber, 2...Door, 3...Main metal plate, 4...Conductor plate, 5...Groove cover, 6...Conductor plate B, _M1 , _M2 ...Groove, b11, b21... ...Groove opening width, b12, b22...Groove short circuit end width, a
11... Width of the opening conductor wire, a12... Width of the conductor wire at the short-circuit termination portion.

Claims (1)

[Scope of Claims] 1. A door covering an opening of a heating chamber of a main body is provided to be openable and closable, and a first groove and a second groove having a groove opening and a short-circuit end are provided in at least one of the parts where the main body and the door face each other. The first groove and the second groove are provided in parallel, and the first groove and the second groove are divided by a conductive plate having notches periodically in the longitudinal direction of the groove, and the first groove and the second groove are The conductor plate is configured such that the groove width of each 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, and A radio wave seal structure having a depth substantially smaller than a quarter of the wavelength used and a characteristic impedance ratio of the opening of each of the first groove and the second groove and the short-circuit termination portion being approximately equal. heating device. 2. A patent claim in which a width dimension of the cut portion of a conductor plate having periodic cut portions in the longitudinal direction of the groove is set to 5 mm or more, and the conductor plate is fixed to the door by spot welding or caulking at the cut portion. The high frequency heating device according to item 1.