JPS6314829B2 - - 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 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 Zin=iZotan (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 to be λo/4. When the inside of the chiyoke groove is filled with a dielectric material (relative dielectric constant ε _r ), 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 chiyoke method, the depth of the chiyoke groove cannot be made substantially smaller than a quarter wavelength, and there is a limit to miniaturization. Figures 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. 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 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,
It can be made smaller by increasing the relative permittivity ε _v . 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. Structure of the Invention 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 . i is the subscript, specifically the groove 2
In the case of divided (a), Z ₂ = jZ ₂₀ tanβl ₂ ≡jx ₂ or less β is β = ² 〓〓 _p Zin ₂ = 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 , in the case of (Z ₁₀ <Z ₂₀ <Z ₃₀ ) (c) Zn=jZnotanβln 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 ≡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 Zin _o =Z ₁₀ Z ₂ +jZ ₁₀ tanβl ₁ /Z ₁₀ +jZ ₂ tanβl ₁ =jZ ₁₀ x _o +Z ₁₀ tanβl ₁ /Z ₁₀ −x _o tanβl ₁ . The above formula is valid if Z ₁₀ and x _o tanβl 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=122.4mm (=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. 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] This result means the following. 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. The dimensional compression ratio of the depth of the groove is almost determined by the opening characteristic impedance _Z10 and the end characteristic impedance Zno, and is hardly influenced by the number n of changes 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 graph 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: Increasing the absolute value of the aperture impedance of the small groove reduces the amount of radio wave leakage. For the groove depth dimensions (l ₁ , l ₂ ) that increase the aperture impedance of small grooves, the calculated values and actual measured values must match accurately. It is possible to reliably reduce the size compared to the depth of the chiyoke groove. The present invention performs impedance inversion using a less than λ/4 line instead of the λ/4 line that has been historically used in the field of radio wave seals. In order to make this principle easier to understand, a part of the analysis results are shown in FIG. In FIG. 9, a groove having an opening B whose tip C is short-circuited is provided in a part of a transmission line in which the A end is an excitation source and the D end is open. The width of the groove on the short circuit side is twice that on the open hole side. When point A is excited under the same conditions and the depth of the groove l _T is changed, the electric field in the transmission line changes as shown in a, b, and c, and in case b the radio wave does not reach end D. , i.e. the groove depth
l _T is about 80% of a quarter wavelength (less than λ/4 line), and even if it is longer or shorter than that (a,
In case c), radio waves leak more than in case b. In actual applications, it is not uncommon to provide a groove cover space (TOP1) and a bending reinforcement space ( _lX1 ). In these cases, compared to the case where the principle is explained, the radio waves are disturbed and the calculated dimensions are slightly deviated. The details of the deviation are shown below. When the dimension of TOP1 is 2mm and l _X1 is 5~6mm
An example is shown below. Figure 10 is an example of a 915MHz sealing device.
This shows the relationship in which the groove depth l _T changes with the dimensions of TOP1.
If the dimension of TOP1 is set to 1 to 3 mm, l _T becomes deeper by 1 to 6 mm. Figure 11 is an example of a 2450MHz sealing device.
The relationship is shown in which the groove depth l _T changes depending on the reinforcement space (l _X1 ) with TOP1 = 2 mm fixed. Space l _X1 2~
By setting it to 6 mm, the groove depth l _T becomes deeper by 1 to 3 mm. DESCRIPTION OF EMBODIMENTS The present invention is constructed by making the dielectric constant of the opening part of the small groove larger than the dielectric constant of the short circuit part, and
Examples are shown in FIGS. In FIG. 12 showing the basic configuration, the small groove 10 has a groove wall surface 6,
In particular, the wall surface 9 is composed of a group of lines having a conductive width a and a pitch p (p>a). 11 is a dielectric material. With this configuration, the characteristic impedance of the groove opening can be made smaller than that near the short circuit. Figure 13 shows a dielectric material with relative permittivity ε _v = 3.5.
Figure a shows the relationship between the calculated aperture impedance (Zin) and the _depth of the small groove when PPS (polyphenylene sulfide) is loaded, and b shows the actually measured radio wave leakage amount P _L and the groove depth. It shows the relationship between
The calculation is performed using the characteristic impedance of the dielectric part as Z ₁₀ , the propagation constant β ₁ , the length l ₁ = 7.5mm, and the remaining space as follows:
When Z ₂₀ , β ₂ , l ₂ , Z ₁₀ = x _o tanβl ₁ and jx _o = jZ ₂₀ tanβ ₂ l ₂ , so Z ₁₀ = Z ₂₀ tanβ ₁ l ₁ tanβ ₂ l _2. Indicates that the step shows the maximum impedance. The correspondence between the graphs a and b shows that the depth of the small groove showing the maximum impedance between the calculated value and the actual value is almost the same as the depth of the groove where the measured leakage amount is the lowest. Figures 14 and 15 show three examples of implementation in high-frequency heaters. 12 is a main body, and 13 is an outer groove. Effect of the invention 1: The depth of the small groove can essentially be made smaller than a quarter wavelength. 2. Since at least one of the walls constituting the small groove is composed of a group of lines, the radio wave propagation pattern in the x direction can be reduced, and the radio wave sealing performance can be improved. 3. Since the amount of dielectric material filled into the groove is small, the size can be reduced using less material. 4. Since there are more dielectric fillings in the opening than in the short-circuit termination, it is easier to insert the dielectric into the small groove.

[Brief explanation of the drawing]

Figures 1 and 2 are diagrams showing conventional examples of chiyoke grooves;
FIG. 3 is a diagram showing a parallel line, FIG. 4 is a perspective view showing an example of the structure of a groove by a modified parallel line, FIGS. 5 to 8 are diagrams for explaining the principle of the present invention, and FIGS.
b, c are electric field analysis diagrams of the groove portion in the present invention, 1st
Figures a, b, and c are cross-sectional views of the device at 915MHz,
Side view, characteristic diagram, Figure 11 a, b, c are 2450MHz
Sectional view, side view, and characteristic diagram of the device in 12th
The figures are perspective views showing embodiments of the present invention, Figure 13a,
14b is a characteristic diagram of the same device, FIGS. 14a and 14b are sectional views of the same device, and FIG. 15 is a perspective view of the same device. 6, 7, 8...Groove wall group, 10...Small groove, 11...Dielectric material, a...Width of conductor, p...Pitch.

Claims (1)

[Claims] 1. At least one of the door or the main body of a high-frequency heater having a door that can be opened and closed has one or more small grooves having a groove opening and a short-circuit end surrounded by a group of groove walls, and at least one of the walls of the group One wall surface is composed of a group of conductor lines in the x direction with a conductor width a and a pitch P such that P>a, and a dielectric material is arranged in the groove with a width smaller than a quarter of the wavelength used. Fill the parts and
By configuring the groove opening part to have a larger effective dielectric constant than the short-circuit end part, and by making the dimensions of the opening part and the short-circuit part almost equal in the depth direction, the effective dielectric constant of the small groove can be reduced. A radio wave sealing device with a depth smaller than a quarter of the wavelength used.