JPH03219699A - Radio wave seal device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a radio wave sealing device for shielding high frequency radio waves.

2. Description of the Related Art A conventional example of this type of radio wave sealing device will be described using a microwave oven that cooks food by dielectrically heating it using high frequency waves. A microwave oven is equipped with a heating compartment that stores food and heats it using high-frequency waves, and a door that can be opened and closed to cover the opening of the heating compartment for putting food in and out. At this time, radio wave sealing measures are taken to prevent high-frequency electromagnetic waves inside the heating chamber from leaking outside the chamber and causing harm to the human body.

As a conventional example, U.S. Patent No. 3,182,164 is
In FIG. 11 shown in the figure, 18 is a heating chamber of a microwave oven, and a door 21 having a handle that covers an opening 19 of this heating chamber 18 so as to be openable and closable is provided. A hollow choke portion 23 having a gap portion 22 opened toward the heating chamber 18 is formed at the peripheral edge of the door 21 . The depth 24 of this choke portion is designed to be substantially one-fourth of the wavelength of the high frequency used.

In this case, the thickness of the field 21 is also one quarter wavelength. In other words, the frequency of electromagnetic waves conventionally used in microwave ovens is 24
Since the wavelength is 50 MHz, a quarter wavelength is approximately 30 MHz.The thickness 21 of the peripheral portion 20 formed in the opening 19 of the heating chamber 18 is approximately 4/4 in order to face the choke portion 23 of this length. The value is larger than one wavelength of . Therefore, heating chamber 1
The effective size of the opening 19 of 8 is slightly smaller by the peripheral edge 20.

Next, as another conventional example, US Patent No. 2,500,676
This example, shown in Figures 12a and 12b, also shows the configuration of a microwave oven, in which high frequency waves obtained by oscillation of a magnetron 27 are supplied to a heating chamber 28, and food 29 is heated and cooked by electromagnetic induction. It is something to do. An opening 30 of the heating storage 28 is provided with a door 31 that covers the opening 30 so as to be openable and closable. A groove-shaped choke portion 32 is also formed at the peripheral edge of this door 31, and this choke portion 32 prevents high frequency waves from leaking to the outside. The depth of this choke portion 32 and 33 are also designed to be a quarter wavelength of the operating frequency. Therefore, the effective size of the opening 30 is slightly smaller than the heating chamber 28, as in FIG.

As mentioned above, the conventional choke section is based on the technical concept of attenuating high frequencies by having a depth of one-quarter wavelength.

That is, when the characteristic impedance of the choke part is Zo and the depth is L, and the end part is shortened, the impedance Z at the opening of the choke part is 2πL Z+++= j Zo tan ()λO (λ is the free space wavelength ) becomes.

The choke-type radio wave attenuation means selects the depth L of the choke part to be 1/4 wavelength, so that π ZIM l = Zo tan (-) = o.

It is based on the principle of achieving

If the choke part is filled with a dielectric (specific dielectric εr), the wavelength λ' of the radio wave will be λ'ζλ. /Jt.

compressed into In this case, the depth L' of the choke part is L''
=L/Jε.

becomes shorter.

Problems to be Solved by the Invention However, the above-mentioned setting of L'=λ'/4 remains the same, and in the choke method, the depth cannot be made substantially smaller than a quarter wavelength. There was a limit to the miniaturization of the choke part.

The present invention provides a radio wave sealing device with a small choke portion.

Means to Solve the Problem This invention is a radio wave seal using a new impedance conversion principle, and by having each of the leakage path and the groove have a characteristic impedance discontinuity configuration, the size is smaller than that of a quarter wavelength. It has a small shape and has a structure in which the opening including the plane of the groove is covered with an insulating sheet.

Effect: The above means can prevent leakage of radio waves, and the insulating sheet can also prevent foreign matter from entering the seal groove.

EXAMPLE The characteristic impedance of a radio wave seal device will be explained below using FIGS. 3 and 4. FIG. 3 is a perspective view of a microstrip line, in which a strip conductor M and a ground conductor G are opposed to each other with a dielectric interposed therebetween. Here, the track width is a
, the line gap is taken as ε, and the dielectric constant of the dielectric medium is taken as ε.

As is well known, the characteristic impedance Z0 in this case can be made small by widening the line width a, narrowing the line gap, and increasing the dielectric constant ε.

FIG. 4 shows an example of the structure of the door. In this case, the wall surfaces G and M provided on the door 4 and extending in the X direction and the conductive path group 13 having a width a and a peach P form a groove 5 having a groove width. In this case, the conductor line group 13 acts as a radio wave propagation system against the wall surface t, which corresponds to the ground plane, but the characteristic impedance of each line has almost the same relationship as in the case of parallel lines. It is maintained.

The present invention will be explained in detail with reference to FIGS. 5 to 8, FIG. 5a.
, b, and C show examples in which the impedance of 2.3, n small grooves is changed. The section of characteristic impedance Z1° has a length of 11, the impedance seen from the impedance change point toward the end of the groove is Z, and from the groove opening,
The impedance when looking at the groove end side is Zinn.

Specifically, in the case of Figure 5a where the groove is divided into two, Z2 = j
Zzotanβ1z=j'Xg or less β is β− λ.

Lo+jZztan βI However, 2+. <72゜) In the case of Figure 5, Z3 = j Z 3otan β13 Zo +j Z3 tan β12 21g + j Z x tan βl However, Z. <72°<23°) In the case of FIG. <Z2゜...< Z z. )Z ＋＊ ＋
j Z z tafl β1.

Therefore, the impedance seen from a small fully open hole is 7, + j Zl in the case of n discontinuous characteristic impedances.
tan βlLo X, tan βl, the above formula is Zl. and xlltan β1. If they become equal, it means that lZi, l=■.

That is, it can be seen that Z , , = X tan β I + is a requirement for increasing the impedance at the groove opening.

λ. = 122.4mn (f = 2450MHz)
- = 30.8 In the example of Fig. 5 a, two discontinuous pieces, the fifth
Zl for the case of three discontinuous pieces in the figure. -X, tanβ
1. l+ 1x(1:+), which satisfies the condition of l t
The combination of otal is the aperture characteristic impedance Z,.

Calculating the ratio of 1:2 to the terminal characteristic impedance Z2° or Z3° results in the following.

(Unit: m) 1%. ,,t=1,+! .

This result means the following. ■Characteristic impedance is Z+*<Zz. Or Zl. <Z,. By setting the angle to <23°, the groove depth l (total) can be made smaller than a quarter wavelength. ■The dimensional compression ratio of the groove depth is determined by the characteristic impedance of the opening part Z1° and the characteristic impedance of the end part Z
1°, and is hardly influenced by the number n of changes in characteristic impedance.

The above explanation is Z2°/z +. −Z3°/z,. = 2, but Figure 6 shows the characteristic impedance ratio when the ratio of dimensions 11 and 1° is varied from 1 to 5 in the case of two divisions, and the small groove depth relative to the choke groove depth. This shows the relationship between the compression ratio when the dimensions are reduced. 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 choke groove.

Figure 7 shows dimensions! When 1 is 12 m, the absolute value of the characteristic impedance of the opening is broadened using the dimension 1□ as a parameter, and it shows that the dimension 1□ takes maximum values at 24 m and 25 m++.

Figure 8 shows the large side value of radio wave leakage. This result also shows that the 12 dimension has a minimum value between 23.5 and 24.5 am, which means the following.

■ Increasing the absolute value of the impedance of the small groove opening reduces the amount of radio wave leakage.

■ The depth dimension (1+12) of the groove that increases the impedance of the opening of the small groove should be a precise match between the calculated value and the actual measurement value.

■ It is possible to definitely downsize compared to the depth of the choke groove.

A specific configuration of the embodiment shown in FIG. 9 is shown. In the present invention, in a case where at least one of the wall groups constituting a small groove has a conductor width smaller than the pitch, the conductor width a of the opening part of each line group is made larger than that of the short-circuit termination part. Take composition. The small groove 5 is constituted by the wall groups 1316 and 17. In particular, the wall surface 13 is characterized in that it consists of a group of lines in which the conductor width a of the opening portion is larger than the conductor width at of the short circuit portion.

The present invention is based on λ, which has been historically used in the field of radio wave seals.
Impedance inversion is performed not on the /4 line but on the less than λ/4 line. In order to facilitate understanding of this principle, a part of the analysis results are shown in FIG. 1O. In FIG. 1θ, a groove having an opening B whose tip C is short-circuited is provided in a part of a transmission line with the A end as an excitation source and the D end 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 groove depth 17 is changed, the electric field within the transmission line changes as shown in a, b, and c, and in case b the radio wave does not reach end D. , that is, when the groove depth l is approximately 80% of a quarter wavelength (less than λ/4 line),
Even if it is longer or shorter (cases a and C), radio waves leak more than in case b.

An embodiment of the present invention is shown in FIG. 1, and a perspective view taken along line AA in FIG. 1 is shown in FIG. A heating wall portion 2 that covers the heating chamber 1, a door 3 that freely opens and closes the heating chamber 1, and the door 3 are formed of a single metal conductor 4. The door 3 is composed of a small groove 5 with a groove width and a plastic cover 6. The groove part further includes an aperture plane 7, a groove aperture part 8, and an outer groove surface 9, and as shown in FIG. Due to the line width al on the hole side 10 and the slot group 15, the line width a2/2 is two lines on the short-circuit end side 11 (
In total, it consists of a2). Further, the fully open holes 7 and 8 are covered with an insulating sheet 12 made of PET (polytetramethylene terephthalate) or the like to prevent food waste from entering the grooves 5.

By adopting such a configuration, the choke groove can be configured in a small size, and furthermore, since the groove opening including the flat surface is covered with an insulating sheet, the workability of making the door can be greatly improved.

Effects of the invention (11) Essentially, the depth of the small groove can 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 component in the X direction can be reduced and the radio wave sealing performance can be improved.

(3) The radio wave seal can be made smaller with a simple configuration of changing the conductor width.

(4) Since the flat surface of the opening is both covered with an insulating sheet, the workability of making the door can be improved.

[Brief explanation of drawings]

FIGS. 1 and 2 are a sectional view and a plan view of a radio wave sealing device according to an embodiment of the present invention, FIGS. 3 and 4 are perspective views for explaining the correspondence between the microstrip line and the door groove structure, and FIGS. 5
The illustration is an interior! Fig. 6, Fig. 7, and Fig. 8 are characteristic diagrams of the articulation device, Fig. 9 is a perspective view of the device, Fig. 10119 is a principle diagram of the device, and Fig. 11
1 and 12 are sectional views of conventional radio wave sealing devices, respectively. 5... (Small groove), 7... Opening part plane, 8... Opening (groove), 12... Insulating sheet, 13. ...Conductor piece (wall surface body), 14...
...Slit group.

Claims (1)

[Claims] Provided with a main body that has an opening and into which radio waves are supplied,
A door is provided to cover the opening of the main body in an openable and closable manner, a groove is provided in at least one of the parts where the main body and the door face each other, and at least one wall surface forming a conductive wire arranged in the groove is provided. A radio wave sealing device is formed of periodically continuous conductor pieces, the width of the conductor pieces is wider on the aperture side and narrower on the short circuit side, and the aperture plane of the groove and the groove are covered with an insulating sheet.