JPS6316862B2 - - 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 has been practically used 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 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 groove depth is l and the terminal ends are short-circuited, the impedance Zin at the chiyoke groove opening is Zin=j
Zotan (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 short as l′≒l/√. However, there is no difference in setting l'=λ'/4. 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. 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 can be reduced to a small value by widening the line width a, narrowing the line gap b, and increasing the dielectric constant εv.
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
Zo 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. In FIG. 5, examples in which the impedance of small grooves is changed by 2, 3, and n are shown in 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, 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 _1
0 < _Z20 ) 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 Zin ₃ =Z ₁₀ Z ₂ +jZ ₁₀ tanβl ₁ /Z ₁₀ +jZ ₂ tanβl ₁ However (Z
₁₀ ＜ Z ₂₀ ＜ Z ₃₀ ) In the case of (c), Zn＝jZno tanβl _o Zn _-1 = Z(n _-1 ) oZn＋jZ(n _-1 ) otanβl(n _- 1)/Z
(n _-1 ) o + jZntanβl (n _-1 ) ......However ...... (Z ₁₀ <Z ₂₀ ...< 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 becomes. 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 =xntanβl 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 ≒zntanβl ₁ is satisfied for the case of two discontinuities in figure a and three discontinuities in figure b. l ₁ , l ₂ ,
The combination of l ₃ , l total with opening characteristic impedance Z ₁₀ and termination characteristic impedance Z ₂₀ or Z ₃₀
If the ratio is 1 to 2, it will be calculated 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 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: 1. Increasing the absolute value of the impedance of the small groove opening reduces the amount of radio wave leakage. 2. Regarding the groove depth dimensions l ₁ and l ₂ that increase the impedance of the small groove opening, the calculated value and the actual measurement value must match with good accuracy. 3. The size can be definitely reduced 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, part of the analysis results are shown in FIG. Figure 9 shows D with the A end as the excitation source.
A groove having an opening B whose tip C is short-circuited is provided in a part of the transmission line with an open end. 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 groove depth lT is changed, the electric field in the transmission line changes as a, b, c, and D
The radio wave does not reach the end in case b, that is, when the groove depth lT is about 80% of a quarter wavelength (less than λ/4 line), and even if it is longer or shorter than that, (In cases a and c), radio waves leak more than in case b. In actual application, the space of the groove cover
TOP ₁ and bending reinforcement space lX ₁ are often provided. 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 TOP ₁ is 2mm and lX ₁ is 5~6
An example is shown when it is set to mm. Figure 10 is an example of a 915MHz sealing device.
This shows the relationship in which the groove depth lT changes with the dimensions of TOP ₁ . If the dimension of TOP ₁ is 1 to 3 mm, lT is 1 to 6
mm deeper. Figure 11 is an example of a 2450MHz sealing device.
The relationship is shown in which the groove depth lT changes with the reinforcing space lX ₁ while fixing TOP ₁ = 2 mm. Space lX ₁ to 2
By setting it to 6 mm, the groove depth lT becomes deeper by 1 to 3 mm. DESCRIPTION OF THE EMBODIMENTS The present invention comprises a line group in which at least one of the wall groups constituting the small groove has a conducting wire width a smaller than the pitch p, and each conducting wire is
The short-circuit portion is made up of a plurality of conducting wires, and the sum of the conducting wire widths in this portion is smaller than the opening portion conducting wire width. Embodiment diagrams are shown in FIG. 12 and FIG. 13. In FIG. 12, the groove wall groups 6, 7, and 8 constitute a small groove, and the groove wall groups 8, 10, and 11 constitute a second small groove. In the diagram, the depth of the groove l
total is between the dimensions l ₁ and l ₂ in the diagram total = l ₁ + l ₂
have the following relationship. The width of each conductor in the part corresponding to the dimension l ₁ in the depth direction of the groove, that is, the opening part, is a ₁ , and
The part corresponding to the dimension l ₂ , that is, the short circuit, has a width a ₂ ′.
It consists of two conductors of a ₂ ″.Here, the above 2
If the sum of the book widths is a ₂ , then a ₂ = a ₂ ′ + a ₂ ″. In the present invention, by creating a relationship between the dimension a ₂ and the dimension a ₁ such that a ₂ < a ₁ , short circuits can be achieved. The groove depth is reduced by changing the characteristic impedance of the groove and the aperture.Dimensions _b11 and _b12 are the groove width and dimension of the aperture of each groove.
b ₂₁ and b ₂₂ are the short-circuit groove widths of each groove. Another embodiment is shown in FIG. This is different from FIG. 12 in that the groove width is not changed in the first groove. In order to compress the depth of the groove to more than one-fourth of the actual wavelength and cause resonance, the ratio K of the characteristic impedance of the opening part and the short-circuit part of the groove should be made larger than 1. To do this, as explained above, the groove width b
However, the conductor width a, which is another factor that defines the characteristic impedance, or both may be changed. Specifically, in FIG. 9, the characteristic impedances of the opening part and the short circuit part, Z ₀₁₁ and Z ₀₁₂ , are respectively Z ₀₁₁ αb ₁₁ /a ₁ and Z ₀₁₂ αb ₂₁ /a ₂ ′+a ₂ ″= b ₂₁ /a ₂ , and therefore the characteristic impedance ratio K ₁ is K ₁ = Z ₀₁₂ /Z ₀₁₁ = a ₁ ×b ₂₁ /a ₂ ×b ₁₁ (where a ₁ > a ₂ ,
b ₂₁ > b ₁₁ ) Similarly, K ₂ = a ₁ × b ₂₂ / a ₂ × b ₁₂ (here b ₂₂ > b ₁₂ ). In Fig. 10, the characteristic impedance ratio K ₁ of the open hole part and the short circuit part for the first groove is equal to the groove width, so K ₁ = a ₁ /a ₂ Similarly to Fig. 9, the characteristic impedance for the second groove is The ratio K ₂ becomes K ₂ =a ₁ ×b ₂₂ /a ₂ ×b ₁₂ . Effect of the invention 1: The depth of the small groove can essentially be made smaller than a quarter wavelength. 2. Since a plurality of line groups are arranged in the x direction on at least one of the walls forming the small groove, the radio wave propagation component in the x direction can be reduced, and the radio wave sealing performance can be improved. 3. Each conductor has a plurality of conductors at the short-circuit portion, so the mechanical strength is greater than in the case of a single narrow conductor.

[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 track, Fig. 4 is a perspective view showing an example of a groove configuration using a modified parallel track, and Figs.
The figure is a diagram for explaining the principle of the present invention, and Figures 9a, b, and c are electric field analysis diagrams of the groove portion in the present invention.
Figures 10a, b, and c are cross-sectional views, side views, and characteristic diagrams of the device at 915MHz; Figures 11a, b, and c are
A cross-sectional view, a side view, a characteristic diagram, and FIGS. 12 and 13 of the device at 2450 MHz are perspective views showing an embodiment of the present invention. 6, 7, 8, 10, 11...Groove wall group, 9, 12
...Small groove, a ₁ ...Width of track at opening, a ₂ (=a ₂ ′+
a ₂ ″)... short circuit line width, p... pitch, b ₁₁ , b ₁₂
...Open hole groove width, _b21 , _b22 ...Short circuit groove width.

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 at least one small groove having a groove opening and a short circuit surrounded by a group of groove walls, and at least one of the wall groups One wall surface is composed of a group of lines in which the conductor width in the x direction is less than the pitch, each line has a groove short-circuited part as a plurality of conductors, and the sum of the above-mentioned conductor widths is less than the conductor width in the opening part. This is a radio wave sealing device in which the width and depth of the small groove are substantially smaller than one-fourth of the wavelength used.