JPS59145599A - Radio wave sealing 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 Conventional Structure and Problems A conventional radio wave sealing device of this type will be described by taking a microwave oven, which cooks food by dielectrically heating it using high frequency waves, as an example. 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, US Pat. No. 3,182,164 is shown in FIG. In FIG. 1, reference numeral 1 denotes a heating chamber for a microwave oven □, and a door 4 having a handle 3 that covers an opening 2 of the heating chamber 1 so as to be openable and closable is provided. A hollow choke part 6 having a gap part 5 opened toward the heating chamber 1 side is formed at the peripheral edge of the door 40. The depth 7 of this choke part 6 is substantially one quarter of the wavelength of the high frequency wave used.
It is designed to. In this case, the thickness of the door 4 is also a quarter wavelength. That is, since the frequency of electromagnetic waves conventionally used in microwave ovens is 2460 MHz, a quarter wavelength is approximately 30 MHz. In order to face the choke part 6 of this length, the thickness 9 of the peripheral part 8 formed in the opening part 2 of the heating chamber 1 has a value larger than a quarter wavelength. Therefore, the effective size of the opening 2 of the heating chamber 1 is slightly smaller due to the peripheral edge 8. Next, as another example of the prior art, US Pat.
No. 76 is shown in Figures 2a and b. This example also shows the configuration of a microwave oven, in which high frequency waves obtained by oscillation of a magnetron 10 are supplied to a heating chamber 11 to cook food 12 by electromagnetic induction. The opening 13 of the heating storage 11 has a door 14 that covers the opening 13 so as to be openable and closable.
is provided. A groove-shaped choke portion 16 is also formed at the peripheral edge of this door 140, and this choke portion 15 prevents high frequency waves from leaking to the outside. The depth 16 of this choke portion 15 is also designed to be a quarter wavelength of the operating frequency. Therefore, the effective size of the opening 13 is slightly smaller than the heating chamber 11, 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 20, the depth is L, and the termination part is shortened, the impedance Z at the opening of the choke part is N (λ is the free space wavelength).

The choke type radio wave attenuation means selects the width L of the choke part to be 1/4 wavelength, so that IZ engineering N1 = Z
otan (-) -c.

It is based on the principle of achieving

If the choke part is filled with a dielectric material (relative dielectric constant εr), the wavelength λ' of the radio wave is compressed to λ'-λ·/6. In this case, the depth L' of the choke part is L'
= L/J5, and becomes shorter. However, it is still L'-λ'/4, and in the choke method, the depth cannot be made substantially smaller than 1/4 wavelength, and there is a limit to the miniaturization of the choke part. In recent years, the development of solid-state oscillators has progressed, and the era of practical use has arrived. Microwave ovens are no exception; traditional magnetron oscillators are being replaced by solid-state oscillators.

The advantages of solid-state oscillators in microwave ovens are as follows.

1 The drive voltage of a magnetron is about 3KV, while the drive voltage of a solid-state oscillator using a transistor etc. is about 40KV.
The voltage may be 0V or less, and in reality, about 40V is used.

Therefore, since the power supply voltage is low, it is safe for the human body, and even if there is a leak, electric shock accidents are unlikely to occur.

Therefore, it becomes possible to create an earthless system, and it is also possible to develop a portable system.

2. While the lifetime of a magnetron is about 5,000 hours, a solid-state oscillator has a long lifetime, about 10 times longer.

3 While the oscillation frequency of a magnetron is fixed,
The oscillation frequency of the solid-state oscillator is variable, for example 9
It can be varied within a range of 13 MHz above and below 15 MHz. Therefore, the load (cooked food)
By automatically tracking the frequency with the magnitude of , the resonance frequency changes and high efficiency operation can be obtained. Experiments have shown that when the frequency is automatically tracked within 2450±50 MHz, the practical load efficiency is approximately 60~60% lower than that of a fixed frequency.
04 Solid-state oscillators, which have been improved by a factor of 80, may become cheaper than magnetrons in the future due to mass production.

Currently, the ISM frequency (Industrial) is internationally assigned for high-frequency cooking.

5 scientific, medical) is 6880
MHz.

2450MHz, 915MHz, 400MHz, etc. - Do not deviate from this. Current magnetrons oscillate at 2450 MHz as mentioned above, but if a solid-state oscillator were used to oscillate at the same frequency (2450 MHz), sufficient output power would not be obtained and the power would be insufficient. Therefore, in order to obtain the desired output power, a lower frequency must necessarily be selected; for example, 915 MHz is suitable. However, since this frequency is about 1/2.7 of the conventional frequency, the wavelength is about 2.7 times, and a quarter wavelength is about 80
It becomes 8. Therefore, if 915 MHz is selected as the frequency of the microwave oven, the thickness of the choke part explained in Figs. This has the disadvantage that it becomes extremely small, making it extremely difficult to put it into practical use.

On the other hand, the oscillation frequency was changed from 2460MHz to 915MHz.
The advantages of changing to are as follows.

Since the Ii length was increased, radio waves penetrated into the interior of the food, making it possible to speed up the cooking time. For example, it takes 2450M1 (Z.

While it took more than 60 minutes with eoow, 915MW z
, it takes less than 50 minutes at 30OW.

2 The cause of uneven burning is standing waves, and the standing wave pitch is correlated with wavelength. When 915 MHz is used, the pitch of the standing wave is too loud, and the unevenness of cooking becomes noticeable.

Therefore, the disadvantage of changing the operating frequency of the microwave oven to 916 MHz is that the radio wave/wavelength means becomes larger.

Note that as one means for reducing the thickness of the choke portion, there is a configuration in which the choke portion is filled with a dielectric material. According to this configuration, the dielectric constant of the choke part increases, so the choke part can be made smaller than a quarter length, and moreover, the choke part can be made smaller than a quarter length.
It has the same effect as a wavelength choke section. However, since the dielectric material is expensive, the price of the microwave oven as a whole becomes expensive, and the manufacturing time and cost are high, which hinders its practical use.

The principle of the conventional example will be theoretically explained below.

That is, the characteristic impedance Iz of the choke groove. .

When the depth of the groove is l and the terminal end is short-circuited, the impedance Zin at the choke groove opening is Zfn = l
It is based on the Iu principle that zin l "zo4an (7r/ ) ==co is achieved. When the inside of the choke groove is filled with a dielectric material (relative permittivity εr), the radio wave wavelength λ' becomes λ
′- There is no difference.

Therefore, in the choke method, the depth of the choke groove cannot be made substantially smaller than a quarter wavelength, and there is a limit to miniaturization.

OBJECT OF THE INVENTION This invention d1 provides a radio wave sealing device in which the size of the choke portion does not increase even if the oscillation frequency is lowered.

Structure of the Invention This invention is a radio wave seal using a new impildance conversion principle, in which each of the leakage path and the groove has a characteristic impedance discontinuous configuration, so that the shape is smaller than the size equivalent to a quarter wavelength. That is.

DESCRIPTION OF THE EMBODIMENTS The characteristic impedance of the radio wave/wire device will be described below with reference to FIGS. 3 and 4. FIG. 3 is a perspective view of a parallel line, where the line width is a, the line gap is ε, and the dielectric constant of the dielectric medium is ε□.

Characteristic impedance Z in this case. is the characteristic impedance Z as is well known. is to widen the track width a,
The value can be reduced by narrowing the line gap and increasing the relative permittivity ε.

FIG. 4 shows an example of the structure of the door (shown. In this case, the wall surface 18, 19 extending in the X direction provided on the door 17, the width a, the peach P
The conductor line group 2o constitutes a groove 21 called groove Il@b. In this case, the conductor line peep 0 is arranged against the wall surface corresponding to the ground plane, and acts as a radio wave propagation system, but the characteristics differ for each line.

The principle of the present invention will be explained using FIGS. 6 to 8. Fifth
Figures a, b, c show small grooves in 2.3. An example is shown in which the impedance is changed n times. Characteristic impedance z1o
The section has a length of 11, and the impedance seen from the impedance change point to the groove end side is 2. Then, the impedance seen from the groove opening toward the groove termination side is Zinn.

Specifically, in the case of FIG. 5A where the groove is divided into two, in the case of FIG. 5S, Z3=jZ3o1anBt3, and in the case of FIG.

Therefore, the impedance seen from the small groove opening becomes the case of n discontinuous characteristic impedances. The above formula is Zl. and 4 tigers nβt1 are equal, then l Zin n 1-o
It means that you can do O. That is, Z1o=Xn βt1
It can be seen that 0λo-122-4□ (f-24bOMHz) is a requirement for increasing the impedance at the groove opening.
tl, t2 (t3), t, which satisfy the condition of Z1oiXn plus βt1 in the case of 2 discontinuities in FIG. 5A and 3 discontinuities in FIG. 5S in the o-30-8 example. When the combination of tY is calculated assuming that the ratio of the opening characteristic impedance Z1o and the termination characteristic impedance Z20" or Z3o is 1:2, the following is obtained.

In the case of two divisions (20/z = 2) 0 This result means the following. ■ By setting the characteristic impedance to Zl.<Z2° or Zl.<Z2°<Z3o, the groove depth t (total) can be made smaller than a quarter wavelength. ■ The dimensional compression rate of the groove depth is almost determined by the aperture part characteristic impedance Z1° and the end part characteristic impedance Z, and the characteristic impedance n.

It is almost unaffected by the number n of changes in the beadance.

The above explanation is for the case where 220/z1o=2white/Z1o=2, but in FIG. It shows the relationship between the compression ratio in which the small groove depth is dimensionally compressed with respect to the choke groove depth. 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 that when the dimension t1 is 12M, the absolute value of the characteristic impedance of the opening section is broadened using the dimension t2 as a parameter, and it shows that the maximum value is obtained at the dimension t2 of 24M and 26 threads. ) Figure 8 shows the measured values of radio wave leakage. This result also shows that the 42 dimensions are 23,511B and 24
．． The minimum value is shown between 511B and this means the following.

■ Increasing the absolute value of the impedance of the small groove opening reduces the amount of radio wave leakage ■ Groove depth dimensions (tl, t2) that increase the impedance of the small groove opening
■ Calculated values and actual measurements must match with high accuracy.■ The size can be reliably reduced compared to the depth of the choke groove.

FIG. 9 shows the specific configuration of the embodiment. The present invention provides a configuration in which at least one of the wall groups constituting the small groove has a conductor width smaller than the pitch, and the conductor width a1 of the opening part of each line group is larger than that of the short-circuit termination part a2. Take. Small groove 425 due to 0 wall group 22°23.24
is composed of In particular, the wall surface 24 is characterized by a group of lines in which the conductor width a of the opening portion is larger than the conductor width a2 of the short circuit portion.

FIGS. 10a and 10b show the structure of an embodiment of the present invention. Reference numeral 26 indicates an outer groove, 27 indicates an outer groove wall surface, and 28 indicates a main body.In particular, each of the conductive wires constituting the wall surface 24 has a bent portion 29 at the tip thereof. FIG. 11 shows a comparison of data on the leakage amount PL (mW/cwt2) of a microwave oven (2450 MHz) with and without the υ bending part 29 near the tip using the groove depth tT as a parameter. As shown in FIG. 11, it is better to have the tip bent portion 29 (LT=2
1Mb) Without bending part (IT=25M)
The groove depth can be shortened compared to the previous one.

The dimensions of each part shown in FIG. 10 are an example of dimensions when applied to a 2450M) 12 microwave oven. In FIG. 10, 30 is a heating chamber, 31 is a door, 32 is a groove opening, and 33 is a short-circuit end portion.

t1 = 10 gifts, 12 = 6 deceptions, t = 0.8 subs, Z3
-161rM, A4= 1.6a+yb, 75=
4. rstrrn, , 76=1 tsrnJlz
t7=10a+y1. , t8=5rub, t9
= 1omrrb.

Effects of the invention (1) The depth of the small groove can essentially be made smaller than a quarter wavelength.

(2) By providing a bent end portion, the groove size can be further shortened.

(3) Since at least one of the walls constituting the small groove is made up 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.

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

(6) The outer groove acts as a second small groove, further improving sealing performance.

[Brief explanation of the drawing]

Figures 1, 2a and 2b are a sectional view of a conventional radio wave sealing device, Figure 3 is a sectional perspective view of a parallel line, Figure 4 is a sectional perspective view of a modified parallel line, and Figure 6a, b and c are diagrams explaining the principle of the radio wave seal device of the present invention, Figures 6, 7, and 8 are characteristic diagrams of the device of the present invention, and Figure 9 is a radio wave seal of an embodiment of the present invention. FIGS. 10a and 10b are a sectional view and a perspective view of the device, and FIG. 11 is a characteristic diagram of the device. 22.23.24...Groove wall, 25...
Groove, 26... Outer groove, 27... Outer groove wall surface, 28... Main body, 2e... End bent portion. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 Figure 1 464 Figure 3 Procedural amendment dated March 9, 1982 Mr. Commissioner of the Japan Patent Office Convulsions 1 1 Indication of case 1988 Patent Application No. 4486 2 Name of invention Radio wave seal device, 3 Make amendments Relationship with A11 Patent Application Address 100 Kadoma, Kadoma City, Osaka Prefecture
Address 6 Name (582) Matsushita Electric Industrial Co., Ltd. Representative Toshihiko Yamashita 4 Agent
〒571 Address: Matsushita Electric Industrial Co., Ltd., 1006 Oaza Kadoma, Kadoma City, Osaka Prefecture Map 6 Contents of amendment (1) Insert the legal text after “Measure.” on page 17, line 7 of the specification. [The present invention implements impedance inversion using a sub-λ/4 line instead of the λ/4 line historically used in the field of radio wave seals.To make this principle easier to understand, Part of the analysis results are shown in Figure 9. Figure 9 shows a part of the transmission line with the A end as the excitation source and the D end open.
A groove having an opening B whose tip C is short-circuited is provided. Is the groove on the short side rather than the open hole side? The lQ width is doubled. 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, Also (cases a and c), radio waves leak more than in case b. In actual application, the groove cover space (TOP
I) and a bending reinforcement space (lX1) 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 dimensions of TOPl are 2ff1m and lX1 is 5~
An example is shown in which the width is set to 6 mm. Figure 10 is an example of a 915 MHz sealing device.
The relationship in which the groove depth lT changes with the dimension of P1 is shown. '
If the dimension of TOP1 is 1 to 3 mm, it will be 7? T is 1-6
It becomes deeper by mm. Figure 11 is an example of a 2450MHz sealing device.
The relationship is shown in which the groove depth 1T changes with the reinforcing space (1X1) while fixing OP1=2m+a. space l x 1 to 2
By setting the groove depth IT to 6 mm, the groove depth IT becomes 1 to 3 mm deeper. (2) Correct "Fig. 1 10" on page 17, line 8, lines 9-10 to "Fig. 13." (3) On page 17, lines 3 to 4, correct "Figure 11" in the 4th line to "Figure 14." (4) "Figure 9 is..." on page 18, lines 16 to 19 will be corrected as follows. "Figures 9a, b, and c are electric field analysis diagrams of the groove in the present invention. Figures 10a and 10c are cross-sectional views, side views, and characteristic diagrams of the device at 915 MHz. Figure 11 a, b, and c are 2450 MHz.
12 is a perspective view of a radio wave sealing device according to an embodiment of the present invention;
The thirteenth factors a and b are a cross-sectional view and a perspective view of the same device, and the fourteenth factor is a cross-sectional view and a perspective view of the same device.
Add Figures 9, 10, and 11. Figure 10 (2L)

Claims (1)

[Claims] A main body having an opening and into which radio waves are supplied is provided, a door is provided to cover the precursor opening of the main body so as to be openable and closable, a groove is provided in at least one of the parts where the main body and the door face each other; At least one wall surface forming the conducting wire arranged in the groove is formed by a plurality of periodically continuous wall bodies, and the pitch of the plurality of wall bodies is formed to be larger than the width of the groove,
The conductive wire has a bent portion in the groove opening portion of the radio wave sealing device 0.